CLASSIFICATION OF POLYMERS

Transcription

1 PLYME High-Molecular Mass Compoud ad Polymer The term high-molecular mass ad polymer are used at preset to deote substace with molecular mass over 5,000 (ad upto may millios) as distict from low-molecular mass substaces, whose molecular masses` comparatively rarely ru ito the hudreds Macromolecules & its chemistry The molecules of polymers are called macromolecules, ad their chemistry is kow as macromolecular or polymer chemistry Polymerizatio Polymerizatio is the combiatio of several simple molecules CLASSIFICATIN F PLYMES Polymers may be classified o the basic of followig poits (1) the basis of reactio to stress ad temperature: (a) Thermoplastic or Thermoplasts: These polymers ca be repeatedly give shapes by heat ad pressure Hece oce used for a particular form, they ca agai be formed ito a differet shape or foud (b) Thermosets: These polymers, oce subjected to heat ad pressure to give a particular form, ca t be formed agai like the thermoplasts (c) ubbers: These polymers, whe subjected to heat ad pressure, behave at first like the thermoplastics ad subsequetly become highly elastic Their elasticity may be arrested at a itermediate stage ad the process of doig so is called valcauisatio or curig () the basis of mechaical stregth & behavior a Elastomers: These are elastic i ature Their extesibility is reversible ad sometime may be as high as 1000% Their elasticity is directly proportioal to the temperature withi a particular rage Whe the temperature i decreased, the extesibility also decreases ad at a temperature called the brittle poit they become brittle 1

2 b Plastic or plastomers: Compared to elastomers, these are less elastic ad less extesible Whe they are deformed, a part of the deformatio is foud to be permaet while a part is reversible They have extesibility ragig from 100 to 00% The extesibility, viscosity ad elastic modular are direct fuctio of temperature c Fibers: They have low extesibility ragig form 10-0% oly Whe subjected to deformatio, most of the deformatio is foud to be permaet ad the rest is reversible ad the reversibility is partly istataeous ad partly delayed (3) the Basis of methods of polymerizatio (a) Additio or chai reactio polymers : These polymers are produced by process called additio or chai reactio polymerizatio I this process, a simple, low molecular weight molecule (moomer) which possesses a least oe double bods, is iduced to break Its double bod resultig i the free valeces which the lik up with other similar molecules to give the polymer Also i this process there is o by productio ad the moomer retais its idetity i the polymer uit Eg Ethylee Polyethylee (b) Codesatio polymers: These polymers are produced by the method of codesatio polymerizatio This process is differet from the additio process o three couts (i) I codesatio polymerizatio the moomers eed ot cotai a double bod (ii) The moomer does ot retai its characteristic molecular formula, i the mesomer (iii) A small molecule is essetially give out ad hece the resultig molecule is codesed is the process Example H - C - - C - H H - ' - H C - - C' - C - - C H di-carboxylic acid alcohol polyster Codesatio polymers are sometimes called rearragemet polymers

3 Eg H H ' NC C NH ' NHC Diol Di-isocyate Polyurethee 4 Molecular arragemet : (a) Liear : All the idetifyig uits are arraged liearly Eg A A A A A or Usually bivalet molecules (mesomers) gives liear polymers (b) Brached : The chai icludes some molecules which have valacies of more tha two As a result, brach origiates i the liear chais Eg A A A A Y A A A Y A A (c) Cross liked : I this type of polymer The brached chais reacts with oe aother & form closed etworks Eg A A A Y A A Y A A A Y A A Y A A (5) the basic of type of mesomer ivolved i the polymers (a) Homopolymers: These are composed of oly oe type of mesomer Eg (b) Hetero polymers: These are composed of more tha oe type of moomers These are called copolymers 3

4 Copolymer may be of several kids, depedig upo the way the moomers exist i the polymer chai (i) adom copolymers have the differet moomers i radom sequece Eg A A B B A B A B A A B Copolymer of viyl chloride ad vieyl acetate (ii) A alteratig copolymers has the followig sequece moomers A B A B A B A Each moomers i alteaively polymerized with oe aother (iii) A block copolymer has differet moomer I blocks of idividual species A A A B B B A A A B B B A A A Eg Block copolymers of ethylee oxide ad ethylee terephthalate C C = Pheylee edical (iv) Graft copolymers has block of oe species of moomer attached to the chai of aother species i a may which makes it appear as if blocks of oe type of moomer have bee grafted o to the chai of aother type B B A A A Y A A A Y A B B B B B B A 4

5 (6) the basis Morphology of the substace : (a) Crystallie : A crystallie state of a polymer is oe i which the chais are very closely packed These polymer are more opagued (b) Amorphous: A amorphous state of a polymer is oe i which the chais are more loosely held These polymers are more trasparet 5

6 NMENCLATUE F PLYMES Nomeclature of carbo- chai polymers (Homopolymers) The ame of carbo chai polymers are usually derived by addig the prefix poly to the ame of the moomer which forms the moomeric uit If the ame of the moomer cosists of more tha oe word it is eclosed i paretheses Eg Moomers Name of Polymers Viyl chloride Poly(viyl chloride) Ethylee Polyethylee Chloropree polychloroprere Polymers obtaied from moosubstituted ethylee derivatives cotaig the viyl radical, =, are combied uder the (geeral) geeric ame of viyl polymers This groups of polymers icludes F Poly (viyl fluoride) Poly (viyl cyaide) H Poly (viyl alcohol) Polymers obtaied form ethylee 1,1-disubstitutes cotaig the viylidie radical C H C are called viylidie polymers Cl Cl Poly (viylidee chloride) F F Poly (viylidee floride) CN CN Poly (viylidee cyaide) All the carbo chai polymers ca be amed o the basis of orgaic chemistry These are as follows 6

7 Saturated hydrocarbos ad their derivatives : Saturated Hydrocarbos Polyethylee Polypropylee 3 Polystyree Halo Derivatives Poly(viylchloride) Cl Polytetrafluroethylee CF CF Alcohols & Esters Poly(viylalcohol) H Poly (allylalcohol) H Poly(viylacetate) C 3 7

8 Aldehydes & lactoes Polyacrolei Poly(viylmethyl ketoe) C 3 Amies Poly(viylmethylamie) 3 NH Acids ad derivatives Poly(acrylic acid) CH Poly(methyl acrylate) C 3 Poly(acrylamide) CNH Poly(acryloitrile) CN 8

9 Usaturated hydrocarbos & their derivatives: - Polybutadiee Polyisopree (Natural rubber) C 3 Depedig o the heteroatom preset i the mai chai, heterochia polymer falls ito oxyge, itroge ad sulphur cotaiig & orgao elemet polymers Eg Poly(ethylee oxide ) & its derivatives C ' Polyacetats Polyformal Polyesters H C ' C H -glycol radical & is a radical of usaturated/aromatic dibasic acid Nitroge cotaiig Proteis NH C Polyurethaes C NH ( ) ' NH C ( ) x y 9

10 Urea formaldehyde & Melamie formaldehyde polymers Sulphur cotaiig ( ) x S Polymers with Iorgaic Mai Chai :- Polysiloxames Si The ame of classes of heterochai polymer are derived from the ame of the class of compouds i questio, to which is added the prefix poly, Eg Polyesters, polyamide, polyurethaes etc Cojugated Bod Polymers : - These icludes both some carbo chai, & some heterochai polymers Followig are some cojugated bod polymers without dividig them ito chemical group Polyitriles C N Polypheylees Poly(pheylee sulphides) S 10

11 SYNTHESIS F PLYME The startig materials for the sythesis of polymers are low molecular mass substaces (moomers) ad, i some cases, oligomers A high molecular mass compoud ca be sythesized if the moomer ca react with at least two other molecular ie, if the moomer is at least bifuctioal Fuctioality of a substace also depeds o the presece i its molecular of double or triple bods or mobile hydroge atoms i its molecule Eg H C CCl HCl [Moofuctioal] H H Br Br 3 Br 3HBr [Trifuctioal] Br Steric (special) factors : I some cases the sythesis of high molecule mass compouds is hidered by steric factors Steric hidraces are especially characteristics of the polymerizatio of usaturated hydrocarbo derivative cotaiig substitutig astoms or r with large rohma The fuctioality of substace is the umber of fuctioal groups cotais per molecule Compouds may be moofuctioal or poly fuctioal (bi, tri, tetra, etc) Moo fuctioal 3 CH Acetic acid 3 H Methyl alcohol Bifuctioal H H Ethylee glycol 11

12 HC ( ) 4 CH Adipic acid Trifuctioal H H H Glycerol Four mai methods of sythesizig polymers i Chai polymerizatio ii Polycodesatio iii Step polymerizatio iv ig scissio (rig opeig) polymerizatio *[Some authors uses the terms additio polymerizatio to deote ay polymerizatio i which o low-molecular weight by product is formed, ad by other to deote chiefty chai polymerizatio] (i) Chai Polymerizatio: Chai polymerizatio is oe of the commoest methods of sythesizig macromolecular compouds Almost all carbo Chai polymers used i egieerig sythetic rubbers ad polyesters for plastic fibers are made by this method This polymerizatio is the combiatio of several simple molecules without, the formatio of product ad, hece icurrig o chage i the elemetary compositio of the reactats Example X X X X Polymerizatio is always composed by a decrease i usaturatio of the reactats, a reductio i the total umber of molecules ad a icrease i average molecular mass Macromolecules obtaied by chai polymerizatio are usually very log, with their molecular masses i the hudreds of thousads or eve millios The molecular mass or fid degree of polymerizatio of a polymer formed by this reactio is obtaied almost istatly The kietics of the reactio is a decisive factor for average molecular mass, degree of polymerizatio & ature of polydispersity Step : 1

13 1 Iitiatio : (formatio active cetre):- equires a high activatio eergy & proceeds slowly Propagatio : low activatio eergy & very high rate Heat effect is also always positive 3 Termiatio : equired small activatio eergy & has a fairly large reactio rate It is evidet that the higher the rate of propagatio compared to the rate of elimiatio, the loger will be the reactio chai ad the larger the molecular mass of polymers Depedig o the ature of active cetres, chai polymerizatio fall ito free radical polymerizatio & ioic polymerizatio 1 Free adical Polymerizatio : The iitiatio of the polymer chai growth is brought about by free-radical produced by the decompositio of compouds called iitiators Iitiators: They are thermally ustable compouds ad decompose ito product called free radicals catalysts Free radical of iitiators ca be formed thermally, by ultraviolet light or by Methods of iitiatig free-radical polymerizatio: 1 I thermal polymerizatio free radical are geerated by heatig May moomers practically do ot polymerize i the absece of Impurities Eg Viyl acetate, acryloitrile, viyl chloride will ot polymerize if heated without oxyge ther like methyl methacrylate polymerizes fairly rapid o heatig I photo polymerizatio, the moomer- absorbs a photo ad becomes exited hv * adicals (Excited state) hv is the eergy of oe quatum of light Eg Viylidie chloride ca be polymerized by UV light at 35 0 C, but it will ot polymerize i the absece of iitiator eve if heated 13

14 3 I radiatio polymerizatio the actio of high eergy radiatios (r- rays, x- rays & accelerated electros) o the moomer also results ito free radical 4 Iitiated polymerizatio, the radicals may be added i the free state or as compouds which decomposes readily durig the polymerizatio to form free-radical Iitiators ca also be iduced to decompose ito free-radical by usig suitable catalyst Eg Bezoyl peroxide ca be decomposed at room temperature with a aromatic tertiary amie Hydroge peroxide ad hydroperoxide ca be decomposed by ferrous io & cobaltous ios respectively Some iitiators ad there produced radicals are as follows : Name Structure Free radical foud (AIBN) CN CN CN Azobicisobutyro-itrile H 3 C C N N C 3 H 3 C C BP Bezoilperoxide C C C & Hydroge Peroxide Peracetic acid H H H 3 C 3 & H H 3 C C H Potessium Persulphate K S S K - K S Tert Butyl peroxide 3 3 H 3 C C C C 3 H 3 C 3 C & Iitiatio : A free radical cotais a upaired electro A upaired electro try to couple with aother upaired electro ad get stabilized 14

15 I the iitiatio free radical eg attacks the double bod i the moomer molecule, reactig i the followig chemical chage X X Mechaical : : r X X X I the double bod oe pair of electro exist as sigma ( б ) electros, while the other, ot so close to ucleolus, exist as pi ( π ) electros e - e - C C C C bod e - I the iitiatio free radical formed from iitiator s decompositio iterferes with oe of π electros which are ot very close to ucleus, so are susceptible to be attacked The free radical forms a б type bod / pair of electro, with oe of the electro ad so the remaiig trasfer to the other ed formig the radical at the other ed Free radical attack is a exothermic process, whereas its formatio by iitiator, decompositio is edothermic PPAGATIN : Propagatio is the process of movig radical from oe ed to the ext molecules ed Propagatio results i a chage of π bods ito б bods This reactio always proceeds with the liberatio of heat due to the differece i eergies betwee π & б bods X X X X 5 Kcal This step results i the likig up of the secod moomer uit to the first ad trasfer of the radical site from the first moomer uit to the secod The additio of icomig moomer to the growig chai ca be of four types 15

16 (i) Head to Tail X X X X (ii) Tail to Tail X X X X (iii) Head to Head X X X X (iv) Tail to Head X X X X Termiatio : Chai termiatio must be related to disappearace of the upaired electro Therefore, as a such termiatio occurs as a result of iteractio of two radicals I the simplest case this may be recombiatio (couplig) of free radicals X X X X ' X X X X ' or Disproportio X X X X ' X X X X ' I the first case, the two growig chais uite by the couplig of the electros preset i each chai to form a electro pair ad, thus, ullify their reactiveess I secod case, oe H from oe growig chai is abstracted by the other growig chais ad utilized by the loe electro for gettig stabilized, while the chai, which has doated the H, gets stabilized by the formatio of a double bods There is yet aother method of chai termiatio, which takes place by trasfer reactio 16

17 AIN TANSFE : I termiatio brought about by couplig or disproportioatio, the products formed or dead or o-reactive, ad, hece, o further chai propagatio is possible I case of trasfer reactio, however, while of growth of polymer chai is stopped, there is a simultaeous geeratio of a ew free-radical capable of iitiatig a fresh polymer chai growth Usually it takes place as a result of iteractio of a active cetre or a growig chai with a impurity or with the solvet eg If the growig chai ( the free polymer radical) possesses sufficiet eergy to break the A B, a saturated molecule s bod, collisio of such will result i termiatio of the chai & geeratio of ew radical X AB X A B 3 CCl 3 CCl 3 Cl CCl 3 (Solvet) (Free radical) Chai trasfer i a No-polar solvet ( H / C ) : Eg I bezee, with the formatio of pheyl radical C 6 H 6 H C 6 collidig of with the moomer this radical may start a ew chais Scheme : Durig chai trasfer to a macromolecule the latter loses, say, a hydroge atom to the growig chai it collides with ad turs ito a macroradical as follows : 17

18 X X X X 3 X X By additig trasfer agets to the reactio system oe ca cotrol the average molecular mass of polymer ad obtai polymers with lower degree of polydispersio ad brachig Such agets are called regulators Followig are used as polymerizatio regulators (1) chloriated hydrocarbos (CCl 4, Cl C=CCl,;Cl 3 C-CCl 3 ) () Mercaptas The amout of regulators added rages from to 6 % of the weight of moomer INHIBITS: These are chemical substaces capable of ihibitig or killig the chais growth by cobblig with the active free radicals ad formig either stable products or iactive free radicals If the formed radical has low activity radical is icapable of further growth ad adds o to a polymer radical ad termiates the chais eg Quioes, itrobezee, diitrobezee, polyatomic pheols, (Hydroquioe etc) aromatic amie sulphur, iodie etc Quioe removes hydroge from a growig chai chagig it ito semiquioe 18

19 X X X X H Because of cojugatio the activity of semiquioe is low ad it adds to the growig chais & termial it Depedig o whether a substace etirely stops or oly shows dow polymerizatio it is called as ihibitor or a retarder respectively Some ihibitors such as dipheyl picryl hydrazide (DPPH) exist i the form of stable free radicals which ca easily stop the chai growth by direct couplig N N N N N P P N N N N N (DPPH) (Dead Polymer Molecule) The atmospheric oxyge is a good ihibitor This is why polymerizatio is geerally carried out uder a itroge atmosphere I idustrial practice, however, they are killed by addig further, quatities of itiators to the moomer KINTETICS : Kietics of this type of polymerizatio ca be derived by usig Bodestei s steady state assumptio, which is essetially as follows : At a certai momet of time the system begis to geerate active cetres at the rate a ad the cocetratio of these cetres ( ) icrease cotiuously Simultaeously active cetres disappear at the rate i as a result of chai termiatio, the rate of which icreases with the cocetratio of active cetres [] After some time the cocetratio of active cetres i the systems becomes costat ie the rate at which active cetres are formed becomes equal to the rate at which they are used up : a t (1) the basis of the steady state assumptio ( ie assumig the rates of active cetre formatio & termiatio to be equal) depedece betwee rate & degree of polymerizatio ad other process variable ca be foud 19

20 The rate of termiatio may be expressed as : K [] t () where [] = Steady-state cocetratio of active cetre K 1 = termiatio rate costats The for steady state coditios K [] a (3) Chai propagatio occurs through iteractio of a active cetre with a moomer molecule ad therefore the rate of this reactio may be evaluated from the equatio p K 1 [][m] (4) Where [ m ] is moomer cocetratio & K = the propagatio rate costat The overall polymerizatio rate uder steady state coditios is equal to the rate of propagatio p K [][m] (5) Substitutig i this equatio the expressio for [ ] from equatio ( 3 ) we have K [ m] a (6) K 1 The average degree of polymerizatio of the resultig polymer is determied by the ratio betwee the propagatio ad termiatio rates p P (7) substitutig the value of equatio (3) ad (4), t K P (8) K 1 m a I iitiated polymerizatio the overall reactio rate ad the average degree of polymerizatio of the resultig polymer ca be formed as fuctio of the iitiator cocetratio [ i ] by assumig rate of active cetre geeratio is equal to the iitiator cocetratio From equatio (6) a K 3 [i] (9) where k 3 = the rate costat of active cetre formatio, we get, 0

21 K K K 1 Assumig [ m ] to be costat ad replacig all the costat by k, the overall polymerizatio rate : 3 [ m] [ i] K [i] (10) Thus the overall rate of polymerizatio is proportioal to the square root of iitiator cocetratio Substitutig i Eq (8 ) the value of a from Eq (9) oe obtais P K K 1 [ m] Assumig [ m ] to be costat, ad represetig all the costats by P K' K 1 3 [ i] [ i] 1 K, we obtai Hece, the average degree of polymerizatio varies iversely as the square root of the iitiator cocetratio Note : The higher the activatio eergy of a reactio, the greater will be the effect of temperature Effect of iitiator cocetratio : Number of free radical formed by decompositio of iitiator icreases with iitiator cocetratio Effect of moomer cocetratios : If carried out i solvet, rate of polymerizatio ad molecular mass icreases with moomer cocetratio Effect of pressure : High ad extremely high pressure ( 3,000 to 5,000 atm ad more) speeds up reactio Pressure of several atmosphere or eve tes of atm has practically o effect INIC PLYMEIZATIN I cotrast to radical polymerizatio, which proceeds by trasfer of a upaired electro alog the chai, ioic polymerizatio ivolves the formatio of a carboium io or a carboio ad subsequet trasfer of a positive or egative chage alog the chai 1

22 Depedig o the catalyst used, ad the sig of the charge formed ioic polymerizatio is distiguished betwee catioic ad aioic polymerizatio 1 Catioic polymerizatio : Catioic polymerizatio occurs i the presece of acids ad friedel craft catalyst ( AlCl 3, BF 3, TiCl 4, SCl 4 etc) Beig electro acceptors, these catalysts add o to the moomer formig a carboium io eactio may be represeted schematically as follows : H 3 C X _ H X Chai propagatio is accompaied by trasfer of a positive charge alog the chai Chai termiator evidetly occurs as a result of proto elimiatio The mechaism of olefi polymerizatio uder the actio of metal halogeides ca be exemplified by the polymerizatio of styree i the presece of ti tetrachloride Whe styree reacts with ti tetrachloride, a complex is formed at first which reacts with the ext styree molecule to form a carboium io active cetre : SCl 4 [SCl 4 ] - C 6 C 6 C 6 Chai propagatio cosists i the additio of moomer molecules with regeeratio of the carboium io at the ed of the chai [SCl 4 ] - C 6 C 6 C 6 [SCl 4 ] - C 6 C 6 Apparetly i this case, collisio betwee the opposite eds of the growig io results i moomolecular chai termiatio with elimiatio of the catalyst ad formatio of a double bod i oe of the ed uits of the macromolecule :

23 [SCl 4 ] - C 6 C 6 C 6 3 SCl 4 C 6 C 6 C 6 I some case itroductio of a catalyst atoe will ot start the polymerizatio For istace, isobutee does ot polymerize at low temperature uder the actio of titaium tetrachloride i the absece of moisture I such reactios water performs the fuctio of co-catalyst Acids are also co catalyst of catioic polymerizatio Mechaism of Co-catalyst : The reactio betwee the co-catalyst ad the catalyst molecule results i elimiatio of proto SCl 4 H H [SCl 4 H] SCl 4 H _ HCl [SCl 4 H] _ Which the reacts with a moomer molecule to form a carboium io active cetre H H C H 3 C I this case chai termiatio occurs as a result of collisio betwee the growig carboium io chai ad aio _ [SCl 4 H] H SCl 4 SCl 4 H Here the catalyst is regeerated 3

24 HCl as co-catalyst : [SCl 4 Cl] Cl SCl 4 SCl 4 HCl Additio of the co-catalyst i a amout ot exceedig the stoichiometric ratio with respect to the catalyst icreases the rate of polymerizatio ad decrease the molecular mass of the polymer ly the co-catalyst molecules that combie with catalyst take part i the reactio The part played by the co-catalyst depeds o the mediums I polar solvet HCl accelerates polymerizatio where as i o-polar solvet, such as CCl 4 rate of polymerizatio decreases KINETICS : Assumig moomolecular mechaism of chai termiatio, the rates of the elemetary reactios of catioic polymerizatio ca be expressed by the followig equatios a K 3 [m][b] p K [m] [] t K 1 [] where, [b] = catalyst cocetratio Makig use of steady state assumptio, oe ca fid depedece of the average degree of polymerizatio P ad the overall rate of reactio v o the catalyst cocetratio P is determied by the equatio : P p t K [ m][ ] K [ ] 1 P K' [ m] ie the average degree of polymerizatio is directly proportioal to the moomer cocetratio ad is idepedet of the catalyst cocetratio The overall rate of polymerizatio ca be formed from the equatio 4

25 a P K 3 [m][b]k'[m] If the moomer cocetratio [ m ] is costatly this equatio becomes Kb ie the overall rate of catioic polymerizatio is directly proportioal to the catalyst cocetratio Aioic polymerizatio : I aioic polymerizatio the attack o π electro pair of the moomer i doe by a egatively charged io ie a aio Such a system has extra electros ad the resultat egative charge attacks the π electro pair, pushig it, as far as possible, that is, to the ed of the molecular At the same time, it forms a sigma bod with the moomer molecule, The electro pair pushed to the ed of the molecule results i the formatio of a carbaio or : or X X X This carbaio thus formed propagates the chai The mechaism ca be exemplified by the polymerizatio of usaturated compouds i the presece of potassium amide ( KNH ) i liquid ammoia solutio 5

26 - K NH K NH NH NH Active cetre formatio NH ( ) - Propogatio NH ( ) -1 NH ( ) -1 NH 3 Termiatio NH ( ) -1 NH Examples : I case of polymerizatio of styree i the presece of potassium amide i liquid ammoia molecular mass of polymer is idepedet of the catalyst cocetratio Ad is directly proportioal to the cocetratio of moomer ad the molecular mass of polymer decreases with icrease i temperature The rate of polymerizatio is proportioal to the square of moomer cocetratio ad to the square root of catalyst cocetratio ther moomer such as acrylic acid derivatives methyl methacrylate, acryloitrile, ad methacryloitrile also polymerize with alkali amide The geeral type of iitiators used i this type of polymerizatio are orgao alkali compouds such as butyl lithium, tripheyl methyl potassium ad ethyl sodium I ioiic polymerizatio, chai propagatio ivolves the participatio of a carbaio or a ioic pair; here the ed group of growig polymer molecule is highly active, but fairly stable That is why aioic polymerizatio ca ofte proceed without chai termiatio (because of absece of impurities) util moomer is completely used up 6

27 Such polymerizatio result i polymers whose macromolecular cotai active cetres ad are capable of iitiatig polymerizatio These polymers are called livig polymers Block copolymers ca be produced by addig other species to livig polymers I presece of org alk compouds polymerizatio proceeds differetly The distiguishig feature of this polymerizatio is the bi-fuctioal additio of the moomer C-CDINATIN PLYMEIZATIN: Aioic polymerizatio is ofte subdivided ito aioic polymerizatio proper ad aio co ordiatio polymerizatio or simply co-ordiatio polymerizatio Co-ordiatio polymerizatio icludes polymerizatio i the presece of oregao metallic compouds which proceeds through a stage of formatio of a itermediate catalyst complex, this beig a moomer with the catalyst liked to it by co-ordiatio bod I the polymerizatio catalyzed by orgao metallic compouds two catalyst cetres participate i the chai propagatio reactio, amely, the metal ad the alkyl ( two cetre polymerizatio mechaism) MEANISM : It is thought that additio of the moomer molecule is proceed by formatio of catalyst complex For example, o polymerizatio of isopree i the presece of a orgaolithium compoud Li (rgao Lithium Compoud) C H H C C (Isopree) 3 Li - - C 3 Sice the metal is joied to the moomer by a co-ordiatio bod, polymerizatio ivolvig the formatio of such complexes are called co-ordiatio polymerizatio The structure of the itermediate complex ad the spatial arragemet of the moomer molecule i it ad so i polymer deped o polarity of the metal carbo bod i the catalyst ad the medium i which the polymerizatio is carried out 7

28 The degree of bod polarity i the orgaic compouds of alkali metal is : Li < Na < K The more polar the bod i the catalyst, the more the mechaism of polymerizatio approaches that of the pure aioic mechaism (due to formatio of free ios) Thus polymerizatio of butadiee i the presece of orgao sodium, or orgao potassium compouds results i a polymer of predomiatly 1,-structure K r Na Whereas i the presece of orgao lithium compouds with HC as solvets the structure is 90 % 1,4 ad the resultig polymer is a stereo regular cis- 1,4 polybutadiee If this polymerizatio is carried out i polar solvets, the effect of the catalyst metal o the reactio is weakeed cosiderably due to the formatio of a metal solvet complex the polymerizatio mechaism the approaches the aioic The costitutio of the alkyl group of the catalyst evidetly also has some effect o the structure of the polymers formed Stereo regular polymers do ot form if the alkyl group of the orgao lithium compouds cotais less tha four carbo atom I the other type of example for the same mechaism propagatio of chai is as follows C H Mt rgaometalic catalyst H C H C Diee moomer - Mt - Moomer - Catalyst complex 8

29 Where Mt represets trasitio metals such as Ti, Mo Cr, V, Ni, etc Mt Mt Mt Soo I co-ordiatio polymerizatio, the catalyst moomer complex is a heterogeeous system The moomer is iserted betwee the metal io ad the carbaio with the result that the polymer chai formed is pushed out from the solid catalyst surface For this reaso, this polymerizatio is also kow as isertio polymerizatio By choosig a proper catalyst / solvet system, the co-ordiatio mechaism ca be used to formulate highly stereo regular polymers The well kow Ziegler Natta catalysts belog to this category ZIEGLE - NATTA CATALYSTS : These catalysts cotai orgao metallic compouds of I III groups metals ad chlorides of IV VII group metals with trasitio valece 9

30 The most commoly used are orgao alumiium compouds ad titaium chlorides Sice the alkyl derivatives of alumiium posses electro acceptor properties ad metals of trasitio valece are electro doers, they form co-ordiatio bods readily It is thought that the active catalyst must have a alkyl group icluded i its co-ordiatio bod Mechaism: Accordiatio to this idea the catalyst cosistig of Al ( C ) 3 ad TiCl 3, used i idustry for the productio of polypropylee, evidetly has the followig structures : Cl Cl C Ti Al Cl C 3 The π electro of the moomer iteracts with the 3d electro of titaium, opeig the bod betwee titaium ad the ethyl group carbo ad formig a co- ordiatio bod betwee titaium ad the methylee group carbo of the moomer Cl Cl C Ti Al Cl C Cl Cl Ti Cl - Al C C 3 with subsequet closig of the cycle Cl Cl Ti Cl Al C C 3 Whe the moomer π bod opes ad a bod forms with the catalyst ethyl group carbo the co-ordiatio bod betwee alumiium ad the ethyl group carbo is broke ad a bod is formed betwee the alumiium ad the moomer carbo: 30

31 Cl Cl Ti Cl Al C C Cl Cl Ti Cl - Al C C 3 3 Cl Cl Ti Cl Al C C 3 The resultig complex serves as a active cetre for polymerizatio Sice Ziegler Natta catalyst are isoluble, polymerizatio i which they are ivolved proceed by heterogeeous catalyst The stereo regularity of polymers is affected greatly by the chemical structure of the catalyst Thus, ethylee polymerizatio with the Ziegler Natta catalyst [ Ti Cl 4 Al ( C 6 ) 3 ] results i a liear crystallie polyethylee, but whe - olefis are polymerized with this catalyst polymer with high cotet of atactive structures are obtaied The stereo regularity of the polymer is sharply reduced by the impurities preset i the reactio medium, ad decreases with icreasig temperature of polymerizatio C-PLYMEIZATIN: Copolymerizatio is the joit polymerizatio of two or more moomer species High molecular mass compouds obtaied by copolymerizatio are called copolymers The copolymerizatio of two moomer ca be described by the equatio: A mb A A B A B B B A A B A By usig differet iitial species ad by varyig their ratios, copolymers of various compositios ad properties ca be obtaied Most copolymers are irregular i structure; the differet moomeric uits are radomly arraged i their molecular chais ad therefore o repeatig sectio of the chai ca be sigled out 31

32 Copolymerizatio has foud extesive practical usage because it eable variatio of the properties of high molecular mass compouds over a wide rage For istace, the copolymer of acryloitrile ad viyl chloride CN CN Cl Is readily soluble i acetoe, whereas polyacryloitrile ad poly(viyl chloride) are soluble oly i high-boilig ad difficulty available solvets Copolymerizatio is widely used i the sythetic rubber idustry Copolymerizatio of butadiee with acryloitrile results i a butadiee itrile rubber kow as SKN m CN CN which possess good oil ad petrol resistace Copolymerizatio of isobutee with a small amout of isopree gives butyl rubber C 3 m C C C C Noted for its high gas impermeability Copolymerizatio ca be brought about by may types of polymerizatio reactios The majority of the commercially importat copolymers, however, are made by free radical, ioic or polycodesatio polymerizatio 3

33 Effect of differet techiques of polymerizatio o copolymers The well kow example is the copolymerizatio of the moomer pair methyl methacrylate styree, whose compositio curves are give below At a iitial equimolar ratio of styree to methyl methacrylate (broke lie), the free-radical polymerizatio usig bezoyl peroxide yields a copolymer cotaiig roughly 50 % of styree; A catioic polymerizatio iitiated by borotrifluoride etherate gives a copolymer cotaiig more tha 95 % styree, while the aioic polymerizatio with tripheyl methyl sodium results i a copolymer havig less tha 5 % styree PLY CNDENSATIN: Poly codesatio is a reactio of combiatio of several molecules accompaied by elimiatio of simple by products such as water, alcohol, ammoia or HCl As distict from polymerizatio products, the elemetal compositio of a codesatio polymer does ot coicide with that of its iitial moomers Poly codesatio is characteristics of compouds cotaiig fuctioal groups Whereas these groups iteract the molecule of a simple compoud is evolved ad a ew group is formed which bids the residues of the reactig molecules For examples the reactio betwee a hydroxyl group ad a carboxylic group, givig a ester ad a water molecules H H C C H 33

34 Aother example ca be take of is poly codesatio of ethylee glycol (EG) ad adipic acid H H HC ( ) 4 CH H C ( ) 4 CH H Apart from o-reactive ester group, this product also cotais two reactive groups at the eds This ca further react with aother molecule of EG ad adipic acid as follows : HC ( ) 4 CH H C ( ) 4 CH H H HC ( ) 4 C C ( ) 4 C H H The resultat molecules cotais reactive group at the eds ad hece if more quatities of EG ad adipic acid are made available, it is capable of reactig further The followig coclusios from the study of poly codesatio are draw: i Moomer should have two reactive fuctioal groups for polymerizatio to proceed ii Polymerizatio proceeds by step-wise reactio betwee reactive fuctioal groups iii ly oe type of reactio (ie codesatio) is ivolved iv Polymer formed still cotais both the reactive fuctioal groups at its chai eds Chai growth may occur by iteractio of either a moomer with polymer molecular or of polymer molecule with oe aother A poly codesatio ivolvig molecules of oe species is called Homopolymerizatio Example is poly codesatio of amio acids A poly codesatio ivolvig differet species of molecules is termed as co-poly codesatio A example is the poly codesatio of adipic acid with hexamethylee diamie to form poly hexamethylee diamide HC ( ) 4 CH NH ( ) 6 NH H C ( ) 4 CNH ( ) 6 NH H (-1)H ad the poly codesatio of terephthalic acid with ethylee glycol, resultig i poly (ethylee terephthalate) 34

35 HC CH H H H C C H (-1)H If the reactats are take i a equimolecular ratio, co-poly codesatio proceeds similarly to homo poly codesatio If the reactats are take i a equimolecular ratio co poly codesatio proceeds similarly to homo polymerizatio Poly codesatio of bi fuctioal compouds gives liear polymers Poly codesatio of compouds havig fuctioality higher tha two results i polymers of brached ad three-dimesioal structure, the umber of fuctioal group of the macromolecule icreasig as the reactio progress This process may be illustrated by the poly codesatio of glycerol ad phthalic acid H H H m HC C 6 H 4 CH C C 6 H 4 C C C 6 H 4 C C C C C 6 H 4 C C 6 C C 6 C C C 6 H 4 C eactio route of poly fuctioal compouds: If a molecule cotais two or more fuctioal groups, the reactio may proceed iter molecularly or itra molecularly (as show below) Itra molecular reactio gives rigs formatio X Y z a 35

36 ig formatio ad liear poly codesatio are competig reactios, ad the yields of the cyclic moomer dimmer, trimer or polymer depeds o the ratio betwee the rates of there reactios EFFECTS : 1 Effect of Moomer Cocetratio o Directio of eactio : Decreasig the moomer cocetratio i the reactio medium lowers the probability of itermolecular iteractio, but leaves the probability of itra molecular reactio ucharged The time t 1 durig which some part x of the total amout a of the iitial substace reacts itra molecularly ca be determied from the kietic equatio of a first order reactio t 1 1 K 1 a l a x ad is idepedet of the cocetratio of the substace The time t durig which the same part of the iitial substace reacts iter molecularly is determied by the kietic equatio of a secod order reactio t 1 K x a( a x) ie, t is iversely proportioal to the iitial cocetratio of the substace Thus, decreasig the cocetratio of the iitial substace promotes rig formatio Effect of temperature o eactio outes : The secod factor determiig the rate of reactio is the temperature, which is related to the reactio rate costat by the arrheius equatio : K Ae E / T The ratio of reactio rate costats of poly codesatio Kp ad cyclizatio Kc determies the ratio of yields of poly codesatio product ad cyclic moomer at costat temperature Ti : L 1 K' K' p e A' A' p e e Ec ET T A A p e e E T If the temperature is raised to T, the yield ratio of the cyclic moomer ad the polymer will be determied by the followig equatio: L1 L Ec ET 1 1 A' " p A e T T1 T e A' A" e p 36

37 Sice the pre-expoetial factor A is idepedet of the temperature to the first approximatio, L L Ec ET T T1 T e If the activatio eergy of both, reactios are equal (Ec = Ep), does ot affect the directio of the reactio L L 1 = l3 ad the temperature But if Ec > Ep the ratio L 1 /L becomes greater tha uity with icreasig temperature ad the (yields of the cyclic ) moomer with risig temperature Hece the effect of the temperature o the route of the reactio depeds o the differeces of activatio eergies of the cyclizatio ad poly codesatio reactios, ad greater is this differece, the greater will be the effect KINETICS: It may be thought that i codesatio reactios the molecular mass of polymer should grow idefiitely ad i the limitig case all the moomer should tur ito a sigle joit molecule ie macromolecule Actually polymers obtaied i this way have a limited molecular mass This is due to the fact that, like all codesatio reactios poly codesatio is a equilibrium reactio Cosider, by way of a simple example, the formatio of ethyl acaetate H 3 C CH C 6 H 3 C C H 5 H If water is ot removed from the system, the reactio will ot go to completio but will stop as soo as the cocetratio of the reactats reaches a certai value depedig o the equilibrium costat K = C 3CCH5 C 3CH C H C CH5H The quatity K, characteristic of a give reactio, determies the fial state of the system The equilibrium costat differs for differet reactig fuctioal groups, but is idepedet of the species of radical Shiftig the equilibrium by removig the codesatio by product say from the sphere of reactio will promote the formatio of a polymer with a higher molecular mass Assumig that the equilibrium costats K are ivariable at all stages of the poly codesatio reactio, oe ca fid the depedece betwee the maximum degree of 37

38 polymerizatio P, the equilibrium costat K, ad the umber of molecules of the by product ivolved Sice the total umber of reactig groups remais ivariable i the course of the reactio, the cocetratios of these groups ca be replaced by their umber We ca use the followig otatios eactio: X Y X z Y (-1)a No: umber of the iitial bi-fuctioal compoud, equal to the umber of X groups ad the umber of Y groups N: umber of macromolecules, equal to the umber of X groups ad the umber of Y groups at the ed of the reactio Na : umber of molecules of the by product at equilibrium Nz: No N v umber of Z bod formed If all the bods i the poly- codesatio product are equivalet ad the equilibrium costat durig this formatio is ivariable K a 3 a a (1) Where, 1 = mole fractio of the moomer, = mole fractios of their dimmer, trimer etc, up to -mer Tha, K N N () N Na Dividig the umerator ad deomiator of the right side of the above equatio by No, we get : N 0 N N 0 0 K (3) N N 0 Na N Here, 38

39 N a N N 0 = z = mole fractio of bods per moomeric uit of the polymer N N 0 = a = umber of moles of by product liberated per moomeric uit of the polymer N o N P average degree of polymerizatio of the resultig polymer Substitutig these values ito Equatio (3) we obtai: Trasformig the above equatio we get : z a K (4) 1 p K 1 P (5) a z If the molecular mass of the poly codesatio product is sufficietly large, the value of Nz approaches uity, because z N N N N N 1 z 0 0 N0 N0, N N 0 beig very small Equatig 1 we, get the approximate expressio of the depedece of the average degree z of polymerizatio o the equilibrium costat ad the costat of the by product liberated durig the reactio P K a The degree of polymerizatio of a poly codesatio product is directly proportioal to the square root of the equilibrium costat ad iversely proportioal to the square root of the molar fractio of the by-product liberated durig the reactio Effect of Moomer cocetratio o ate of poly codesatio ad molecular mass of polymer The equilibrium costat is idepedet of the moomer cocetratio because dilutio chages the cocetratio of all the compoets participatig i the reactio proportioally, 39

40 Whe the reactio is coducted to equilibrium, the molecular mass of polymer is also idepedet of the moomer cocetratio But the rate of poly codesatio is proportioal to the cocetratio of the reactats Icreasig moomer cocetratio reduces the time eeded to reach equilibrium ad obtai a polymer with maximum mass Effect of temperature o ate of poly codesatio ad molecular mass of polymer The rate of poly codesatio icreases with temperature The heat effect of the reactio by isochore (isobar) equatio : K L K Q 1 T1 T 1 1 It follows from the equatio that with risig temperature the equilibrium costat icreases i edothermal reactios ad decreases i exothermal reactios The maximum mol Mass of polymer varies i accordace with the value of the equilibrium costat Fig Depedece of the degree of polymerizatio of a poly codesatio product o the temperature T > T 1 ) Icreasig the temperature ofte facilitates removal of the by product, which shifts the equilibrium ad results i the formatio of higher molecular mass polymers PLYME DEGADATIN : Defiitio : Degradatio reactios are reactios ivolvig breakage of bods i the mai molecular chai ad resultig i a decrease i molecular mass of polymer without alterig its chemical compositio (Ed group May be eglected) 40

41 Degradatio is a very importat reactio the chemistry of high molecular mass compouds It is used for determiig the structure of polymeric compouds, ad for obtaiig valuable low molecular mass substaces from atural polymers eg glucose from cellulose ad starch The splittig of polymeric macromolecular to form free macro radicals is employed for sythesizig modified polymers Degradatio of polymers may occur uder the actio of chemical agets (water acids, alcohols, oxyge etc) or as a result of physical iflueces (low, light, high eergy radiatio etc) Chemical degradatio is the most characteristic type i the case of hetero chai polymers ad ivolves selective rapture of the carbo hetero atom bod; the ultimate product of chemical degradatio is the moomer Chemical degradatio of carbo chai polymers i possible oly u8der very vigorous coditios Degradatio of polymers by physical iflueces is usually o selective, because the eergy characteristics of all chemical bods are quite close Methods of Determiig Extet of Degradatio : These methods are based o determiig the umber average or the mass average molecular mass of polymers The kietic ivestigatios of polymer degradatio oe determies the chage i umber average molecular mass per uit time because the chage i umber of particles (molecules) o degradatio of the polymer is proportioal to the umber of bods ruptured, ad is idepedet of the iitial molecular mass of the polymer The umber of bods ruptures ca be established directly by the umber of fuctioal groups formed o degradatio, ie by determiig the molecular mass ther methods of determiig the umber average molecular mass may also be used Types of Degradatio : 1 Chemical Degradatio: Chemical degradatio proceeds uder the actio of polar substaces such as water, acids, amies, alcohols or oxyge Hydrolysis ad Alcoholysis: Hydrolysis is the most commo type of chemical degradatio of polymers Cleavage of a chemical bod with additio of a water molecule Hydrolysis is catalyzed by hydroge or hydroxyl ios Hydrolysis of a polymer depeds o the ature of the fuctioal groups ad bods it is composed The ed group of the ewly formed molecules do ot differ i ature from those of the iitial polymer f great practical importace is the hydrolysis of atural polyacetals poly saccharides 41

42 Complete hydrolysis of starch ad cellulose gives glucose Starch Maltose glucose C 6H105 C1H 11 C6H16 CH 5H C I recet years cellulose cotaiig waste of plat materials are used istead of foodstuff for makig alcohol Polyester also hydrolyze i the presece of acids ad alkalis, hydrolytic cleavages of the ester bod results i alcoholic ad acidic ed groups Poly (ethylee terephthalate) is sythesized from ethers of the acid rather tha from the free acid Hece, it is more expediet to split up the waste by alcoholysis ( glycoholysis) tha by hydrolysis Thus, treatmet of the PET with boilig ethylee glycol results i a diglycolic ester of terephthalic acid H H ( ) C C 6 H 4 C ( ) H H C C 6 H 4 C xidative Degradatio : Though oxidative degradatio is a chemical cleavage process, it proceeds much less selectively tha other types of chemical degradatio xidative degradatio is characteristics ot oly of heterochais but, also of homochais polymers The oxidatio of paraffi hydrocarbo ivolvig opeig of a bod betwee carbo atoms ad the formatio of oxyge cotaiig compouds ( acids, aldehydes ad alcohols) with a smaller umber of carbo atoms This process is used for the commercial productio of higher fatty acids 4

43 The rate of oxidative degradatio of polymers icreases cosiderably i the presece of substaces which break dow readily ito free radicals, ad also i the presece of i sigificace quatities of metals of variable valece, such as Fe, Cu, M ad Ni Thus, the presece of iro stearate cosiderably icreases the rate of oxidatio of atural umber (figure A ) (Fig a) Effect of iro stearate o rate of oxidatio of refied atural rubber at 10 0 C 1 without catalyst 05 percet iro stearate 3 1 % iro stearate 4 15 % iro stearate I the presece of ihibitors of free- radical chai processes the rate of oxidatio ad degradatio of polymer icreases cosiderably After the ihibitor is used up, the oxidatio proceeds at almost the same rate as without the ihibitor The effect of the chemical structure of a polymer o its resistace to oxidative degradatio is already fairly clear I the H/C series this depedece ca be observed by competig the rate of oxidative degradatio of poly ethylee ad poly propylee (figure b) 43

44 (Figure-B) Absorptio of oxyge by various poly olefis at C (iitial press 600 mm hg fig) 1 High pressure polyethylee (PE) Low pressure PE 3 Ethylee propylee copolymer 4 Polypropylee The presece of tertiary carbo atom i polypropylee sharply lowers its resistace to oxidative degradatio 3 Degradatio by Physical Iflueces : The degradatio of polymers uder the actio of lumious eergy high eergy radiatio, ad mechaical or thermal eergy proceeds accordig to a chai mechaism with the itermediate formatio of free radicals The rate of idividual steps of the chais process vary depedig o the kid of eergy used, ivolvig a chage i structure of the polymer ca either ( 1 ) be completely depressed or ( ) made predomiat I the first case the reactio results i a decreased i molecular mass of polymer, i the latter ease, all its physicochemical ad mechaical properties are chaged The first step / stage of the chai process which develops i the polymer uder the actio of some kid of eergy is the appearace of free radicals 44

45 Coversio of macromolecule to macro radical may result i rapture of a adjacet carbo carbo bod with the formatio of a ew free radical Trasfer of the upaired electro (chai propogatio) may also occur itramolecularly with elimiatio of a moomer molecule C H At chai termiatio step the reactio may be accompaied by a chage i structure of polymer This may ivolve combiatio of the radicals to form liear, brached, ad three dimetioal polymers Liear Brached 45

46 Three-dimetioal Photo chemical Degradatio : eactio occurrig upo irradiatio of polymers play a importat part i ageig processes, ad ofte determie the life time of atural ad sythetic fibers, rubber goods etc The chief process causig the chage i properties of the polymer is i most cases the photo chemical chai reactio of scissio of its molecular chai, activated by atmospheric oxyge The itesity of processes occurrig depeds o the wave legth ad itesity of irradiatio, the presece of iitiators, ad the ature of polymer eg At a elevated temperature (150 0 C) UV light causes depolymerizatio (photolysis) of rubber with the liberatio of isopree The rate icreases sharply i the presece of atmospheric oxyge Light weatherig decomposes polyethylee i or 3 years, whereas i the dark at ordiary temperature it does ot decomposes at all i the same period of time The additio of carbo black to rubbers ad polyethylee icreases their resistace to ageig Light of wavelegth less tha to 4 comes oly photo degradatio i cellulose, but light of a greater wavelegth causes oxidative degradatio ad hydrolysis as well as photodegradatio Cellulose ester ad polyamides are also degraded by UV light Stabilizatio of polymers to photo chemical degradatio is based o additio to the polymer of compouds like bezopheoe ad its derivative, which readily absorb lumious eergy ad trasform it so that it is radiated by tha i quata of lower eergy which are harmless to the polymer 46

47 Actio of High Eergy adiatios : Uder the ifluece of ioizig radiatios polymer udergo profoud chemical ad structural chages affectig all its physiochemical ad mechaical properties as well Irradiated PE possesses very high resistace to heat ad chemical agets, as well as other valuable properties Irradiatio of polymers is accompaied by the formatio of double bods Degradatio ad formatio of 3-dimetioal structures always occurs simultaeously whe polymers are irradiated, but some polymers are completely degraded by high eergy radiatios, while i other cross likig of macromolecules predomiates Example of polymers that are cross liked ad degraded o irradiatio are give below : Polymers that form 3-dimesioed Polymer that udergo degradatios Structure 3 3 Polyethylee 3 3 Polyisobutae Polypropylee C 6 C 6 Poly--methylstryre C 6 C 6 Polysturee 3 3 Cl Cl Poly(viychloride) ubber Polyamides etc C CNH Polymethacrylamide C CNH - Flourie cotaiig polymers - Cellulose - Cellulose ester Thermal degradatio: The stability of polymers to heatig, the rate of their thermal decompositio, ad the atures of the resultig products deped o their chemical structure of the polymer Like ay other chai reactio, thermal degradatio is accelerated by substaces which decompose readily ito free radicals, ad is slowed dow i the represeted of substaces which are free radical acceptors 47