21. olymers There are two types of polymerisatio additio ad codesatio Additio olymerisatio A additio polymer forms whe usaturated moomers react to form a polymer Moomers cotai = bods oly(alkees) are chemically iert due to the strog - ad - bods ad o-polar ature of the bods ad therefore are o-biodegradable. hai forms whe same basic uit is repeated over ad over. You should be able to draw the polymer repeatig uit for ay alkee It is best to first draw out e.g. For but-2-ee the moomer with groups 3 of atoms arraged aroud 3 3 the double bod 3 3 3 odesatio olymerisatio The two most commo types of codesatio polymers are polyesters ad polyamides which ivolve the formatio of a ester likage or a amide likage. I codesatio polymerisatio there are two differet moomers that add together ad a small molecule is usually give off as a side-product e.g. 2 or l. The moomers usually have the same fuctioal group o both eds of the molecule e.g. di-amie, di carboxylic acid, diol, diacyl chloride. Formig polyesters ad polyamide uses these reactios we met earlier i the course arboxylic Acid Alcohol Ester water Acyl chloride Alcohol Ester l arboxylic Acid Amie amide water Acyl chloride Amie amide l If we have the same fuctioal group o each ed of molecule we ca make polymers so we have the aalogous equatios dicarboxylic acid diol poly(ester) water diacyl dichloride diol poly(ester) l dicarboxylic acid diamie poly(amide) water diacyl dichloride diamie poly(amide) l Usig the carboxylic acid to make the ester or amide would eed a acid catalyst ad would oly give a equilibrium mixture. The more reactive acyl chloride goes to completio ad does ot eed a catalyst but does produce hazardous l fumes. Terylee- a commo polyester Bezee-1,4-dicarboxylic acid 2 2 Ethae-1,2-diol Terylee fabric is used i clothig, tire cords 2 2 2-1 2 The -1 here is because at each ed of the chai the ad are still preset ( 2 ) 3 l l etaedioyl dichloride Bezee-1,4-diol ( 2 ) 3 2-1 l Goalby chemrevise.org 1
ylo 6,6 - a commo polyamide ( ( 2 ) 4 2 ) 6 hexaedioic acid exae-1,6-diamie (2)4 (2)6 The 6,6 stads for 6 carbos i each of the moomers. Differet legth carbo chais produce differet polyamides Kevlar- a commo polyamide 2-1 2 2 2 2 2 2-1 2 ote o classificatio for codesatio polymers If asked for type of polymer It is polyamide or polyester Whereas type of polymerisatio is codesatio It is also possible for polyamides ad polyesters to form from oe moomer, if that moomer cotais both the fuctioal groups eeded to react ( 2 ) 3 l 4-hydroxybutaoyl chloride ( 2 ) 3 ( 2 ) 3 3 repeatig uits ( 2 ) 3 2 3 repeatig uits 3 2-hydroxypropaoic acid (lactic acid) 3 3 3 3 repeatig uits poly(lactic acid) 2 lactic acid molecules ca also form a rig diester 4-hydroxypetaoic acid It is possible for some of these compouds to form various cyclic esters uder differet coditios from formig the polymer. You do ot eed to lear these but may be asked to deduce structures from iformatio give 1 repeatig uit Goalby chemrevise.org 2
roperties of polymers Low desity (LD) ad high desity (D) poly(ethee) are produced from ethee, usig differet catalysts ad reactio coditios. I DE the polymer chais are sigle strads ad ca closely lie up i parallel (called a crystallie structure). I LDE, the chais are irregularly packed, brached chai polymers therefore they caot get as close together. The polymer chais i DE ca form stroger va der waals forces betwee them. l oly(chloroethee) is a polymer that is water proof, a electrical isulator ad does t react with acids. I its pure form it is a rigid plastic. The strog permaet-dipole itermolecular bodig betwee polymer chais prevets them movig over each other. I this uplasticised form it is used make uv widow frame coverigs ad gutterig. F F olytetrafluoroethee (TFE, or Teflo ) is very resistat to heat ad chemical corrosio. It is used o ostick cookware. It has strog va der waals forces betwee chais F F Itermolecular bodig betwee codesatio polymers chais olyesters have permaet dipole forces betwee the = groups i the differet chais i additio to the istataeous temporary dipole forced betwee the chais. olyamides (ad proteis) have hydroge bodig betwee the loe pairs o oxyge i = groups ad the i the groups i the differet chais. There are also istataeous temporary dipole forces which are large because there are may electros i the molecule olyamides will therefore have higher meltig poits tha polyesters. ydroge bodig betwee Kevlar chais causes chais to lie up ito very strog sheets. It is used to make bullet proof clothig. Goalby chemrevise.org 3
roteis rimary Structure of roteis roteis are polymers made from combiatios of amio acids. The amio acids are liked by peptide liks, which are the amide fuctioal group. The primary structure of proteis is the sequece of the 20 differet aturally occurrig amio acids joied together by codesatio reactios with peptide liks 3 3 3 S S 2 3 2 2 2 Secodary Structure of a rotei. Secodary Structure α-helix The 3D arragemet of amio acids with the polypeptide chai i a corkscrew shape is held i place by ydroge bods betwee the of group ad the of = of the fourth amio acid alog the chai The -groups o the amio acids are all poited to the outside of the helix Secodary Structure β-leated Sheet Structure of roteis The secodary structure ca also take the form of a β pleated sheets The protei chai folds ito parallel strads side by side The protei chai is held ito a the pleated shape by ydroge bods betwee the of - group ad the of = of the amio acid much further alog the chai i the parallel regio. Goalby chemrevise.org 4
Tertiary Structures of roteis The tertiary structure is the foldig of the secodary structure ito more complex shapes. It is held i place by iteractios betwee the - side groups i more distat amio acids. These ca be a variety of iteractios icludig hydroge bodig, sulphursulphur bods ad ioic iteractios By Elizabeth Speltz (SpeltzEB) (w work) [ublic domai], via Wikimedia ommos ydroge bods 2 2 3 2 3 2 ydroge bods could form betwee two serie side chais i differet parts of the folded chai. (ther amio acids chais ca also hydroge bod) ioic iteractios 3 2-3 3 Ioic iteractios could form betwee acidic amio acids such as aspartic acid ad basic amio acids such as lysie. There is a trasfer of a hydroge io from the - to the - 2 group to form zwitterios just as i simple amio acids. Sulphur bridges 3 3 S 2 S 2 3 2 S 3 2 S If two cysteie side chais ed up ear each other due to foldig i the protei chai, they ca react to form a sulphur bridge, which is a covalet bod. 2 S 2 You do t eed to lear the details of these iteractios o this page but uderstad the priciples of how the tertiary structure is held i place. cysteie (cys) Goalby chemrevise.org 5
DA Key molecules i DA - phosphate io 2 2-deoxyribose (a petose sugar) The 4 bases 2 2 3 Adeie (A) Guaie (G) 2 Thymie (T) ytosie () The structures of these substaces are give i the hemistry Data Booklet. ucleotides A ucleotide is made up from a phosphate io boded to 2-deoxyribose which is i tur boded to oe of the four bases adeie, cytosie, guaie ad thymie - 3 phosphate - 2 base - 2-2 sugar Although the structures will be give i the data sheet you eed to lear which atoms o the base jois o to the sugar ad how the sugar attaches to the phosphate ios Goalby chemrevise.org 6
Sugar- phosphate chai - 2-2 A sigle strad of DA (deoxyriboucleic acid) is a polymer of ucleotides liked by covalet bods betwee the phosphate group of oe ucleotide ad the 2- deoxyribose of aother ucleotide. - - 2 2-2 This results i a sugar-phosphatesugar- phosphate polymer chai with bases attached to the sugars i the chai. arefully lear how these joi together DA exists as two complemetary strads of the sugar phosphate polymer chai arraged i the form of a double helix. ydroge bodig betwee base pairs leads to the two complemetary strads of DA. - Guaie pairs with cytosie by 3 hydroge bods - - 3 Adeie pairs with thymie by 2 hydroge bods - Goalby chemrevise.org 7
o-solvet based adhesives Most adhesives are solvet based. They harde whe the solvet evaporates. The followig harde i a differet way. Epoxy resi glues The glues have two compoets oe cotaiig polymers chais ad the other a hardeer (which is a cross-likig aget). They are mixed together whe the glue is applied. As the glue sets the hardeer forms cross liks betwee the polymer chais formig a strog thermosettig structure. 2 2 3 3 2 2 pre-polymer with epoxy group Diamie is crosslikig hardeer 2 2 2 2 2 2 2 2 polymer chais cross liked ito a strog thermosettig structure Eds of polymer chais ross liks i thermosettig polymers ted to be covalet bods which are strog ad ot easy to break. ce formed the polymer caot be melted You do t eed to remember the details of the substaces here- just the process of crosslikig. olymers with oly weaker itermolecular forces betwee chais ca geerally be heated up to melt ad chage their shape. These are called thermosofteig polymers. Superglue The moomer i superglue polymerises o exposure to moisture i the atmosphere to form a strog additio polymer moomer ethyl 2-cyaoprop-2-eoate You do t eed to remember the details of the substaces here oductig polymers poly(ethye) Ethye has a triple bod. It ca form a additio polymer that has alterate double sigle bods. Ethye oly(ethye) also kow as polyacetylee oly(ethye) coducts electricity. It coducts through its log chai of delocalised electros. It ca delocalise because the polymer chai is plaar so the π bods overlap with each other. Goalby chemrevise.org 8
Degradable polymers oly(alkees) are chemically iert ad ca therefore be difficult to biodegrade oly(alkees) are chemically iert due to the strog - ad - bods ad o-polar ature of the bods ad therefore are o-biodegradable. Some codesatio polymers may be photodegradable as the = bod absorbs radiatio. hemical reactivity of codesatio polymers polyesters ad polyamides ca be broke dow by hydrolysis ad are, therefore, biodegradable The reactivity ca be explaied by the presece of polar bods which ca attract attackig species such as ucleophiles ad acids ydrolysis olyesters ad polyamides ca be hydrolysed by acid ad alkali The hydrolysis will result i the origial moomers formig- although the carboxylic acid or amie group will be i salt form depedig o whether the coditios are alkalie or acidic ( 2 ) 4 ( 2 ) 6 l 3 3 -( 2 ) 4 ( 3 ) 2 2 - This polymer has both a amide ad ester lik a - - 2 ydrolysis of di-peptides/proteis If proteis are heated with dilute acid or alkali they ca be hydrolysed ad split back ito their costituet amio acids. 3 3 3 2 3 3 The compositio of the protei molecule may the be deduced by usig TL chromatography 3 3 3 2 3 3 3 3 2 2 a 2-2 - 2 2 - Goalby chemrevise.org 9