Samples questions on Polymer Chemistry

Size: px

Start display at page:

Download "Samples questions on Polymer Chemistry"

Allan Brown
6 years ago
Views:

1 Samples questios o Polymer Chemistry Symbols carry usual meaigs Module 1: Lecture For a polydisperse polymer sample rak the M, M w, M z, ad M v accordig to their values. I 10 g of a polystyree sample (M 30,000; Mw 60,000), you add 1 g of a moo-disperse polystyree sample of (i) M w = M = 10,000 (ii) M w = M = 30,000 (iii) M w = M = 45,000 (iv) M w = M = 60,000 (v) M w = M = 80,000. What would be the M w ad M for ew mixed samples lower or higher tha the first sample? Betwee M w ad M which oe will chage more (i terms of %)? 2. A 1 L of polymer solutio cotais 10 g of a polymer. A o-solvet was added to the solutio i steps ad differet fractios of polymer samples were precipited out i each step of o-solvet additio. The polymer fractios were washed, dried, weighed, ad subjected to M determiatio. Assumig that for each fractio M = M w calculate the M, M w, ad PDI of the origial polymer sample that was dissolved at the begiig. Fractio No. Weight (g) M (= M w ) (g mol -1 ) , , , , , What is the o. average degree of polymerizatio (DP) of each of the followig polymers with M 254,000? H N CH 2 C 5 CH 2 CH 2 C Cl C CH 2 C Cl C

2 4. Draw the repeat uit of the polymer that would be obtaied i the polymerizatio of the followig moomers. Also write ames of the followig polymers ad classify them whether they are codesatio or additio polymers, formed by chai or step or rig opeig polymerizatio. H Cl Cl H 2 N NH 2 + H H ClC CCl CH 3 NC H H NC H H Cl Cl H H

3 5. I 10 g of a polystyree sample (M 30,000; M w 60,000), you add 1 g of polystyree sample with (i) M 20,000, PDI=2; (ii) M 40,000, PDI=2. Will the % chage, (+ve or ve), of M w ad M be same i (i) or (ii)? Justify your aswer. 6. Write characteristics of chai growth ad step growth polymerizatio with respect to the followig features if the reactio is stopped before completio (say at 80% Coversio) (i) MW as a fuctio of coversio (show schematically); (ii) Compositio of reactio medium. 7. Give A ad B are two moomers, write geeric structures of Radom, Alteratig, Block, Graft, Start copolymers. 8. Draw schematically how the stress vs. strai plots would look like for followig polymer samples whe the stress is applied i the logitudial directio fibre, flexible plastics, rigid plastics, ad elastomers. Module 2: Lecture Calculate the M of a mixture of adipic acid ad hexamethylee diamie for extet of reactio (p) of Molar ratio of adipic acid to hexamethylee diamie take i the feed is 0.95 : 1.0. Assume o side reactios. 10. The followig data were obtaied durig exterally catalyzed codesatio of 12-hydroxyl stearic acid (MW ~ 300) at K. [CH] was determied for each sample by titratig with ethaolic sodium hydroxide. How log it would take to build a M of 30000? t (h) [CH] (mol dm -3 ] A high molecular weight copolyester was sythesized by reactig the two diacids with a diol. The compositio of the moomer mixture was HC-R 1 -CH : HC-R 2 -CH : H- R-H = 1 : 1 : 2 (by mole); reactivity of R 1 -CH group towards R-H is higher compare to the reactivity of R 2 -CH group towards R-H. Estimate the compositio (mole ratio) of R 1, R 2, R i the fial copolymer? Justify your aswer i brief by assumig that it has the most probable distributio of molar mass. 12. Everythig else remaiig same, i which of the followig two cases the chaces of formig cyclic products is more for a step-growth polymerizatio process: coc. of moomer is 2 M, ad 0.5 M. Explai briefly. 13. Show that the time required for reachig p = 0.98 to p = 0.99 is very close to the time to reach p = 0.98 from the start of polymerizatio for the exteral acid-catalyzed polymerizatio of a equimolar mixture of a diol ad a diacid. (p is the fractio of fuctioal group reacted i the polymerizatio).

4 14. A polyamide was prepared by bulk polymerizatio of hexamethylee diamie ( g) with adipic acid (14.6 g) at 300 C. Aalysis of the whole reactio product showed that it cotaied mol of carboxylic acid groups. Evaluate the umber-average molar mass, M, of the polyamide, ad also estimate its weight-average molar mass, M w, by assumig that it has the most probable distributio of molar mass. 15. Whe a equilibrium step- growth polymerizatio is 99% complete what fractio of the reactio mixture is still moomer? (a) o a mole basis? (b) o a weight basis? 16. I the polymerizatio of H 2 N(CH 2 ) 5 CH to form Nylo-6, what weight fractio of the reactio mixture has the followig structure whe 99% of the fuctioal groups have reacted? HN CH 2 C Ca the followig polyester recipe be carried to complete coversio without gellig? Petaerythritol (1.2 mol), phthalic ahydride (0.5 mol) ad tricarballyic acid (0.49 mol). 18. Whe caprolactam is polymerized ito 6-ylo, 5 wt. % of the moomer is left uchaged, ad remaiig 95 % is coverted to polymer havig the Flory distributio of molecular weight ad X w = 500. Later the mixture was extracted by that removed all species up through that with x = 5. Calculate X for the followig: a. The polymer with X w = 600. b. The mixture of 10 % moomer ad 90 % polymer. 19. Discuss the possibility of cyclizatio i the polymerizatio of H 2 N CH 2 CH HC CH 2 CH + H CH 2 H 2 For the cases where has values from 2 to 12? At what stage(s) i the reactio is cyclizatio possible? What factors determie whether cyclizatio or liear polymerizatio is the predomiat reactio? 20. For each of the followig reactios system idicate whether the product is a liear, brached, cross-liked, or hyper brached polymer. a. A 2 + B 2 b. AB 2 c. AB 3 d. A 2 + B3 e. AB 2 + B 3 f. AB + B The polymerizatio betwee equimolar amouts of a di-ol ad di-acid proceeds with a equilibrium costat of 100. What will be the expected degree of polymerizatio ad extet of reactio if the reactio is carried out i a closed system without removal of by-product water? To what level must [H 2 ] be lowered i order to obtai a degree of polymerizatio of 100 if the iitial cocetratio of carboxyl groups is 1 M?

5 Module 3: Lecture For a moomer of geeral structure CH 2 =CHX, complete the followig table. Put + if the moomer ca be polymerized by the method metioed at the top of the colum, ad - if polymerizatio by the method is ot feasible. Briefly justify your aswer. X Free radical Aioic Catioic -CN -Ph -CH 3 -CCH Derive a expressio for the rate of polymerizatio i a radical polymerizatio reactio. Assume steady state, termiatio of reactio is oly by bimolecular reactio betwee propagatig species, equal reactivity of differet propagatig chais. 24. A typical radical polymerizatio is beig carried out with the followig assumptios: iitiatio by thermal dissociatio of iitiator, steady state ad equal reactivity of propagatig radicals, termiatio of reactio is oly by bimolecular couplig, ad o chai trasfer. What will happe to the polymer MW ad Rp if oe icreases: (i) iitiator coc. (ii) moomer coc. Justify your aswer. 25. Arrage i icreasig order of X of polymers obtaied by polymerizatio of styree iitiated by thermal decompositio of bezoyl peroxide at 80 C i the followig solvets bezee, 1-butaethiol, isopropylbezee, carbo tetrachloride. Assume chai trasfer oly to solvet. Briefly explai your aswer. 26. Assumig that i free radical polymerizatio the rate costat ca be replaced by the appropriate Arrheius expressios: K d = A d exp (-E d /RT); K p = A p exp (-E p /RT); K t = A t exp (-E t /RT) Calculate the chages i the rate of polymerizatio ad the degree of polymerizatio caused by icreasig the temperature of polymerizatio of styree i bezee iitiated by AIBN from 60 C to 70 C give that: E p = 34 kj mol -1 ; E t = 10 kj mol -1 ; E d = 126 kj mol -1. State ay assumptio made by you. 27. Metio two advatages ad two disadvatages of solutio polymerizatio over bulk polymerizatio. 28. Write the mai igrediets required i a emulsio polymerizatio. Metio oe disadvatage ad oe advatage of emulsio polymerizatio over dispersio polymerizatio. How ca oe icrease Rp without compromisig o molecular weight i a emulsio polymerizatio? 29. Explai briefly autoacceleratio i radical polymerizatio? Why does it happe?

30. Write the costitutioal isomers of polyisopree possible whe it is sythesized from isopree by radical chai polymerizatio process.

I a typical free-radical polymerizatio rak the followig accordig to their values (a) R i, R p, R t (b) k d, k p, k t 32.

The followig data were obtaied from the experimets. Commet o the differece i the moomer bottles. Assume all other coditios remaied same.

Metio two techiques of livig radical polymerizatio. Give a example of block copolymer thatt is usually sythesized by livig aioic polymerizatio. 34.

Metio two possible termiatio steps of polymerizatio of isobutylee by iitiatig system BF 3 + H 2. 36.

After all the acryloitrile was polymerized, 1 M methylmethacrylate (MMA) was added maitaiig the perfect iert atmosphere.

6 30. Write the costitutioal isomers of polyisopree possible whe it is sythesized from isopree by radical chai polymerizatio process. Commet o the relative proportio of these isomers at the ed of polymerizatio reactio doe at various temperatures. 31. I a typical free-radical polymerizatio rak the followig accordig to their values (a) R i, R p, R t (b) k d, k p, k t 32. Styree was polymerized by heatig to 100 C (self iitiated). Styree was take from four differet bottles for four reactios. The followig data were obtaied from the experimets. Commet o the differece i the moomer bottles. Assume all other coditios remaied same. Module 4: Lecturee Defie of livig polymerizatio. Metio two beefits of livig polymerizatio i geeral over covetioal o-livig polymerizatios. Metio two techiques of livig radical polymerizatio. Give a example of block copolymer thatt is usually sythesized by livig aioic polymerizatio. 34. Show the possible propagatio steps of polymerizatio of styree iitiated by Na + aphthalee. 35. Metio two possible termiatio steps of polymerizatio of isobutylee by iitiatig system BF 3 + H A livig aioic polymerizatio (without ay side reactio) of 1 M acryloitrile was iitiated by 0.01M C 4 H 9 Li (butyl lithium). After all the acryloitrile was polymerized, 1 M methylmethacrylate (MMA) was added maitaiig the perfect iert atmosphere. Whe alll the MMA was cosumed, little amout of water added to quech the livig chai eds. (i) Write the structure of the fial polymer produced icludig the ed groups. (ii) What is the M of the fial polymer? 37. How are ioic chai polymerizatios differet to radical chai polymerizatio i regard to solvet polarity ad iheret termiatio steps? 38. Write three mechaistic features for propagatio step i Ziegler-Natta polymerizatio.

7 39. Cosider the followig reactivity ratios for the copolymerizatio of three moomer pairs: Case r 1 (for M 1 ) r 2 (for M 1 ) (i) (ii) (ii) (iv) Specify the type of copolymer (radom/alt/block). Which of the two moomers (M 1 or M 2 ) would be preset i higher mole fractio i each case? Assume polymer sample is isolated at low coversio, feed ratio of M 1 :M 2 =1: Show the possible stereochemical forms of polymers derived from moomers of the type CH 2 =CXY. Metio i which coditio it is possible to sythesize these differet stereochemical forms. 41. Write the chemical structure ad ames of the polymers produced by rig-opeig polymerizatio of the followig moomers C NH Discuss the effect of rig size o the tedecy of a cyclic moomer toward rig-opeig polymerizatio. Module 5: Lecture Write the expressios of root-mea-square ed-to-ed distace for a volumeless polymer chai i the followig cases a) freely-joited ad freely-rotated; b) with restrictios i both bod agle ad rotatio aroud sigle bod; c) free-joited but restricted rotatio. Also write the expressio for case b) whe polymer chai is a true chai with defiite volume (this is case d). Rak the values of rms ed-to ed distace for the above four cases. Metio two coditios whe the values i cases b) ad d) become equal. 43. I referece to above questio, how will the magitude of (c) differ (more/less/equal) from (b) i followig cases: pure amorphous polymer; polymer i a good solvet; polymer i a theta solvet; polymer i a o-solvet. 2 1/ For the same polymer chai what would happe to the value of cotour legth, r o ad 2 2 r 1/ o icreasig the temperature assumig all other parameters remai same. Explai your aswer i brief. 45. Why do we eed to add a expasio factor over uperturbed dimesio to get a true dimesio of polymer chai? 46. Write the Flory-Huggis equatio for Gibbs free eergy of mixig of a polymer solutio describig all the terms. Write two limitatios of this with brief explaatio.

8 47. From Flory-Huggis equatio it ca be show that for the formatio of a solutio from a moodisperse polymer the partial molar Gibbs free eergy of mixig, G 1 for solvet is give by 1 2 G 1 = RT l( 1 2 ) (1 ) 2 2 r where 2 is the volume fractio of polymer, r is the ratio of the molar volume of the polymer to that of the solvet, ad is the polymer-solvet iteractio parameter. Show that the solutio behaves like a ideal solutio whe the value of equals to Explai why thermodyamically it is always difficult to form miscible bleds of two high molecular weight polymers. I what coditio do two high molecular weight polymers become miscible? 49. A dilute polymer solutio obeys Eistei equatio for o-draiig polymers. Derive Mark- Houwik equatio from this. 50. Write Mark-Houwik expressio. How ca you determie MW of a ukow polymer sample usig this equatio? 51. I a sigle setece defie biodal compositios. slowly addig a o-solvet to a polymer solutio which fractio of the polymer sample precipitates first ad why? 52. I have take a 10% solutio of a polymer ad o decreasig the temperature of the solutio the polymer precipitated at 15 C, ca you call 15 C is the UCST of the polymer i that solvet? 53. What are LCST ad UCST? For which type of polymer LCST ad UCST exists. Explai with the help of thermodyamic parameters. Give example of oe polymer i each case. 54. Two differet polymers havig high molecular weight were mixed ad they were foud to form a miscible bled. Which is more likely to be observed for this system - LCST or UCST ad why? 55. What is solubility parameter? How this is determied for small orgaic molecules ad polymers. Module 6: Lecture Complete the table with respect to the MW obtaied by the followig techiques of measuremet - Techique Viscosity GPC Light scatterig smotic pressure Ed group by NMR Absolute or Relative M w or M or M v or M z Commet of applicability rage

9 57. State the methods you would use to determie - a) M for samples of PEG with values i the rage of to g mol -1, b) M for samples of PAN with values i the rage of to g mol -1, c) the polydispersity idices of samples of PS with molar masses i the rage 10 4 to 10 6 g mol -1. For each method, give the reasos for your choice, ad discuss briefly possible errors i the determiatios. 58. smotic pressure ( ) of solutios cotaiig differet cocetratio (c) a polymer was measured. /c was foud to be idepedet of c. What would happe to the solutio(s) if you add aother solvet to it where the added solvet is a o-solvet for the polymer? Explai your aswer i brief. 59. For a polydisperse sample, show that measuremet of ay colligative property would give iformatio about M. 60. Explai why the value of R for polymer solutios depeds o? Two polymers have same Mw but they have differet shapes Coil ad rod. Will the light scatterig itesity at 45 be differet for the solutios cotaiig same cocetratio of the two polymers? 61. You are provided with a polymer sample, a solvet for the polymer, a balace, ad a multiagle laser light scatterig istrumet. Describe the steps you will take to costruct Zimm Plot. (Values of 0, d/dc, ad other istrumet parameters are also provided). From the Zimm Plot what are the iformatio you ca get about the polymer, polymer/solvet system ad how? 62. What is the pricipal behid gel permeatio chromatography? What are the types of detector ca be use to detect polymer cocetratio at the ed a GPC ru give two example. 63. You are give three moo-disperse polystyree sample of same M W (as determied by light scatterig) but of differet shape viz. Coil, Rod, Sphere. If these three samples are passed through GPC colum uder same experimetal coditio (colum, solvet, temperature, flow-rate, detector positio) what would the order of elutio? Justify your aswer. 64. How would itrisic viscosity chage (decrease or icrease) i followig cases - a) icrease chai legth (MW) of liear molecule, b) icrease mass of chai segmets, keepig chai legth costat, c) icrease stiffess of chai, d) add braches to chai keepig MW costat. 65. You have sythesized a polymer by chai growth mechaism ad subsequetly submitted for molecular weight determiatio. You have bee provided with the followig report i) M measured by light scatterig method is 55,000 g/mol; ii) M ad M w measured by GPC are 95,000 g/mol ad 55,000 g/mol respectively. Idetify the error(s) i the report i) ad ii). 66. Why M v measured by viscosity method is ot a absolute molecular weight? 67. Why polymers made by step-growth mechaism are usually ot used as GPC stadard? 68. The table below gives the mea flow times (t) i a suspeded-level viscometer recorded for solutios of oe of the five moodisperse samples of polystyree (sample B) at various cocetratios (c) i cyclohexae at 40 C. Uder these coditios, the mea flow time (t 0 ) for cyclohexae is s.

10 Cocetratio 10 3 (g cm -3 ) Time (s) Determie the itrisic viscosity of the sample. The itrisic viscosities of the other three polystyree samples were evaluated uder the same coditios ad are give i the followig table together with their Mw values determied by light scatterig. Sample Mw (g mol -1 ) [ ] (cm 3 g -1 ) A 370, B 102,000 - C 269, D 690, Usig these data together with the calculated values of itrisic viscosity of sample B, evaluate the costats of the Mark-Houwik equatio for polystyree i cyclohexae at 40 C. 69. The chemical structure of a copolymer is give below. Quatitative 1 H ad 13 C NMR spectra are available for the copolymer. How ca you use the NMR spectra to derive at the followig iformatio about the copolymer: Compositio of the two moomers i the copolymer (x:y); ature of the copolymer (alt/ra/block), ad value of. x CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 y Module 6: Lecture A polymer is beig cooled from a temperature above T m to a temperature below T m. What are the possible states possible just below the T m a) 100% crystallie solid; b) polymer remais i melt form; c) part of it is melt ad part is crystallie solid. Explai your aswer i brief. 71. The RMS ed-to-ed distace of three polymers i their respective theta solvet follows the followig order PolyA > PolyB > PolyC. Assumig that solubility parameters of the polymers are similar what could be the possible rak of the three polymers accordig to their T g. Explai your aswer i brief. 72. Same umber of moles of two moomers (A ad B) was mixed ad polymerized ad the product was aalysed after completio of reactio. Two Tg was obtaied for the reactio product. Which oes from the below cases are feasible a) immiscible bled of Poly A +

11 Poly B, b) Poly A - block - Poly B, c) miscible bled of Poly A + Poly B, d) poly (A-ra-B), poly(a-alt-b) 73. Draw schematically modulus (or logarithm of it) vs. temperature curve to show the four (or five) differet regios of viscoelasticity that a amorphous polymer experiece whe heated from a temperature below T g. 74. What are two mai factors which helps crystallizatio of polymers? Briefly explai. 75. A copolymer was sythesized by reactig equimolar mixture of moomer A (mol. weight. 100 g/mol) ad moomer B (mol. wt. 150g/mol). The T g s of homopolymers of A ad B are 100 C ad 200 C respectively. What would be the T g of the copolymer if it was a) a completely radom copolymer ad b) a pure block copolymer. 76. Which of the polymers i each pair is expected to have higher T g ad why? (i) polyethylee ad polypropylee, (ii) poly(but-1-ee) ad poly(but-2-ee), (iii) CH 3 CH 2 C C R = -CH 3 ad R= -CH 2 CH 2 CH 3 R 77. Draw schematically stress-strai curve(s) to show the followig elastic elogatio, tesile stregth, yield stress, ultimate stregth, elogatio at break, toughess. 78. State some of the mechaisms with examples by which additives work as fire retardat i polymer.

POLYMERS

POLYMERS Short Aswer Questios: **1.What is PHBV? How is it useful to ma? As. PHBV is Poly β-hydroxy butyrate-co- β-hydroxy valerate.it is a biodegradable polymer. It is used i speciality packig, orthopaedic