PTFE4775_EXAM1 - Qu e s tion 1 a) Two s ampl e s o f...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Qu e s tion 1 a) Two s ampl e s o f polypropyl e n e , A and B , hav e t h e s am e M n and M w . Bo t h ar e lin e ar c hain s wi t h no bran c hing (r e p e a t uni t CH 2 CHCH 3 ) . Sampl e A i s st i ff e r and ha s high e r d e n s i t y t han B . Al s o , s ampl e A i s opaqu e wh e r e a s B i s c l e ar e r . Wha t di ff e r e n ce in t h e ir mol ec ular st ru c t ur e s c an e xplain t h e di ff e r e n ce s in prop e r t i e s ? The differences (stiffness, density, transparency) probably arise from difference in crystallinity. In terms of the molecular structure s, they are likely stereoisomers: A must be isotactic or syndiotactic, B must be atactic. b) L e t R t h e RMS e nd- t o- e nd di st an ce o f a random c oil . A polym e r wi t h a mol . w t . o f 100 k g / mol ha s a m e a s ur e d R o f 10 nm . Wha t mol ec ular w e igh t o f t h e s am e polym e r will giv e an R o f 30 nm? Show your r e a s oning bri e f ly . R = <r o 2 > 1/2 = n 1/2 l. R n 1/2 M 1/2 (since n M). = is proportional to A 3-fold increase in R corresponds to a 3-fold increase in n 1/2 , or a 9-fold increase in n. Answer: 900 kg / mol . c) Fill in th e blank s . - The main difference in structure between thermoplastics and thermosets is that thermoplastics are usually un c ro ss link e d lin e ar c hain s whereas thermosets are c ro ss link e d n e twork s .- A polymer with a structure ....-A-B-A-B-A-B-A-B-... is called alt e rnating copolymer, whereas one with a structure ...-A-A-A-A-A-B-B-B-B-.... is called blo c k copolymer. - Polymers with C=C double bonds in their backbone may exhibit c i s-and-tran s isomerism. - The crystalline lamellae of polymer crystals may assemble to form larger structures called s ph e rulit e s- Faster cooling rate typically leads to high e r glass transition temperature. d) For each line below, c hoo s e on e type of reaction ( A to H ) that the statement fits best. - Makes monodisperse polymers. (D) c ontroll e d living - Involves an immiscible solvent and a surfactant. (C) e mul s ion - Reaction between diol and diacid, for example. (H) c ond e n s ation- Can be used to produce isotactic polypropylene (A) Zi e gl e r-Natta - All polymerizations that have no side product. (B) addition- Re-distributes the mol. wt. of a Nylon batch, for example. (F) amid e int e r c hang e Qu e s tion 2 Compl...
View Full Document

This note was uploaded on 09/09/2011 for the course PTFE 4775 taught by Professor Unknown during the Fall '10 term at Georgia Institute of Technology.

Page1 / 3

PTFE4775_EXAM1 - Qu e s tion 1 a) Two s ampl e s o f...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online