91Ó°ÊÓ

Lexan can also be prepared by the acid-catalyzed reaction of diphenyl carbonate with bisphenol A. Draw a stepwise mechanism for this process.

(a) Draw the structure of the prepolymer \(\textbf{A}\) formed from 1,4-dihydroxybenzene and excess epichlorohydrin. (b) Draw the structure of the cross-linked polymer \(\textbf{B}\) formed when \(\textbf{A}\) is treated with H\(_2\)NCH\(_2\)CH\(_2\)CH\(_2\)NH\(_2\) as the hardening agent.

Why can't chemical recycling\(-\)that is, the conversion of polymer to monomers and re-conversion of monomers to polymer\(-\)be done easily with HDPE and LDPE?

Draw a short segment of each polymer: (a) isotactic poly(vinyl chloride); (b) syndiotactic polyacrylonitrile; (c) atactic polystyrene.

\(\textbf{ABS}\), a widely produced copolymer used for high-impact applications like car bumpers and crash helmets, is formed from three monomers\(-\)acrylonitrile (CH\(_2 =\) CHCN), 1,3-butadiene (CH\(_2\) \(=\) CH \(-\) CH \(=\) CH\(_2\)), and styrene (CH\(_2 =\) CH Ph). Draw a possible structure for ABS.

Draw a stepwise mechanism for the polymerization of isoprene to gutta-percha using (CH\(_3\))\(_3\)CO\(-\)OC(CH\(_3\))\(_3\) as the initiator.

Explain why acrylonitrile (CH\(_2 =\) CHCN) undergoes cationic polymerization more slowly than 3-butenenitrile (CH\(_2 =\) CHCH\(_2\)CN).

Draw a stepwise mechanism for the anionic polymerization of styrene (CH\(_2 =\) CHPh) to form polystyrene \(-\)[CH\(_2\)CHPh]\(_n -\) using Buli as the initiator. Use CO\(_2\) as the electrophile that terminates the chain mechanism.

In the presence of H\(_3\)O\(^+\), 2-methylpropene oxide undergoes chain-growth polymerization such that nucleophilic attack occurs at the more substituted end of the epoxide. Draw a stepwise mechanism for this process, and explain this regioselectivity.

Draw a stepwise mechanism for the reaction of an alcohol with an isocyanate to form a urethane.