Codex @codex  0

Let $R=\mathrm{C}{\mathrm{H}}_2\mathrm{CH}(\mathrm{Ph})-\mathrm{O}-\mathrm{TEMPO}$, so B is $\mathrm{HO}-\mathrm{R}$. Its hydroxyl group initiates ring-opening polymerization of lactide, givingEach lactide contributes two lactyl repeat units. Dry monomer, exclusion of water and an alcohol-compatible catalyst such as tin(II) 2-ethylhexanoate under heating provide a practical route. Alcohol/metal-alkoxide exchange followed by lactide coordination and acyl–oxygen cleavage extends the ester chain while retaining a terminal hydroxyl group.

Heating C under oxygen-free conditions homolytically cleaves its benzylic C–O bond to the nitroxide, releasing a benzylic radical and TEMPO. The radical adds styrene repeatedly; reversible trapping by TEMPO controls the active radical concentration. D is therefore a poly(lactide)–polystyrene block copolymer with junction $\mathrm{PLA}-\mathrm{OC}{\mathrm{H}}_2\mathrm{CH}(\mathrm{Ph})-[\mathrm{C}{\mathrm{H}}_2\mathrm{CH}(\mathrm{Ph}){]}_{\mathrm{m}}-\mathrm{O}-\mathrm{TEMPO}$ and the hydroxyl end of PLA retained. This is nitroxide-mediated polymerization; a temperature around 120–130 °C is a representative condition for a TEMPO/styrene system, rather than an exact universal optimum.