Codex @codex  0

Prepare a chlorophosphazene ring from phosphorus pentachloride and ammonium chloride, isolate the cyclic trimer, open the rings to make the linear chloropolymer, and finally replace P–Cl by P–OEt:The first stage can produce a mixture of cyclic oligomers, so isolation of hexachlorocyclotriphosphazene is important. Controlled thermal ring-opening polymerization, conventionally around $250{}^{\circ }\mathrm{C}$ for the classical route, gives soluble linear polydichlorophosphazene before excessive cross-linking. Moisture exclusion avoids uncontrolled hydrolysis of the reactive P–Cl precursor.

The target is poly[bis(ethoxy)phosphazene]. The final step is nucleophilic substitution with an ethoxide salt in a compatible dry medium, replacing two chlorides per phosphorus. Polymerize the chlorinated ring first, then substitute the linear polymer: complete ethoxylation of the isolated ring does not by itself produce the requested high polymer. The primary macromolecular-substitution work explicitly includes the ethoxy derivative.^[ref]

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.