Poly (anhydrides). 2. One-Step Polymerization Using Phosgene or Diphosgene as Coupling Agents

Two approaches for one-step solution polymerization of poly(anhydrides) at ambient temperature were developed. In the first approach highly pure polymers (>99.7%) were obtained by the use of sebacoyl chloride, phosgene, or diphosgene as coupling agents and poly(4-vinylpyridine) or K₂CO₃ as insoluble acid acceptors. In this approach, the polymer is exclusively soluble in the reaction solution and the only byproduct formed is the insoluble acid acceptor-hydrochloric acid salt. Polymerization of sebacic acid with phosgene, either as a gas or in solution, or diphosgene as a coupling agent with triethylamine as an acid acceptor yielded a polyanhydride with a weight average molecular weight up to 16300. This poly(anhydride) was contaminated with Et₃N-HCl (up to 80%, mol %). The use of insoluble acid acceptors gave pure polymers (>99.7%) with a weight average molecular weight up to 13950. The second approach for one-step synthesis of pure poly-(anhydrides) was the use of an appropriate solvent where the polymer is exclusively soluble but the corresponding polymerization byproduct (e.g., Et₃N-HCl) is insoluble. Under this condition polymerization of sebacic acid gave the best results in N,N-dimethylformamide and in toluene.