Polylactones. 59. Biodegradable networks via ring-expansion polymerization of lactones and lactides with a spirocyclic tin initiator.

Spirocyclic tin initiators were prepared by condensation of commercial hydroxyethylated pentaerythritol with Bu(2)Sn(OMe)(2). These tin-containing spirocycles served as initiators for the ring-expansion polymerization of epsilon-caprolactone, beta-D,L-butyrolactone or D,L-lactide. The in situ polycondensation of these expanded spirocycles with terephthaloyl chloride or sebacoyl chloride yielded the desired biodegradable networks with elimination of the Bu(2)Sn group. The segment length (pore size) could be controlled via the monomer-initiator ratio (M/I) of the ring-expansion polymerization. Biodegradable networks were also obtained when Sn-containing spirocyclic polylactones were polycondensed with diphenyl dichlorosilane, benzene phosphonic dichloride, and phenyl phosphoric dichloride.