Versatile and controlled synthesis of resorbable star-shaped polymers using a spirocyclic tin initiator - Reaction optimization and kinetics

A spirocyclic tin initiator was synthesized from pentaerythritol ethoxylate and dibutyltin oxide and used to polymerize L-lactide with dichloromethane, chloroform, toluene, and chlorobenzene as solvents. The reactions were performed at different temperatures and it is concluded that neither the temperature nor the solvent affects the molecular weight or the molecular weight distribution of the star-shaped polymers. The reaction rate was significantly increased by raising the reaction temperature or choosing a solvent with a low dielectric constant. All polymers showed a molecular-weight distribution below 1.19 and a molecular-weight determined by the initial monomer to initiator concentration ([M](0)/[1]). No induction period was seen for the polymerizations. They were all first order in initiator and the degree of aggregation in toluene at 110 degrees C was found to be 4/5. The glass transition temperature and the melting temperature of the star-shaped polymers increase with increasing arm length. (c) 2005 Wiley Periodicals, Inc.