Polymers of carbonic acid, 30 - Ring-expansion polymerization of trimethylene carbonate (TMC, 1,3-dioxanone-2) with dibutyltin succinate or adipate

Full Paper: Macrocyclic crystalline dibutyltin succinate (Bu(2)SnSuc) and a dipate (Bu(2)SnAd) were prepared in high yields from Bu2SnO and dicarboxyli c acid. According to vapor pressure osmometry and MALDI-TOF mass spectromet ry, Bu(2)SnSuc is a cyclic trimer and Bu(2)SnAd a cyclic dimer. These macro cycles initiate a faster polymerization of TMC at 80 degreesC than Sn(II) o ctanoate or Bu2Sn octanoate. The resulting polyTMC does not contain succina te or adipate groups, and the molecular weight ((M) over bar (n)) is indepe ndent of the monomer to initiator ratio (M/I). Above 120 degreesC a complet e esterification and incorporation of the dicarboxylic acids takes place, a nd the identification of CH2OH end groups suggest that a ring-expansion pol ymerization via insertion of TMC into Sn-O-CH2 bonds proceeds. The number-a verage molecular weights increase with the M/I ratio, but do not exactly pa rallel it. At longer reaction times the molecular weights are affected by " back-biting" degradation.