Organocatalyzed regio-regular polymerization of α-aryl trimethylene carbonate

Abstract

Polymerization of α-substituted trimethylene carbonate (TMC) can give access to novel aliphatic polycarbonates. To combine the tunability provided by an aromatic substituent and the controlled polymerization conditions available for the synthesis of aliphatic polycarbonates, we have developed a regio-regular ring opening polymerization (ROP) of α-aryl trimethylene carbonate (α-ArTMC). Regio-regular ROP of α-methyl trimethylene carbonate (α-MeTMC) has been reported previously. Recently, it has been shown that phosphazene bases can catalyze the regio-regular ROP of α-methyl-trimethylene carbonate (α-MeTMC). When ROP of α-PhTMC was carried out under these conditions, we obtained a regio-random polymer (Xreg = 0.03). Using 1,5,7-triazabicyclo-[4.4.0]-dec-5-ene (TBD), as the catalyst, we were able to polymerize α-ArTMCs with improved regio-regularity. A large dependence of the regio-regularity on para substituent of the aryl ring was observed. By varying the substituent pattern in the aromatic ring, regio-regularities ranging from Xreg = 0.51 to Xreg = 0.89 were obtained. Changing the α-substituent in TMC from a methyl group to a phenyl group resulted in a substantial increase in glass transition temperature (Tg) of the corresponding polymer. The Tg of the polymers was shown to increase with an increase in regio-regularity to a certain extent. Overall a range of Tgs from 39 to 66 °C was observed upon changing regio-regularity and substituent pattern.