Copolymerizations of omega -pentadecalactone (PDL) with trimethylene carbonate (TMC) were studied using chemical and enzyme catalysts. By using stannous octanoate, methylaluminoxane (MAO), or aluminum isopropoxide, copolymerizations of PDL with TMC with 1:1 feed ratio resulted in either homo-polyTMC or PDL/TMC block copolymers. These catalysts polymerize TMC more rapidly than PDL. A copolymerization catalyzed by MAO gave poly(TMC-co-16 mol % PDL) with M-n 26.4 x 10(3)g/mol and randomness numder (B) about 1.1. The sodium ethoxide-catalyzed copolymerization led to products with low M-n (<6.8 x 10(3)) but nearly random sequence distribution. The copolymerization of PDL with TMC was also studied by using lipase catalysts. Of the six lipases evaluated for PDL/TMC copolymerizations in toluene at 70 degreesC, an immobilized form of lipase B from Candida antarctica (Novozyme-435) was preferred. Changing the PDL/TMC comonomer feed ratio from 1:10 to 10:1 (mol/mol) provided copolymers that ranged in M, and PDL mol % from 7.3 x 10(3) to 25.2 x 10(3) and 28 to 88, respectively. In contrast to the chemical catalyst systems, Novozyme-435 catalysis showed that PDL was consumed more rapidly than TMC. Also, in contrast to most of the chemical catalysts, H-1 and C-13 NMR analyses showed that the copolymers from Novozyme-435 catalysis were able to give a random distribution of the repeat units at extended reaction times. Furthermore, in contrast to TMC polymerization in the presence of preformed polyPDL with MAO, Novozyme-435 catalyzed polymerization led to random copolymers.