Block and Random Copolymers of 1,2-Cyclohexyl Cyclocarbonate and l-Lactide or Trimethylene Carbonate Synthesized by Ring-Opening Polymerization

Abstract

The sequential and random ring-opening polymerizations (ROP) of racemic-trans-cyclohexene carbonate (rac-CHC) or enantiopure trans-(R,R)-cyclohexene carbonate ((R,R)-CHC) with l-lactide (LLA) or trimethylene carbonate (TMC) have been performed. Catalytic systems based on zinc diaminophenolate [(NNO)ZnEt] ((NNO)− = 2,4-di-tert-butyl-6-{[(2′-dimethylaminoethyl)methylamino]methyl}phenolate)) or tris[N,N-bis(trimethysilyl)amide]yttrium (Y[N(SiMe3)2]3) complexes, or a guanidine-type organocatalyst (1,5,7-triazabicyclo[4.4.0]dec-5-ene, TBD), combined to an alcohol (BnOH or iPrOH) as initiator/chain-transfer agent were used. Well-defined diblock P(rac-CHC)-b-PLLA and P((R,R)-CHC)-b-PLLA and random P(rac-CHC)-co-PLLA and P(rac-CHC)-co-PTMC copolymers were thus synthesized with molar mass values up to Mn,NMR = ca. 34 000 g mol–1 and rather narrow dispersity values (ĐM = 1.2–1.7). 1H and 13C{1H} NMR characterizations of the copolymers revealed the presence of −OBn or −OiPr chain-end groups, thereby supporting the active role of exogenous alcohol as initiator. No decarboxylation reaction was ever observed during any copolymerization, thus providing PCHC/PLLA and PCHC/PTMC copolymers void of ether defects. Thermal analysis of the copolymers assessed by DSC and TGA confirmed their block or random structure. The block PCHC-b-PLA and the random PCHC-co-PLLA and PCHC-co-PTMC copolymers represent the first examples of such copolymers synthesized by ring-opening copolymerization of the two comonomers. The latter PCHC-co-PTMC copolymers randomly combining CHC and TMC units are the first examples ever reported.