Controlled synthesis of polycarbonate diols and their polylactide block copolymers using amino-bis(phenolate) chromium hydroxide complexes

A diamine-bis(phenolate) chromium(iii) complex, CrOH[L] ([L] = dimethylaminoethylamino-N,N-bis(2-methylene-4,6-tert-butylphenolate)), 2, in the presence of tetrabutylammonium hydroxide effectively copolymerizes CO2 and cyclohexene oxide (CHO) into a polycarbonate diol. The resultant low molar mass (6.3 kg mol-1) diol is used to initiate ring-opening polymerization of rac-lactide with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) giving ABA-type block copolymers with good molar mass control through varying rac-LA-to-diol loadings and with narrow dispersities. As the degree of rac-LA incorporation increases, the glass transition temperatures (Tg) are found to decrease, whereas decomposition temperatures (Td) increase. (Diphenylphosphonimido)triphenylphosphorane (Ph2P(O)NPPh3) was used as a neutral nucleophilic cocatalyst with 2, giving phosphorus-containing polycarbonates with an Mn value of 28.5 kg mol-1, a dispersity of 1.13, a Tg value of 110 degrees C and a Td value of over 300 degrees C. A related Cr(iii) complex (4) having a methoxyethyl pendent group rather than a dimethylaminoethyl group was structurally characterized as a hydroxide-bridged dimer. A chromium hydroxide diamino-bis(phenolate) complex copolymerizes cyclohexene oxide and CO2 to a polycarbonate diol, which acts as a macroinitiator for the polymerization of lactide to give a polycarbonate-block-polyester copolymer.

Automated summary

In this study, a chromium(III) complex has been reported, which can effectively copolymerize carbon dioxide and cyclohexene oxide into a polycarbonate diol, and then be used to polymerize lactide to produce polycarbonate-block-polyester copolymers.