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 CO 2 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 ( T g ) are found to decrease, whereas decomposition temperatures ( T d ) increase. (Diphenylphosphonimido)triphenylphosphorane (Ph 2 P(O)NPPh 3 ) was used as a neutral nucleophilic cocatalyst with 2, giving phosphorus-containing polycarbonates with an M n value of 28.5 kg mol -1 , a dispersity of 1.13, a T g value of 110 °C and a T d value of over 300 °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.