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-,-bis(2-methylene-4,6--butylphenolate)), 2, in the presence of tetrabutylammonium hydroxide effectively copolymerizes CO and cyclohexene oxide (CHO) into a polycarbonate diol. The resultant low molar mass (6.3 kg mol) diol is used to initiate ring-opening polymerization of -lactide with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) giving ABA-type block copolymers with good molar mass control through varying -LA-to-diol loadings and with narrow dispersities. As the degree of -LA incorporation increases, the glass transition temperatures () are found to decrease, whereas decomposition temperatures () increase. (Diphenylphosphonimido)triphenylphosphorane (PhP(O)NPPh) was used as a neutral nucleophilic cocatalyst with 2, giving phosphorus-containing polycarbonates with an value of 28.5 kg mol, a dispersity of 1.13, a value of 110 °C and a 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.