화학공학소재연구정보센터
Macromolecules, Vol.27, No.15, 4134-4144, 1994
Macromolecular Engineering of Polylactones and Polylactides .18. Synthesis of Star-Branched Aliphatic Polyesters Bearing Various Functional End-Groups
Three-arm star-branched aliphatic polyesters have been synthesized by an appropriate termination reaction of the living chains prepared by ring-opening polymerization with aluminum alkoxides. The use of functional aluminum alkoxides, Et2AlOCH2X with X = CH2CH2CH=CH2 and (CH2)10Br, has led to X functional end-capped star-branched polyesters. Trimesic acid trichloride has proved to be an efficient termination agent for the living poly(epsilon-caprolactone) [PCL] chains ended with a reactive aluminum alkoxide group. A quantitative end functionalization has been reported for bromide and 1-pentene end-capped star-branched PCL. The bromide end groups have been converted into azido end groups, which have been subsequently reduced to the expected primary amine end-capped star-branched PCL by catalytic transfer hydrogenation in DMF. In contrast to living PCL, reaction of trimesic acid chloride with the aluminum alkoxide end group of living poly(L,L)lactide [P(L,L)LA] and living poly(epsilon-caprolactone-b-(L,L)lactide) [P(CL-b-(L,L)LA] chains has produced star-branched polyesters within a very poor yield. This result is more likely due to a steric effect of the methyl group in a-position of the terminal aluminum alkoxide. This drawback has been overcome to some extent by initiating the living polymerization of (L,L)LA with primary amine end-capped star-branched PCL in the presence of triethylaluminum. Formation of a hydroxyl end-capped star-branched poly(epsilon-caprolactone-b-(L,L)lactide) diblock copolymer has accordingly been reported.