Dendritic Homopolymers and Block Copolymers: Tuning the Morphology and Properties

Abstract

The synthesis and characterization of dendritic homopolyniers and block copolymers of ε-caprolactone and lactide (L-lactide and racemic lactide) were performed with multifunctional initiators in combination with living polymerization and the selective placement of branching junctures in a divergent growth strategy. A hexahy-droxy-functional 2,2-bis(hydroxymethyl) propionic acid derivative was used as an initiator for the stannous-2-ethylhexanoate-catalyzed living ring-opening polymerization of ε-caprolactone, L-lactide, and racemic L,D-lactide. Branching junctions at the chain ends were introduced with benzylidene-protected 2,2-bis(hydroxymethyl) propionic acid. Subsequent generations were then polymerized, after deprotection, from these star-shaped macroinitiators. Successive chain end capping and initiation produced three generations of polymers with molecular weights in excess of 130,000 g/mol and narrow polydispersities (<1.20). It was possible to prepare diblock and triblock copolymers with phase-separated morphologies, and with L-lactide or D,L-lactide, semicrystalline and amorphous morphologies were demonstrated. The polymers were characterized by 1H NMR, 13C NME, size exclusion chromatography, and differential scanning calorimetry. The compositions of the block copolymers and the conformational structures of the optically active polymers were also confirmed by optical rotation measurements. © 2004 Wiley Periodicals, Inc.