Polyester hydrogels with swelling properties controlled by the polymer architecture, molecular weight, and crosslinking agent

Hydrogels of poly(1,5-dioxepan-2-one) and hydrogels of block copolymers of poly(1,5-dioxepan-2-one) and poly(L-lactide) were synthesized. Both star-shaped polymers and linear polymers were polymerized with ring-opening polymerization and crosslinked in situ with a tetrafunctional acid chloride (1,2,3,4-cyclopentane tetracarboxylic acid chloride) or a difunctional acid chloride (succinyl chloride). Different network architectures were synthesized in this way. The initial monomer concentrations and the molecular weights of the macromonomers were also altered. The networks were characterized with H-1 NMR and differential scanning calorimetry, and the swelling abilities of the different hydrogels were investigated in water and dichloromethane. The ratio of the monomer to the crosslinking agent was assessed by the quantification of the signal intensities in the H-1 NMR spectra of the swelled network and agreed with the theoretical crosslinking density. Both the homopolymers of 1,5-dioxepan-2-one and the copolymers of 1,5-dioxepan-2-one and L-lactide swelled to a high degree in water. The swelling properties of the materials could be varied over a broad range by changes in the architecture, molecular weight, and content of the precursor in the network. Star-shaped poly(1,5-dioxepan-2-one) crosslinked with a difunctional acid chloride had the highest degree of swelling among the different homopolymer hydrogels. This network also had the lowest glass-transition temperature because of the flexible units in the structure. The same trends found for the homopolymer hydrogels were also seen in the hydrogels with block copolymers. The hydrogels swelled enormously in dichloromethane, and as in water, the star-shaped copolymer crosslinked with a difunctional acid chloride had the highest degree of swelling. (C) 2003 Wiley Periodicals, Inc.