Copolymer hydrogels of 2-hydroxyethyl methacrylate with n-butyl methacrylate and cyclohexyl methacrylate: synthesis, characterization and uptake of water

The bulk free radical copolymerizations of 2-hydroxyethyl methacrylate (HEM A) with n-butyl methacrylate (BMA) or cyclohexyl methacrylate (CHMA) were s tudied over the composition mole fraction interval of 0-1 for HEMA in the m onomer feed. The C-13 NMR (125 MHz) spectra of the copolymers were analysed to determine the copolymer composition and the stereochemical configuratio n of the copolymers. The terminal model reactivity ratios of HEMA and BMA w ere found to be r(HEMA) = 1.73 and r(BMA) = 0.65 and for HEMA and CHMA, r(H EMA) = 1.26 and r(CHMA) = 0.31. The BMA and CHMA homopolymers were found to be predominantly syndiotactic with isotacticity parameters of theta(BB) = 0.18 and theta(CC) = 0.19, respectively. The copolymers were also found to be predominantly syndiotactic, indicating a strong tendency for racemic add itions of the monomers in the formation of the copolymers. The diffusion of water into cylinders of poly(HEMA-co-BMA) and poly(HEMA-co-CHMA) was studi ed over a range of copolymer compositions and was found to be Fickian. The diffusion coefficients of water at 37 degrees C were determined from swelli ng measurements and were found to vary from 1.72 x 10(-11) m(2) s(-1) for p olyHEMA to 0.97 x 10(-11) m(2) s(-1) for poly(HEMA-co-BMA) having a mole fr action F-HEMA = 0.80 and to 0.91 x 10(-11) m(2) s(-1) for a poly(HEMA-co-CH MA) also having F-HEMA = 0.80. The mass of water absorbed at equilibrium re lative to the mass of dry polymer varied from 58.8 for polyHEMA to 27.2% fo r poly(HEMA-co-BMA) having F-HEMA = 0.85 and to 21.3% for poly(HEMA-co-CHMA ) having F-HEMA = 0.80. (C) 1999 Elsevier Science Ltd. All rights reserved.