SYNOPSISIn general, segmented polyurethane elastomers are prepared by reacting an isocyanatecapped polyol prepolymer with a short-chain diol chain extender, yielding an elastomer with hard segments of uniform size. However, the hard segment size will not be uniform if the polyurethane polymer is prepared by forming the hard segment first, followed by soft segment formation. Because the mechanical properties of polyurethane elastomers depend on the relative ratio of the hard to soft segments as well as the effectiveness of the hard segment as a physical crosslinker, the control of the size distribution of the hard segment is a key factor in designing polyurethane elastomers. It was found that reaction conditions can affect the size distribution of hard segments derived from an aliphatic diisocyanate with differential reactivity between the two isocyanate groups. Lower reaction temperatures and simultaneous mixing of all reactants gave the preferred size distribution of hard segments. 0 1995 John Wiley & Sons, Inc.

N-Vinylpyrrolidone (NVP) and methacrylates are frequently copolymerized to give hydrogels useful as contact lenses. However, the nature of their copolymerization was not well understood. In this study, the effect of a crosslinker on the photocopolymerization of NVP and 2-hydroxyethyl methacrylate (HEMA) was discussed. It was found that crosslinkers with a vinyl carbonate group can copolymerize with NVP better than those containing an allyl group, which, in turn, are better than those containing a methacrylate group. A crosslinker with a vinyl carbonate and a methacrylate group can copolymerize NVP and HEMA the best in terms of giving hydrogels with the highest water content, followed by a crosslinker with a combination of allyl and methacrylate groups. Crosslinkers with only methacrylate or vinyl carbonate groups gave hydrogels either too fragile or too stiff to be useful.

SYNOPSISPoly(2,6-dimethyl-p-phenylene) oxides (PPO) grafted with nylon 6 were prepared by first quantitatively brominating the PPO, followed by reacting the brominated products with nylon 6 of different molecular weights. The molecular weights of PPOs were kept intact during bromination. These graft copolymers with well-defined structures were used as compatibilizers for nylon 6/PPO blends. Some compatibilization phenomena were observed, as indicated by the mechanical properties of the blends. The best compatibilization was achieved when the graft copolymer is most block-copolymer-like. 0 1994

Methacryloxyethyl vinyl carbonate, a novel crosslinker containing a vinyl carbonate and a methacrylate group which is capable of copolymerizing N‐vinyl pyrrolidone and methacrylates, was prepared. With this crosslinker, N‐vinyl pyrrolidone (NVP) and methacrylates can copolymerize efficiently under strictly UV conditions. It was found that this crosslinker was able to give hydrogels with higher water content, higher tear strength, and lower modulus, compared to a traditional dimethacrylate crosslinker. In addition, hydrogel lenses fabricated by UV curing of formulations using this crosslinker were found to be superior to those fabricated with established process in terms of optical quality. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1039–1046, 1997

SynopsisA series of alternating silarylene-siloxane polymers of moderate molecular weights was prepared by -the step-growth polymerization reactions of 1,4-bis(dimethylhydroxysilyl)benzene and three different dichlorosilanes: methylphenyldichlorosilane, dimethyldichlorosilane, and methylvinyldichlorosilane. The reactions were monitored by gel permeation chromatography (GPC). The polymers were characterized by 'Hand '3C-NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Polymers with number-average degrees of polymerization ranging from 90 to 350, based on the use of polystyrene standards in GPC analysis, were obtained. For the two homopolymers and a series of copolymers that contained either or both dimethylsiloxyl and methylphenylsiloxyl units, the glass temperatures and thermal stabilities increased substantially with increasing methylphenylsiloxyl unit content.