SYNTHESIS, CHARACTERIZATION, AND MECHANICAL-PROPERTIES OF PMMA POLY(AROMATIC ALIPHATIC SILOXANE) SEMIINTERPENETRATING POLYMER NETWORKS

Semi-interpenetrating polymer networks (IPNs) composed of poly(methyl methacrylate) (PMMA) and aromatic/aliphatic siloxanes have been made v ia sequential and simultaneous polymerizations. As the percentage of a liphatic siloxane increases, flexibility and, in general, toughness of the IPNs increases and clarity is reduced. This loss in clarity is du e to the mismatch of refractive indices (1.49 form PMMA vs. 1.43 for a liphatic siloxane). PMMA is quite transparent. On the other hand, in m aking aromatic siloxane/PMMA IPNs clarity is retained as aromatic silo xane is increased due to better matching refractive index -1.49 for PM MA and -1.49 for poly(diphenyl siloxane). Gel permeation chromatograph y (GPC) indicates slightly crosslinked IPNs with the THF soluble porti ons having number-average molecular weight, (M) over bar(n), of 10(5)- 10(6). NMRs of IPNs essentially show peaks for the components, PMMA an d the siloxane, which make up the respective IPNs. Si-29-NMRs indicate crosslinking and grafting. Mechanical properties show increased tough ness of IPNs versus PMMA as percentage of siloxane and crosslinker inc reases, but with a corresponding loss in tensile strength. (C) 1996 Jo hn Wiley & Sons, Inc.