High-molecular-weight polybenzoxazine prepolymers containing polydimethylsiloane unit in the main-chain have been synthesized from a,x-bis(aminopropyl)polydimethylsiloxane (PDMS) (molecular weight ¼ 248, 850, and 1622) and bisphenol-A with formaldehyde. Moreover, another type of prepolymers was prepared using methylenedianiline (MDA) as codiamine with PDMS. The weight average molecular weight of the obtained prepolymers was estimated from size exclusion chromatography to be in the range of 8000-11,000. The chemical structures of the prepolymers were investigated by 1 H NMR and IR analyses. The prepolymers gave transparent free standing films by casting their dioxane solution. The prepolymer films af-ter thermally cured up to 240 C gave brown colored transparent and flexible polybenzoxazine films. Tensile test of the films revealed that the elongation at break increased with increasing the molecular weight of PDMS unit. Dynamic mechanical analysis of the thermosets showed that the T g s were as high as 238-270 C. The thermosets also revealed high thermal stability as evidenced by the 5% weight loss temperatures in the range of 324-384 C from thermogravimetic analysis. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: [5945][5946][5947][5948][5949][5950][5951][5952] 2010
Novel polymer alloys were prepared by curing the mixture of a high-molecular-weight benzoxazine (B-oda) that was synthesized from 4,4′-oxydianiline (oda), bisphenol-A, and formaldehyde and a typical epoxy resin prepolymer, epoxy-terminated copolymer of bisphenol-A and epichlorohydrin, up to 240°C. It was confirmed by differential scanning calorimetric and infrared (IR) investigations that the novel alloys had ether linkages that was formed by the reaction between the phenolic hydroxyl groups formed from the thermal ring-opening polymerization of B-oda and the epoxy groups of the epoxy resin. The properties of the alloy films were compared with polybenzoxazine (PB-oda), the pristine polybenzoxazine obtained by curing B-oda without the epoxy resin. The alloy films were more flexible and were found to have higher glass transition temperatures ( Tgs) from the dynamic mechanical analyses. From the IR analyses of the films, the polymer alloys were found to have higher amount of intermolecular hydrogen bonding compared with the pristine PB-oda. It was suggested that this increase of the hydrogen bonding was the cause of the higher Tgs of the polymer alloys.
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