Preparation of High Molecular Weight Polybenzoxazine Prepolymers Containing Siloxane Unites and Properties of Their Thermosets

High molecular weight polybenzoxazine prepolymers containing polydimethylsiloane unit in the main chain have been synthesized from alpha omega bis(aminopropyl)polydimethylsilox ane (PDMS) (molecular weight = 248 850 and 1622) and bisphenol A with formaldehyde Moreover another type of pre polymers was prepared using methylenedianiline (MDA) as codi amine with PDMS The weight average molecular weight of the obtained prepolymers was estimated from size exclusion chro matography to be in the range of 8000-11 000 The chemical structures of the prepolymers were investigated by H-1 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 degrees 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 analy sis of the thermosets showed that the T(g)s were as high as 238-270 degrees C The thermosets also revealed high thermal stability as evidenced by the 5% weight loss temperatures in the range of 324-384 degrees C from thermogravimetic analysis (C) 2010 Wiley Peri odicals Inc J Polym Sci Part A Polym Chem 48 5945-5952 2010