Synthesis, characterization, and thermally activated curing of oligosiloxanes containing benzoxazine moieties in the main chain

Oligosiloxanes containing thermally curable benzoxazine units in the main chain have been synthesized. For this purpose, first the diallyl functional monomer is synthesized through the Mannich and ring closing reaction of 4,4′-isopropylidenediphenol (bisphenol A), formaldehyde and allylamine. Hydrosilylation reaction of the resulting diallylic monomer (B-ala) with 1,1,3,3-tetramethyldisiloxane (TMDS) in the presence of Pt catalyst yields the corresponding poly(B-ala-tetramethyl disiloxane)s (PBTMDS) with the molecular weights in the range of 1800-4100 Da. The structures of the precursor diallyl monomer and the resulting polymers are confirmed by FT-IR and ¹H NMR analysis. Curing behavior of both the monomer and polymers has also been studied by Differential Scanning Calorimetry (DSC). Flexible free standing transparent films of the oligosiloxanes are obtained by solvent casting from dichloromethane solution on Teflon plates. The films preserve shape and, to some extent, toughness after thermal curing between 100 and 180 °C Thermal properties of the cured polymers are also investigated by thermogravimetric analysis (TGA).