Some properties of networks produced by the Diels-Alder reaction between poly(styrene-co-furfuryl methacrylate) and bismaleimide

Poly (styrene-co-furfuryl methacrylate) networks were prepared by the Diels-Alder (D-A) reaction in solution at 25 °C between the linear copolymer and bismaleimide (BM). The resultant crosslinked polymers were swollen to equilibrium in toluene at 25 °C and swelling properties were studied by gravimetric and dimensional measurements. The swelling behaviour of these organogels depended on the composition of the copolymer and the concentration of BM used. Shear and Young's moduli and the effective crosslinking densities (ν_e) were determined by compression (stress)-strain measurements. The theoretical crosslinking density was higher than the ν_e for all the crosslinked copolymers. An endothermic peak without T_g was observed on the DSC curve on heating the dry crosslinked polymer. On reheating a T_g at ≈98 °C was found, which is attributed to presence of linear copolymer produced by the retro D-A reaction in the first heating. The thermal stability of a crosslinked copolymer under nitrogen and air showed differences with the stability of the linear copolymer. The increase in viscosity of the solution during the D-A reaction was followed with time, for initial linear copolymers of different molecular weights. It was found that onset of gelation increased to longer reaction times the lower the molecular weight of copolymer.