Self-catalytic cross-linking reaction and reactive mechanism studies of α-aminomethyl triethoxysilanes for α,ω-dihydroxy poly(dimethylsiloxane)

Some kinds of aminomethyl triethoxysilanes, cross-linkers of α,ω-dihydroxy poly(dimethylsiloxane) (PDMS), can act as catalyst to self-catalyze the cross-linking reaction with PDMS, as found in our studies. Three kinds of α-aminomethylsilanes, [(diethyl)aminomethyl triethoxysilane (DMTS), anilinomethyl triethoxysilane (AMTS) and cyclohexylaminomethyl triethoxysilane (CMTS)], and two kinds of γ-aminopropyl silanes, [(γ-aminopropyl triethoxysilane (APTS) and (N-β-aminoethyl)-γ-aminopropyl triethoxysilane (AATS)] were selected to study the self-catalytic cross-linking reaction and its mechanism. The reactivity of the cross-linkers determined by n-hexane extraction experiments, was found to be DMTS > CMTS ≫ AMTS, but APTS and AATS could not react with PDMS without catalysis. The cross-linking degree was increased with the reactivity. The results of extraction experiments and Fourier transform infra-red (FT-IR) spectra indicated that the cross-linking reaction was an equimolar reaction between the Si–OH groups and Si–OC2H5 groups. Formation of electron conjugation of N and Si in α-aminomethyl triethoxysilane molecules has been proposed to elucidate the mechanism of the self-catalytic cross-linking reaction. The Modulated Differential Scanning Calorimeter (MDSC) results showed that the increase of the glass-transition temperature (Tg) of the cross-linked products was dependent on the reactivity of the cross-linkers. The thermo-gravimetric analysis (TGA) results demonstrated that the thermal stabilities of the cross-linked products were also related to the reactivity and the structures of the cross-linkers.