Synthesis and characterization of bis(methoxyl hydroxyl)-functionalized disiloxane and polysiloxane oligomers derivatives therefrom

With purpose to prepare waterborne polyurethane with improved performance, bis(methyoxyl hydroxyl)-functionalized polysiloxanes with different dimethylsiloxane segment length were prepared. The preparation includes three steps, the first is synthesis of 1,3-bis(glycidoxypropyl)tetramethyldisiloxane (compound I) via hydrosilylation of allylglycidyl ether with tetramethyldisiloxane, followed by a subsequent methoxylation of the resultant compound from the hydrosilylation to give 1,3-bis(3-(1-methoxy-2-hydroxypropoxy)propyl)tetramethyldisiloxane (compound II). Using this compound II and octamethylcyclotetrasiloxane (D₄), an equilibrium reaction was carried out to obtain the target Product III, i.e. bis(methoxyl hydroxyl)-functionalized polysiloxanes. The ratio of D₄/compound II was varied in order to prepare product III with different segment length consisting of dimethylsiloxane units. At each step, the outcome compounds were characterized through Infrared, ¹H NMR, ¹³C NMR as well as H-H and H-C Correlated Spectroscopy (COSY). The results showed that each step was successfully carried out and objective products were achieved. It was estimated that compound II was not exclusive in the methoxylation step. Characterizations of the compound II enabled us to give a reliable quantitative amount for the by-products for the first time. In addition, the molecular weights of the final product III with varying dimethylsiloxane length were estimated by hydroxyl group analysis, ¹H NMR and GPC, which showed a good agreement between the theoretical molecular weights and those from these tests.