Preparation of Composite Membranes from Polydecylmethylsiloxane and Polymethylpentafluoropropylacrylatesiloxane Copolymer: Effect of the Conversion Degree and Polymer Solution Rheology

Preparation of composite membranes is a complex technological task. To ensure high permeability and selectivity of these membranes, preliminary preparation of a selective layer polymer solution is of importance. In this work, the copolymer of polydecylmethylsiloxane and polymethylpentafluoropropylacrylatesiloxane with a theoretical block ratio of 1 : 1 has been synthesized for the first time. According to ¹Н NMR studies, with increasing the time of hydrosilylation of the reaction mixture from 10 to 50 min the degree of substitution of Si–H bonds increases, with the degree of conversion of pentafluoropropyl acrylate being close to quantitative (100 mol %). A change in the hydosilylation degree affects the nature of the rheological behavior of the solution: in 50 min the polymer solutions change from a Newtonian fluid to a gel-like state, which has a crucial effect on changes in their viscosity and ability to form a uniform defect-free coating on a MFFK‑1 microfiltration support. Based on the data on the surface morphology and elemental analysis and the gas permeability of the membranes, the optimal range of polymer solution viscosity is determined, which allows the production of defect-free composite membranes with the minimal flow of the selective layer polymer into the pores of the support. It has been demonstrated that the polymer flow into the support pores and the thickness of the selective layer can be controlled by changing the viscosity of the polymer solution. It has been revealed that the viscosity of the polydecylmethylsiloxane–polymethylpentafluoropropylacrylatesiloxane copolymer solution on the order of ~0.005–0.006 Pa s is optimal for producing composite membranes.