Poly(methylmethacrylate-dimethylsiloxane) triblock copolymers synthesized by transition metal mediated living radical polymerization: bulk and surface characterization

Well-defined poly(MMA-b-DMS-b-MMA) triblock copolymers were prepared by copper(I) mediated living radical polymerization. This was achieved by polymerization of methylmethacrylate (MMA) with different concentrations of 2-bromoisobutyrate terminated polydimethylsiloxane (PDMS). The polymerization occurred in controlled manner with the molecular weight found by ¹H NMR close to that predicted and a narrow molecular weight distribution (M_w/M_n∼1.2). Copolymers were obtained with M_n=2100, 4900, 10 100 and 29 500 g mol⁻¹ respectively with poly(MMA) (PMMA) terminal blocks and a central PDMS block of 5500 g mol⁻¹ in each case.DSC analysis showed most of the poly(MMA-b-DMS-b-MMA) triblock copolymers exhibits two T_g’s, one at low temperature corresponding to the T_g of PDMS microphase and a second at high temperature corresponding to the T_g of the PMMA microphase. TEM images show microphase segregation morphology in bulk for the triblock copolymers, with a higher degree of segregation for copolymers containing higher PDMS content. XPS measurements were performed to determine the chemical composition at the surface. For all the copolymers PDMS enrichment is observed at the surface. Copolymers containing higher percentage of PDMS exhibit higher phase separation and better enrichment of PDMS at the surface. The surface tension determined by contact angle measurements of the copolymer film containing 59 mol% of PDMS was 19.15 mN m⁻¹.