Synthesis and comparison of two poly (methyl methacrylate-b-3-(trimethoxysilyl)propyl methacrylate)/SiO2 hybrids by “grafting-to” approach

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Two copolymer/SiO2 hybrids are prepared by growing SiO2 on the template of well -structured diblock copolymer PMMA-b-PMPS using a “grafting-to” approach. PMMA-b-PMPS is obtained by atom transfer radical polymerization (ATRP) of methyl methacrylate (PMMA) and 3-(trimethoxysilyl)propyl methacrylate (PMPS) using a brominated initiator end group termed 1H,1H,2H,2H-heptadecafluoro (F–Br) and a conventional initiator of ethyl 2-bromoisobutyrate (EBiB), respectively. The “grafting-to” approach is controlled at HCl for 24h by hydrolysis and condensation of Si(OCH3)3 groups in PMPS with tetraethyl orthosilicate (TEOS) to gain both hybrids of F-PMMA-b-PMPS/SiO2 (by F–Br initiator) and E-PMMA-b-PMPS/SiO2 (by EBIB initiator). Comparatively, a little amount of fluorine content provided by F–Br is able to tighten the size of self-assembled micelles, to improve wettability and the viscoelasticity of F-PMMA-b-PMPS film due to F–Br migrating onto the film surface. Therefore, the surface of F-PMMA-b-PMPS film is sufficiently hydrophobic (99° and Δf=2941Hz) than E-PMMA-b-PMPS film (94°and Δf=4820Hz), and the viscoelasticity of the adsorbed layer for F-PMMA-b-PMPS (ΔD/Δf=−0.112) film is much harder than E-PMMA-b-PMPS/SiO2 (ΔD/Δf=−0.071). On the other hand, the cross-linked silica in PMMA-b-PMPS/SiO2 could also increase water contact angels of films (100–107°) and decrease the water absorption (Δf=704–798Hz). The influence on the viscoelasticity of the adsorbed layer by the fluorine group is much more obvious than the cross-linked silica, therefore F-PMMA-b-PMPS/SiO2 (ΔD/Δf=−0.347) and F-PMMA-b-PMPS (ΔD/Δf=−0.112) films have harder adsorbed layer than E-PMMA-b-PMPS/SiO2 (−0.071) and F-PMMA-b-PMPS films (−0.042). However, compared with a slightly improvement in thermo stability by F–Br, the cross-linked silica in PMMA-b-PMPS/SiO2 performs significantly improving thermal decomposition temperature at 300°C and 350°C.