Surface Enrichment and Bulk Morphology in Mixtures of Poly(methyl methacrylate) with Poly(dimethylsiloxane)

Abstract

KEY WORDSPoly(dimethylsiloxane) / Poly(methyl methacrylate) / Surface Enrichment / Morphology / Cross-linking / Solvent Evaporation / [DOI 10.1295/polymj.36.556] Because Si-containing polymers have extremely low surface energy, they show unique behavior in polymer materials. Therefore, the properties and synthesis of the Si-containing polymeric materials have been extensively investigated. 1-15The extremely low surface energy of the Si-containing polymers, such as poly(dimethylsiloxane) (PDMS), causes surface segregation in the polymer blends and block copolymer in analogy with fluorocontaining polymers. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] In addition, gradient morphologies are rarely formed in the immiscible polymer blends containing the PDMS or fluoro-containing polymers. 20,21 This kind of heterogeneity should be originated from coupling the large difference of the surface energies of the components with the other factors dominating thermodynamic situation, molecular dynamics, and so on.22,23 Therefore, various morphologies should be prepared by adjustment balance of the surface energy and the other variable factors in these polymer blends. When these types of the polymer blends are prepared by solution casting, it has been found that rate of solvent evaporation and miscibility is one of the most dominate factors to determine the distribution of the dispersed domains. [24][25][26][27] If the systems contain cross-linkable (reactive) components, the reactions should also be a dominate factor on the morphological heterogeneity. Therefore, in the polymer blends containing the cross-linkable ,!-divinyl terminated PDMS, 28,29 the morphologies should be changed with the heterogeneity of compositional distributions and cross-linking reaction. Thus, in this study, we investigate morphologies of the cross-linkable PDMS-containing polymer blends prepared by solution casting. EXPERIMENTAL,!-Divinyl-terminated PDMS, platinum-divinyltetramethylsiloxane (Pt), and cyclic hydride-containing cross-linking agent (CHC) were supplied from Dow Corning Asia Ltd. Poly(methyl methacrylate) (PMMA) was supplied from Mitsubishi Rayon Co., Ltd. Molecular characteristics of PDMS and PMMA were listed in Table I. All the samples were used as received.PMMA/PDMS blend films containing 10 wt % PDMS were prepared by solution casting. The polymers were dissolved in chloroform (CHCl 3 ) or tetrahydrofuran (THF) at 5 wt %. CHC (2 wt % to the PDMS) and small amount of Pt were added to them. The solutions were stirred until they became homogeneous. After that, the solvents were evaporated on glass plate for 24 h at ambient temperature. The resulting uncross-linked PMMA/PDMS films with ca. 200 mm thickness were further dried in reduced pressure for 1 week. The uncross-linked PMMA/PDMS (90/10) blends prepared from CHCl 3 and THF solutions are represented as UCL-C and UCL-T, respectively. Rates of solvent evaporation in preparation of the UCL-C and UCL-T are 1.3 and 25% evaporation min À1 , respectively. Finally, the uncross-...