Preparation of Macroporous Poly(divinylbenzene) Gels via Living Radical Polymerization
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Preparation of Macroporous Poly(divinylbenzene) Gels via Living Radical Polymerization Joji Hasegawa1, Kazuyoshi Kanamori1, Kazuki Nakanishi1, Teiichi Hanada1, Shigeru Yamago2 1 Department of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto, 606-8502, Japan 2 Institute for Chemical Research, Kyoto University, Uji, 611-0011, Japan ABSTRACT Macroporous cross-linked polymeric dried gels have been obtained by inducing phase separation in a homogeneous poly(divinylbenzene) (PDVB) network formed by organotelluriummediated living radical polymerization (TERP). The living polymerization reaction of DVB with the coexistence of a non-reactive polymeric agent, poly(dimethylsiloxane) (PDMS), in solvent 1,3,5-trimethylbenzene (TMB) resulted in polymerization-induced phase separation (spinodal decomposition), and the transient structure of spinodal decomposition has been frozen by gelation. Well-defined macroporous monolithic dried gels with bicontinuous structure in the micrometer scale are obtained after removing PDMS and TMB by simple washing and drying. The properties of the macropores have been controlled by changing starting composition. INTRODUCTION The heterogeneous networks formation by the conventional free radical polymerization is widely applied to prepare porous polymeric materials (polymer monoliths) [1]. Using “porogen”, which is usually poor solvent for the network-forming components, results in the substantial heterogeneity in the network, and thus phase separation of microgels in the porogen is induced. The resultant morphology is composed of aggregated-microgels (-particles) and the solvent (porogen). In this way the porous structure can be obtained after removal of the solvent. Polymer monoliths thus prepared are applied especially to liquid-phase separation or reaction media [2,3]. However, a fine tuning of pore properties such as pore size, pore volume and morphology is relatively difficult because the pores are formed in-between segregated microgel particles that aggregate at random. For the purpose of improved efficiency in such applications, the pore properties should be adequately controlled. In this study, organotellurium-mediated radical polymerization (TERP) [4] is for the first time applied to prepare polymer monoliths based on spinodal decomposition. The TERP technique, as well as atom transfer radical polymerization (ATRP) and reversible additionfragmentation chain transfer (RAFT) etc., is known as one of the versatile living radical polymerization techniques which affords well-defined linear polymers [5]. Using DVB as a monomer, poly(dimethylsiloxane) (PDMS) as a polymeric agent, and 1,3,5-trimethylbenzene (TMB) as solvent, phase separation behavior is investigated when changing the concentration of TMB or PDMS.
EXPERIMENT Divinylbenzene (DVB) (80% mixture of isomers) was purchased from Sigma-Aldrich Co. (USA). The solvent 1,3,5-trimethylbenzene (TMB) was purchased from Kishida Chemical Co., Ltd. (Japan). Polydimethylsiloxane (PDMS) (trimethyl
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