Abstract
A 1,1-diphenylethylene (DPE) derivative with an alkoxysilyl group (DPE-SiOEt) was synthesized. It was end-capped with poly(styryl)lithium (PSLi) and then copolymerized with styrene via living anionic polymerization (LAP) in a non-polar solvent at room temperature. The observed side coupling reaction was carefully investigated by end-capping the polymer. Changes in molecular weight support the plausibility of a mechanism involving living anionic species (PSLi or lithiated DPE-end-capped polystyrene, PSDLi) and the alkoxysilyl groups. Through a series of copolymerizations with different feed ratios, the kinetics of the side coupling reaction were also studied. The results showed that the side reactions could be controlled using an excess feed of DPE-SiOEt, a potentially useful strategy for the synthesis and application of well-defined alkoxysilyl-functionalized polymers via LAP.
Highlights
Living anionic polymerization (LAP) enables the synthesis of well-defined polymers with controllable molecular weights and narrow distribution, and has important applications in the synthesis of functionalized [1,2,3,4] and topological polymers [5,6]
living anionic polymerization (LAP), even if conducted at low temperature, is unsuitable for synthesizing alkoxysilyl-functionalized polymers because of the unavoidable side reactions between the alkoxysilyl groups and the living species [18]. To avoid these side reactions, DPE has been used as an end-capped initiator for the LAP of acrylate and methacrylate since its bulk structure and stable electron cloud can inhibit the carbanion from attacking the carbonyl group of these monomers [12,23,24]
Samples P-5 to P-1, products of the copolymerization of styrene and DPE-SiOEt with a designed molecular weight of approximately 10 kg/mol, increased in molecular weight, and molecular weight distributions increased as the molar feed ratio (St/DPE) increased. These results suggest that a minor side reaction led to a decrease in active center concentration
Summary
Living anionic polymerization (LAP) enables the synthesis of well-defined polymers with controllable molecular weights and narrow distribution, and has important applications in the synthesis of functionalized [1,2,3,4] and topological polymers [5,6]. Polymer chemists have investigated these side reactions between certain functional groups and living anionic centers and developed some strategies to prevent them [9,10,11]. Lowering the polymerization temperature [9], protecting the functional groups [9], and reducing the activity of the living anionic species [10,11] have been employed to stabilize the reactive center and avoid unwanted side reactions. These reactions are still the primary problem for chemists attempting to develop functionalized polymers. More investigations are needed to design new functional monomers with functional groups that can tolerate the harsh conditions of LAP and prevent side reactions during polymerization
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