Synthetic Procedures for Preparing Cross-Linkable Acrylic Comb-Like Copolymers Via Macromonomers
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SYNTHETIC PROCEDURES FOR PREPARING CROSS-LINKABLE ACRYLIC COMB-LIKE COPOLYMERS VIA MACROMONOMERS GANG-FUNG CHEN* AND FRANK N. JONES Polymers & Coatings Dept., North Dakota State University, Fargo, ND 58102. *Present address: Ashland Chemical Company, Columbus, Ohio ABSTRACT A versatile procedure was developed for synthesis of acrylic comb-like copolymers in three steps: (i) Hydroxyl terminated oligomers were synthesized from methyl methacrylate, butyl acrylate and glycidyl acrylate by free-radical initiated addition polymerization using a functional chain (2) The transfer agent, 2-mercaptoethanol, and very low initiator levels. oligomers were converted to macromonomers by reaction with isocyanatoethyl methacrylate. (3) The macromonomers were polymerized by free-radical initiation. Conditions during the first stage must be carefully selected to minimize formation of difunctional material which could cause gelation in the third stage. A variety of structures can be made such as comb-like copolymers with homopolymer tines or comb-like homopolymers with copolymer tines. Functional groups can be introduced by copolymerizing glycidyl Assignment of comb-like structures is not acrylate into the macromonomer. rigorously proven but is strongly supported by the synthetic route and by DSC, FT-IR and chromatographic data. INTRODUCTION Comb-like polymers are distinguished from graft polymers by the close and regular spacing of their side chains and from star polymers by the attachment of the side chains to a polymeric chain rather than to a central core. They share with star polymers the potentially useful property of having much lower solution and bulk viscosities than linear polymers of similar molecular weight. Comb-like copolymers are generally synthesized by polymerization of macromonomers -- oligomers or polymers that contain a single polymerizable group on one end. Macromonomers have been synthesized by a variety of techniques [1] involving anionic [2], cationic [3], and group transfer [4,5] polymerization. Until recently there have been few reports of synthesis of If macromonomers by routes involving free-radical chain polymerization. such a process could be developed it would open an economical route to a very wide variety of comb-like polymers including, possibly, structures that A major have reactive sites for subsequent modification or cross-linking. obstacle to development of such a process is the difficulty of attaching a polymerizable group to one end of the great majority of macromonomer molecules while suppressing the formation of molecules having two or more reactive groups. A macromonomer contaminated with with polyfunctional material can be expected to gel when polymerization is attempted. In 1986 Albrecht and Wunderlich showed that these difficulties can be They synthesized overcome in the case of Loly(methyl methacrylate) [6]. PMMA macromonomers with M 's of 6500 to 23,000 by free-radical polymerization of MMAin the presence of a functional chain transfer agent, 2-mercaptoethanol (2-ME), followed by fractio
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