Synthesis, Polymerization Kinetics, and Applications of Novel Macromonomer-Based Degradable Materials
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The ability to design materials with controlled degradation rates has stimulated the development of polyesters for a range of applications, from biomedical to environmental. Although attractive because they become increasingly hydrophilic upon hydrolysis, many polyester materials need high molecular weight (MW) for the good colloidal stability and mechanical properties required for end-use applications. As degradation rates are directly linked to polyester chain length, this precludes potential applications that require both high MW and fast hydrolysis. “Grafting through” radical polymerization (RP) of short-chain polyester macromonomers (1-5 units) decouples hydrolysis time and MW by efficiently imparting polyester material properties onto a much higher MW comb-polymer frame. These macromonomers are synthesized by a ring opening polymerization (ROP) in which the type and stoichiometric ratio of cyclic monomer to initiator controls the final comb-polymer degradability. In this work, several ROP initiators are implemented to produce four new methacrylate macromonomer families with different end-group functionalities (alkyl, tertiary amine, quaternary ammonium, and carboxyl). The utility of these new end-group functionalities in comb-polymer materials is demonstrated by proof of concept application developments conducted in cooperation with three research groups. Alkyl macromonomers provide a means to delay the onset of comb-polymer hydrolysis, cationic macromonomers are polymerized to produce novel flocculants with hydrolysis-triggered enhanced sediment dewaterability, while a biorenewable material is modified with tertiary amine macromonomers to have both pH responsive and tunable hydrophobicity characteristics. In each application, the ability to easily tune the material’s performance by specifying the functional group density in the ROP step is emphasized. To facilitate the efficient production of comb-polymer materials, macromonomer radical (co)polymerization kinetics are studied in bulk, solution, and micellar media. The alkyl terminated macromonomer bulk homopropagation rate constants determined by pulsed laser polymerization are invariant to the number of polyester units in the methacrylic ester side chain. In addition, macromonomer relative consumption behavior in solution copolymerization with styrene is determined by the chemical identity up to several units away from the methacrylic ester, independent of the polyester type, length, and end-group functionality. As further product development opportunities emerge, this kinetic knowledge will enable improved control of comb-polymer composition and MW.
URI for this recordhttp://hdl.handle.net/1974/15662
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