Synthesis Of Core Cross-linked Star Polymers Research Articles

Microwave-Assisted Synthesis of Core-Crosslinked Star Polymers with Benzophenone Derivatives in the Core

Core-crosslinked star polymers, which have polyethylene oxide (PEO) as a shell and cross-linked poly(2-{4′-iodobenzoyloxy}-ethyl methacrylate) (PIEMA) with benzophenone derivatives as a core, have been successfully synthesized by an “arm-first” method. PEO-b-PIEMA was prepared via atom transfer radical polymerization (ATRP) of 2-{4′-iodobenzoyloxy}-ethyl methacrylate (4-IEMA) with preformed PEO-Br as a macroinitiator. Core-crosslinked star polymers (CCSP) were efficiently synthesized by ultrafast carbonylation reactions under air by flash microwave irradiation in the presence of dicobalt octacarbonyl in 6 min. Gel permeation chromatography (GPC) trace of CCSP showed a drastic shift to a higher molecular weight when compared to precursor polymer, PEO-b-PIEMA diblock copolymer, indicating that the carbonylation reaction was fully progressed. The CCSP with benzophenone was successfully immobilized on a silicon wafer through a photochemical reaction under UV irradiation.

A highly efficient macromonomer approach to core cross-linked star (CCS) polymers via one-step RAFT emulsion polymerization

We have developed a highly efficient, one-step approach for the synthesis of core cross-linked star (CCS) polymers using commercial macromonomers (polyethylene glycol methyl ether methacrylates) as the arms via RAFT-mediated emulsion polymerization in aqueous media. This approach employs a small molecular chain transfer agent (CTA), commercial macromonomer, hydrophobic cross-linker, and optional hydrophobic spacing monomer as the polymerization recipe to synthesize CCS polymers via direct one-step polymerization in aqueous buffer solution. Various polymerization parameters, including buffer concentration and molar ratio of macromonomer/cross-linker/spacing monomer relative to CTA, were investigated. CCS polymers of high yield and low dispersity were obtained within 4 h under a wide range of conditions. Analysis of polymerization kinetics and macromolecular parameters of the generated polymeric species during the polymerization process led to insights into the mechanistic aspects of the CCS formation process, which was proposed to involve three stages, i.e., polymer chain growth, cross-linking to form CCS, and CCS growth. Finally, synthesis of CCS polymers using macromonomers of different molecular weights pointed to the necessity for optimization of the polymerization conditions for each macromonomer, possibly due to different polymerization rates and steric hindrance.