Surface-initiated photopolymerization of poly(ethylene glycol) methyl ether methacrylate on a diethyldithiocarbamate-mediated polymer substrate

Grafting efficiency and graft conversion have been investigated for poly(ethylene glycol) methyl ether methacrylate (m-PEGMA) polymerized on the surface of diethyldithiocarbamate-containing polymer substrates. The substrate is prepared by copolymerization of a mixture of methacrylic monomers with a methacrylic diethyldithiocarbamate molecule, which serves as a photoiniferter that is chemically anchored on the surface of and throughout the substrate. Surface initiation was revealed by FTIR measurements of m-PEG200MA monomer conversion for two different monomer layer thicknesses; however, side reactions including chain transfer to PEG units affect surface-initiated polymerization of m-PEG200MA monomer significantly. Chain transfer causes a sharp decrease in the measured grafting efficiency at the beginning of this surface-mediated polymerization. Addition of N,N,N',N'-tetraethylthiuram disulfide (TED), which suppresses chain transfer to PEG units, and the use of octyl methacrylate as the grafting monomer result in an increase in graft efficiency at early stages of the polymerization. Specific polymerization events that relate the chain transfer of PEG units to the graft properties of the photoiniferter-mediated polymerization are discussed.