Radical ring-opening copolymerization of 2-methylene 1,3-dioxepane and methyl methacrylate: Experiments originally designed to probe the origin of the penultimate unit effect

Pulsed-laser polymerization experiments were conducted on the copolymerizat ion of 2-methylene 1,3-dioxepane (MDO) and methyl methacrylate (MMA) at 40 degrees C. Reactivity ratios, based on the terminal model, were determined from copolymer compositional analyses as r(MDO) = 0.057 and r(MMA) = 34.12. The average propagation rate coefficients, [k(p)], were determined for a n umber of feed compositions ranging from an MDO mole fraction of 0 to 0.916. It was not possible to obtain a [k(p)] value for the homopolymerization of MDO as the PLP experiment was compromised by high chain transfer rates to polymer and monomer. The data mere fitted to a number of copolymerization m odels, viz, the terminal and the explicit and implicit penultimate unit mod els and the bootstrap solvent dependence model. It was found that the termi nal and penultimate unit models for copolymerization could not adequately d escribe the experimental results. A fit to a bootstrap model was successful , but the values obtained indicated a very large, unprecedented, partitioni ng effect.