Radical-initiated polymerization of β-methyl-α-methylene-γ-butyrolactone

β‐Methyl‐α‐methylene‐γ‐butyrolactone (MMBL) was synthesized and then was polymerized in an N,N‐dimethylformamide (DMF) solution with 2,2‐azobisisobutyronitrile (AIBN) initiation. The homopolymer of MMBL was soluble in DMF and acetonitrile. MMBL was homopolymerized without competing depolymerization from 50 to 70 °C. The rate of polymerization (Rp) for MMBL followed the kinetic expression Rp = [AIBN]0.54[MMBL]1.04. The overall activation energy was calculated to be 86.9 kJ/mol, kp/kt1/2 was equal to 0.050 (where kp is the rate constant for propagation and kt is the rate constant for termination), and the rate of initiation was 2.17 × 10−8 mol L−1 s−1. The free energy of activation, the activation enthalpy, and the activation entropy were 106.0, 84.1, and 0.0658 kJ mol−1, respectively, for homopolymerization. The initiation efficiency was approximately 1. Styrene and MMBL were copolymerized in DMF solutions at 60 °C with AIBN as the initiator. The reactivity ratios (r1 = 0.22 and r2 = 0.73) for this copolymerization were calculated with the Kelen–Tudos method. The general reactivity parameter Q and the polarity parameter e for MMBL were calculated to be 1.54 and 0.55, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1759–1777, 2003 β‐Methyl‐α‐methylene‐γ‐butyrolactone (MMBL) was synthesized, homopolymerized, and copolymerized with styrene (2,2‐azobisisobutyronitrile initiation) in N,N‐dimethylformamide. MMBL was compared with related monomers with respect to the effect of the enforced planarity and β‐methyl group on the growing radical. The rate law (rate of polymerization = [I]1/2[MMBL]1), the activation energy (86.9 kJ/mol), kp/kt1/2 (0.050, where kp is the rate constant for propagation and kt is the rate constant for termination), the rate of initiation (2.17 × 10−8 mol L−1 s−1), and the initiation efficiency (∼1) were determined for homopolymerization. The reactivity ratios for styrene copolymerizations (r1 = 0.22 and r2 = 0.73) gave the general reactivity parameter (Q = 1.54) and the polarity parameter (e = 0.55) for MMBL. This reactivity was much higher than that of acyclic analogues because of the enforced planarity.