Reactivity in the radical copolymerization of poly(2-oxazoline) macromonomers with methacrylate monomers

The radical copolymerization of vinylbenzyl-terminated poly(7-methyl-2-oxaz oline) macromonomers (1 Me-n; rr (degree of polymerization)=3, 15, 28, 31) (M-1) with vinyl monomers (M-2), i.e., methyl methacrylate (MMA) and 2-hydr oxyethyl methacrylate (HEMA) was performed using 2, 2'-azobis(isobutyronitr ile) (AIBN) as an initiator at 60 degrees C in ethanol (EtOH), CD3OD, or CD 3CN. Monomer reactivity ratios r(1) and r(2) were evaluated based on the te rminal model. Copolymerization of I Me-3 with MMA gave reactivity ratios as r(1) = 1.86 +/- 0.15 and r(2) = 0.07 +/- 0.03 in EtOH, and r(1) = 1.25 +/- 0.10 and r(2)=0.18+/-0.05.in CD,OD, exhibiting remarkably higher reactivit y of the Me-3 compared with the comonomers and corresponding small monomer, styrene. In CD3CN, however, copolymerization of 1 Me-3 with MMA gave r(1) = 0.41 +/- 0.10 and r(2)=0.66+/-0.10, showing rather lower reactivity of th e macromonomer compared with MMA. With HEMA, 1 Me-3 showed high reactivity in EtOH, i.e., r(1) = 1.44+/-0.10, r(2)=0.04+/-0.02. The reactivity of HEMA against the macromonomers was found higher than that of MMA, possibly due to affinity to aprotic poly(2-methyl-2-oxazoline) graft chains on growing s pecies. The high reactivity of 1 Me-n in EtOH and CD,OD would be due to the formation of a micelle-like state. The reactivity of macromonomers decreas ed generally with chain length (rr).