POLY(AMMONIUM ALKOXYDICYANOETHENOLATES) AS NEW HYDROPHOBIC AND HIGHLY DIPOLAR POLY(ZWITTERIONS) .2. MECHANISTIC ASPECTS OF THE POLYMERIZATION

Some mechanistic aspects of the polymerization of 2,2-dicyano-1-[2-(2-(methacryloyloxy)-ethyl)dimethylammonio)ethoxy]ethenolate were studied to check the possible influence of the highly dipolar lateral zwitterionic group (mu congruent-to 26 D) on the polymerization of this methacrylate. Kinetics of the free-radical polymerization in homogeneous dimethylformamide (DMF) solution were analyzed by calorimetry. The molar heat of polymerization, DELTA-H(p,0) = -58 kJ.mol-1, is very similar to those generally observed for alkyl methacrylates. The increase of the activation parameters E(a) and A derived from the overall rate constant K(K = A exp(-E(a)/RT) = (k(p)2fk(d)/k(t))0.5) observed in the presence of preformed poly(zwitterion) in the reaction medium (E(a) = 71 +/- 2 kJ.mol-1, ln A = 19.5 +/- 1 (A in (L.mol-1)0.5.s-1) with respect to blank experiments (E(a) = 61 +/- 2 kJ.mol-1, ln A = 16 +/- 0.5 (A in (L.mol-1)0.5.s-1) is not compatible with genuine template effects. Stereoregularity of the radical poly(zwitterions) (H-1 NMR of the alpha-CH3 backbone at 400 MHz) is barely sensitive to temperature within the range -20 to +140-degrees-C and to solvent effects (trifluoroethanol, NaSCN (3 M) aqueous solution): the chains are significantly less syndiotactic ((mm) = 0.09 +/- 0.02, (mr) = 0.44 +/- 0.04, (rr) = 0.47 +/- 0.05) than PMMA. Anionic polymerization of the zwitterionic monomer may be initiated by fluorenyllithium in DMF solution at -40-degrees-C: it results in heterotactic polymers ((mm) = 0.22, (mr) = 0.58, (rr) = 0.20), in sharp contrast with methyl methacrylate, probably as a result of strong specific ion-dipole interactions between the zwitterionic groups and the terminal reactive ion pair of the growing chain in the transition state.