Stereocontrol in the free radical polymerization of N‐vinylcarbazole

Abstract

AbstractThe free radical polymerization of N‐vinylcarbazole (VK) was investigated in hexane, nonane, toluene, HMPT, DMF, DMAC, and DMSO. Isotactic propagation was found to be energetically favoured by between 1500 and 4600 J · mol−1 for all the solvents investigated, although the entropy difference between syndiotactic and isotactic propagation strongly favoured syndiotactic propagation by between 11 and 20 J · mol−1K−1. Variation in the steric microstructure between an isotactic mole fraction of 0,25 and 0,47 was obtained by varying the polymerization temperature and solvent. The activation enthalpy differences between isotactic and syndiotactic propagation (ΔH≠s/i − ΔH≠i/s), for the free radical polymerization of methyl methacrylate (MMA) and VK were compared and the steric configurations involved in the propagation process considered. It was concluded that electronic interaction between radical and monomer appeared to determine the energetic preference of the growing chain for isotactic or syndiotactic propagation in free radical propagation. This energetic preference was correlated with the e‐factor in the Q − e scale. Data for the free radical polymerization of VK, MMA, and vinyl trifluoroacetate showed that solvent polarity has a weak influence on the energetic preference of the growing chain for isotactic or syndiotactic propagation. This energetic preference was correlated with the π* solvent polarity scale.