Homo-and Random Copolymerization Of Cyclic Easters Catalyzed By 4-Methyl-Benzo-18-Crown-6 Imidazol Carbene

4-Methyl-benzo-18-crown-6 imidazol carbene(B18C6imY)has been synthesized and used to catalyze ring-opening polymerization(ROP) of ?-caprolactone(CL) and copolymerization of 2,2-dimethyltrimethylenecarbonate(DTC) with CL in the presence of benzyl alcohol(BnOH) as the initiator in THF. In order to assess the catalytic activity of B18C6 im Y in the polymerization, the effects of reaction conditions, including reaction time and temperature, the molar ratio of monomer to catalyst, the molar ratio of monomer to initiator, the monomer feed ratios, and the concentration of monomer, on monomer conversion, Mn and PDI of PCL were discussed in this paper. The study has been shown that B18C6 im Y was an efficient catalyst for the ROP of CL under mild conditions. And the kinetics of ring-opening homopolymerization and the reactivity ratios of two monomers have been studied in detail. The structural features and polymerization mechanism of the polymers obtained by B18C6 im Y were chazcterized by IR and 1H NMR.The polymer with Mn of 40.4 kg/mol and PDI of 1.48 can be obtained after 60 min at [CL]/[C]=700, [CL]/[I]=200, and [M]=3, in THF at 10?. Kinetic studies indicated that the polymerization rate was first order with respect to both monomer and catalyst concentration, respectively. According to the Arrhenius equation, the apparent activation energy of the polymerization is 22.38 KJ/mol. 1H NMR end group analysis on the polymer demonstrsted the ROP proceeded according to a monomer-activated mechanism.The optimum conditions for the ring-opening copolymerization of DTC with ?-CL can be described as: [DTC]/[CL]=50:50 in feed, [DTC+CL]/[C]=400, [DTC+CL]=3.0 mol/L,[DTC+CL]/[I]=200, 10?, 50 min. The copolymerization proceeded under mild operating conditions(10 ?, THF, 50 min) affording copolymer with Mn values up to 39.9 kg/mol(95%) and rather moderate dispersity value(PDI=1.49). Thermal transition temperatures measured by DSC further supported the random nature of these copolymers. The relative contents of each monomer in the copolymers were determined by 1H NMR spectroscopy in CDCl3, through the ratio of the integrated values of the methylene signals of the ?-CL units around 2.3 ppm and the methine signals of DTC around 1.0 ppm. The [DTC]/ [CL] ratios in the polymers are in good agreement with the feeding ratios. We used the instantaneous polymer with different compositions at a low conversion(total monomer conversation < 15 %) to determine reactivity ratios. The reactivity ratios of CL and DTC are measured to be rCL=0.32, rDTC=3.28. The values rDTC× rCL ? 1 indicated an nearly ideal random copolymerization. The DSC curves of the p( DTC-co-CL) with various compositions show a single glass transition temperature(Tg) between that of PCL(- 63.8?) and PDTC(about- 28?), confirming the random nature of the copolymers. The random structure of the copolymer can be confirmed by 1H NMR analysis. The mechanism study showed that the polymerization of DTC and CL proceeds catalyzed by B18C6 im Y via the activated-monomer mechanism.