The Ring-Opening Polymerization Ofε-Caprolactone Initiated By Yttrium Phenolate With Polyol And Monte Carlo Simulation

Yttrium phenolate (Y(OC6H5)3) was used to catalyze the ring-opening polymerization (ROP) of ε-caprolactone (CL) in the presence of glycerol to synthesize three-arm star-shaped PCLs. The polymerization was carried out in DMF at100℃, achieving high yields (>90%) in8hours. The molecular weights (MWs) of these three-arm PCL stars increased with the increase in the feeding molar ratio of [CL]/[OH]. According to the]H NMR, more than80%of the secondary hydroxyl groups initiated ROP of CL. Y(OC6H5)3was also used to catalyze ROP of CL in the presence of pentaerythritol at100℃in DMAc. The yields of these polymerization reached90%in4hours, and the MWs of the prepared four-arm star-shaped PCLs could be easily controlled by the molar ratio of [CL]/[OH]. With the ratio of [CL]/[OH] increasing from4.7to19.4, the hydroxyls in pentaerythritol which had initiated the polymerization increased from76%to90%. Therefore, compared to the reported stannous octoate catalytic system, Y(OC6H5)3produced PCL stars at lower temperature and shorter time. In addition, there was only one melting peak without any shoulder detected in differential scanning calorimetry (DSC) curves of the obtained PCL stars.Unmodified β-Cyclodextrin (CD) was directly used to initiate ROP of CL catalyzed by Y(OC6H5)3. Well-defined CD-centered star-shaped PCLs was successfully synthesized containing definite average numbers of arms (Narrn=4～6) and narrow PDIs below1.10. The number-average molecular weight (Mn,NMR) and average molecular weight per arm (Mn,arm) were well controlled by the feeding molar ratio of monomer to initiator. X-ray diffraction (XRD) and DSC analyses indicated the prepared star-PCL with Mn,NMR of2.7×103was fully amorphous and that with Mn,NMR of13.3×103was crystallized. In addition, the obtained PCL stars with various MWs had different solubilities in methanol and THF, which could be applicable for further modifications.Transesterification is an important side reactionin ROP of CL initiated by rare earth catalysts. The chain transfer reactions were investigated using tris(2,6-di-tert-butyl-4-methylphenolate)s as a catalyst. In the experiments, the chain transfer reations significantly decreased MWs and broadened PDIs of PCL, and the intra-and intermolecular transesterification reactions were demonstrated. Monte Carlo program was used to simulate the chain transfer kinetics and quantitatively reproduced the increase of the numer of cyclic molecules, the decrease of MWs and the broadening of PDIs. When the number of cyclic molecules kept stead after long enough reaction time, ring-chain equilibrium was reached.