Crystallization of cyclic polymers: Synthesis and crystallization behavior of high molecular weight cyclic poly(ε-caprolactone)s

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High molecular weight poly(ε-caprolactone)s (PCL) were synthesized via zwitterionic polymerization of ε-caprolactone initiated with N-heterocyclic carbenes. Ring-opening polymerization of ε-caprolactone (1 M) with carbenes 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (1) or 1,3,4,5-tetramethylimidazol-2-ylidene (3) affords cyclic PCL with molecular weights up to Mn = 114-000 g/mol. Crystallization of the cyclic PCL was investigated by synchrotron small-angle X-ray scattering experiments and differential scanning calorimetry. High molecular weight cyclic poly(ε-caprolactone) crystallizes with a similar lamellar thickness and long period spacing as linear poly(ε-caprolactone), but the crystallization of cyclic poly(ε-caprolactone) is faster than that of linear poly(ε-caprolactone) for molecular weights greater than 75-000 g/mol. These results imply that the polymer topology does not have a significant influence on the crystal structure or morphology but can have a significant influence on the rate of crystallization from the melt. © 2011 American Chemical Society.