New insights on the crystallization and melting of cyclic PCL chains on the basis of a modified Thomson–Gibbs equation

• Published in: Polymer (Guilford) Vol. 54; no. 2; pp. 846 - 859
• Main Authors: Su, Hsuan-Han, Chen, Hsin-Lung, Díaz, Angélica, Casas, María Teresa, Puiggalí, Jordi, Hoskins, Jessica N., Grayson, Scott M., Pérez, Ricardo A., Müller, Alejandro J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 24-01-2013; Elsevier
• Subjects: Applied sciences; Crystallization; Cyclic chains; Equilibrium melting point; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Poly(ε-caprolactone); Properties and characterization; Poly(ε-caprolactone); Equilibrium melting point; Cyclic chains; Experimental study; Monodispersed polymer; Melt crystallization; Cyclic polymer; Linear polymer; Solution crystallization; Kinetics; Crystal morphology; Polycaprolactone; Isothermal crystallization; Comparative study
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2012.11.066

Low polydispersity linear and cyclic poly(ε-caprolactone) with molecular weights of 2–7.5 kg/mol were synthesized. Differences in the morphology of cyclic and linear single crystals (obtained from solution at identical temperatures) indicate that cyclic PCL crystals were obtained at higher supercoolings than linear ones. Cyclic PCL crystals (both crystallized from solution and from the melt) exhibited higher melting point values (Tm) than analogous linear PCL lamellae. In addition, cyclic PCLs crystallize from the melt at higher rates than linear PCLs at identical crystallization temperatures. Results showed that cyclic PCLs possess a higher equilibrium melting point (Tm0) than linear PCL crystals. A modified Thomson–Gibbs equation and a modified Hoffman–Weeks equation have been derived in this work to demonstrate that the higher Tm0 of the cyclic polymer stemmed from the negative cyclization entropy associated with the absence of chain ends and the more collapsed conformation of the cyclic chain in the melt state.
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