Synthesis, Morphology, and Crystallization Kinetics of Polyheptalactone (PHL)

Abstract

Aliphatic polyesters are widely studied due to their excellent properties and low-cost production and also because, in many cases, they are biodegradable and/or recyclable. Therefore, expanding the range of available aliphatic polyesters is highly desirable. This paper reports the synthesis, morphology, and crystallization kinetics of a scarcely studied polyester, polyheptalactone (PHL). First, we synthesized the η-heptalactone monomer by the Baeyer−Villiger oxidation of cycloheptanone before several polyheptalactones of different molecular weights (in the range between 2 and 12 kDa), and low dispersities were prepared by ringopening polymerization (ROP). The influence of molecular weight on primary nucleation rate, spherulitic growth rate, and overall crystallization rate was studied for the first time. All of these rates increased with PHL molecular weight, and they approached a plateau for the highest molecular weight samples employed here. Single crystals of PHLs were prepared for the first time, and hexagonal-shaped flat single crystals were obtained. The study of the crystallization and morphology of PHL revealed strong similarities with PCL, making PHLs very promising materials, considering their potential biodegradable character.

Correction to Crystal Structure of Poly(7-heptalactone)

“…In fact, we wrote that “poly­(7-heptalactone) (PHL) was synthesized by a combination of ring-opening polymerization of η-heptalactone (Scheme 1) and reversible addition–fragmentation chain transfer (RAFT) polymerization, using diphenyl phosphate (DPP) as catalyst and 4-cyano-4-(((ethyl­thio)­carbono­thioyl)­thio) pentanoic acid as initiator and chain transfer agent”. The sample has been, instead, synthesized, as described in our previous paper, by ring-opening polymerization of η-heptalactone using diphenyl phosphate as catalyst and 4-cyano-4-(((ethyl­thio)­carbono­thioyl)­thio)­pentanoic acid as initiator.…”