Poly(butylene succinate-ran-ε-caprolactone) copolyesters: Enzymatic synthesis and crystalline isodimorphic character

Abstract

In this paper, the preparation of PBS-ran-PCL copolyesters by enzymatic ring opening polymerization is presented for the first time. The copolyesters were produced in a wide composition range and free of metallic contaminants, so they may be regarded as potential biomaterials. The copolymers have been characterized by proton and carbon nuclear magnetic resonance (1 H and 13 C NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized light optical microscopy (PLOM) and wide angle X-ray scattering (WAXS). The PBS-ran-PCL copolyesters were able to crystallize in the entire composition range and displayed a pseudo-eutectic region. Most copolymers away from the pseudo-eutectic region exhibited a single crystalline phase (PBS-rich or PCL-rich crystalline phase), while within the pseudoeutectic region the copolymers were double crystalline. Observations by PLOM, during isothermal crystallization showed that both nucleation density and spherulitic growth rate of the copolyesters are determined by the component that constitutes the majority phase. WAXS studies revealed that d spacings of selected crystallographic planes depend on composition. Therefore, both DSC and WAXS results suggest that the copolymers are probably isodimorphic, as the PBS-rich crystalline phase may contain small inclusions of PCL co-units, while the PCL-rich crystalline domains may also contain a minor quantity of PBS co-units inside.

Crystallization of isodimorphic aliphatic random copolyesters: Pseudo-eutectic behavior and double-crystalline materials

“…Tan et al suggested that such small changes may be attributed to lattice distortions due to the accumulation of excluded commoner at the surface of the crystals, although no specific evidences for such accumulation were provided [15]. However, this interpretation would not be in agreement with the relevant changes in the thermal properties (See Figure 2 and bottom part of Figure 5) observed in these systems, in parallel with the changes in the lattice spacings [4,11,16,19,25]. In fact, several theories of comonomer inclusion in the crystal predict the observed trend of (equilibrium) melting temperatures with composition, as it will be described in a forthcoming section.…”

“…Deviations from the linear dependence [19,23,25,28] are typically described according to Fox [29] and Gordon-Taylor [30] equations.…”

“…Isodimorphic copolyesters usually exhibit typical spherulitic morphology, commonly identified by polarized light optical microscopy (PLOM). In one of our recent works [25], we studied the effect of copolymer composition and crystallization temperature (T c ) on the spherulitic texture of P(BS-ran-CL) copolyesters. In another recent paper, the morphology of non-isothermally crystallized PBSA copolymers was analyzed [19].…”

“…An intriguing aspect of copolymer crystallization at compositions close to the pseudo-eutectic one, is the presence of a double melting peak, related to the formation of two different crystalline phases, rich in one and in the other type of comonomers, respectively [15,16,19,24,25]. This observation will be discussed in more details in section 3.…”

Blocky poly(ɛ‐caprolactone‐co‐butylene 2,5‐furandicarboxylate) copolyesters via enzymatic ring opening polymerization

“…PCL is invariably produced by ROP of ɛ‐caprolactone by using either chemical or enzymatic methods. ROP copolymerization of CL with a wide variety of other cyclic monomers has been extensively examined with the purpose of designing PCL copolyesters with improved thermal and mechanical properties . In this sense, the PCL copolyesters containing aromatic units and synthesized by ROP, as they are PCL‐PHT and PCL‐PBT, are particularly noteworthy in the present context.…”