A systematic study on the synthesis and characterization of di-block copolymers based on aliphatic polyesters such as poly(L-lactic acid) (PLLA) and poly(-caprolactone) (PCL), performed varying both the length of the blocks as well as the relative content of each block in the copolymers, is reported. The block-length and the molecular weight of each synthesized PCL-b-PLLA di-block copolymer were analyzed by nuclear magnetic resonance spectroscopy. The influence of the block length and of the amount of each block on the thermal properties and the morphology, was evaluated by differential scanning calorimetry and by small angle X-Ray scattering experiments. In particular, the correlation between the molecular weight of each block and its amorphous and/or crystalline structure was obtained, evidencing that the crystallization of the PLLA block was not influenced by the presence of PCL and depends mainly on its molecular weight but the crystallization of PCL is strongly interfered by the crystallization of PLLA. In particular PLLA blocks are amorphous for short lengths (≤ 672 g/mol, that means ≤ 9.3 LA repeat units) and start to crystallize for molecular weight ≥ 964 g/mol, that means ≥ 13.4 LA repeat units.

Asymmetric telechelic α-hydroxyl-ω-(carboxylic acid) poly(ε-caprolactone) (HA-PCL) and α-hydroxyl-ω-(carboxylic acid) poly(δ-valerolactone) (HA-PVL) were synthesized by ring-opening polymerization of ε-caprolactone (CL) and δ-valerolactone (VL), respectively. HA-PCL oligomers were obtained at 150 °C in 2 h using ammonium decamolybdate (NH4)8[Mo10O34] as catalyst and water as initiator. A control of the number-average molecular weight (measured by NMR) can be achieved in the range between 212 and 2198 Da, based on the initial monomer/initiator ratio. Number-average molecular weight (M n) shows a linear dependence with CL/H2O ratio in this range. The nature of hydroxyl and carboxylic acid end groups of HA-PCL and HA-PVL was studied by MALDI-TOF and 1H and 13C NMR. Changes in the chemical shifts observed in the NMR spectra as a function of molecular weight were explained in terms of hydrophobic interactions. Formation of macrocyclic species was studied by MALDI-TOF. It was found that macrocyclic species are favored at longer reaction times. Insertion of alcohols and polycondensation reactions occurring after complete monomer conversion were also studied. Alcohol insertion for this system depends on the nature of alcohol. Polycondensation reactions vary with reaction times and affect the polymer molecular weight in a nonlinear manner. Finally, the α-hydroxyl-ω-(sodium carboxylate) PCL salt (HC-PCL) was prepared from HA-PCL and characterized by FT-IR and solution and solid-state NMR. Important differences between CP-MAS and MAS spectra are observed and discussed in terms of morphology and polarization transfer.

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Twenty seven poly(ester−urethane−amide)s (PEUAs) were synthesized from the reaction of α,ω-telechelic poly(ε-caprolactone) diols, 1,6-hexamethylene diisocyanate, and three different diamide−diol chain extenders derived from ε-caprolactone and three aliphatic diamines with increasing length (n = 2, 4, and 6). The hard segment (HS) was designed to be crystalline and to introduce amide groups, more susceptible to hydrolysis than urethane or urea groups. Crystallization of the HS was achieved even at very low HS content, leading to a phase-separated material. Furthermore, HS crystallinity recovered from the material homogeneous melt on cooling. Thermal degradation was well above HS melting point, allowing for melt processing of these materials. HS melting point was affected by HS content, poly(ε-caprolactone) diol length, and chain extender length. The length scale of the phase-separated morphology lied in between 11 and 13 nm up to ∼60% HS content and decreased at higher HS content values. HS content was the main parameter affecting the mechanical properties. The prepared PEUAs degraded hydrolytically at very long times by surface erosion.

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