A series of copolymers with various compositions were synthesized by one‐step and two‐step bulk ring‐opening polymerizations of L‐lactide (LA) and ε‐caprolactone (CL) using stannous octoate [Sn(Oct)2] and 1‐hexanol as the initiating system. For the sequential two‐step polymerization, a poly(ε‐caprolactone) (PCL) prepolymer was polymerized first to a percent conversion of approximately 70% and LA then added in order to produce a copolymer with a chain microstructure different from that obtained from the corresponding one‐step reaction. The resulting copolymers were characterized using a combination of nuclear magnetic resonance spectroscopy (1H‐ and 13C‐NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and gel permeation chromatography (GPC). The average sequence lengths of the lactidyl ($l_{{\rm LL}}^{\rm e}$) and caproyl ($l_{{\rm cap}}^{\rm e}$) units, the degree of randomness (R) and the transesterification coefficient (T(II)) were calculated from the 13C‐NMR spectra. The appearance of a signal due to CapLCap sequences was directly attributable to transesterification of lactidyl (LL) units. It was found that both $l_{{\rm LL}}^{\rm e}$ and $l_{{\rm cap}}^{\rm e}$ values from the two‐step syntheses were significantly longer than from the corresponding one‐step syntheses, leading to different semi‐crystalline morphologies and chain microstructures. The copolymers all showed at least some blocky chain structure as a result of the significant difference in monomer reactivity (LA > CL) between LA and CL. Thermal properties including stability depended on both composition and chain microstructure which could be controlled by the method of synthesis. From their DSC curves, the two‐step copolymers were seen to be semi‐crystalline whereas the one‐step copolymers were mainly amorphous. A more blocky microstructure, as obtained from the two‐step method, appeared to result in a lower thermal stability. Copyright © 2007 John Wiley & Sons, Ltd.

Biodegradable blends of poly(L-lactide) (PLL) toughened with a polycaprolactone-based thermoplastic polyurethane (TPU) elastomer and compatibilized with a purpose-designed poly(L-lactide-co-caprolactone) (PLLCL) copolymer were prepared. Both 2-component (PLL/TPU) and 3-component (PLL/TPU/PLLCL) blends of various compositions were prepared by melt mixing, hot-pressed into thin films and their properties tested. The results showed that, although the TPU could toughen the PLL, the blends were immiscible leading to phase separation with the TPU domains distributed in the PLL matrix. However, addition of the PLLCL copolymer could partially compatibilize the blend by improving the interfacial adhesion between the two phases. Biodegradability testing showed that the blends were biodegradable and that the PLLCL copolymer could increase the rate of biodegradation under controlled composting conditions. The 3-component blend of composition PLL/TPU/PLLCL = 90/10/10 parts by weight was found to exhibit the best all-round properties.

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The bulk ring-opening polymerizations (ROP) of e-caprolactone (e-CL) initiated by synthesized tributyltin n-butoxide (nBu 3 SnOnBu) initiator were conducted at 120°C and the molecular mass and polydispersity index of poly(e-CL), PCL, were determined. The coordinationinsertion ROP of e-CL was confirmed by 1 H-NMR. The molecular mass of PCL was successfully controlled with monomer to initiator concentration ratio. The kinetics and thermodynamics of ROP were investigated by differential scanning calorimetry (DSC) using both non-isothermal and isothermal methods. From the non-isothermal method, the activation energy (E a ) of ROP of e-CL initiated by 1.0, 1.5, and 2.0 mol% of nBu 3 SnOnBu was derived from the method of Kissinger (78.3, 61.1, and 59.9 kJ mol -1 ) and Ozawa (82.8, 66.2, and 64.9 kJ mol -1 ). For isothermal method, the values of E a for these three concentrations of nBu 3 SnOnBu were 74.2, 65.8, and 62.0 kJ mol -1 , respectively. The first-order reaction model was employed to determine the apparent rate constant (k app ). The degree of aggregation (m) of nBu 3 SnOnBu in e-CL was also determined using isothermal method which confirmed its nonaggregated form. In addition, the activation enthalpy (DH = ) and entropy (DS = ) were estimated to be 70.5 kJ mol -1 and -100.3 J mol -1 K -1 by isothermal DSC. The Friedman, Kissinger-Akahira-Sunose, and Flynn-Wall-Ozawa isoconversional methods were also applied to non-isothemal DSC data to investigate the dependence of E a with monomer conversion (a). The results of all three methods were discussed and compared with isothermal and non-isothermal methods at 1.0 mol% of nBu 3 SnOnBu. The overall results demonstrate that DSC is a fast, convenient, and reliable method for studying the kinetics and thermodynamics of ROP of e-CL initiated by nBu 3 SnOnBu.