Polymorphic crystalline structure has been a key factor determining the mechanical property and degradation behavior of biodegradable polymers. Herein, we report on the polymorphic crystalline structure, phase transition, and their effects on the mechanical property and degradation behavior of poly­(p-dioxanone) (PPDO), a typical biodegradable and bioabsorbable semicrystalline polymer for biomedical applications. Both the polymorphic crystalline structure and crystallization kinetics of PPDO depend on crystallization temperature (T c) drastically. Melting enthalpy and degree of crystallinity of PPDO first decrease and then increase with increasing T c. PPDO forms a new mesomorphic polymorph (denoted as the α′-form) during crystallization at low T c (≤10 °C), in contrast to the common α crystals generated at high T c (≥60 °C). The α′ crystals have weaker interchain interactions and a shorter long period than the common α crystals, indicating the looser chain packing of α′ crystals. The α′ crystals are metastable, and they transform into the thermodynamically stable α crystals during heating. The α′-form PPDO possesses a slower degradation rate, higher flexibility, but lower strength and modulus than its α counterpart. This would provide a feasible way to tailor the degradation and mechanical properties of PPDO by varying crystal modification.

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Polymer/mosquito-repellent scaffolds exhibit increasing importance in long-lasting human skin protection to be used as wearable devices and allowing for controlled release of repellents. In this study, ethyl butylacetylaminopropionate (IR3535) was used as a human and environmental friendly active mosquito-repellent serving as a solvent to form functional poly­(l-lactic acid) (PLLA) scaffolds by crystallization-based solid–liquid thermally induced phase separation. Crystallization of PLLA in the presence of IR3535 is faster than melt-crystallization of neat PLLA, and in the investigated concentration range from 5 to 50 mass % PLLA, its maximum crystallization rate increases with the PLLA content, by both, increases of the maximum crystal growth rate and of the nuclei density. By adjusting the polymer concentration and the crystallization temperature, microporous scaffolds of different fine structures are obtained, hosting the mosquito-repellent in intra- and interspherulitic pores for its intended later evaporation.

Development of effective organocatalysts for the living ring‐opening polymerization (ROP) of lactones is highly desired for the preparation of biocompatible and biodegradable polyesters with controlled microstructures and physical properties. Herein, a new class of hydrogen‐bond donating bisurea catalysts is reported for the ROP of lactones under solvent‐free conditions. ROP of lactones mediated by the bisurea/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (MTBD) catalyst exhibits a living/controlled manner, affording the polymers and copolymers with the well‐defined structure, predictable molecular weight, narrow molecular weight distribution, and high selectivity for monomer at low catalyst loadings at ambient temperature. The possible mechanism of bisurea/MTBD‐catalyzed ROP of lactones is proposed, in which the bisurea activates the carbonyl group of lactones while MTBD facilitates the nucleophilic attack of the initiating/propagating alcohol by hydrogen bonding. Moreover, the poly(ε‐caprolactone‐co‐δ‐valerolactone) [P(CL‐co‐VL)] random copolymers with various compositions were synthesized using the bisurea/MTBD catalyst. The measurements of thermal properties and crystalline structure demonstrate that the CL and VL units are cocrystallized in the crystalline phase of P(CL‐co‐VL) copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 90–100

The insect repellent ethyl butylacetylaminopropionate (IR3535) was used as a functional additive for poly (l-lactic acid) (PLLA) to modify its structure and mechanical properties and achieve insect repellency. PLLA/IR3535 mixtures at various compositions were prepared via melt extrusion. In the analyzed composition range of 0 to 23 m% IR3535, PLLA and IR3535 were miscible at the length scale represented by the glass transition temperature. Addition of IR3535 resulted in a significant decrease in the glass transition temperature of PLLA, as well as in the elastic modulus, indicating its efficiency as a plasticizer. All mixtures were amorphous after extrusion, though PLLA/IR3535 extrudates with an IR3535 content between 18 and 23 m% crystallized during long-term storage at ambient temperature, due to their low glass transition temperature. Quantification of the release of IR3535 into the environment by thermogravimetric analysis at different temperatures between 50 and 100 °C allowed the estimation of the evaporation rate at lower temperatures, suggesting an extremely low release rate with a time constant of the order of magnitude of 1–2 years at body temperature.

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Vitrimers have been widely employed in self-healing, recyclable, and shape-shifting materials. However, the application of catalyst-free vitrimers to create self-healable and mechanically robust gel polymer electrolytes (GPEs) remains a challenge, often limiting the potential of vitrimer-based materials. Herein, we utilized a catalyst-free dynamic covalent bond (silyl ether) as a linkage to prepare self-healable and mechanically robust GPEs, which are fully reprocessable. By incorporating polymeric ionic liquids into the dynamically cross-linked networks, both ion conductivity and mechanical properties can be flexibly tuned. The dynamic property of the network was demonstrated through frequency sweep rheology, which revealed a rubbery-like behavior at high frequencies and a liquidlike behavior at low frequencies. This dynamic feature enables self-healing and allows for reprocessing via embedding of such dynamic covalent networks into the GPEs. The GPEs containing 80 wt % of a bis(trifluoro­methansulfonamide) lithium/ionic liquid (LiTFSI/IL) mixture exhibited good ion conductivites of 0.13 mS/cm at 20 °C and 1.88 mS/cm at 80 °C. Furthermore, the elastic modulus of the GPEs could reach a value of 0.24 MPa and was able to persist through electrode-volume expansions during charging/discharging.The tunable dynamic properties, coupled with high ion conductivity and a high modulus, indicate promising applications for this type of dynamic bond in sustainable solid electrolytes.