Real-Time Structure Changes during Uniaxial Stretching of Poly(ω-pentadecalactone) by in Situ Synchrotron WAXD/SAXS Techniques

Chemically Recyclable Linear and Branched Polyethylenes Synthesized from Stoichiometrically Self-Balanced Telechelic Polyethylenes

High-density polyethylene (HDPE) is a widely used commercial plastic due to its excellent mechanical properties, chemical resistance, and water vapor barrier properties. However, less than 10% of HDPE is mechanically recycled, and the chemical recycling of HDPE is challenging due to the inherent strength of the carbon-carbon backbone bonds. Here, we report chemically recyclable linear and branched HDPE with sparse backbone ester groups synthesized from the transesterification of telechelic polyethylene macromonomers. Stoichiometrically self-balanced telechelic polyethylenes underwent transesterification polymerization to produce the PE-ester samples with high number-average molar masses of up to 111 kg/mol. Moreover, the transesterification polymerization of the telechelic polyethylenes and the multifunctional diethyl 5-(hydroxymethyl)isophthalate generated branched PE-esters. Thermal and mechanical properties of the PE-esters were comparable to those of commercial HDPE and tunable through control of the ester content in the backbone. In addition, branched PE-esters showed higher levels of melt strain hardening compared with linear versions. The PE-ester was depolymerized into telechelic macromonomers through straightforward methanolysis, and the resulting macromonomers could be effectively repolymerized to generate a high molar mass recycled PE-ester sample. This is a new and promising method for synthesizing and recycling high-molar-mass linear and branched PE-esters, which are competitive with HDPE and have easily tailorable properties.

Long-Chain Branched Bio-Based Poly(butylene dodecanedioate) Copolyester Using Pentaerythritol as Branching Agent: Synthesis, Thermo-Mechanical, and Rheological Properties

The introduction of long-chain branched structures into biodegradable polyesters can effectively improve the melt strength and blow-molding properties of polyesters. In this study, pentaerythritol (PER) was used as a branching agent to synthesize branched poly(butylene dodecanedioate) (PBD), and the resulting polymers were characterized by Nuclear Magnetic Resonance Proton Spectra (1H NMR) and Fourier Transform Infrared spectroscopy (FT-IR). It was found that the introduction of a small amount of PER (0.25-0.5 mol%) can generate branching and even crosslinking structures. Both impact strength and tensile modulus can be greatly improved by the introduction of a branching agent. With the introduction of 1 mol% PER content in PBD, the notched impact strength of PBD has been increased by 85%, and the tensile modulus has been increased by 206%. Wide-angle X-ray diffraction and differential scanning calorimetry results showed that PER-branched PBDs exhibited improved crystallization ability compared with linear PBDs. Dynamic viscoelastics revealed that shear-thickening behaviors can be found for all branched PBD under low shear rates.

In-Situ Synchrotron X-ray Study on the Structure Variation of Morphology-Identified Injection-Molded β-Nucleated iPP under Tensile Deformation

The deformation behavior of semi-crystalline polymers is strongly dependent on the morphology formed during processing. In this study, in-situ synchrotron X-ray was firstly used to identify the morphological distributions of injection-molded isotactic polypropylene (iPP) with different concentrations of β-nucleating agent. It was found that under relatively high concentration of β-nucleating agent (i.e., ≥0.03 wt.%), the outer region (skin and shear region) of the iPP was dominated by mainly highly oriented α-phase as well as certain amount γ-phase, while the core region was rich in β-crystals with little if any orientation. The addition of the β-nucleating agent was beneficial for the formation of lamellae with large lamellar stacking distance in the shear layer. Then the synchrotron X-ray was applied to study the structure variation of those morphology-identified samples under tensile deformation. It was found that voids and cavities along the stretching direction existed in the deformed iPP samples and their volume increased with increasing concentration of β-nucleating agent. The increased volume of void and cavity was associated with the β to α phase transition, which mainly occurred at the core region. In addition, upon stretching crystalline fragmentation and rearrangement took place following the formation of thinner lamellae.

Recent advances in the synthesis of biodegradable polyesters by sustainable polymerization: lipase-catalyzed polymerization

Over the past three decades, enzymatic polymerization has dramatically developed and gradually broadened as a creative methodology in the construction of polymeric materials with tailor-made structures and properties. Compared with transition metal catalyst polymerizations, enzymatic polymerization is more attractive in the biomedicine field due to the metal-free residue, good biocompatibility, and few by-products. Meanwhile, enzymatic polymerization has far more activity towards macrolides. In this review, the synthesis of lipase-catalyzed polymer materials is systematically summarized, focusing on the synthesis of the complex and well-defined polymers. The enzymatic polyester synthesis was then discussed concerning the different reaction types, including ring-opening polymerization, polycondensation, a combination of ring-opening polymerization with polycondensation, and chemoenzymatic polymerization. Besides, exploration of novel biocatalysts and reaction media was also described, with particular emphasis on the enzymes obtained via immobilization or protein engineering strategies, green solvents, and reactors. Finally, recent developments in catalytic kinetics and mechanistic studies through the use of spectroscopy, mathematics, and computer techniques have been introduced. Besides, we addressed the remaining central issues in enzymatic polymerization and discussed current studies aimed at providing answers.

Ring opening polymerization of macrolactones: high conversions and activities using an yttrium catalyst

The ring-opening polymerization of macrolactones (C₁₅–C₂₃) is reported using an yttrium catalyst which shows high rates and conversions in the production of long-chain aliphatic polyesters.

Drawing in poly(ε-caprolactone) fibers: tuning mechanics, fiber dimensions and surface-modification density

This work describes the complex interplay between mechanical manipulation of coextruded fibers and the resulting photochemical yield of surface modification.

Polylactide/Poly(ω-hydroxytetradecanoic acid) Reactive Blending: A Green Renewable Approach to Improving Polylactide Properties

A green manufacturing technique, reactive extrusion (REx), was employed to improve the mechanical properties of polylactide (PLA). To achieve this goal, a fully biosourced PLA based polymer blend was conceived by incorporating small quantities of poly(ω-hydroxytetradecanoic acid) (PC14). PLA/PC14 blends were compatibilized by transesterification reactions promoted by 200 ppm titanium tetrabutoxide (Ti(OBu)4) during REx. REx for 15 min at 150 rpm and 200 °C resulted in enhanced blend mechanical properties while minimizing losses in PLA molecular weight. SEM analysis of the resulting compatibilized phase-separated blends showed good adhesion between dispersed PC14 phases within the continuous PLA phase. Direct evidence for in situ synthesis of PLA-b-PC14 copolymers was obtained by HMBC and HSQC NMR experiments. The size of the dispersed phase was tuned by the screw speed to "tailor" the blend morphology. In the presence of 200 ppm Ti(OBu)4, inclusion of only 5% PC14 increased the elongation at break of PLA from 3 to 140% with only a slight decrease in the tensile modulus (3200 to 2900 MPa). Furthermore, PLA's impact strength was increased by 2.4× that of neat PLA for 20% PC14 blends prepared by REx. Blends of PLA and PC14 are expected to expand the potential uses of PLA-based materials.

Lamellae evolution of poly(butylene succinate-co-terephthalate) copolymer induced by uniaxial stretching and subsequent heating

The structural evolution of biodegradable poly(butylene succinate-co-terephthalate) copolymer was investigated during the uniaxial stretching and following heating processes via in situ small-angle X-ray scattering.