Macromolecular Chemistry and Physics最新文献

Traditional benzoxazine and epoxy resins often require high curing temperatures, leading to increased energy consumption and potential limitations in processing. In this study, an effort has been made to lower the curing temperature by introducing a catalytic system that improves polymerization kinetics. Various catalysts, including dithiopropionic acid, thiodipropionic acid, and mercaptopropionic acid, were explored to study the curing process using DSC. Further sulfur-hydrazide catalyst was introduced into epoxy, benzoxazines, and benzoxazine-epoxy system, a considerable reduction in curing temperature was noted. DGEBA and DGEBF with sulfur hydrazide catalyst resulted in dual exothermic peaks at 106°C/156°C and 98°C/152°C respectively. Moreover, curing kinetics were carried out for the benzoxazine-epoxy system with sulfur-hydrazide catalyst using the Kissinger and Ozawa methods. The results showed that the chosen catalysts considerably lowered the curing temperature while maintaining desirable performance characteristics, making the modified benzoxazine-epoxy systems more energy efficient and suitable for advanced composite applications.

This study investigates the effects of precatalyst-cocatalyst structure, α-olefin type, temperature, and catalyst active site physical residential environment on ethylene−α-olefin elastomeric copolymerization; catalyst activation, deactivation, and dormancy; and copolymer average composition, microstructure, reactivity ratios, and phase morphology. The copolymerization was conducted using a Spaleck metallocene and a Dow CGC Post-metallocene, separately preactivated with methylaluminoxane and tritylborate-excess triisobutyl aluminum cocatalysts. Five pending catalytic issues were addressed. Modeling ethylene solubility and the liquid phase compressibility factor quantified catalyst active site physical residential environment. The predicted ethylene solubilities, matching experimental data, correct the error that occurs, in calculating monomer−α-olefin reactivity ratios, due to ignoring copolymerization propagation kinetics and ethylene concentration. Catalyst active site physical residential environment and the polymeryl pseudo-single site catalyst concept, introduced herein, better address catalyst activation, deactivation, and dormancy; copolymerization mixture ensemble; MW−temperature relation; and MWD broadening. This work correctly elucidates the origin of elastomer phase morphology and the role that the α-olefin side chain flexibility plays to regulate T_g. The catalyst ion-pair concept was especially evaluated by studying the macroscopic vs. microscopic catalyst deactivation and dormancy. The elastomer inter-backbone interaction was modeled. The present study results will help design and develop better catalysts and processes for making gaseous monomer−α-olefin elastomers.

Poly(ester-imide)s (PEIs) are well-known for their ultralow dissipation factor (D_f) of 0.003 at 10 GHz recently. However, the dielectric constant (D_k) and D_f seem to be two difficult-to-reconcile indexes in PEIs, a relatively high D_k of 3.2 confines the insulating capability of PEIs, owing to the trade-off between the polymer's free volume and rigidity. To address this difficulty, a cross-linking strategy of polymer backbones is proposed to increase the free volume and maintain a rigid structure in PEIs. In this research, the crystallinity of a liquid-crystal-like PEI is gradually diminished, and the molecular chain spacing is slightly enlarged as the degree of cross-linking increases. Besides, the degree of the in-plane orientation of this PEI is obviously reduced, indicating the loose stacking of molecular chains. Consequently, the D_k at 10 GHz of this PEI is decreased from 3.26 to 2.85 after cross-linking. Furthermore, the D_f of the cross-linked PEI is remained as low as 0.00237. In addition, the tensile strength and elongation at break of this PEI are increased from 219 MPa and 7.4% to 231 MPa and 9.7% after cross-linking, respectively. And the thermal stabilities of the cross-linked PEI are also decent as a candidate for low dielectric materials.

Hydrogels, particularly adhesive hydrogels, garner increasing attention for applications in flexible electronics. However, their susceptibility to water evaporation undermines long-term stability in everyday environments. Moreover, the adhesive properties of most existing adhesive hydrogels depend on specific adhesive groups, such as dopamine and nucleobases, which restrict the versatility of gel design. This work designs a gel by replacing water with PEG-modified polydimethylsiloxane as the macromolecular solvent and introduces anionic monomers to regulate its mechanical properties, self-bonding capability, and adhesion performance. The anionic monomers reduce hydrogen bonding via interchain repulsion, lowering stress and modulus, though elongation decreases slightly. The modified gel shows reduced hysteresis, enhanced fatigue resistance, and unchanged mechanical properties after 90 days, demonstrating long-term durability. It also exhibits strong self-bonding and versatile adhesion, enabling reliable attachment to diverse substrates, including skin. Flexible sensors made by integrating the gel with liquid metal display high sensitivity, low-strain detection, and stable performance after 90 days. The skin-adhesive sensor effectively monitors joint movements and respiratory rates. This work highlights the potential of polymer solvent-based systems as alternatives to aqueous solutions for developing gel materials in flexible electronics, while its scalable design and durability offer new perspectives for future wearable device engineering.

Polypropylene (PP) has attracted significant attention as a recyclable thermoplastic for high-voltage direct current (HVDC) cable insulation, potentially replacing conventional cross-linked polyethylene (XLPE). This study systematically investigates the effects of cooling rate (10, 20, and 30°C/min) during melt processing on the crystalline structure and electrical properties of PP insulation material. Through comprehensive characterization using polarized optical microscopy, X-ray diffraction, and differential scanning calorimetry, the results indicate that increased cooling rates effectively suppress spherulite formation, reducing average spherulite diameter and decreasing crystallinity from 52% to 44%. These structural modifications yield a 450% enhancement in volume resistivity from 4.11 × 10¹³ to 2.26 × 10¹⁴ Ω m, along with a 21.4% improvement in DC breakdown strength from 224 to 272 kV/mm when measured at 70°C. However, space charge measurements reveal the presence of space charge accumulation at elevated temperatures, which we attribute to lattice defects induced by rapid crystallization. The results establish a quantitative processing-structure-property relationship, showing that controlled cooling rate optimization can significantly enhance PP's electrical performance for HVDC applications while maintaining its recyclability advantage over XLPE.

The aim of this study was to incorporate attapulgite (ATP) (a naturally abundant nanoclay found in Algeria) into biodegradable poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in order to enhance the thermal, crystallization, and viscoelastic properties of the resulting bionanocomposites. PHBV/ATP bionanocomposites containing 3 and 5 wt.% ATP was fabricated via melt compounding. Comprehensive physicochemical characterization of purified ATP confirmed its nano-fibrous morphology and excellent thermal stability, as evidenced by SEM and TGA analyses. At 3 wt.% loading, ATP was homogeneously dispersed within the PHBV matrix, leading to significant improvements in thermal stability (increased onset decomposition temperature), enhanced crystallization behavior (higher crystallinity degree), and improved complex viscosity and storage modulus, indicating a reinforcement effect on the polymer's viscoelastic response. These enhancements are attributed to effective polymer-clay interfacial interactions and the high aspect ratio of ATP nanorods. However, at 5 wt.% ATP, SEM revealed partial aggregation of the nanoclay, which disrupted the polymer matrix continuity and resulted in marginally reduced performance compared to the 3 wt.% formulation. This work highlights the potential of valorizing locally sourced Algerian ATP as a sustainable nanofiller for producing high-performance, eco-friendly PHBV-based bionanocomposites for applications such as packaging and agricultural materials.

Photoresists (PRs) are light-sensitive polymers used in photolithography to fabricate micropatterns on substrates. This study proposes a microphase separation strategy to overcome the flexibility limitations associated with typical acrylic-based PRs in patterning applications by incorporating poly(ε-caprolactone)-b-poly(n-butyl acrylate) (PCL-b-PnBA) block copolymer (BCP) additives. A BCP additive was prepared using a dual-functional initiator, ethyl 2-hydroxyethyl-2-bromoisobutyrate (HEBiB), which can efficiently combine two eco-friendly polymerization techniques of ring-opening polymerization (ROP) and supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) (i.e., ROP-Є-SARA ATRP), allowing for precise control over compositions and compatibility. For synthesizing the PRs, methyl methacrylate (MMA), acrylic acid (AA), and maleic anhydride (MAn) monomers were utilized to afford two randomly copolymerized pre-polymers, namely, P(MMA-r-AA) and P(MMA-r-MAn). Following esterification with allyl bromide and hydroxyethyl methacrylate (HEMA), two PR systems (abbreviated as PMAV and PMMAnMA, respectively) were prepared. By mixing various amounts of the PCL₁₁₉-b-PnBA₉₆ (M_n,NMR = 26,080; Φ_PCL = 0.49; Đ = 1.28) and two PRs following UV-curing reactions, high transmission films can be obtained. Their photopatterning and mechanical properties were improved, owing to the occurrence of microphase separation within the matrix. Microstructure-containing matrices were characterized by small-angle X-ray scattering (SAXS). The compatibility of the BCP additive with commercially available polyimide acrylate (PIA) and polyurethane acrylate (PUA) PRs was examined. Lithographic evaluations showed improved resolution, uniformity, and developer resistance, highlighting the potential of PCL-b-PnBA-modified resins for high-performance photoresists in flexible electronic fabrications and next-generation lithography.

Stretchable electronic devices have increasingly received interest both in the academic and industrial communities because of their potential to break the limitations of traditional rigid devices and further expand the fields of applications, especially in wearable and implantable devices. As the key component of stretchable transistors in stretchable electronics, the design of a suitable stretchable semiconductor is extremely urgent and essential, while the natural flexibility of polymer semiconductor makes it a promising material for stretchable electronics. However, high mechanical stretchability and high mobility simultaneously in one polymer semiconductor is still a challenge, because the two properties are opposite in relationship. In this review, recent strategies to enhance mechanical stretchability in polymer semiconductors while maintaining the mobilities are discussed, including molecular design, physical blending, and near-amorphous polymer, with emphasis on the control of both thin-film morphology and polymer-chain dynamics in the stretchable polymer semiconductor film. Last, challenges and outline future research perspectives of stretchable polymer semiconductors are discussed in conclusions and future prospects.