Macromolecular Chemistry and Physics最新文献

Epoxy resin-based polymer coatings characterized by high heat resistance and shear strength serve as critical adhesive materials in high-end power equipment. In particular, semiconductive variants of such coatings can effectively suppress the nonlinear variation of insulation resistance in DC voltage proportional standard devices, thereby enhancing measurement accuracy. However, as the DC voltage level increases, the operational conditions under extreme temperatures impose more demanding requirements on the heat resistance and tensile shear strength of semiconductive polymer coatings. Currently, there remains a lack of effective methods to enhance the tensile shear strength of such high-heat-resistant resin-based polymer coatings. To address these challenges, this study proposes a multifaceted modification strategy. By constructing a rigid molecular backbone, optimizing the ratio of rigid to flexible segments within the resin network, and incorporating a polyethersulfone (PES) toughening agent to promote plastic deformation of the resin matrix, the glass transition temperature and tensile shear strength of the coating were increased to 451.15 K and 14 MPa, respectively. Furthermore, the addition of 0.5 wt.% carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs) as conductive filler reduced the absolute value of the minimum resistance–voltage proportionality coefficient by 73%, indicating a significant suppression of the nonlinear insulation resistance effect.

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.