Reactive & Functional Polymers最新文献

Reducing the impact of polyolefins on the environment is a difficult task not only because of its ubiquity in everyday items, but also because these polymers are used on a massive scale as high-performance materials, for example in electronics and automotive applications. This is the case for polypropylene that behaves as a robust and efficient dielectric in capacitors as a result of its high melting temperature and very low dielectric dissipation factor. The current challenge is to increase its low permittivity, in order to improve energy density and, at the same time, to contribute to the reduction of production, thus progressively increasing the miniaturization of devices.

Low content functionalisation has been found to be an efficient route to rise the polypropylene (PP) permittivity, without compromising the mechanical and thermal stability of the material. Recent work has shown that decreasing chain mobility in the amorphous phase is key to maintaining dielectric loss into the low level of PP. This has been achieved by inserting carbazole or N-alkyl pyrrole groups. The former increases the T_g due to their characteristic π-π stacking interactions and both enable tailored crosslinking, UV and thermally activated respectively.

The present study analyses the synthesis and thermal and dielectric stabilities of poly-(propylene-co-9-(undec-10-en-1-yl)-9H-fluorene), with fluorene contents up to 3 mol%, as another example of PP grade that has both enhanced T_g and crosslinking potential under UV radiation. Initial results reveal that these materials have a relative permittivity (ɛ_r) up to 3 and dielectric losses under 0.005. As in the case of carbazole, the strong π-π stacking between fluorene units improves the thermal, mechanical and dielectric responses and also, that further improvement in stability would be possible under appropriate post-processing irradiation conditions.

Bio-based bisphenol compounds were prepared using eugenol from biomass as the initial raw material. A reaction of nucleophilic substitution takes place with 4-nitrophthalonitrile in an environmentally friendly solvent to produce bio-based propenyl-derived phthalonitrile monomers. The effective preparation of compounds was proven using hydrogen and carbon nuclear magnetic resonance and fourier transform infrared spectroscopy (FT-IR). By employing the process of free radical catalysis, it is possible to directly cure the novel phthalonitrile monomers without the need for a specific small molecule curing agent. The cured resin was reported to have high glass transition temperature, good thermal stability, and processing properties by FT-IR, differential scanning calorimetry, thermogravimetric analyzer, dynamic mechanical analyzer, and rheometer techniques. The flexural test and scanning electron microscopy results show that both resins have a consistent, flawless structure and improved mechanical properties. Eugenol is derived from sustainable biomass, offering an environmentally friendly approach to utilizing biological monophenols effectively. It provides the benefits of carbon reduction and renewability, making it a valuable and eco-conscious resource.

In order to address the relative brittleness and non-recyclability defects of traditional cross-linked epoxy resins, a novel self-healing and reprocessable epoxy resin based on dynamic piperazine-hindered urea bonds (PA-HUBs) was synthesized. Piperazine is a cheap cyclic diamine, which can regulate the skeleton stiffness of epoxy network and control the mechanical properties of epoxy materials. The tensile strength of cured epoxy resin reaches 103 MPa. In addition, the piperazine monomer contains two methyl substituents and an asymmetric aliphatic ring structure, which provides sufficient chain mobility to activate dynamic exchange reactions, and imparts highly dynamic properties to the conventional urea bond, allowing the urea bonds to possess both stability and dynamic properties. Consequently, the synthesized epoxy resin exhibits not only the excellent mechanical performance but also the remarkable self-healing, reprocessable, shape memory and shape reconfiguration capabilities. The epoxy samples with scratches can basically achieve self-healing within 10 min, and the mechanical properties recovery rate of welded splines is as high as 80 %. Furthermore, we also regulated the content of dynamic PA-HUBs and the cross-linking density of the resin network to examine their impact on the dynamic properties and mechanical performance. Further analysis showed that the higher dynamic bond content and lower cross-linking density increase the free volume of dynamic bond exchange and the stress relaxation rate, which further improves the exchange efficiency of dynamic bonds and endows the resin with better self-healing ability. This kind of piperazine-hindered urea bond, which is dynamically adjustable and has both mechanical stability and dynamic properties, introduces a novel approach for solving the balance problem between the mechanical and dynamic performance of thermosets and preparing dynamic polymer materials with excellent performance.

In this work, poly(butylene 2,5-thiophenedicarboxylate-co-glycolate) (PBTFGA) copolyesters were synthesized from 2,5-thiophenedicarboxylic acid, 1,4-butanediol and glycolic acid. The influence of the glycolic acid content on thermal properties, mechanical properties and degradation capacity of copolyesters was systematically investigated. The glass transition temperature of copolyesters closely matched that of poly(butylene 2,5-thiophenedicarboxylate) (PBTF). While also demonstrating good thermal stability. When the glycolic acid content was low, the copolyesters exhibited some crystallization capability, but they gradually became fully amorphous as the glycolic acid content increased. The tensile tests revealed that the young's modulus of the PBTFGA copolyesters ranged from 69.2 MPa to 221.4 MPa. With elongation at break exceeding 659%, outperforming most biodegradable packaging materials. Copolyesters exhibited excellent gas barrier properties to both oxygen (PO₂ = 0.024 barrer) and carbon dioxide (PCO₂ = 0.029 barrer), both of which are superior to poly(butylene 2,5-thiophenedicarboxylate). The incorporation of glycolic acid significantly reduced the crystalline content of the copolyesters, facilitating the interaction of water molecules with ester bonds in the polymer backbone. The weight of poly(butylene 2,5-thiophenedicarboxylate-co-glycolate) was decreased significantly during enzymatic hydrolysis, indicating excellent degradation performance