Macromolecular Chemistry and Physics最新文献

Copolymers of N-vinylcaprolactam (NVCL) and N-vinylimidazole (NVI) of different compositions were synthesized by the solvent-free free radical copolymerization. The order-disorder conformational transitions of the copolymers in diluted aqueous solutions at pH 7.4 (20 mm imidazole buffer) were studied by high-sensitivity differential scanning calorimetry. Dependences of the transition temperature, enthalpy, and heat capacity increment of the copolymers on the NVI content were obtained. The transition temperature did not depend on the composition of the copolymers (T_t = 34.8 ± 2.0°C). Alternatively, the transition enthalpy decreased, and the heat capacity increment approached zero upon the increase in the NVI content in the copolymers. These trends displayed a decrease in the content of the long enough NVCL sequences in the copolymer structure capable of the cooperative order-disorder transitions. The Schröder−Van Laar equation fitted well to the integral transition curves of the copolymers at a quite appropriate polymerization degree of the Kuhn segment for NVCL sequences, n_K = 10.7 ± 1.3. A copolymer with an NVI content of 45 mol. % was found to demonstrate a protein-like behavior in salt-free solutions. It underwent a cooperative order-disorder transition without precipitation from solution.

Herein, we have designed Pyrrole-based hypercrosslinked hollow nanosphere reactors (Ppy-HHNRs) qualified for confining near-infrared light inside the hollow spheres and for optical monitoring of the process of thermal activation reactions. The wall of the hollow nanospheres consists of pyrrole with strong adsorption at near-infrared light as well as high photothermal conversion, and styrene 1 to 1 equivalent composition. In order to demonstrate the photothermal conversion effect of the nanoreactors, a thermally driven Diels–Alder cycloaddition reaction has been conducted in the interiors of the hollow nanospheres. Subsequently, it is found that the thermally driven Diels–Alder reaction can take place in the cavities of the nanospheres stimulated by near-infrared light reflected multiple times inside, but the temperature of the solvent system outside increases slightly. And further research shows that the process of thermally driven Diels–Alder reaction can be controlled by turning near-infrared light on or off.

The accumulation of end-of-life plastic materials and composite reinforcement waste materials has brought much attention to developing sustainable alternatives and their re-processability. Incorporating covalent adaptable networks (CANs) into the crosslinked network bridges the concept of reversibility into the otherwise conventional non-reversible networks. This study investigates the structure-property relation in two reversible hardener systems derived from vanillin using Schiff base chemistry. The “CAN” systems were synthesized by condensation of vanillin with two amines, 4,4'-oxydianiline and tris(2-aminoethyl)amine, respectively, to form Va_ODA and Va_TAEA. The epoxy thermosets exhibited glass transition temperatures (T_g) of 125°C and 115°C, respectively, for Va_ODA and Va_TAEA, which is superior to most reversible vanillin-based systems reported. The vitrimer-thermosets exhibited promising mechanical and thermal properties, and reshaping abilities as a function of applied temperatures, indicating the dynamic nature of linkages. Chemical degradability was demonstrated by heating to 80°C for 12 h in aqueous acidic medium or excess amine. The fabricated glass fiber composites exhibited good mechanical properties with tensile strength of 361 MPa and degradability in acetic acid/water mixture with a fiber recovery of >98 %. The recovered glass fiber exhibited almost similar tensile strength as the virgin glass fiber, demonstrating its potential reusability. The epoxy vitrimers underwent mechanical reprocessing through hot-pressing, as well as chemical reprocessing via 3D printing and by regeneration of imine bonds to form an epoxy resin.

Synthesis of graphene-containing polymethacrylates was performed by radical polymerization of methacrylate monomers with 1 wt.% of commercially available graphene or lignin-derived graphene. Among the synthesized polymethacrylates, the glass transition temperatures (T_gs) of poly-MMA, poly-PhMA, and poly-tert-BMA containing both graphene compounds were higher than those of the corresponding polymethacrylates without the graphene compounds, owing to the restricted molecular motion of the polymer chains by graphene compounds. Experimental results and DFT-calculated differences in rotational barrier energy suggest that the higher the intrinsic mobility of the monomer substituent, the more effectively the graphene compounds restrict the motion of polymer chains. Additionally, the T_g-enhancing effects of both graphene compounds were also observed in the networked copolymers. These findings indicate that the lignin-derived graphene compound can function as an effective additive for improving the thermal stability of polymers, comparable to its commercial counterpart.

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.