Three aromatics endcapped hyperbranched polyimides (HBPIs), with triphenylamine derivative (A 3 ) as core, 4,4-(hexafluoroisopropylidene)diphthalic anhydride as B 2 monomer , phthalic anhydride (PA), 1,8-Naphthalic anhydride (NA) and 3,4-perylenedicarboxylic anhydride (PDA) as endcapping reagents are explored as polymer memory materials. All these HBPIs showed excellent solubility in various organic solutions. Tunable memory characteristics from volatile to nonvolatile were obtained by adjusting the endcapping groups. Compared to PA endcapped HBPI, NA and PDA endcapped HBPIs exhibited enhanced nonvolatile memory behaviors with switch voltages low to 0.8 V and 1.0 V, and outstanding thermal stability with 5% weight loss temperatures reaching up to 533 °C and 554 °C, respectively. Such superior performance can be attributed to the introduced polycyclic arenes end-groups, which leads to stronger conjugation intensity, better hole transport ability and higher charge separation stability.
Different from the conventional surface modification strategy, the end reaction based on the active aldehyde groups of cellulose nanocrystal (CNC) provides a targeted modification under the protection of its surface chemistry. With the purpose of promoting its redispersibility in water, the strategy of triazole end-grafting performed on CNC was proposed in this study, exhibiting the significant improvement on the redispersion and stability of nanocrystals in the aqueous suspension attributed to synergistic effect of steric stabilization and electrostatic repulsion. The end-modified CNC was then introduced into a natural rubber (NR) matrix to fabricate the composites with reactive compatibility from a thiol–ene click reaction. Ascribed to the formation of covalent linkage between nanofillers and matrix together with the architecture of the rigid percolating network, the mechanical properties of obtained composites were remarkably advanced. With the introduction of 10 wt % end-modified CNC, the tensile strength, Young’s modulus, and storage modulus of the prepared composite increased by 160, 468, and 1041% in contrast with those of the neat NR material. More importantly, this composite retained a high level of elongation at the break (1575%) similar to that of the raw rubber material attributed to the designed covalent linkage and resultant reactive enhancement of end-modified CNCs to the NR matrix.
A novel and convenient synthetic method for the preparation of α,ω-bis(2,6-dimethylphenol)-poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-2OH) oligomer in water is presented. It is based on the oxidative copolymerization of 2,6-dimethylphenol (DMP) and aromatic diols in the presence of Cu-ethylene diamine tetraacetic acid catalyst in water. It was found that the mole fraction of PPO-2OH in the product was affected by species of aromatic diols and mole ratio of DMP to aromatic diols. Species and concentration of surfactants were demonstrated to be significant factors that would influence molecular weight (Mn) and yield of PPO-2OH. The synthesized PPO-2OH was end-group modified with methacryloylchloride (MAC) to obtain dimethacryloyl chloride telechelic PPO (PPO-2MAC). The relationship between glass transition temperature (Tg) and Mn of PPO-2OH is in good agreement with the Flory–Fox equation. Thermal polymerized low-molecular-weight PPO-2MAC has a constant Tg at about 208 °C.
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