Microphase Separation and Thermal Properties for High‑χ Ionic Homopolymers: Effect of Side-Chain Dipole Orientation

The heterogeneity of the microstructure for polymer materials determines the differential performance of their macroscopic properties. In this work, <i>para</i>-ionic homopolymers (P4VBC_n-(i)imi) and <i>meta</i>-ionic homopolymers (P3VBC_n-(i)imi) were prepared by reacting poly(4-vinylbenzyl chloride) and poly(3-vinylbenzyl chloride) with long-chain alkyl imidazole, respectively. Microphase separation was achieved through the dominance of long-chain crystallization, resulting in lamellar nanopatterns below 5 nm. The thermal properties of <i>para</i>-ionic homopolymers were higher than those of <i>meta</i>-ionic homopolymers in terms of polymer bulk and microphase separation structure, reflecting a significant dependence of thermal properties on the dipole orientation of the side chains. For the first time, the calculation of the Flory–Huggins parameter (χ) was introduced into the homopolymer systems, providing a simple and efficient method for investigating the effects of the side-chain dipole orientation and ionization on ionic homopolymers. Calculation results showed that the side-chain dipole orientation differentiates χ values for ionic homopolymers. These findings provided a novel research strategy for the correlation between the microstructure and macroscopic properties of homopolymer materials and offered new ideas for the design and manufacture of homopolymer patterned materials.