Sulfone-Functionalized Polyacrylamides as An Emergent Family of Dipolar Glass Polymers

Dipolar glass polymers achieve high glass transition temperatures, high dielectric constants, and low dielectric loss through the incorporation of dipolar groups with high dipole moments. However, a high density of dipolar groups often leads to strong dipole–dipole interactions, which restrict dipole reorientation under an electric field and consequently limit further enhancements in dielectric performance. To address this limitation, we propose the introduction of alkyl tails of appropriate length at the terminal of the dipolar groups, to modulate the dipole–dipole interactions and promote the dipole mobility. A series of sulfone–functionalized 2-(alkylsulfonyl)ethyl acrylamide monomers with tailored alkyl tails was designed, and their corresponding polyacrylamide homopolymers were synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. The influence of alkyl chain length on their dielectric performance was investigated in terms of their thermal decomposition temperature (Ti), glass transition temperature (Tg), activation energy (Ea), and dielectric constant (εr′). While the Ti of these polymers remained consistently high (330–340 °C), the Tg decreased from 114 to 79.4 °C as the alkyl tail length increased from methyl to propyl. Broadband dielectric spectroscopy (BDS) demonstrated high dielectric constants (5.15–9.76 at 1 kHz and 20 °C) and relatively low dielectric loss (0.0156–0.0224). The εr′ increased with longer alkyl tails, while the Ea values for the β relaxation remain constant, indicating that the appended alkyl tails effectively increase the dipole mobility, possibly by weakening the dipole–dipole interactions. However, this benefit is accompanied by a lower Tg and a narrower temperature window between the β and α relaxations. Overall, this study demonstrates that rational tailoring of pending alkyl tail length is an effective molecular design strategy to achieve a high dielectric constant and low loss in dipolar glass polymers by modulating dipole interactions.