Contrasting the Impacts of Alkyl, Ether, and Aryl Spacers on Electroactive Poly(N-carbazolyl acrylates)

Non-conjugated pendant electroactive polymers (NCPEPs) have recently emerged as a promising alternative to conjugated polymers, offering advantages such as synthetic access to advanced polymer architectures as well as the potential for improved stability and mechanical properties while showing good electronic performance. These polymers are accessible through well-established living polymerization techniques and amenable to efficient post-polymerization modification reactions, allowing structural modifications that influence material properties. In this study, the critical variable of the structure of the spacer connecting the pendant group to the polymer backbone was investigated. Using anionic polymerization, we first synthesized poly(methyl acrylate), followed by a straightforward post-polymerization functionalization via transesterification to obtain a family of poly(N-carbazolyl acrylates) with varying spacer units. These spacers fall into three categories: alkyl, ether, and aryl/aryl ether, differing in length, flexibility, and degree of hydrophilicity. The effects on the physical and electronic properties of the resulting polymers were investigated. The findings reveal that shorter and more rigid aryl spacers lead to significantly higher glass transition (T_g) temperatures, reaching up to 110 °C, while the other two classes of spacers showed T_g values between 29 to 56 °C. These results demonstrate structural tunability of polymer physical properties through spacer structure. Additionally, polymers with rigid spacers exhibit the highest hole mobilities (2.07 × 10^-5 cm² V^-1 s^-1) in the absence of thermal annealing. Upon annealing, a decline in mobility is observed for rigid aryl spacers, while flexible ether spacers remain unaffected. In contrast, alkyl spacers were the most responsive to thermal annealing, showing improved mobilities. Overall, this study provides experimental evidence that the nature of the spacer in NCPEPs plays a significant role in tuning both the physical and electronic properties, offering an avenue for tailoring advanced electroactive materials.