Thermal control of multiblock sequence using anion-migrated ring-opening polymerization

The construction of well-defined multiblock copolymers in a facile manner is a meaningful but challenging task in polymer synthesis. Herein, we disclose that the sequence distribution of 1-cyclopropylvinylbenzene (CPVB) and p-tert-butylstyrene (t-St) units along the chain exhibits great discrepancies at different reaction temperatures during living anionic polymerization when the feeding ratio of CPVB to t-St was 15/4, i.e., the copolymer generated at 20 degrees C exhibits a tapered structure (t-St units are dominant), but displays a gradient structure at 60 degrees C (transitioning from t-St to CPVB units). Utilizing this unique characteristic, temperature and time programs are synchronously applied to logically control the compositions and chain lengths of each segment in the multiblock copolymers. Therefore, di-/tri-/hexa-block copolymers with utterly distinct block numbers and compositions are readily prepared. Furthermore, the obtained polymers with different sequence structures underwent a further cationic cyclization reaction, and all the obtained cyclized polymers exhibited unique fluorescence properties and excellent thermal resistance. Additionally, only the continuous insertion of CPVB units in the chain can achieve a further cationic cyclization reaction; thus, the cyclized gradient polymers exhibit a more tightly stacked structure than the cyclized tapered polymer, which induces the cyclized gradient polymer to emit bright light compared to the cyclized tapered structure. Moreover, all the gradient segments are separated by tapered segments in cyclized tri-/hexa-block copolymers, which results in the corresponding polymers emitting faint light with an extension in the distance between the fluorescent clusters. The block sequence can be easily regulated through switching reaction temperatures during the anionic copolymerization of 1-cyclopropylvinylbenzene (CPVB) and p-tert-butylstyrene (t-St).