Interaction between four-armed TPE core and grafted PLLA chains with tunable chain lengths

To explore the aggregation behavior of small molecules and macromolecules at different scales, this study employed aggregation-induced emission (AIE) molecule tetraphenylethylene-polyol (TPE-4OH) as a polyol initiator to synthesize four-armed poly( l -lactic acid) (4a-TPE-PLLA) with varied chain lengths. Moreover, comparative studies with pentaerythritol-initiated four-armed PLLA revealed significant mutual regulatory relationships between self-aggregation of TPE groups and PLLA crystallization. Lower glass transition temperatures (48.0°C of 4a-TPE-PLLA-S and 49.4°C of 4a-TPE-PLLA-M) and rheological results indicated that when PLLA chains are short (28 repeating units) or medium (48 repeating units) in length, TPE groups weakened the PLLA interchain interactions and promoted the segmental mobility of of PLLA chains. While longer PLLA chains (78 repeating units) were easier to restrict the conformation of TPE, which showed higher photoluminescence quantum yield (PLQY) values. In-situ polarized microscopy revealed TPE aggregates promoted the nucleation of PLLA. Higher PLQY was observed after 4a-TPE-PLLA crystallization, especially, the PLQY of 4a-TPE-PLLA-M increased from 58.23% to 65.36%. And 4a-TPE-PLLA also showed the potential application of phase separation indicator due to its fluorescence properties. This work provides some insights into the multi-scale aggregation mechanisms of PLLA chains and AIE molecules.