Thermoresponsive gels based on ABA triblock copolymers: Does the asymmetry matter?

Abstract

The aim of this study was to investigate the effect of the asymmetry of the triblock copolymers on their thermoresponsive self‐assembly behavior. To this end, nine ABA‐type triblock copolymers with n‐butyl methacrylate and 2‐(dimethylamino)ethyl methacrylate (DMAEMA) consisting of the A and the B blocks, respectively, were synthesized. Polymers of three different DMAEMA contents (50, 60, and 70 wt %) were synthesized while varying the length ratio of the two hydrophobic A blocks. Specifically, one symmetric ABA triblock copolymer and two asymmetric ABA′ triblock copolymers with the length of the second A block to be twice or four times bigger than the length of the first A block (AB2A and AB4A triblock copolymer) were synthesized for each DMAEMA composition. Three statistical copolymers were also synthesized for comparison. The thermoresponsive behavior of the copolymers was studied and it was found that the cloud point and rheological properties of the polymers were strongly affected by the architecture (statistical vs. block) and less strongly by the DMAEMA composition and the asymmetry of the polymers. Nevertheless, interestingly the asymmetry of the ABA triblock copolymers did influence the thermoresponsive behavior with the more symmetric polymers presenting a sol–gel transition at lower temperatures. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2850–2859.

Tuning the gelation of thermoresponsive gels

“…45,54 This effect was observed for both bipolymers [59][60][61] and terpolymers 45,47,54 (two and three component based polymers, respectively). For bipolymers these were observed for diblock copolymers based on 2-(2-ethoxy)ethoxyethyl vinyl ether (EOEOVE) and 2-(tertbutyldimethylsilyloxy)ethyl vinyl ether (BMSiVE) 59 and EOEOVE and 2-methoxyethyl vinyl ether (MOVE).…”

“…47 This was attributed to 16 insufficient bridging of the flower-like micelles to form a gel when the polymers are less symmetric.…”

“…Specifically in many occasions where random and block copolymers were compared the random polymer either did not form a gel 47,54,[59][60][61] or formed a less stable gel at higher T gel . 45,54 This effect was observed for both bipolymers [59][60][61] and terpolymers 45,47,54 (two and three component based polymers, respectively).…”

“…47 The B and A blocks 9 were based on DMAEMA and BuMA units, respectively. In all four families, an increase in composition of the hydrophobic BuMA decreased the T gel which is consistent with the previous observations.…”

“…47 Specifically, the symmetric ABA triblock copolymers were compared with the ABA' and ABA'' with the same composition;…”