Double thermoresponsive block–random copolymers with adjustable phase transition temperatures: From block‐like to gradient‐like behavior

Abstract

Stimuli‐responsive block–random copolymers are very useful “smart” materials as their switching behavior can be tuned by simply adjusting the composition of the random copolymer block. Because of that, we synthesized double thermoresponsive poly(N‐acryloylpyrrolidine)‐block‐poly(N‐acryloylpiperidine‐co‐N‐acryloylpyrrolidine) (PAPy‐b‐P(APi‐co‐APy)) copolymers via reversible addition fragmentation chain transfer (RAFT) polymerization and investigated their temperature‐induced self‐assembly in aqueous solution. By varying the APi/APy ratio in the random copolymer block, its phase transition temperature (PTT1) can indeed be precisely adjusted while the temperature‐induced collapse upon heating leads to a fully reversible well‐defined micellization. By making the two blocks compositionally similar to more than 60%, the polymers' mechanistic thermoresponsiveness can furthermore be changed from block‐like to rather gradient‐like behavior. This means the micellization onset at PTT1 and the corona collapse at the PTT of the more hydrophilic pure PAPy block (PTT2) overlap resulting in one single broad transition. This work thus contributes to the detailed understanding of design, synthesis and mechanistic behavior of tailored “on‐demand” switchable materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 399–411

Hydroperoxide Traces in Common Cyclic Ethers as Initiators for Controlled RAFT Polymerizations

“…[22] In a recent publication, we have discussed the synthesis of poly(N-acryloylpyrrolidine) (PAPy) macro-RAFT agents with a high theoretical livingness [23,24] by using very low amounts of the radical initiator (i.e., [RAFT]/[initiator] = 150/1). [25] We have reported there, however, that even in the case of this high theoretical livingness dead chains are accumulated during the RAFT polymerization process (see also Figure S1 in the Supporting Information). This becomes especially observable when the synthesis of the macro-RAFT agent is quenched at higher N-acryloylpyrrolidine (APy) conversions, i.e., above 80%, and indicates a higher actual radical concentration in the system than the theoretical one.…”

“…In a recent publication, we have discussed the synthesis of poly( N ‐acryloylpyrrolidine) (PAPy) macro‐RAFT agents with a high theoretical livingness by using very low amounts of the radical initiator (i.e., [RAFT]/[initiator] = 150/1) . We have reported there, however, that even in the case of this high theoretical livingness dead chains are accumulated during the RAFT polymerization process (see also Figure S1 in the Supporting Information).…”

The Importance of Cooperativity in Polymer Blending: Toward Controlling the Thermoresponsive Behavior of Blended Block Copolymer Micelles

“…However, this technique is somewhat limited for controlling and predicting self‐assembly behavior and thermoresponse, with a trial and error approach often required to target specific polymer properties. Moreover, statistical copolymerization is not always possible and thus the resultant microstructure could adversely alter self‐assembly behavior and polymer properties 24–26. In light of these limitations, an alternative strategy has been developed involving copolymer blending, whereby two or more block copolymers that vary in functionality or stimuli‐responsiveness are mixed to obtain polymer nanostructures with a range of compositions and properties that are intermediate of the constituent polymers 27–30.…”

“…www.advancedsciencenews.com www.mrc-journal.de behavior and polymer properties. [24][25][26] In light of these limitations, an alternative strategy has been developed involving copolymer blending, whereby two or more block copolymers that vary in functionality or stimuli-responsiveness are mixed to obtain polymer nanostructures with a range of compositions and properties that are intermediate of the constituent polymers. [27][28][29][30] The inherent advantages of this copolymer blending methodology are that it precludes exhaustive synthesis as well as offering a scalable and facile route for targeting a wide array of polymer nanostructures.…”

Solubility behaviour of random and gradient copolymers of di- and oligo(ethylene oxide) methacrylate in water: effect of various additives

“…This characteristic makes such gradient copolymers a great potential in biomimetic applications. [21][22][23][24][25][26][27][28][29] Various studies are done on the effect of additives on the solubility behavior of thermoresponsive polymers [30][31][32][33][34][35][36][37][38][39] including POEOMAs, [40][41][42][43][44] but so far there is no comprehensive study to compare the effect of different additives on the phase transition of thermoresponsive copolymers with different structure.…”