‘Isothermal’ phase transitions and supramolecular architecture changes in thermoresponsive polymers via acid-labile side-chains

Abstract

Polymers designed to change their conformation via a phase transition triggered by acidic cleavage of a hydrophobic side-chain have been synthesized and characterised. The new materials were prepared by co-polymerising N-isopropylacrylamide with an acetal-containing pH-sensitive monomer N-(2-(2,4,6-trimethoxyphenyl)-1,3-dioxan-5-yl)acrylamide (TMPDA) and then grafting the resultant linear co-polymers to branched poly(ethyleneimine). The final three-component polycations exhibited Lower Critical Solution Temperature (LCST) behaviour. The structures of these polymers, their solution behaviour and their self-association were characterized by DLS and TEM in water and buffer solutions. The acid-triggered hydrolysis of trimethoxybenzeneacetal side-chains on the poly(N-isopropylacrylamide-co-TMPDA) grafts resulted in changes in lower critical solution temperatures and in solution self-assembly; thus in effect creating an ‘isothermal’ phase transition. The changes in polymer conformation, at acidity levels corresponding to those in cell endosomes, offer promise for these polymers to act as controlled release materials

Tunable stimuli-responsive self-assembly system that forms and stabilizes nanoparticles by simple mixing and heating/cooling of selected block copolymers

“…There has been increased interest in amphiphilic block copolymers due to their potential to form core-shell type nanoassemblies in aqueous solutions. [1][2][3][4][5][6][7][8] Stimuli-responsive ''smart'' polymers enable nanoassembly applications in biomedicine, in particular drug delivery systems, because they can sense specific environmental changes in biological systems, and adjust in a predictable manner. [9][10][11][12][13][14][15] Recent progress in smart polymer synthesis has led to intriguing new amphiphilic polymers that respond to double or multiple stimuli.…”

Towards being genuinely smart: ‘isothermally-responsive’ polymers as versatile, programmable scaffolds for biologically-adaptable materials

“…The incorporation of 5 -10% TEMPO groups in the copolymer structure was sufficient to afford the material with redox-responsive LCST behaviour: At a polymer concentration of 10 mg.mL -1 , reduction with 19.2 mM ascorbic acid increased the LCST by 14 °C whilst reoxidation with 48 mM K 3 [Fe(CN) 6 ] largely reversed the change. 98 Acetals have also been employed by Zhang et al to raise the cloud point of tri(ethylene glycol) acrylatebased co-polymers upon cleavage. 89,90 Likewise, Peng and co-workers has used host-guest complexation between ferrocene and β-cyclodextrin as a means of modulating the LCST of a thermoresponsive co-polymer comprising N,N-dimethylacrylamide and ferrocene.…”

Tailoring the morphology of branched poly(N-isopropylacrylamide) via self-condensing atom-transfer radical copolymerization and its unique self-assembly behavior in alcohol

“…[30][31][32] Another important way is to control the chain architectures, such as star, 33 cyclic, 34 comblike 35 and branched 2,36-55 ones. Branched PNIPAM was commonly obtained by grafting linear PNIPAM chains onto hyperbranched poly(ethyleneimine)s, [36][37][38][39] poly(ether amide)s 40 and poly(ethylene glycol)s. [41][42][43] Copolymerization of NIPAM with divinylbenzene also resulted in a hyperbranched structure. 44 Of special note, self-condensing RAFT copolymerization 2,[45][46][47][48][49] was mostly used to prepare highly branched PNIPAM with a controlled degree of branching and designed endgroups, e.g.…”