Surface and Bulk Collapse Transitions of Thermoresponsive Polymer Brushes

Abstract

We elucidate the sequence of events occurring during the collapse transition of thermoresponsive copolymer brushes based on poly(di(ethyleneglycol) methyl ether methacrylate) chains (PMEO2MA) grown by atom-transfer radical polymerization (ATRP). The collapse of the bulk of the brush is followed by quartz crystal microbalance measurements with dissipation monitoring (QCM-D), and the collapse of its outer surface is assessed by measuring equilibrium water contact angles in the captive bubble configuration. The bulk of the brush collapses over a broad temperature interval (approximately 25 degrees C), and the end of this process is signaled by a sharp first-order transition of the surface of the brush. These observations support theoretical predictions regarding the occurrence of a vertical phase separation during collapse, with surface properties of thermoresponsive brushes exhibiting a sharp variation at a temperature of T(br)(surf). In contrast, the bulk properties of the brush vary smoothly, with a bulk transition T(br)(bulk) occurring on average approximately 8 degrees C below T(br)(surf) and approximately 5 degrees C below the lower critical solution temperature (LCST) of free chains in solution. These observations should also be valid for planar brushes of other neutral, water-soluble thermoresponsive polymers such as poly(N-isopropylacrylamide) (PNIPAM). We also propose a way to analyze more quantitatively the temperature dependence of the QCM-D response of thermoresponsive brushes and deliver a simple thermodynamic interpretation of equilibrium contact angles, which can be of use for other complex temperature-responsive solvophilic systems.

Functionalized Stimuli-Responsive Nanocages from Photocleavable Block Copolymers

“…The collapse of the nanocages observed here is attributed to the reduction of the mobility of the PDMAEMA chains due to the cross-linking. The decrease of the LCST of thermo-responsive polymers upon a reduction of chain mobility has already indeed been previously observed for poly(oligoethylene glycolmethacrylate) (POEGMA) brushes on silica surfaces 40 and for POEGMA and poly(Nisopropylacrylamide) (PNIPAm) brushes grafted on polystyrene latex particles. 41,42 In order to confirm this hypothesis, the thermo-responsive behavior of PtBA 118 -hv-PDMAEMA 141 micelles was monitored at pH = 6.…”

A star-shaped amphiphilic block copolymer with dual responses: synthesis, crystallization, self-assembly, redox and LCST–UCST thermoresponsive transition

“…37 Chen and Li et al prepared covalent dynamic poly(triazole) gels containing both acylhydrazone and disufide bonds by crosslinking of benzohydrazide-containing poly(triazole) with disulfide-containing dialdehyde in DMF at ambient temperature. [40][41][42][43][44][45][46][47][48][49][50] The majority of these smart materials are based on the lower critical solution temperature (LCST) of the polymer, i.e. 39 Moreover, temperature-responsive amphiphilic polymers have been one of the greatest research focuses in recent years as temperature signal can be operated easily in vivo and a large amount of promising biomaterials can be used for hyperthermia-induced drug delivery, smart bioactive surface, protein chromatography and tissue engineering.…”

Thermoresponsive Behavior of Mixtures of Epoxy Functionalized Oligo(ethylene glycol) Methacrylate Copolymers

“…However, thermoresponsive (meth)acrylic polymers containing short oligo(ethylene glycol), OEG, side chains, P(OEG x MA), were recently proposed as a very attractive alternative. [16][17][18][19][20][21][22][23][24] They also show a sharp and reversible LCST, which values depend on the length of the OEG side chain but moreover, they present some other advantages. On the one hand, the LCST can be modulated by copolymerisation of several of these macromonomers.…”