Temperature-induced phase-transitions of methoxyoligo(oxyethylene) styrene-based block copolymers in aqueous solution

Abstract

Novel well-defined diblock copolymers based upon styrene substituted with pendant methoxyoligo(oxyethylene) groups (4-CH 3 O(EO) 4 St, TrEGS) were prepared by sequential atom transfer radical polymerization. Polystyrene (PS) was synthesized as the first block in the copolymer using (1bromoethyl)benzene as the initiator. This was followed by growth of a second block composed of PTrEGS. Each copolymer exhibits a lower critical solution temperature (LCST) in aqueous solution, and the LCST depends on the length of the PTrEGS block and the copolymer composition. Longer PTrEGS chains result in higher LCST values in aqueous solutions. The cloud points (T c s) of PS-b-PTrEGS copolymers are lower than that of PTrEGS homopolymer as determined by UV-visible spectroscopy.Variable-temperature NMR spectra show that the intensity of proton signals from oxyethylene groups dramatically decreases at temperatures above the cloud point, indicating phase transition due to hydrogen bonding changes. Dynamic light scattering (DLS) measurements indicate that micelles are formed, where the PS backbone serves as the core at 25 C. Each of these block copolymer solutions transformed from transparent bluish solutions to white gels above certain concentrations ($10 wt%) and temperatures (lower critical gelation temperature, LCGT). The gelation process is thermally reversible, implying physical crosslinking through hydrophobic interactions.

Examination of the fundamental relation between ionic transport and segmental relaxation in polymer electrolytes

“…Five polymers were synthesized using conventional free radical (co)polymerization and anionic polymerization [17,23,24]: poly(vinyl ethylene carbonate)-co-poly(vinyl acetate) (PVEC-PVAc, weight-average molecular weight M w = 32.4 kg/mol, polydispersity index PDI = 1. kg/mol, PDI = 1.26). The first three polymers, PVEC-PVAc, PVEC-PMEA, and PVC-PPEGMEMA, were based on the carbonate structure, whereas the last two polymers, PMOEOMSt and PPEOSt-PSt, were based on the polystyrene backbone.…”

Doubly thermoresponsive brush-linear-linear ABC triblock copolymer nanoparticles prepared through dispersion RAFT polymerization

“…In recent years, thermoresponsive block copolymer nano‐objects have aroused great interest because of their potential use in drug delivery, tissue engineering scaffolds, biological separation, and biochemical sensors . The general method to prepare thermoresponsive nano‐objects is through the micellization strategy, following which the thermoresponsive block copolymer is initially dissolved in a common solvent for all the blocks and then micellization is triggered by stepping across the critic temperature of the lower critical solution temperature (LCST) . Based on the number of the thermoresponsive blocks in the block copolymers, single‐ or multithermoresponsive block copolymers are classified.…”

“…Based on the number of the thermoresponsive blocks in the block copolymers, single‐ or multithermoresponsive block copolymers are classified. Compared with the general thermoresponsive block copolymers containing a single thermoresponsive block, these multithermoresponsive block copolymers contain two or more thermoresponsive blocks and therefore much complex phase behavior is demonstrated . In fact, various multithermoresponsive block copolymer nano‐objects have been fabricated through the micellization strategy, and the size and even the morphology of the multithermoresponsive block copolymer nano‐objects can be tuned by increasing/decreasing the temperature above/below LCST of the thermoresponsive blocks.…”

“…Various PNIPAM‐based thermoresponsive block copolymers have been prepared by the controlled radical polymerization techniques such as atom transfer radical polymerization, nitroxide‐mediated polymerization, and reversible addition‐fragmentation chain transfer (RAFT) polymerization . Besides linear thermoresponsive polymers, the nonlinear poly(meth)acrylates, for example, poly[oligo(ethylene glycol) methyl ether methacrylate], and polystyrenics, for example, poly[poly(ethylene glycol) methyl ether vinylphenyl] (PmPEGV), both of which have short poly(ethylene glycol) (PEG) side‐chains, are found to exhibit LCST in water. These thermoresponsive nonlinear PEG analogues have received tremendous attention due to their well‐established biocompatibility and potential applications in biomedical materials.…”