Multicompartment thermoresponsive gels: Does the length of the hydrophobic side group matter?

Multicompartment thermoresponsive gels are novel materials with fascinating self-assembly and interesting applications. The aim of this study was to investigate for the first time the effect of the length of the alkyl side group of a hydrophobic monomer on the thermoresponsive and self-assembly behaviour of terpolymers. Specifically twelve well-defined terpolymers based on the hydrophilic monomers 2-(dimethylamino)ethyl methacrylate (DMAEMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA), and on the hydrophobic monomer ethyl-, n-butyl or n-hexyl methacrylate (EtMA, BuMA or HMA) of varying architectures (ABC, ACB, BAC and statistical) were synthesised using Group Transfer Polymerisation. The A, B and C blocks were based on PEGMA, the alkyl containing methacrylate monomer, and DMAEMA, respectively. The molecular weights (MWs) and compositions of the polymers were kept the same. The polymers and their precursors were characterised in terms of their MWs, MW distributions and compositions. Aqueous solutions of the polymers were studied by turbidimetry, hydrogen ion titration, light scattering and rheology to determine their cloud points, pKas, hydrodynamic diameters and thermoresponsive behaviour and investigate the effect of the architecture and the hydrophobic alkyl side group of the terpolymers. It was found that the pKas and the Tgs were mostly affected by the hydrophobicity of the side groups and not by the architecture, while the cloud points and the sol-gel transition of the polymers were affected by both the length of the alkyl side group and the polymer architecture. Interestingly the sharpest sol-gel transitions and stable multicompartment hydrogels were observed for the ABC triblock copolymers with the short alkyl-side groups even though the sol-gel transition occurred at higher temperatures

Autonomous self-healing structural composites with bio-inspired design

Strong and tough natural composites such as bone, silk or nacre are often built from stiff blocks bound together using thin interfacial soft layers that can also provide sacrificial bonds for self-repair. Here we show that it is possible exploit this design in order to create self-healing structural composites by using thin supramolecular polymer interfaces between ceramic blocks. We have built model brick-and-mortar structures with ceramic contents above 95 vol% that exhibit strengths of the order of MPa (three orders of magnitude higher than the interfacial polymer) and fracture energies that are two orders of magnitude higher than those of the glass bricks. More importantly, these properties can be fully recovered after fracture without using external stimuli or delivering healing agents. This approach demonstrates a very promising route towards the design of strong, ideal self-healing materials able to self-repair repeatedly without degradation or external stimuli

ABC block copolymer micelles driving the thermogelation:Scattering, imaging and spectroscopy

Thermoresponsive polymers have attracted much scientific attention due to their capacity for temperature-driven hydrogel formation. For biomedical applications, such as drug delivery, this transition should be tuned below body temperature to facilitate controlled and targeted drug release. We have recently developed a thermoresponsive polymer that forms gel at low concentrations (2 w/w%) in aqueous media and offers a cost-effective alternative to thermoresponsive systems currently being applied in clinics. This polymer is an ABC triblock terpolymer, where A, B, and C correspond to oligo(ethylene glycol) methyl ether methacrylate with average Mn 300 g mol−1 (OEGMA300), n-butyl methacrylate (BuMA), and di(ethylene glycol) methyl ether methacrylate (DEGMA). To investigate the self-assembly and the gelation mechanism in diluted solutions, we used small-angle neutron scattering (SANS) on 1 w/w% (below the gelation concentration) and 5 w/w% solutions (above the gelation concentration). As a comparison, we also investigated the solutions of the most studied thermoresponsive polymer, namely, Pluronic F127, an ABA triblock bipolymer made of ethylene glycol (A) and propylene glycol (B) blocks. SANS revealed that the in-house synthesised polymer forms elliptical cylinders, whose length increases significantly with temperature. In contrast, Pluronic F127 solutions form core-shell spherical micelles, which slightly elongate with temperature. Transmission electron microscopy images support the SANS findings, with tubular/worm structures being present. Variable-temperature circular dichroism (CD) and proton nuclear magnetic resonance (1H NMR) spectroscopy experiments reveal insights on the tacticity, structural changes, and molecular origin of the self-assembly

Thermoresponsive triblock copolymers based on methacrylate monomers: Effect of molecular weight and composition

A series of amphiphilic thermoresponsive ABC triblock copolymers was synthesised by Group Transfer Polymerisation (GTP). In total nine polymers were prepared based on the non-ionic hydrophobic n-butyl methacrylate (BuMA), the ionisable hydrophilic and thermoresponsive 2-(dimethylamino)ethyl methacrylate (DMAEMA) and the non-ionic hydrophilic methoxy poly(ethylene glycol) methacrylate (PEGMA). The architecture of the copolymers was kept constant with the hydrophobic block in the middle and the two hydrophilic blocks at the two ends, while the composition and the molecular weight of the polymers were varied. Specifically the molecular weight of the polymers was varied while the composition and the architecture were kept constant. The precursors to the polymers and the polymers were characterised in terms of their molecular weight and composition using gel permeation chromatography and proton nuclear magnetic resonance spectroscopy, respectively. Aqueous solutions of the polymers were studied by turbidimetry, hydrogen ion titration and light scattering to determine their cloud points, pK as, and hydrodynamic diameters and investigate the effect of the composition and the molecular weight of the copolymers. Finally, the thermoresponsive behaviour of the copolymers was also studied and it was found that the cloud point and gel point of the polymers were strongly affected by both the composition and molecular weight of the triblock copolymers

Anionic amphiphilic end-linked conetworks by the combination of quasiliving carbocationic and group transfer polymerizations

A series of amphiphilic end-linked conetworks was synthesized by the combination of two "quasiliving" polymerization techniques, quasiliving carbocationic (QLCCP) and group transfer polymerizations (GTP). The hydrophobic monomer was polyisobutylene methacrylate synthesized by the QLCCP of isobutylene and subsequent terminal modification reactions. The hydrophilic monomer was methacrylic acid (MAA) introduced via the polymerization of 2-tetrahydropyranyl methacrylate followed by acid hydrolysis after (co)network formation. The conetwork syntheses were performed by sequential monomer/crosslinker additions under GTP conditions. All the precursors and the extractables from the conetworks were characterized by gel permeation chromatography and H-1 NMR. The resulting polymer conetworks were investigated in terms of their degree of swelling (DS) in aqueous media and in tetrahydrofuran (THF) over the whole range of ionization of the MAA units and in n-hexane for uncharged conetworks. The DSs in water increased with the degree of ionization (DI) of the MAA units and the hydrophilic content in the conetwork, whereas the DSs in THF increased with the reduction of the DI of the MAA units. The effective pK of the MAA units in the conetworks increased from 8.4 to 10.5 with decreasing MAA content. These findings can facilitate the design of similar unique conetworks with adjustable swelling behavior and composition-de pendent pK values. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4289-4301, 200

"Comb-like" non-ionic polymeric macrosurfactants

A series of non-ionic comb-like polymeric macrosurfactants were synthesized by group transfer polymerisation. Specifically, nine amphiphilic block copolymers were prepared based on the hydrophobic n-hexyl methacrylate and the hydrophilic poly(ethylene glycol) methacrylate. The molecular weights (MWs) and the compositions of the polymer precursors and polymers were confirmed by GPC and NMR, respectively. Dynamic light scattering measurements in tetradecane polymer solutions were made. The micelles' diameter increased by increasing the MW and the hydrophobic content of copolymers. The emulsifying ability of all the polymers was also investigated. Interestingly not all the block copolymers were able to form stable emulsions and the emulsification was affected by the polymer composition and MW. A tendency for improvement of the emulsion stability with the simultaneous increase of the MW and HEMA fraction of the block copolymers has been observed. The best emulsifier was the diblock copolymer with the highest content in HEMA and the highest MW

Water-in-water emulsions based on incompatible polymers and stabilized by triblock copolymers-templated polymersomes

Aqueous solutions containing a mixture of polyethylene glycol (PEG) and dextran homopolymers form an aqueous two-phase system which can be emulsified to give a water-in-water emulsion. We show how these emulsions can be stabilized using triblock polymers containing poly[poly(ethylene glycol) methyl ether methacrylate] (PEGMA), poly (n-butyl methacrylate) (BuMA), and poly[2-(dimethylamino) ethyl methacrylate] (DMAEMA) blocks of general structure Pp-Bb-Dd, in which the middle BuMA block is hydrophobic. Low-energy input stirring of mixtures containing equal volumes of PEG- and dex-rich aqueous phases plus 1 wt % of Pp-Bb-Dd stabilizer all form dex-in-PEG emulsions (for the range of Pp-Bb-Dd triblock polymers used here) which have a polymersome-like structure. In favorable cases, the emulsion drop (or templated polymersome) sizes are a few micrometers and are stable for periods in excess of 6 months. The emulsions can be inverted from dex-in-PEG to PEG-in-dex by increasing the volume fraction of dex-rich aqueous phase. We demonstrate that both high and low molecular weight fluorescent solutes “self-load” into either the dex- or PEG-rich regions and that solute mass transfer across the water–water interface occurs on a timescale of less than 1 min

ABC triblock copolymer micelles: Spherical versus worm-like micelles depending on the preparation method

Well-defined ABC triblock copolymers based on two hydrophilic blocks, A and C, and a hydrophobic block B are synthesized and their self-assembly behaviour is investigated. Interestingly, at the same solvent concentration, pH, and temperature, different shape micelles are observed, spherical and worm-like micelles, depending on the preparation method. Specifically, spherical micelles are observed with bulk rehydration while both spherical and worm-like micelles are observed with film rehydration