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Abstract: Poly(l-arginine) (PARG) and poly(l-glutamic acid) (PLGA) homopolypeptides were custom synthesized by precision N-carboxyanhydride ring-opening polymerization methods with two molar masses, matched for pairs of cationic and anionic polypeptides (degrees of polymerization n = 100 and n = 500). The conformations of the homopolypeptides were probed using circular dichroism (CD) and FTIR spectroscopy which showed the presence of mainly polyproline II (PPII) conformation. Small-angle X-ray scattering (SAXS) showed concentration-dependent polyelectrolyte peaks and form factor with high q scaling due to the excluded volume behaviour of the wormlike chains. We then examined polyelectrolyte complexation in mixtures of pairs of PARG and PLGA polypeptides with matched molar masses. Precipitation was generally observed and the structures of precipitates, supernatant and resuspended precipitates were investigated using CD, SAXS and cryo-TEM. These revealed that, contrary to prior suggestions in the literature, the precipitates contain mostly polypeptides in a PPII-like conformation, and there is only a minimal β-sheet content (which is enhanced upon drying the sample during preparation for certain measurements). The precipitates have a fractal-like structure as revealed by cryo-TEM and SAXS. Our findings on the structure of polypeptide complex precipitates contribute to the understanding of phase separation of polyelectrolyte complexes and coacervation and may shed light on the formation of inter-cellular bodies of proteins and peptides such as Lewy and other inclusion bodies.

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Abstract: Improving the performance of polyurethane is a crucial endeavor due to its versatile properties that make it suitable for various uses, especially as a matrix in the field of composite materials. The current work investigates the influence of the addition of two types of graphene derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), to hard copolymer polyurethane (HCPU). HCPUs as nanocomposites were synthesized using melt-mixing approaches with different weight ratios of nanofiller additives. The transmission electron microscopy and scanning electron microscopy displayed the morphology through the incorporation of nanofillers within the HCPU structure. Thermogravimetric analysis (TGA) testing showed an increase in the thermal stability of HCPU with the addition of GO and rGO. Herein, the overall HCPU crystallinity/microphase separation decreased after the addition of GO and rGO compared to unfilled HCPU samples. The thermal stability test showed significant enhancement with increasing GO and rGO incorporated weight ratio due to the barrier and tortuous path effects of nanofillers. A clear increase in thermal and electrical conductivity is found, in particular at greater content of addition (5 wt%) of rGO in comparison with neat HCPU. The rheological behavior showed that the storage modulus of HCPU nanocomposites increased from that of pure HCPU, proving the formation of a filler-polymer network interaction within the HCPU chain structure. Dispersion and physical and/or chemical interaction of the GO and rGO within polyurethane chains plays a major role in enhancing the morphology and thermal and rheological properties, and thus represents a significant improvement for the final properties of HCPU nanocomposites.

Open Access

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Abstract: Polymerization-induced self-assembly (PISA) is widely recognized to be a powerful technique for the preparation of diblock copolymer nano-objects in various solvents. Herein a highly unusual non-aqueous emulsion polymerization formulation is reported. More specifically, the reversible addition–fragmentation chain transfer (RAFT) polymerization of N-(2-acryloyloxy)ethyl pyrrolidone (NAEP) is conducted in n-dodecane using a poly(stearyl methacrylate) (PSMA) precursor to produce sterically-stabilized spherical nanoparticles at 90 °C. This relatively high polymerization temperature was required to ensure sufficient background solubility for the highly polar NAEP monomer, which is immiscible with the non-polar continuous phase. A relatively long PSMA precursor (mean degree of polymerization, DP = 36) was required to ensure colloidal stability, which meant that only kinetically-trapped spheres could be obtained. Dynamic light scattering (DLS) studies indicated that the resulting PSMA36–PNAEPx (x = 60 to 500) spheres were relatively well-defined (DLS polydispersity <0.10) and the z-average diameter increased linearly with PNAEP DP up to 261 nm. Differential scanning calorimetry studies confirmed a relatively low glass transition temperature (Tg) for the core-forming PNAEP block, which hindered accurate sizing of the nanoparticles by TEM. However, introducing ethylene glycol diacrylate (EGDA) as a third block to covalently crosslink the nanoparticle cores enabled a spherical morphology to be identified by transmission electron microscopy studies. This assignment was confirmed by small angle X-ray scattering studies of the linear diblock copolymer nanoparticles. Finally, hydrophobic linear PSMA36–PNAEP70 spheres were evaluated as a putative Pickering emulsifier for n-dodecane–water mixtures. Unexpectedly, addition of an equal volume of water followed by high-shear homogenization always produced oil-in-water (o/w) emulsions, rather than water-in-oil (w/o) emulsions. Moreover, core-crosslinked PSMA36–PNAEP60–PEGDA10 spheres also produced o/w Pickering emulsions, suggesting that such Pickering emulsions must be formed by nanoparticle adsorption at the inner surface of the oil droplets. DLS studies of the continuous phase obtained after either creaming (o/w emulsion) or sedimentation (w/o emulsion) of the droplet phase were consistent with this interpretation. Furthermore, certain experimental conditions (e.g. ≥0.5% w/w copolymer concentration for linear PSMA36–PNAEPx nanoparticles, ≥0.1% w/w for core-crosslinked nanoparticles, or n-dodecane volume fractions ≤0.60) produced w/o/w double emulsions in a single step, as confirmed by fluorescence microscopy studies.

Open Access

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Abstract: Reversible addition–fragmentation chain transfer (RAFT) mediated dispersion polymerisation in supercritical carbon dioxide (scCO2) is an efficient and green method for synthesising block copolymer microparticles with internal nanostructures. Here we report for the first time the synthesis of phase separated poly(methyl methacrylate-block-styrene-block-4-vinylpyridine) (PMMA-b-PS-b-P4VP) triblock terpolymer microparticles using a simple two-pot sequential synthesis procedure in scCO2, with high monomer conversions and no purification steps. The microparticles, produced directly and without further processing, show a complex internal nanostructure, appearing as a “lamellar with spheres” [L + S(II)] type morphology. The P4VP block is then exploited as a structure-directing agent for the fabrication of TiO2 microparticles. Through a simple and scalable sol–gel and calcination process we produce hollow TiO2 microparticles with a mesoporous outer shell. When directly compared to porous TiO2 particles fabricated using an equivalent PMMA-b-P4VP diblock copolymer, increased surface area and enhanced photocatalytic efficiencies are observed.

Open Access

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Abstract: We have previously reported the synthesis of thermoresponsive poly(stearyl methacrylate)-poly(benzyl methacrylate) [PSMA-PBzMA] diblock copolymer vesicles in mineral oil via polymerisation-induced self-assembly (PISA). Such vesicles undergo a vesicle-to-worm transition on heating, which provides an interesting new oil-thickening mechanism (see M. J. Derry, et al., Angew. Chem., 2017, 56, 1746–1750). In the present study, we report an unexpected reduction in dispersion viscosity when heating vesicles of approximately the same composition above a certain critical temperature. Transmission electron microscopy (TEM) studies indicate rich thermoresponsive behavior, with vesicles present at 20 °C, worms being formed at 130 °C and spheres generated at 180 °C, indicating that a worm-to-sphere transition occurs after the initial vesicle-to-worm transition. Moreover, we have also prepared a series of new thermoresponsive diblock copolymer vesicles by RAFT dispersion copolymerization of n-butyl methacrylate (BuMA) with benzyl methacrylate (BzMA) using a poly(stearyl methacrylate) precursor in mineral oil. This model system was developed to examine whether statistical copolymerization of a suitable comonomer (BuMA) could be used to tune the critical onset temperature required for the vesicle-to-worm transition. Indeed, oscillatory rheology studies confirmed that targeting membrane-forming blocks containing up to 50 mol% BuMA lowered the critical onset temperature required to induce the vesicle-to-worm transition to 109 °C, compared to 167 °C for the reference PSMA14-PBzMA125 diblock copolymer. Variable temperature small-angle X-ray scattering (SAXS) experiments confirmed a vesicle-to-worm transition, with the vesicles initially present at 20 °C being converted into worms when heated above 130 °C. Furthermore, a substantial reduction in dispersion viscosity was again observed when heating above the critical onset temperature. TEM and shear-induced polarized light imaging (SIPLI) studies indicate that linear worms are no longer present at 160 °C and 170 °C respectively, suggesting a subsequent worm-to-sphere transition. The thermal transitions studied herein proved to be irreversible on cooling on normal experimental timescales (hours).