Synthesis of Cross-Linked Block Copolymer Nanoassemblies and their Coating Application.

Since the discovery of polymerization-induced self-assembly (PISA), convenient synthesis of concentrated block copolymer nanoassemblies dispersed in solvent has been achieved. Now, application of block copolymer nanoassemblies should be paid more attention. In this study, corona-cross-linked block copolymer nanoparticles of poly[dimethylacrylamide-co-(diacetone acrylamide)]-b-polystyrene [P(DMA-co-DAAM)-b-PS] containing the poly(DAAM) segment in the hydrophilic P(DMA-co-DAAM) block are synthesized initially by PISA following dispersion reversible addition-fragmentation chain transfer polymerization and then by covalent intraparticle cross-linking through the poly(DAAM) segment and adipic acid dihydrazide. Coating application of the corona-cross-linked block copolymer nanoassemblies is tried, and much higher water resistance of the corona-cross-linked block copolymer nanoassemblies than that of the linear block copolymer nanoassemblies is demonstrated.

Thermoresponsive Polymers Based on Tertiary Amine Moieties.

Thermoresponsive polymers exhibiting unique reversible phase transition properties in aqueous solution in response to temperature stimuli have been extensively investigated. In the past two decades, thermoresponsive polymers based on tertiary amine moieties have achieved considerable progress and become an important family of thermoresponsive polymers, including tertiary amine functionalized poly((meth)acrylamide)s, poly((meth)acrylate)s, poly(styrene)s, poly(vinyl alcohol)s, and poly(ethylene oxide)s, which exhibit lower critical solution temperature and/or upper critical solution temperature in water or aliphatic alcohols. Their phase transition behavior can be modulated by the solution pH and CO2 due to the protonation of tertiary amine moieties in acidic condition and deprotonation in alkaline condition and the charged ammonium bicarbonate formed by the tertiary amine moieties and CO2 . The aim of this review is to summarize the recent progress in the thermoresponsive polymers based on tertiary amine moieties.

ICAR ATRP in PEG with Low Concentration of Cu(II) Catalyst: A Versatile Method for Synthesis of Block Copolymer Nanoassemblies under Dispersion Polymerization.

A versatile method for synthesis of block copolymer nanoassemblies via initiators for continuous activator regeneration (ICAR) atom transfer radical polymerization (ATRP) dispersion polymerization in a low molecular weight poly(ethylene glycol) (PEG) is discussed. This ICAR ATRP dispersion polymerization uses a low concentration of CuBr2 catalyst, which is stable under atmospheric conditions and is soluble in most polar solvents and employs a polymerization medium of viscous and nonvolatile PEG. Through this ICAR ATRP dispersion polymerization, various block copolymer nanoassemblies, including poly(ethylene glycol)-block-polystyrene, poly(ethylene glycol)-block-poly(methyl methacrylate), and poly(2-hydroxypropyl methacrylate)-block-poly(methyl methacrylate), have been synthesized. The parameters affecting the size and morphology of the block copolymer nanoassemblies are briefly discussed.

Peptide-crosslinked molecularly imprinted polymers for efficient separation of immunoglobulin G from human serum.

Low-cost and highly effective methods are highly desirable to replace the costly ethanol fractionation and affinity chromatography in IgG isolation from human plasma. Molecularly imprinted polymers (MIPs) of IgG are potential candidates, however, they still suffer from severe problems such as difficult template removal and low imprinting efficiency. Here, a recently developed strategy was adopted to overcome these problems. The MIPs were synthesized using poly(L-glutamic acid) (PLGA) peptide crosslinkers instead of commonly used crosslinkers, such as N,N-methylenebisacrylamide (BIS). Because of the pH-induced helix-coil transition and the precise folding of the peptide segments in the polymers, the imprint cavities can be enlarged by adjusting the pH from 5.0 to 7.0, but their original size and shape are restored when the pH is adjusted back. Therefore, the IgG template can be eluted completely under mild conditions, and significantly improved imprinting efficiency can be achieved. Compared with BIS-crosslinked MIP, 8.6 times more binding sites can be created by molecular imprinting PLGA-crosslinked MIP. The factors influencing the performance of the MIP were studied systematically. An optimized MIP with a high adsorption capacity (612.5 mg g-1), high IF (4.92), and high selectivity was obtained. The adsorption capacity and selectivity of the MIP are much higher than the previously reported IgG MIPs. Because of its high adsorption capacity and selectivity, it can separate IgG from human serum effectively, affording high purity products.

Synthesis of hierarchical hollow silica microspheres containing surface nanoparticles employing the quasi-hard template of poly(4-vinylpyridine) microspheres.

A facile method of preparing hierarchical hollow silica microspheres containing surface silica nanoparticles (HHSMs) through the sol-gel process of tetraethylorthosilicate employing a quasi-hard template of non-cross-linking poly(4-vinylpyridine) microspheres is proposed. The quasi-hard template contains the inherent catalyst of the basic pyridine group, and a few of the polymer chains can escape from the template matrix into the aqueous phase, which initiates the sol-gel process spontaneously both on the surface of the template used to prepare the hollow silica shell and in the aqueous phase to produce the surface silica nanoparticles. By tuning the weight ratio of the silica precursor to the quasi-hard template, HHSMs with a size of about 180 nm and a shell thickness ranging from 14 to 32 nm and surface silica nanoparticles ranging from 17 to 36 nm are produced initially through the deposition of surface silica nanoparticles onto the silica shell, followed by template removal either by calcination or solvent extraction. The synthesized HHSMs are characterized, and a possible mechanism for the synthesis of HHSMs is proposed.

Pd-catalyzed C-C cross-coupling reactions within a thermoresponsive and pH-responsive and chelating polymeric hydrogel.

A porous, thermoresponsive and pH-responsive, and chelating hydrogel of poly(N-isopropylacrylamide)-co-poly[2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxypropyl ester] (PNIPAM-co-PMACHE) is proposed as both a reaction medium and the Pd catalyst support for organic synthesis. Organic synthesis within the PNIPAM-co-PMACHE hydrogel has three merits. First, organic reactions such as Suzuki and Heck reactions within the hydrogel can be accelerated due to the enriched Pd catalyst and reactants within the hydrogel by the reversible deswelling/swelling. Second, organic synthesis within the PNIPAM-co-PMACHE hydrogel, which holds about approximately 300 times of water and is similar to the environmentally benign reaction medium of water, can be performed efficiently without surfactant or cosolvent being added. Third, the PNIPAM-co-PMACHE hydrogel itself and the therein-immobilized Pd catalyst can be easily recycled since the hydrogel/Pd composite can reversibly swell/deswell.

A general method to synthesis of amphiphilic colloidal nanoparticles of CdS and noble metals.

Amphiphilic colloids of CdS and noble metal nanoparticles, which can be dispersed both in water and organic solvents such as ethanol, N,N-dimethylformamide, chloroform, and toluene, are studied. The amphiphilic colloidal nanoparticles are synthesized by grafting the amphiphilic and thermoresponsive polymer of thiol-terminated poly(N-isopropylacrylamide) to CdS and noble metal nanoparticles. The size and morphology of the PNIPAM-grafted colloidal nanoparticles of CdS@PNIPAM can be tuned by changing the molar ratio of PNIPAM/CdS. The size of CdS@PNIPAM nanoparticles slightly decreases first from 5.5 to 4.4 nm then slightly increases from 4.4 to 6.1 nm with the decrease in the molar ratio from 1/1 to 1/10. Spherical nanoparticles of CdS@PNIPAM are synthesized at a higher molar ratio and worm-like nanoparticles are obtained at a lower molar ratio. The resultant PNIPAM-grafted colloidal nanoparticles of CdS@PNIPAM, Au@PNIPAM, Pd@PNIPAM, and Ag@PNIPAM are thermoresponsive in water and show a cloud-point temperature at about 32.5 degrees C.

Synthesis of porous poly(styrene-co-acrylic acid) microspheres through one-step soap-free emulsion polymerization: whys and wherefores.

Synthesis of porous poly(styrene-co-acrylic acid) (PS-co-PAA) microspheres through one-step soap-free emulsion polymerization is reported. Various porous PS-co-PAA microspheres with the particle size ranging from 150 to 240 nm and with the pore size ranging from 4 to 25 nm are fabricated. The porous structure of the microspheres is confirmed by the transmission electron microscopy measurement and Brunauer-Emmett-Teller (BET) analysis. The reason for synthesis of the porous PS-co-PAA microspheres is discussed, and the phase separation between the encapsulated hydrophilic poly(acrylic acid) segment and the hydrophobic polystyrene domain within the PS-co-PAA microspheres is ascribed to the pore formation. The present synthesis of the porous PS-co-PAA microspheres is anticipated to be a new and convenient way to fabricate porous polymeric particles.

Thermoresponsiveness of hybrid micelles from poly(ethylene glycol)-block-poly(4-vinylpyridium) cations and SO4(2-) anions in aqueous solutions.

The SO4(2-)-induced micellization of poly(ethylene glycol)-block-poly(4-vinylpyridium) (PEG110-b-P(4-VPH+)35) and the thermoresponsiveness of these hybrid micelles are studied by dynamic and static light scattering. When the concentration of H2SO4 is high enough, PEG110-b-P(4-VPH+)35 forms stable hybrid micelles with an ionic core of P(4-VPH+)35/SO4(2-) and a PEG corona at 25 degrees C. The formation of the hybrid micelles is reversible. A thermodynamic equilibrium exists between the hybrid micelles and PEG110-b-P(4-VPH+)35 unimers. The shifts of the equilibrium are mainly attributed to the variation of the electrostatic energy and entropic energy of the system. Therefore, the temperature can determine the states of the equilibrium, which means that the dissociation or the formation of the hybrid micelles can be triggered by just varying the temperature.