Synthesis, characterization and evaluation of amphiphilic star copolymeric emulsifiers based on methoxy hexa(ethylene glycol) methacrylate and benzyl methacrylate

Amphiphilic star copolymers were synthesized by sequential monomer and cross-linker additions using group transfer polymerization (GTP). Benzyl methacrylate (BzMA) and methoxy hexa(ethylene glycol) methacrylate (HEGMA) served as the hydrophobic and hydrophilic monomers, respectively, whereas the also hydrophobic ethylene glycol dimethacrylate (EGDMA) was used as the cross-linker. In total, twelve star copolymers were prepared, covering three different overall hydrophobic compositions, 39, 53 and 70% w/w, and four different architectures, AB star-block, BA star-block, heteroarm star and random star. The theoretical molecular weight of each arm was kept constant at 5000 g mol⁻¹. The molecular weights and molecular weight distributions of the linear precursors and of all the star copolymers were characterized by gel permeation chromatography (GPC) in tetrahydrofuran (THF), while their compositions were confirmed by proton nuclear magnetic resonance (¹H NMR) spectroscopy. Moreover, all the star copolymers were characterized by static light scattering (SLS) in THF to determine the absolute weight-average molecular weight, M_w, and the weight-average number of arms. After polymer characterization, xylene-water and diazinon (pesticide)-water emulsions were prepared using these star copolymers as stabilizers at 1% w/w copolymer concentration and at different overall organic phase/water ratios. The most important factor in determining the emulsion type was the star copolymer composition in hydrophobic units. The four most hydrophilic star copolymers (39% w/w hydrophobic composition) always formed o/w emulsions, while the four most hydrophobic star copolymers (70% w/w hydrophobic composition) always formed w/o emulsions. The type of the emulsion in the case of the star copolymers with the more balanced composition, 53% w/w hydrophobic units, also depended on the emulsion content in the organic solvent, similar to particulate-stabilized emulsions. Considering that the best o/w emulsifier is that star copolymer which can emulsify the largest quantity of organic phase in water resulting in low viscosity, o/w emulsions without excess oil or water phase, it appeared that the most hydrophilic random copolymer star is the optimal emulsifier. Moreover, this star copolymer presented the smallest droplet size in its emulsions. It is also noteworthy that the resulting emulsions almost never had high viscosity, a feature attributable to the compact nature of star polymers.     

Synthesis, characterization and evaluation of amphiphilic diblock copolymer emulsifiers based on methoxy hexa(ethylene glycol) methacrylate and benzyl methacrylate

Linear, amphiphilic diblock copolymers based on the nonionic, hydrophilic monomer methoxy hexa(ethylene glycol) methacrylate (HEGMA) and the hydrophobic monomer benzyl methacrylate (BzMA) of different molecular weights and compositions were synthesized by group transfer polymerization. The molecular weights and comonomer compositions of these copolymers were characterized by gel permeation chromatography and proton nuclear magnetic resonance (¹H NMR) spectroscopy, respectively. Dynamic light scattering on aqueous solutions of the diblock copolymers indicated that all the copolymers formed aggregates whose size increased with the % w/w BzMA composition and with the overall molecular weight of the linear chains. Turbidimetry on 1% w/w aqueous copolymer solutions was used to determine the cloud points, which were found to increase with the composition in hydrophilic units and the linear chain molecular weight. After polymer characterization, xylene/water and diazinon (pesticide)/water emulsions were prepared using the above polymers as stabilizers at 1% w/w polymer concentration and at different overall organic phase/water ratios. At an organic phase/water mass ratio of 4/1, the lower molecular weight (2500 and 5000 g mol⁻¹) diblock copolymers provided stable single-phase o/w emulsions, matching the behavior of commercially available hydrophilic Pluronics.     

疏水改性温敏水凝胶的合成及应用研究进展

N-异丙基丙烯酰胺（NIPAM）类水凝胶是典型的温敏水凝胶,通常含有亲水性酰胺基和疏水性异丙基,具有随温度变化而发生可逆溶胀/收缩的特殊性质,作为一种新型的智能材料得到广泛的应用。本文主要论述了NIPAM类疏水改性温敏水凝胶的合成,在骨架中引入疏水单体可以改善其疏水特性,同时提高其温度敏感性,使其在药物释放、物质分离及生物医用材料等领域具有独特的应用价值。目前对疏水改性温敏水凝胶的理论研究尚浅,仍需拓展其在实际方面的应用,今后可考虑改善疏水单体的官能团结构提高疏水性能,合成更具温度响应性和环境友好性的智能温敏水凝胶,拓展其在催化、水处理、生物化工等领域的广泛应用。     

Complexation of macroporous amphoteric cryogels based on N,N‐dimethylaminoethyl methacrylate and methacrylic acid with dyes,surfactant, and protein

Macroporous amphoteric cryogels based on N,N‐dimethylaminoethylmethacrylate and methacrylic acid p(DMAEM‐co‐MAA) crosslinked by N,N′‐methylenebisacrylamide (MBAA) were synthesized by radical copolymerization of monomer mixtures in cryoconditions. The structure and morphology of cryogels were evaluated by FTIR and SEM. Cryogels exhibited interconnected porous structure with pore size ranging from 40 to 80 µm, which depended on their crosslinking degree. The value of the isoelectric point (IEP) of equimolar amphoteric cryogel determined from the water flux was equal to 4.4, while the IEP of cryogel with the excess of DMAEM units was equal to 7.1. The mechanical strength of equimolar amphoteric cryogels increases with increasing amount of crosslinking agent. The complexation ability of amphoteric cryogels with respect to surfactant, dyes, and protein was demonstrated. The adsorption isotherms with respect to anionic surfactant—sodium dodecylbenzene sulfonate (SDBS) and protein—lysozyme correspond to Langmuir equation, while adsorption isotherms of anionic and cationic dyes—methylene blue (MB) and methyl orange (MO) are well described by Freundlich equation. It was found that the binding ability of p(DMAEM‐co‐MAA) with respect to various low‐ and high‐molecular weight compounds changes in the following order: SDBS > lysozyme ? MO > MB. The preferential adsorption of MB from the mixture of protein and MB was shown. The quantitative release of protein, surfactant and dye molecules from the matrix of cryogels takes place at the IEP of cryogel. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43784.     

Ultra-thin films of cationic amphiphilic poly(2-(dimethylamino)ethyl methacrylate) based block copolymers as surface wettability modifiers

Ultra-thin films of cationic amphiphilic block and statistical copolymers were applied on silica surfaces from aqueous solutions through electrostatic interactions, and the resulting modification in the wettability of the surfaces was studied. A copolymer series from 2-(dimethylamino)ethyl methacrylate with methyl methacrylate and butyl methacrylate was polymerized by ATRP. Subsequently, the conformation of the polymers in aqueous solutions was studied by surface tension measurements, dynamic light scattering, ¹H NMR and cryogenic transmission electron microscopy. Unimeric conformation, equilibrium micelles or frozen micellar structures were observed, depending on polymer composition and the ionic strength of the solution. The polymers were applied on silica from aqueous solutions by either spin coating or adsorption. The formed ultra-thin film surfaces were studied by AFM and water contact angle measurements. The spin-coated surfaces were highly hydrophilic with rapidly dropping contact angles, whereas the surfaces prepared by adsorption had stable water contact angles between 30-60°, depending on polymer. The difference between the spin-coated and adsorbed surfaces is explained by the formation of a monolayer in the adsorbed surfaces.     

两亲嵌段共聚物的合成及其自组装研究进展

作者介绍了两亲嵌段共聚物的活性阴离子聚合、基团转移聚合、开环歧化聚合、活性阳离子聚合、活性／可控自由基聚合、缩聚法、嵌段共聚物化学改性法等合成方法,并对其自组装形成聚合物纳米胶束的制备方法、形成机理以及在药物控制释放领域的应用进行了综述,并对其未来发展趋势进行了展望。     

Synthesis and characterization of amphiphilic conetworks based on multiblock copolymers

Model amphiphilic conetworks based on cross-linked block copolymers of the hydrophilic ionizable 2-(dimethylamino)ethyl methacrylate (DMAEMA, 25 nominal units per block) and the hydrophobic n-butyl methacrylate (BuMA, 5 nominal units per block) bearing three, five, seven and nine blocks were synthesized using group transfer polymerization. 1,4-Bis(methoxytrimethylsiloxymethylene)cyclohexane and ethylene glycol dimethacrylate were used as the bifunctional initiator and the cross-linker, respectively. Network synthesis was performed by sequential monomer/cross-linker additions to the reaction flask, which was pre-loaded with tetrabutylammonium bibenzoate (polymerization catalyst), tetrahydrofuran (THF, solvent), and initiator. All linear conetwork precursors were characterized using gel permeation chromatography and proton nuclear magnetic resonance spectroscopy and found to have molecular weights (MWs) and compositions reasonably close to the theoretically expected values. All polymer conetworks were characterized in terms of their degree of swelling (DS) in THF, in neutral water, and in aqueous media as a function of the solution pH. It was found that the DSs were highest in acidic pH due to the repulsive forces and the osmotic pressure developed by the ionization of the DMAEMA units. Intermediate values of the DSs were observed in THF, whereas the lowest DSs were measured in neutral water. In THF, the DSs increased with the MWs of the (final) linear (co)polymer precursors, while in acidic water the DSs increased with the DMAEMA content in the (co)networks.     

pH- and temperature-responsive amphiphilic diblock copolymers of 4-vinylpyridine and oligoethyleneglycol methacrylate synthesized by RAFT polymerization

Diblock copolymers of 4-vinylpyridine (4VP) and oligoethyleneglycol methyl ether methacrylate (OEGMA) were synthesized for the first time using RAFT polymerization technique as potential drug delivery systems. Effects of the number of ethylene glycol units in OEGMA, chain length of hydrophobic P4VP block, pH, concentration and temperature on the solution behavior of the copolymers were investigated comprehensively. Copolymer chains formed micelles at pH values higher than 5 whereas unimeric polymers were observed to exist below pH 5, owing to the repulsion between positively charged P4VP blocks. The size of the micelles was dependent on the relative length of blocks, P4VP and POEGMA. Thermo-responsive properties of copolymers were investigated depending on the pH and length of P4VP block. The increase in the length of P4VP block decreased the LCST substantially at pH 7. At pH 3, LCST of copolymers shifted to higher temperatures due to the increased interaction of copolymers with water through positively charged P4VP block.     

Fabrication of amphiphilic copolymeric gels with enhanced activity of immobilized enzymes in organic media

Novel amphiphilic copolymeric gels were developed to immobilize lipase. NIPA‐co‐PEGMEA gels were prepared by copolymerizing N‐isopropylacrylamide (NIPA) as a thermosensitive and amphiphilic component and poly(ethylene glycol) methyl ether acrylate (PEGMEA) as a hydrophilic component in aqueous media. The gels can absorb organic solvents at temperatures higher than the lower critical solution temperature owing to the thermosensitive and amphiphilic properties of poly(NIPA). The lipase immobilized within the NIPA‐co‐PEGMEA gel, which had a NIPA : PEGMEA composition of 950 : 50 mol/m³, successfully catalyzed the esterification of oleic acid and ethanol without loss of activity during repeated use within 20–40°C. The activity of the immobilized lipase was considerably higher than that of free lipase. The NIPA‐co‐PEGMEA gels provide a structure that allows the immobilized lipase to work actively in an aqueous environment and with the dispersed state of the lipase in the gels. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41905.     

Synthesis and characterization of novel hydrophobically modified polybetaines as pour point depressants

A novel hydrophobic monomer was synthesized from the acetoacetic ester and dodecylamine by condensation reaction in mild conditions. The modification by the dodecyl groups monomer was involved in the Michael addition reaction with acrylic (or methacrylic) acid followed by radical polymerization. Both linear and crosslinked novel betaine‐type polyampholytes bearing hydrophobic “tail” and hydrophilic “head” were obtained. The linear polymer was characterized by viscometry, FTIR, and Raman spectroscopy. Swelling–shrinking behavior of linear and crosslinked samples was studied in water–DMF and water–DMSO mixtures. The applicability of hydrophobically modified polybetaines as pour point depressants (fluidity improvers) was also demonstrated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1042–1048, 2004     

Synthesis and pH-dependent micellization of 2-(diisopropylamino)ethyl methacrylate based amphiphilic diblock copolymers via RAFT polymerization

The polymerization of 2-(diisopropylamino)ethyl methacrylate (DPA) by RAFT mechanism in the presence of 4-cyanopentanoic acid dithiobenzoate in 1,4-dioxane was studied. The DPA homopolymer was employed as a macro chain transfer agent to synthesize pH-sensitive amphiphilic block copolymers using poly(ethylene glycol) methyl ether methacrylate (PEGMA) as the hydrophilic block. ¹H NMR and GPC measurements confirmed the successful synthesis of these copolymers. Potentiometric titrations and fluorescence experiments proved that the copolymers underwent a sharp transition from unimers to micelles at a pH of ∼6.7 in phosphate buffered saline solutions. It was found that the hydrophilic/hydrophobic balance of these block copolymers had no apparent effect on their pH-induced micellization behaviors. The DLS investigation revealed that the micelles have a mean hydrodynamic diameter below 60 nm with a narrow size distribution.     

Swelling behavior of physical and chemical DNA hydrogels

DNA hydrogels were prepared from aqueous solutions of double‐stranded DNA (about 2000 base pairs long) by physical and chemical means. Physical gels were obtained via denaturation–renaturation cycle of 5% aqueous DNA solutions between 25 and 90°C. Although physical DNA gels exhibit a high modulus of elasticity, the crosslinks holding the DNA network together are destroyed during the expansion of gels in water or in dilute salt solutions. It was shown that these gels can be used for the controlled release of DNA in aqueous media. Chemical DNA gels formed using ethylene glycol diglycidyl ether crosslinker are stable in water with a wide range of swelling ratios that could be adjusted by the amount of DNA at the gel preparation. Swelling behavior of chemical DNA gels in acetone/water mixtures as well as in aqueous salt solutions is very similar to that of synthetic polyelectrolyte hydrogels. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Characteristics of cellulase modified with amphiphilic copolymer in organic solvent

Characteristics of modified cellulases in organic solvents were studied. Cellulases modified with amphiphilic copolymer of polyoxyalkylene (POA)-derivative and maleic acid anhydride (MAA). Amino groups of the cellulase molecule were easily coupled with the MAA functional group of the copolymer. At the maximum degree of modification (DM) of 55%, the activity of modified cellulase retained more than 80% of the unmodified native cellulase activity. The modified cellulase using AKM-1511 with DM greater than 40% was found to be more than 90% soluble in aqueous solution of acetone and ethanol, leaving the native cellulase and impurities in the fermentation broth with the residue. Modified cellulase showed excellent stability against water-insoluble solvent. Moreover, cellulase modified with hydrophobic copolymer, which consists of ethylene oxide (EO) and propylene oxide (PO), could be dissolved in these solvents.     

基于偶氮苯的超分子凝胶材料的研究进展

基于偶氮苯的光响应型凝胶对光刺激可以保证连续性和精确性感知, 并在刺激过程中有显著的响应行为性, 是目前研究最多的光响应材料之一。本文将含偶氮苯的凝胶体系分成超分子有机凝胶、超分子水凝胶、超分子凝胶体系和有机无机杂化型体系, 较系统地综述了近三年来基于偶氮苯的光响应型超分子凝胶的结构特点和研究进展。重点阐述了凝胶因子的分子大小和形态, 涵盖了小分子、树枝状大分子、嵌段共聚物、超支化分子等;分析了发挥自组装驱动力的超分子之间的作用, 涵盖了氢键、静电相互作用、π-π作用、疏水效应等;总结了自组装聚集形态的构造, 涵盖了胶束、囊泡、纤维束、纳米棒等;最后展望了各类凝胶体系在光控开关、药物释放、生物材料等领域的应用前景。     

Swelling behaviour of a new kind of polyampholyte hydrogel composed of dimethylaminoethyl methacrylate and acrylic acid

Poly[(dimethylaminoethyl methacrylate)‐co‐(acrylic acid)] [poly(DMAEMA‐co‐AAc)] hydrogels have been synthesized by UV‐induced copolymerization of dimethylaminoethyl methacrylate (DMAEMA) and acrylic acid monomer. The effects of pH and ionic strength on the swelling behaviour of poly(DMAEMA‐co‐AAc) hydrogels were investigated in detail. It was found that there is minimal equilibrium swelling ratio (ESR) for the hydrogels with the change of pH, and the pH at minimal ESR of the hydrogels was defined by the isoelectric points (IEP), similar to the situation with protein molecules. The IEP of the hydrogels shifted to higher values with increase in the DMAEMA content in the hydrogels. Antipolyelectrolyte behaviour of the hydrogels at a pH near the IEP was observed as well, and the ESR increased with increasing ionic strength. The study of swelling kinetics of the hydrogels showed that the swelling process was Fickian at the IEP and non‐Fickian when the pH deviated from the IEP. Copyright © 2003 Society of Chemical Industry     

Mechanistic study of the formation of amphiphilic core-shell particles by grafting methyl methacrylate from polyethylenimine through emulsion polymerization

The mechanism for the formation of amphiphilic core-shell particles in water is elucidated via a kinetic study of semi-batch polymerization of methyl methacrylate (MMA) grafted from polyethylenimine (PEI) initiated with tert-butyl hydroperoxide in an emulsion polymerization. The monomer conversion, the polymerization kinetics, the particle size, the particle number density, the poly(methyl methacrylate) (PMMA) core diameter, the percentage of unbound PEI, and the grafting efficiency of PMMA were determined at various times during the polymerization. The particle number density and the percentage of unbound PEI were almost independent of the controllable variables. The particle sizes and the core diameters increased with each consecutive batch of monomer addition, while the grafting efficiency of PMMA decreased. These data supported the hypothesis that the PEI-g-PMMA graft copolymers were formed early in the polymerization and later self-assembled to a new phase, micellar microdomains. These microdomains act as loci for subsequent MMA polymerization as the monomer is fed into the reaction, without subsequent formation of new particles. The size of the resulting highly uniform core-shell particles (99-147 nm) can be controlled by choosing the amount of monomer charged. Thus, this polymerization method is viable for a large scale production of core-shell particles with high solids content.     

Formation and structure of poly(methyl methacrylate) gels containing triphenyl vinyl silane

A series of Poly(methyl methacrylate) gels (PMMA) were prepared for making optical lenses by solution free radical crosslinking copolymerization of 2,2,2,‐trifluoroethyl methacrylate (TFEMA), methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDM), and triphenyl vinyl silane (TPVS) comonomer systems. They were then studied in toluene at a total monomer concentration of 5 molL^?1 and 70°C. The conversion of monomer, volume swelling ratio, weight fraction, and gel point were measured as a function of the TPVS concentration, temperature, and chain transfer agents up to the onset of macrogelation. Structural characteristics of the gels were examined by using equilibrium swelling in toluene, gel fraction, and Fourier‐transform infrared (FTIR) analysis. The morphology of the copolymers was also investigated by Scanning electron microscopy (SEM). The dilution of the monomer mixture resulted in an increase in the gel point and swelling degree and a decrease in the percentage of conversion and gel fraction. Finally, TPVS is a compatible vinyl type silicone comonomer for this system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Interpolymer complexes between hydrophobically modified poly(methacrylic acid) and poly(N-vinylpyrrolidone)

The formation and structure of interpolymer complexes between amphiphilic multi-block copolymers—poly(dimethylsiloxane-N-vinylpyrrolidone) and poly(dimethylsiloxane-methacrylic acid)—were studied using potentiometric and conductometric titration, viscometry and fluorescence spectroscopy. The ratio of hydrophobic/hydrophilic groups in the copolymer and the molecular weight of each sequence were varied in order to establish the influence of these parameters on the interactions between the components. The complexation between pairs of block copolymers, of block copolymers and homopolymers as well as between homopolymer pairs was considered. The complexes were formed through the hydrogen bonding. They have a compact structure with a non-stoichiometric composition of pyrrolidone to methacrylic acid groups ratio around 0.6-0.7, with the exception of complexes formed between pairs of homopolymers and of copolymers with the shortest siloxane block. The difference between the new complexes and the ones formed from homopolymers, with equimolar composition, is explained by the spatial non-complementarity of the copolymers having a ‘flower-like’ structure in aqueous solutions.     

Synthesis and micelle behavior of (PNIPAm-PtBA-PNIPAm)m amphiphilic multiblock copolymer

A linear amphiphilic multiblock copolymer (PNIPAm-PtBA-PNIPAm)_m was successfully synthesized by a two-step reversible addition-fragmentation transfer (RAFT) polymerization in the presence of a cyclic trithiocarbonate as RAFT agent. The micelle behavior of (PNIPAm-PtBA-PNIPAm)_m multiblock copolymer in aqueous solution was then investigated by means of normal TEM, cryo-TEM, static and dynamic light scattering. The morphology, size, and size distribution of (PNIPAm-PtBA-PNIPAm)_m micelles were found to be dependent on the initial concentration of multiblock copolymer in THF. Spherical micelles, associated aggregates of spherical micelles, cage-like micelles, layered structures, and vesicular micelles were experimentally observed, which were in good agreement with the prediction of theory and simulations on linear amphiphilic multiblock copolymer in selective solvent. The (PNIPAm-PtBA-PNIPAm)_m micelles also exhibit thermo-sensitive behavior in aqueous solution because of the PNIPAm blocks.     

Synthesis and rheological behavior of hydrophobically modified block copolymers

Hydrophobically modified polymers were synthesized via esterification reactions between a commercial triblock copolymer composed of ethylene oxide (EO) and propylene oxide (PO) segments (EO₂₀PO₇₀EO₂₀) and lauric and oleic acids. Rheological studies of aqueous systems containing the original copolymer and the synthesized products were performed to evaluate the effects of chemical modification, the presence of salt, and temperature on the rheology of the systems due to changes in the micellar structures. It was verified that the systems containing the synthesized products presented shear‐thinning behavior even in the absence of salt. In addition, increasing the temperature and salt concentration enhanced the hydrophobic character of the poly(propylene oxide) segment and reduced the hydration of the poly(ethylene oxide) segment; this favored the adequate packing needed to form long, wormlike micelles and resulted in pronounced shear thinning. The formation of a complex micelle structure probably occurred in the systems above the critical micellar temperature of the original copolymer because under this condition the molecules presented three alternate hydrophobic segments that had to dive into the micelle structure. The formation of long, wormlike micelles was also evidenced by the Maxwellian behavior observed in rheological oscillatory measurements. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010