Size-controlled and monodisperse enzyme-encapsulated chitosan microspheres developed by the SPG membrane emulsification technique

The amphiphilic gradient copolymers of 2,2,2-trifluoroethyl methacrylate (TFEMA) and acrylic acid (AA) have been synthesized by using amphiphilic RAFT agent via emulsifier-free emulsion polymerization with a starved feed method of adding TFEMA. Different cosolvents are added into polymerization system to inhibit AA's homopolymerization of in aqueous phase. RAFT polymerization kinetics under different reaction conditions are discussed in detail. (1)H NMR results indicate that the obtained copolymer has a chain structure with AA segments gradually changing to TFEMA segments. The copolymer latexes exhibit good pH stability (pH value from 5 to 14) and Ca(2+) stability. The self-assembly behavior of gradient copolymers in selective solvents are observed and studied by transmission electron microscopy. All the copolymers can form spherical micelles, but the homogeneity and size of micelles are different.     

In situ small-angle X-ray scattering studies during the formation of polymer/silica nanocomposite particles in aqueous solution

This study is focused on the formation of polymer/silica nanocomposite particles prepared by the surfactant-free aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) in the presence of 19 nm glycerol-functionalized aqueous silica nanoparticles using a cationic azo initiator at 60 °C. The TFEMA polymerization kinetics are monitored using ¹H NMR spectroscopy, while postmortem TEM analysis confirms that the final nanocomposite particles possess a well-defined core–shell morphology. Time-resolved small-angle X-ray scattering (SAXS) is used in conjunction with a stirrable reaction cell to monitor the evolution of the nanocomposite particle diameter, mean silica shell thickness, mean number of silica nanoparticles within the shell, silica aggregation efficiency and packing density during the TFEMA polymerization. Nucleation occurs after 10–15 min and the nascent particles quickly become swollen with TFEMA monomer, which leads to a relatively fast rate of polymerization. Additional surface area is created as these initial particles grow and anionic silica nanoparticles adsorb at the particle surface to maintain a relatively high surface coverage and hence ensure colloidal stability. At high TFEMA conversion, a contiguous silica shell is formed and essentially no further adsorption of silica nanoparticles occurs. A population balance model is introduced into the SAXS model to account for the gradual incorporation of the silica nanoparticles within the nanocomposite particles. The final PTFEMA/silica nanocomposite particles are obtained at 96% TFEMA conversion after 140 min, have a volume-average diameter of 216 ± 9 nm and contain approximately 274 silica nanoparticles within their outer shells; a silica aggregation efficiency of 75% can be achieved for such formulations.

SAXS is used to study the formation of polymer/silica nanocomposite particles prepared by surfactant-free aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate in the presence of silica nanoparticles using a azo initiator at 60 °C.     

Hierarchical dual-sized film surface morphologies self-generated from fluorinated binary latex blends boost hydrophobicity and lipophobicity

Latex films with controlled dual-level nanorough surfaces were obtained by casting from binary blends of fluorinated copolymer particles with a nanostructured core-shell morphology, narrow size dispersity and large size ratios. For this purpose, particles with different size, a common unfluorinated acrylic core copolymer of the self-crosslinking trimethoxysilylpropyl methacrylate (TSPMA) and a hard shell copolymer of either 2,2,2-trifluoroethyl methacrylate (TFEMA) or 1H,1H,2H,2H-heptadecafluorodecyl methacrylate (FMA) were synthesized by multistage emulsion polymerization. The FMA-based particles showed patchy morphologies dictated by the type of β-cyclodextrin used as FMA phase carrier in their synthesis. Four series of binary blends of either TFEMA or FMA copolymer particles with large (3-4 diameters) size ratios were cast into latex films with controlled hydrophobicity and lipophobicity. AFM and electron microscopy results indicate that addition of the small particles disrupts the hexagonal compact packed 3D organization of the large particles, resulting in dual-level nanorough surfaces and high water contact angles (up to θ(w)=127° in the as cast films, and θ(w)=135° upon aging or thermal annealing causing surface restructuring and TSPMA sol-gel condensation) with respect to the parent single component films. The proposed approach provides a straightforward route for the fabrication of robust coatings and films with tunable lipophobic and highly hydrophobic surfaces.     

含氟丙烯酸酯与苯乙烯共聚物的RAFT合成及表征

通过可逆加成-断链链转移(RAFT)溶液聚合,以三硫代碳酸酯为RAFT试剂,偶氮二异丁腈(AIBN)为引发剂,1,4-二氧六环为溶剂,制备甲基丙烯酸(2,2,2-三氟)乙酯(TFEMA)和苯乙烯(St)共聚物.详细研究了不同引发剂的用量、RAFT试剂与引发剂摩尔比以及聚合温度等实验条件对聚合反应过程的影响.通过GPC、FTIR测试共聚物的分子量、分子量分布和分子结构,并用静态接触角仪和AFM分别表征聚合物膜的接触角、表面能及膜的表面形貌.     

Designing superhydrophobic surface based on fluoropolymer–silica nanocomposite via RAFT‐mediated polymerization‐induced self‐assembly

Superhydrophobic surfaces (SHS) find versatile applications as coatings due to their very high water‐repellency, self‐cleaning, and anti‐icing properties. This investigation describes the preparation of a SHS from surfactant‐free hybrid fluoropolymer latex. In this case, reversible addition‐fragmentation chain transfer (RAFT) polymerization was adopted to prepare a copolymer of 4‐vinyl pyridine (4VP) and vinyl triethoxysilane (VTES), where the pyridine units were quaternized to make the copolymer soluble in water. The copolymer was further used as a macro‐RAFT agent to polymerize 2,2,2‐trifluoroethyl methacrylate (TFEMA) in a surfactant‐free emulsion via polymerization‐induced self‐assembly (PISA). The macro‐RAFT agent contained a small amount of VTES as co‐monomer which was utilized to graft silica nanoparticles (SNPs) onto the P(TFEMA) spheres. The film prepared using the nanocomposite latex exhibited a nano‐structured surface as observed by SEM and AFM analyses. Surface modification of the film with fluorinated trichlorosilane produced an SHS with a water contact angle (WCA) of 151.5°. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 266–275     

Copolymer of trifluoroethylmethacrylate–N-p-methoxyphenyl citraconimide as high TgE-beam resist

Copolymers of 2,2,2-trifluoroethyl methacrylate (TFEMA) and N-p-methoxyphenyl citraconimide (MCM) have been synthesized. The T_g varies with composition reaching 150°C with 34% MCM. The copolymer has good radiation sensitivity according to both G values for chain scission and E-beam measurements. Though they have lower contrast than PMMA, they have much higher resistance to plasma etching. The resistance increases markedly with MCM content to values comparable to that for polyimides. Therefore, TFEMA–MCM copolymers of high MCM content can be useful as high temperature plasma etchable positive E-beam resists.     

Properties of polyurethane-polystyrene graft copolymer membranes used for separating water-ethanol mixtures

Polyurethane prepolymers (PU) based on hydrophilic poly(ethylene glycol) (PEG), hydroxypropyl acrylic acid (HPA), 2,4-toluene diisocyanate (TDI), and butanediol (BDO) were prepared by one-step polymerization with butanediol as the chain extender. Polyurethane-polystyrene graft copolymers (PU-g-PS) were synthesized by free radical copolymerization of PU with styrene (ST), 2,2′-azobisisobutyronitrile (AIBN) was used as initiator and toluene as solvent. Experimental results showed that the crosslinked membranes of PU-PS graft copolymers could be used for separating ethanol-water mixtures. The highest value of the separation factor (α) of the crosslinked separation membranes can reach 17.3. Scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to characterize the properties of PU-PS crosslinked membranes.     

聚氨酯脲-丙烯酸酯水分散液的粒径及形态研究

研究了羧基含量、异氰酸酯指数（［ － ＮＣＯ］／［ － ＯＨ］） 、聚氨酯脲与聚丙烯酸酯组成比（ＰＵＵ／ＰＡ） 以及一系列制备工艺因素对聚氨酯脲—丙烯酸酯（ＰＵＡ） 水分散液粒子尺寸及形态的影响。结果表明：羧基含量和ＰＵＵ／ＰＡ 组成比增大或异氰酸酯指数减小都会导致分散液粒径减小;ＰＵＡ 中ＰＡ 含量越大,ＰＵＡ 水分散液粒子形态越不规整;工艺因素如搅拌强度、升温速率等对ＰＵＡ 水分散液粒子尺寸及形态的影响不符合传统乳液聚合的规律。     

Synthesis of sterically stabilized polystyrene latex particles using cationic block copolymers and macromonomers and their application as stimulus-responsive particulate emulsifiers for oil-in-water emulsions

2-(Dimethylamino)ethyl methacrylate (DMA) was block copolymerized with methyl methacrylate (MMA) using group transfer polymerization to give four AB diblock, ABA triblock, and BAB triblock copolymers of low polydispersity (Mw/Mn < 1.20). In addition, a near-monodisperse styrene-functionalized DMA-based macromonomer was synthesized via oxyanionic polymerization using a potassium 4-vinylbenzyl alcoholate initiator. These five well-defined, tertiary amine methacrylate-based copolymers were evaluated as steric stabilizers for the synthesis of polystyrene latexes via emulsion and dispersion polymerization. The most efficient steric stabilizers proved to be the DMA-MMA diblock copolymer and the DMA-based macromonomer. The polystyrene latexes were characterized in terms of their particle size and morphology, stabilizer content, surface charge, and surface activity using dynamic light scattering, scanning electron microscopy, 1H NMR spectroscopy, aqueous electrophoresis measurements, and surface tensiometry, respectively. The pH-dependent surface activity exhibited by selected latexes suggests potential applications as stimulus-responsive particulate emulsifiers for oil-in-water emulsions.     

硅氧烷改性水性聚氨酯的制备及性能

A series of novel aqueous emulsion of siloxane modified polyurethane (PU(PE-PSI)) were synthesized based on poly(propylene glycol) (PPG), polyether-grafted polysiloxane (PE PSI), 2,4-tolylene diisocyanate (TDI), dimethylol propionic acid (DMPA) and 1,4 butanediol (BDO) through a direct water emulsification of triethylamine (TEA). The aqueous emulsion was transparent and had a good stability. Fourier transform infrared spectroscopy (FTIR) was used to identify the structure of PU (PE PSI), indicating that the polysiloxane segment had been incorporated with polyurethane chain. Investigation of Electron Spectroscopy for Chemical Analysis (ESCA) and the water contact angle demonstrated that the siloxane migrated to the surface of film. The results also showed that PU(PE-PSI) was still a very good elastomer. With increasing the content of PE PSI, the resistance to water improved and tensile strength increased, while the ultimate elongation decreased slightly for the PU(PE-PSI) film.     

Semibatch emulsion polymerization of methyl methacrylate using different polyurethane particles

Aqueous acrylic‐polyurethane (AC–PU) hybrid emulsions were prepared by semibatch emulsion polymerization of methyl methacrylate (MMA) in the presence of four polyurethane (PU) dispersions. The PU dispersions were synthesized with isophorone diisocyanate (IPDI), 1000 and 2000 molecular weight (MW) poly(neopentyl) adipate, 1000 MW polytetramethyleneetherglycol, butanediol (BD), and dimethylol propionic acid (DMPA). MMA was added in the monomer emulsion feed. We studied the effect of the use of different PU seed particles on the rate of polymerization, the particle size and distribution, the number of particles, and the average number of radicals per particle. The PU rigidity was controlled by varying the polyol chemical structure, the polyol MW (M_n), and by adding BD. The monomer feed rate was varied to study its influence on the process. It was observed that the PU particles that had been prepared with a higher MW polyol swelled better with MMA before the monomer‐starved conditions occurred. There seemed to be no significant discrepancies between the series with different PU seeds in the monomer‐starved conditions. The overall conversion depended on the monomer addition rate, and the polymerization rate acquired a constant value that was comparable to the value of the monomer addition rate. The instantaneous conversion increased slightly. The average particle size increased, and the total particle number in the reactor was constant and similar to the number of PU particles in the initial charge. The average number of radicals per particle increased. The differences between the system with a constant particle number and average number of radicals per particle and the system with a fixed radical concentration are discussed. The semibatch emulsion polymerization of MMA in the presence of PU particles studied was better compared to the system with a fixed radical concentration. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 844–858, 2005     

Polyurethane Ionomers from Cycloaliphatic Diisocyanate and Polytetramethylene Glycol

Abstract

Segmented polyurethane (PU) ionomers were prepared from cycloaliphatic diisocyanate [methylene bis(4-cyclohexyl isocyanate) (H₁₂MDI) and isophoron diisocyanate (IPDI)] and polytetramethylene glycol (PTMG) by using an anionic-type chain extender, viz., dimethylol propionic acid (DMPA). The effect of ionic content and butanediol (BD) on the state of dispersion and physical properties of emulsion-cast film was determined using Autosizer, transmission electron microscopy (TEM), Instron, and Rheovibron. With increased incorporations of DMPA in PU, particle size of emulsion decreased asymptotically, tensile modulus and strength increased, and the glass transition temperature (T _g) moved toward the higher temperature. On the other hand, with increased incorporation of BD in PU, particle size of emulsion, tensile modulus, and strength of the emulsion cast film increased, and the major transition of soft segment moved toward higher temperature. With regard to the structural effect of the isocyanate, H₁₂MDI gave finer dispersion and better mechanical properties over IPDI.     

SiO2@P（MMA/BA/3FMA）复合纳米粒子的制备及膜性能

通过溶胶-凝胶法与半连续种子乳液聚合法相结合,以正硅酸乙酯(TEOS)制备的纳米SiO2为核,以甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)和甲基丙烯酸三氟乙酯(3FMA)的共聚物P(MMA/BA/3FMA)为壳,合成了SiO2@P(MMA/BA/3FMA)核-壳结构纳米复合粒子.为防止纳米SiO2的团聚,提高其与共聚物的结合力,用乙烯基三甲氧基硅烷(VTMS)对纳米SiO2进行改性.通过红外光谱、透射电子显微镜、动态激光散射粒度仪、静态接触角测试仪、X射线光电子能谱分析和热重分析等表征了乳液结构及膜性能.结果表明,获得的复合纳米粒子呈现粒径分布为40～50 nm的核-壳结构球型颗粒.由于含氟官能团的迁移使得氟元素在膜-空气界面富集,有效降低了膜的表面自由能.当3FMA质量分数达到25%时,膜表面自由能达到最低值(23.13 mN/m).随着3FMA含量的增加,共聚物初始热分解温度由350℃提高到390℃.     

Synthesis of nearly micron-sized particles by soap-free emulsion polymerization of methacrylic monomer using an oil-soluble initiator

Methacrylic monomer was used in soap-free emulsion polymerization in order to obtain a stable dispersion containing particles of the polymerized monomer. 2,2′-Azobis(2-methylpropionitrile) (AIBN) or 1,1′-azobis(1-acetoxy-1-phenylethane) (OT_AZO-15) were used as the radical initiator. Although particles with a size of about 1.0 μm were obtained when using methyl methacrylate as the monomer and AIBN as the initiator, the particles did not exhibit good dispersion stability. When OT_AZO-15, which has phenyl rings, was used as the initiator, the monomer phase solidified instead of forming particles in the aqueous phase. Benzyl methacrylate (BMA) monomer, which contains a phenyl ring, was polymerized using AIBN. Negatively charged particles with a size of 0.90 μm were formed. These particles exhibited good dispersion stability probably because of the pi electrons of the phenyl ring in the BMA monomer. The method in this study allows the synthesis of nearly micron-sized particles without surfactant, organic solvent, and electrolyte.     

Structural, thermal and morphological properties of aqueous hybrid emulsion of silylated poly (urethane)/organic modified montmorillonite nanocomposites based on a new silicone and imide ring containing vinylic macromonomer

A new silicone and imide ring containing vinylic macromonomer, N-trimethylsiloxyethyltrimellitilimidomethacrylate (TMSETMIM), has been synthesized for the formulation of waterborne polyurethane (PU). A vinyl group containing silicone, the (3-methacryloyloxypropyl) trimethoxysilane (MPTMS) was used for comparison of the effects of silicone type with TMSETMIM on the PU. Then, a series of new siliconized PU hybrid nanocomposites, were successfully synthesized by the emulsion polymerization in the presence of organic modified montmorillonite (OMMT) and an aqueous PU dispersion using ammonium peroxodisulfate (APS) as an initiator. The PU dispersion was synthesized by a polyaddition reaction of hexamethylene diisocyanate (HMDI), on polypropylene glycol (PPG-1000) and dimethylol propionic acid (DMPA) as a chain extender. The obtained NCO chain ends reacted with water (which acts as a further chain extender producing some urea bonds). The structural elucidation of monomer was carried out by FTIR, ¹H-NMR, and ¹³C-NMR spectroscopic techniques. The copolymers were also characterized by using FTIR. Thermal properties of the copolymers were studied by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The morphologies of the copolymers were characterized with scanning electron microscopy (SEM) and transition electron microscopy (TEM) and then the effects of silicone concentrations on the water absorption ratio was examined. The formed film from the hybrid emulsion containing TMSETMIM could provide obviously higher water-resistance property in comparison with MPTMS. Also, the heat stability increases while the T _g decreased.     

Synthesis of Amphiphilic ABCBA-Type Pentablock Copolymer from Consecutive ATRPs and Self-Assembly in Aqueous Solution

Summary: A novel amphiphilic ABCBA-type pentablock copolymer with properties that are sensitive to temperature and pH, poly(2-dimethylaminoethyl methacrylate)-block-poly(2,2,2-trifluoroethyl methacrylate)-block-poly(ε-caprolactone)-block-poly(2,2,2- trifluoroethyl methacrylate)-block-poly(2-dimethylaminoethyl methacrylate) (PDMAEMA- b-PTFEMA-b-PCL-b-PTFEMA-b-PDMAEMA), was synthesized via consecutive atom transfer radical polymerizations (ATRPs). The copolymers obtained were characterized by gel permeation chromatography (GPC) and ¹H nuclear magnetic resonance (NMR) spectroscopy, respectively. The aggregation behaviors of the pentablock copolymers in aqueous solution with different pH (pH = 4.0, 7.0 and 8.5) were studied. Transmission electron microscopic images revealed that spherical micelles from self-assembly of the pentablock copolymer were prevalent in all cases. The mean diameters of these micelles increased from 34, 46, to 119 nm when the pH of the aqueous solution decreased from 8.5, 7.0, to 4.0, respectively.     

Preparation of polyurethane dispersions by miniemulsion polymerization

With a two‐step miniemulsion polymerization, hydrophobic polyurethane (PU) dispersions were prepared with a cosurfactant, the costabilizer hexadecane (HD) in the oil phase, and sodium dodecyl sulfate (SDS) in the water phase. The first step involved the formation of NCO‐terminated prepolymers between isophorone diisocyanate and poly(propylene glycol) oligomer in toluene. Next, PU dispersions were produced by a miniemulsion method in which an oil phase containing NCO‐terminated prepolymers, HD, the chain extender 1,4‐butanediol (BD), the crosslinking agent trimethylol propane (TMP), and the catalyst dibutyltin dilaurate was dispersed in the water phase containing SDS. The influence of experimental parameters, such as the ultrasonication time, concentrations of SDS and HD, and TMP/BD and NCO/OH equivalent ratios, on the sizes of the miniemulsion droplets and polymer particles, as well as the molecular weights and thermal properties of the PU polymer, was examined. The chemical structure of the produced PU polymer was identified with a Fourier transform infrared spectrometer. The molecular weight distribution and average particle size were measured through gel permeation chromatography and dynamic light scattering, respectively. The thermal stability of the PU polymer was characterized with thermogravimetric analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4870–4881, 2005     

Tacticity control in the radical polymerization of 2,2,2-trifluoroethyl methacrylate with fluoroalcohol

The free-radical polymerization of 2,2,2-trifluoroethyl methacrylate (TEMA) was carried out in fluoroalcohols to achieve stereoregulation. The polymerization reactivity at low temperature and syndiotactic specificity were enhanced by the use of fluoroalcohol as a solvent. The polymer having triad syndiotacticity (rr) of 70% was obtained in perfluoro-t-butyl alcohol. It was noted that the stereochemistry was nearly independent of reaction temperature. The stereoeffect of fluoroalcohols seemed to be due to the hydrogen-bonding interaction between the alcohol and the monomer or growing species. The hydrogen-bonding formation was determined by FTIR. The copolymerization of TEMA with methyl methacrylate (MMA) in hexafluoroisopropanol afforded a copolymer with syndiotactic specificity. By this method, a cladding material for an optical fiber based on poly(methyl methacrylate) (PMMA) with high mechanical strength and low refractive index could be obtained.     

Low-fluorinated homopolymer from heterogeneous ATRP of 2,2,2-trifluoroethyl methacrylate mediated by copper complex with nitrogen-based ligand

We report the preparation of low-fluorinated homopolymer via heterogeneous atom transfer radical polymerization (ATRP) of 2,2,2-trifluoroethyl methacrylate (TFEMA) using 2,2′-bipyridine (bpy), N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA), and tris(2-(dimethylamino)ethyl)amine (Me₆TREN) as representatives for di-, tri-, and tetradentate amine ligands, respectively. The ATRP was better controlled, yielding polymers with controlled molecular weights and low polydispersities (M_w/M_n ca. 1.11) when bpy was used as a ligand than when PMDETA was used. This was further supported by the results of our kinetic and chain extension studies. However, the ATRP of TFEMA had lower monomer conversions and gel formation when Me₆TREN was used as the ligand. Further reported are the thermal-properties, as well as the surface properties of the films from the resulting polymers with different molecular weights.     

Facile fabrication of monodisperse polymer hollow spheres

This article reports the facile synthesis of monodisperse polymer hollow spheres by seeded emulsion polymerization without additional treatment. In this method, P(St-MMA-MAA) copolymer latex particles were first prepared by emulsifier-free emulsion polymerization and then used as seeds to carry out emulsion polymerization of methyl methacrylate (MMA), divinyl benzene (DVB), and 2-hydroxyethyl methacrylate (HEMA) with potassium persulfate (KPS) as initiator at 80 degrees C. The void of hollow spheres was readily adjusted by changing the monomer/seed weight ratio, and it could be enlarged while the diameters of hollow spheres changed little after etching by dimethyl formamide (DMF). The effects of synthetic parameters including the monomer composition and the properties of seeds on the morphology of hollow spheres were investigated in detail. On the basis of the experimental results, it seemed reasonable to conclude that the formation of hollow spheres was due to the "dissolution" of seeds in monomers and phase separation between the constituent polymers. As a thermodynamic factor, sodium dodecyl sulfate (SDS) would allow the preparation of solid particles depending on its level.