Preparation,morphology, and thermoresponsive properties of poly(N‐isopropylacrylamide)‐based copolymer microgels

In this research, thermoresponsive copolymer latex particles with an average diameter of about 200–500 nm were prepared via surfactant‐free emulsion polymerization. The thermoresponsive properties of these particles were designed by the addition of hydrophilic monomers [acrylic acid (AA) and sodium acrylate (SA)] to copolymerize with N‐isopropylacrylamide (NIPAAm). The effects of the comonomers and composition on the synthesis mechanism, kinetics, particle size, morphology, and thermoresponsive properties of the copolymer latex were also studied to determine the relationships between the synthesis conditions, the particle morphology, and the thermoresponsive properties. The results showed that the addition of hydrophilic AA or SA affected the mechanism and kinetics of polymerization. The lower critical solution temperature (LCST) of the latex copolymerized with AA rose to a higher temperature. However, because the strong hydrophilic and ionic properties of SA caused a core–shell structure, where NIPAAm was in the inner core and SA was in the outer shell, the LCST of the latex copolymerized with SA was still the same as that of pure poly(N‐isopropylacrylamide) latex. It was concluded that these submicrometer copolymer latex particles with different thermoresponsive properties could be applied in many fields. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 356–370, 2006     

Thermosensitive and control release behavior of poly (N‐isopropylacrylamide‐co‐acrylic acid) latex particles

In this work, poly(N‐isopropylacrylamide‐co‐acrylic acid) (poly(NIPAAm‐AA)) copolymer latex particles (microgels) were synthesized by the method of soapless emulsion polymerization. Poly(NIPAAm‐AA) copolymer microgels have the property of being thermosensitive. The concentration of acrylic acid (AA) and crosslinking agent N,N′‐methylenebisacrylamide were important factors to influence the lower critical solution temperature (LCST) of poly(NIPAAm‐AA) microgels. The effects of AA and crosslinking agent on the swelling behavior of poly(NIPAAm‐AA) microgels were also studied. The poly(NIPAAm‐AA) copolymer microgels were then used as a thermosensitive drug carrier to load caffeine. The effects of concentration of AA and crosslinking agent on the control release of caffeine were investigated. How the AA content and crosslinking agent influenced the morphology and LCST of the microgels was discussed in detail. The relationship of morphology, swelling, and control release behavior of these thermosensitive microgels was established. A new scheme was proposed to interpret the control release of the microgels with different morphological structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5734–5741, 2008     

Synthesis and characteristics of poly(N‐isopropylacrylamide‐co‐methacrylic acid)/Fe3O4/poly(N‐isopropylacrylamide‐co‐methacrylic acid) two‐shell thermosensitive magnetic composite hollow latex particles

In this study, the poly(N‐isopropylacrylamide‐methylacrylate acid)/Fe₃O₄/poly(N‐isopropylacrylamide‐methylacrylate acid) (poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA)) two‐shell magnetic composite hollow latex particles were synthesized by four steps. The poly(methyl methacrylate‐co‐methylacrylate acid) (poly(MMA‐MAA)) copolymer latex particles were synthesized first. Then, the second step was to polymerize NIPAAm, MAA, and crosslinking agent in the presence of poly(MMA‐MAA) latex particles to form the linear poly(MMA‐MAA)/crosslinking poly(NIPAAm‐MAA) core–shell latex particles. Then, the core–shell latex particles were heated in the presence of NH₄OH to dissolve the linear poly(MMA‐MAA) core to form the poly(NIPAAm‐MAA) hollow latex particles. In the third step, the Fe₃O₄ nanoparticles were generated in the presence of poly(NIPAAm‐MAA) hollow polymer latex particles and formed the poly(NIPAAm‐MAA)/Fe₃O₄ magnetic composite hollow latex particles. The fourth step was to synthesize poly(NIPAAm‐MAA) in the presence of poly(NIPAAm‐MAA)/Fe₃O₄ latex particles to form the poly(NIPAAm‐MAA)/Fe₃O₄/poly(NIPAAm‐MAA) two‐shell magnetic composite hollow latex particles. The effect of various variables such as reactant concentration, monomer ratio, and pH value on the morphology and volume‐phase transition temperature of two‐shell magnetic composite hollow latex particles was studied. Moreover, the latex particles were used as carriers to load with caffeine, and the caffeine‐loading characteristics and caffeine release rate of latex particles were also studied. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2880–2891     

Synthesis and characteristics of poly(N‐isopropylacrylamide‐co‐methacrylic acid)/Fe3O4 thermosensitive magnetic composite hollow latex particles

In this study, the poly(NIPAAm–MAA)/Fe₃O₄ hollow latex particles were synthesized by three steps. The first step was to synthesize the poly(methyl methacrylate‐co‐methylacrylate acid) (poly(MMA‐MAA)) copolymer latex particles by the method of soapless emulsion polymerization. Following the first step, the second step was to polymerize N‐isopropylacrylamide (NIPAAm), MAA, and crosslinking agent (N,N'‐methylene‐bisacrylamide (MBA)) in the presence of poly(MMA‐MAA) latex particles to form the linear poly(MMA‐MAA)/crosslinking poly (NIPAAm‐MAA) core‐shell latex particles. After the previous processes, the core‐shell latex particles were heated in the presence of NH₄OH to dissolve the linear poly(MMA‐MAA) core in order to form the poly(NIPAAm‐MAA) hollow latex particles. In the third step, Fe²⁺ and Fe³⁺ ions were introduced to bond with the ? COOH groups of MAA segments in the poly(NIPAAm‐MAA) hollow polymer latex particles. Further by a reaction with NH₄OH and then Fe₃O₄ nanoparticles were generated in situ and the poly(NIPAAm‐MAA)/Fe₃O₄ magnetic composite hollow latex particles were formed. The concentrations of MAA, crosslinking agent (N,N'‐methylene bisacrylamide), and Fe₃O₄ nanoparticles were important factors to influence the morphology of hollow latex particles and lower critical solution temperature of poly(NIPAAm–MAA)/Fe₃O₄ magnetic composite hollow latex particles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characteristics of poly(methacrylic acid‐co‐N‐isopropylacrylamide) thermosensitive composite hollow latex particles and their application as drug carriers

In this work, the poly(methacrylic acid‐co‐N‐isopropylacrylamide) thermosensitive composite hollow latex particles was synthesized by a three‐step reaction. The first step was to synthesize the poly(methyl methacrylate‐co‐methacrylic acid) (poly(MMA‐MAA)) copolymer latex particles by the method of soapless emulsion polymerization. The second step was to polymerize methacrylic acid (MAA), N‐isopropylacrylamide (NIPAAm), and N,N′‐methylenebisacrylamide in the presence of poly(MMA‐MAA) latex particles to form the linear poly(methyl methacrylate‐co‐methacrylic acid)/crosslinking poly(methacrylic acid‐co‐N‐isopropylacrylamide) (poly(MMA‐MAA)/poly(MAA‐NIPAAm)) core–shell latex particles. In the third step, the core–shell latex particles were heated in the presence of ammonia solution to form the crosslinking poly(MAA‐NIPAAm) thermosensitive hollow latex particles. The morphologies of poly(MMA‐MAA)/poly(MAA‐NIPAAm) core–shell latex particles and poly(MAA‐NIPAAm) hollow latex particles were observed. The influences of crosslinking agent and shell composition on the lower critical solution temperature of poly(MMA‐MAA)/poly(MAA‐NIPAAm) core–shell latex particles and poly(MAA‐NIPAAm) hollow latex particles were, respectively, studied. Besides, the poly(MAA‐NIPAAm) thermosensitive hollow latex particles were used as carriers to load with the model drug, caffeine. The effect of various variables on the amount of caffeine loading and the efficiency of caffeine release was investigated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5203–5214     

Synthesis and characteristics of poly(methyl methacrylate‐co‐methacrylic acid)/poly(methacrylic acid‐co‐N‐isopropylacrylamide) thermosensitive semi‐hollow latex particles and their application to drug carriers

In this work, the poly(methyl methacrylate‐co‐methacrylic acid)/poly(methacrylic acid‐co‐N‐isopropylacrylamide) thermosensitive composite semi‐hollow latex particles was synthesized by three processes. The first process was to synthesize the poly(methyl methacrylate‐co‐methacrylic acid) (poly (MMA‐MAA)) copolymer latex particles by the method of soapless emulsion polymerization. The second process was to polymerize methacrylic acid (MAA), N‐isopropylacrylamide (NIPAAm), and crosslinking agent, N,N′‐methylenebisacrylamide, in the presence of poly(MMA‐MAA) latex particles to form the linear poly(methyl methacrylate‐co‐methacrylic acid)/crosslinking poly(methacrylic acid‐co‐N‐isopropylacrylamide) (poly(MMA‐MAA)/poly(MAA‐NIPAAm)) core–shell latex particles with solid structure. In the third process, part of the linear poly(MMA‐MAA) core of core–shell latex particles was dissolved by ammonia to form the poly(MMA‐MAA)/poly(MAA‐NIPAAm) thermosensitive semi‐hollow latex particles. The morphologies of the semi‐hollow latex particles show that there is a hollow zone between the linear poly(MMA‐MAA) core and the crosslinked poly(MAA‐NIPAAm) shell. The crosslinking agent and shell composition significantly influenced the lower critical solution temperature of poly(MMA‐MAA)/poly(MAA‐NIPAAm) semi‐hollow latex particles. Besides, the poly(MMA‐MAA)/poly(MAA‐NIPAAm) thermosensitive semi‐hollow latex particles were used as carriers to load with the model drug, caffeine. The processes of caffeine loaded into the semi‐hollow latex particles appeared four situations, which was different from that of solid latex particles. In addition, the phenomenon of caffeine released from the semi‐hollow latex particles was obviously different from that of solid latex particles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3441–3451     

Surface modification of iron oxide nanoparticles by a phosphate‐based macromonomer and further encapsulation into submicrometer polystyrene particles by miniemulsion polymerization

A new strategy relying on the use of a phosphate‐based macromonomer (PAM200) to modify the surface of iron oxide nanoparticles was developed for the synthesis of submicrometer polystyrene (PS) magnetic particles. First, iron oxide nanoparticles were synthesized using the coprecipitation of ferrous and ferric salts in alkaline medium. Besides the classical oleic acid (OA)/octane‐based ferrofluid, styrene‐based ferrofluids were elaborated with either OA or PAM200 as the stabilizer. In all cases, maghemite (γ‐Fe₂O₃) was clearly identified, with nanoparticles rather spherical in shape but exhibiting broad particle size distribution (PSD). Both OA and PAM200 led to stable maghemite‐based ferrofluids showing superparamagnetic properties. Further use of these ferrofluids in styrene miniemulsion polymerization resulted in inhomogeneous distribution of maghemite among and inside the polymer particles with OA‐based ferrofluids, whereas PAM200/styrene‐based ferrofluids led to magnetic particles with homogeneous distribution of maghemite inside PS particles. Broad PSD and small nonmagnetic particles were however observed. The true mechanisms operating in these systems are still to elucidate, but this study validates PAM200 as an efficient compatibilizing agent between hydrophilic maghemite and hydrophobic PS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 327–340, 2008     

Preparation of polymer hollow microspheres covered by polymer solid particles via two polymerization steps

A novel surface modification method for titania nanoparticles is provided via the surface‐initiated photocatalytic polymerization with the aid of acrylic acid (AA) or sodium styrene sulfonate (NaSS). The properties of modified titania nanoparticles are investigated with aqueous electrophoresis measurements, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Then the modified titania is used as Pickering stabilizer for further polymerization and the morphology of the resulted polymer microspheres is characterized by TEM and field‐emission scanning electron microscopy. It is proven that the addition of AA or NaSS for the surface‐initiated polymerization can obviously affect the structure and morphology of the final polymer composite microspheres. The formation mechanism of several kinds of polymer particles is also proposed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation of novel suspensions of ZnO/living block copolymer latex nanoparticles via pickering emulsion polymerization and their long term stability

In this work, we present the first Pickering emulsion polymerization with a controlled/living character. Pickering emulsion polymerization in the presence of a novel suspension of zinc oxide/poly(sodium 4‐styrenesulfonate) (ZnO/PSS^?) nanocomposite particles was applied to prepare ZnO/living block copolymer latexes. In the emulsion system, 1,1‐diphenylethene (DPE)‐controlled radical polymerization of poly(methyl methacrylate)‐b‐poly(butyl acrylate) (PMMA‐b‐PBA) was proceeded in oil phase. The nanocomposite particles of ZnO/PSS^? with an average diameter of 20 nm and negatively charged zeta potential around ?30 mV were synthesized via hydrothermal method then served as an effective emulsion stabilizer at the oil/water interface. Living polymerization was carried out using DPE‐capped PMMA as the macroinitiator and PMMA‐b‐PBA block copolymer latex was successfully prepared with coverage of ZnO/PSS^? nanoparticles. Narrow size distributions of the droplets as well as latex particles were obtained, and the livingness of block copolymers was comparable to that of emulsions stabilized by conventional surfactants. The controlled/living character in Pickering emulsion polymerization was slightly influenced by the amount of PSS^? immobilized into the ZnO/PSS^? nanoparticles, whereas it was significantly influenced by the weight ratios between ZnO/PSS^? and oil phase. The Pickering latexes showed excellent long term stability against either coalescence or sedimentation over several months. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation of composite polyacrylate latex particles with in situ‐formed methylsilsesquioxane cores

Composite polyacrylate latex particles were prepared through a simple method by dissolving organosilicon monomer methyltrimethoxysilane in a monomer mixture of acrylic monomers methyl methacrylate (MMA), n‐butyl acrylate (n‐BA), and acrylic acid (AA). With the addition of water needed for hydrolysis, methyltrimethoxylsilane hydrolyzed under catalysis by AA and further condensed to form polymeric methylsilsesquioxane (MSQ). The monomer mixture containing in situ‐formed MSQ was then subjected to emulsification and emulsion polymerization. Transmission electron microscopy (TEM) images showed that the obtained latex particles had a core–shell structure. Differences between the X‐ray photoelectron spectroscopy (XPS) results of the contents of silicon atoms on surfaces of films formed at temperatures above and below glass transition temperatures (T_gs) of polyacrylate evidenced that the cores were made up of MSQ and the shells were made up of polyacrylate. The static water contact angle measurements indicated that the incorporation of MSQ can result in composite latex with higher hydrophobicity. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and morphology of Fe3O4/polystyrene/poly(isopropylacrylamide‐co‐methyl acrylate acid) magnetic composite latex – 2,2′‐azobis (2‐methylpropionamidine) dihydrochloride as initiator

In this work, Fe₃O₄/polystyrene/poly(N‐isopropylacryl amide‐co‐methylacrylate acid) (Fe₃O₄/PS/P(NIPAAM‐co‐MAA)) magnetic composite latex was synthesized by the method of two stage emulsion polymerization. In this reaction system, 2,2′‐azobis(2‐methyl propionamidine) dihydrochloride (AIBA) was used as initiator to initiate the first stage reaction and second stage reaction. The Fe₃O₄ particles were prepared by a traditional coprecipitation method. Fe₃O₄ particles were surface treated by either PAA oligomer or lauric acid to form the stable ferrofluid. The first stage for the synthesis of magnetic composite latex was to synthesize PS in the presence of ferrofluid by soapless emulsion polymerization to form the Fe₃O₄/PS composite latex particles. Following the first stage of reaction, the second stage of polymerization was carried out by the method of soapless emulsion polymerization with NIPAAM and MAA as monomers and Fe₃O₄/PS latex as seeds. The magnetic composite particles, Fe₃O₄/PS/P(NIPAAM‐co‐MAA), were thus obtained. The mechanism of the first stage reaction and second stage reaction were investigated. Moreover, the effects of PAA and lauric acid on the reaction kinetics, morphology, and particle size distribution were studied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3912–3921, 2007     

Synthesis and morphology of an iron oxide/polystyrene/poly(isopropylacrylamide‐co‐methacrylic acid) thermosensitive magnetic composite latex with potassium persulfate as the initiator

In this work, an iron oxide (Fe₃O₄)/polystyrene (PS)/poly(N‐isopropylacryl amide‐co‐methacrylic acid) [P(NIPAAM–MAA)] thermosensitive magnetic composite latex was synthesized by the method of two‐stage emulsion polymerization. The Fe₃O₄ particles were prepared by a traditional coprecipitation method and then surface‐treated with either a PAA oligomer or lauric acid to form a stable ferrofluid. The first stage for the synthesis of the thermosensitive magnetic composite latex was to synthesize PS in the presence of a ferrofluid by emulsion polymerization to form Fe₃O₄/PS composite latex particles. Following the first stage of reaction, the second stage of polymerization was carried out with N‐isopropylacryl amide and methacrylic acid as monomers and with Fe₃O₄/PS latex as seeds. The Fe₃O₄/PS/[P(NIPAAM–MAA)] thermosensitive magnetic particles were thus obtained. The effects of the ferrofluids on the reaction kinetics, morphology, and particle size of the latex were discussed. A reaction mechanism was proposed in accordance with the morphology observation of the latex particles. The thermosensitive property of the thermosensitive magnetic composite latex was also studied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3062–3072, 2007     

Thermosensitive and control release behavior of poly(N-isopropylacrylamide-co-acrylic acid)/nano-Fe3O4 magnetic composite latex particle that is synthesized by a novel method

In this study, a novel method was used to synthesize the poly(N-isopropylacrylamide-co-acrylic acid)/Fe₃O₄ (poly(NIPAAm-AA)/Fe₃O₄) magnetic composite latex. The crosslinked poly(NIPAAm-AA) polymer latex particles were first synthesized by the method of soapless emulsion polymerization, then Fe²⁺ and Fe³⁺ ions were introduced to bond with the -COOH groups of AA segments in poly(NIPAAm-AA) polymer latex particles. Further by a reaction with NH₄OH, Fe₃O₄ nanoparticles were generated in situ. The concentrations of acrylic acid (AA), crosslinking agent (N,N′-methylene bisacrylamide (MBA)), and Fe₃O₄ nanoparticles were important factors to influence the morphology and lower critical solution temperature (LCST) of poly(NIPAAm-AA)/Fe₃O₄ magnetic composite latex particles. The poly(NIPAAm-AA)/Fe₃O₄ latex particles were used as a thermosensitive drug carrier to load caffeine. The control release of caffeine was studies. Morphology-based schematic models were proposed to explain the control release behavior of the composite particles with different compositions. Moreover, the protein (albumin, acetylated from bovine serum (BSA)) was bound on the surface of poly(NIPAAm-AA)/Fe₃O₄ composite latex particles. The effects of AA, crosslinking agent and Fe₃O₄ contents on the amount of BSA binding were investigated at different temperatures and pH values. The composition-morphology-BSA conjugation relationship was established.     

Preparation and clinical application of immunomagnetic latex

Magnetic poly(methyl methacrylate) (PMMA)/poly(methyl methacrylate‐co‐methacrylic acid) [P(MMA–MAA)] composite polymer latices were synthesized by two‐stage soapless emulsion polymerization in the presence of magnetite (Fe₃O₄) ferrofluids. Different types and concentrations of fatty acids were reacted with the Fe₃O₄ particles, which were prepared by the coprecipitation of Fe(II) and Fe(III) salts to obtain stable Fe₃O₄ ferrofluids. The Fe₃O₄/polymer particles were monodisperse, and the composite polymer particle size was approximately 100 nm. The morphology of the magnetic composite polymer latex particles was a core–shell structure. The core was PMMA encapsulating Fe₃O₄ particles, and the shell was the P(MMA–MAA) copolymer. The carboxylic acid functional groups (COOH) of methacrylic acid (MAA) were mostly distributed on the surface of the composite polymer latex particles. Antibodies (anti‐human immunoglobulin G) were then chemically bound with COOH groups onto the surface of the magnetic core–shell composite latices through the medium of carbodiimide to form the antibody‐coated magnetic latices (magnetic immunolatices). The MAA shell composition of the composite latex could be adjusted to control the number of COOH groups and thus the number of antibody molecules on the magnetic composite latex particles. With a magnetic sorting device, the magnetic immunolatices derived from the magnetic PMMA/P(MMA–MAA) core–shell composite polymer latex performed well in cell‐separation experiments based on the antigen–antibody reaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1342–1356, 2005     

Ab initio RAFT emulsion polymerization of butadiene using the amphiphilic poly(acrylic acid‐b‐styrene) trithiocarbonate as both surfactant and mediator

Ab initio reversible addition fragmentation chain transfer (RAFT) emulsion polymerization of butadiene was investigated by using the amphiphilic poly(acrylic acid_n‐b‐styrene₅) trithiocarbonate as both surfactant and mediator. The neutralization on acrylic acid (AA) units played significant influence on the gelation. When half of the AA units were neutralized, the gelation occurred in the early stage of the polymerization so that the highest accessible molecular weight of polybutadiene was as low as 5 kg mol^?1. In the non‐neutralized conditions, the gelation was much retarded so that the highest accessible molecular weight was increased up to 23 kg mol^?1. In the non‐neutralized conditions, potassium persulfate could not initiate the polymerization. When azobisisobutyronitrile was used as initiator, the polymerization mediated by poly(acrylic acid₂₇‐b‐styrene₅) trithiocarbonate could proceed much faster than the solution polymerization did. The latex was stable. Before the gel point, molecular weight agreed well with the theoretical prediction while PDI was relatively high due to the branching reaction. The poly(butadiene‐b‐styrene) core/shell particles could obtained by extending polybutadiene. When the n value in poly (acrylic acid_n‐b‐styrene₅) trithiocarbonate was lower than 20, the coalescence would occur, leading to the formation of some coagulum. On the other hand, when n value was as high as 60, the molecular weight was out of control. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation and characterization of biotinylated and enzyme‐immobilized heterobifunctional latex particles as nanobio devices

A novel biotinylated and enzyme‐immobilized nanobio device was prepared with heterobifunctional composite latex particles. Hemispherical poly(glycidyl methacrylate‐co‐divinylbenzene)/polystyrene [P(GMA‐DVB)/PSt] particles with epoxy and hydroxyl groups were prepared by soap‐free seeded emulsion polymerization with P(GMA‐DVB) seed particles. Hydroxyl groups were introduced to PSt chain terminals in the seeded stage by adding 2‐mercaptoethanol as a chain‐transfer agent. To obtain the desired hemispherical structure particles, we studied the effects of the preswelling process, the type and amount of solvents added in the seeded polymerization step, the weight ratio of the secondary monomer (styrene) to the seed particle (M/P), and the type of initiators. Under suitable conditions, heterobifunctional P(GMA‐DVB)/PSt was obtained, which was confirmed by observing the binding of streptavidin–colloidal gold with transmission electron microscopy (TEM). To obtain biotinylated and enzyme‐immobilized particles, 5‐(N‐succinimidyloxycarbonyl)pentyl D‐biotinamide was first reacted with the hydroxyl group on the PSt domain of the particle. Pyruvate kinase (PK) was then directly immobilized to the biotinylated particles through a reaction with the epoxy group in the PGMA domain. The monolayer of PK on the latex particle surface was considered to be formed by covalent binding. The activity of immobilized PK was almost conserved, even after being stored at 4 °C for 48 days. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 562–574, 2005     

Thermo‐ and pH‐induced self‐assembly of P(AA‐b‐NIPAAm‐b‐AA) triblock copolymers synthesized via RAFT polymerization

A series of environmentally sensitive ABA triblock copolymers with different block lengths were prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization from acrylic acid (AA) and N‐isopropylacrylamide (NIPAAm). The GPC and ¹H NMR analyses demonstrated the narrow molecular weight distribution and precise chemical structure of the prepared P(AA‐b‐NIPAAm‐b‐AA) triblock copolymers owing to the controlled/living characteristics of RAFT polymerization. The lower critical solution temperature (LCST) of the triblock copolymers could be tailored by adjusting the length of PAA block and controlled by the pH value. Under heating, the triblock copolymers underwent self‐assemble in dilute aqueous solution and formed nanoparticles revealed via TEM images. Physically crosslinked nanogels induced by inter‐/intra‐hydrogen bonding or core‐shell micelle particles thus could be obtained by changing environmental conditions. With a well‐defined structure and stimuli‐responsive properties, the P(AA‐b‐NIPAAm‐b‐AA) copolymer is expected to be employed as a nanocarrier for biomedical applications in controlled‐drug delivery and targeting therapy. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1109–1118     

Emulsion synthesis of nanoparticles containing PEDOT using conducting polymeric surfactant: Synergy for colloid stability and intercalation doping

Poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is a widely used conductive aqueous dispersion synthesized by using emulsion polymerization method. To further enhance its solution processability and conductivity of PEDOT derivatives, we proposed to replace the nonconductive PSS with conductive poly[2‐(3thienyl)‐ethoxy‐4‐butylsulfonate] (PTEB) as surfactant for the emulsion polymerization of PEDOT. The reaction involved colloid stabilization and doping in one step, and yielded PEDOT:PTEB composite nanoparticles with high electrical conductivity. Contrary to its counterpart containing nonconductive surfactant, PEDOT: PTEB showed increasing film conductivity with increasing PTEB concentration. The result demonstrates the formation of efficient electrical conduction network formed by the fully conductive latex nanoparticles. The addition of PTEB for EDOT polymerization significantly reduced the size of composite particles, formed stable spherical particles, enhanced thermal stability, crystallinity, and conductivity of PEDOT:PTEB composite. Evidence from UV–VIS and FTIR measurement showed that strong molecular interaction between PTEB and PEDOT resulted in the doping of PEDOT chains. X‐ray analysis further demonstrated that PTEB chains were intercalated in the layered crystal structure of PEDOT. The emulsion polymerization of EDOT using conducting surfactant, PTEB demonstrated the synergistic effect of PTEB on colloid stability and intercalation doping of PEDOT during polymerization resulting in significant conductivity improvement of PEDOT composite nanoparticles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2536–2548, 2008     

P(AA-SA) latex particle synthesis via inverse miniemulsion polymerization-nucleation mechanism and its application in pH buffering

In this work, poly(acrylic acid-co-sodium acrylate) P(AA-SA) latex particles were prepared by inverse miniemulsion polymerization and used as a pH buffering agent for application. The polymerization was quickly initiated by a redox initiator (ammonium persulfate/sodium metabisulfite) at 0-5 degrees C. Thus the possibility of monomer dissolving in a solvent was reduced, which enhanced the degree of droplet nucleation. The effects of costabilizer and the ratio of SA/(AA+SA) in functional latex particles on the nucleation mechanism and emulsion stability were investigated. The apparent pK(a) values of the synthesized P(AA-SA) latex particles were determined by titration experiments. Their properties on pH buffering were also studied, including the pH temporal response and pH buffering ability. The results showed that sodium hydroxide, which was introduced as the costabilizer to enhance the osmotic pressure and to increase the deprotonation of acrylic acid, was effective in guaranteeing droplet nucleation predominantly. Meanwhile, the surfactant concentration was controlled to be less than its critical micelle concentration (CMC) value to avoid micellar nucleation. Furthermore, the P(AA-SA) latex particles thus synthesized were found to be an excellent material for pH buffering. The pH temporal response was very rapid and related to the crosslinking degree of the latex particles. The terminal range of pH buffering for latex particles was controllable by the ratio of SA/(AA+SA).     

Electrical and optical properties of ceramic–polymer nanocomposite coatings

Transparent, conductive composite coatings were fabricated from suspensions of poly(vinyl acetate‐acrylic) (PVAc‐co‐acrylic) copolymer latices (50–600 nm) and nanosized antimony‐doped tin oxide (ATO) particles (～15 nm). The suspensions were deposited as coatings onto poly(ethylene terephthalate) substrates and dried at 50 °C. Microstructure studies using field emission scanning electron microscopy and tapping‐mode atomic force microscopy (TMAFM) indicated that the latex particles coalesced during drying and forced the ATO particles to segregate into the boundaries between the latex particles. Low phase contrast was observed with TMAFM; this result was consistent with the presence of PVAc‐co‐acrylic in the ATO‐rich phase of the composite. The conductivity of the composite coatings followed a percolation power‐law equation, with the percolation threshold between 0.05 and 0.075 volume fractions of ATO and the critical conductivity exponent ranging from 1.34 to 2.32. The highest direct‐current conductivity of the composite coatings was around 10^?2 S/cm. The optical transmittance and scattering behavior of the coatings were also investigated. Compared with the PVAc‐co‐acrylic coating, the composite coatings had lower transparency because of the Rayleigh scattering. The transparency of the composite coatings was improved by a reduction in the coating thickness. The best transparency for the coatings with a direct‐current conductivity of approximately 10^?2 S/cm was around 85% at a wavelength of 600 nm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1744–1761, 2003