One‐stage synthesis of narrowly dispersed polymeric core‐shell microspheres

A method of one‐stage soap‐free emulsion polymerization to synthesize narrowly dispersed core‐shell microspheres is proposed. Following this method, core‐shell microspheres of poly(styrene‐co‐4‐vinylpyridine), poly(styrene‐co‐methyl acrylic acid), and poly[styrene‐co‐2‐(acetoacetoxy)ethyl methacrylate‐co‐methyl acrylic acid] are synthesized by one‐stage soap‐free emulsion polymerization of a mixture of one or two hydrophobic monomers and a suitable hydrophilic monomer in water. The effect of the molar ratio of the hydrophobic monomer to the hydrophilic one on the size, the core thickness, and the shell thickness of the core‐shell microspheres is discussed. The molar ratio of the hydrophobic and hydrophilic monomers and the hydrophilicity of the resultant oligomers of the hydrophilic monomer are optimized to synthesize narrowly dispersed core‐shell microspheres. A possible mechanism of one‐stage soap‐free emulsion polymerization to synthesize core‐shell microspheres is suggested and coagglutination of the oligomers of the hydrophilic monomers on the hydrophobic core is considered to be the key to form core‐shell microspheres. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1192–1202, 2008     

RAFT‐mediated batch emulsion polymerization of styrene using poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride] trithiocarbonate as both surfactant and macro‐RAFT agent

Poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride] trithiocarbonate, which contains the reactive trithiocarbonate group and the appending surface‐active groups, is used as both surfactant and macromolecular reversible addition‐fragmentation chain transfer (macro‐RAFT) agent in batch emulsion polymerization of styrene. Under the conditions at high monomer content of ～20 wt % and with the molecular weight of the macro‐RAFT agent ranging from 4.0 to 15.0 kg/mol, well‐controlled batch emulsion RAFT polymerization initiated by the hydrophilic 2‐2′‐azobis(2‐methylpropionamidine) dihydrochloride is achieved. The polymerization leads to formation of nano‐sized colloids of the poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride]‐b‐ polystyrene‐b‐poly[N‐(4‐vinylbenzyl)‐N,N‐dibutylamine hydrochloride] triblock copolymer. The colloids generally have core‐shell structure, in which the hydrophilic block forms the shell and the hydrophobic block forms the core. The molecular weight of the triblock copolymer linearly increases with increase in the monomer conversion, and the values are well‐consistent with the theoretical ones. The molecular weight polydispersity index of the triblock copolymer is below 1.2 at most cases of polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

RAFT‐mediated emulsion polymerization of styrene using brush copolymer as surfactant macro‐RAFT agent: Effect of the brush copolymer sequence and chemical composition

The nonionic amphiphilic brush polymers such as poly[poly(ethylene oxide) methyl ether vinylphenyl‐co‐styrene] trithiocarbonate [P(mPEGV‐co‐St)‐TTC] and poly[poly(ethylene oxide) methyl ether vinylphenyl‐b‐styrene‐b‐poly(ethylene oxide) methyl ether vinylphenyl] trithiocarbonate [P(mPEGV‐b‐St‐b‐mPEGV)‐TTC] with different monomer sequence and chemical composition are synthesized and their application as macro‐RAFT agent in the emulsion RAFT polymerization of styrene is explored. It is found that the monomer sequence in the brush polymers exerts great influence on the emulsion RAFT polymerization kinetics, and the fast polymerization with short induction period in the presence of P(mPEGV‐co‐St)‐TTC is demonstrated. Besides, the chemical composition in the brush polymer macro‐RAFT agent effect on the emulsion RAFT polymerization is investigated, and the macro‐RAFT agent with high percent of the hydrophobic PS segment leads to fast and well controlled polymerization. The growth of triblock copolymer colloids in the emulsion polymerization is checked, and it reveals that the colloidal morphology is ascribed to the hydrophobic PS block extension, and the P(mPEGV‐co‐St) block almost have no influence just on the size of the colloids. This may be the first example to study the monomer sequence and the chemical composition in the macro‐RAFT agent on emulsion RAFT polymerization, and will be useful to reveal the block copolymer particle growth. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of methacrylate derivatives oligomers by dithiobenzoate‐RAFT‐mediated polymerization

Reversible addition fragmentation chain transfer (RAFT) was used to synthesize methacrylic acid oligomers and oligo(methacrylic acid)‐b‐poly(methyl methacrylate) (PMAA‐b‐PMMA) with targeted degree of polymerization ≈ 10. Characterization is by size‐exclusion chromatography (SEC) and electrospray mass‐spectrometry. SEC data are presented as hydrodynamic volume distributions (HVDs), the only proper means to present comparative and meaningful SEC data when there is no unique relationship between size and molecular weight. The RAFT agent, (4‐cyanopentanoic acid)‐4‐dithiobenzoate (CPADB), produced dithiobenzoic acid as a side product during the polymerization of methacrylate derivatives. Precipitation in diethyl ether proved to be an easy way to remove this impurity from the PMAA‐RAFT oligomers. Both unpurified and purified macro‐RAFT agent were used to prepare amphiphilic PMAA‐b‐PMMA copolymers. Diblock copolymer prepared from the purified PMAA homopolymer had a narrower HVD in comparison to those obtained from the equivalent unpurified macro‐RAFT agent. This work shows that while cyanoisopropyl‐dithiobenzoate or CPADB are good RAFT agents for methacrylate derivatives, they exhibit some instability under typical polymerization conditions, and thus when oligomers are targeted, optimal control requires checking for the degradation product and appropriate purification steps when necessary (the same effect is present for larger polymers but is unimportant). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2277–2289, 2008     

Brush macro‐RAFT agent mediated dispersion polymerization of styrene in the alcohol/water mixture

Dispersion RAFT polymerization of styrene in the alcohol/water mixture mediated with the brush macro‐RAFT agent of poly[poly(ethylene oxide) methyl ether vinylphenyl‐co‐styrene] trithiocarbonate [P(mPEGV‐co‐St)‐TTC] with similar molecular weight but different chemical composition is investigated. Well‐controlled RAFT polymerization including an initial slow homogeneous polymerization and a subsequent fast heterogeneous polymerization at almost complete monomer conversion is achieved. The molecular weight of the synthesized block copolymer increases linearly with the monomer conversion, and the polydispersity is relatively narrow (PDI < 1.3). The RAFT polymerization kinetics is dependent on the chemical composition in the brush macro‐RAFT agents, and those with high content of hydrophobic segment lead to fast RAFT polymerization. The growth of the block copolymer nano‐objects during the RAFT polymerization is explored, and various block copolymer nano‐objects such as nanospheres, worms, vesicles and large‐compound‐micelle‐like particles are prepared. The parameters such as the chemical composition in the brush macro‐RAFT agent, the chain length of the solvatophobic block, the concentration of the feeding monomer and the solvent character affecting the size and morphology of the block copolymer nano‐objects are investigated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3177–3190     

Preparation of poly(n‐butyl acrylate)‐b‐polystyrene particles by emulsifier‐free,organotellurium‐mediated living radical emulsion polymerization (emulsion TERP)

We have successfully demonstrated the preparation of poly(n‐butyl acrylate)‐b‐polystyrene particles without any coagulation by two‐step emulsifier‐free, organotellurium‐mediated living radical emulsion polymerization (emulsion TERP) using poly(methacrylic acid) (PMAA)–methyltellanyl (TeMe) (PMAA₃₀‐TeMe) (degree of polymerization of PMAA, 30) and 4,4′‐azobis(4‐cyanovaleric acid) (V‐501). The final particle size was ～30 nm and second particle nucleation was not observed throughout the polymerization. M_n increased linearly in both steps with conversion and blocking efficiency was ～75%. PDI was improved by increasing radical entry frequency into each polymer particle due to an increase of the polymerization temperature. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Monodisperse superparamagnetic pH‐sensitive single‐layer chitosan hollow microspheres with controllable structure

Facile strategy was developed for the fabrication of the monodisperse superparamagnetic pH‐sensitive single‐layer chitosan (CS) hollow microspheres with controllable structure. The carboxyl group‐functionalized polystyrene microspheres prepared by soap‐free emulsion polymerization were used as the templates. After the Fe₃O₄ nanoparticles were in situ formed onto the surface of the templates, the single‐layer CS was self‐assembled and cross‐linked with glutaraldehyde subsequently. Then, the magnetic single‐layer CS hollow microspheres were obtained after the templates were removed. It was found that the feeding ratio of the monomer acrylic acid in the soap‐free emulsion polymerization had played an important role on the particle size and surface carboxyl group content of the templates, which determined the particle size and shell thickness of the magnetic single‐layer CS hollow microspheres in the proposed strategy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Reversible addition–fragmentation chain transfer polymerization of 2‐naphthyl acrylate with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate as a chain‐transfer agent

The reversible addition–fragmentation chain transfer (RAFT) polymerizations of 2‐naphthyl acrylate (2NA) initiated by 2,2′‐azobisisobutyronitrile were investigated with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as a RAFT agent at various temperatures in a benzene solution. The results of the polymerizations showed that 2NA could be polymerized in a controlled way by RAFT polymerization with CPDN as a RAFT agent; the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with the monomer conversion. The polydispersities of the polymer were relatively low up to high conversions in all cases. The chain‐extension reactions of poly(2‐naphthyl acrylate) (P2NA) with methyl methacrylate and styrene successfully yielded poly(2‐naphthyl acrylate)‐b‐poly(methyl methacrylate) and poly(2‐naphthyl acrylate)‐b‐polystyrene block polymers, respectively, with narrow polydispersities. The P2NA obtained by RAFT polymerization had a strong ultraviolet absorption at 270 nm, and the molecular weights had no apparent effect on the ultraviolet absorption intensities; however, the fluorescence intensity of P2NA increased as the molecular weight increased and was higher than that of 2NA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2632–2642, 2005     

Surfactant‐free synthesis of amphiphilic diblock copolymer in aqueous phase by a self‐stability process

Amphiphilic polymeric particles with hydrophobic cores and hydrophilic shells were prepared via living radical emulsion polymerization of styrene using a water‐soluble poly(acrylamide)‐based macro‐RAFT agent in aqueous solution in the absence of any surfactants. Firstly, the homopolymerization of acrylamide (AM) was carried out in aqueous phase by reversible addition‐fragmentation chain transfer radical polymerization (RAFT) using a trithiocarbonate as a chain transfer agent. Then the PAM‐based macro‐RAFT agent has been used as a water‐soluble macromolecular chain transfer agent in the batch emulsion polymerization of Styrene (St) free of surfactants. The RAFT controlled growth of hydrophobic block led to the formation of well‐defined poly(acrylamide)‐copolystyrene amphiphilic copolymer, which was able to work as a polymeric stabilizer (self‐stability). Finally, very stable latex was prepared, having no visible phase separation for several months. FTIR and ¹H‐NMR measurements showed that the product was the block copolymer PAM‐co‐PS in the form of stable latex. Atomic force microscope (AFM), transmission electron microscope (TEM), and dynamic light scattering (DLS) studies indicated that the nanoparticles have a narrow particle size distribution and the average particle hydrodynamic radius was kept in the diameter of 58 nm. Core‐shell structure of the copolymer was also recorded by TEM. The mechanism of the self‐stability of polymer particles during the polymerization in the absence of surfactants was studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3098–3107, 2008     

Self‐assembly of amphiphilic tris(2,2′‐bipyridine)ruthenium‐cored star‐shaped polymers

Amphiphilic tris(2,2′‐bipyridine)ruthenium‐cored star‐shaped polymers consisting of one polystyrene block and two poly(N‐isopropylacrylamide) blocks were prepared by the “arm‐first” method in which RAFT polymerization and nonconvalent ligand–metal complexation were employed. The prepared amphiphilic star‐shaped metallopolymers are able to form micelles in water. The size and distribution of the micelles were studied by dynamic light scattering and transmission electron microscopy techniques. Preliminary studies indicate that the polymer concentration and the hydrophilic poly(N‐isopropylacrylamide) block length can affect the morphologies of the formed metal‐interfaced core–shell micelles in water. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4204–4210, 2007     

Thermoresponsive diblock copolymer micellar macro‐RAFT agent‐mediated dispersion RAFT polymerization and synthesis of temperature‐sensitive ABC triblock copolymer nanoparticles

The micellar macro‐RAFT agent‐mediated dispersion polymerization of styrene in the methanol/water mixture is performed and synthesis of temperature‐sensitive ABC triblock copolymer nanoparticles is investigated. The thermoresponsive diblock copolymer of poly(N,N‐dimethylacrylamide)‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine] trithiocarbonate forms micelles in the polymerization solvent at the polymerization temperature and, therefore, the dispersion RAFT polymerization undergoes as similarly as seeded dispersion polymerization with accelerated polymerization rate. With the progress of the RAFT polymerization, the molecular weight of the synthesized triblock copolymer of poly(N,N‐dimethylacrylamide)‐block‐poly[N‐(4‐vinylbenzyl)‐N,N‐diethylamine]‐b‐polystyrene linearly increases with the monomer conversion, and the PDI values of the triblock copolymers are below 1.2. The dispersion RAFT polymerization affords the in situ synthesis of the triblock copolymer nanoparticles, and the mean diameter of the triblock copolymer nanoparticles increases with the polymerization degree of the polystyrene block. The triblock copolymer nanoparticles contain a central thermoresponsive poly [N‐(4‐vinylbenzyl)‐N,N‐diethylamine] block, and the soluble‐to‐insoluble ‐‐transition temperature is dependent on the methanol content in the methanol/water mixture. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2155–2165     

Immobilization of RAFT agents on silica nanoparticles utilizing an alternative functional group and subsequent surface‐initiated RAFT polymerization

Silica–polystyrene core‐shell particles were successfully prepared by surface‐mediated reversible addition fragmentation chain transfer (RAFT) polymerization of styrene monomer from the surfaces of the silica‐supported RAFT agents. Initially, macro‐RAFT agents were synthesized by RAFT polymerization of γ‐methacryloxypropyltrimethoxysilane (MPS) in the presence of chain transfer agents (CTAs). Immobilization of CTAs onto the silica surfaces was then performed by reacting silica with macro‐RAFT agents via a silane coupling. Grafting of polymer onto silica forms core‐shell nanostructures and shows a sharp contrast between silica core and polymer shell in the phase composition. The thickness of grafted‐polymer shell and the diameter of core‐shell particles increase with the increasing ratio of monomer to silica. A control experiment was carried out by conventional free radical emulsion copolymerization of MPS‐grafted silica and styrene under comparable conditions. The resulting data provide further insight into the chemical composition of grafted‐polymers that are grown from the silica surface through RAFT process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 467–484, 2009     

Facile synthesis of core‐surface crosslinked nanoparticles by interblock RAFT polymerization

A new, efficient method for synthesizing stable nanoparticles with poly(ethylene oxide) (PEO) functionalities on the core surface, in which the micellization and crosslinking reactions occur in one pot, has been developed. First, amphiphilic PEO‐b‐PS copolymers were synthesized by reversible addition fragmentation chain transfer (RAFT) radical polymerization of styrene using (PEO)‐based trithiocarbonate as a macro‐RAFT agent. The low molecular weight PEO‐b‐PS copolymer was dissolved in isopropyl alcohol where the block copolymer self‐assembled as core‐shell micelles, and then the core‐shell interface crosslink was performed using divinylbenzene as a crosslinking agent and 2,2′‐azobisisobutyronitrile as an initiator. The design of the amphiphilic RAFT agent is critical for the successful preparation of core‐shell interface crosslinked micellar nanoparticles, because of RAFT functional groups interconnect PEO and polystyrene blocks. The PEO functionality of the nanoparticles surface was confirmed by ¹H NMR and FTIR. The size and morphology of the nanoparticles was confirmed by scanning electron microscopy, transmission electron microscopy, and dynamic laser light scattering analysis. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

The Effect of Hydrophile Topology in RAFT‐Mediated Polymerization‐Induced Self‐Assembly

Polymerization‐induced self‐assembly (PISA) was employed to compare the self‐assembly of different amphiphilic block copolymers. They were obtained by emulsion polymerization of styrene in water using hydrophilic poly(N‐acryloylmorpholine) (PNAM)‐based macromolecular RAFT agents with different structures. An average of three poly (ethylene glycol acrylate) (PEGA) units were introduced either at the beginning, statistically, or at the end of a PNAM backbone, resulting in formation of nanometric vesicles and spheres from the two former macroRAFT architectures, and large vesicles from the latter. Compared to the spheres obtained with a pure PNAM macroRAFT agent, composite macroRAFT architectures promoted a dramatic morphological change. The change was induced by the presence of PEGA hydrophilic side‐chains close to the hydrophobic polystyrene segment.     

Synthesis and characterization of tris(2,2′‐bipyridine)ruthenium‐cored star‐shaped polymers via RAFT polymerization

A new bipyridine‐functionalized dithioester was synthesized and further used as a RAFT agent in RAFT polymerization of styrene and N‐isopropylacrylamide. Kinetics analysis indicates that it is an efficient chain transfer agent for RAFT polymerization of the two monomers which produce polystyrene and poly(N‐isopropylacrylamide) polymers with predetermined molecular weights and low polydispersities in addition to the end functionality of bipyridine. The bipyridine end‐functionalized polymers were further used as macroligands for the preparation of star‐shaped metallopolymers. Hydrophobic polystyrene macroligand combined with hydrophiphilic poly(N‐isopropylacrylamide) was complexed with ruthenium ions to produce amphiphilic ruthenium‐cored star‐shaped metallopolymers. The structures of these synthesized metallopolymers were further elucidated by UV–vis, fluorescence, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC) as well as NMR techniques. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4225–4239, 2007     

Synthesis and characterization of spherical and hemispherical polyepoxide micrometer‐sized particles of narrow size distribution by a single‐step swelling of uniform polystyrene template microspheres with glycidyl methacrylate

Polystyrene template microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2‐methoxy ethanol. Spherical and hemispherical polystyrene/poly(glycidyl methacrylate) microspheres of narrow size distribution were prepared by a single‐step swelling of the polystyrene template microspheres with the swelling solvent monomer glycidyl methacylate, followed by polymerization of the monomer within the swollen template microspheres at 73 °C. Uniform polystyrene/poly(glycidyl methacylate‐ethylene glycol dimethacrylate) polyepoxide composite microspheres were synthesized similarly, substituting glycidyl methacylate for glycidyl methacylate and ethylene glycol dimethacrylate. Uniform crosslinked poly(glycidyl methacylate‐ethylene glycol dimethacrylate) polyepoxide microspheres have been prepared by dissolution of the PS template polymer of the former composite microspheres. Particles with different properties, for example size, size distribution, shape, surface morphology, surface area, and so forth, were prepared by changing various parameters belonging to the swelling and/or polymerization steps, for example, volume of the swelling monomer/s and/or the swelling solvent dibutyl phthalate. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4612–4622, 2007     

Influence of a reversible addition–fragmentation chain transfer agent in the dispersion polymerization of styrene

Dispersion polymerization was applied to the controlled/living free‐radical polymerization of styrene with a reversible addition–fragmentation chain transfer (RAFT) polymerization agent in the presence of poly(N‐vinylpyrrolidone) and 2,2′‐azobisisobutyronitrile in an ethanol medium. The effects of the polymerization temperature and the postaddition of RAFT on the polymerization kinetics, molecular weight, polydispersity index (PDI), particle size, and particle size distribution were investigated. The polymerization was strongly dependent on both the temperature and postaddition of RAFT, and typical living behavior was observed when a low PDI was obtained with a linearly increased molecular weight. The rate of polymerization, molecular weight, and PDI, as well as the final particle size, decreased with an increased amount of the RAFT agent in comparison with those of traditional dispersion polymerization. Thus, the results suggest that the RAFT agent plays an important role in the dispersion polymerization of styrene, not only reducing the PDI from 3.34 to 1.28 but also producing monodisperse polystyrene microspheres. This appears to be the first instance in which a living character has been demonstrated in a RAFT‐mediated dispersion polymerization of styrene while the colloidal stability is maintained in comparison with conventional dispersion polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 348–360, 2007     

RAFT polymerization of activated 4‐vinylbenzoates

The reversible addition fragmentation chain transfer (RAFT) polymerization of five active ester monomers based on 4‐vinylbenzoic acid had been investigated. Pentafluorophenyl 4‐vinylbenzoate could be polymerized under RAFT conditions yielding polymers with very good control over molecular weight and narrow molecular weight distributions. Following the synthesis of diblock copolymers consisting of polystyrene, polypentafluorostyrene, poly(4‐octylstyrene), or poly(4‐acetoxystyrene) as an inert block and poly(pentafluorophenyl 4‐vinylbenzoate) as a reactive block was successfully performed. The diblock copolymer poly(pentafluoro styrene)‐block‐poly(pentafluorophenyl 4‐vinylbenzoate) had been analyzed by ¹⁹F NMR spectroscopy in solution, demonstrating the synthetic potential of pentafluorophenyl 4‐vinylbenzoate as an extremely valuable monomer for the synthesis of highly functionalized polymeric architectures. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1696–1705, 2009     

Polytetrahydrofuran amphiphilic networks. IV. Swelling behavior of poly(acrylic acid)‐l‐polytetrahydrofuran and poly(methacrylic acid)‐l‐polytetrahydrofuran networks

Poly(acrylic acid)‐l‐polytetrahydrofuran (PAA‐l‐PTHF) and poly(methacrylic acid)‐l‐polytetrahydrofuran (PMAA‐l‐PTHF) networks were synthesized by the free‐radical copolymerization of hydrophobic polytetrahydrofuran diacrylates with hydrophilic acrylic acid and methacrylic acid. Their swelling behavior was studied. Both PAA‐l‐PTHF and PMAA‐l‐PTHF networks had four solubility parameters, which indicated that they exhibited not only the properties of both hydrophobic and hydrophilic segments but also the combined properties of these two segments. The swell of these two series of networks was composition‐dependent in organic solvents and water. The relationship between the equilibrium swelling ratio (SR_e) in nonpolar solvents and the composition of the networks [the weight fraction of the PTHF segment (PTHF%)] may be expressed with a linear equation: SR_e = A × PTHF% + B. A and B are parameters that relate to the interaction of hydrophilic and hydrophobic segments with nonpolar solvents and to the properties of the networks, respectively. Because of the presence of a ? COOH group, these two network series were pH‐sensitive when the content of hydrophilic segments was higher. The pH sensitivity of networks could be controlled not only by the composition of the networks but also by the hydrophobic degree of the hydrophilic segments. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1784–1790, 2001     

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