Latex interpenetrating polymer networks: From structure to properties

Latex interpenetrating and semi-interpenetrating polymer networks (LIPNs and semi-LIPNs) combine the morphological characteristics of bulk-polymerized IPNs with the characteristics of polymers produced by emulsion polymerization; there are IPN structures within the latex particles. These LIPNs can be injection-molded using standard thermoplastic methods and machinery. A dual thermoset—thermoplastic nature characterizing the LIPN manifests itself in the mechanical and rheological behavior reflecting unique morphologies. These morphologies result from a sequential two-stage latex (TSL) polymerization and include core—shell, domain, interpenetrating polymer networks and various other combinations. Elastomeric TSL with crosslinked polyacrylates (xPA) as the first stage and crosslinked polystyrene (xPS) as the second, each stage lightly crosslinked, yield IPN-nano-domain structural particles. Upon molding, the particles become interconnected by joint PS nanodomains, introducing a particle—particle strength-forming mechanism. The intraparticle glassy PS nanodomains reinforce the soft elastomeric particles enhancing their modulus. Glassy “all-styrene” semi-LIPNs made of PS and xPS show improved mechanical performance compared to PS, while exhibiting good transparency. Volumetric crazing in these PS/xPS materials develops in tension-improving elongation and strength. The presence of xPS particles, denser and thus stiffer than the PS matrix, renders a higher modulus. Essentially xPS highly filled blends are achieved along with significant particle—matrix interactions. The ability to generate a controlled plethora of morphologies offers a wealth of potential applications, from reinforced elastomers to high impact plastics. Poly(acrylonitrile—butadiene—styrene), a semi-LIPN, is a commodity plastic, clearly demonstrating the utilization potential of the TSL procedure for generating very fine multiphase materials of scientific and technological merits.     

Synthesis of submicron-sized peanut-shaped poly(methyl methacrylate)/polystyrene particles by seeded soap-free emulsion polymerization

Submicron-sized peanut-shaped poly(methyl methacrylate)/polystyrene(PMMA/PS) particles were successfully synthesized by seeded soap-free emulsion polymerization of styrene on the spherical crosslinked PMMA seed particles.The obtained peanut-shaped particles showed a novel internal morphology:PS phase formed one domain which linked to the other domain having PMMA core encased by PS shell.     

Structure and properties of polyurethane/polyacrylate latex interpenetrating networks hybrid emulsions

Some new kinds of novel polyurethane (PU)/polyacrylate (PA) latex interpenetrating networks (LIPNs) were synthesized. Firstly PU dispersions were synthesized by self-emulsification polymerization. Then PU/PA LIPNs using PU dispersion as the seed were prepared by soap free emulsion polymerization. The effects of different PU/PA ratios, the blending method and the NCO/OH molar ratio of PU components on PU/PA LIPNs performance were also investigated. The structure and properties of PU/PA LIPNs such as mechanical properties, particle size, morphology of the surface were characterized by dynamic mechanical analysis, scanning electron microscopy, and dynamic light scattering. It was found that PU/PA LIPNs can markedly improve the water resistance and the mechanical properties of PU latex much more than those of PU/PA physical blends due to a great deal of interpenetrating and entangling between PU and PA latex. Moreover, the particle size of PU/PA LIPNs is related to the PA content and NCO/OH molar ratio of PU components: the higher the NCO/OH molar ratio in PU dispersions, the larger is the particle size of PU/PA LIPNs, and the average particle size of PU/PA LIPNs becomes larger with an increase in PA content.     

Morphology of micron-sized monodispersed composite polymer particles produced by seeded polymerization for the dispersion of highly monomer-swollen polymer particles

 Monodispersed polystyrene (PS)/poly(n-butyl methacrylate) (PBMA) composite particles having 9.4 μm in diameter were produced by seeded polymerization for the dispersion of highly n-butyl methacrylate (BMA)-swollen PS particles, and their morphologies were examined. The highly BMA-swollen PS particles (about 150 times the weight of the PS seed particles) were prepared by mixing monodispersed 1.8 μm-sized PS seed particles and 0.7 μm sized BMA droplets prepared with an ultrasonic homogenizer in ethanol/water (1/2, w/w) medium at room temperature. After NaNO₂ aqueous solution as inhibitor was added in the dispersion, the seeded polymerization was carried out at 70 °C. In an optical microscopic observation, one or two spherical high contrast regions which consisted mainly of PS were observed inside PS/PBMA composite particles. In the PS domain, there were many fine spherical PBMA domains. Such morphologies were based on the phase separation of PS and PBMA within the homogeneous swollen particles during the seeded polymerization. Received: 04 June 1997 Accepted: 27 August 1997     

Surface modification of polystyrene latex particles via atom transfer radical polymerization

The atom transfer radical polymerization (ATRP) technique using the copper halide/ N,N′,N′,N″,N″‐pentamethyldiethylenetriamine complex was applied to the graft polymerization of methyl methacrylate and methyl acrylate on the uniform polystyrene (PS) seed particles and formed novel core‐shell particles. The core was submicron crosslinked PS particles that were prepared via emulsifier‐free emulsion polymerization. The crosslinked PS particles obtained were transferred into the organic phase (tetrahydrofuran), and surface modification using the chloromethylation method was performed. Then, the modified seed PS particles were used to initiate ATRP to prepare a controlled poly(methyl methacrylate) (PMMA) and poly(methyl acrylate) (PMA) shell. The final core‐shell particles were characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, thermogravimetric analysis, and elementary analysis. The grafting polymerization was conducted successfully on the surface of modified crosslinked PS particles, and the shell thickness and weight ratio (PMMA and PMA) of the particles were calculated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 892–900, 2002; DOI 10.1002/pola.10160     

P(VA-co-DBM)/PVA乳胶IPN阻尼材料的合成及动态力学性能

用种子乳液聚合法合成了聚（醋酸乙烯酯－co-马来酸二丁酯）／聚醋酸乙烯酯乳胶互穿聚合物网络阻尼材料,动态力学谱结果表明,该阻尼材料在较宽的温域具有很高的阻尼因子。     

Synthesis of graft copolymers onto styrenic polymer backbone via “grafting from” raft process

A new synthetic methodology is developed for preparing graft copolymers via RAFT polymerization method by the “R group approach” onto styrenic polymers. In this approach, latent sites of the styrenic polymer was brominated first and then converted into macro‐RAFT agents with pyrazole and thio dodecyl as the Z groups. This was used to synthesize graft copolymer such as polystyrene‐graft‐polymethyl methacrylate (PS‐g‐PMMA), polystyrene‐graft‐poly(isobornyl acrylate), polystyrene‐graft‐poly[2‐(acetoacetoxy)ethyl methacrylate] (PS‐g‐PAEMA), and poly(para‐methoxystyrene)‐graft‐polystyrene (P(p‐MS)‐g‐PS). The polymers are characterized by gel permeation chromatography, ¹H NMR, IR, and atomic force microscopy (AFM). The morphology of PS‐g‐PMMA in THF was investigated using AFM and island‐like features were noticed. The AFM studies of the PS‐g‐PAEMA graft copolymers revealed the formation of globules and ribbon‐like morphological features. The PS‐g‐PAEMA graft copolymers form complex with Fe(III) in dimethylformamide and the AFM studies suggest the formation of globular superstructures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation of micron-sized composite polymer particles containing hydrophilic 2-hydroxyethyl methacrylate and their biomedical applications

Micron-sized polystyrene or PS particles were first prepared by dispersion polymerization. Then a series of polystyrene/poly(styrene-2-hydroxyethyl methacrylate) or PS/P(S-HEMA) composite polymer particles was prepared by seeded copolymerization using different amounts of 2-hydroxyethyl methacrylate (HEMA) at the constant core/shell ratio of 1/0.5. The produced PS seed and composite polymer particles were characterized by transmission electron microscopy. Adsorption behaviors of some biologically active macromolecules were studied under similar conditions. In each case the magnitude of adsorption on composite polymer particles decreased with the increase in HEMA content in the recipe, which means that the hydrophobic interaction between the surface of the particles and biomolecules decreased. The specific activities of trypsin aqueous solution and adsorbed trypsin on PS seed and composite polymer particles prepared with different HEMA contents were also measured and compared. The activity of adsorbed trypsin on composite polymer particles improved significantly with the incorporation of hydrophilic HEMA.     

Fabrication of cage-like particles via unstable seeded dispersion polymerization: A new concept in the polymerization-induced self-assembly

The formation mechanism of hollow micron-sized polystyrene (PS) particles having numerous dents on the surface, so-called cage-like particles, obtained from seeded dispersion polymerization (SDP) of 2-ethylhexyl methacrylate (EHMA) with low molecular weight (MW) PS particles stabilized by poly(vinyl alcohol) (PVA) in the presence of hexadecane droplets was investigated. It was found that association of poly(2-ethylhexyl methacrylate) (PEHMA)/hexadecane phases which occurs due to the instability of the obtained composite particles followed by a diffusion of PS ellipsoidal particles into each other is the main process responsible for the production of such unique morphology. Time course monitoring of the SDP showed that diffusion of hexadecane and/or PS and/or PEHMA phase into PS/PEHMA/hexadecane composite particles through PS shell which happens based on Ostwald ripening is the main phenomenon which results in the formation of the dents on the surface of final particles. Moreover, the experimental results revealed that in this reaction system, the polymerization develops in a faster manner rather than the SDP employing seed particles having higher MWs. Furthermore, it was observed that particles with different surface morphologies can be produced by using different hydrocarbons. The elimination of small particles which are produced in addition to the cage-like ones via decreasing the concentration of the stabilizer was another interesting finding of this research. The acquired results showed that unstable SDP is expected to be a new concept in polymerization-induced self-assembly (PISA) which employs instability of a dispersion for self-assembly of polymeric particles, and therefore, production of polymeric unique objects.     

Production of micron-sized monodispersed core/shell composite polymer particles by seeded dispersion polymerization

 The effect of the weight ratio of seed polymer/monomer on the morphology of the poly(methyl methacrylate) (PMMA)/polystyrene (PS) monodispersed composite particles produced by batch seeded dispersion polymerization of styrene with 1.64-μm-sized monodispersed PMMA seed particles in a methanol/water medium (4/1 w/w) was examined. In the PMMA/PS weight ratios of 3/1 and 2/1, the composite particles had a clear morphology consisting of a PMMA core and a PS shell. In the ratio of 1/1, a lot of small PS domains were observed in the PMMA core though the PS shell was still formed. By stepwise addition of styrene monomer, the formation of the small PS domain was depressed and complete core/shell morphology was formed. Absorption/release treatments of toluene into/from the PMMA/PS (1/1 w/w) composite particles resulted in a drastic morphological change from the core/shell structure to a multi- layered one. Received: 2 February 1999 Accepted in revised form: 7 April     

Preparation of nonspherical particles via dual-seeded dispersion polymerization in the presence of saturated hydrocarbon droplets

In this study, the effect of various polymerization conditions on the shape of the particles produced by dual-seeded dispersion polymerization of a second monomer with polystyrene (PS) and poly(methyl methacrylate) (PMMA) seed particles in the presence of saturated hydrocarbon droplets in a polar media was discussed. It was observed that with changing the affinity between the hydrocarbon and PS seed particles, second monomer type, polarity, and alcohol type of the medium nonspherical particles with a variety of shapes can be produced. Furthermore, we suggested that the presence of PMMA seed particles in the medium affects the distribution of the second polymer domains on the surface of the PS seed particles in addition to the absorbed amount of the hydrocarbon by PS particles and second polymer domains and the distribution of the hydrocarbon between them. Moreover, the experimental results showed that almond shell-like PS particles can be prepared under certain conditions.     

Production of micron-sized monodispersed cross-linked polymer particles having hollow structure

4 μm-sized monodispersed cross-linked polymer particles having hollow structure were produced as follows. First, 1.7 μm-sized monodispersed polystyrene (PS) seed particles produced by dispersion polymerization were dispersed in ethanol/water (7/3, w/w) solution in which divinylbenzene (DVB), benzoyl peroxide (BPO), poly(vinyl alcohol), and toluene was dissolved. The PS seed particles were swollen with DVB, toluene and BPO maintaining high monodispersity throughout the dynamic swelling process where water was slowly added continuously. And then, the seeded polymerization of the (toluene/DVB)-swollen PS particles was carried out.     

Preparation of micron-sized nonspherical polystyrene/poly(styrene-<Emphasis Type="Italic">co</Emphasis>-ethyleneglycol dimethacrylate) particles by seeded soap-free emulsion polymerization

Micron-sized nonspherical polymer particles having different morphologies were synthesized by seeded soap-free emulsion polymerization of styrene(St) and ethyleneglycol dimethacrylate(EGDMA,used as a crosslinker) on spherical, linear polystyrene(PS) seed particles.The morphology of the resulting PS/poly(St-co-EGDMA) particles was dependent on the crosslinker concentration and polymerization temperature.     

Semi-continuous emulsion polymerization of styrene in the presence of poly(methyl methacrylate) seed particles. Polymerization conditions giving core-shell particles

This work reports the morphology of two-phase latex particles prepared by semi-continuous seed emulsion polymerization of styrene in the presence of polar poly(methyl methacrylate), PMMA, seed particles, using different conditions of non-polar styrene feed rate, rate of initiation, seed particle concentration and temperature of polymerization.The expected latex particle morphology at thermodynamic equilibrium is an inverted core-shell structure where the non-polar polystyrene would form the core. However, depending on the set of process conditions used the morphology of the resulting two-phase particles varied from that of a pure core-shell structure, over intermediate structures in which a shell of PS surrounded a PMMA core containing an increasing number of PS phase domains, to a structure in which the entire PS phase was present as discrete PS phase domain, more or less evenly distributed in a matrix of PMMA.By the use of a caloirimetric reactor system the monomer concentration in the particles during the different polymerization experiments could be calculated by comparing the integral of the polymerization rate curve with the integral of the monomer feed rate. A comparison between particle morphology and the calculated concentration of plasticizing monomer in the polymerizing particles strongly suggested that the diffusivity of the entering oligo radicals determined by the difference between polymerization temperature and the glass transition temperature of the monomer-swollen core polymer is a key factor determining the morphology of two-phase particles prepared by semi-continuous seed emulsion polymerization.Two-phase particles with a true core-shell structure were obtained in experiments where the estimated glass transition temperature of the PMMA phase was only a few degrees below the polymerization temperature. The results show that such particles can be obtained under conditions of high as well as low styrene feed rates, provided that the rate of initiation is properly adjusted.     

Preparation of novel and unique nonspherical particles with almond-shell-like shape via dual-seeded dispersion polymerization in the presence of saturated hydrocarbon droplets

In this study, the preparation of micron-sized polymer particles having a novel and unique nonspherical shape which we called almond-shell-like by dual-seeded dispersion polymerization (DSDP) of 2-ethylhexyl methacrylate (EHMA) with polystyrene (PS) and poly(methyl methacrylate) (PMMA) seed particles in the presence of decane droplets and evaporation of decane after the polymerization was discussed. The experimental results showed that mushroom-like morphology which is a precursor of the almond-shell-like shape was obtained from DSDP of EHMA. It was found that with changing the PS/PMMA seed particles' weight ratio, the size of the dents on the surface of the particles can be controlled. Furthermore, it was observed that various nonspherical particles can be produced using different methacrylic seed particles and initiators.     

Polystyrene (1)/poly(butyl acrylate/amide type functional monomer) (2) two-stage emulsion polymers. Synthesis and thermomechanical properties of latex films

Polystyrene (PS) (1)/Poly (n-butyl acrylate (BA)/amide type functional monomer) (2) structured latex particles were prepared through emulsion polymerization varying the hydrophilicity of the functional monomer employed. The second-stage polymerization kinetics, the size and morphology of latex particles, and the location of the functional groups in the final latexes were studied, in order to relate them to the thermomechanical properties of films cast from these latexes. It has been shown that, as expected, increasing the hydrophobicity leads to a better homogeneity in the copolymer formed during the second-stage polymerization, while the more hydrophilic functional monomer partly homopolymerizes in a separate phase. However, the functionalization by all the monomers used in this work, prevents the PS seed particles to form a continuous skeleton (percolated network). Further heat treatments at 140°C do not lead to the formation of a continuous PS phase as for pure BA/pure PS two-stage particles. In addition, some thermally induced crosslinking effects are discussed in relation with the functional monomer location within the particles. © 1995 John Wiley & Sons, Inc.     

Micron-sized monodispersed polymer particles produced by seeded polymerization for the dispersion of high swelling of polymer particles with a large amount of monomer

 Micron-sized monodispersed polystyrene (PS)/poly(n-butyl methacrylate) composite particles were produced as follows. First, 1.77 μm-sized monodispersed PS seed particles produced by dispersion polymerization were dispersed in ethanol/water (1/2, w/w) medium dissolving poly(vinyl alcohol) as a stabilizer. n-Butyl methacrylate (BMA) monomer dissolving benzoyl peroxide initiator was emulsified in ethanol/water (1/2, w/w) solution of sodium dodecyl sulfate as emulsifier with ultrasonic homogenizer, and the BMA monomer emulsion was mixed with the PS seed emulsion. The PS seed particles absorbed with a large amount of BMA (about 150 times weight of the seed particles) for 2 h to about 10 μm in diameter while keeping good monodispersity and BMA droplets disappeared finally. The seeded polymerization was carried out at 70 °C after a certain amount of water was added to depress the redissolving of BMA from the swollen particles into the medium by raising from room temperature to the polymerzation temperature. Received: 21 February 1996 Accepted: 4 September 1996     

Morphologies of micron-sized monodispersed composite polymer particles having crosslinked structures produced by seeded polymerizations

Three kinds of micron-sized monodispersed polystyrene (PS)/ poly(styrene - divinylbenzene) composite particles were produced by two kinds of seeded copolymerizations of styrene (S) and divinylbenzene (DVB) (PS seed/ (S+DVB)=2/1, wt. ratio; S/DVB=1/1, molar ratio) in the presence of about 2 μm-sized monodispersed PS particles, and their morphologies were examined. One was produced by a seeded dispersion copolymerization where almost monomers and initiators exist in an ethanol/water (12.6/4.0, w/w) medium. The others two were produced by seeded copolymerizations with the dynamic swelling method where almost monomers exist in the monomer-swollen particles using 2, 2'-azobisisobutyronitrile in monomer-swollen PS seed particles or using 4, 4'-azobis (4-cyanopentanoic acid) in an ethanol/water (7/43, w/w) medium. In the former polymerization, the produced composite particles had a high dense crosslinked shell, whereas in the latter two polymerizations, they did the comparatively homogeneous crosslinked structures.     

Synthesis and characterization of poly (n-butyl acrylate)-poly (methyl methacrylate) latex interpenetrating polymer networks by radiation-induced seeded emulsion polymerization

A series of latex interpenetrating polymer networks (LIPNs) were prepared via a two-stage emulsion polymerization of methyl methacrylate (MMA) or mixture of MMA and n-butyl acrylate (n-BA) on crosslinked poly(n-butyl acrylate)(PBA) seed latex using ⁶⁰Co γ-ray radiation. The particles of resultant latex were produced with diameters between 150 and 250 nm. FTIR spectra identified the formation of crosslinked copolymers of PMMA or P(MMA-co-BA). Dynamic light scattering (DLS) showed that with increasing n-BA concentration in second-stage monomers, the particle size of LIPN increased. Transmission electron microscope(TEM) photographs showed that the morphology of resultant acrylate interpenetrating polymer network (IPN) latex varied from the distinct core-shell structure to homogenous particle structure with the increase of n-BA concentration, and the morphology was mainly controlled by the miscibility between crosslinked PBA seed and second-stage copolymers and polarity of P(MMA-co-BA)copolymers. In addition, differential scanning calorimeter (DSC) measurements indicated the existence of reinforced miscibility between PBA seed and P(MMA-co-BA)copolymer in prepared LIPNs.     

Monodisperse polystyrene particles crosslinked with poly(dimethyl siloxane) diacrylate using dispersion polymerization and their monomer swelling capability

A flexible poly(dimethyl siloxane) diacrylate (PDMSDA) crosslinker was synthesized using different molecular weights of poly(dimethyl siloxane) (PDMS, M _n =550, 1,700, 4,000 g/mol). The monodisperse polystyrene (PS) particles crosslinked with various contents of PDMSDA were prepared by dispersion polymerization, and applied as seed particles in the seeded polymerization. The crosslinking density of the PS particles was determined from the rate of transport of the monomer molecules to the crosslinked seed particles. It was confirmed that the monomer swelling capacity of seed particles and final morphological changes of polymer beads were determined significantly by the crosslinking density of the seed particles. In addition, the morphological change was not observed without the oligomer swelling step in the seeded polymerization due to the hydrophobic property of PDMS. When highly crosslinked seed particles were used in the seeded polymerization, peculiar morphology (doublet structure) of polymer beads appeared.