Encapsulation of Jojoba and Andiroba Oils by Miniemulsion Polymerization. Effect on Molar Mass Distribution

Summary: This paper aims to study the encapsulation of jojoba and andiroba oils via miniemulsion polymerization. The effect of different hydrophilic monomers (acrylic or methacrylic acid), co-stabilizers (hexadecane, jojoba oil or andiroba oil) and initiator concentrations were evaluated. Results indicated the formation of particles with nanocapsule morphology when either hexadecane or jojoba oils were used. When andiroba oil was used no phase separation could be detected in polymer particles and molar mass distributions showed a shoulder of intermediate molar masses between those of the oil and of the pure polymer.     

Effects of polyaniline chain structures on proton conduction in a PEM host matrix

This study examined the effects of the conjugated chain structure of polyaniline (PAn) on proton transport in a proton exchange membrane (PEM) containing a small amount of PAn colloidal particles. The PEM host matrix consisted of a hydrophobic three-component polymer blend (TCPB) of poly(4-vinylphenol-co-methylmethacrylate) P(4-VP-MMA), poly(butyl methacrylate) (PBMA), and Paraloid^® B-82 acrylic copolymer resins; in which a hydrophilic network of 2-acrylamido-2-methyl propanesulfonic acid (AMPS), 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol)dimethylacrylate (PEGDMA) was formed upon embedded polymerization. Colloidal PAn particles were added to the PEM matrix during the embedded polymerization of PEM. Two types of PAn colloidal particles with different chain structures and morphologies were synthesized by inverse miniemulsion polymerization and interfacial polymerization. The PAn(1) particles from inverse miniemulsion polymerization were bar-shaped, contained a higher fraction of quinoid diimine units than the scaffold-like PAn(2) particles from interfacial polymerization, and displayed a strong promotional effect on proton conduction. The oxidation state of the PAn particles was also varied by post-synthesis treatments to evaluate the effect of oxidation state on proton conduction. It was found that a mixed oxidation state such as the emeraldine form of PAn had the best enhancement effect. The PAn loading optimal for proton conductivity enhancement of the composite PEM was determined to be about 2 wt% of PAn(1).     

ZnO/PS core-shell hybrid microspheres prepared with miniemulsion polymerization

The hybrid microspheres of ZnO/PS with different core-shell structures were prepared in miniemulsion polymerization. 3-(trimethoxysilyl)propyl methacrylate (MPS) was used as a functional co-monomer to enhance the surface polarity of ZnO nanoparticles and to prevent water from quenching the luminescent properties of ZnO. The morphology of hybrid particles was examined with a transmission electron microscope. The luminescence spectra were measured using a Shimadzu RF-5301 PC spectrofluorimeter (Xe source) at room temperature. The crystallization structure of samples was characterized with a Rigaku wide-angle X-ray diffractometer. The chemical composition and structure of the ZnO colloids, MPS-modified ZnO colloids, and ZnO/PS hybrid microspheres were analyzed with IR.     

八甲基环四硅氧烷正离子细乳液开环聚合动力学

以十二烷基苯磺酸钠(SDBS)为乳化剂,硫酸或盐酸为催化剂,八甲基环四硅氧烷(D4)为单体,十六烷为共稳定剂,超声预乳化,制备了聚硅氧烷细乳液,研究了超声时间、催化剂用量、乳化剂用量和温度对聚合动力学的影响.结果表明,在一定酸度范围内,聚合速度与硫酸浓度0.81次方、与盐酸浓度1.02次方、与乳化剂浓度-0.66次方成正比,反应的表观活化能为40.56kJ/mol.     

Miniemulsion polymerization of styrene with chain transfer agent as cosurfactant

Miniemulsion polymerization of styrene with the chain transfer agent n-dodecyl mercaptan (DDM) used as cosurfactant was studied. Droplet size and shelf life for unpolymerized miniemulsions were measured and compared with those of equivalent macroemulsions. The miniemulsion monomer droplets with dodecyl mercaptan as cosurfactant were very stable. Shelf lives were from 17 h to 3 months. The kinetics of miniemulsion polymerization were studied. Unlike other miniemulsion systems where the cosurfactant does not act as a chain transfer agent, the polymerization rate falls with cosurfactant level because the chain transfer agent enhances radical desorption from the particles. The polymerization rate in all the miniemulsions was lower than that of the corresponding macroemulsions. Polymerized particles were larger than in the corresponding macroemulsions, but molecular weights were lower. Results indicate that DDM can serve as an effective cosurfactant as well as a chain transfer agent. The fact that the molecular weights are lower in the miniemulsion reactions indicates predominant droplet nucleation. © 1997 John Wiley & Sons, Inc.     

Characterization of deposits formed on diesel injectors in field test and from thermal oxidative degradation of n-hexadecane in a laboratory reactor

Solid deposits from commercially available high-pressure diesel injectors (HPDI) were analyzed to study the solid deposition from diesel fuel during engine operation. The structural and chemical properties of injector deposits were compared to those formed from the thermal oxidative stressing of a diesel fuel range model compound, n-hexadecane at 160°C and 450 psi for 2.5 h in a flow reactor. Both deposits consist of polyaromatic compounds (PAH) with oxygen moieties. The similarities in structure and composition of the injector deposits and n-hexadecane deposits suggest that laboratory experiments can simulate thermal oxidative degradation of diesel in commercial injectors. The formation of PAH from n-hexadecane showed that aromatization of straight chain alkanes and polycondensation of aromatic rings was possible at temperatures as low as 160°C in the presence of oxygen. A mechanism for an oxygen-assisted aromatization of cylcoalkanes is proposed.     

Synthesis of phosphonate-functionalized polystyrene and poly(methyl methacrylate) particles and their kinetic behavior in miniemulsion polymerization

Phosphonate-functionalized polymer nanoparticles were synthesized by free-radical copolymerization of vinylphosphonic acid (VPA) with styrene or methyl methacrylate (MMA) using the miniemulsion technique. The influence of different parameters such as monomer and surfactant type, amount of vinylphosphonic acid on the average particle size, and size distribution was studied using dynamic light scattering and transmission electron microscopy. Depending on the amount and type of the surfactant used (ionic or non-ionic), phosphonate-functionalized particles in a size range from 102 to 312 nm can be obtained. The density of the phosphonate groups on the particle surface was higher in the case of using MMA as a basis monomer than polystyrene. The kinetic behavior of VPA copolymerization with styrene or MMA using a hydrophobic initiator was investigated by reaction calorimetry. Different kinetic curves were observed for miniemulsion (co)polymerization of styrene- and MMA-based nanoparticles indicating different nucleation mechanisms.     

Synthesis of narrowly size-distributed metal salt/poly(HEMA) hybrid particles in inverse miniemulsion: versatility and mechanism

Hybrid particles containing different hydrophilic metal salts such as tetrafluoroborates of iron(II), cobalt(II), nickel(II), copper(II), and zinc(II), and nitrates of cobalt(II), nickel(II), copper(II), zinc(II), and iron(III), and cobalt(II) chloride were synthesized via inverse miniemulsion polymerization of 2-hydroxyethyl methacrylate (HEMA). All salts delivered narrowly size-distributed hybrid particles with the exception of iron(III), where only the nitrate salt could be successfully employed. The size and size distribution of the hybrid particles were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The particle morphology and the distribution of salt in the dried particles were observed by TEM. The influences of the type of metal salts and salt content on the particle size distribution were extensively investigated.     

Amphiphilic Triblock Copolymers Based on Acrylic Acid and Alkyl Acrylates Synthesized via RAFT Polymerization-Induced Self-Assembly and RAFT Miniemulsion Polymerization

The aim of this research is to reveal the advantages and limitations of different heterophase polymerization methods, such as dispersion, emulsifier-free emulsion and miniemulsion polymerization, for the obtaining of in situ self-assembled amphiphilic triblock copolymer core-shell particles. In the present research, we addressed the problems of the controlled synthesis of two- and three-component amphiphilic ABA triblock copolymers based on acrylic acid, fluoroalkyl acrylates and butyl acrylate via polymerizationinduced self-assembly and reversible addition fragmentation chain transfer polymerization (RAFT) miniemulsion polymerization using symmetrical trithiocarbonates.     

Synthesis of liquid‐filled nanocapsules via the miniemulsion technique

This study describes the synthesis of well‐defined nanocapsules via the miniemulsion technique. Pentaerythritol tetrakis(3‐mercaptopropionate) (TetraThiol) or 1,6‐hexanediol di(endo, exo‐norborn‐2‐ene‐5‐carboxylate) (DiNorbornene) is used as the oil phase. TetraThiol is encapsulated via the miniemulsion technique without polymerization, as this monomer would simultaneously act as a chain‐transfer agent, and DiNorbornene is encapsulated via miniemulsion polymerization of styrene. Various styrene‐maleic anhydride (PSMA) copolymers and poly(styrene‐maleic anhydride)‐block‐polystyrene (PSMA‐b‐PS) block copolymers were used as surfactant for the synthesis of well‐defined nanocapsules with TetraThiol as the core material. The nanocapsules had a diameter of 150–350 nm and the particle size distribution was narrow. The use of PSMA‐b‐PS block copolymers as surfactant in combination with post‐addition of formaldehyde provided improved stability to the nanocapsules. DiNorbornene was encapsulated via miniemulsion polymerization of styrene, and a stable latex with a bimodal particle size distribution was obtained. The distribution of small particles had a size of 60 nm and the distribution of large particles had a size of 150 nm. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

The influence of surfactant coverage of the minidroplets on RAFT miniemulsion polymerization

The surfactant coverage of minidroplets was tuned by postaddition of more surfactants after preparation of the miniemulsion of styrene. The influence of surfactant coverage on reversible addition‐fragmentation chain transfer (RAFT) miniemulsion polymerization of styrene was investigated. When the surfactant (sodium dodecyl sulfate; SDS) coverage was as low as 40%, two kinds of particles, denoted as polymer and oligomer particles, were formed in the early stage of the polymerization. Polymer chains within two kinds of particles grew in a parallel way during the rest period of the polymerization. The oligomer particles contributed less than 10% to the final monomer conversion but consumed over one in third the original RAFT agent molecules. Oligomer particles were larger in size but much lower in molecular weight. Both the particle size and molecular weight distributions were bimodal. With increase of SDS coverage, the formation of oligomer particles was suppressed. As a result, the nucleation efficiency of the minidroplets was greatly enhanced and the molecular weight and particle size distributions were dramatically narrowed. The formation of the oligomer particles was ascribed to the superswelling occurring in the beginning stage of the polymerization. The experimental observations are in excellent accord to the superswelling theory. Postaddition of surfactant presents a novel method to narrow particle size and molecular weight distributions in RAFT miniemulsion polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2293–2306, 2006     

Preparation of dually, pH- and thermo-responsive nanocapsules in inverse miniemulsion

pH- and thermo-sensitive nanocapsules were successfully synthesized via inverse miniemulsion copolymerization of N-isopropyl acrylamide (NIPAM), N,N'-methylene bisacrylamide (MBA), and a functional monomer, 4-vinyl pyridine (4-VP). The size and size distribution of nanocapsules were measured by dynamic light scattering (DLS). The particle morphology was observed by transmission electron microscopy (TEM). The final morphology of particles was strongly influenced by the hydrophobicity of functional monomers. The use of a hydrophilic functional monomer, acrylic acid, led to the formation of solid particles, while the use of the more hydrophobic functional monomer, 4-VP, resulted in the formation of nanocapsules. The particle morphology, size, and size distribution were investigated in terms of the content of 4-VP, MBA, and the type and content of surfactant. The pH- and thermo-sensitivities were characterized by measuring the size variation with the change of temperature and pH. The organic-inorganic nanocapsules were prepared by coating a layer of silica particles on the surface of the sensitive nanocapsules.     

Encapsulation of inorganic particles via miniemulsion polymerization

The encapsulation of TiO₂ particles via miniemulsion polymerization is strongly dependent on the size and stability of the inorganic particles in the monomer medium in which they are initially dispersed. It was found from XPS and FT‐IR studies that both the hydrophilic and hydrophobic TiO₂ particles, which were studied, have hydroxyl groups present on their surfaces, which can strongly interact with the amine end‐groups of the polymeric stabilizer, OLOA370 (polybutene‐succinimide diethyl triamine). It was found from the dispersion and adsorption studies that the amount of OLOA370 retained on the TiO₂ particles is strongly dependent on the area exposed by the sonification that is applied to break up the aggregates in the dispersion process. The TiO₂ dispersions in styrene monomer were themselves dispersed as miniemulsion droplets and subsequently polymerized. It was concluded from the density gradient column (DGC) analysis of the latexes obtained from the encapsulation polymerizations, that the stability of the inorganic particles in the monomer, as well as their particle size, significantly influence the encapsulation efficiencies. The use of the hydrophilic titanium dioxide particles in combination with the stabilizer, OLOA370, resulted in a good dispersibility, dispersion stability, and small TiO₂ particle size. This lead to better encapsulation efficiencies compared to the hydrophobic particles. The poorer results obtained with the hydrophobic TiO₂ particles were attributed to their larger particle size, which resulted from the reduced adsorption of the OLOA370. Fewer hydroxyls and the presence of the trimethoxy octyl silane (TMOS) groups, which themselves are unable to provide sufficient steric stability, are proposed to explain these findings.     

Preparation of hydrophilic molecularly imprinted polymers for tetracycline antibiotics recognition

Hydrophilic molecularly imprinted polymers(MIPs) were prepared using tetracycline as template,methacrylic acid as monomer and glycidilmethacrylate as pro-hydrophilic co-monomer.Compared with common MIPs,the imprinting effect and adsorption amounts of hydrophilic MIPs for tetracycline(TC) were greatly improved in water media.Furthermore,the electrochemical sensor fabricated by modifying hydrophilic MIPs on glassy carbon electrode was developed for the determination of TC in foodstuff samples.     

Structure control in PMMA/silica hybrid nanoparticles by surface functionalization

Hydrophilic silica particles need to be hydrophobized to be encapsulated in a polymeric environment, which can be achieved by different methods. We report on the relationship between different hydrophobization techniques of silica and the final structure of poly(methyl methacrylate)/silica hybrid nanoparticles obtained by miniemulsion polymerization. Hydrophobization by cetyltrimethylammonium chloride (CTMA-Cl) uses the ionic interaction between the positively charged ammonium salt and the negatively charged silica surface, as shown by isothermal titration calorimetry. In this case, the interaction between polymer and silica surface needs to be enhanced, so 4-vinylpyridine (4-VP) was used as a co-monomer. Alternatively, the condensation reactions of 3-methacryloxypropyltrimethoxysilane (MPS) and octadecyltrimethoxysilane (ODTMS) were used to provide a covalent bond to the silica surface. The condensation reaction of the trimethoxysilane groups onto the silica surface was proven by Fourier transform infrared spectroscopy and thermogravimetric analysis. Hybrid nanoparticles were successfully formed with silica particles functionalized with the different functionalization agents. However, the structure of the resulting hybrid particles (i.e., the distribution of the silica particles within the polymer matrix) depends on the agent. The MPS-functionalized silica particles copolymerize with poly(methyl methacrylate), leading to a fixation of the silica particles inside the polymer and to a homogeneous distribution. The CTMA-Cl- and ODTMS-functionalized silica particles cannot copolymerize, but aggregate at the interface, leading to a Janus-like structure.     

Preparation of colored latex with polyurea shell by miniemulsion polymerization

Colored latexes with polyurea shell were prepared by applying interfacial polycondensation reaction to the miniemulsion polymerization process. These colored latexes were composed of polystyrene core and polyurea shell, and their particle size was adjusted to <100 nm. Diisocyanate was used as a hydrophobic monomer, and the equivalent mole of diamine was used as a hydrophilic monomer for interfacial polymerization. It was important to control the rate of interfacial polycondensation reaction in order to prepare small particles. Dye preservation property of colored latex loaded with oil-soluble dye was investigated. Polyurea shell formed at the surface of latex particles could restrain the migration of dyes from the latex particles and improve the dye preservation property. The ability to prevent dye migration depended on the composition of the polyurea shell.     

Preparation of functionalized polystyrene latexes by radiation-induced miniemulsion polymerization using a Y-type polymerizable surfactant as sole stabilizers

Functionalized polystyrene latexes were prepared by miniemulsion polymerization using a Y-type polymerizable surfactant bearing a carboxylic acid group as sole stabilizers. Kinetics analysis showed that there was no constant rate stage, which coincided with the kinetics mechanism of the typical miniemulsion polymerization. The latexes obtained were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. It was found that the latexes prepared by miniemulsion polymerization initiated by gamma-ray had more narrowly particle size distribution compared with by potassium persulfate. XPS and FTIR results indicated that the carboxyl group was present on the surface of the polymer particles.     

Antibacterial Activity of Polymeric Quaternary Ammonium Compounds Tuned by Incorporating Hydrophilic co-Monomer

Copolymers of quaternary ammonium monomer(QAM) and hydrophilic co-monomer were successfully synthesized by free radical polymerization. It was discovered that the hydrophilic co-monomers with poor antibacterial activity significantly enhanced the activity of QAM substituted with a long alkyl chain[i.e., N,N-dimethyl-N-dodecyl methacrylate ammonium bromide(DMAEMA-DB)]. When a suitable molar ratio of DMAEMA-DB to co-monomer was selected, the activity of the copolymers was up to 123 times that of the homopolymer of DMAEMA-DB against S. aureus, and 282 times that of it against E. coli. But unlike DMAEMA-DB, the co-monomers might weaken the activity of QAM substituted with a short alkyl chain[i.e., N,N-dimethyl-N-butyl methacrylate ammonium bromide(DMAEMA-BB)]. Moreover, it was found that copolymers of DMAEMA-DB were much more biocidal than those of DMAEMA-BB. Therefore, it could be speculated that the long alkyl chain plays an important role in the antibacterial activity, and that the hydrophilic co-monomers are beneficial to polymeric guaternary ammonium compounds(PQACs) to exert the positive effect of the long alkyl chain to the greatest degree.     

Synthesis of bio-based poly(methacrylates) using SG1-containing amphiphilic macroinitiators by nitroxide mediated miniemulsion polymerization

SG1-based amphiphilic macroinitiators were synthesized from oligoethylene glycol methyl ether methacrylate and 10 mol% acrylonitrile or styrene (as the controlling comonomer) to conduct the nitroxide mediated polymerization of bio-based methacrylic monomers (isobornyl methacrylate (IBOMA) and C13 alkyl methacrylate (C13MA)) in miniemulsion. The effect of the addition of surfactant (DOWFAX 8390), co-stabilizer (n-hexadecane) and different reaction temperatures (80, 90 and 100°C) on polymerization kinetics was studied. We found that the NMP of IBOMA/C13MA using amphiphilic macroalkoxyamines were most effective during miniemulsion polymerization (linear trend of M_n versus conversion and high latex stability) in presence of 2 wt% surfactant and 0.8 wt% co-stabilizer (relative to monomer) at 90°C. The effect of surfactant, co-stabilizer and temperature on particle size during the polymerization was studied and suggested a decrease in initial particle size with the addition of surfactant and co-stabilizer. Finally, the thermal properties of IBOMA/C13MA polymers, prepared by amphiphilic macroinitiators, were examined thoroughly, indicating a T_g in the range of −44°C < T_g < 109°C.     

Effects of addition of hydrophobic sucrose fatty acid oligoesters on crystallization rates of n-hexadecane in oil-in-water emulsions

Ultrasonic velocity measurements were made on crystallization rates of n-hexadecane dispersed in an oil-in-water (O/W) emulsion (20 wt.% oil and 80 wt.% water) in which Tween 20 was employed for emulsification. Highly hydrophobic emulsifiers, sucrose fatty acid oligoesters involving stearic acid (S-170), lauric acid (L-195) and oleic acid (O-170) moieties, were added to n-hexadecane in an attempt to modify the crystallization rate of n-hexadecane. The crystallization process of n-hexadecane was monitored by variations in the ultrasonic velocity values, which increase with increasing amount of crystal fractions in the oil phase of the emulsion. In comparison with the results of the O/W emulsion systems with the additive P-170 (a sucrose palmitate) (N.Kaneko et al., J. Crystal Growth 197 (1999) 263), the following results were obtained: (a) the addition of S-170 accelerated the nucleation in the emulsion system in the same manner as P-170, no acceleration was revealed with the additive O-170, and L-195 showed moderate effects; (b) the rate of crystal growth was retarded by S-170 and L-195, but not by O-170; (c) the effects of acceleration of nucleation occurred singly in the emulsion system, but not in the bulk system; and (d) the acceleration of nucleation was exhibited through two stages with increasing concentrations of the additives. These results showed the remarkable influence of the fatty acid chain structures of sucrose oligoesters on the acceleration of heterogeneous nucleation of n-hexadecane in the O/W emulsions. The heterogeneous nucleation effected by the addition of S-170 and P-170 was discussed taking into account the adsorption at the oil-water interface and the formation of reversed micelles of the sucrose oligoesters added in the oil phase.