Multihollow polymer microcapsules by water-in-oil-in-water emulsion polymerization: morphological study and entrapment characteristics

Multihollow cross-linked poly(methyl methacrylate) (PMMA) microcapsules were produced by water-in-oil-in-water emulsion polymerization and their applicability to encapsulate water-soluble ingredients was evaluated. In the microscopic analysis, all the PMMA microcapsules showed multihollow structures. In order to evaluate the entrapment efficacy, continuously, a water-soluble ingredient (monosodium phosphate, MSP) was incorporated into the inner voids of the microcapsules, and then its releasing profiles were measured with the storage conditions in pure water. In the releasing test, it was observed that the degree of cross-linking of PMMA had a significant influence on the migration of MSP through the polymer phase. At a sufficient degree of cross-linking of the polymer phase, the leakage of MSP out of the microcapsules was stopped successfully. It is believed that the extremely small network size and the mechanically strong network structure hindered effectively the water flow caused by the concentration gradient between water-soluble ingredients.     

Quantitative analysis of polymer additives in low density polyethylene using supercritical fluid extraction/supercritical fluid chromatography

Analysis of low concentration polymer additives has been a challenging problem. The commonly used methods of analysis involve the initial extraction of polymer additives with solvents, often in a Soxhlet apparatus, followed by liquid, size exclusion, or gas chromatography. This paper describes the on-line super-critical fluid extraction (SFE)-supercritical fluid chromatographic (SFC) determination of different additives from low density polyethylene. Cryogenic collection was used as an interface between SFE and SFC to focus the extraction eluate before transfer to an analytical SFC column for quantitative analysis.     

PMMA/PS纳米复合材料的制备及分散相稳定性研究

纳米复合材料具有许多优异的性能,但是由于纳米粒子常常很难以纳米尺寸均匀地分散在基体中,有时即使实现了纳米级分散,在后加工或应用过程中又会发生二次团聚,使得纳米材料的特性不能充分发挥．因此,要获得性能优异的纳米复合材料首先必须解决纳米材料在基体中的均匀、稳定分散问题．     

Cellulose acetate/poly(methyl methacrylate) interpenetrating networks: synthesis and estimation of thermal and mechanical properties

IPN-type composites consisting of cellulose acetate (CA) and poly(methyl methacrylate; PMMA) were successfully synthesized in film form. In this synthesis, a mercapto group (SH)-containing CA, CA-MA, was prepared in advance by esterification of CA with mercaptoacetic acid, and then intercomponent cross-linking between CA-MA and PMMA was attained by thiol–ene polymerization of methyl methacrylate (MMA) onto the CA-MA substrate. For comparison, polymer synthesis was also attempted to produce a semi-IPN type of composites comprising CA and cross-linked PMMA, via copolymerization of MMA and ethylene glycol dimethacrylate as cross-linker in a homogeneous system containing CA solute. Thermal and mechanical properties of thus obtained polymer composites were investigated by differential scanning calorimetry, dynamic mechanical analysis, and a tensile test, in correlation with the mixing state of the essentially immiscible cellulosic and methacrylate polymer components. It was shown that the specific IPN technique using thiol–ene reactions usually resulted in a much better compatibility-enhanced polymer composite, which exhibited a higher tensile strength and even an outstanding ductility without parallel in any film sample of CA, PMMA, and their physical blends.     

Synthesis of cross-linked poly(methyl methacrylate) via dispersion polymerization in supercritical carbon dioxide

Cross-linked poly(methyl methacrylate) particles were prepared via dispersion polymerization in supercritical carbon dioxide (scCO₂) using poly(heptadecafluorodecyl methacrylate) (PHDFDMA) and 2,2′-azobisisobutyronitrile as the dispersant and the initiator, respectively. The following chemicals were used as cross-linking agents: ethylene glycol dimethacrylate (EGDMA), 1,4-buthanediol di(meth)acrylate (1,4-BD(M)A), and trimethylolpropane trimethacrylate. PHDFDMA was synthesized by solution polymerization in scCO₂. We investigated the effect of the chemical structure, concentration of the cross-linking agents, reaction pressure, and CO₂ density on the morphology, the polydispersity, and the cross-linking density of polymer particles. The resulting polymer particle was characterized by field emission SEM, differential scanning calorimetry, and thermal gravimetric analysis. The cross-linked PMMA particles is more agglomerate as the cross-linking agent concentration increased and as pressure decreased at constant temperature. Glass-transition temperature (T _g) of the resulting polymer increased as the cross-linking agent increased with temperature and pressure increasing at the same CO₂ density. Decomposition temperature is slightly increased as 1,4-BDA concentration increased. From these results, we can confirm that the thermal stability of the polymer increased as the cross-linking agent and EGDMA is the best cross-linking agent in term of the thermal stability.     

Characterisation of macroporous poly(methyl methacrylate) coated with plasma-polymerised poly(2-hydroxyethyl acrylate)

Macroporous poly(methyl methacrylate) networks with varying cross-linking density and porosity were coated with plasma-polymerised poly(2-hydroxyethyl acrylate) grafted on the pores surface. The result is a mechanically reinforced hydrogel (PMMA-gr-plPHEA) whose properties are characterised in this work using several experimental techniques. Bulk PMMA and bulk PHEA were also characterised as reference materials. The diffusion and water sorption properties of these hydrogels were studied through equilibrium water sorption isotherms and desorption starting with the sample equilibrated in immersion in liquid water or in a vapour atmosphere. Glass transition, dynamic-mechanical relaxation and thermal degradation were characterised in order to study the interphase interaction in these biphasic systems. All these experimental techniques suggested that plasma-polymerised PHEA is more homogeneously interpenetrated with highly cross-linked macroporous PMMA than if the porous substrate is a loosely cross-linked polymer network.     

A Facile Photo-cross-linking Method for Polymer Gate Dielectrics and Their Applications in Fully Solution Processed Low Voltage Organic Field-effect Transistors on Plastic Substrate

A simple and effective photochemical method was developed for cross-linking of polymer gate dielectrics.Laborious synthetic processes for functionalizing polymer dielectrics with photo-cross-linkable groups were avoided.The photo-cross-linker,BBP-4,was added into host polymers by simple solution blending process,which was capable of abstracting hydrogen atoms from polymers containing active C―H groups upon exposure to ultraviolet(UV) radiation.The cross-linking can be completed with a relatively long wavelength UV light(365 nm).The approach has been applied to methacrylate and styrenic polymers such as commercial poly(methylmethacrylate)(PMMA),poly(iso-butylmethacrylate)(Pi BMA) and poly(4-methylstyrene)(PMS).The cross-linked networks enhanced dielectric properties and solvent resistance of the thin films.The bottom-gate organic field-effect transistors(OFETs) through all solution processes on plastic substrate were fabricated.The OFET devices showed low voltage operation and steep subthreshold swing at relatively small gate dielectric capacitance.     

Thermotropic liquid-crystal/polymer microcapsules prepared by in situ suspension polymerization

In this study, thermotropic liquid-crystal/polymer microcapsules were produced via in situ suspension polymerization. The phase separation between cholesteryl liquid crystal (CLC) and poly(methyl methacrylate) (PMMA) in the droplets was induced by polymerization, resulting consequently in uniform liquid-crystal-containing polymer microcapsules. The phase behavior of the microcapsules was dependent on the loading amount of the liquid crystals and the degree of cross-linking of the polymer phase. Above 30% loading amount of CLC, the liquid crystals started to appear clearly. It was found that the spherical morphology of the microcapsules was achieved within a slight degree of cross-linking of the PMMA phase. At a high degree of cross-linking, nonspherical particles with a rough surface and deeper dents were obtained, which was due to the elastic-retractive force of the cross-linked network. The liquid-crystal/polymer microcapsules produced in this study could find great applicability in pharmaceutics and electronics as a smart drug carrier.     

The morphology of composite polymer particles produced by multistage soapless seeded emulsion polymerization

 Composite polymer particles which contain poly(methyl methacrylate) (PMMA) and polystyrene (PS) components (PMMA/PS composite particle) were synthesized by the method of multistage soapless seeded emulsion polymerization. In this study, the process of multistage soapless seeded emulsion polymerization included two-stage polymerization, three-stage polymerization or four-stage polymerization. The morphologies of the PMMA/PS composite particles were studied. The kinetic factor was the main force to control the morphology of the linear PMMA–PS composite particles which were synthesized by the method of two-stage reaction. Both the kinetic factor and the thermodynamic factor decide the morphology of the linear composite particles which were synthesized by the method of either three-stage or four-stage reaction. However, the thermodynamic factor cannot influence the morphology of the PMMA/PS composite particles with a cross-linked structure which were synthesized by the method of three-stage reaction. The cross-linked composite polymer particles had the morphology of a multilayer structure, which showed that the polymer layers accumulated in their order of production. Received: 9 January 2001 Accepted: 14 June 2001     

Gel permeation chromatography – Atmospheric pressure chemical ionization – Mass spectrometry for characterization of polymer additives

The study presents the possibility to use gel permeation chromatography (GPC) with atmospheric pressure chemical ionization (APCI)-mass spectrometry for the analysis of polymer additives having molecular weights up to 2,000?g?mol^?1. Irganox 1010, Irganox 1035, Irganox 1076, and Irganox 3114 were analyzed in chloroform using 2.1-mm-internal-diameter GPC columns at the optimum flow rate of 50?µL min^?1. Based on the chemical formula, the APCI interface combined with chlorine ionization enabled us to predict the expected mass spectrum and to build libraries without needing to inject each additive separately. Quantification limits of about 100?µg of additive in 1?g of polymer (100?ppm) can be reached using single-ion-monitoring methods based on the calculated isotope distribution.     

A novel method for encapsulation of a liquid crystal in monodisperse micron-sized polymer particles

Liquid crystals (LCs) encapsulated in monodisperse micron-sized polymer particles were prepared to control the size and size distribution of LC droplets in polymer-dispersed LCs. The poly(methyl methacrylate) (PMMA) seed particles were swollen with the mixture of liquid crystal, monomers (methyl methacrylate and styrene) and initiator by using a diffusion-controlled swelling method. A single LC domain was produced by the phase separation between PMMA and LC through polymerization. The optical microscopy and scanning electron microscopy showed that the particles are highly monodisperse with core–shell structure. Moreover, monodisperse LC core domains were confirmed from polarized optical microscope observations. The final particle morphology was influenced by the cross-linking of the seed particle. When linear PMMA particles, which are not cross-linked, were used as a seed, the microcapsules were distorted after annealing for a few days; however, in the case of cross-linked PMMA particles, the core–shell structure was sustained stably after annealing. Received: 22 November 2000 Accepted: 12 March 2001     

Analysis of citrates and benzoates used in poly(vinyl chloride) by supercritical fluid extraction and gas chromatography

Supercritical fluid extraction (SFE) has been demonstrated to be a useful tool in the determination of additives in polymeric materials. This paper describes the determination of some citrates and benzoates in poly(vinyl chloride) blended with 33–34% of plasticizer using off-line SFE followed by gas chromatography. Experimental factors affecting SFE have been studied by gravimetric analysis, followed by analysis of the extracts using a gas chromatograph equipped with a flame ionization detector. The extraction process is governed by the solubility of the plasticizers in the supercritical fluid or by their diffusion through the polymer matrix, which depend on the pressure and temperature used. Maximum extraction (>99%) is obtained at pressures and temperatures higher than 40 MPa and 80 °C, respectively. Due to purge losses, the collection efficiency of plasticizers into a liquid solvent ranges from 85 to 90%. The applicability of the SFE method is demonstrated using real samples and comparing the results with those obtained by conventional Soxhlet extraction.     

Stabilization of superparamagnetic iron oxide nanoclusters in concentrated brine with cross-linked polymer shells

Iron oxide nanoparticles, in the form of sub-100-nm clusters, were synthesized in the presence of poly(acrylic acid) (PAA) or poly(styrene sulfonate-alt-maleic acid) (PSS-alt-MA) to provide electrosteric stabilization. The superparamagnetic nanoclusters were characterized using a superconducting quantum interference device (SQUID), transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and zeta potential measurements. To anchor the polymer shell on the nanoparticle surface, the polymer was cross-linked for a range of cross-linking densities. For nanoclusters with only 12% (w/w) PSS-alt-MA, electrosteric stabilization was sufficient even in 8 wt % NaCl. For PAA, the cross-linked polymer shell was essentially permanent and did not desorb even upon dilution of the nanoparticles for iron oxide concentrations down to 0.014 wt %. Without cross-linking, over half of the polymer desorbed from the particle surfaces. This general approach of the adsorption of polymer stabilizers onto nanoparticles followed by cross-linking may be utilized for a wide variety of cross-linkable polymers without the need to form covalent bonds between the nanoparticles and polymer stabilizer. Thus, this cross-linking approach is an efficient and inexpensive method of stabilizing nanoparticles for large-scale applications, including the electromagnetic imaging of subsurface reservoirs, even at high salinity.     

Energy transfer and radical formation in the system poly(methyl methacrylate)–2-methyltetrahydrofuran

ESR spectra of γ-irradiated poly(methyl methacrylate) (PMMA) at 77°K and the effect of additives have been studied. γ-Irradiation of PMMA containing a small amount of 2-methyltetrahydrofuran as an additive at 77°K gives MTHF radical. Yields of MTHF radical increase with increasing MTHF concentration and reach a plateau value, and are independent of photobleaching with visible light. Yeilds of polymer radical are reduced by the addition of MTHF. Some elementary processes for the MTHF radical formation are proposed on the basis of the experimental results.     

Supercritical Fluid Extraction (SFE) Optimization by Full-Factorial Design for the Determination of Irganox 1076, Irgafos 168, and Chimassorb 81 in Virgin and Recycled Polyolefins

The performance and feasibility of supercritical fluid extraction (SFE) applied to the extraction of some antioxidants (Irganox 1076, Irgafos 168) and one UV-stabilizer (Chimassorb 81) from both virgin and recycled low density polyethylene (LDPE), and virgin high density polyethylene (HDPE) are studied. Due to the high number of variables a full-factorial design has been applied to minimize the number of experiments required to reach the optimum extraction conditions. Further analysis has been carried out off-line by reversed-phase HPLC. Modification of the physical properties of the polymeric matrix and increased number of recycling cycles as well as the influence of physical properties on the efficiency of SFE are also discussed.     

Evaluation of the effect of additives on thermo-oxidative and hydrolytic stabilization of recycled post-consumer poly (ethylene terephthalate) using Design of Experiments

The recycling of poly (ethylene terephthalate) (PET), mainly from bottles, has been considered the most promising alternative to reduce municipal solid waste in Brazil. Stabilization processes of this polymer during recycling aim to maintain and improve its physicochemical properties and enhance its applicability. Several classes of additives may be used for PET stabilization, such as antioxidants, metal deactivator or anti-hydrolysis. However, there are no studies in literature about the synergistic or antagonistic effect of the individual or combined use of these additives for the stabilization of PET. The present investigation uses Design of Experiments (DoE) to analyze the effects of the variables that influence the stabilization of post-consumer PET. The variables were humidity and three different classes of additives represented by antioxidants (Irganox 1010® and Irganox B561®), a metal deactivator (Irganox MD1024®) and an anti-hydrolysis (Stabaxol KE7646®), known as polycarbodiimide. Taking intrinsic viscosity into consideration, the post-consumer PET flakes were processed with different additive contents in order to understand both the individual and combined effects that influence stabilization and generate the response surfaces. The results showed that the samples stabilized with polycarbodiimide had an effective increase in intrinsic viscosity. In addition, samples stabilized with antioxidants had lower contribution and the metal deactivator had no effect on the stabilization of recycled PET. Our findings indicate that the hydrolysis overlaps the thermo-oxidative degradation effects and is the main form of PET degradation in the course of recycling. Moreover, besides being marketed as an anti-hydrolysis, results suggest polycarbodiimide is an effective chain extender. Finally, this study sheds some light on the influence of the main additives and variables that influence the degradation and stabilization of PET. The increase in PET intrinsic viscosity promotes its physicochemical properties and allows the recycled polymer to be used in broader market segments.     

Effect of hyperbranched surface-migrating additives on the electrospinning behavior of poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA) was electrospun in the presence of a low molecular weight, hyperbranched poly(ethylene imine) additive partially functionalized with perfluorinated and aliphatic end-groups (M(n) approximately 1600 g/mol). The additive exhibited surface segregation with an insignificant influence on the rheological behavior of PMMA solutions. A morphological transition from beaded electrospun fibers to uniform fibers was observed upon introduction of additive at low PMMA concentrations. XPS revealed a surface enrichment of fluorine and nitrogen, which are both present in the hyperbranched additive. Surface fluorine content depended primarily on the amount of additive in solution, and a dependency on the PMMA/additive weight ratio was not observed.     

Extraction and Quantitation of Polyolefin Additives

Abstract

The extraction and subsequent separation and quantitation of polymer additives in polyolefins has proven to be a challenge for the analytical chemist. There have been several workers over the years who have investigated the separation of additives in polyolefins (1–7), but the extraction and recovery (at > 90%) in reasonable times has been most difficult. the Soxhlet extraction technique has been used for many years, but suffers in that it takes over twelve hours to extract most of the additives used in polyolefin formulations. Some workers have used the ultrasonic bath (7), but not very much work has been done with the microwave oven. We have investigated some ways to extract the additives from polyolefins, namely, microphye oven and ultrasonic bath techniques for high density polyethylene (HDPE), low density polyethylene (LDPE), and polypropylene. We have concentrated on identifying and quantitating recoveries for typical polyolefin

antioxidants, 20 such as Irganox 1010, Irgafors 68, and Cyasorb UV 531. the extraction times are typically 20 minutes for the microwave oven and 30–60 minutes for the ultrasonic bath with 90+% recoveries being obtained. Both normal phase isocratic (used when phosphites are present) and reverse phase gradient LC techniques are discussed. We have also extracted the slip agent, erucamide, from LDPE, using reverse phase, at 200nm.     

Miscible blends of amorphous polymers

Thirty-five polymethacrylate/chlorinated polymer blends were investigated by differential scanning calorimetry. Poly(ethyl), poly(n-propyl), poly(n-butyl), and poly(n-amyl methacrylate)s were found to be miscible with poly(vinyl chloride) (PVC), chlorinated PVC, and Saran, but immiscible with a chlorinated polyethylene containing 48% chlorine. Poly(methyl) (PMMA), poly(n-hexyl) (PHMA), and poly(n-lauryl methacrylate)s were found to be immiscible with the same chlorinated polymers, except the PMMA/PVC, PMMA/Saran, and PHMA/Saran blends, which were miscible. A high chlorine content of the chlorinated polymer and an optimum CH₂/COO ratio of the polymethacrylate are required to obtain miscibility. However, poly(methyl), poly(ethyl), poly(n-butyl), and poly(n-octadecyl acrylate)s were found to be immiscible with the same chlorinated polymers, except with Saran, indicating a much greater miscibility of the polymethacrylates with the chlorinated polymers as compared with the polyacrylates.     

The crystallinity and miscibility of syndiotactic polystyrene blends after mixing with low molar mass liquid crystal or commercial lubricant

The quantities of the crystallinity of syndiotactic polystyrene (SPS) blended with another polymer in the group of poly(α-methyl styrene), poly(n-butyl methacrylate) or poly(cyclohexyl acrylate) with or without the additives were measured by X-ray diffraction and calculated by Ruland’s method. The SPS was synthesized by using metallocene catalyst and modified-methylaluminoxane as cocatalyst. The additive of low molar mass liquid crystal chemical (cyclohexyl-biphenyl-cyclohexane (CBC33)) or lubricant (glycerol monostearate (GMS)) was individually added to the blends of SPS in order to investigate the effects on the crystallinity of the blended SPS. From the experimental results, it was found that the percent crystallinities of the blends decreased with decreasing the percent of SPS in the blend because of the dilution of SPS. The depression of the percent crystallinity was in the order of PaMS > PCHA > PBMA according to the compatibility with SPS. The addition of GMS or CBC33 slightly decreased the percent crystallinity of the pure SPS. The addition of GMS impeded the depression of the SPS crystallinity in the blends, because their percent depression from pure SPS is similar (at around 25%) regardless to the components of the blends. The blends with added CBC33 have the similar depression of crystallinity as the pure blends because of the low concentration of CBC33 and the good compatibility of CBC33 with the SPS.