The characterization of latex particles prepared by pulsed electron beam induced emulsion polymerization

The emulsion polymerization of styrene (St) and methyl methacrylate (MMA) induced by 10 MeV pulsed electron beams (PEB) was investigated. The monomer conversion of MMA and St was found to be very low so that the final prepared poly(methyl methacrylate) (P(MMA)) and polystyrene (PS) latex particles exhibit porous structures, as verified by TEM and SEM observations. The results of dynamic light scattering (DLS) and gel permeation chromatography (GPC) showed that both the particle size and the molecular weight of PS and PMMA latexes decrease with the increase of the absorbed dose. However, the molecular weights and the particle sizes of the PS and PMMA latexes change differently with the irradiation time. This work indicated that emulsion polymerization induced by high energy electron beam has an advantage over that induced by γ-ray or chemical initiators in the preparation of latex with a low molecular weight and porous structure.     

The effect of molecular properties on mechanical behaviour of PMMA—III. Environmental stress crazing in methanol

The correlation between the stress-relaxation curves of methanol-equilibrated poly(methyl methacrylate) (PMMA) and environmental fracture behaviour indicates the role of molecular entanglements in determining if the fracture process of PMMA in methanol occurs via stress-cracking (Regime II) or stress-crazing (Regime I and Transition Regime). The fracture data for high molecular weight (MW) PMMA (Regime I) and medium MW PMMA (Transition Regime) were analyzed by linear, elastic fracture-mechanics (LEFM) and Williams-Marshall (WM) theory. High MW PMMA absorbed more energy and had a wider crack-opening-displacement (COD) than medium MW PMMA, due to a thicker primordial craze thickness. Craze matter in the high MW sample gave a slower crazing stress decay and a better stretching capability with time than that of medium MW sample. The craze-initiation and the craze-growth obeyed a flow-controlled mechanism and relaxation-controlled mechanism, respectively.     

Composition and origin of trace elements in fog water studied by INAA

Characterization of dilute solution of gamma-irradiated polymethyl methacrylate (PMMA) in acetone has been carried out. The polymer sample in form of natural beads was administered a gamma-ray dose of 30 kGy by a cobalt-60 radiationsource. Various types of viscosities, viscosity average molecular weight, shape and size of irradiated PMMA and its two fractions were calculated. The results were compared with those for unirradiated PMMA. Degradation of PMMA as a result of irradiation has been observed.     

Fracture surface morphology and phase relationships of polystyrene/poly(methyl methacrylate) systems. I. Low-molecular-weight polystyrene in poly(methyl methacrylate)

Samples of low-molecular-weight polystyrene (PS) in poly(methyl methacrylate) (PMMA) were prepared by first dissolving PS in methyl methacrylate monomer and then polymerizing the monomer. Forty-three specimens of varying number-average molecular weight (2100–49,000) and composition (5–40 wt %) of PS were prepared, and the surface morphology and phase relationships studied by scanning electron microscopy. Four distinct types of phase relationships were observed: (i) a single phase consisting of PS dissolved in PMMA; (ii) PS dispersed in PMMA; (iii) PMMA dispersed in PS; and (iv) regions of PS dispersed in PMMA coexisting with regions of PMMA dispersed in PS. Values of the size and population density of the dispersed particles are reported. Finally, the size and distribution of the dispersed particles and the various types of phase relationships are discussed in terms of the ternary polystyrene/poly(methyl methacrylate)/methyl methacrylate phase diagram.     

Synthesis of cardanol-based photo-active SET-LRP initiator and its application to preparation of UV-cured resin

A benzophenone-containing SET-LRP initiator based on renewable and abundant cardanol was synthesised in 71 % yield using the selective etherification reaction. Next, methyl methacrylate (MMA) as a monomer was polymerised under SET-LRP conditions using the newly prepared initiator to prepare cardanol-end poly(methyl methacrylate) (PMMA). The kinetic results of the polymerisation indicated that the reaction was controllable when the monomer conversion was lower than approximately 50 %, and the molecular masses of PMMA measured by GPC were higher than the theoretical values while the monomer conversion was more than 50 %. In addition, most of the carbon-carbon double bonds of the side hydrocarbon chain of the end-cardanol group in the PMMA were kept intact from ¹H NMR spectrum characterisation. Accordingly, when the cardanol-end PMMA together with a tertiary amine-containing cardanol derivative was irradiated by UV light, the corresponding UV-cured resin was obtained. The chemical resistance and hardness of the UV-cured film were enhanced with the increasing irradiation time.     

The effect of molecular properties on the mechanical behaviour of PMMA—IV. The role of chain entanglements in fracture processes

The fracture-toughness—entanglement correlation was shown to be a more fundamental concept than the fracture-toughness—glass transition temperature or the fracture-toughness—solubility-parameter correlations in predicting the effect of molecular weight, molecular weight distribution, stereoregularity and temperature on the fracture behaviour of poly(methyl methacrylate) (PMMA). Morphological study of the fracture surface by scanning electron microscopy (SEM) of high molecular weight PMMA in good and bad solvents and blends of isotactic PMMA and low molecular weight atactic PMMA supports the relationship between molecular entanglements and fracture behaviour. The entanglement network at the crack tip determines whether failure occurs in solvents by rapid stress-cracking or stress-crazing with long-craze growth.     

Large core-shell poly(methyl methacrylate) colloidal clusters: synthesis, characterization, and tracking

We present a multistep procedure yielding large (diameter > 2 μm) monodisperse, fluorescently labeled core-shell poly(methyl methacrylate) (PMMA) latex particles via dispersion polymerization. The particles' physical properties were controlled by adjusting two reaction parameters, the initiator and chain transfer agent concentrations, which influence the molecular weight of the PMMA. Under certain conditions, particles with the requisite properties for fabricating colloidal clusters were synthesized. The resulting clusters represent a new type of nonspherical colloid that can be dispersed in a density- and refractive index-matching solvent, making them ideal for quantitative studies using confocal microscopy. To demonstrate the utility of our clusters, we measured the translational and rotational diffusion coefficients of a tetrahedral cluster by tracking the motion of its constituent particles in three-dimensional space. More broadly, our findings provide new insights concerning PMMA dispersion polymerization in apolar media.     

Mechanistical studies on the electron-induced degradation of polymethylmethacrylate and Kapton

Mechanisms for the electron-induced degradation of poly(methyl methacrylate) (PMMA) and Kapton polyimide (PMDA-ODA), both of which are commonly used in aerospace applications, were examined over a temperature range of 10 K to 300 K under ultra high vacuum (～10(-11) Torr). The experiments were designed to simulate the interaction between the polymer materials and secondary electrons produced by interaction with galactic cosmic ray particles in the near-Earth space environment. Chemical alterations of the samples were monitored on line and in situ by Fourier-transform infrared spectroscopy and mass spectrometry during irradiation with 5 keV electrons and also prior and after the irradiation exposure via UV-vis. The irradiation-induced degradation of PMMA resulted in the formation and unimolecular decomposition of methyl carboxylate radicals (CH(3)OCO) forming carbon monoxide (k = 4.60 × 10(-3) s(-1)) and carbon dioxide (k = 1.29 × 10(-3) s(-1)). Temperature dependent gas-phase abundances for carbon monoxide, carbon dioxide, and molecular hydrogen were also obtained for the PMMA and Kapton samples. The lower gas yields detected for irradiated Kapton were typically one or two orders of magnitude less than PMMA suggesting a higher degradation resistance to energetic electrons. In addition, UV-vis spectroscopy revealed the propagation of conjugated bonds induced by the irradiation of PMMA and indicated a decrease in the optical band gap by an increase in absorbance above 500 nm in irradiated Kapton.     

Seed Dispersion Polymerization to Micron-Size Monodisperse Polymer Particles

Abstract

Seed dispersion polymerization of methyl methacrylate (MMA) in the presence of monodisperse PMMA particles was carried out in an aqueous methanol using poly(methacrylic acid) stabilizer. The polymerization using 2. 5 μ. m-sized seed particles gave monodisperse PMMA particles in the diameter up to 4. 9 μm. The solvent composition and monomer concentration greatly affected the polymerization behavior. Under appropriate conditions, monodisperse PMMA particles in the diameter up to 8. 9 μ, m was prepared from 4. 6 μm-sized seed particles. The seed dispersion polymerization of styrene in the presence of the seed particles produced monodisperse PMMA-polystyrene particles in the micron range. The particles were supposed to have a structure consisting of PMMA-core and polystyrene-shell from ESCA analysis.     

Radiation-induced heterogeneous polymerization of methyl methacrylate in precipitants

The radiation-induced heterogeneous polymerization of methyl methacrylate in various precipitants, mainly methyl alcohol, was carried out, and the effects of reaction conditions on the polymerization behavior and the molecular weight distribution of polymer were studied. Bimodal molecular weight distributions were found for the polymer produced by the heterogeneous polymerizations in methyl alcohol and in tert-butyl alcohol. The apparent activation energy is 1.0 and 4.5 kcal/mole, respectively, for the polymerization at a monomer concentration of 10 vol-% in methyl alcohol above and below 35°C. The polymerization at a monomer concentration lower than 40 vol-% in methyl alcohol proceeded with the precipitation of polymer. The dose rate exponent of the mean rate of heterogeneous polymerization decreased from 0.5 to a smaller value as the polymerization progressed. The ratio of the two peaks in the bimodal molecular weight distributions of polymer produced in methyl alcohol was affected by the reaction conditions. These results show the coexistence in the polymerizations of two different physical states of propagating chain, a loose state and a rigid one. The reaction scheme is discussed in connection with the physical factors which affect the solubility or the mobility of propagating chains, and the rate of elementary reactions, which influences the degree of propagating chains.     

Effect of Tacticity of Poly(Methyl Methacrylate) on Conductivity of Poly(Ethylene Oxide)-Poly(Methyl Methacrylate) Blend-Based Polymeric Electrolytest

Abstract

Polymer electrolytes based on blends of poly(ethylene oxide) (PEO) with various stereoisomers of poly(methyl methacrylate) (PMMA) were studied by means of impedance spectroscopy and DSC. It was found that isotactic poly(methyl methacrylate) (1PMMA)-based electrolytes exhibit ambient temperature conductivities at least one order of magnitude higher than the electrolytes containing other stereoisomers of PMMA. The highest value of room temperature conductivity equal to 9 × 10^?5 S/cm was measured for a sample containing 30 wt% IPMMA. The effect observed results from the presence of a flexible amorphous phase in PEO-IPMMA blends which is favorable for fast ionic transport. A small increase of ionic conductivity with decreasing molecular weight of the added atactic poly(methyl methacrylate) was also observed.     

Thermal and photo induced reactions in blends of polypropylene and poly(methyl methacrylate)

Thermal Volatilization Analysis (TVA) demonstrates that poly(methyl methacrylate) (PMMA) is stabilized by blending with polypropylene (PP). Although well-defined radical reactions occur in both polymers under 2537 Å radiation, there is no evidence of the formation of block or graft copolymers when blends of the two are irradiated. Preirradiation suppresses the amount of monomeric methyl methacrylate formed on subsequent thermal degradation. The missing methyl methacrylate units appear in the chain fragment fraction. The characteristics of the thermal degradation of blends of unirradiated PP with preirradiated PMMA are similar to those of unirradiated rather than pre-irradiated blends, thus emphasizing the importance of the PP component in determining the thermal stability of blends after irradiation. These observations are discussed mechanistically.     

用微模塑直接在聚合物曲面上制备微图形

用聚二甲基硅氧烷制备的,表面复制有微图形的"弹性印章"直接在聚乙烯,聚丙烯,聚苯乙烯和聚甲基丙烯酸甲酯等热塑性聚合物表面上进行热微模塑,无需复杂设备并可在普通实验室条件下,复制微图形,甚至在小试管外壁的曲面上或在用毛细管形成的微突起表面上也能制备出微曲面图形.讨论了不同聚合物对生成微图形的影响,认为结晶性聚合物以及在温度变化时有较大收缩率的聚合物在微模塑中难以获得清晰图形.无定形聚合物如聚苯乙烯和聚甲基丙烯酸甲酯等能够获得清晰的微结构.     

Controlling the size of nanostructures in thin films via blending of block copolymers and homopolymers

The effects of molecular weight and concentration of poly (methyl methacrylate) (PMMA) homopolymer or symmetric short polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer on the size of the nanostructures of its blends with symmetric long PS-b-PMMA diblock copolymer have been investigated by atomic force microscopy. By careful controlling of the film thickness, solvent selectivity, and annealing time, PMMA cylindrical microdomains oriented normal to the film surface were obtained in all thin films. With the addition of both low- and high-molecular-weight PMMA homopolymers, the cylindrical domain sizes increased although it was less obvious for the lower molecular weight homopolymer. In contrast to the homopolymer, adding the short chain diblock copolymer resulted in a decrease in the cylindrical domain size, which was ascribed to the reduction of the interfacial tension and increase in the stretching energy.     

Effect of chain transfer agent on the radiation grafting of methyl methacrylate onto chromium(III) crosslinked collagen

Thioglycolic acid is an efficient agent for controlling the lengths of poly(methyl methacrylate) (PMMA) chains grafted onto collagen. The addition of 0.006 mol of thioglycolic acid per one mol of methyl methacrylate (MMA) has no effect on the yield of grafting, but brings about a decrease in the molecular weight of grafted PMMA by about 50%. The mechanism of the grafting reaction in the presence of the chain transfer agent thioglycolic acid is discussed on the basis of the results.     

Radiation induced effects on the microhardness measurements of poly(methyl methacrylate): poly (vinylidene fluoride) polyblends

Solution-mixed poly(methyl methacrylate) (PMMA): poly(vinylidene fluoride) (PVDF) polyblends with different weight percentage ratios were irradiated with various doses of gamma irradiation (1–100 Mrad). The effect of irradiation on the strength of blend specimens was studied by measuring the surface microhardness using a Vickers microhardness tester attached to a Carl Zeiss NU-2 Universal research microscope. The irradiation was found to produce hardening in the blend specimens; however, the degree of hardening depends upon the dose level, testing conditions and also on the miscibility of PMMA and PVDF in the blend specimens. The increase and decrease in microhardness has been explained on the basis of crosslinking and scissioning. The two limits of irradiation dose were 1 and 75 Mrad where significant changes in mechanical strength were observed.     

Thermal Decomposition and Glass Transition Temperature of Poly(methyl Methacrylate) and Poly(isobutyl Methacrylate)

Abstract

The thermal decomposition and the glass transition temperatures of poly(methyl methacrylate) (PMMA) and poly(isobutyl methacrylate) (PiBuMA) were studied with a differential scanning calorimeter (DSC). The undecomposed and decomposed polymers were analyzed by gel permeation chromatography (GPC) for molecular weight distributions and by DSC for changes in the thermal properties and glass transition temperatures, T. In the isothermal decomposition of PMMA and PiBuMA, depolymerization reactions exclusively are operative. During low temperature decompositions, longer PMMA chains depolymerize first. These are followed by the shorter chains. In the case of PiBuMA, the shorter chains depolymerize first. Some of these undergo chain recombinations to yield very high molecular weight products. For identical values of weight loss, the respective decomposition temperatures for PiBuMA are 40 to 70 K lower than those for PMMA. The activation energies of decomposition (42 kJ/mol for PMMA and 67 kJ/mol for PiBuMA) have been found to be lower than those reported in the literature. Although T_g∞ of PiBuMA (331 K) agrees well with the literature value (326 K), T_g∞ of atactic PMMA (394 K) is higher than the reported value (378 K).     

Synthesis of core/shell structure of glycidyl–functionalized poly(methyl methacrylate) latex nanoparticles via differential microemulsion polymerization

The differential microemulsion polymerization technique was used to synthesize the nanoparticles of glycidyl-functionalized poly(methyl methacrylate) or PMMA via a two-step process, by which the amount of sodium dodecyl sulfate (SDS) surfactant required was 1/217 of the monomer amount by weight and the surfactant/water ratio could be as low as 1/600. These surfactant levels are extremely low in comparison with those used in a conventional microemulsion polymerization system. The glycidyl-functionalized PMMA nanoparticles are composed of nanosized cores of high molecular weight PMMA and nano-thin shells of the random copolymer poly[(methyl methacrylate)-ran-(glycidyl methacrylate)]. The particle sizes were about 50 nm. The ratios of the glycidyl methacrylate in the glycidyl-functionalized PMMA were achieved at about 5–26 wt.%, depending on the reaction conditions. The molecular weight of glycidyl-functionalized PMMA was in the range of about 1 × 10⁶ to 3 × 10⁶ g mol⁻¹. The solid content of glycidyl-functionalized PMMA increased when the amount of added glycidyl methacrylate was increased. The glycidyl-functionalized polymer on the surface of nano-seed PMMA nanoparticles was a random copolymer which was confirmed by ¹H-NMR spectroscopy. The amounts of functionalization were investigated by the titration of the glycidyl functional group. The structure of the glycidyl-functionalized PMMA nanoparticles was investigated by means of TEM. The glycidyl-functionalized PMMA has two regions of T_g which are at around 90 °C and 125 °C, respectively, of which the first one was attributed to the poly[(methyl methacrylate)-ran-(glycidyl methacrylate)] and the second one was due to the PMMA. A core/shell structure of the glycidyl-functionalized PMMA latex nanoparticles was observed.     

Thermogravimetric analysis of thermal stability of poly(methyl methacrylate) films modified with photoinitiators

Films of poly (methyl methacrylate) (PMMA) were prepared by the addition of photoinitiator to the polymer. The influence of five organic photoinitiators on thermal stability of poly(methyl methacrylate) was studied by thermogravimetric analysis. Next, the PMMA films doped with these photoinitiators were UV irradiated and investigated in terms of changes in their thermal stability. It was found that the photoinitiators had accelerated thermal degradation of non-irradiated PMMA films due to the action of free radicals coming from the additives’ thermolysis. For UV-irradiated specimens, the effect of photoinitiator on PMMA thermal stability depended on the chemical structure of organic compound modifying the polymer. In general, thermal stability of irradiated samples was higher in the presence of additives. Thermal destruction of modified PMMA can be explained by the formation of resonance structures in aromatic photoinitiators and consumption of energy in dissipation processes.     

Free radical polymerization within mesoporous zeolite channels

Free radical polymerization of methyl methacrylate (MMA) within the uniform channels of the mesoporous zeolite MCM-41 proceeds at 100°C to give a high molecular weight polymer (PMMA). The formation of long-living propagating polymer-radicals is observed by electron paramagnetic resonance (EPR). The molecular weight of PMMA within the mesopores can be controlled over a wide range by changing the monomer-to-initiator mole ratio.