Glass Transition Temperature Of PMMA Research Articles

Cryogenic Mechanical Alloying of Poly(methyl methacrylate) with Polyisoprene and Poly(ethylene-alt-propylene)

Mechanical alloying is performed at cryogenic temperatures to incorporate polyisoprene (PI) or its hydrogenated analogue poly(ethylene-alt-propylene) (PEP) into poly(methyl methacrylate) (PMMA) as an example of high-energy solid-state blending. Morphological characterization of the blends by X-ray and electron microscopies confirms that the degree of dispersion of the constituent polymers improves with increasing milling time. Such dispersion in the PEP/PMMA blends is, however, ultimately compromised by phase coarsening when the materials are postprocessed above the PMMA glass transition temperature in the melt. Milling-induced PI cross-linking serves to suppress phase coarsening in PI/ PMMA blends, which remain relatively well-dispersed even after postprocessing. These blends are generally less fracture-resistant than the as-received PMMA due mainly to the accompanying reduction in PMMA molecular weight. Their optical transparency is observed to decrease dramatically with increasing PEP or PI concentration until they appear opaque. An overall improvement in blend properties by mechanical alloying is, however, anticipated upon judicious selection of more degradation-resistant polymers.

Effect of temperature on ortho-positronium in poly(methyl methacrylate)

Positron annihilation lifetimes (PAL) were measured for two viscosity-average molecular weights of poly(methyl methacrylate), PMMA, as a function of temperature. The PAL measurements were performed under vacuum in the temperature range from 22 to 150°C with interval of 10°C. The lifetime spectra were analysed using two methods: (1) average results of the ortho-positronium ( o-Ps) lifetime and its intensity obtained by PATFIT program, and (2) the o-Ps lifetime and o-Ps hole volume distributions given by Bayes' theorem and the maximum entropy principle using MELT program. The value of the o-Ps lifetime in the sample with the lower viscosity–average molecular weight is higher than that with the higher viscosity-average molecular weight while it increases with increasing temperature. On the other hand, the o-Ps intensity as well as the relative fractional of the o-Ps hole volume shows behaviour in contrast to the o-Ps lifetime with the viscosity–average molecular weight. Within the temperature range two different transitions are observed. The first is due to the reduction of non-equilibrium states that are frozen below this temperature. The other one is in agreement with the glass transition temperature of PMMA.

Blends of poly(methyl methacrylate) (PMMA) with PMMA ionomers: Mechanical properties

Rigid–rigid blends made of ionomer and ionomer precursor polymer, based on poly(methyl methacrylate) (PMMA), have been investigated. Two series of blends have been prepared for studying mechanical properties. In one series, dynamic mechanical properties were determined over a wide range of temperatures. As the weight fraction of the ionomer was increased, there was a modest increase of modulus at ambient temperature and a very large increase in the rubbery modulus at elevated temperatures above the glass transition temperature of PMMA. In a second series of tests, tensile stress–strain measurements, made at an ambient temperature, were carried out over a wide range of blend compositions. For all blends tested, the mechanical properties exhibited a synergistic enhancement, i.e., average values of modulus, strength and fracture energy were all higher than expected based on the rule of mixtures. Measurements of fracture toughness also exhibited synergy, with a maximum value, higher than the value of either blend component, being attained in blends containing about 30 wt % of the PMMA ionomer. These results are interpreted in terms of a higher resistance to fracture of the more chain-entangled ionomer phase and good interfacial adhesion between the two components of the blend. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1235–1245, 1998

Secondary Ion Mass Spectrometry of Polymers: a ToF SIMS Study of Monodispersed PMMA Standards

This paper is concerned with the effects that polymer molecular weight, casting solvent, sonification (with a non-polymer solvent) and annealing have upon the secondary ion mass spectrometry (SIMS) of polymers. Films of a series of monodispersed poly(methyl methacrylate) (PMMA) standards, Mw 2965–1200000, were prepared by solution casting from four solvents (tetrahydrofuran (THF), 2-butanone, toulene and chloroform) onto clean aluminium (Al) substrates. The PMMA films were characterized by high- and unit-mass resolution time-of-flight secondary ion mass spectrometry (ToF-SIMS). To determine the significance of variations seen in ion intensities, one PMMA sample was re-analysed 24 times, and the scatter in the absolute counts and normalized and ratioed ion intensities for specific (termed ‘key’) positive and negative ions were calculated. This provided 95% confidence error bars, which were subsequently employed. The 95% confidence limits were significantly reduced by normalizing or ratioing. Molecular weight was found to have the greatest effect in the SIMS spectra obtained, with the differences being most marked between Mw=2965 and Mw=89100. This was seen in both the total negative ion counts (m/z 31–200) and the key negative ion ratios. An explanation based on the surface concentration of chain ends is presented. Negative ion ratios were shown to be very sensitive to trace amounts of residual solvents. By annealing above the PMMA glass transition temperature Tg solvent-free films were produced from three solvents and these were spectrally indistinguishable. Solvent-free films could not be produced from THF. Residual solvent was identified by high mass resolution ToF-SIMS. Sonification with hexane, a polymer non-solvent, had a considerable effect on the total negative ion counts (m/z 31–200). No concomitant chemical changes were detected, so this effect is thought to arise from a physical perturbation of the surface. © 1997 by John Wiley & Sons, Ltd.

Surface enrichment in thin films of PVC and PMMA

AbstractThe surface enrichment in thin bilayer films of poly(vinyl chloride) (PVC) and deuterated poly(methyl methacrylate) (PMMAd) was studied by neutron reflectometry, X‐ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS). In a layer system, where the PVC film is placed on top of a thin PMMA film, the PMMA chains migrate to the surface, although annealing of the films is performed below the glass transition temperature of PMMA. In addition, the surface segregation in blends of these materials was studied by XPS and SSIMS. In all cases PMMA is enriched at the surface. Results from the different techniques, probing different, sample depths, are consistent, if an exponential concentration profile of PMMAd at the surface is assumed. Concentration profiles at the surface are discussed with respect to theoretical models and diffusion coefficients are estimated.

The damping properties of dealloyed porous copper and its PMMA composite

Incramute Cu-Mn alloys were dealloyed to remove Mn by selective electrolytic separation. The porous dealloyed specimens were compressed at 0.17-14 GPa, resulting in densities of 55-88% of the density of pure copper. Some porous copper specimens before compression were soaked in a mixture of monomer (MMA) and the initiator (AIBN), compressed, and then polymerized by heating. Young's moduli of both the dealloyed porous copper and its PMMA composite were found to decrease exponentially with porosity and volume fraction of PMMA, respectively. The apparent activation energy for damping of Cu-PMMA composite near the glass transition temperature of PMMA was found to increase with decreasing volume fraction of PMMA.

Ethanol‐induced crack healing in poly(methyl methacrylate)

AbstractThe crack healing induced by ethanol in poly(methyl methacrylate) (PMMA) has been studied at temperatures of 40–60°C. Crack healing occurs because the effective glass transition temperature of PMMA is reduced to below the test temperature by ethanol plasticization. It is found that crack closure rate is constant at a given temperature. The fracture strength of healed PMMA is lower than that of the original samples. By comparing the fracture stress with the morphology of the crack edge on the PMMA surface, we found that a high degree of swelling is responsible for the incomplete recovery of mechanical strength. The fractography of the completely healed sample shows a very different fracture morphology from that of virgin PMMA. The transport of ethanol in PMMA also is studied. At lower temperatures, transport is described by ideal Case II behavior. As the temperature increases, the kinetics shift from ideal Case II to anomalous behavior. The first stage of crack healing is controlled by Case I transport. © 1994 John Wiley & Sons, Inc.

Phase behaviour of poly(ethylene oxide)/poly(methyl methacrylate) blends containing alkali metal salts

The effect of alkali metal salts on the phase behaviour of poly(methyl methacrylate) (PMMA)/poly(ethylene oxide) (PEO) blends was studied using d.s.c. Addition of lithium trifluoromethane sulfonate (LiT) to the normally miscible PEO/PMMA blends induced phase separation with the formation of a crystalline PEO phase, a crystalline PEO/salt complex phase and an amorphous PMMA phase. When potassium thiocyanate was used instead of LiT the mixture separated into two amorphous phases. Phase separation in these blends was not merely a result of the expected PEO/salt interaction, but also of the interaction of the salt with the PMMA. The evidence for this second interaction comes from an observed increase in the PMMA glass transition temperature with the addition of salt. Weak shifts in the carbonyl peaks in the i.r. spectra of the PMMA in the PMMA/salt mixtures suggest that the oxygen atom in the carbonyl interacts with the cation in the salt.

Methanol‐induced opacity in poly (methyl methacrylate)

AbstractMethanol‐induced opacity in poly (methyl methacrylate) (PMMA) is investigated subject to two cooling processes; furnace cooling and air cooling. The glass transition temperature of PMMA decreases with increasing time of exposure to methanol at 40–60°C and then increases during cooling, due to progressive desorption. Voids form during cooling as long as specimen temperature remains above its glass transition temperature. Since furnace cooling affords enough time for holes to expand larger than the light wavelengths, the transmittance of furnace‐cooled PMMA is independent of wavelength. The transmittance of PMMA subjected to rapid cooling in the air is wavelength dependent due to scattering by holes smaller than light wavelengths. The transmittance of PMMA bearing a given weight gain of methanol (measured at absorption temperature) prior to cooling for furance cooling is lower than that for the same material subjected to air cooling. A sharp front between outer and inner regions is found in specimens removed quickly from the thermostated water bath to air at ambient temperature.

Gas chromatographic determination of the interaction parameter of poly(ethylene oxide)/poly(methyl methacrylate) blends

AbstractInverse gas chromatography (IGC) has been used to investigate thermodynamic miscibility of a molten poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blend. Toluene, benzene, and chloroform have been employed as probes in pure and mixed stationary phases of these polymers. Experimental measurements have been taken over a narrow range of temperatures because of the high PMMA glass transition temperature as well as the degradation of the PEO. The interaction parameter χ23 determined at 150°C is slightly negative and dependent on the interacting probe, as has been also noted in previous chromatographic studies on polymer‐polymer miscibility. The last section is devoted to a model calculation, using Flory's equation of state theory. Different χ23‐concentration curves have been simulated, with the interaction energy parameter X23 as an adjustable parameter.