High-pressure sorption of carbon dioxide in solvent-cast poly(methyl methacrylate) and poly(ethyl methacrylate) films

Carbon dioxide sorption isotherms in poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) are reported for pressures up to 20 atm. Temperatures between 35 and 80°C were studied for PMMA and temperatures between 30 and 55°C were studied for PEMA. Typical dual mode sorption isotherms concave to the pressure axis were observed in all cases. The measured Langmuir sorption capacities of both polymers extrapolated to zero at the glass transition (T_g) consistent with the behavior of other glassy polymer/gas systems. Sorption enthalpies for CO₂ in the Henry's law mode for PMMA and PEMA are in the same range (?2 to ?4 kcal/mole) as has been reported for a variety of other glassy polymers such as poly(ethylene terephthalate), polycarbonate, and polyacrylonitrile. Some of the data suggest that postcasting treatment of the PEMA films left a small amount of residual solvent in the film. the presence of the trace residual solvent during quenching from the rubbery to the glassy state after annealing appears to cause a dilation of the Langmuir capacity and an alteration in the apparent Langmuir affinity constant of the PEMA film. These results suggest the possibility of tailoring physical properties of glassy polymers such as sorptivity, permeability, impact strength, and craze resistance by doping small amounts of selected residuals into polymers prior to quenching to the glassy state from the rubbery state.     

Swelling of poly(methyl methacrylate) thin films in low molecular weight alcohols

The effects of solvent size, temperature, and polymer molecular weight on the swelling of poly(methyl methacrylate) (PMMA) thin films in low molecular weight alcohols were investigated using an in situ ellipsometer. Apparent activation energies were indicative of non-Fickian diffusion, although optical data showed substantial Fickian character for swelling in methanol and moderate Fickian character in ethanol. Penetration rates were strongly dependent on the solvent molar volume for methanol, ethanol, and isopropanol, but 1-butanol and 2-pentanol had rates similar to isopropanol. The effective cross sections of these longer molecules are similar to isopropanol, and this apparently explains the similar penetration rates. The effect of polymer molecular weight (MW) on methanol penetration rates (21–27°C) was investigated with monodisperse PMMA (M_n = 6.4–40.0 × 10⁴ g/mol). A minimum at intermediate MW was observed. Isopropanol swelling rates (45–52°C) were insensitive to MW. The swelling data were also used to determine parameters for transport models that describe the swelling of thin polymer films.     

Conductive polyaniline/poly(methyl methacrylate) films obtained by electropolymerization

Electrochemical polymerization of aniline, on a Pt foil electrode coated with poly(methyl methacrylate) (PMMA), produces a homogeneous, free-standing, flexible, and conductive polymer film. The conductivity of the films depends on the aniline content and reaches 0.1–0.2 S/cm for films having aniline content of 15% or more. The optimum thickness of precoated PMMA to obtain durable conducting films was found to be in the range of 10–15 μm. Cyclic voltammetric investigation revealed that aniline exhibits a similar electrochemical behavior on a PMMA coated platinum electrode similar to a bare Pt surface. The film gives a fast and reproducible response against ammonia gas within a concentration range of 1.0–0.01%. Scanning electron micrographs indicate that the films have a rough structure consisting of globular regions. © 1996 John Wiley & Sons, Inc.     

Carbon dioxide sorption in conventional and plasma polymerized methyl methacrylate thin films

CO₂ sorption isotherms are reported for plasma polymerized methyl methacrylate (ppMMA) and the conventionally polymerized analog, poly(methyl methacrylate) (PMMA). The isotherms are measured at temperatures ranging from 20 to 95 °C and analyzed using the Dual-Mode sorption model. In the lower temperature range, the magnitude of the Henry's law (k_D) and the coupled Langmuir component parameters (C′_Hb) for both materials are similar. The expected collapse of the Langmuir sorption mode in conventional PMMA near the glass transition temperature is clearly observed. However, the Langmuir component in the plasma polymerized material does not diminish in the same manner as that for the conventional polymer analog. In contrast with the ppMMA, the PMMA materials are shown to exhibit significant dilation for extended conditioning times at high CO₂ pressures. The response of the isotherms for the two materials to ‘quench’ and ‘slow cool’ thermal conditioning protocols are similar, but small.     

Miscibility of poly(methoxymethyl methacrylate) and poly(methylthiomethyl methacrylate) with poly(methyl methacrylate)

Summary Poly(n-propyl methacrylate) is known to be immiscible with poly(methyl methacrylate) (PMMA). However, we have found that poly(methoxymethyl methacrylate) is miscible with PMMA, indicating the importance of ether oxygen atoms in achieving miscibility. On the other hand, poly(methylthiomethyl methacrylate) is immiscible with PMMA.     

Sorption of water vapour by atactic and isotactic poly (methyl methacrylate)

For the purpose of studying the relation between the stereoregularity and the sorption properties of atactic (a-PMMA) and isotactic (i-PMMA) poly(methyl methacrylate) samples, the isotherms for the sorption of water vapour by these polymers were determined. The glass transition temperatures, T_g and the densities of both PMMA samples were also measured under different conditions of moisture content. The amount of water vapour sorbed by i-PMMA was found, in this study, to be greater than that by a-PMMA. This is rather peculiar when we consider that the former has a high crystallinity (76%) and the latter is non-crystalline in nature. It was concluded that water vapour is sorbed by a-PMMA by a mechanism whereby the water molecules sorbed, fill pre-existing sites (polar groups) and spaces occupied by microvoids or free volumes in the polymer without causing any swelling in the latter; and that the extra sorption of water vapour by i-PMMA was due to a mechanism by which the water molecules sorbed cause the polymer to swell, and thus increase its sorption capacity.     

Water sorption of poly(methyl methacrylate): 2. Effects of crosslinks

Glassy crosslinked networks were made by copolymerization of methyl methacrylate both with ethylene glycol dimethacrylate and with triethylene glycol dimethacrylate, using a redox initiator. Residual monomer was largely or wholly removed by extraction with water, by heating at 100°C, or by γ-irradiation. Water sorption conformed approximately to Fick's laws but with a retarded swelling component which increased with crosslink density. Approximate values were obtained for apparent diffusion coefficients both in sorption and desorption. The pattern of results was similar for both dimethacrylate systems. Values of diffusion coefficients were little influenced by crosslink density up to a dimethacrylate feed of 50 wt%. The saturation value for water uptake increased with increasing feed of dimethacrylate to more than twice the value for the linear polymer, i.e. poly(methyl methacrylate).     

Dissolution rates of poly(methyl methacrylate) films in mixed solvents

A laser interferometer has been used to measure in situ the dissolution rates of thin films of poly(methyl methacrylate) (PMMA). The most significant finding is that addition of small amounts of a low-molecular weight nonsolvent can increase the rate obtained with a higher molecular weight solvent. In this study, silicon wafers were coated with polymer (about 1 μm thick) and annealed at 155°C for 1 h. The dissolution rates were measured at 17.5, 22.5, and 27.5°C. All the mixtures contained methyl ethyl ketone (MEK) (2-butanone), as the major component. The minor component was water, methanol, ethanol, 1-propanol, 2-propanol, or ethylene glycol. Water and methanol showed the greatest effects. Both were able to increase the dissolution rate as much as two-fold. All the mixtures exhibit the same activation energy (25 kcal/mol) despite their wide differences in dissolution rate.     

The transport of methyl methacrylate monomer in poly(methyl methacrylate)

The absorption kinetics and equlibria of methyl methacrylate monomer into poly(methyl methacrylate) were studied over a range of penetrant activities. The interval sorption kinetics at elevated activities were determined, compared, and contrasted with the integral sorption experiments in previously unpenetrated film samples. The sorption kinetics in previously unpenetrated films were predominantly case II or relaxation controlled at high activities. A Fickian contribution to the overall kinetics was apparent at lower activities. In contrast, interval sorption, at elevated activities in previously equilibrated and plasticized samples, followed Fickian kinetics rather closely, whereas resorption, over an activity range which involved a traversal of the effective T_g, was characterized by more complicated kinetics involving a super case II mechanism at long times. These composite results reinforce the notion that the kinetics describing penetration of a single penetrant into a single polymer are extremely sensitive to the boundary condition imposed upon the polymeric sorbent.     

Characterization of glassy state relaxations by low pressure carbon dioxide sorption in poly(methyl methacrylate)

Poly(methyl methacrylate) (PMMA) microspheres were swollen in methanol vapor, the swelling penetrant was quickly evacuated, and the subsequent relaxation of the polymer under vacuum was monitored by determination of the rate of settling of rapidly measured low pressure pseudoequilibrium CO₂ sorption isotherms. The decrease in CO₂ sorption capacity occurred very rapidly at short times, but the final stages of consolidation were protracted. In all cases, the microspheres were under vacuum between isotherm determinations. A single relaxation time is not sufficient to describe the relaxation processes characterized by the time-dependent sorption measurements. The sorption relaxation curves are similar in shape to volume relaxation curves for glassy polymers following imposition of a large pressure or temperature step change. The observed similarity between the sorption relaxation curves and classical volume relaxation curves is consistent with the notion that the excess sorption capacity introduced by methanol preswelling results from excess unrelaxed volume introduced into the glass by the quickly removed alcohol. As the excess volume relaxes, the excess sorption capacity decreases. One can, therefore, monitor the subtle process of consolidation using CO₂ as a probe of the excess volume introduced by the swelling perturbation. Subatmospheric pressure CO₂ sorption isotherms measured between 20 and 40°C for two different diameter microsphere samples (5436 Å and 1453 Å) for pressures up to 700 mm Hg were concave to the pressure axis. Such general isotherm shapes can be described by a two-term expression consisting of a Henry's law term and a Langmuir term. The Langmuir term, which arises due to unrelaxed volume in the nonequilibrium glass, is responsible for the observed concavity in the sorption isotherm. Annealing the sample, increasing the temperature of the sorption experiment closer to the T_g of the PMMA or permitting the preswollen sample to relax tends to reduce the concavity of the isotherm relative to the corresponding case for sorption in the preswollen sample measured at 25°C. This trend is presumably a consequence of the reduction in unrelaxed volume in the glass which attends either annealing, approaching the glass transition temperature of the polymer, or consolidation of excess volume following exposure to a swelling penetrant.     

Water sorption of poly(methyl methacrylate): 1. Effects of molecular weight

A sample of poly(methyl methacrylate), PMMA, of low molecular weight (10⁴ D) took up less water (1.2%) than samples of high molecular weight (10⁶ D: 2.0%). In contrast, the uptake of water was only slightly dependent on molecular weight for samples made by radiolysis in the glassy state. It is concluded that uptake of water depends on the closer molecular packing possible in polymers of lower molecular weight. However during radiolysis in the glassy state, this potential is not fully realized because of limited mobility. In more detail, the small changes in the diffusion coefficient and uptake of water in irradiated samples were consistent with closer packing in samples with M_n ⩽ 10 000. It is concluded that molecular packing proceeds more readily below the critical molecular weight for formation of an entangled network.     

Anomalous sorption in poly(ethyl methacrylate)

Vapor sorption data were obtained for the ethylbenzene–poly(ethyl methacrylate) system at 120°C. Successive step-change sorption experiments carried out at two-film thicknesses indicate the presence of maxima in the sorption curves. The fractional amount of overshoot decreased as the final pressure or weight fraction of the experiment increased and as the sample thickness increased. It is proposed that the maxima in the sorption curves are caused by structural rearrangements produced by relaxation of polymer chains.     

Ultrasonic characterization of water sorption in poly(2-hydroxyethyl methacrylate) hydrogels

A complex mechanism characterizes the water uptake kinetics in hydrogels, as a consequence of the strong structural changes occurring in the material during the sorption process. The water sorption involves the transformation of a glassy, moderately crosslinked polymer in a rubbery material. In this study, the changes in the ultrasonic attenuation and velocity in crosslinked poly(2-hydroxyethyl methacrylate) [poly-(HEMA)] hydrogel films during water sorption are measured by scanning laser acoustic microscopy (SLAM) and a pulse–echo system. In particular, the pulse–echo technique provides additional valuable information, thanks to its capability for monitoring the position of the swollen/unswollen fronts during water sorption. The evolution of the attenuation observed by SLAM is analyzed in terms of reflections on macroscopic discontinuities and absorption mechanisms. Finally, the propagation of ultrasonic waves acts as a dynamic mechanical test of the material; and, therefore, the measured longitudinal velocity and ultrasonic attenuation are applied to the calculation of the storage bulk longitudinal modulus of the poly(HEMA) hydrogels during water sorption. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:823–831, 1998     

Crystalline structures in ultrathin poly(ethylene oxide)/poly(methyl methacrylate) blend films

Amorphous poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blend films in extremely constrained states are meta-stable and phase separation of fractal-like branched patterns happens in them due to heterogeneously nucleated PEO crystallization by diffusion-limited aggregation. The crystalline branches are viewed flat-on with PEO chains oriented normal to the substrate surface, upon increasing PMMA content the branch width remains invariant but thickness increases. It is revealed that PMMA imposes different effects on PEO crystallization, i.e. the length and thickness of branches, depending on the film composition.     

Thermo-oxidative stability of poly(methyl methacrylate)/poly(methyl methacrylate)-grafted SiO2 nanocomposites

Thermo-oxidative stability of PMMA-grafted SiO₂ and PMMA/PMMA-grafted SiO₂ nanocomposites was investigated by conventional non-isothermal gravimetric technique. It was interesting to find that PMMA-grafted SiO₂ nanoparticles exhibited higher thermo-oxidative stability than that of PMMA. The apparent activation energy of PMMA-grafted SiO₂ nanoparticles increased with the grafting ratio of PMMA from SiO₂, which was estimated by Kissinger method. This indicates that the strong interactions existing between the grafted chains are responsible for the enhanced thermo-oxidative stability of PMMA-grafted SiO₂ nanoparticles. However, the grafting ratio of PMMA from SiO₂ in nanoparticles has only limited effect on the thermo-oxidative stability of PMMA/PMMA-grafted SiO₂ nanocomposites due to a much lower content of grafted PMMA in the nanoparticles relative to PMMA. The increased thermo-oxidative stability of PMMA/PMMA-grafted SiO₂ nanocomposites is possibly resulted from the increased SiO₂ content in the nanocomposites, in which the grafting ratio of PMMA in PMMA-grafted SiO₂ nanoparticles is kept almost as a constant. The glass transition temperature (T _g) of PMMA/PMMA-grafted SiO₂ nanocomposites is about 25 °C and is higher than that of PMMA. The grafting ratio of PMMA from SiO₂ in the nanoparticles has no qualitative effects on the T _g of the nanocomposites.     

Self assembled hydrophobic nanoclusters of poly(methyl methacrylate) embedded into polyvinyl alcohol based hydrophilic matrix: Preparation and water sorption study

Hydrophilic matrices containing nanosized clusters of hydrophilic moieties have demonstrated potential applications in biomedical field. A novel hydrogel containing nanosized domains (20–35 nm) of hydrophobic moieties of poly(methyl methacrylate) (PMMA) was prepared by grafting crosslinked poly(acrylic acid‐co‐methyl methacrylate) chains onto polyvinyl alcohol (PVA) backbone using an efficient redox system. The graft copolymerization process was investigated to observe the influence of gel components on the kinetic parameters of grafting such as rate of grafting (R_g), grafting yield (G_y) and grafting efficiency (G_e). The prepared graft nanohydrogel was evaluated for its water sorption potential under varying chemical composition of the gel and changing pH, temperature, and ionic strength of the swelling bath. The swelling process was also examined mechanistically and diffusion constants (D) of water molecules through the swellable nanohydrogel were also evaluated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Degradation of poly (methyl methacrylate) by flash irradiation

Degradation of poly(methyl methacrylate) (PMMA) caused by irradiation of flash light from discharged xenon lamp was investigated in a vacuum and in the presence of nitrogen. Degradation products at a sequence of flashes were analysed by a gas chromatograph with hydrogen flame ionization detector after each flash. Among the degradation products of PMMA in vacuum by regular flash light, an amount of monomer was detected with the significant production of methanol and gaseous mixture. The molecular weight of the residual polymer decreased markedly by the first several flashes, showing that chain scission occurred. By filtering the u.v. component of flash light the monomer formation and molecular weight decrease were not observed. From these facts the flash degradation of PMMA in vacuum was concluded to be conducted by a photodegradation mechanism. The absorption of u.v. light by ester groups forms active radicals, which initiate chain scissions and depolymerization of main chains following methanol and monomer formation. At the flash degradation in nitrogen at atmospheric pressure PMMA degraded in the different manner. At the initial several flashes the photodegradation mechanism is also conducted in the polymer matrix and decomposed secondarily at the subsequent flashes to form a significant amount of carbon particles. Thereafter, carbon particles acted as a photoabsorber, and the thermal degradation of the polymer occurred predominantly around the heated carbon particles.     

Anomalous sorption kinetics in the methanol vapor–poly(methyl methacrylate) system

The non‐Fickian sorption kinetics of methanol vapor in poly(methyl methacrylate) films 8 and 51 μm thick at 25°C are presented. The behavior of the system was studied in series of interval and integral absorption runs. The relevant diffusion coefficient and viscous relaxation processes were studied separately by kinetic analysis of the first and second stages of sorption kinetic curves. The sorption isotherm concaved upward at high activities, this being typical of Flory–Huggins behavior, whereas it exhibited a convex‐upward curvature at low methanol vapor activities, this indicating sorption in the excess free volume of the polymer matrix. After excess free‐volume fill‐up, the concentration dependence of the diffusion coefficient was found to be well represented by the free‐volume theory of Vrentas and Duda. Relaxation frequencies calculated from the second stage of two‐stage curves exhibited a weak dependence on the concentration. Integral sorption experiments indicated that the system exhibited nearly case II kinetics at high methanol vapor activities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1184–1195, 2005     

Characterization of physical aging of poly(methyl methacrylate) powders by a novel high pressure sorption technique

High pressure CO₂ sorption isotherms were measured at 35°C in previously dilated PMMA microspheres, which were subsequently aged in vacuum at 35°C. The dilation was induced by preswelling with high activity methanol vapor at 13°C, or alternatively with CO₂ at a pressure of 20 atm and a temperature of 5°C. The state of the samples during long-term aging was probed by rapid and intermittent determination of complete high pressure CO₂ isotherms. The dilation increased the sorption levels observed in the sorption experiments compared to those observed in untreated samples and, as the aging time increased, the sorption level progressively decreased. The isotherms under all conditions were well described by the dual mode sorption model. The observed time dependence of the isotherms was successfully described by confining all changes in sorption capacity to a systematic decay of the Langmuir capacity parameter. The equilibrium parameters of the model, however, were essentially unaffected by the preswelling and aging histories.     

A study of electrostatically stabilized poly(methyl methacrylate) latex

Poly(methy methacrylate) latex with various solid contents, stabilized electrostatically, was studied. The hydrodynamic layer (H.L.) extends rapidly at volume fraction larger than 0.35. The agglomeration of particles was found. When the reduced thickness (δ/r) of H. L. exceeds 3.0, particle agglomeration becomes more serious and the gel-like product forms. In comparison, the value of (δ/r) is much smaller than 3.0 when the H. L. begins to contact each other. Using a higher amount of emulsifier, the thickness of H. L. decreases. This is attributed to the fact that more free emulsifier presenting in the aqueous phase leads to more depletion stabilization. Meanwhile, in the presence of unreacted monomer, the use of the monomer-swollen volume fraction is suggested to replace the unswollen volume fraction. © 1994 John Wiley & Sons, Inc.