Dynamics of adsorbed poly(methyl acrylate) and poly(methyl methacrylate) on silica

Deuterium NMR and modulated differential scanning calorimetry (MDSC) were used to probe the behavior of ultrathin adsorbed poly(methyl acrylate) (PMA). The spectra for the bulk methyl-labeled PMA-d₃ were consistent with the motions of the polymer segments being spatially homogeneous. For the polymers adsorbed on silica, multicomponent line shapes were observed. The segmental mobility of the surface polymers increased with increased adsorbed amounts. In contrast to the behavior of the polymers in bulk, the adsorbed lower-molecular-mass PMA-d₃ was less mobile than the adsorbed high-molecular-mass polymer. The presence of a polymer overlayer was sufficient to suppress the enhanced mobility of the more-mobile segments of the adsorbed (inner) polymer. MDSC studies on adsorbed poly(methyl methacrylate) showed that the glass-transition temperature of the thin polymer films increased and broadened compared to the behavior of the polymer in bulk. The presence of a motional gradient with the less-mobile segments near the solid-polymer interface and the more-mobile segments near the polymer-air interface was consistent with the experimental observations.     

Photodegradation of poly(methyl methacrylate)

The vacuum photodegradation at 30°C. of poly(methyl methacrylate) and copolymers with acrylaldehyde, methacrylaldehyde, and methyl acrylate has been studied. The polymers were examined in the form of expanded films as produced by a freeze-drying technique. At least one molecule of carbon monoxide is evolved for each chain scission. It is concluded that chain scission in poly(methyl methacrylate) is primarily the result of photoinduced aldehyde groups.     

Methanol-induced opacity in poly (methyl methacrylate)

Methanol-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.     

Fabrication of poly(methyl methacrylate) capillary electrophoresis microchips by in situ surface polymerization

A novel method based on in situ surface polymerization of methyl methacrylate (MMA) has been developed for the rapid fabrication of poly(methyl methacrylate) (PMMA) capillary electrophoresis (CE) microchips. MMA containing both thermal and ultraviolet (UV) initiators was allowed to prepolymerize in a water bath to form a fast curing molding solution that was subsequently sandwiched between a nickel template and a PMMA plate. The images of the raised microchannels on the nickel template were precisely replicated into the synthesized PMMA substrates during the UV-initiated polymerization of the molding solution within 30 min under ambient temperature. The attractive performances of the novel PMMA microchips have been demonstrated in connection with amperometric detection for the separation and detection of several model analytes. The new approach significantly simplifies the process for fabricating PMMA devices and could be applied to other materials that undergo light-initiated polymerization.     

Compatibilization of blends of polybutadiene and poly(methyl methacrylate) with poly(butadiene-block-methyl methacrylate)

Compatibilization of blends of polybutadiene and poly(methyl methacrylate) with butadiene-methyl methacrylate diblock copolymers has been investigated by transmission electron microscopy. When the diblock copolymers are added to the blends, the size of PB particles decreases and their size distribution gets narrower. In PB/PMMA7.6K blends with P(B-b-MMA)25.2K as a compatibilizer, most of micelles exist in the PMMA phase. However, using P(B-b-MMA)38K as a compatibilizer, the micellar aggregation exists in PB particles besides that existing in the PMMA phase. The core of a micelle in the PMMA phase is about 10 nm. In this article the influences of temperature and homo-PMMA molecular weight on compatibilization were also examined. At a high temperature PB particles in blends tend to agglomerate into bigger particles. When the molecular weight of PMMA is close to that of the corresponding block of the copolymer, the best compatibilization result would be achieved. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 85–93, 1998     

Thermophysics of a crack propagating in poly(methyl methacrylate)

Temperature kinetics along the crack propagation path in the bulk of PMMA at 20°C and under impact loading is explained. The initial experimental data are taken from [1, 2]. The kinetic temperature-time curve includes six different regions. In this study, the sequence of regions in the temperature kinetics is interpreted as a sequence of stages corresponding to the extension and breakdown of polymer chains in a microregion with dimensions of ≈130 μm located on the trajectory of crack propagation. At the first stage with a duration of ≈8 μs, the temperature increases by ≈10°C. This temperature rise that is related to the arrival of a loading wave front. At the second stage with a duration of ≈5 μs, temperature decreases by ≈8°C. This process is controlled by the thermal elasticity of polymer chains. At the third stage, temperature increases up to ≈90°C owing to the plastic flow of the material. At this stage, ahead of a crack, a craze is formed. Rearrangement of the isotropic polymer structure into an anisotropic polymer structure proceeds within ≈7 μs. At the fourth stage, temperature strongly decreases (nearly down to −150°C). This temperature reduction is provided by thermoelastic deformation of valence angles and chemical C-C bonds of the polymer backbone. At the fifth stage, the material heats up owing to the dissipation of the stored elastic energy due to the breakdown of extended polymer chains. This stage of the temperature rise on polymer chains spans over ≈18 μs. This phenomenon indicates the marked spatial continuity (diffuse character) of a crack tip and is related to a broad length distribution of ruptured chains. During the sixth stage, temperature remains at a constant level of ≈100°C for more than 100 μs. This stage reflects the emergence of exothermic processes on the newly formed fractured surface.     

Nanohole structure prepared by a polystyrene-block-poly(methyl methacrylate)/poly(methyl methacrylate) mixture film

Cylindrical nanoporous structures were prepared by using a mixture film of polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) and PMMA homopolymer (hPMMA), and they were analyzed by transmission electron microtomography (TEMT), X-ray reflectivity (XR), and grazing incidence small-angle X-ray scattering. For this purpose, the mixture film was spin-coated onto a silicon wafer modified by a neutral brush for PS and PMMA blocks, which generates PMMA cylindrical microdomains oriented normal to the substrate. Two methods were employed to prepare nanoporous structures: (1) all of the PMMA phase (PMMA block and PMMA homopolymer) in the film was removed by UV irradiation, followed by rinsing with a selective solvent (acetic acid) to PMMA and (2) only PMMA homopolymer was removed by selective solvent etching without UV irradiation. We found via TEMT and XR that the nanoporous structure in the film prepared by UV irradiation exhibited almost perfect cylindrical shape throughout the entire film thickness. However, when the film was rinsed with a selective solvent, nanoporous structures were not straight cylinders but had a funnel shape in which the diameter of nanopores located near the top of the film was larger than that located near the bottom of the film.     

Positron annihilation investigations on poly(methyl methacrylate)

Positron lifetime and Doppler broadened annihilation radiation were measured for seven different samples of poly(methyl methacrylate) at room temperature in vacuum. The polymerisation of methyl methacrylate was carried out as a bulk polymerisation in the presence of benzoyl peroxide as an initiator. The effect of the amount of the initiator on the viscosity-average molecular weight was studied. It was found that the viscosity-average molecular weight decreased with increasing amount of the initiator. The average lifetime and intensity of ortho-positronium (o-Ps) increased with increasing viscosity-average molecular weight up to 6.85 × 10⁴ and remained constant after that. The S-parameter showed a similar behaviour as that of the o-Ps intensity.     

Thermoluminescence of irradiated poly(methyl methacrylate)

Thermoluminescence of poly(methyl methacrylate) (PMMA) irradiated with x rays, has been studied in the temperature range 100 to 460°K. Two glow peaks with maxima at 136 and 368°K have been observed. These are analyzed by three methods and the results are compared. Both curves obey second order kinetics and correspond to activation energies of 0.17 and 0.88 eV, respectively. It is possible to identify the centers responsible for the two peaks by correlation with electron spin resonance and optical data obtained for the same samples irradiated under the same conditions. Spectral studies of the emission show that the low temperature peak has its maximum at 365 nm while the high temperature peak has its maximum at 480 nm.     

Branching of anionic poly(methyl methacrylate)

A viscometric determination of the degree of branching γ, of poly(methyl methacrylate) obtained by anionic polymerization proved the reaction of the growing center of poly(methyl methacrylate) with the ester group of another polymer molecule, accompanied by the formation of a trifunctional branch point. This reaction occurs if the solution polymerization of methyl methacrylate is initiated: (1) with butyllithium at ?78°C only on attaining 100% conversion and after a long time or at +20°C immediately after the polymerization has set in; (2) with lithium tert-butoxide at +20°C after a long time. The degree of branching of poly(methyl methacrylates) obtained under similar conditions in the presence of tetrahydrofuran reaches higher values than for polymers prepared in toluene. The tacticity of polymers does not affect the experimentally determined γ values.     

Electron-beam charging of poly(methyl methacrylate)

The charging of bulk poly(methyl methacrylate) by irradiation with electrons of 2 MeV energy at room temperature in vacuum was studied. The experimental data obtained using the split Faraday cup are compared with the results of numerical simulation assuming one-dimensional geometry with allowance for the spatial distribution of dose rate and injected-electron current, nonlinear properties of radiation-induced conductivity in the prebreakdown electric-field region, and the intrinsic conductivity of poly(methyl methacrylate). It was shown that published data on the electric field strength measured by means of the electro-optical Kerr effect in electron-beam charged poly(methyl methacrylate) agree satisfactorily with the calculation results.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 3, 2005, pp. 183–189.Original Russian Text Copyright © 2005 by Sadovnichii, Tuytnev, Milekhin.     

Synthesis of poly(methyl methacrylate) macromonomer

Anionic polymerization of methyl methacrylate (MMA) was carried out in tetrahydrofuran (THF) or THF/toluene mixture at ?78°C initiated by triphenylmethyl sodium or lithium as initiators. Highly syndiotactic PMMA of low polydispersity (M _w/m _n = 1.11–1.17) could be prepared with triphenylmethyl lithium in THF or THF/toluene mixture at ? 78°C. Moreover, PMMA macromonomer having one vinylbenzyl group per polymer chain was prepared by the couplings of living PMMA initiated by triphenylmethyl lithium with p-chloromethyl styrene (CMS) at ?78°C. The coupling reaction of living PMMA initiated by triphenylmethyl sodium with CMS was scarcely occurred.     

Radical polymerization of methyl methacrylate in the presence of isotactic poly(methyl methacrylate)

Methyl methacrylate (MMA) was polymerized by radical initiation at 25°C in DMF in the presence of preformed isotactic PMMA (iMA) with about 90% isotactic triads and different M?_v's, viz., iMA-1: 7.2 × 10⁵; iMA-2, 5.0 × 10⁵; iMA-3, 3.5 × 10⁵; iMA-4, 1.25 × 10⁵; and iMA-5, 1.15 × 10⁵. The MMA:iMA ratio was 6:1. The collected polymers were separated into two fractions by extraction with boiling acetone and characterized by 60 MHz NMR. It is found that the M?_v of the polymer formed ran parallel to the M?_v of iMA. In all cases syndiotactic PMMA (s-PMMA) was produced which associated with the isotactic substrate to form acetone-insoluble stereocomplexes. The syndiotactic polymers probably consist of long syndiotactic and heterotactic sequences. The syndiotacticity decreased with conversion and was generally highest in the presence of iMA-1. With iMA-1 even the formation of some additional i-PMMA (in the acetone-insolubles) was indicated, especially in the later stages of the polymerization. Characterization of the acetone-soluble fractions indicated that i,s-stereoblock polymers were also produced, of which the persistence ratios ρ increased with the M?_v of iMA. From these results it is concluded that this reaction differs from the conventional radical polymerization and can be considered a stereospecific replica polymerization, the driving force being the strong tendency of i- and s-PMMA to associate. The formation of i,s-stereoblock polymers and additional i-PMMA indicates that s-PMMA in its turn can also act as a polymer matrix.     

Radical polymerization of methyl methacrylate in the presence of low-molecular-weight poly(methyl methacrylate)

The kinetics of the bulk radical polymerization of methyl methacrylate and the structure and properties (physicomechanical and thermomechanical, as well as diffusion and sorption) of the polymers were examined in relation to the amount of low-molecular-weight poly(methyl methacrylate) added.     

Solvent bonding of poly(methyl methacrylate) microfluidic chip using phase-changing agar hydrogel as a sacrificial layer

In this report, a solvent bonding method based on phase-changing agar hydrogel has been developed for the fabrication of poly(methyl methacrylate) (PMMA) microfluidic chips. Prior to bonding, the channels and the reservoir ports on PMMA channel plates were filled with molten agar hydrogel that could gelate to form solid sacrificial layers at room temperature. Subsequently, PMMA cover sheets were covered on the channeled plates and 1,2-dichlororethane was applied to the interspaces between them. The agar hydrogel in the channels could prevent the bonding solvent and the softened surface of the PMMA cover sheets from filling in the channels. After solvent bonding, the agar hydrogel in the channels and the reservoir ports was melted and removed under pressure. The sealed channels in the complete microchips had been examined by an optical microscope and a scanning electron microscope. The results indicated that high-quality bonding was achieved at room temperature. The prepared microfluidic microchips have been successfully employed in the electrophoresis separation and detection of three cations in combination with contactless conductivity detection.     

Characteristics of a liposome immunoassay on a poly(methyl methacrylate) surface

Liposome immunoassay (LIA) is based on enzyme immunoassay (EIA) but the detection sensitivity could be significantly enhanced by using antibody-coupled immunoliposomes encapsulating HRP (horse radish peroxidase). Here, we applied LIA to non-porous poly(methyl methacrylate) (PMMA) and polystyrene (PS) surfaces to compare its detection sensitivity with that of EIA, using rabbit IgG (a ligand molecule) and anti-rabbit IgG antibody (a capture molecule) as the model system. LIA developed much stronger color signals than EIA, especially at a lower concentration range (< ca. 1 μg mL⁻¹). PMMA showed higher affinity toward rabbit IgG than the PS surface, and the anti-rabbit IgG antibody adsorbed on PMMA was more stable than that on PS. Furthermore, the effects of spot volume and antibody concentration on the signal density were analyzed. The signal density increased as the antibody concentration increased, but it was not significantly affected by the spot volume (2.5–20 μL). In conclusion, LIA on PMMA as a solid support is a very useful, highly sensitive microarray detection system. Sang Youn Hwang and Yoichi Kumada have same rights on this paper.     

Ethanol-induced crack healing in poly(methyl methacrylate)

The 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.     

Methyl methacrylate oligomerically-modified clay and its poly(methyl methacrylate) nanocomposites

A methyl methacrylate oligomerically-modified clay was used to prepare poly(methyl methacrylate) clay nanocomposites by melt blending and the effect of the clay loading level on the modified clay and corresponding nanocomposite was studied. These nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry. The results show a mixed intercalated/delaminated morphology with good nanodispersion. The compatibility between the methylacrylate-subsituted clay and poly(methyl methacrylate) (PMMA) are greatly improved compared to other oligomerically-modified clays.