Dependence of the glass transition temperature of poly(methyl methacrylate) on tacticity and molecular weight

The preparation of five samples of poly(methyl methacrylate) covering a wide range of tacticity and their electron irradiation to produce series of varying molecular weight are described. The glass transition temperature T_g of each polymer was determined by DTA techniques. Plots of T_g and the reciprocal of the molecular weight are well fitted in every case by a straight line. The data are also fitted to the Gibbs-DiMarzio theory and the values of the energy and free-volume parameters obtained are discussed. A method of estimating T_g of pure syndiotactic poly(methyl methacrylate) by extrapolation is presented, the value obtained being 160°C.     

Photon correlation spectroscopy of poly(methyl methacrylate) near the glass transition

Poly(methyl methacrylate) (PMMA) has been studied by photon correlation spectroscopy in the temperature range 120–150°C. The relaxation functions for longitudinal density fluctuations were determined and analyzed using the empirical function ?(t) = exp[?(t/τ)^β]. The average relaxation times were calculated for each temperature and compared to mechanical and dielectric relaxation data. The agreement between the various techniques for the primary glass–rubber relaxation was good. The relaxation function observed by light scattering became increasingly broad as the temperature was lowered. This is similar to the results reported previously for poly(ethyl methacrylate) (PEMA). In fact, the light-scattering relaxation function is dominated by the secondary relaxations in these two polymers. Nevertheless, the average relaxation time 〈τ〉 is dominated by the longest relaxation times associated with the primary glass–rubber relaxation.     

Viscoelastic properties of poly(methyl methacrylate) with high glass transition temperature by lithium salt addition

The effect of ion‐dipole interaction between lithium cations and oxygen atoms in poly(methyl methacrylate) (PMMA), which leads to the great enhancement of glass transition temperature (T_g), on the linear viscoelastic properties is studied using binary blends of PMMA and lithium trifluoromethanesulfonate (LiCF₃SO₃). The strong interaction at low temperature leads to the high modulus in the glassy region even near T_g. The interaction becomes weak as increasing the temperature. Consequently, the rheological terminal region is clearly detected without a marked enhancement of steady‐state compliance, although the zero‐shear viscosity increases by the LiCF₃SO₃ addition. The result indicates that the crosslinking due to the ion‐dipole interaction has a lifetime that decides the longest relaxation time. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2388–2394     

Determination of the glass transition temperature of polystyrene,poly(vinyl chloride) and poly(methyl methacrylate) using gas chromatography

The glass transition temperatures, Tg, of polystyrene, poly (vinyl chloride) and poly(methyI methacrylate) have been determined from gas chromatographic measurements using n-hexane, n-heptane, meta-xylene and para-xylene solvents. The glass transition temperatures were detected on the z-shaped retention diagrams which were produced from the plot of the logarithm of the specific retention volumes of the above-mentioned solvents against the reciprocal of temperature, i.e. log V${}_{\text{g}}^{\text{º}}$ vs. 1/T. The glass transition temperature is specified by the temperature where the slope of log V${}_{\text{g}}^{\text{º}}$ vs. 1/T changes abruptly. The observed glass transition temperature of polystyrene produced by this technique was found to be in good agreement with those produced by other techniques such as the differential scanning colorimeter. The industrial importance of the glass transition temperature, T_g, might be due to the dramatic changes in the physical properties of the polymer, such as hardness and elasticity, which take place in the vicinity of this temperature. However, perfectly crystalline polymers do not exhibit glass transitions, because their chains are incorporated in regions of three-dimensional order, called crystallites. Completely amorphous polymers and semi-crystalline polymers usually exhibit both glass transition and melting.     

Pulse radiolysis studies of poly(methyl methacrylate) containing pyrene

A pulse radiolysis study of poly(methyl methacrylate) in the presence of pyrene has been carried out in the temperature range 100–295 K. The concentration of pyrene was changed from 10⁻³ to 10⁻¹ mol dm⁻³. The absorption/emission spectra and kinetics of solute excited states and solute radical ions were investigated. It was found that pyrene excited states were formed as a result of their radical ion recombination in a time scale up to seconds. The decay of solute radical ions was influenced by photobleaching and can be described by a time-dependent rate constant. The activation energy of Py ions decay was temperature dependent and was equal to 35.7 and 1.2 kJ/mol for temperatures >T_γ and <T_γ, respectively, where T_γ ∼ 175 K represented the transition temperature responsible for γ-relaxation. The reaction mechanism was proposed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1209–1215, 1998     

Depression of the glass transition temperature of poly(methyl methacrylate) by plasticizers: Conformity with free volume theory

Mixtures of poly(methyl methacrylate) (PMMA) and plasticizer were made by γ-irradiation of mixtures of methyl methacrylate with diethyl phthalate or with dioctyl phthalate. The glass transition temperature T_g was determined by differential scanning calorimetry. Plots of T_g versus volume fraction of PMMA were found to conform to the simple free volume theory of Kelley and Bueche, using physical property values either reported in the literature or else calculated by Bondi's procedures.     

Dependence of the glass transition temperature of poly (methyl methacrylates) on their tacticity

The specific isobaric heat capacities of poly (methylmethacrylates) (PMMA) having various tacticities were measured by the DSC method within a broad range of temperatures including the glass transition. Glasses with uniform thermal history were used in the measurements and the data were treated by employing a procedure which provided the thermodynamic T_g independent of the experimental conditions. The semiquantitative validity of Boyer's empirical relationT _g ×c_p=const. was confirmed; also it was found that within the limits of experimental accuracy the c_p,g values at 298 K andC _p,l values at 400 K are independent of the tacticity of the sample.Using the data thus measured and linearized equations representing the dependence ofT _g on the content of iso-, syndio- and heterotriads, the T_g values of pure isotactic PMMA and pure syndiotactic PMMA were found to be respectively 315 K and 397 K.Dedicated to Professor Dr. F. H. Müller.     

Glass transition temperature and stress relaxation of methanol equilibrated poly(methyl methacrylate)

Glass transition temperatures are reported for narrow MWD PMMA for a range of MW, where the polymer is (a) free of methanol, and (b) equilibrated with methanol. The relationship between the glass transition temperature and MW is discussed in terms of current empirical and thermodynamic theories.     

Effect of water on the glass transition temperature of poly(hydroxy methylene)

The effect of moisture on the glass transition temperature of poly(hydroxy methylene) was investigated by thermal analysis which entailed combinations of DTA and DSC with TGA techniques. As the moisture content increased, the glass transition temperature (T_g) decreased monotonically from a value (T_go) of 134°C for the dry polymer toward a finite value (T_gt) of about 39°C. This response of T_g to an increase in the moisture content (w) was adequately represented by the general relationship T_g = (ΔT_g)0 exp{–[ln(ΔT_g)₀]w/τw_l} + T_gl, recently developed for correlating T_g and moisture content of nylon 6 and and found generally applicable to hydrophilic polymers. With (ΔT_g)0 = 95, τ = 0.555, and w_l = 0.375, good agreement was found between experimental and calculated values for poly(hydroxy methylene).     

Rayleigh-brillouin spectroscopy of syndiotactic poly(n-butyl methacrylate) near the glass transition

We present Rayleigh-Brillouin light scattering data of highly syndiotactic poly(n-butyl methacrylate) [PBMA] whose glass transition temperature as measured by DSC is 55°C. The Brillouin peak shifts, Brillouin peak widths, and Landau-Placzek ratios from ?15 to 130°C are reported. The Brillouin peak widths decrease continuously through the glass transition region. This indicates a continual decrease in the strength of processes whose relaxation times are about 10^?10 s with decreasing temperature even as the system becomes glassy. The Landau-Placzek ratio above the glass transition is about 3, indicating the high optical purity of our sample. This low Landau-Placzek ratio arises from the sample's homogeneous stereochemistry. Some of the anomalous behavior observed around 40–50°C in previous PBMA studies is explained in terms of syndiotactic regions within a largely atactic sample.     

Impact of low‐molecular mass components (oligomers) on the glass transition in thin films of poly(methyl methacrylate)

Commercial polydisperse atactic poly(methyl methacrylate) (PMMA) exhibits a decreased glass transition temperature (T_g) when the film thickness is less than ～60 nm, whereas more model atactic PMMA shows an increased T_g in thin films supported on clean silicon wafers. NMR indicates no difference in tacticity, so the divergent thin film behavior appears related to the relative distribution of molecular mass. Extraction of some low molecular weight PMMA components from the commercial sample results in a significant modification of the thin film T_g compared with the initial PMMA fraction. The extracted sample exhibits initially a slight decrease in T_g as the film thickness is reduced below ～60 nm, but then T_g appears to increase for films thinner than 20 nm. These results illustrate the sensitivity of polymer thin film properties to low‐molecular mass components and could explain some of the contradictory reports on the T_g of polymer thin films that exist in the literature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Isobaric temperature dependence of radical generation in poly(methyl methacrylate)

In this study the effect of temperature on the generation of free radicals accompanying the decomposition of benzoyl peroxide in poly(methyl methacrylate) was studied. The concentration of the chain-end radicals was determined by the ESR method. The known nine-line spectrum of the chain-end radicals of poly(methyl methacrylate) was observed. This spectrum was affected by the contribution of chain radicals at higher temperatures. The dependence of the chain-end radical concentration on the annealing temperature of polymer found for different pressures gives information on the conditions under which free radicals arise and decay in the temperature range between 90 and 170°C at pressures ranging from 2000 to 12000 atm.     

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.     

Effect of tacticity on permeation properties of poly(methyl methacrylate)

The effect of stereoregularity on gas permeation properties of poly(methyl methacrylate) (PMMA) was investigated. The gas permeability coefficients for He, H₂, O₂, N₂, Ar, CH₄, and CO₂ at 35°C near atmospheric pressure have been measured for three different PMMAs. Apparent diffusion and solubility coefficients were obtained from time lag data, and these were compared with data for a commercial PMMA previously reported. The permeability, solubility, and diffusion coefficients increase as the content of syndiotactic sequences increases. These observations are consistent with more dense packing of the isotactic form in the glassy state that stems in part from its lower glass transition temperature. The transport behavior for a 50:50 isotactic/syndiotactic blend was also studied. These so-called stereocomplexes exhibit permeation behavior comparable to other weakly interacting miscible blend systems.     

Photon correlation spectroscopy of bulk poly(n-hexyl methacrylate) near the glass transition

Slowly relaxing longitudinal density fluctuations in an optically perfect sample of bulk poly(n-hexyl methacrylate) (PHMA) have been studied by photon correlation spectroscopy in the temperature range 10–36°C. The glass transition temperature for this sample was measured to be T_g = −3°C by differential scanning calorimetry. The optical purity of the sample was verified by Rayleigh-Brillouin spectroscopy and the Landau-Placzek ratio was observed to be 2.3 at 25°C. Light-scattering relaxation functions were obtained over the time range 10⁻⁶-1 s. The shape of the relaxation functions broadened as the temperature was lowered towards the glass transition. Quantitative analysis of the results was carried out using the Kohlrausch-Williams-Watts (KWW) function to obtain average relaxation times, 〈τ〉, and width parameters, β. The width parameter decreased from 0.43 to 0.21 over the temperature interval, as suggested by visual inspection. Average relaxation times shifted with temperature in a manner consistent with previous mechanical studies of the primary glass-rubber relaxation in PHMA. The relaxation functions were also analyzed in terms of a distribution of relaxation rates, G(Γ). The calculated distributions were unimodal at all temperatures. The average relaxation times obtained from G(Γ) were in agreement with the KWW analysis, and the shape of the distribution broadened as the sample was cooled. The rate at which G(Γ) displayed a maximum correlated well with the corresponding frequency of maximum dielectric loss for PHMA. The temperature dependence of these two quantities could be reproduced with an Arrhenius activation energy of 21 Kcal/mol. A consistent picture of the molecular dynamics of PHMA near the glass transition requires a strong secondary relaxation process with a different temperature dependence from the primary glass-rubber relaxation. The present results suggest that the behavior of PHMA is similar to the other poly(alkyl methacrylates). © 1996 John Wiley & Sons, Inc.     

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.     

Photon correlation spectroscopy of syndiotactic poly (n-butyl methacrylate) near the glass transition

Slow relaxing longitudinal density fluctuations in bulk syndiotactic poly (n-butyl methacrylate) [PBMA] were studied by photon correlation spectroscopy as a function of temperature from 70 to 90°C. The shape of the light-scattering relaxation function broadened as the temperature approached the glass transition (T_g = 55°C). The average relaxation time shifted with temperature, consistent with previous studies of PBMA. The relaxation functions were analyzed in terms of a distribution of relaxation rates. The calculated distribution was clearly bimodal and the shape altered with temperature. The higher frequency peak in the distribution corresponds well with previous mechanical and dielectric relaxation studies of the intramolecular relaxation of the acrylate ester side chain. The resolution of the distribution into two modes is due to a well-defined side-chain motion with relaxation strength comparable to the primary glass-rubber relaxation. © 1994 John Wiley & Sons, Inc.     

A model for transition to the mesomorphic state in poly(methyl methacrylate)

The structural instability of a polymer crystal may be due to the involvement of various lattice vibrations in nonlinear resonance. The condition of this involvement is the prevalence of intramode anharmonicity over intermode interaction. A model of phase transitions in polymers of the PMMA type was constructed. Below transition points, coherent states of orientational vibrations of heavy side pendants are formed. The thermodynamic characteristics of these states were found. The structural instability of the polymer lattice is a second-order phase transition.