Molecular mobility of poly(methyl methacrylate) glass during uniaxial tensile creep deformation

An optical photobleaching method has been used to measure the segmental dynamics of a poly(methyl methacrylate) (PMMA) glass during uniaxial creep deformation at temperatures between T_g ? 9 K and T_g ? 20 K. Up to 1000‐fold increases in mobility are observed during deformation, supporting the view that enhanced segmental mobility allows flow in polymer glasses. Although the Eyring model describes this mobility enhancement well at low stress, it fails to capture the dramatic mobility enhancement after flow onset, where in addition the shape of the relaxation time distribution narrows significantly. Regions of lower mobility accelerate their dynamics more in response to an external stress than do regions of high mobility. Thus, local environments in the sample become more dynamically homogeneous during flow. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1713–1727, 2009     

Does the strain hardening modulus of glassy polymers scale with the flow stress?

Using a generic coarse‐grained bead‐spring model, Hoy and Robbins reproduced important experimental observations on strain hardening, specifically the generally observed Gaussian strain hardening response and its dependence on network density and temperature. Moreover, their simulation results showed that the strain hardening response at different strain rates collapses to a single curve when scaled to the value of the flow stress, a phenomenon that has not yet been verified experimentally. In the present study, the proposed scaling law is experimentally investigated on a variety of polymer glasses: poly(methyl methacrylate), poly(phenylene ether), polycarbonate, polystyrene, and poly(ethylene terephthalate)‐glycol. For these polymers, true stress–strain curves in uniaxial compression were collected over a range of strain rates and temperatures and scaled to the flow stress. It was found that, generally, the curves do not collapse on a mastercurve. In all cases, the strain hardening modulus is observed to increase linearly, but not proportionally to the flow stress. The experimental data, therefore, unambiguously demonstrate that the proposed scaling law does not apply within the range of temperature and strain rate covered in this study. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2475–2481, 2008     

Elastic modulus of single-walled carbon nanotube/poly(methyl methacrylate) nanocomposites

Dynamic mechanical analysis, nuclear magnetic resonance, and thermogravimetric analysis experiments were performed on pure poly(methyl methacrylate) and on in situ polymerized single-walled carbon nanotube (SWNT)/PMMA nanocomposites. The addition of less than 0.1 wt % SWNT to PMMA led to an increase in the low-temperature elastic modulus of approximately 10% beyond that of pure PMMA. The glass-transition temperature and the elastic modulus at higher temperatures of the nanocomposites remained unchanged from those of pure PMMA. These changes were associated with excessive cohesive interactions between the large-surface area nanotubes and PMMA and were not due to changes in the microstructural features of the polymer during synthesis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2286–2293, 2004     

Effects of humidity on Young's modulus in poly(methyl methacrylate)

Tensile tests on poly (methyl methacrylate) (PMMA) were conducted to clarify the effects of humidity and strain rate on tensile properties, particularly Young's modulus. Prior to the tensile tests, specimens were kept under various humidity conditions at 293 K, which were the same as the test conditions, for a few months to adjust the sorbed water content in the specimens. The tensile tests were performed under each humidity condition at three different strain rates (approximately 1.4 × 10^?3, 1.4 × 10^?4, and 1.4 × 10^?5 s^?1). Stress‐strain curves changed with humidity and strain rate. Young's moduli were also measured at small applied stresses (below 6.7 MPa) under various humidity conditions at 293 K. Young's modulus decreases linearly with increasing humidity and a decreasing logarithm of strain rate. These results suggest that Young's modulus of PMMA can be expressed as a function of two independent parameters that are humidity and strain rate. A constitutive equation for Young's modulus of PMMA was proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 460–465, 2002; DOI 10.1002/polb.10107     

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     

Sorption of light gases in glassy poly(ethyl methacrylate)

Although gas sorption in glassy polymers is a well‐studied phenomenon, no general microscopical model is developed which is able to describe the gas sorption in a wide temperature range using only characteristics of polymer and gas molecule. In this work, sorption isotherms and desorption kinetics of O₂, Ar, and N₂ for glassy poly(ethyl methacrylate) have been measured in the temperature range from 160 to 308 K. To describe both the phenomena, the model is developed which postulates that, in the frozen structure of glassy polymer, any cavities between macromolecules are the sorption sites for small molecules. The cavities of small size can expand elastically to accommodate a gas molecule. The sorption sites are considered to be the potential wells and their depths are distributed according to Gaussian law. The concentration of sorption sites, their mean depth and depths dispersion, and the frequency of molecules oscillations in the sorption sites are the only parameters which determine both the gas transport and sorption. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 288–296     

Methacrylate modified clays and their polystyrene and poly(methyl methacrylate) nanocomposites

Two methacrylate‐modified clays have been prepared and used to produce nanocomposites of polystyrene and poly(methyl methacrylate) by in situ polymerization. These nanocomposites have been characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), cone calorimetry and the evaluation of mechanical properties. When the clay contains only a single methacrylate unit, the styrene system is exfoliated but methacrylate is intercalated. When two methacrylate units are present on the cation of the clay, both systems are exfoliated. TGA data show that the thermal stability of all the nanocomposites is improved, as expected. The relationships between the fire properties and nanostructure of the nanocomposites are complicated, as shown by cone calorimetry. The conclusions that one may reach using cone calorimetry do not completely agree with those from XRD and TEM. The evaluation of mechanical properties shows an increase in Young's modulus for all nanocomposites along with a decrease in elongation; tensile strength is decreased for methacrylate nanocomposites but increased for styrenics systems. Copyright © 2004 John Wiley & Sons, Ltd.     

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.     

Thermodynamic analysis of the plastic deformation of glassy poly(methyl methacrylate)

A thermodynamic analysis of the thermally activated yielding of glassy atactic poly(methyl methacrylate) has been carried out. Samples were deformed in compression at a constant strain rate in the temperature range 150–330 K. Two different deformation modes are rate controlling below and above a critical temperature T_c of the order of 200 K. The low-temperature mode is characterized by a purely exponential stress dependence of the strain-rate, and thus defines a true stress-activation volume. The higher-temperature mode reveals a stress dependence of the strain rate in the form of a power law with a constant activation energy.     

Preparation and properties of cross-linked fluorescent poly(methyl methacrylate) latex colloids

We report a single step preparation of monodisperse fluorescent poly(methyl)methacrylate (PMMA) lattices cross-linked with ethylene glycol dimethacrylate with radii in the range 150-1000 nm using dispersion polymerization. The particles are applied as fluorescent cores in core-shell PMMA particles for confocal microscopy (Dullens et al. Langmuir 2003, 19, 5963). Contrary to un-cross-linked particles, these cross-linked colloids are stable in good solvents for PMMA as well. Therefore we studied the properties of the cross-linked PMMA particles in the good solvents tetrahydrofuran (THF), chloroform, and toluene using light scattering and confocal scanning laser microscopy. We show that the particles swell instantaneously and that their volume can increase up to more than seven times their volume in poor solvents. Further, it is very likely that the particles are charged in THF.     

Macroporous poly(methyl methacrylate) produced by phase separation during polymerisation in solution

Polymethyl methacrylate (PMMA) sponges were obtained by polymerization in a solution with monomer/ethanol ratios up to 20:80. The material obtained after the elimination of the solvent present a homogeneous distribution of dispersed pores up to a monomer/ethanol ratio lower than 40:60. For higher ethanol contents in the reacting mixture, the morphology of the sponge corresponds to a network of PMMA microparticles, leaving large empty spaces leading to highly porous structure. The monomer/ethanol ratio during polymerization has a large influence on the porosity, thermal, and mechanical properties of the material and, for large solvent contents, on the size of the polymer microparticles.     

Fracture behavior of amorphous and semicrystalline blends of poly(vinylidene fluoride) and poly(methyl methacrylate)

The fracture behavior of blends of poly(vinylidene fluoride) and poly(methyl methacrylate) was investigated all over the composition range. A detailed analysis of the net stress versus crack opening displacement curves was performed. Fracture surface observations allowed statements on the process zone characteristics ahead of the crack tip. For the amorphous blends, the crack initiation energy is well related to the glass transition temperature. For the semicrystalline blends, the fracture energy is correlated with the degree of crystallinity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Infrared spectroscopic study of thermal transitions in poly(methyl methacrylate)

The ester CD₃ stretching modes in a partially deuterated poly(methyl methacrylate) sample have been studied as a function of temperature and bands in the CD stretching region assigned to fundamentals in Fermi resonance with overtone/combination modes. Changes in band parameters (widths, shapes) are observed at specific temperatures. Time correlation functions and their variation with temperature were calculated for the most intense modes observed in this region of the spectrum. The correlation functions were modeled by assuming that there is a fast relaxation process characterized by a single relaxation time that is inhomogeneously broadened by a slower process, also characterized by a single relaxation time. The fast modulation is in the sub picosecond time range, while the slower process has a relaxation time of the order of 1-10 ps. Relaxation times and other parameters are sensitive to transitions observed both below and above the glass transition, as well as at the T_g itself. The high temperature transition corresponds to a liquid-liquid transition observed in other studies and predicted by theory. The lower temperature transition appears to correspond to the Vogel-Fulcher or Kauzmann temperature. Infrared spectroscopy and band shape analysis appear to be a useful probe of these transitions.     

Vibration damping materials based on interpenetrating polymer networks of carboxylated nitrile rubber and poly(methyl methacrylate)

Interpenetrating polymer networks (IPNs) based on carboxylated nitrile rubber (XNBR) and poly(methyl methacrylate)s were synthesized. Crosslinked XNBR was swollen in methyl methacrylate containing benzoyl peroxide as initiator and tetraethylene glycol dimethacrylate as crosslinking agent. The compositions of the IPNs were varied by changing the swelling time of the rubber in the methacrylate monomer. The dynamic mechanical properties of the IPNs were studied. The dynamic mechanical properties in the range 1–10⁵ Hz were obtained by the time‐temperature superposition of the data under multifrequency mode, which indicated high tan δ with good storage modulus in the entire frequency range. This indicates the suitability of these IPNs as vibration and acoustic dampers. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis of cross-linked poly(methyl methacrylate) via dispersion polymerization in supercritical carbon dioxide

Cross-linked poly(methyl methacrylate) particles were prepared via dispersion polymerization in supercritical carbon dioxide (scCO₂) using poly(heptadecafluorodecyl methacrylate) (PHDFDMA) and 2,2′-azobisisobutyronitrile as the dispersant and the initiator, respectively. The following chemicals were used as cross-linking agents: ethylene glycol dimethacrylate (EGDMA), 1,4-buthanediol di(meth)acrylate (1,4-BD(M)A), and trimethylolpropane trimethacrylate. PHDFDMA was synthesized by solution polymerization in scCO₂. We investigated the effect of the chemical structure, concentration of the cross-linking agents, reaction pressure, and CO₂ density on the morphology, the polydispersity, and the cross-linking density of polymer particles. The resulting polymer particle was characterized by field emission SEM, differential scanning calorimetry, and thermal gravimetric analysis. The cross-linked PMMA particles is more agglomerate as the cross-linking agent concentration increased and as pressure decreased at constant temperature. Glass-transition temperature (T _g) of the resulting polymer increased as the cross-linking agent increased with temperature and pressure increasing at the same CO₂ density. Decomposition temperature is slightly increased as 1,4-BDA concentration increased. From these results, we can confirm that the thermal stability of the polymer increased as the cross-linking agent and EGDMA is the best cross-linking agent in term of the thermal stability.     

End-functional poly(methyl methacrylate)s via group transfer polymerization

Hydroxyl-, amine-, and lactone-end-functional poly(methyl methacrylate)s (PMMA) were prepared with controlled molecular weights and M_w/M_n = 1.06–1.19 via group transfer polymerization. This was achieved by the electrophilic termination of silyl ketene acetal ended PMMAs with benzaldehyde, N-trimethylsilyl benzaldimine, and 5,6-dihydro-2H-pyran-2-one, respectively. The number-average degree of functionalization, as determined by NMR/SEC, was in the range of 0.70–0.85. A Lewis acid was used for terminating silyl ketene acetal ended PMMA with N-trimethylsilyl benzaldimine, whereas tetra-n-butyl ammonium bibenzoate was used in the case of benzaldehyde and 5,6-dihydro-2H-pyran-2-one. MALDI-TOF MS analysis of the end-functional polymers indicated the competing formation of cyclic end groups due to a back-biting reaction along with end-functional PMMAs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2514–2531, 2007     

Structures and thermal properties of chitosan-modified poly(methyl methacrylate)

The emulsion polymerization of methyl methacrylate in the presence of chitosan with potassium persulfate (KPS) as an initiator was examined in a previous article. The free radicals that dissociated from KPS not only initiated the polymerization but also degraded the chitosan molecules. Therefore, in addition to its role as a cationic surfactant, chitosan also participated in the polymerization reaction. When the polymerization was complete, the latex polymer consisted of poly(methyl methacrylate) (PMMA) homopolymer and chitosan–PMMA copolymer. In this article, the structures and thermal properties of latex polymers are examined. Gel permeation chromatography was used to measure the molecular weight of the PMMA homopolymer, with the copolymer composition determined by an elemental analyzer. Scanning and transmission electronic microscopes were used to measure the size of latex particles from different reaction systems. The surface charges of latex particles at several different pH values were determined by the measurement of the ζ potential. All results agreed with the reaction mechanism proposed in the previous article. Finally, the presence of rigid chitosan increased the glass-transition temperature of the final latex polymers. Thermogravimetric analysis showed that the degradation behavior of latex polymers was similar to the unzipping mechanism of PMMA, yet the presence of chitosan units hindered the unzipping of the main chains in chitosan–PMMA copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1646–1655, 2001     

Polarized light‐induced photoisomerization in glassy poly(methyl methacrylate) and local relaxation processes of the polymer matrix

Photoisomerization kinetics of trans 4‐methoxystilbene induced by irradiation with linearly polarized light was investigated in the glassy state of poly(methyl methacrylate)(PMMA). The reaction was strongly selected by linearly polarized light as revealed by a large dichroic absorption generated upon irradiation. The optical anisotropy increases with increasing irradiation time and passes through a maximum before approaching an equilibrium value, which strongly depends on the experimental temperatures. From the decay of the total absorbance of the trans‐isomer observed upon irradiation with 313 nm UV light, it was found that the rates of the photoisomerization trans → cis were not significantly changed within the temperature range of the experiments. On the other hand, the reorientational relaxation times of the stilbene, which were directly measured by the annealing‐after‐irradiation techniques, depend strongly on temperature. These relaxation data were compared to the previous results obtained with dopants of the size larger than the stilbene and were discussed in conjunction with the local relaxation processes of the PMMA matrix. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 682–690, 2000