Effect of ZnO and organo-modified montmorillonite on thermal degradation of poly(methyl methacrylate) nanocomposites

Since a few years ago, a topic of interest consists in developing composites filled with nanofillers to improve thermal degradation and flammability property of poly(methyl methacrylate) (PMMA). In the present work, the effects of ZnO nanoparticles and organo-modified montmorillonite (OMMT) on the thermal degradation of PMMA were investigated by thermogravimetric analysis (TGA). PMMA-ZnO and PMMA-OMMT nanocomposites were prepared by melt blending with different (2, 5, and 10 wt%) loadings. SEM and TEM analyses of nanocomposites were performed in order to investigate the dispersion of nanofillers in the matrix. According to TGA results, the addition of ZnO nanoparticles does not affect the thermal degradation of PMMA under an inert atmosphere. However, in an oxidative atmosphere, two contrary effects were observed, a catalytic effect at lower concentration of ZnO in the PMMA matrix and a stabilizing effect when the ZnO concentration is higher (10 wt%). In contrast, the presence of OMMT stabilizes the thermal degradation of PMMA whatever be the atmosphere. Differential thermal analysis (DTA) curves showed surprising results, because a dramatic change of exothermic reaction of the PMMA degradation process to an endothermic reaction was observed only in the case of OMMT. During the degradation of PMMA-ZnO nanocomposites, pyrolysis-gas chromatography coupled to mass spectrometer (Py-GC/MS) showed an increase in the formation of methanol and methacrylic acid while a decrease in the formation of propanoic acid methyl ester occurred. In the case of PMMA-OMMT systems, a very significant reduction in the quantity of all these degradation products of PMMA was observed with increasing OMMT concentration. It is also noted that during PMMA-OMMT degradation less energy was released as the decomposition is an endothermic reaction and the material was cooled.     

The absorption coefficient spectrum of poly(methyl methacrylate) in the soft X-ray region

The total photoabsorption cross section for poly(methyl methacrylate) (PMMA) is measured experimentally, using synchrotron radiation, over the photon energy range 40 < E < 1000 eV. The experiments utilize nominally monochromatic radiation from a grazing incidence grating monochromator (the “Grasshopper” at the Canadian Synchrotron Radiation Facility) on the storage ring “Aladdin” at the University of Wisconsin. The raw experimental data are corrected for the spectral contamination of the incident radiation from the monochromator by utilizing a calculated photoabsorption spectrum for PMMA. The calculations are carried out using the “mixture” rule and reliable dipole oscillator strength distributions for smaller molecules related to PMMA.     

Methyl methacrylate in poly(methyl methacrylate)--validation of direct injection gas chromatography

Gas chromatography (GC) was investigated for the determination of residual methyl methacrylate (MMA) in heat-processed poly(methyl methacrylate) (PMMA) denture base material emphasizing recovery and validation. Standard solutions of MMA and emulsion-polymerized PMMA in dichloromethane were analysed, before and after distillation by a room-temperature air stream into a liquid nitrogen trap, and in the presence of PMMA by direct injection. Quantitative NMR analysis using dimethyl sulphoxide as internal calibration standard in deuterated chloroform solutions provided validation. Good concordance was observed between results under all conditions; no problems arose from direct injection of PMMA solution for GC. Good straight line responses in log-log plots were generally observed. For GC and MMA: log-log calibration curve (slope: 0.9552 +/- 0.0051, r2: 0.9992, n = 32) indicated some non-linearity (t = 8.875, p approximately 4 x 10(-10)). Distillation gave slope: 0.9751 +/- 0.0213 (NS versus unity; t = 1.172, p > 0.25). For PMMA solutions, distillation (r2: 0.9301) gave greater scatter than direct injection (r2: 0.9704). For NMR: log-log plot of calculated versus actual MMA (slope: 0.9363 +/- 0.0157, r2: 0.9969, n = 13) again indicated non-linearity (t = 4.0682, p = 0.0019). PMMA solutions gave slope: 0.9477 +/- 0.0328, r2 = 0.9858 (NS versus unity; t = 1.5941, p = 0.13). Determination of MMA in PMMA by GC is recommended.     

The degradation of poly(methyl methacrylate) in the effect of negative thixotropy

An investigation of the degradation of poly(methyl methacrylate) in the case of negative thixotropy of its solutions in tricresyl phosphate showed that the number of polymer bonds broken by flow as expressed through the decrease of molecular weight in the course of the effect is determined by shear energy imposed on the system, irrespective of the velocity gradient and temperature used.     

Catalytic effects of sulfates on thermal degradation of waste poly(methyl methacrylate)

The thermal degradation of waste poly(methyl methacrylate) (PMMA) in the presence of ferric sulfate, cupric sulfate, aluminum sulfate, magnesium sulfate, and barium sulfate was studied by using thermogravimetric analysis (TGA) in air atmosphere. The values of apparent activation energies (E_a) calculated by Flynn-Wall-Ozawa method were found to be in the order of PMMA + Fe₂(SO₄)₃ < PMMA + Al₂(SO₄)₃ < PMMA + MgSO₄ < PMMA + CuSO₄ < PMMA + BaSO₄ < PMMA. The mechanism of catalytic degradation of PMMA in presence of the sulfates was discussed and the results showed that the catalytic effects of sulfates have a relationship with the acidity of their respective metal ions.     

Characterization and degradation of the poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymer

Poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymers (PSXE-g-PMMA) were prepared by condensation reaction of poly(methylphenylsiloxane)-containing epoxy resin (PSXE) with carboxyl-terminated poly(methyl methacrylate) (PMMA), and they were characterized by gel permeation chromatography (GPC), infrared (IR), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The microstructure of the PSXE-g-PMMA graft copolymer was investigated by proton spin–spin relaxation T₂ measurements. The thermal stability and apparent activation energy for thermal degradation of these copolymers were studied by thermogravimetry and compared with unmodified PMMA. The incorporation of poly(methylphenylsiloxane) segments in graft copolymers improved thermal stability of PMMA and enhanced the activation energy for thermal degradation of PMMA. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2521–2530, 1998     

Light scattering studies of stereocomplex formation of stereoregular poly(methyl methacrylate) in solutions

The structure and stereocomplex formation of multi-stereoblock poly(methyl methacrylates) in three different solvents, acetone, tetrahydrofuran (THF) and chloroform, corresponding to strongly-, weakly- and non-complexing solvent, respectively, were investigated by a combination of static and dynamic laser light scattering. Our results revealed that the stereocomplex was caused by weak interactions, and could be melted at higher temperatures. In THF, the intermolecular and intramolecular interactions could be clearly separated at lower temperatures, and the structure of aggregated chains was linear. In acetone, a more compact structure was obtained, which was corroborated by the fact that the stereocomplex had a higher melting temperature than in THF.     

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.     

Characterization and degradation of poly(methylphenylsiloxane)–poly(methyl methacrylate) interpenetrating polymer networks

Poly(methylphenylsiloxane)–poly(methyl methacrylate) interpenetrating polymer networks (PMPS–PMMA IPNs) were prepared by in situ sequential condensation of poly(methylphenylsiloxane) with tetramethyl orthosilicate and polymerization of methyl methacrylate. PMPS–PMMA IPNs were characterized by infrared (IR), differential scanning calorimetry (DSC), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The mobility of PMPS segments in IPNs, investigated by proton spin–spin relaxation T₂ measurements, is seriously restricted. The PMPS networks have influence on the average activation energy E_a,av of MMA segments in thermal degradation at initial conversion. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1717–1724, 1999     

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     

On oxygen diffusion in poly(methyl methacrylate) films

ESR spectroscopy has been used to follow the kinetics of decay of radicals produced by UV-radiation in PMMA films upon exposure to oxygen in the temperature range 160-210 K. In the same films and at the same conditions, decay kinetics of phenanthrene phosphorescence has been studied at 180-220 K. Both types of the experiments give the same values for diffusion coefficients of oxygen in PMMA. Thus, from the oxygen diffusion standpoint, the sites of the radical stabilization and phenanthrene molecule localization in the polymer matrix do not differ.     

Glass transition of thin films of poly(2-vinyl pyridine) and poly(methyl methacrylate): nanocalorimetry measurements

Glass transitions were observed in thin films of poly(2-vinyl pyridine) (P2VP) and poly(methyl methacrylate) (PMMA) using a scanning nanocalorimetry technique which has both high sensitivity (10⁻⁹ J/K) and high scan rates (10⁴-10⁵ K/s). Samples were deposited by the spin-cast method. The thickness of samples was 100-400 nm. Glass transition temperature, obtained by nanocalorimetry, is shifted toward higher temperatures by 10-20 K and activation enthalpy of glass transition is shifted to lower values by factor of 2-4. The glass transition characteristics of both polymers are discussed in terms of the standard Tool-Narayanaswamy-Moynihan (TNM) multi-parameter model.     

Thermal degradation processes of poly(carbonate) and poly(methyl methacrylate) in blends coalesced either from their common inclusion compound formed with γ-cyclodextrin or precipitated from their common solution

Direct insertion probe pyrolysis mass spectrometry (DIP-MS) analyses of a PC/PMMA blend, coalesced from their common inclusion compound (ICs) formed with host γ-cyclodextrin (γ-CD) through removal of the γ-CD host, and a physical PC/PMMA blend, precipitated from their common solution, have been performed and compared with those of the coalesced and as-received homopolymers. A slight increase in the thermal stability of the PMMA component in the presence of PC was recorded both by TGA and DIP-MS compared to the corresponding homopolymers. The DIP-MS observations pointed out that the thermal stability and degradation products of these polymers are affected once they are included inside the IC channels created by the stacked host CDs. DIP-MS observations suggested that for both coalesced and physical PC/PMMA blends, an exchange reaction occurs between carbonates of PC and MMA, formed by depolymerization of PMMA above 300 °C, most likely due to diffusion of MMA monomer at the interface or even into the PC domains, where it can react producing low molecular weight PC bearing methyl carbonate and methacrylate chain ends. The results also indicated an ester-ester interchange reaction between PC and PMMA yielding a graft copolymer and low molecular weight PC chains bearing methyl carbonate end groups in the case of the coalesced blend. This can be atttributed to the presence of specific molecular interactions between the intimately mixed PMMA and PC chains in the coalesced PC/PMMA blend.     

The absorption coefficient spectrum and radiation degradation of poly(butene-1 sulfone) in the soft x-ray region

The interaction of soft x-rays with poly(butene-1 sulfone) (PBS) has been examined in detail, using monochromatized synchrotron radiation from the Canadian Synchrotron Radiation Facility (CSRF). The total photoabsorption cross section and neutral fragment yields of poly(butene-1 sulfone) (PBS) were measured over the photon energy range 20 ≤ hv ≤ 1000 eV. Energy deposition in this energy region results primarily in mass loss due to depolymerization. The chemical byproducts were detected using an in situ mass spectrometer. The experimental absorption data was corrected for spectral contamination of the incident monochromator radiation through the use of calculated photoabsorption cross sections. The calculations incorporated reliable dipole oscillator strength distributions of smaller molecules chemically related to PBS as input, and the results are reliable over the absorption regions away from the edges. The corrections thus applied to the initial experimental data have produced the most reliable spectrum available presently for PBS. The near-edge extended x-ray absorption fine structures (NEXAFS) were measured and assigned for the sulfur 2p (L_2,3), carbon 1s (K) and oxygen 1s (K) edges. The sulfur 2p edge of PBS was found to be very similar to that found in the photoabsorption spectrum of gaseous SO₂, particularly in the continuum region. The two broad peaks in the continuum have been assigned as σ*-shape resonances caused by a centrifugal potential barrier. Ionization of the valence orbitals of PBS produced a significant increase in the depolymerization reaction, and subsequent neutral yields of sulfur dioxide (SO₂) and 1-butene. © 1993 John Wiley & Sons, Inc.     

Preparation of poly (methyl methacrylate)/LDH nanocomposite by exfoliation-adsorption process

Exfoliated nanocomposite based on Mg, Al layered double hydroxide (Mg,Al-LDH) and poly(methyl methacrylate) (PMMA) has been prepared by exfoliation/adsorption process with acetone as co-solvent. The product was characterized by X-ray diffraction (XRD), thermal analysis and High Resolution Transmission Electronic Microscope (HREM). The results suggest that the brucite-like sheets of LDH disperse individually in the polymer matrix, and the thermal stability of the nanocomposite increases highly.     

Organic–inorganic hybrid materials. V. Dynamics and degradation of poly(methyl methacrylate) silica hybrids

Poly(methyl methacrylate)–silica hybrid materials (PMMA–SiO₂) were prepared by in situ polycondensation of alkoxysilane in the presence of trialkoxysilane‐functional PMMA. Infrared, differential scanning calorimetry, ²⁹Si and ¹³C nuclear magnetic resonance spectroscopy, and thermogravimetric analysis were used to study the PMMA–SiO₂ hybrids. The effects of the content and kind of the alkoxysilane on the dynamics and stability of the PMMA–SiO₂ hybrids were investigated in this study.The dynamics of SiO₂within hybrids were investigated with ²⁹Si–¹H cross‐polarization. The spin‐diffusion path length was on a nanometer scale estimated with the spin–lattice relaxation time in the rotating frame (T). The apparent activation energies for the degradation of the hybrids under air and nitrogen were evaluated by the van Krevelen method. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1972–1980, 2000     

Preparation of poly(methyl methacrylate) microcapsules by in situ polymerization on the surface of calcium carbonate particles

Poly(methyl methacrylate) (PMMA) microcapsules were prepared by the in situ polymerization of methyl methacrylate (MMA) and N,N′-methylenebisacrylamide on the surface of calcium carbonate (CaCO₃) particles, followed by the dissolution of the CaCO₃ core in ethylenediaminetetraacetic acid solution. The microcapsules were characterized using fluorescence microscopy, atomic force microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. The average sizes of the CaCO₃ particles and PMMA capsules were 3.8 ± 0.6 and 4.0 ± 0.6 μm, respectively. A copolymer consisting of MMA and rhodamine B-bearing MMA was also used to prepare microcapsules for fluorescent microscopy observations. Fluorescein isothiocyanate-labeled bovine serum albumin was enclosed in the PMMA microcapsules and its release properties were studied.     

Preparation and characterization of carboxylic-containing poly(methyl methacrylate) nanolatexes

Poly(methyl methacrylate) (PMMA)-based latex particles bearing carboxylic groups at the surface were prepared via emulsion polymerization. The polymerization recipe and process were optimized in order to target monodisperse particles with diameters around 100 nm. The polymerizations were performed using 4,4-azobis(4-cyanopentanoic) acid (ACPA) as initiator and sodium dodecyl sulphate (SDS) as surfactant. The polymerization conversion was determined by both gas chromatography and gravimetry. The final latexes were characterized with respect to particle size, size distribution, surface charge density, electrokinetic properties (i.e. electrophoretic mobility vs pH and ionic strength) and colloidal stability (i.e. coagulation rate constants vs pH and stability factor vs ionic strength).     

The influence of β-FeOOH nanorods on the thermal stability of poly(methyl methacrylate)

Colloidal dispersions consisting of β-FeOOH nanorods with three different aspect ratios (4, 75 and 120) were synthesized using thermal hydrolysis of FeCl₃ solutions. After surface modification with oleic acid, the β-FeOOH nanorods were incorporated in poly(methyl methacrylate). Transmission electron microscopy and X-ray diffraction were applied for structural characterization of the β-FeOOH nanorods. The influence of inorganic phase on the thermal properties of PMMA matrix was studied using thermogravimetry and differential scanning calorimetry. Improvement of the thermal stability and increase of the glass transition temperature were found with the increase of content of inorganic phase and the increase of aspect ratio.