Electrospinning of cyclodextrin functionalized poly(methyl methacrylate) (PMMA) nanofibers

Cyclodextrin functionalized PMMA nanofibers (PMMA/CD) were successfully produced by electrospinning technique with the goal to develop functional nanowebs. Bead-free uniform electrospun PMMA/CD nanofibers were obtained from a homogeneous solution of CDs and PMMA in dimethylformamide (DMF) using three different types of CDs, α-CD, β-CD and γ-CD. The electrospinning conditions were optimized in order to form bead-free PMMA/CD nanofibers by varying the concentrations of PMMA and CDs in the solutions. The concentration of CDs was varied from 5% up to 50% w/w, with respect to the PMMA matrix. We find that the presence of the CDs in the PMMA solutions facilitates the electrospinning of bead-free nanofibers from the lower polymer concentrations and this behavior is attributed to the high conductivity and viscosity of the PMMA/CD solutions. The X-ray diffraction (XRD) spectra of PMMA/CD nanowebs did not show any significant diffraction peaks indicating that the CD molecules are homogeneously distributed within the PMMA matrix and does not form any phase separated crystalline aggregates. Furthermore, attenuated total reflection Fourier transform infrared (ATR-FTIR) studies elucidate that some CD molecules are located on the surface of the nanowebs. This suggests that these CD functionalized nanowebs may have the potential to be used as molecular filters and/or nanofilters for waste treatment purposes.     

Degradation of poly(methyl methacrylate) (PMMA) with aluminum nitride and alumina

This paper deals with the thermal and thermal-oxidative degradation of pure poly(methyl methacrylate) (PMMA), PMMA/A1N and PMMA/Al₂O₃ composites. Kinetic parameters were determined from the weight loss data using non-isothermal Thermogravimetric Analysis (TGA). The amount and morphology of the carbon residue in the burnt samples under N₂ and air atmospheres were also investigated using a Leco combustion analyzer. This study also showed that the normally accepted three-stage polymer thermal degradation, and hence three regions of Arrhenius linearity, can be treated with one value of activation energy. This is a basic departure from the normally accepted three different regions and applying the same diffusion equation (such as Jander diffusion) separately to each region. In nitrogen atmosphere, the activation energy of pure PMMA was 129.4 kJ/mol; however, the activation energies of 14% PMMA/AlN and PMMA/Al₂O₃ were found to be 119.5 and 118.2 kJ/mol, respectively.     

Halofluorocarbon plasma treatments of polystyrene and poly(methyl methacrylate) surfaces

The effect of halofluorocarbon (CF₄, CF₃Cl, CF₃Br) discharges on polystyrene (PS) and poly(methyl methacrylate) (PMMA) has been studied. It has been shown that, depending on the halogen/halocarbon radical ratio, polymerization or etching can occur. The discharge chemistry has been altered by changing the excitation electrode material, and thus enhancing or depressing the amount of halocarbon radicals in the discharge. In CF₃Br and CF₃Cl plasmas, mass spectroscopy revealed the formation of molecular chlorine and bromine. Ion bombardment has been shown, in both PS and PMMA, to enhance etch rates and to depress the deposition of plasma polymer. While the etch rates of PMMA by CF₄, CF₃Cl and CF₃Br have the same kinetic dependence on bias voltage, the same is not true for PS. In this case the etch rates by CF₃Cl and CF₃Br discharges are preferentially enhanced, due to the different interaction with the species present in the discharge. As to derivatization, the introduction of halogens is more efficient in PS than in PMMA. Interestingly, the introduction of Cl and Br is enhanced much more than that of F, possibly due to the interaction of the PS aromatic ring with molecular chlorine and bromine present in the discharge.     

Optical and thermal spectroscopic studies of luminescent dye doped poly(methyl methacrylate) as solar concentrator

A luminescent solar concentrator was prepared that was based on a bulk sheet of poly(methyl methacrylate) doped with different luminescent dyes (K1, K27, and Lpero) during the polymerization process. Photo‐ and thermal‐stability studies revealed that the Lpero dye system is the most stable one. The electronic transition mechanism for the concentrator systems was obtained by the darktrap and phototrap spectroscopy technique. The results were correlated with the outdoor test measurements over 1 year. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3316–3323, 1999     

Stress optical studies of oriented poly(methyl methacrylate)

A series of samples of oriented poly(methyl methacrylate) was produced by hydrostatic extrusion at temperatures below the glass transition temperature. The development of orientation in the process was monitored by the measurement of birefringence which was shown to depend on the extrusion temperature as well as on the applied deformation. Additional information to characterize the oriented state was obtained by measuring the shrinkage force which developed when the oriented sample, constrained to constant length, was heated to a temperature just above the glass transition temperature; specimens free to contract all recovered to the isotropic state and original dimensions on annealing at this temperature. Most measurements were made on specimens ‘as extruded’ with additional studies made on specimens annealed at temperatures above the extrusion temperature but below the glass transition. The data, which have strong implications with regard to deformation mechanisms, are interpreted both at a molecular level in terms of deviations from an ideal rubber network, and at a more phenomenological level in terms of the Mooney-Rivlin equation.     

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.     

Rheological behavior of blends of poly(methyl methacrylate) (PMMA) and poly(acrylonitrile-stat-styrene)-graft-polybutadiene (ABS)

The rheological behavior of blends of poly(methyl methacrylate) (PMMA) and poly(acrylonitrile-stat-styrene)-graft-polybutadiene (ABS) was investigated using a cone-and-plate rheometer. The rheological properties measured were shear stress (σ₁₂), viscosity (η), and first normal stress difference (N₁) as functions of shear rate (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma$ \end{document}) in steady shearing flow, and storage modulus (G′) and loss modulus (G″) as functions of frequency (ω) in oscillatory shearing flow. It has been found that the rheological behavior of blends of ABS and PMMA was very similar to that of blends of poly(styrene-stat-acrylonitrile) (SAN) and PMMA, in that N₁ in logarithmic plots of N₁ versus σ₁₂, and G′ in logarithmic plots of G′ versus G″, vary regularly with blend composition. This has led us to conclude that the rubber particles that are grafted on an SAN resinous matrix in ABS resin plays only a minor role in influencing the compatibility of ABS/PMMA blends, and that the SAN chains attached to the surface of rubber particles, and the SAN matrix phase, play a major role in compatibilizing ABS resin with PMMA.     

Influence of molecular weight on the fracture of poly(methyl methacrylate) (PMMA)

A model is proposed to explain the dependence of fracture parameters on the molecular weight of glassy polymers. The model assumes that the fracture event occurs in two stages; the first involves the orientation of polymer chain segments between entanglement points and the second, the fracture itself. A value has been calculated, (～0.6J m^?2), for the fracture surface energy corresponding to the lower critical molecular weight between entanglements, M=M_e. Allowing for the simplifying assumptions made in its derivation, this value is in good agreement with that found experimentally. It is proposed that, after the chain segments between entanglements crossing a plane have been fully extended, two possible mechanisms are involved; chain ‘pull-out’ up to a maximum governed by the time scale of the local fracture event, or chain scission. Using the concept of a reptating chain it is proposed that above M ～2 M_e there is a relationship between the fracture energy (γ) and the molecular weight of the form γ∝ ∝M² up to a critical value of M, above which γ is constant. It has been shown that there is some agreement with experimental relationships determined independently.     

Synthesis and properties of poly(methyl methacrylate)/montmorillonite (PMMA/MMT) nanocomposites

PMMA/MMT nanocomposites were successfully synthesized via in situ intercalative polymerization, and characterized by means of wide‐angle X‐ray diffractometry, transmission electron microscopy, thermal gravimetric analysis, dynamic mechanical analysis and Fourier‐transform infrared analysis. The nanocomposites possess partially exfoliated and partially intercalated structure, in which the silicate layers are exfoliated into nanometre secondary particles with thickness of less than 20 nm and uniformly dispersed in the polymer matrix. In comparison with pure PMMA, the thermal stability, glass transition temperature, and mechanical properties of the polymer are notably improved by the presence of the nanometric silicate layers. It was found that part of the PMMA chains in the nanocomposites are well immobilized inside and/or onto the layered silicates and, therefore, the unique properties of the nanocomposites result from the strong interactions between the nanometric silicate layers and the polymer chains. Copyright © 2003 Society of Chemical Industry     

Pyrolysis-evolved gas-infrared spectroscopic characterization of poly(methyl methacrylate) copolymer glazing materials

The linear temperature programmed pyrolysis of some commercial crosslinked poly(methyl methacrylate) copolymers has been examined by the technique of pyrolysis-evolved gas-infrared analysis. Methyl methacrylate monomer, methanol, and carbon dioxide were detected in the pyrolysis gases. The profiles of rate of evolution against temperature were used to identify the presence of occluded monomer and thermally unstable and groups such as unsaturation. The evolution profiles for methyl methacrylate and methanol were found to be characteristic for each type of crosslink. Evolution of methanol between 250°C and 300°C, and between 300°C and 350°C has been attributed to condensation reactions of carboxylic acid and primary amide groups, respectively, with adjacent ester groups. The evolution profiles were used to distinguish between samples from different manufacturers, and to identify material in aircraft canopies.     

Viscoelastic behaviour of epoxy resins modified with poly(methyl methacrylate)

The viscoelastic behaviour of a stoichiometric diglycidyl ether of bisphenol-A, (DGEBA), 4,4′-diaminodiphenylmethanes (DDM)s epoxy matrix modified with several amounts of poly(methyl methacrylate) (PMMA) has been studied by dynamic-mechanical analysis. Mixtures pre-cured at 80°C ranged from transparency to opacity as thermoplastic content changed from 5 to 15wt%. These changes have been attributed to variations in the ratio between polymerization rate and phase separation rate when PMMA content increased in the mixtures. When PMMA segregated from the epoxy matrix during curing, it had no influence on the crosslinking density of the epoxy phase. The clear decrease of temperature and activation energy of the β relaxation with respect to those values for the neat matrix, observed for the 5wt% PMMA-containing mixture but not for the 15wt% PMMA-containing one, are proposed to be a consequence of physical interactions between the PMMA chains and some epoxy oligomers. The dissimilar variation of the height of the ω relaxation with frequency when compared to that for the other relaxations studied, outlines the significance of physical factors influencing this relaxation. © 1998 Society of Chemical Industry     

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.     

Mechanical property studies of poly(methyl methacrylate)-grafted viscose fibers

Graft copolymerization of methyl methacrylate (MMA) on viscose fibers (grade 1.5 × 51 mm; Nagda; grey staple; bright bleached) was studied under a photoactive condition with visible light using conventional Mohr's salt–potassium persulphate as the redox initiator. The mechanical properties of the grafted viscose fiber, such as tenacity, breaking extension, and initial modulus were studied. The effect of monomer–solvent combination on viscoelastic nature (elasticity work recovery and stress relaxation) of the grafted fibers have also been explained. The moisture regain characteristics of the grafted fibers were also studied. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2585–2591, 1998     

Surface studies of polystyrene–poly(methyl methacrylate) diblock copolymers precipitated by different precipitants

Diblock copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with varying compositions in the mole fractions of PS were prepared, and were obtained in particle state by different methods of precipitation. The morphology of the precipitates was studied by electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and viscometry. From these studies it was found that the precipitates of diblock copolymers have core-micelle structures, the components of the core and the surrounding micelle being different by precipitation histories.     

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.     

Thermodynamic, morphological, mechanical and fracture properties of poly(methyl methacrylate)(PMMA) modified divinylester(DVE)/styrene(St) thermosets

Modified St/DVE cured materials were formulated with a commercial DVE_C (M_n=1015 g/mol) and a synthesized (583 g/mol) DVE_L resins and styrene, adding a high molecular weight PMMA as modifier. A thermodynamic analysis of the initial miscibility for the St-PMMA and DVE-PMMA quasibinary systems was realized using the experimental cloud-point curves (CPC), in order to determine the binary interaction parameters. Calculated CPC for the quasiternary St/DVE/PMMA at 25 °C showed that St/DVE_L/PMMA is miscible in the whole concentration range, while the St/DVE_C/PMMA becomes partially miscible almost at the start of curing reaction (very low conversions). This miscibility behavior originates quite different morphologies in the systems cured at room temperature. Final materials with DVE_L showed typical nodular microphase morphologies generated by polymerization induced phase separation (PIPS) mechanism. Materials with DVE_C showed typical macrophase morphologies characterized by droplets-like domains, with secondary phase separation inside the droplets and in the mother phase. These morphological structures were directly related to the thermal and mechanical properties of the final systems. The low molecular weight resin generates a thermoset of higher glass transition temperature, bending modulus, and compression yield stress, but lower fracture resistance than the high molecular weight commercial resin. The addition of a thermoplastic modifier allowed to improve the fracture resistance without the unwanted reduction in modulus, which is inevitable when using elastomeric additives. The reason for the existence of an optimum modifier concentration is also discussed.     

Stereocomplex formation in polybutadiene-syndiotactic poly(methyl methacrylate) block copolymers blended with isotactic poly(methyl methacrylate)

Summary The process of stereocomplexation in blends of isotactic poly(methyl methacrylate)s and polybutadiene-syndiotactic poly(methyl methacrylate) diblock copolymers was studied by differential scanning calorimetry as a function of molar mass of the constituents, annealing time and temperature. The amount of complex formed is dependent on these three parameters, while the temperature of decomposition of the complex is only dependent on the annealing temperature. Complex formation can be observed in blends containing a copolymer with a very low molar mass syndiotactic poly(methyl methacrylate) block (Mn=700). In contrast to homopolymer blends, for which two endotherms of decomposition were generally reported, only one endotherm is observed for copolymer-homopolymer blends. This behavior is attributed to the elastomer block.     

The limits of linear viscoelasticity in poly(methyl methacrylate) and poly(ethyl methacrylate)

The limit of linear viscoelasticity is determined for poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) in uniaxial tension creep over the temperature range of 20° to T_g ?10°C. The time span covered is from 10 to 1000 sec. The linear limit is defined as the point at which the creep compliance deviates by more than 1% from its mean value in the linear viscoelastic range. For both materials, the stress limit of linear viscoelasticity falls to a minimum or plateau level at a temperature below T_g. It is suggested that the β-mechanism plays an important role in the existence of this minimum.     

Surface modification of poly(vinyl chloride) with poly(methyl methacrylate)/poly(dimethyl siloxane) graft copolymers

X-ray photoelectron spectroscopy is used to study the surface segregation of siloxane in dilute blends of poly(methyl methacrylate)/poly(dimethyl siloxane) graft copolymers in poly(vinyl chloride)(PVC). The graft copolymers are found to be extremely efficient surface modifiers, which form, when added in amounts of 0.5% or more, a continuous siloxane overlayer on the surface of PVC. © 1995 John Wiley & Sons, Inc.