Glassy Polymer Matrix Research Articles

Temperature dependence of ESR spectra of nitroxide spin probe in glassy polymers

AbstractTemperature dependencies of ESR spectra of nitroxide spin probes in glassy polymers near and below glass transition temperature were examined in detail. Three temperature ranges, each characterized by specific changes in spectral shape, were defined. (i) In the low temperature range, ESR spectra of nitroxide radical in glassy polymer matrix weakly depend on temperature and remain qualitatively the same. (ii) In the intermediate temperature range, significant changes in the shape of spectra are observed. (iii) A new phenomenon was revealed near and below glass transition temperature: narrowing of linewidths occurs while the ratio of amplitudes of different components varies insignificantly. Analysis of molecular rotational mobility was carried out by means of commonly used empirical approaches. It was shown that widely used formulas and empirical approaches are not applicable for characterization of molecular mobility in glassy polymers. Mechanisms of rotational molecular movements in glassy polymers are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 563–575, 2009

Synthesis of small polymeric nanoparticles sized below 10 nm via polymerization of a cross-linker in a glassy polymer matrix

Small polymeric nanoparticles sized below 10 nm were effectively synthesized via free radical polymerization of a cross-linker in a glassy polymer matrix, owing to the successful prohibition of aggregation between the primary nanoparticles by the matrix.

Molecular Dynamics Simulation Study of Water in Amorphous Kapton

Molecular dynamics (MD) simulations of more than 40 model systems of dry and hydrated poly(pyromellitimide-1,4-diphenyl ether) (PMDA-ODA) polyimide, also known as Kapton, were undertaken in order to study the specific interactions between water and a glassy polymer matrix. Dry amorphous Kapton models were generated using a hybrid pivot Monte Carlo-MD single-chain sampling technique and were found to reproduce many features found experimentally. Water was subsequently introduced into the polyimide systems with weight percentages ranging from 1.4 to 10 wt % at 373 K. At the lower concentrations, water is found to occupy the pre-existing void space in the polymer matrix. On the other hand, there are significant changes in the volumetric, energetic, and conformational properties of the chains for water contents above ∼3%. The static and dynamic properties of the hydrogen bonds have been analyzed. In all cases under study, water is preferentially hydrogen-bonded to two sites, thus forming bridges. These water ...

Behaviour of the heterogeneous glassy polymers: Computational modelling and experimental approach

In the present study we have investigated the mechanical behaviour of multi-phase solid materials by using the micro–macro computational approach. Spherical rubber particles embedded in amorphous glassy polymer matrix are taken into account as the heterogeneous composite system. In order to predict the micromechanical deformation behaviour of the composite, we propose a combination of an appropriate elastic–viscoplastic constitutive equation describing the nonlinear behaviour of the polymeric matrix with a hyperelastic model for the rubbery phase. The resulting hyperelastic–viscoplastic model accurately predicts the intrinsic strain rate, the temperature dependent behaviour and the subsequent strain hardening of rubber modified polymer. The representative volume element (RVE) selected in the homogenisation process by finite element analysis, is constructed by assuming local spatial periodicity of the microstructure. The macroscopic stresses and strains are obtained by averaging RVE stress–strain field. The validity of both homogenisation procedure and the constitutive model is achieved by comparison with experimental data for uniaxial compression tests on PMMA and RT-PMMA at different temperatures. A fair agreement is obtained between numerical and experimental results.

Gas permeation in poly(ether imide) nanocomposite membranes based on surface-treated silica. Part 1: Without chemical coupling to matrix

The long range objective of this research is to understand to what extent the presence of nanosized particles may change the local properties, and specifically permselectivity characteristics, of a glassy polymer matrix or whether conventional composite theory can be applied to such composites, i.e., the matrix properties are not changed by the filler. In this work, nanocomposite membranes based on an amorphous, glassy poly(ether imide) were formed by incorporating three kinds of hydrophobically treated fumed silica by solution casting and melt processing techniques. However, there is considerable evidence that these nanocomposites contain voids or defects, probably at the polymer–particle interface or within aggregates, that increase gas permeability and decrease selectivity. Thus, the primary focus of this paper is the relation between the extent of voids formed in the nanocomposite and the permeation properties. In addition, this paper deals with techniques for dispersing nanosized particles, fumed silica, in the polymer matrix, characterization of morphology of this mixture using TEM and SEM, and evaluation of local properties based on gas permeation.

Free Volume Determination of Azobenzene−PMMA Copolymer by a Pulsed Low-Energy Positron Lifetime Beam with in-Situ UV Illumination

The free volume properties of a poly(methyl methacrylate)−azobenzene copolymer were for the first time directly probed by use of a low-energy positron lifetime beam with in-situ excitation capabilities, showing that the free volume cavity size was not appreciably influenced by photoisomerization and thermal isomerization in the temperature range 34−180 °C. Isomerization is therefore suggested to occur without any molecular rearrangement of the glassy polymer matrix, which would also account for the lack of any shift to shorter wavelengths for the photoisomerization occurring in a glassy polymer in comparison to a chloroform solution. A decrease in the thermal isomerization rate at room temperature caused by the glassy polymer is explained in terms of a model in which only a fraction of the azobenzene is free to isomerize. The cis-azobenzene was found to be an efficient inhibitor of positronium formation, which enabled measurements of thermal isomerization rates and changes in the steady-state concentration of cis-azobenzene for an illuminated sample as a function of temperature.

Relaxation processes in a glassy polymer containing methanol molecules

Abstract The interaction of small guest molecules with the molecular degrees of freedom of a glassy polymer matrix is investigated, i.e. (i) the dynamics of these guest molecules and (ii) their effect on the secondary ‘β’ and main ‘α’ relaxations of the host polymeric matrix. The system considered here is the glassy poly(methyl metacrylate) modified by introduction and desorption of methanol. The dynamics of the system is observed by means of low-frequency mechanical and wide band dielectric spectroscopies. The presence of small molecules in the PMMA glassy matrix induces several effects, namely (i) a strong relaxation peak develops at low temperature (near 120 K at 1 Hz and called α m in the following), (ii) the strength of the β relaxation is increased while the temperature of the maximum shifts towards the low temperatures, (iii) a sharp peak appears superimposed on the β peak, and finally (iv) the α relaxation shifts towards the low temperatures. Dielectric and mechanical spectroscopies results are in agreement and make it possible to capture the dynamical behavior in a wide frequency range (eight decades). The experimental results are explained on the basis of physical concepts recently introduced in the physics of glassy matter: cooperativity and nanoheterogeneity. In particular, the low-temperature relaxation process α m is attributed to cooperative motions in methanol clusters which form in the nanoheterogeneous polymeric matrix, in agreement with small angle X-rays scattering and low-frequency Raman scattering observations recently reported.

Analysis of butyl acrylate diffusion in a glassy polystyrene matrix to predict gradient structure

AbstractTo be able to control composition structure in gradient polymers prepared by sequential polymerization, diffusion phenomena has to be considered, particularly for the first 100% weight increment in a glassy polymer matrix. With that purpose, an analytical model to predict diffusion in that region has been developed for amorphous polymers. The inclusion of a relaxation time to estimate surface concentration changes during sorption led to diffusion coefficients one order of magnitude higher than Fickian coefficients. However, adding a volume increment term to account for polymer swelling, diffusion coefficients went up to 48 times the Fickian values. Experimentally, butyl acrylate with a small amount of photosensitizer was diffused into a slightly crosslinked polystyrene slab matrix at different temperatures in the glassy region. After fixing the gradient composition by photopolymerization, chemical structures throughout the slab were determined by FTIR. The proposed model was confronted with experimental sorption showing a close fit at the different temperatures in the region of interest. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1343–1348, 2001

Diffusion of Liquid Polystyrene into a Glassy Poly(phenylene oxide) Matrix. Diffusion Mechanisms and Experimental Verification

The diffusion of a liquid polymer into a glassy polymer matrix has been studied in a range of temperatures below the glassy matrix glass transition temperature (Tg) and for different diffusion times. The liquid polymer used is low-molecular-weight polystyrene (PS) with a narrow molecular weight distribution, and the glassy matrix is poly(phenylene oxide); the two are miscible at any concentration. A simple physical diffusion model is proposed to correlate and predict diffusion rates, assuming a relatively rapid dissolution of the high-Tg polymer at the liquid−solid interface and a relatively slow diffusion process that produces a thick interphase. The local chemical compositions, local glass transition temperatures, and local PS monomeric friction coefficients change markedly along the diffusion path across the interphase; these changes are well predicted by the diffusion model and have also been experimentally verified. The large changes in local Tg values cause huge changes in the PS monomeric friction ...

Sorption and diffusion of low molecular weight gases and vapors in glassy polymers at high concentration of sorbate

A theoretical approach has been developed to describe the sorption and diffusion processes of low weight molecular gases and vapors in polymers at wide ranges of sorbate concentration. The equation of an S-shaped gas sorption isotherm in glassy polymer matrix has been derived. The concentration dependence of the sorbate molecule diffusion coefficient has been established. For an S-shaped sorption isotherm, this dependence is nonmonotonous. The conditions of cluster formation of sorbate molecules have been analyzed within the proposed approach, in which it is possible to determine a correlation between these conditions and parameters of sorption isotherm. The comparison of the experimental and theoretical data provides an assessment of the microscopic characteristics of investigated polymer–vapor systems, such as the distances between vapor molecules in a matrix corresponding to intermolecular repulsion and attraction. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2314–2323, 1999

Sorption and diffusion of low molecular weight gases and vapors in glassy polymers at high concentration of sorbate

A theoretical approach has been developed to describe the sorption and diffusion processes of low weight molecular gases and vapors in polymers at wide ranges of sorbate concentration. The equation of an S-shaped gas sorption isotherm in glassy polymer matrix has been derived. The concentration dependence of the sorbate molecule diffusion coefficient has been established. For an S-shaped sorption isotherm, this dependence is nonmonotonous. The conditions of cluster formation of sorbate molecules have been analyzed within the proposed approach, in which it is possible to determine a correlation between these conditions and parameters of sorption isotherm. The comparison of the experimental and theoretical data provides an assessment of the microscopic characteristics of investigated polymer–vapor systems, such as the distances between vapor molecules in a matrix corresponding to intermolecular repulsion and attraction. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2314–2323, 1999

Relative rates of photooxidation of benzil to benzoyl peroxide in various polymer matrices

Benzil (BZ), 16 wt.-%, has been irradiated (>400 nm) at ambient temperature in aerated polystyrene (PS), poly(methyl methacrylate) (PMMA), polycarbonate (PC), polysulfone (PSF) and poly(vinyl chloride) (PVC) films. The rate of BZ consumption, leading primarily to the formation of benzoyl peroxide, was followed by infrared spectroscopy. The rate of reaction is sensitive to the nature of the glassy polymer matrix and decreases in the order: PS > PC > PVC > PSF > PMMA. The dependence of the rate of BZ consumption on the concentration of dissolved molecular oxygen in the polymer matrices is rather complex. A kinetic treatment, assuming steady-state conditions, leads to the conclusion that the sum of the rates of bimolecular formation of benzoyl peroxide and quenching of BZ triplets by molecular oxygen, (k ox + k q )[ 3 O 2 ], represents only 0.8-13% of the sum of the unimolecular rates of radiationless and radiative deactivation (including k p , the pseudo first-order rate constant for reaction of BZ triplets with the polymer), (k d + k ph + k p ), in the various polymer matrices.

Effect of postmold curing on plastic IC package reliability

Nearly all IC encapsulating compounds require a postcure treatment to ensure integrated circuit (IC) package reliability. The issue of postcuring and this effect on IC package reliability performance are considered in this article. We examined the development of various encapsulating compounds' properties with various durations of postcure time. It was found that the mechanical strength, glass transition, and adhesion strength were increased with increasing duration of postcure time compared to as-molded samples. However, these properties could reach ultimate values after postcuring for 1–2 h. It was also seen that the moisture uptake was increased for samples that have been post-mold-cured due to increased crosslinking density causing a large free volume in the glassy polymer matrix. C-mode scanning acoustic microscopy (C-SAM) analyses were performed to investigate the effect of the duration of postcure time on the IC package reliability and they show a good relationship with the evolution of the compound's properties during the postcure process. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2187–2193, 1998

Morphological and Chemical Characterization of a Mechanically Alloyed Rubber Toughened PMMA With X-Ray Spectromicroscopy

Abstract Rubber toughening was first developed about seventy years ago as a method of increasing the impact resistance of brittle glassy polymers. Since that time, a wide variety of techniques have been developed to produce discrete dispersions of rubber within a glassy polymer matrix. We are exploring a new route to rubber-toughen polymer through the non-equilibrium process of mechanical alloying (high-energy ball milling). Here we have blended poly(methyl methacrylate) (PMMA) with polyisoprene (PI) (see the insets in Fig. 1 for chemical structures) and have characterized the resultant blends with Scanning Transmission X-ray Microscopy (STXM) in order to obtain chemical, as well as morphological, information about the blends. The STXM technique utilizes tuneable soft x-rays that are focused with a diffraction zoneplate to a microprobe of 45 nm full width at half maximum. Thin sections of the sample are placed at the microprobe and the transmitted photon intensity is measured.

Structure−Activity Relationship of New Nonlinear Optical Organic Materials Based on Push−Pull Azo Dyes. 3. Guest−Host Systems

Several new push−pull azobenzene dyes with different electron-withdrawing groups, steric hindrance, and hydrogen-bonding capabilities were dispersed in poly(N-methacryloyl-N‘-phenylpiperazine), a glassy polymer matrix. After orientation by corona poling, the second harmonic generation (SHG) signals of the guest−host systems were measured as a function of time and temperature and fitted with Kohlrausch−Williams−Watts (KWW) stretched exponentials. The variations of their nonlinear susceptibilities at time zero and in their relaxation behavior were correlated with the changes of the chromophore chemical structure. Rigid rod structures always presented the best orientability and stability of the nonlinear optical properties.

Calorimetric probes of carbon dioxide sorption in bisphenol-A based polymers

We present direct measurements of the partial molar enthalpy of carbon dioxide sorption in a family of structurally related bisphenol-A based polymers. Polymers included in this study are: bisphenol-A polycarbonate, tetramethyl polycarbonate, tetrachloro polycarbonate and tetrabromo polycarbonate. All samples were conditioned at 300 psig prior to measurement. Enthalpy changes were determined using a Setaram C80D microcalorimeter equipped with high pressure cells. The magnitude of the heat of sorption does not correlate well with polymer free volume, gas solubility or gas partial molar volume. However, the values are consistent with heats of sorption calculated from the temperature dependence of solubility. The results suggest that free volume regions are not uniformly accessible; occupation of some free volume regions requires unfavourable deformation of the glassy polymer matrix. The measured heat of sorption represents an energetically weighted average of those free volume regions which are occupied.

A Double-Modulation ESR Study of Internal Dynamics in the Glassy Polymer Matrix Detected by a Nitroxide Spin Probe

The double-modulation ESR spin-probe technique was employed to study slow-motional dynamics in amorphous polymer matrices of polybutadiene, polyisobutylene, poly(methyl methacrylate), and paraffin. It was shown that the low-lying excitation levels of the polymer matrix, found in the range from 77 to 190 K below the internal spin-probe transition, affect the effective relaxation rate of a perdeuterated nitroxide probe. The interrelationship between the effective relaxation rates and the local molecular dynamics of side-chain groups attached to the polymer backbone was observed. Possible relaxation mechanisms are discussed within the electron–nuclear dipolar interaction.

In-situ determination of photoresist glass transition temperature by wafer curvature measurement techniques

The glass transition temperature (Tg) is an important feature of the glassy polymer matrix that forms the structure of lithographic films. Tg is usually determined through thermal analysis, generally using Differential Scanning Calorimetry (DSC). However, this kind of equipment, encountered in a laboratory environment, is not easily available on an industrial site. This paper demonstrates that the Tg of photoresists can also be determined using wafer curvature measurement (WCM) techniques. This non destructive technique can easily be performed in a clean-room environment. This new possibility for determining the Tg of resist films in an industrial environment should facilitate the understanding and control of lithographic processes.

Relationship between reorientational motions of a photochromic dopant and local relaxation processes of a glassy polymer matrix

The reorientational relaxation process of the photochromic molecule 9-hydroxymethyl-10-[(naphthylmethoxy)-methyl]anthracene (HNMA) was observed in glassy poly(methyl methacrylate) (PMMA). For this purpose, the intramolecular photodimerization of HNMA incorporated in a PMMA matrix was selectively induced by irradiation with linearly polarized light. The optical anisotropy created in this way in the sample was allowed to relax to equilibrium by annealing at different temperatures. The reorientational relaxation of HNMA associated with this thermal treatment was subsequently observed by monitoring the time dependence of the two dichroic absorbance components of the anthracene moieties of HNMA. It was found that this relaxation process is well described by the sum of an exponential function of annealing time and a baseline which strongly depends on temperature. This fact implies that HNMA was not completely randomized in the glassy state of PMMA upon annealing. Furthermore, within the range of experimental temperatures, the activation energy of the reorientational relaxation rates of HNMA is close to that of the γ-process of the PMMA matrix, suggesting that the relaxation of the anthracene moieties is affected by the rotational motions of the α-methyl groups on the PMMA chain backbone. These preliminary results might provide some helpful guiding principles for controlling the stability of host/guest polymer materials using non-linear optical dyes.

Optimized poling of nonlinear optical polymers based on dipole-orientation and dipole-relaxation studies

Nonlinear optical polymers contain molecular dipoles with very large hyperpolarizabilities in a glassy polymer matrix. Two typical examples—a guest-host system with dispersed polar dye molecules and a side-chain material with chemically attached molecular dipoles—were investigated by means of poling experiments, dielectric spectroscopy, thermally stimulated depolarization, and electro-optical thermal analysis. The dielectric behavior of both polymers can be described by the phenomenological Havriliak–Negami equation, and the existence of master curves for both materials demonstrates the validity of the time-temperature superposition principle above the respective glass transitions. Temperature-dependent mean relaxation times and relaxation-time distributions calculated from the dielectric data allow for an optimization of poling times. The dielectric relaxation strengths obtained from poling current and field, from dielectric measurements, and from thermally stimulated depolarization are in very good agreement and thus represent a useful measure of the polarization in poled polymers. From the temperature dependence of the polarization, optimal poling temperatures may be derived. Electro-optical thermal analysis yields the same temperature-stability curves as thermally stimulated depolarization and is therefore a valuable tool for investigating the stability of poled polymers, especially since it is not sensitive to charge effects. Optimal poling fields and currents must be selected as a compromise between high dipole mobilities (short relaxation times) and low bulk conductivities.