Atactic Poly Methyl Methacrylate Research Articles

Breaking of the Supercooled State of Water by a Nanocavity with Disordered Atomic Configuration I: Freezing Behavior of Sorbed Water into Polymethylmethacrylate Film As Examined by Fourier Transform Infrared Spectroscopy

A freezing behavior of sorbed water into an annealed atactic polymethylmethacrylate (PMMA) film was examined by Fourier transform infrared (IR) spectroscopy. Temperature dependence of IR spectra of the sorbed water indicated that nonfreezable water in the PMMA film formed associated waters on cooling and were not universally nonfreezable. Its freezing temperature was found to be 249 K, which is much higher than the homogeneous nucleation temperature of water, 236 K. This result suggests that a disordered atomic configuration of a nanocavity wall with hydrogen bond acceptors induces a breaking of the supercooled state of water. The former two findings were visibly clarified by the vibrational spectroscopic method for the first time, and the latest finding was different from the literature on supercooled water in small spaces.

Theory of relaxation and elasticity in polymer glasses

The recently developed activated barrier hopping theory of deeply supercooled polymer melts [K. S. Schweizer and E. J. Saltzman, J. Chem. Phys. 121, 1984 (2004)] is extended to the nonequilibrium glass state. Below the kinetic glass temperature T(g), the exact statistical mechanical relation between the dimensionless amplitude of long wavelength density fluctuations, S(0), and the thermodynamic compressibility breaks down. Proper extension of the theory requires knowledge of the nonequilibrium S(0) which x-ray scattering experiments find to consist of a material specific and temperature-independent quenched disorder contribution plus a vibrational contribution which varies roughly linearly with temperature. Motivated by these experiments and general landscape concepts, a simple model is proposed for S(0)(T). Deep in the glass state the form of the temperature dependence of the segmental relaxation time is found to depend sensitively on the magnitude of frozen in density fluctuations. At the (modest) sub-T(g) temperatures typically probed in experiment, an effective Arrhenius behavior is generically predicted which is of nonequilibrium origin. The change in apparent activation energy across the glass transition is determined by the amplitude of frozen density fluctuations. For values of the latter consistent with experiment, the theory predicts a ratio of effective activation energies in the range of 3-6, in agreement with multiple measurements. Calculations of the shear modulus for atactic polymethylmethacrylate above and below the glass transition temperature have also been performed. The present work provides a foundation for the formulation of predictive theories of physical aging, the influence of deformation on the alpha relaxation process, and rate-dependent nonlinear mechanical properties of thermoplastics.

Segmental orientations of trains versus loops and tails: the adsorbed polymethylmethacrylate system when the surface coverage is incomplete

We measure, for the first time, the separate surface coverage-dependent orientations of trains and of loops/tails in the structure of an adsorbed polymer, and show that these have different average orientations. The system was PMMA (atactic polymethylmethacrylate) adsorbed onto oxidized silicon from dilute solution in carbon tetrachloride at 25.0°C. The method was FTIR-ATR (infrared spectroscopy in attenuated total reflection). With increasing surface coverage, train segments were observed to maintain constant average anisotropy with respect to the solid surface. Free segments were preferentially flattened when the surface coverage was low, but with increasing surface coverage became progressively more random in orientation. Free and bound segments were separated according to shifts of the vibrational frequencies of carbonyl segments upon hydrogen-bonding to the surface silanol groups. The dependence of segmental orientation on molecular weight of the chain is also discussed.

Morphology, crystallization, and thermal behavior of isotactic polypropylene/polymethylmethacrylate blends: Effects of the addition of a graft copolymer of propylene with methylmethacrylate

Optical microscopy, differential scanning calorimetry, and small angle X-ray scattering techniques were used to study the influence of crystallization conditions on the morphology and thermal behavior of samples of ternary blends constituted of isotactic polypropylene (iPP), atactic polymethylmethacrylate (aPMMA), and a novel graft copolymer of unsaturated propylene with methylmethacrylate (uPP-g-PMMA). The purpose was to assess the uPP-g-PMMA capability to act as compatibilizer for iPP/aPMMA materials. It was shown that the presence of uPP-g-PMMA copolymer affects the interfacial tension between the iPP and aPMMA phase in the melt state, the aPMMA particle size, and particle-size distribution is modified. After complete crystallization of the iPP phase at relatively low undercooling, in a range of crystallization temperatures, the presence of the uPP-g-PMMA phase was found to modify both mode and state of dispersion of minor component and spherulitic texture and inner structure of spherulites fibrillae. The extent of the induced modifications was dependent on a combination of composition and undercooling. Also, relevant thermodynamic parameters of the iPP phase, such as the equilibrium melting temperature and the surface free energy of folding, were strongly affected by the presence of the uPP-g-PMMA phase, opposite effects being observed depending on the uPP-g-PMMA content. The observed melting temperature and surface free energy of folding values were accounted for by the growth of iPP lamellar crystals with different perfection, thickness, and surface disorder.

Thermal expansion and glass transition of polymethylmethacrylate after exposure to 60Co gamma irradiation

A study is made of the thermal expansion coefficient and the glass transition temperature in atactic polymethylmethacrylate (PMMA) irradiated first with γ-ray doses between 50 and 200 kGy, The change of the molecular weight due to the damage of the polymer chain produced by the γ-irradiation was also measured. Besides the glass transition temperature, the α′ transition is observed in our dilatometric tests and this transition shifts to lower values of temperatures at higher doses and virtually disappears at 200 kGy. This result suggests that the irradiation changes the degree of atacticity of the polymer.

FTIR ATR analysis for microstructure and water uptake in poly(methyl methacrylate) spin cast and Langmuir-Blodgett thin films

Spin cast and Langmuir-Blodgett (LB) films of atactic PMMA (poly(methyl methacrylate)) were studied at 25 C by FTIR ATR (Fourier transform infrared spectroscopy, attenuated total reflection) spectroscopy before and after annealing at 140 C and after contact with water vapor or liquid. The dichroic ratios of the carbonyl groups revealed that the average molecular orientations of the films remained unchanged upon annealing and also upon exposure to water. However, annealing helped avoiding cracks which appeared in the nonannealed film after contacting liquid water. The absorbances of individual water bands (of the non-hydrogen-bonded monomers, hydrogen-bonded dimers, larger clusters, and associated chains of water) were determined by detailed spectral analysis and compared with a one-dimensional Fickian model. The absorbance data for the annealed spin cast film of thickness of 5.4 pm showed poor fit to the one-dimensional Fickian diffusion model, but the apparent diffusion coefficient, DBpp, ranged from 5 x to 4 x lo- cm2/s. The process of film hydration was found to precede the transfer of bulklike water. For the annealed LB and spin cast films of thickness of 0.1 pm, Dapp ranged between and cm2/s. It was estimated from ATR carbonyl band intensities that the thin films were about 44% more dense than the thick film, indicating that they had a tighter structure with fewer structural defects or voids. Having more hydrophobic and less rough surface, the LB film showed a longer initial delay in liquid water transport than the spin cast film of the same thickness.

A reinvestigation of the hypersonic properties and the specific heat capacity of PMMA around the quasi-static glass transition II. High performance caloric investigations

To continue dynamicc p measurements in the range of smallest temperature rates and non-linear thermal relaxation investigations into the linear range, simultaneousc p and thermal relaxation measurements were carried out in an adiabatic vacuum calorimeter, using the pulse heating method. The rate-dependentc p behaviour, known from dynamic measurements, does not continue at small temperature rates. This is confirmed by the relaxation process which is observed. The results suggest an extended interpretation of the glass transition in atactic polymethylmethacrylate (PMMA).

Plastic deformation of glassy amorphous polymers: influence of strain rate

The compressive deformation of glassy atactic polymethyl methacrylate has been studied in the temperature range 150<T<330 K as a function of applied strain rate. Special emphasis is given to the definition of an elementary activation rate, i.e. the characteristic frequency of the successful plastic deformation events. This determines the frequency at which the elastic counteraction of the medium to the nucleation of plasticity has to be taken into account, in order to ensure self-consistence of the kinetic and thermodynamic analysis of deformation previously proposed.

Radial distribution functions of non-crystalline polymers and their application to the structural analysis of PMMA

The use of Radial Distribution Functions (RDFs) in the determination of the structure of non-crystalline polymers is briefly reviewed. Particular aspects of the procedure for preparing RDFs from X-ray scattering are discussed in detail; namely the employment of an energy dispersive detector to remove the Compton component of the scattered X-rays and the application of the method of sampled transforms. A RDF is presented for atactic polymethylmethacrylate (PMMA) and its precision and reliability are discussed. It is analysed by comparison with RDFs calculated from computer-generated atom co-ordinates for isolated lengths of PMMA chains in different conformations. Methods are introduced by which the calculated RDFs are smeared to account for random disorder in the real chain and normalized so that, despite the finite range of the model, they can be immediately compared with the difference RDF which is directly obtained by transforming the data. Comparison between experimental and calculated RDFs shows that reasonable agreement is only obtained for a very limited range of conformations corresponding to sequences of backbone bond rotation angles of (10‡, 10‡, −10‡, −10‡) and the bond angles alternately 110‡ and 128‡. The form of the RDF appears very sensitive to important aspects of the molecular structure. The results both confirm and refine an earlier proposal from this laboratory which was based on comparisons between experimental and calculated functions in reciprocal space.

Detection of elastic strain in an amorphous polymer by X-ray scattering

For crystalline solids, the displacement of diffraction peaks with applied elastic strain is the basis of one method of measuring internal stress1,2. The effect has been exploited for both metals3 and crystalline polymers4. Hitherto, the diffuse character of diffraction peaks obtained from non-crystalline materials has discouraged similar measurements on them. Working with atactic polymethyl methacrylate (a-PMMA) as an example of non-crystalline polymer glasses (which can sustain elastic strains up to several per cent before plastic yield or fracture), a displacement of the most intense diffraction peak has been observed in response to applied elastic strain. This peak corresponds to intermolecular correlations in the polymer5,6.

Fractionation of Atactic Polymethyl Methacrylate by thin Layer Chromatography

Fractionation of Atactic Polymethyl Methacrylate by thin Layer Chromatography

Molecular alignment in polymethyl methacrylate and polystyrene

Abstract Chain alignment has been induced in commercial atactic polymethyl methacrylate and atactic polystyrene by deformation just below the glass transition temperature. The resultant fiber-type X-ray diffraction patterns when azimuthally averaged are not distinguishable from the concentric diffuse halos typical of the “as-received” polymers. The conclusion is drawn that both the polymers examined contain domains within which neighboring chains are aligned parallel. The experiment also indicates that the extra structural information which can be extracted from the fiber-type diffraction pattern of the deformed polymers is also relevant to the unoriented state.

Amorphous structure heat: Molecular structure from solution heats of polymethylmethacrylate in orthodichlorobenzene

The heats of solution in orthodichlorobenzene were measured as a function of temperature for both as-reprecipitated and quenched atactic polymethylmethacrylate. The as-reprecipitated curve decreases linearly with a slope of 0.096 cal/g°C from room temperature to 90°C, and above 110°C has a constant value of +1.5 cal/g. The quenched material data decreases linearly with a slope of 0.12 cal/g°C from room temperature to 55°C, jumps +2 cal/g at 55°C, and continues the linear decrease with a slope of 0.096 cal/g°C from 55 to 90°C. The data suggests that isotactic stereochemical impurities in the atactic material are able to crystallize at 55°C which is the Tg of i-PMMA, and therefore must be associated as i-PMMA islands in a rigid atactic-syndiotactic PMMA matrix. This also suggests that the β transition in PMMA may be associated with the isotactic impurities

Light scattering of polymethylmethacrylate solutions in binary solvent mixtures. Part 2. In acetone/benzene mixtures

AbstractAn isotactic and an atactic polymethylmethacrylate have been investigated by light scattering measurements at 25°C in acetone/benzene mixtures in order to see the effects of the difference in the microstructures between the two stereoisomers on the preferential solvation and some other molecular parameters of the polymers. The extreme differences due to the structural effects between the stereoregular and the stereoirregular polymers appear in the mixed solvents with higher content of acetone.

Association phenomena of PMMA in solutions and gels

AbstractStereocomplex formation of isotactic and syndiotactic polymethylmethacrylate (PMMA) could be demonstrated using X‐ray, NMR, and viscosity techniques. In this paper it is shown by measurements of viscosity and investigation of swelling properties that the association of isotactic and syndiotactic sequences of the polymer occurs as well in the solutions and gels of atactic PMMA. From the temperature dependence of the reduced specific viscosity and the swelling it can be deduced that association causes network formation due to microcrystalline regions which have a melting point range. In solutions of toluene with mixtures of isotactic and syndiotactic PMMA an intermolecular association, with atactic PMMA an intramolecular association is discussed. In chloroform no association could be observed.

Thermal degradation of gamma irradiated isotactic and atactic polymethyl methacrylate

Thermal behaviour of gamma irradiated free radical and isotactic polymethyl methacrylate has been studied at 256°. It is shown that radiolysic chain scissions do not produce unsaturated chain ends identical to those formed by disproportionation during free radical polymerization. Furthermore, initial terminal double bonds present in samples prepared by that mechanism are progressively transformed during the radiolysis in such a way that they become more reactive and able to initiate depolymerization at 256° with a higher rate.

Birefringence and stress-strain diagrams for oriented atactic polymethyl methacrylate and polystyrene films

The stress-strain diagrams of amorphous linear polymers oriented under different conditions are examined; a comparison is made with the parameters of their internal structure. It is shown that the shape of the diagram for rigid polymers is basically determined by the degree of orientation of the links of the macromolecules irrespective of the molecular weight of the polymer and the extension conditions. It is established that the moment of failure can not be determined from this parameter alone. It is found that when the oriented polymer is tested close to the softening point the correlation between the shape of the diagram and the birefringence, characterizing the degree of orientation of the links of the macromolecules, is disturbed.

The Heats of Dilution in Atactic Polymethyl Methacrylate Solutions

Abstract In order to ascertain the dependence of the interaction parameter, χH, between the polymer and the solvent molecules on the polymer concentration, the heats of dilution in an atactic polymethyl methacrylate solution have been measured for the polymers with the degrees of polymerization of 3000 and 7800. It was found that the values of χH obtained are dependent on the concentration in all the solvents used, as in the solutions of polystyrene and polybutadiene reported as in previous papers. χH depends also on the molecular weight, this is in agreement with the suggestion by Huggins (J. Am. Chem. Soc., 86, 3535 (1964)).

Conformation of polymethyl methacrylate stereochemical isomers in non-interacting media

Isotactic, syndiotactic and atactic polymethyl methacrylate were prepared by proper methods and fractionated. With these fractions, the theta temperatures and the entropy parameters,ψ 1, were determined in four solvent systems from the precipitation measurements, and the intrinsic viscosities were compared between isotactic and atactic modifications at the theta temperatures. It was pointed out that the unperturbed dimension and the entropy parameter of the isotactic species, respectively, are larger than those of the atactic species. Also, it was found that the temperature dependence of the unperturbed dimensions is quite different for both isomeric forms. The molecular dimensions of the isotactic modification in non-interacting media were interpreted in accordance with the semi-flexible chain treatment ofFlory.