In the light of the strong and fragile classification of simple liquids we review some of the relaxation data for some well-known polymers to see the extent to which a similar pattern may be manifested. Relaxation time data rather than viscosity data are used in the polymer case to avoid complications from long chain effects on the Vogel-Fulcher equation pre exponent. A combination of light scattering and 13C NMR data seem to provide the most reliable guide to the microviscosity of interest to the classification. A pattern similar to that for viscous liquids is recovered with polyisobutylene, the “strongest” chain polymer and bisphenol polycarbonate, the most fragile. The extent to which correlations of other properties with fragility, found in the non-polymeric liquids cases, will carry over to the polymer case is still being evaluated, though the work of Hodge on the analysis of the more complicated problem of non-linear thermal relaxation, suggests the carry over may be extensive.

The Adam-Gibbs (AG) expression linking relaxation times with configurational entropy gives an excellent account of the nonlinearity observed in enthalpy relaxation of amorphous polymeric, inorganic, and simple molecular materials near and below Tg. Data analyses yield zero entropy temperatures that are comparable with available Kauzmann values. The AG formulation, when coupled with a few plausible ancillary assumptions, predicts correlations between the Arrhenius parameters x, Δh*, and the KWW exponent β that are observed experimentally. It is suggested that the AG primary activation energy, Δμ, is the single causative factor that generates these correlations.

The effects of Lewis acid complexation on the glass transition temperature (Tg) of several polymers with strong intermolecular interactions was investigated. The decrease in the Tg due to GaCl3 complexation of aliphatic and aromatic polyamides was 40–600° C and 148° C, respectively, and was shown to originate from scission of the intermolecular hydrogen bonds. The reduction in the Tg due to GaCl3 complexation of rigid–chain polymers was greater that 325° C and can be explained by the mitigation of the otherwise strong van der Waals forces in the pristine polymers. Thus, the dominant effect of intermolecular interactions on the Tg of several polymers has been probed by Lewis acid complexation.

Miscibility enhancement of polymer blends is a current topic of considerable activity. Many approaches have been suggested, though all involve the development of specific interactions between the two polymers. These interactions include hydrogen bonding, ion-dipole and ion-ion interactions, donor-acceptor interactions and transition metal complexation.

An optically homogeneous sample of highly syndiotactic poly(n-butyl methacrylate) (PBMA) has been prepared. The glass transition temperature was observed to be Tg=55C. Measurements of the scattered intensity of the sample followed the expected behavior for a pure liquid above Tg. The intensity rose as the sample was cooled further towards the glass transition temperature for atactic PBMA. These results illuminate the importance of regions of different stereoisomers in methacrylate polymers. Measurements of the Rayleigh- Brillouin spectrum were carried out from -15 to 130 C. The ratio of the the central peak intensity to the Brillouin intensities at temperatures above Tg was consistent with a viscoelastic liquid and had a magnitude near 3. The Brillouin linewidth remained large near Tg. and decreased continuosly with no apparent change in slope in the glass transition region. The presence and importance of rapid motions in polymers near the glass transistion is demonstrated by these results. Slowly relaxing density fluctuations near Tg. were measured by photon correlation spectroscopy. Relaxation functions were obtained from 10−6 to 10 s. Average relaxation times <τ> were obtained from the integral of the relaxation function and were found to follow the relation <τ>=Aexp(B/(T−T0)), where for our sample B=2940K and T0=273K. The observed relaxation function decayed over a wider time range as the sample was cooled. Quantitative analysis of this effect using the Williams-Watts empirical function yielded a decrease in β from 0.35 at 90 C to 0.18 at 65 C. The relaxation functions were also analyzed to give a distribution of relaxation rates. The observed distributions were bimodal at 70 and 80 C. The two features behaved in a manner consistent with the primary and secondary relaxations observed for methacrylate polymers by other techniques.

A theoretical model was developed to describe the physical aging during photopolymerizations and crosslinking reactions of diacrylates and dimethacrylates. The model incorporates the strong coupling between the volume relaxation and the kinetics observed in these reactions. Model predictions are presented for the reaction kinetics, volume relaxation, radical concentration and maximum conversion as a function of light intensity and relaxation time of the polymer.

We have developed a theory for the evolution of concentration fluctuations after a temperature quench which takes the effect of slow structural relaxation into account. In its linear and non-linear forms, it generalizes the theories of Cahn, Hilliard and Cook, and of Langer, Bar-on and Miller.

Using newly developed test equipment, the fatigue behavior of nylon 66 monofilaments was studied under two loading conditions, pure bending or simple torsion. In each case, the deformation was applied in balanced cycles of positive and negative strains. For each mode, results are expressed in terms of the measured decay in stiffness with numbers of cycles over a range of maximum applied strain levels. Fatigue lifetimes are presented in S-N format where the log number of cycles of fatigue for a 40% decay in stiffness (N) is plotted as a function of applied strain (S). The failure mechanism for these fibers in each fatigue mode reflects the morphology of semicrystalline oriented synthetic fibers. In torsion, many longitudinal cracks formed around the perimeter of the fiber as the result of cleavage of the relatively weak interfibrillar bonds in the nylon 66 fibers. In bending, cracks grew across the fiber at an oblique angle to the fiber axis along kink band boundaries.

Glassy polycarbonate was subjected to cyclic stresses and the changes in its structure were studied by DSC, positronium annihilation lifetime spectroscopy (PALS), and small and medium angle X-ray scattering. Upon increased exposure to cyclic loading, the enthalpy overshoot near Tg increased in a manner similar to increasing physical aging. However, the “hole” size as revealed by PALS increased, unlike physical aging. SAXS reveals an increase in the short range order and the amplitude of density fluctuation. These results can be explained in a consistent manner. We conclude that mechanical loading does cause changes in the glassy structure.

A molecular model for cooperative segmental relaxation has been proposed, which leads to the Adam-Gibbs type dependence of the characteristic relaxation time on temperature and the configurational entropy. When the size distribution for the cooperative domains is introduced, the resulting relaxation spectrum is similar to the Kohlrausch-Williams-Watts (KWW) equation in the frequency range near the loss maximum, but the fit is actually better in the high frequency extremes where the KWW equation always underpredicts the intensity. The model also predicts the broad spread of the spectrum in the non-equilibrium state from the distribution of the apparent activation energy arising from the different sizes of domains.

We now extend this model to the yield phenomenon in glassy polymers. Under the stress, a domain has two alternatives to dissipate the strain energy. One way is to relieve the stress at the rate dictated by the linear viscoelastic relaxation time. This process is possible only when the strain rate is low. At above a certain strain rate, the stress reaches the strength of the domain, forcing to irreversibly break up the domain structure in the manner that can be described by the classical plasticity. It can be shown that the yield stress of a real polymer is a combination of the above two types of stresses. Namely, at a given strain rate, the small domains with short relaxation time will attain the linear viscoelastic steady stress while the larger domains reach the (limiting) plastic yield stress. Thus, the strain rate dependence of yield stress can be predicted from the linear viscoelastic relaxation spectra, even though the yield phenomenon is clearly in the realm of nonlinear viscoelasticity.

We present torsional dilatometry experiments to simultaneously measure torque relaxation and volume recovery in an epoxy glass quenched from above its glass transition temperature to below it. Two strain histories are employed: one with strains of equal sizes and a second where small strains follow a large one. The baseline for the thermally induced volume recovery is insensitive to intermittent torsional strains whose magnitude can be well into the non-linear regime. The torque relaxations from equal intermittent mechanical stimuli can be superposed by a time-aging time shift in a way that indicates fast changes cease to occur at ∼104 seconds after the quench, a “mechanical equilibration” time. Stimuli of different sizes can confound superposition via nonlinear effects, but do not affect the ultimate volume recovery of the glass or its mechanical equilibration time. Our results show the signature of rejuvenation; however, this may result from the nonlinear response of the material in a nonisochoric strain history. Our data firmly show that mechanical stimuli do not erase aging or rejuvenate this epoxy.

Studies are discussed which show that the segmental mobility In polycarbonate (Lexan from General Electric Co.) increases when a static deformation in either extension or simple compression (uniaxial stress) is applied to a specimen, but thereafter the mobility decreases progressively. These changes can be termed erasure (partial) of physical aging (strain softening) and physical aging (hardening), respectively. Because the volume of a specimen deformed in simple compression decreases, reversal of aging (de-aging) cannot be attributed to an increase in free volume, as usually defined. A proposed explanation will be mentioned. A study was also made of the yield stress modified by unconventional methods at several temperatures. The results can be explained In terms of the rate of physical aging and its temperature dependence determined on specimens at 2.6% extension over a broad range of temperatures. These results show that yielding results from progressive de-aging. The yield phenomena obtained by special methods results from both physical aging and de-aging.

PPS is increasingly interesting as a high performance polymer material. Recently, Cheng, et al. [1] reported observation of rigid amorphous phase (RAP) in the amorphous phase of semicrystalline PPS using differential scanning calorimetry. Using the heat of fusion from DSC to obtain the degree of crystallinity of the semicrystalline samples, a simple rule of mixtures was applied to calculate the change in heat capacity step. The heat capacity decreased much more than could be accounted for using the measured crystallinity. Thus, these authors assumed the existence of a rigid amorphous phase which did not become liquid-like at Tg. The ratio of heat capacity step at Tg of semicrystalline PPS to that of the purely amorphous polymer was used to find the fraction of amorphous chains that do become liquid-like at Tg. The amount of RAP was then obtained by assuming a three phase model.

The KAHR model was used to predict the transient volumetric response of poly(vinyl acetate) (PVAc) and polystyrene (PS) glasses in various experiments involving controlled variations of temperature and pressure in the vicinity of the glass transition. The experiments considered include contraction following a quench from equilibrium, expansion after a temperature “jump,” and pressure-induced densification. The model parameters of PVAc were obtained by fitting experimental data via a 4-parameter Levenberg-Marquardt optimization. The optimized parameters were then used to predict the response of the material in three different experiments. The response of PS in a pressure densification experiment was also analyzed and compared with existing data. Generally, the predicted response of PVAc in the various temperature jump experiments is in excellent agreement with observation. The prediction of the response of PS in the pressure densification experiment is also in line with observation although the data for this case is limited and the results are still inconclusive.

Phosphorous and proton line shape studies of a trioctyl phosphate diluent in polycarbonate and in a fifty-fifty blend of polystyrene with polyphenylene oxide have been performed to monitor diluent dynamics. Both the phosphorous and proton line shapes are superficially bimodal with a narrow, mobile component of the line shape appearing at temperatures well below the thermal glass transition temperatures. Plots of the h.ction of mobile material versus temperature show two step increases separated by a plateau region. This behavior is analyzed in terms of a distribution of activation energies which results in a bimodal description. The bimodal activation energy distribution corresponds to a bimodal correlation time distribution. The more mobile material is identified with diluent molecules in contact with other diluent molecules in a lattice description which assumes a single phase system is assumed with a purely random distribution of diluent and polymer on the lattice.

Solid state NMR and dynamic mechanical analysis (DMA) techniques have been used to study the “antiplasticization” effects of dihexyladipate (DHA) and tricresylphosphate (TCP) on poly(vinyl butyral-co-vinyl alcohol) (PVB) and poly(2,6-dimethyl phenylene oxide) (PPO) respectively. The DHA and TCP diluents decrease the primary viscoelastic transition temperatures (ax processes) along with their apparent activation energies [1,2] However, glassy state mechanical transitions (P processes) are characterized by increased activation energies. Similarly, carbon T1, T1p, and inversion recovery cross polarization (IRCP) experiments generally show that DHA and TCP suppress motion in the MHz, KHz, and near static frequency regimes. These results collectively suggest that the extent of antiplasticization is dependent on both the frequency regime of observation, and the morphology of the polymers.

Two-dimensional NMR methods allow a determination of the relative orientations of nearby molecules in polycrystalline and noncrystalline solids. We describe these methods and present applications to the determination of the crystal structures of two forms of polycrystalline methanol and to the investigation of short range molecular orientational ordering in methanol glass and in atactic PMMA.

Two dimensional solid state NMR exchange spectroscopy can be used to monitor slow motions on time scales comparable to dynamical mechanical spectroscopy. Polyphenylene oxide, carbon-13 labeled in a methyl position, was blended with polystyrene. The resulting compatible blends have single thermal glass transitions (Tg) at temperatures between those of the homopolymers. The chemical shift anisotropy line shape of the labeled methyl shows reorientational exchange at temperatures near the thermal glass transition. The 2D exchange pattern contains information on the rate and amplitude of the motion. The data indicate Brownian rotational angular diffusion of the phenylene oxide units with rates in the millisecond to second range. The motional description associated with the glass transition is contrasted with those appropriate to single component polymeric glasses. It is concluded that in the blend system the onset of motion occurs at a lower temperature relative to the DSC Tg than in the homopolymer and there is evidence for considerably more dynamic heterogeneity.

Polymer blend technology is attractive from the standpoint of both science and industry, and many combinations have been studied. Recently, the polymer blends, including liquid crystalline polymer, have been especially worthy of notice, [1,2,3]. In order to obtain materials with a high mechanical strength and moldability for use in thin molded items, we chose polyamide (PA)-liquid crystalline polymer (LCP) blends. In this study, we first measured the mechanical properties, then studied the features of the polymer structure. We also examined the relationship between morphology and mechanical properties. As a result, we found that the mechanical properties of the blends depended largely on blend morphology, and that mechanical strength increased as blend compatibility increased. On the other hand, we also found that the blends showed compatible and microheterogeneous dispersion at less than 25 wt% LCP, while at more than 30 wt% LCP, blends tended to show twophase separation.

The permeation rates of alkanes, alcohols, and aromatic hydrocarbons through untreated, fluorinated, and sulfonated high-density polyethylene (HDPE) were measured at a variety of temperatures and solvent compositions. The results were then analyzed to separate the individual contributions that solubility and diffusion make to the overall permeation rate. These results are discussed in terms of the chemical characteristics of the permeating constituents, and the barrier treatments on the HDPE surface.