TSC study of length ester side group effect on sub-vitreous relaxations in poly(n-alkyl methacrylates)

A comparative study by thermo-stimulated currents (TSC) of three poly(n-alkyl methacrylates) is performed. TSC complex spectra exhibit two dipolar relaxations considered in the following: the glass relaxation and a secondary relaxation related to motion of ester side groups. For each sample, the fractional polarisations protocol is applied to describe the fine structure of these complex spectra. It allows us to define the evolution of activation parameters with temperature. The influence of side chain architecture is then considered. It emphasises that the β mode is independent of the ester group length. On the contrary, the α mode is highly sensitive to structural change. These results are finally explained in terms of molecular mobility.     

Dielectric relaxations in poly(vinyl alcohol)

Dielectric constant and loss of poly(vinyl alcohol) films of different stereoregularity and crystallinity are measured at frequencies from 30 cps to 3 Mcps in the temperature range from ?50 to 25°C. The relaxation strength of local mode relaxation is higher for atactic and syndiotactic samples than for isotactic samples when compared at zero crystallinity. This behavior is reasonably explained in terms of interchain hydrogen bonds in the former and intrachain hydrogen bonds in the latter. Dielectric constant and loss of the crystal aggregate of atactic poly(vinyl alcohol) are measured at temperatures from ?50 to 140°C. The relaxation strength of the crystalline relaxation is in good agreement with the theory in which the relaxation is attributed to torsional vibration of crystalline chains. The weak loss peak at low temperatures which almost agrees with the local mode relaxation of bulk samples in the frequency-temperature position is ascribed to the surface disorder of single crystals.     

Dielectric relaxations in poly(monocyclohexyl itaconate)

A study of the dielectric relaxation spectrum of poly(monocyclohexyl itaconate) (PMCHI) is performed by means of two experimental techniques: first, at variable frequency in the audio zone and, second, by thermally stimulated depolarization currents. Because of the high conductivity of the samples, there is a hidden dielectric relaxation that can be detected by using the macroscopic dynamic polarizability ε^* defined in terms of the dielectric complex permittivity α^* by means of the equation (ε^* = 1)/(ε^* + 2). The transformation performed through this equation is discussed in order to obtain the dielectric relaxations in the zone of high temperatures and low frequencies of the spectrum.     

Ultraviolet irradiation of poly(alkyl acrylates) and poly(alkyl methacrylates)

Acrylic and methacrylic homopolymers containing different side groups were irradiated with ultraviolet light in the presence of air. The changes of molecular weight distributions of the irradiated polymers were analyzed by means of gel permeation chromatography (GPC), and the rates of chain scission and crosslinking were estimated. As the result of this study, it was found that chain scission takes place more easily in polyalkyl methacrylates than in polyalkyl acrylates.     

Metallographic characterization of rubber-modified poly(methyl methacrylates)

The microstructure of rubber-modified samples of poly(methyl methacrylates) was characterized by depositing a thin layer of gold on a polished surface and then applying the conventional techniques of metalography. Samples were prepared with a known volume fraction of rubber comprising particles of known size. It was shown that the methods of quantitative microscopy were successful in estimating these parameters. The method was also shown to provide information about crazing or cracking, which was viewed near the tip of an arrested crack. It is recommended that adoption of the metallographic method be extended to characterize other polymeric systems.     

Ultrasonic studies of solid poly(alkyl methacrylates)

The attenuation and velocity of ultrasonic longitudinal waves of frequencies 5–35 MHz in poly (methyl methacrylate), poly(ethyl methacrylate), poly (n-butyl methacylate) and poly(isobutyl methacrylate) between 233 and 363K are reported. The methyl and ethyl polymers showed evidence of a single relaxation process (associated with cooperative main chain and ester group motions), but the butyl polymers showed also a second relaxation at about 200–230K. This is associated with conformational rearrangement of the alkyl group, and the acoustic energetics are in line with theoretical predications for this process.The velocity data show the expected decreases due to the main glass transition (and cooperative processes) and to reduction of the intermolecular interaction force constant with increasing size of the alkyl group. Attempts to calculate an acoustic low temperature specific heat yielded values lower than expected from calorimetric observations, showing that the acoustic modes are capable of greater energy storage than is involved in the longitudinal perturbation, and/or that calculation based on a Debye T³ law are invalid for these glassy polymers.     

Dielectric and viscoelastic relaxations in poly(dicyclohexyl itaconate)

The relaxation spectrum of poly(dicyclohexyl itaconate) (PDCHI) was studied by dynamic mechanical, DC dielectric and thermally stimulated current measurements. Four relaxations, α, β, γ and δ, were obtained. The only method by which all four peaks were observed is that of dynamic dielectric measurements because of the broad range of frequencies employed. The β, γ and δ relaxations were characterized by the activation energy in a relaxation map. A tentative explanation of the molecular origin of each absorption is proposed. In the case of the α relaxation we have used two transformations, one from the permittivity to polarizability and the second from compliance to deformability in order to make evident the existence of this relaxation.     

Glass transition temperatures Tg of poly(tolyl methacrylates) and poly(di-xylenyl itaconates)

Summary Glass transition temperatures of poly(phenyl methacrylates) and poly(diphenyl itaconats) with one and two methyl substituents in the phenyl ring were determined by DSC. Within the group of 17 investigated polymers it was attempted to correlate the T_g values obtained with the polymer repeat unit structure, considering steric effects and dipole/dipole interactions, inherent to various modes of (di)substitution. Dedicated to Prof. Dragutin Fleš on the occasion of his 70th birthday     

Analysis of poly(chlorophenyl methacrylates) by ultraviolet spectroscopy

Summary A number of copolymers of methyl methacrylate and chlorophenyl methacrylates of different structure was prepared and analyzed by ultraviolet spectroscopy. It was found that the copolymer composition can be determined using a calibration curve based on mixtures of the appropriate homopolymers. The U. V. spectroscopical results are in good agreement with the chlorine analysis.     

Crystallization and morphology of isotactic poly(methyl methacrylates)

Several isotactic poly (methyl methacrylates) (iPMMA), with isotactic triad contents ranging from 46 to 100%, have been investigated after crystallization in the melt at different temperatures by differential scanning calorimetry, polarizing microscopy and small-angle light scattering. It was found that the crystallization of iPMMA, even of samples with high isotactic content, is slow. It never gives high degrees of crystallinity, but nevertheless leads to a spherulitic structure.     

Viscoelastic behavior of poly(cyanate epoxy)

The viscoelastic behavior of poly(cyanate epoxy) has been investigated by dynamic mechanical analysis and thermostimulated creep. First, the coherence of both sets of data has been shown. The analysis of the fine structure of the low temperature retardation mode has revealed the existence of four cooperative sub modes. The high temperature retardation mode corresponds to the anelastic manifestation of the glass transition. The elementary processes constituting this mode are characterized by retardation times following a compensation law with a compensation temperature T_c ～ T_g + 60°. The broad range of activation enthalpies reveals that cooperative movements are highly delocalized. The compensation parameters together with the range of activation enthalpy define the microstructure of poly(cyanate epoxy) and allow us to follow its relationship with the viscoelastic behavior.     

Viscoelastic properties of poly(ethylene-co-styrene) copolymers

The viscoelastic properties of narrowly distributed linear poly(ethylene-co-styrene) copolymers with different mole fractions of styrene (x_S = 0–20.5 mol %) and molecular weights (M_w = 64–214 kg/mol) were analyzed in the molten state at different temperatures by means of oscillatory rheometry. Analyzing the thermorheological properties of the polymers, we found that the time temperature superposition principle is fulfilled. The corresponding shift factors follow up to 16.5 mol % of styrene units the Arrhenius behavior of neat polyethylene. For a styrene content of about 20 mol %, the polymers no longer crystallize and a transition from Arrhenius to WLF behavior of pure polystyrene was observed. The zero shear viscosity, η₀, of the polymers was derived from the mastercurves. The determination of the plateau modulus by the well-known tan δ-min criterion is not possible due to the beginning crystallization in the corresponding temperature range. An approximate calculation of this value is based on the characteristic relaxation time λ_x = 1/ω_x, corresponding to the crossover of G′ and G′. Indeed, the characteristic modulus G_px calculated as η₀/λ_x is a good approximation for the plateau modulus G_p. The viscosity–molecular weight and relaxation time–molecular weight scaling relations were established for three copolymers with different molecular weights and nearly the same styrene content. For both material parameters, the scaling exponent is around 3.4, confirming the linear architecture of the investigated polymers. The mixing rules describing the change of such material parameters like zero shear viscosity or plateau modulus independent of styrene content are of logarithmic linear character using the weight fraction of styrene units instead of the mole fraction. The relations found allow the prediction of melt state properties for polymers with arbitrary styrene content. In the future, when catalysts with sufficient activity for the synthesis of high styrene content copolymers are available, these predictions will have to be checked. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:209–215, 1997     

Viscoelastic properties of poly(propylene glycols)

The relaxational and retardational properties of poly(propylene glycol) liquids, of nominal molecular weights 400 and 4000, are described. The viscoelastic behaviour of each liquid has been determined over a wide temperature range, using high frequency shear wave techniques operating at 30 and 454 MHz. It is found that the complex compliance $\text{J1(jω)}$ is described in terms of the viscosity ν, the limiting high frequency compliance J_∞, the retardational compliance J_r and a characteristic retardation time $\text{т}{}_{\mathrm{r}}$ by:

$\text{J}{}^1\text{(jω)=J}{}_{\mathrm{\infty }}\text{+}\text{1}\text{jωη}\text{+}\text{j}{}_{\mathrm{r}}\text{(1+jωτ}{}_{\mathrm{r}}\text{)}{}^{\mathrm{\beta }}$

where β is a parameter of the retardation time distribution.For the lower molecular weight liquid, $\text{J}{}_{\mathrm{r}}\text{J}{}_{\mathrm{\infty }}\text{= 17.4}$, β = 0.45 and $\text{т}{}_{\mathrm{r}}\text{т}{}_{\mathrm{m}}$ increases with decreasing temperature, reaching a limit of 170 near 0°C. This liquid shows no evidence of polymeric behaviour.For the other, $\text{J}{}_{\mathrm{r}}\text{J}{}_{\mathrm{\infty }}$, β = 0.76, $\text{т}{}_{\mathrm{r}}\text{т}{}_{\mathrm{m}}\text{= 15.4}$ and is constant over the temperature range investigated. The main difference between the two liquids appears as an additional retardational or relaxational process for the higher molecular weight material which occurs in the initial or low frequency part of the relaxation region. This process is characterized by a single time, but with relaxation time $\text{1}\text{7}$ and a stiffness 7 times the values calculated for the first Rouse mode of polymer chain motion.     

Dielectric relaxations in poly(methyl acrylate), poly(ethyl acrylate), and poly(butyl acrylate)

A comparative study is undertaken of the dielectric relaxation spectra of poly(methyl acrylate), poly(ethyl acrylate), and poly(butyl acrylate), taking into consideration the spectra of the corresponding polymers in the series of the polymethacrylates. The three polymers, PMA, PEA, and PBA, present an α relaxation zone clearly separated from the secondary relaxations. Its shape is not altered with temperature, and it is possible to construct a master curve. With increasing length of the side chain, its distribution of relaxation times broadens and the temperature of the maximum of the relaxation decreases. A β relaxation with decreasing intensity as the length of the side chain increases is clearly perceptible in PMA and PEA, but almost not perceptible at all in PBA. In PEA this relaxation appears split into two peaks. Computer simulation of restricted motions of the side chain discard an origin similar to that of the γ relaxation in PPA or PBA for the lowest temperature component of the relaxation, and suggests the conjunction of two rotation mechanisms in this relaxation for the polyacrylates. For the experimental temperatures of our tests a γ relaxation shows up only in PBA. Its apparent activation energy, higher than in related polymers of the polymethacrylate series, suggests that the tighter packing of monomeric units in polyacrylates leads to a significant increase in the intermolecular contribution to the potential energy barrier responsible for the relaxation.     

Cryogenic relaxations of polystyrene and poly(fluorinated styrenes)

The effect of structural and morphologic modifications of styrene and fluorinated styrene polymers on their internal friction was studied by means of a free-oscillating torsional pendulum at temperatures from 300° to 4.2°K and frequencies of 1 to 2 Hz. Atactic and isotactic polystyrene gave the previously observed δ and β′ loss peaks at 38° and 100°K, respectively. These losses decrease in intensity with crystallinity in isotactic polystyrene but remain relatively unchanged in uniaxially drawn atactic polymer. Atactic polypentafluorostyrene showed an intense δ loss peak at 52°K and a broad shoulder around 100°K, which extends toward the β′ relaxation. In poly-α,β,β-trifluorostyrene, the δ loss peak is largely suppressed, the logarithmic decrement showing only broad maxima at 22° and 100°K. Plasticization of atactic polystyrene with 2% mineral oil gives rise to a sharp loss maximum at 100°K, which does not occur in the pure atactic polymer.     

Revisiting the thermal relaxations of poly(vinyl alcohol)

The molecular dynamics of poly(vinyl alcohol) (PVA) were studied by dielectric spectroscopy and dynamic mechanical analysis in the 20–300°C range. The well-established plasticizing effect of water on the glass-transition temperature (T_g) of PVA was revisited. Improper water elimination analysis has led to a misinterpretation of thermal relaxations in PVA such that a depressed T_g for wet PVA films (ca. 40°C) has been assigned as a secondary β relaxation in a number of previous studies in the literature. In wet PVA samples, two different Vogel–Fulcher–Tammann behaviors separated by the moisture evaporation region (from 80 to 120°C) are observed in the low- (from 20 to 80°C) and high- (>120°C) temperature ranges. Previously, these two regions were erroneously assigned to two Arrhenius-type relaxations. However, once the moisture was properly eliminated, a single non-Arrhenius α relaxation was clearly observed. X-ray diffraction analysis revealed that the crystalline volume fraction was almost constant up to 80°C. However, the crystallinity increased approximately 11% when temperature increased to 180°C. A secondary β_c relaxation was observed at 140°C and was related to a change in the crystalline volume fraction, as previously reported. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and molecular weights of metal poly(methyl methacrylates)

Summary Methyl methacrylate colloids were obtained by codeposition at 77K of the monomer with several metals such as: Au, Pd, Cu, Ge, Ga, In, Sn, Sb and Bi. The colloids were polymerized with different amounts of initiator (AIBN) at 60°C and a wide range of viscosity average molecular weights (Mv; 10⁴–10⁵) were obtained depending upon the metal used. The metal colloid concentrations are reported. The thermal stability and metal composition are also described. The polymers are stable even at 350°C and the metal content is 0.7 to 3.1%.     

Viscoelastic properties of phenolphthalein poly(ether ketone)

Stress relaxation and dynamic mechanical behavior of phenolphthalein poly(ether ketone) (PEK-C) have been investigated. Using Ferry's reduction method, the master curve was obtained. From the experimental results, we found that the WLF equation is not appropriate in the lower-temperature range (T < T_g). The relaxation spectrum was calculated according to the first approximation method proposed by Schwarzl and Staverman. In addition to the α-transition region, a second transition zone is revealed at low temperature. This transition is probably due to a restricted motion of its main chain. © 1995 John Wiley & Sons, Inc.     

Dynamic mechanical and dielectric relaxations in poly(di-n-chloroalkylitaconates)

Dielectric and viscoelastic relaxation measurements have been carried out on poly(2-chloroethyl diitaconate) (PDCEI) and poly(3-chloropropyl diitaconate) (PDCPI) between 123 K and temperatures about 293 K above the glass transition temperatures.The two polymers exhibit three peaks, a γ-relaxation in the range from 133 to 193 K (at 1 Hz), a broad β-process, in the range from 193 to 293 K and a third peak observed in mechanical measurements at 323 K (PDCEI) and 293 K (PDCPI) probably corresponding to the α dynamic glass transition phenomena. In dielectric measurements, conductive contributions overlap the α-relaxation precluding the observation of peaks at temperatures above room temperature. The apparent activation energies for the γ-relaxation according to the mechanical and dielectric measurements are close to the values derived from the empirical force field molecular mechanics calculations. A comparison is made between the relaxational data of PDCEI and PDCPI by one hand and poly(di-n-propyl itaconate) (PDPI) and poly(di-n-butyl itaconate) (PDBI) by other. This comparison allows us to conclude the relevant role played by the chlorine atoms not only in the γ relaxations but also in the β relaxations of PDCEI and PDCPI.     

Studies on semiinterpenetrating polymer networks based on poly(vinyl chloride-co-vinyl acetate) and poly(alkyl methacrylates)

A number of semi-interpenetrating polymer networks (IPNs) based on linear poly(vinyl chloride-co-vinyl acetate) and poly(alkyl methacrylates) were synthesized. The semi-IPNs were found to be transparent, high strength materials. The IPNs show only one glass-transition temperature and it is dependent on the composition as studied by differential scanning calorimetry and dynamic mechanical analysis. These IPNs are also characterized by high tan δ values. The tensile strength of the IPNs were found to be higher compared to the starting polymers. In order to compare the properties of these IPNs with the corresponding homopolymers and blends, the latter were synthesized and the properties were studied. © 1994 John Wiley & Sons, Inc.