Note on the glass transition temperature of Poly(vinylphenol)

Critical overview of literature data on the glass transition temperature T_g of poly(4-vinylphenol) PVPh revealed a large scatter of values ranging between 53 and 194 °C, which can only partially be attributed to molecular-mass effect. The reason could be seen in residual moisture and/or solvent in samples subjected to insufficient or even no drying. Based on selected two thirds of literature data, a regression equation is proposed for the dependence of T_g on 1/M_n. Two samples of commercial PVPh (M_n 11,500; M_w 22,100) and (M_n 19,700; M_w 40,900) were studied by DSC, ATR-FTIR, and SEC methods. A procedure of preparing well defined samples is proposed: PVPh vacuum-dried at 140 °C for 24 h is dissolved in tetrahydrofuran and precipitated in hexane. The precipitate is vacuum-dried at 40 °C for 24 h, weighed into a pierced DSC pan. After final vacuum drying at 140 °C for 24 h, the sample is analyzed. The PVPh samples treated in this way showed T_g of 175.0 °C and 179.6 °C, respectively.     

Effects of moisture on glass transition and microstructure of glycerol-plasticized soy protein

The glass transition behavior of the glycerol-plasticized soy protein sheets (SL series) at various relative humidity (RH) was investigated by using differential scanning calorimetry with the aluminum pan and O-ring-sealed stainless steel capsule, and the microstructure of these sheets was detected on small-angle X-ray scattering. The results revealed that there were three glass transitions (Tg1, Tg2 and Tg3), corresponding to glycerol-rich, protein-rich and protein-water domains, in the protein-glycerol-water ternary system. The Tg1 values of the SL-series sheets at 75% RH decreased from -49.3 to -83.8 degrees C with an increase of glycerol content from 10 to 50 wt.-%, whereas Tg2 and Tg3 were almost invariable at about 60 degrees C and 3 degrees C, respectively. In addition, the Tg1, Tg2 and Tg3 values of the SL-25 containing 25 wt.-% glycerol at 0%, 35%, 58%, 75% and 98% RH were in the range of -12.7 - -83.2 degrees C, 65.8 - 53.1 degrees C and 3.5 - 1.9 degrees C, respectively. The result from small-angle X-ray scattering indicated that the radii of gyration (Rg) of protein-rich domain were in the range of 60-63 nm; this suggested the existence of protein macromolecules as aggregates in the stable protein-rich and protein-water domains. With an increase of RH, the tensile strength and Tg values of the SL-series sheets decreased, but the elongation at break increased. In view of the results above, the moisture in ambient environment significantly influenced the Tg values and microstructures of the glycerol-plasticized soy protein sheets, leading to the changes of the mechanical and thermal properties.     

Study of poly(bisphenol A carbonate) relaxation kinetics at the glass transition temperature

In this work, the variations of the relaxation times are investigated above and below the glass transition temperature of a model amorphous polymer, the polycarbonate. Three different techniques (calorimetric, dielectric and thermostimulated currents) are used to achieve this goal. The relaxation time at the glass transition temperature was determined at the temperature dependence convergence of the relaxation times calculated with dynamic dielectric spectroscopy (DDS) for the liquid state and thermostimulated depolarisation currents (TSDC) for the vitreous state. We find a value of τ(T_g) = 110 s for PC samples. The knowledge of the temperature dependence, τ(T), and the value τ(T_g) enables to determine the glass-forming liquid fragility index, m. We find m = 178 ± 5.     

Glass transition investigated by a combined protocol using thermostimulated depolarization currents and differential scanning calorimetry

Relaxation times of bisphenol A polycarbonate around the glass transition temperature are estimated using the combination of differential scanning calorimetry (DSC) and thermostimulated depolarization currents (TSDC). These measurements are performed using samples with different thermal histories below and above the vitrification transformation. This protocol enables the extension of the range of equilibrium relaxation times measured by dielectric spectroscopy. By this mean we may recalculate the values of the Kauzmann temperature and fragility index.     

Effect of hydrophilicity of polymer particles on their glass transition temperatures in the emulsion state

The glass transition temperatures (Tg) of three kinds of poly(methyl methacrylate)-based copolymer emulsions having wide polymer compositions, which were prepared by emulsifier-free emulsion copolymerizations of methyl methacryalate with ethyl acrylate, n-buthyl methacrylate and methacrylic acid, were measured with a power compensation-type highly sensitive differential scanning calorimeter. The Tg values of the copolymers in their emulsion state (Tg _E) were always lower than those in their dry states (Tg _D), and the difference between Tg _E and Tg _D increased with an increase in copolymer hydrophilicities.Part CCLIII of the series Studies on Suspension and Emulsion     

On the glass transition temperature of styrene-n-butyl methacrylate copolymers in dependence on chemical composition,molecular weight,and mixtures

For statistic copolymers of styrene and n-butyl methacrylate, the relation between the glass transition temperature and the chemical composition or molecular weight of the copolymers has been determined. Further, the dependence of the glass transition temperature on the composition of binary and ternary blends from statistical poly (styrene-co-n-butyl methacrylates) of a nearly equal chemical composition but a very different molecular weight has been studied. Among several equations considered for the correlation between glass transition temperature and composition of the mentioned copolymers with relatively low molecular weights, the Gordon/Taylor and Couchman equations gave the best agreement with the experimental results. For the glass transition temperature of poly(styrene-co-n-butyl methacrylate) with an n-butyl methacrylate content of about 30 wt % in dependence on the molecular weight, the Kanig-Ueberreiter and Fox-Flory equations proved to be useful for the examined molecular weight range. The glass transition temperatures of the polymer blends have been studied for a low/high-molecular component system, a system of two low-molecular components, as well as for systems with a third component. The glass transition temperatures of the mixtures frequently exceeded those of their individual components. © 1994 John Wiley & Sons, Inc.     

Glass transition temperature and thermal decomposition of cellulose powder

Cellulose powder and cellulose pellets obtained by pressing the microcrystalline powder were studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermal gravimetry (TG). The TG method enabled the assessment of water content in the investigated samples. The glass phase transition in cellulose was studied using the DSC method, both in heating and cooling runs, in a wide temperature range from −100 to 180 °C. It is shown that the DSC cooling runs are more suitable for the glass phase transition visualisation than the heating runs. The discrepancy between glass phase transition temperature T _g found using DSC and predictions by Kaelbe’s approach are observed for “dry” (7 and 5.3% water content) cellulose. This could be explained by strong interactions between cellulose chains appearing when the water concentration decreases. The T _g measurements vs. moisture content may be used for cellulose crystallinity index determination.     

Determination of the glass transition temperature of latex films: Comparison of various methods

The glass transition temperature (T_g) for two latices with different styrene/butadiene compositions was determined by the thermal SPM probe resonance frequency method. The results were compared with the T_g values obtained by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), process rheometer (PR) and thermo-mechanical analyzer (TMA) measurements. The T_g values detected by the thermal SPM method agreed well with the T_g values obtained by DSC and calculated by the Fox–Flory equation. DMA, on the other hand, showed a significantly higher T_g value for both latices than those obtained from theoretical calculations, the thermal SPM method and DSC. The T_g obtained from the PR curve was slightly higher for the latex with a low styrene content, whereas good agreement was obtained with the thermal SPM data for the latex with a high styrene content. The glass transition temperature determined by TMA agreed fairly well with the thermal SPM data for the latex with the low styrene content, whilst the value of T_g for the second latex was much less than those obtained by the other methods. The thermal SPM method detects changes in thermal behavior (thermal diffusivity, heat capacity) during heating of the latex films rather than changes in the mechanical properties. Information about the sample history could be seen in the thermal SPM curves, which was further associated with the degree of latex film formation, especially when the roughness of the films was taken into consideration.     

Effect of copolymer composition and conversion on the glass transition of methyl acrylate–methyl methacrylate copolymers

The glass transition of methyl methacrylate methyl acrylate copolymers over a wide range of conversion and sequence distribution have been analyzed with the only purpose of predicting the change in the glass transition in copolymers as a function of conversion and consequently of comonomer sequence distribution. © 1994 John Wiley & Sons, Inc.     

Glass transition and enthalpy relaxation of ethylene glycol and its aqueous solution

Differential scanning calorimetry (DSC) and cryomicroscopy were employed to investigate the glass transition and enthalpy relaxation behaviors of ethylene glycol (EG) and its aqueous solution (50% EG) with different crystallization percent. Isothermal crystallization method was used in devitrification region to get different crystallinity after samples quenched below glass transition temperature. The DSC thermograms upon warming showed that the pure EG has a single glass transition, while the 50% EG solution has two if the solution crystallized partially. It is believed that the lower temperature transition represents the glass transition of bulk amorphous phase of EG aqueous solution glass state, while the higher one is related to ice inclusions, whose mobility is restricted by ice crystal. Cryomicroscopic observation indicated that the EG crystal has regular shape while the ice crystal in 50% EG aqueous solution glass matrix has no regular surface. Isothermal annealing experiments at temperatures lower than T_g were also conducted on these amorphous samples in DSC, and the results showed that both the two amorphous phases presented in 50% EG experience enthalpy relaxation. The relaxation process of restricted amorphous phase is more sensitive to annealing temperature.     

Phase and state transition effects on dielectric, mechanical, and thermal properties of polyols

The present study investigated the glass transition, crystallisation and melting behaviour of erythritol, xylitol, and glucitol (sorbitol) using dielectric analysis (DEA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Sorbitol and xylitol were plasticised by water and their glass transition temperatures decreased when water content was increased. Erythritol crystallised rapidly, and its water plasticisation behaviour could not be determined. Melting of the crystalline polyols occurred at their specific melting temperatures. Melts of erythritol and xylitol crystallised on recooling and no glass transition was apparent on reheating. Quench cooled sorbitol melt remained amorphous and showed a glass transition on reheating. Glass transition and crystallisation were apparent in the DSC thermogram and the dielectric and the dynamic mechanical spectra of mixtures of amorphous and crystalline xylitol.     

Glass transition temperature of allyl methacrylate‐n‐butyl acrylate gradient copolymers in dependence on chemical composition and molecular weight

Glass transition temperatures (T_gs) of P(AMA‐co‐BA) copolymers and the corresponding homopolymers, where AMA is allyl methacrylate and BA is n‐butyl acrylate, obtained by means of atom transfer radical polymerization were measured using differential scanning calorimetry. Because of the (pseudoliving) nature of this polymerization technique an increase in molecular weight (MW) is produced as the reaction progresses, which gives rise to an increase in T_gs. This increment can be adequately described by the Fox–Flory's equation in both homopolymers. However, in the spontaneous gradient copolymers of P(AMA‐co‐BA), the expected increase in T_g with the augment of the monomer conversion is compensated by the enrichment of BA as the polymerization reaction progresses. These opposite effects with respect to the T_g values almost balance each other, and therefore no significant influence on the MW or on conversion is found. This fact establishes that T_gs can be used to describe the profile of these gradient copolymers, and can be theoretically determined because of its dependence on the molar fraction in the copolymer. From this dependence on chemical composition along with the experimental behavior, a prediction of the T_g variation with the MW was performed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1845–1855, 2007     

Monitoring the glass transition temperature of polymeric composites with carbon nanotube buckypaper sensor

Carbon nanotube (CNT) Buckypapers can be infused with resin and easily incorporated into conventional fiber reinforced composites. In this paper, we propose to use Buckypaper (BP) as a new measuring method to determine the glass transition temperature of polymeric composites. The CNT-only BP was fabricated by spray-vacuum filtration method with monodispersion of multi-wall carbon nanotubes, and then co-cured with polymeric composites. After manufacturing, the glass transition temperature of polymeric composites could be obtained from the relationship between resistance and temperature of BP during the dynamic heating process. Experimental results show that the glass transition temperature of composite samples A and B monitored by BP sensors were 127 °C and 180 °C, while such temperatures obtained from a dynamical mechanical analyzer (DMA) were 128 °C and 184 °C respectively. This paper not only reveals the ability of BP as a sensor for monitoring the glass transition temperature of composite but also provides a new way to understand the glass transition phenomenon of composite.     

Calorimetric study of the conformational relaxation times in polystyrene

The temperature dependence of the relaxation times of the structural relaxation process of polystyrene is determined by temperature-modulated differential scanning calorimetry (TMDSC) and by conventional differential scanning calorimetry (DSC) in the latter by modelling the experimental heat capacity curves measured in heating scans after different thermal histories. The good agreement between both measuring techniques in the temperature interval just above the glass-transition temperature is a guide for the interpretation of the results of the TMDSC technique in the glass-transition region. In addition, the same model applied to DSC scans is used to simulate the TMDSC experiment and the calculated response is compared with the measured scans. Received: 22 February 1999 Accepted in revised form: 11 June 1999     

Glass-forming composition regions and glass transition temperature in nonaqueous electrolyte solutions

With an interest in assessing the suitability of various nonaqueous solutions for electrolyte studies in the viscous region of the liquid state, the glass-forming properties of solutions of calcium nitrate dissolved in various nonaqueous solvents have been determined and compared with the corresponding aqueous solution properties. Solutions in dimethyl formamide prove of particular interest. The composition dependence of the glass temperature is similar in all solvents at high salt contents. Ideal glass temperatures, estimated from thermodynamic data for the pure solvents, are compared with experimental or extrapolated values.     

Dependence of the glass transition temperature of poly (methyl methacrylates) on their tacticity

The specific isobaric heat capacities of poly (methylmethacrylates) (PMMA) having various tacticities were measured by the DSC method within a broad range of temperatures including the glass transition. Glasses with uniform thermal history were used in the measurements and the data were treated by employing a procedure which provided the thermodynamic T_g independent of the experimental conditions. The semiquantitative validity of Boyer's empirical relationT _g ×c_p=const. was confirmed; also it was found that within the limits of experimental accuracy the c_p,g values at 298 K andC _p,l values at 400 K are independent of the tacticity of the sample.Using the data thus measured and linearized equations representing the dependence ofT _g on the content of iso-, syndio- and heterotriads, the T_g values of pure isotactic PMMA and pure syndiotactic PMMA were found to be respectively 315 K and 397 K.Dedicated to Professor Dr. F. H. Müller.     

Effects of organophilic montmorillonite on hydrogen bonding, free volume and glass transition temperature of epoxy resin/polyurethane interpenetrating polymer networks

Epoxy resin nanocomposites containing organophilic montmorillonite (oM) and polyurethane were prepared by adding oM to interpenetrating polymer networks (IPNs) of epoxy resin and polyurethane (EP/PU). The dispersion degree of oM in EP/PU matrix was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Fourier transform infrared spectrometry (FT-IR) showed that strong interactions existed between oM and EP/PU matrix, and oM had some effect on hydrogen bonding of these EP/PU IPNs nanocomposites. Positron annihilation spectroscopy (PALS) and differential scanning calorimetry (DSC) measurements were used to investigate the effect of oM and PU contents on free volume and glass transition temperature (T_g) of these nanocomposites. The PALS and DSC results clearly showed that the presence of oM led to a decrease in the total fractional free volume, which was consistent with increasing T_g upon addition of oM, ascribed to increasing hydrogen bonding in interfacial regions of oM and EP/PU matrix and enhancing the miscibility between EP phase and PU phase. In addition, with increasing PU content, the total fractional free volume increased, corresponding to decreasing T_g.     

Calorimetric glass transition temperature and absolute heat capacity of polystyrene ultrathin films

The absolute heat capacity and glass transition temperature (T_g) of unsupported ultrathin films were measured with differential scanning calorimetry with the step-scan method in an effort to further examine the thermodynamic behavior of glass-forming materials on the nanoscale. Films were stacked in layers with multiple preparation methods. The absolute heat capacity in both the glass and liquid states decreased with decreasing film thickness, and T_g also decreased with decreasing film thickness. The magnitude of the T_g depression was closer to that observed for films supported on rigid substrates than that observed for freely standing films. The stacked thin films regained bulk behavior after the application of pressure at a high temperature. The effects of various preparation methods were examined, including the use of polyisobutylene as an interleaving layer between the polystyrene films. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3518–3527, 2006     

Chemical structure and glass transition temperature of non-ionic cellulose ethers

New zinc(II) propionate complexes (CH₃CH₂COO)₂Zn·Ln·xH₂O, where n=1-2, x=0 or 2, were prepared by reaction of zinc(II) propionate with heterocyclic ligands (L=theophylline, nicotinamide, methyl-3-pyridyl carbamate) and their thermal properties were studied. The prepared complex compounds were characterized by elemental analysis and IR spectra. TG/DTG and DTA measurements of the prepared compounds were performed in the air atmosphere under dynamic conditions. The thermal decomposition can be characterized as a multi-step process. The first step is attributed to the elimination of water or N-donor ligand molecules. It is followed by the decomposition of propionate anion when diethyl ketone and carbon dioxide were released. Zinc oxide was found as a final product of the thermal decomposition of the complex compounds under study. The volatile intermediate products of the thermal decomposition of zinc(II) propionate complexes were identified by IR-spectroscopy, qualitative chemical analyses and final solid product by X-ray powder diffraction method. Moreover, IR spectra suggest monodentate coordination of propionate anion to zinc. The complexes were tested against bacteria and filamentous fungi and show both antimicrobial activity and fungistatic effect towards pathogens as well as probiotic activity towards Lactobacillus paracasei.