Preparation and thermal characterization of the glass transition temperatures of sulfonated polystyrene-metal ionomers

The glass transition temperatures and heat capacity changes in the transition region are reported for six sulfonated linear polystyrenes in the hydrogen form, H-SPS, in the 3.4–20.1 mol % sulfonation range and 76 metal SPS ionomers in the 3.4–12.8 mol % range. The metals are those which interact predominantly ionically and include +1, +2, and +3 ions of the alkali metal, alkaline earth, and rare earth (lanthanide) series. The results show the effect of H₂O or coordinating ligands on glass transition temperatures (T_g) and the importance of eliminating it to obtaining reproducible values for T_g and ΔC_p. The T_g values of dry M-SPS ionomers depend only on the sulfonation level despite wide variation in metal ion charge and size. The variation of ΔC_p with sulfonation level is interpreted as showing that at high levels a few unsulfonated styrene units adjacent to sulfonated ones are constrained, presumably by clustering, from participation in the polystyrene-like cooperative rearrangements in the transition region.     

Challenge and Solution of Characterizing Glass Transition Temperature for Conjugated Polymers by Differential Scanning Calorimetry

Thermomechanical properties of polymers highly depend on their glass transition temperature (T _g). Differential scanning calorimetry (DSC) is commonly used to measure T _g of polymers. However, many conjugated polymers (CPs), especially donor–acceptor CPs (D–A CPs), do not show a clear glass transition when measured by conventional DSC using simple heat and cool scan. In this work, we discuss the origin of the difficulty for measuring T _g in such type of polymers. The changes in specific heat capacity (Δc _p) at T _g were accurately probed for a series of CPs by DSC. The results showed a significant decrease in Δc _p from flexible polymer (0.28 J g^?1 K^?1 for polystyrene) to rigid CPs (10^?3 J g^?1 K^?1 for a naphthalene diimide‐based D–A CP). When a conjugation breaker unit (flexible unit) is added to the D–A CPs, we observed restoration of the Δc _p at T _g by a factor of 10, confirming that backbone rigidity reduces the Δc _p. Additionally, an increase in the crystalline fraction of the CPs further reduces Δc _p. We conclude that the difficulties of determining T _g for CPs using DSC are mainly due to rigid backbone and semicrystalline nature. We also demonstrate that physical aging can be used on DSC to help locate and confirm the glass transition for D‐A CPs with weak transition signals. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1635–1644     

Radiothermoluminescence. I. Radiothermoluminescence for investigation of thermal and radiation-induced crosslinking of rubber mixtures

Phase heterogeneity of vulcanizates based on cis-polybutadiene (cis-Europrene) and SBR (Europrene 1500) blends obtained by radiation, thermal, two-stage radiation-thermal, and two-stage thermal-radiation processes was investigated by the radiothermoluminescence method. Unvulcanized blends of these polymers are found to be heterogeneous, exhibiting two glass transition temperatures T_g, which coincide with the values for the initial components. Following vulcanization, the difference between the two T_g values for a polyblend decreases. The decrease is more distinct for polyblends crosslinked at high temperatures. When the vulcanization temperature exceeds 140°C and the crosslink density (or 1/M_c) exceeds 5 × 10^?5–1 × 10^?4 mole/cm³, the glass temperature ranges of the crosslinked blend are practically superimposed. Such crosslinked mixtures should be considered pseudohomogeneous in phase.     

Synthesis, curing kinetics and thermal properties of bisphenol-AP-based benzoxazine

A novel bisphenol-AP-aniline-based benzoxazine monomer (B-AP-a) was synthesized from the reaction of 4,4′-(1-phenylethylidene) bisphenol (bisphenol-AP) with formaldehyde and aniline. The chemical structures were identified by FT-IR, ¹H and ¹³C NMR analyses. The polymerization behavior of the monomer and the types of hydrogen bonding species were monitored by differential scanning calorimetry (DSC) and FT-IR. The curing kinetics was studied by isothermal DSC and the isothermal kinetic parameters were determined. The thermal properties of cured benzoxazine were measured by DSC and thermogravimetric analysis (TGA). The bisphenol-AP-aniline-based polybenzoxazine (poly(B-AP-a)) exhibited higher glass transition temperature (T_g) and better thermal stability than corresponding bisphenol A-aniline-based polybenzoxazines (poly(BA-a)). The T_g value of poly(B-AP-a) is 171 °C. The temperatures corresponding to 5% and 10% weight loss is 317 and 347 °C, respectively, and the char yield is 42.2% at 800 °C. The isothermal curing behavior of B-AP-a displayed autocatalysis and diffusion control characteristics. The modified autocatalytic model showed good agreement with experimental results.     

Thermal behavior of ferroelectric Polyamide 11 in relation to pyroelectric properties

The pyroelectric properties of oriented thin films of ferroelectric Polyamide 11 have been studied in the temperature range of −100°C up to +140°C. The temperature dependence of the experimental pyroelectric coefficient has been analyzed. Three changes of slope of the pyroelectric coefficient are observed at −20, +50, and +100°C. The origin of the lower temperature event has not yet been defined. The upper transition is attributed to chain movements in crystalline regions, and more precisely, to a crystalline phase transition. The intermediate event is close to the glass transition temperature T_g observed by DSC. It is attributed to the manifestation of the glass transition. Below T_g, the variations of the pyroelectric coefficient are very small. For higher temperatures, it increases rapidly, attesting to a major contribution of secondary pyroelectricity and dimensional effects above T_g. The breaking of hydrogen bonds occurring at the glass transition temperature observed on DSC thermograms does not affect pyroelectric properties. Pyroelectric properties are mildly reduced after annealing at temperatures up to +140°C. A comparative study of oriented ferroelectric films prepared by quenching from the melt and nonoriented slowly cooled samples has been carried out by means of DSC. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 715–723, 1999     

Glass transition temperature for epoxy-diamine networks

The glass transition temperature of systems based on epoxy resin and a number of diamines has been determined by using a torsion pendulum. An equation relating composition and crosslink density with the glass transition temperature has been established which gives reasonable predictions of the glass transition temperatures for systems based on aliphatic or aromatic amines and methylated amines and for systems containing a monofunctional epoxy diluent. The equation may be used to predict T_g for systems with non-stoichiometric quantities of curing agent and blends of amines. Deviation of the predicted and observed values for T_g is interpreted in terms of differences between definitions of T_g used by other workers and, also the occurrence of competing side reactions during polymerization which lead to additional crosslinks.     

Hydrogen bonding in butadiene copolymers. I. Network formation

The incorporation of comonomers bearing functional groups yields butadiene copolymers capable of hydrogen bonding. Three such butadiene-based materials were studied: methacrylic acid copolymers, 2-methyl-5-vinylpyridine copolymers, and stoichiometric mixtures of the acidic and basic copolymers. The elastic effects of intermolecular hydrogen bonding were determined by comparing the simple weighted average of the moduli of the parent copolymers with the observed modulus of their stoichiometric mixture. The results show that measurable increases in the moduli of the mixtures persist even above the glass temperature T_g, which is itself elevated in the mixtures. These increases may be treated as temperature-dependent temporary crosslinks.     

A partial phase diagram for a mixture of polystyrene with a low molecular weight styrene-dimethylsiloxane block copolymer

Differential scanning calorimetry (DSC) was used to examine the miscibility of polystyrene (PS), mol. wt. 10⁵, with a phase-separated styrene-dimethylsiloxane (S-DMS) diblock copolymer, M_n = 3800, 86 wt% S. Mixtures whose S content varied from 4 to 96 wt% PS were examined at a 10 K min^?1 heating rate following a 200 K min^?1 cooling rate from temperatures varying from 403 to 573 K. At some compositions, two glass transition temperatures, T_gs, corresponding to PS transitions were observed; at others only a single T_g was observed. When it was assumed that the 200 K min^?1 cooling rate corresponded to quenching from the starting temperature, and when the heat capacity changes at the S glass transitions were used to calculate the percentage of S repeat units undergoing each glass transition, it was possible to calculate an approximate partial phase diagram for this mixture. At 96 wt% PS, there was evidence for a small amount of mixed S phase, possibly block copolymer micelles, in equilibrium with PS; from about 60 to 90 wt% PS, the S repeat units from the block copolymer appeared to be completely mixed with the PS. At lower wt% PS, unmixed block copolymer was in equilibrium with block copolymer whose S segments were mixed with the PS. The phase diagram appeared to vary only slightly with temperature.     

Thermal transitions of gelatin evaluated using DSC sample pans of various seal integrities

Differential scanning calorimetry (DSC) has become a popular tool to investigate thermal transitions in food ingredients such as gelatin. Upon heating commercial gelatin samples beyond glass transition (T _g) and melting (T _m) temperatures, a relatively large endothermic transition (T _i) can be observed. We have observed that both the peak temperature and the enthalpy of the T _i transition are influenced by the integrity of the seal of the DSC pans used for the analysis. This study shows that escape of moisture from the DSC pan appears to be responsible for this effect. The effect of different types of DSC pans, as well as technique of sealing them on the T _i transition were evaluated using DSC, SDT, and TG–MS.     

Argon sorption and partial molar volume in poly(ethyl methacrylate) above and below the glass transition temperature

Sorption and dilation isotherms for argon in poly(ethyl methacrylate) (PEMA) are reported for pressures up to 50 atm over the temperature range 5–85°C. At temperatures below the glass transition (T_g=61°C), sorption isotherms are well described by the dual-mode sorption model; and isotherms above T_g follow Henry's law. However, isotherms for dilation due to sorption are linear in pressure at all temperatures over the range investigated. Partial molar volumes of Ar in PEMA are obtained from these isotherms. The volumes are approximately constant above T_g (about 40 cm³/mol), whereas the volumes below T_g are smaller and dependent on both temperature and concentration (19–26 cm³/mol). By analyzing the experimental data according to the dual-mode sorption and dilation model, the volume occupied by a dissolved Ar molecule and the mean size of microvoid in the glass are estimated to be 67 129 ų, respectively. The cohesive energy density of the polymer is also estimated as 61 cal/cm³ from the temperature dependence of the dual-mode parameters.     

Comparison of the mechanical properties of styrene‐based ionomers containing either crown ether or pentaethylene glycol with those of underneutralized ionomers

Dynamic mechanical properties of styrene‐based ionomers containing varying amounts of either 15‐crown‐5 ether (CE) or pentaethylene glycol (PG) are compared with those of ionomers of varying degree of neutralization (ND). The cluster T_g (T_g,c) and ionic modulus of the ionomers decrease with increasing amount of CE or PG or decreasing ND. Thus, we propose that the CE binds Na⁺ strongly to form a large‐sized complex. Thus, the electrostatic interactions between charges decrease, leading to lower T_g,c. For the PG‐containing ionomers, the PG acts as polar plasticizer, further lowing the T_g,c. In the case of the underneutralized ionomers, the T_g,c is reduced by the existence of both relatively weak hydrogen bonds between carboxylic acid groups and relatively strong ionic bonds between ion pairs in the multiplets. The small‐angle X‐ray scattering results are also supportive of the above interpretations. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1358–1367     

Glass transitions in hydrogen-bonded polymer complexes

Mutual precipitates of poly (N, N-dimethyl acrylamide) and poly (4-hydroxystyrene) were collected from dioxane, methanol, or acetone. The glass transition (T_g) temperatures of the precipitates are higher than the weight-average values. Clear films cast from dimethylformamide solutions have lower T_g values. Complexation also occurred between poly (ethyl oxazoline) and poly (4-hydroxystyrene) in dioxane and between poly (vinyl pyrrolidone) and poly (4-hydroxystyrene) in methanol. Again, the glass transition temperatures of the precipitates are higher than the values for the blend films. The ΔC_p values associated with the glass transitions of the complexes are smaller than those of the blends having the same compositions. Negative excess heat capacities of mixing have been observed for several precipitates.     

Composition dependence of glass transition temperature of sulfonated-polystrene ionomers

The glass transition temperatures of alkali (Na, K, Rb, Cs) and alkaline-earth (Ba, Sr, Ca, Mg) ionomers of sulfonated polystyrenes (PSSA) with 3.4, 6.9, 12.7, and 16.7% of the styrene moieties sulfonated are reported. For the alkali-metal PSSA ionomers, T_g depends on the degree of sulfonation, at least up to 13%, but not strongly on the nature of the cation. For the alkaline-earth analogs T_g does not depend strongly on either the cation or the degree of sulfonation until the 16.7% level is reached. These and other reported data are discussed in terms of the role of cations in determining morphology.     

Glass transition kinetics of some Se-Te-Ag chalcogenide glasses

Summary The present paper reports the Differential Scanning Calorimetric (DSC) study of some Ag doped Se-Te chalcogenide glasses. DSC runs were taken at different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition and crystallization temperatures. The variation of glass transition temperature T_gwith Ag concentration has been studied. It has been found that T_gdecreases with increase in Ag concentration. The heating rate dependence of T_gis used to evaluate the activation energy of glass transition (DE_t). The value of<span style='font-size:10.0pt; font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>DE_thas been found to increase with increase in Ag concentration followed by nearly constant value at higher concentrations of Ag.     

Preparation and Characterization of Blend Films of Poly(Vinyl Alcohol) and Sodium Alginate

Blend films of poly(vinyl alcohol) (PVA) and sodium alginate (NaAlg) were prepared by casting from aqueous solutions. This blend films were characterized by tensile strength test, Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The miscibility in the blends of PVA and NaAlg was established on the basis of the thermal analysis results. DSC showed that the blends possessed single, composition‐dependent glass transition temperatures (T_gs), indicating that the blends are miscible. FT‐IR studies indicate that there is the intermolecular hydrogen bonding interactions, i.e. –OH…^?OOC– in PVA/NaAlg blends. The blend films also exhibited the higher thermal stability and their mechanical properties improved compared to those of homopolymers.     

Effects of Na‐sulfopropyl groups on the mechanical properties and morphology of polystyrene‐co‐methacrylate ionomers

The dynamic mechanical properties and morphology of poly(styrene‐co?3‐sulfopropyl sodium‐methacrylate) SSPMANa ionomers were investigated. It was found the increasing rate of ionic moduli of the SSPMANa ionomer was very low, and the cluster T_g of the ionomers remained more or less constant with increasing ion content. A well‐developed SAXS peak was seen for low ion content SSPMANa ionomers and the peak position changed slightly with ion content. Thus, it was suggested that the presence of the alkyl ester side chains made the ion pairs form multiplets more easily at their prevalent distances, and the small‐agglomerated multiplets were dispersed in the polymer matrix relatively evenly. The interpretation of ionic moduli using a number of theories implied that the multiplets and clusters acted as effective crosslinks and filler particles, respectively, and the size and shape of the clusters were irregular. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1043–1053     

Conductivity,structure, and thermal properties of chitosan‐based polymer electrolytes with nanofillers

This paper focus on the effect of nanosize (<50 nm BET) inorganic alumina (Al₂O₃) filler on the structural, conductivity, and thermal properties of chitosan‐based polymer electrolytes. Films of chitosan and its complexes were prepared using solution‐casting technique. Different amounts of Al₂O₃ viz., 3, 4.5, 6, 7.5, 9, 12, and 15 wt% were added to the highest room temperature conducting sample in the chitosan–salt system, i.e. sample containing 60 wt% chitosan–40 wt% NH₄SCN. The conductivity value of the sample is 1.29 × 10^?4 S cm^?1. On addition of 6 wt% Al₂O₃ filler the ionic conductivity increased to 5.86 × 10^?4 S cm^?1. The amide and amino peaks in the spectrum of chitosan at 1636 and 1551 cm^?1, respectively, shift to lower wavenumbers on addition of salt. The glass transition temperature T_g for the highest conducting composite is 190°C. The increase in T_g with increase in more than 6 wt% filler content is attributed to the increase in degree of crystallinity as proven from X‐ray diffraction studies. Copyright © 2009 John Wiley & Sons, Ltd.     

Exciton transitions in quasi-one-dimensional crystals. 9,10-dichloroanthracene

Polarized reflection spectra of the first singlet transition of the α-crystalline form of 9,10-dichloroanthracene are reported. Crystal faces (001), (011) and (010) were examined in spectral range 450 to 350 nm at two temperatures, 5 K and 300 K. Two systems of transitions were observed. The first system is assigned to neutral excitons. Spectral similarities with unsubstituted anthracene and arguments based on the one-dimensional stacking of molecules are used to construct a model of the exciten band structures. The M-polarized ππ* molecular transition gives rise to a four branch band with two allowed transitions. The 0-0_b (A_g → A_u) transition lies 50–100 cm^?1 above the bottom of the exciton band and the 0-0_c′ (A_g → B_u) transition lies at the top of the band. In the reflection spectrum the Davydov splitting c′b for transverse excitons is 210 cm^?1. The exciton band of the 00 molecular transition is not isolated but overlaps the two-particle manifold of the 0–1 vibronic transition. As a result of the 0–1_c′ transition is unexpectedly strong in the spectra of the (010) face. The second system is polarized along the stack-axis a and starts 2500 cm^?1 above the first system. It is tentatively assigned as |a(A_g → B_u) charge transfer exciton transition in agreement with earlier observations.     

Thermal analysis of the influence of water content on glass transitions

Starch is an important natural substance in which the water content has a significant influence on its structure and properties. In the present study, the effect of the water content on glass transition temperatures T _g and heat capacities C _p of wheat, maize and potato starches were investigated by high-sensitivity differential scanning calorimetry (temperature modulated TMDSC and conventional DSC). Thermal analysis measurements were performed on starch samples with different water contents. The exact water mass percentage of each sample was determined using the Karl-Fischer method. The obtained results show that the water content does influence the starch thermal properties in a systematic and measurable trend, the higher the water% the lower the glass transition temperature, and the higher the heat capacity jump during gelatinisation. At this stage possible interpretations of the results are just put forward and should be confirmed through complementary measurements.     

Effects of the type of crosslink on viscoelastic properties of natural rubber

The viscoelastic properties of various crosslinked natural rubbers, NR, were investigated by mechanical spectroscopy. The glass transition temperature, T_g, was found to be dependent on both the crosslink density and the crosslink type. Higher values of T_g were obtained for sulfur-crosslinked NR than for peroxide-crosslinked NR at the same crosslink density. The greater influence of the sulfur content on T_g may be attributed to polysulfidic crosslinks and cyclic sulfide structures favored at high sulfur contents. Sulfur-vulcanized NRs with monosulfidic crosslinks, favored at relatively high accelerator/sulfur ratios, have properties more similar to the peroxide-cured NR with simple carbon(SINGLE BOND)carbon crosslinks covalent bonds, resulting in only small shifts in T_g. A qualitative analysis of monosulfidic crosslinks and polysulfidic structures was performed with ¹³C solid-state NMR spectroscopy. The storage modulus, E′, in the rubbery plateau region increased with increasing crosslink density. However, the crosslink type did not influence the moduli values as much as it influenced the T_g values. Different methods of detecting the crosslink density were also discussed. © 1996 John Wiley & Sons, Inc.