Ion-aggregation and thermal expansion in styrene-based ionomers

The linear thermal-expansion coefficients (α) of styrene–sodium methacrylate copolymers were studied as a function of the concentration of sodium methacrylate comonomer. Over the concentration range studied (0.61–9.0 mole % sodium methacrylate), the expansion coefficients of the glass α_g and of the liquid α_l were independent of ion concentration. Average values for these quantities were α_g = (6.9 ± 0.9) × 10^?5 deg^?1 and α_l = (16.0 ± 2.0) × 10^?5 deg^?1. When samples of concentrations above 6 mole % were heated from room temperature, a low value for the liquid-expansion coefficient α_l was observed in the first runs. This quantity had an average value of (12.0 ± 1.9) × 10^?5 deg^?1. Heating of the 6.5 mole % sample from room temperature followed by cycling from the glass transition temperature T_g to successively higher temperatures resulted in a gradual increase in liquid-expansion coefficient. The results are consistent with the hypothesis of the existence of various types of ionic aggregates in these polymers, with the state of aggregation changing at approximately (5–6) % of ions. Experimental T_g values, which increase with ion concentration over the entire range, are consistent with the results of previous studies.     

Enthalpy relaxation of low molecular weight amorphous styrene oligomers measured with an adiabatic calorimeter

Herein, we measured the enthalpy relaxation of three styrene oligomers with different molecular weights (styrene oligomer with M_w?=?4.53?×?10²: PSA-300, styrene oligomer with M_w?=?5.89?×?10²: PSA-500, and styrene oligomer with M_w?=?1.01?×?10³: PSA-1000) near their respective glass transition temperatures (T_g) using an adiabatic calorimeter. We determined the relaxation rates and the amounts of configurational enthalpy released from the temperature dependence of the temperature drift rates around T_g. Based on our experimental findings, we found the amounts of configurational enthalpy release per monomer unit to be 0.8, 3.5, and 1.6 kJ mol^?1 for PSA-300, PSA-500, and PSA-1000, respectively. These values were 3.9–18 times larger than that of glycerol, which is a typical glass-forming liquid.

     

Infrared spectroscopic studies of polymer transitions. III. Effects of sodium ion on glass transitions in styrene-based ionomers

The glass transition in styrene-based ionomers was investigated by means of infrared spectroscopy and differential scanning calorimetry (DSC). Transition temperatures were determined from the temperature dependence of the peak absorbances of the 1700 and 1745 cm^?1 bands. These transition temperatures agreed with glass transition temperatures (T_g) determined by DSC. With increasing degree of ionization, T_g and the enthalpy ΔH of the residual intermolecular hydrogen bonding increased. The values of T_g obtained were analyzed by the theory of Fox and Loshaek for the effect of crosslinks. It is concluded that sodium ions probably from ionic domains and act as crosslinks to reinforce the residual hydrogen bonding and may increase T_g. The absorbance at 1560 cm^?1 (ν_COO^?) did not change at T_g. This suggests that the glass transition observed here is not due to the onset of the mobility in ionic domains, as has been proposed for ethylene-based ionomers on the basis of dielectric measurements.     

Longitudinal volume viscosity of poly(methyl methacrylate)

Volume flow of poly(methyl methacrylate) (PMMA) (M?_n = 43,000 and T_g = 384) has been measured in an Instron Capillary Rheometer. Elastic modulus of the longitudinal wave, longitudinal volume viscosity, initial longitudinal volume viscosity, and retardation times are described at temperatures above T_g (418–483K) and compression rates of about 1.00–200.00 × 10⁵ s^?1. An initial increase followed by a decrease in longitudinal volume viscosity has been observed as the compression rate increases and the volume deformation decreases, this last behavior being at the lowest values of the compression rate (6.0 and 30.0 × 10^?5 s^?1) a typical nonequilibrium one. η_L also increases with increasing temperature (T_g decreases 0.18°C/MPa), and volume flow activation energy decreases as the volume deformation increases.     

Polymer electrolyte membranes by in situ polymerization of poly(ethylene carbonate‐co‐ethylene oxide) macromonomers in blends with poly(vinylidene fluoride‐co‐hexafluoropropylene)

Salt‐containing membranes based on polymethacrylates having poly(ethylene carbonate‐co‐ethylene oxide) side chains, as well as their blends with poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP), have been studied. Self‐supportive ion conductive membranes were prepared by casting films of methacrylate functional poly(ethylene carbonate‐co‐ethylene oxide) macromonomers containing lithium bis(trifluorosulfonyl)imide (LiTFSI) salt, followed by irradiation with UV‐light to polymerize the methacrylate units in situ. Homogenous electrolyte membranes based on the polymerized macromonomers showed a conductivity of 6.3 × 10^?6 S cm^?1 at 20 °C. The preparation of polymer blends, by the addition of PVDF‐HFP to the electrolytes, was found to greatly improve the mechanical properties. However, the addition led to an increase of the glass transition temperature (T_g) of the ion conductive phase by ～5 °C. The conductivity of the blend membranes was thus lower in relation to the corresponding homogeneous polymer electrolytes, and 2.5 × 10^?6 S cm^?1 was recorded for a membrane containing 10 wt % PVDF‐HFP at 20 °C. Increasing the salt concentration in the blend membranes was found to increase the T_g of the ion conductive component and decrease the propensity for the crystallization of the PVDF‐HFP component. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 79–90, 2007     

Surface glass transition of miscible amorphous polymers blends

The surface glass transition temperature (T _g ^surface) of the bulk samples of miscible blends formed of amorphous polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been characterised in terms of an adhesion approach we proposed recently. T _g ^surface has been measured as the temperature transition “occurrence of autoadhesion–nonoccurrence of autoadhesion” by employing a lap-shear joint mechanical testing method. The effect of the reduction in T _g ^surface with respect to the glass transition temperature of the bulk (T _g ^bulk), which had been observed earlier in pure homopolymers, has been found to exist in the blends of PS with PPO as well. The values of this effect for the blends have been compared with those for pure homopolymers, and the differences found have been discussed.     

Comparison of electrical conductivity and thermal properties of borosilicate glass with and without simulated radioactive waste

Electrical conductivity and percentage linear thermal expansion of the borosilicate glass (BSG) and simulated waste-loaded borosilicate glass (BSGW) were measured in the temperature range of 300–780 K and compared. Pronounced increase in electrical conductivity was observed around glass transition temperature (T _g) of BSG and BSGW. The activation energy (E _a) of electrical conduction determined from the measured data for BSG and BSGW is 0.961 ± 0.005 and 0.960 ± 0.005 eV, respectively. The % average linear thermal expansion of BSGW showed a slight decreasing trend compared with pristine BSG. The average coefficient of thermal expansion determined from dilatometry data is 12.87 ± 0.24 × 10^?6 and 11.94 ± 0.23 × 10^?6 K^?1 for BSG and BSGW, respectively. The T _g measured by dilatometry is 806 ± 24 K for BSG and 790 ± 23 K for BSGW, respectively. The T _g measured by DTA was found to be 820 ± 7 and 805 ± 5 K for BSG and BSGW, respectively, for heating cycle. The T _g values obtained from DSC measurements are 805 ± 5 and 803 ± 5 K for BSG and BSGW, respectively. The T _g of BSGW showed a slight decrease compared with that of BSG. The values obtained by DSC examination also showed the lowering of T _g values for the waste-loaded composition. The lowering of T _g may be attributed to the interaction of glass-forming agents and simulated waste elements.     

SURFACE RHEOLOGY OF POLYMERIC SOLIDS

Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of scanningviscoelasticity microscopic (SVM) and lateral force microscopic (LFM) measurements. SVM and LFM measurements werecarried out for films of conventional monodisperse polystyrene (PS) with sec-butyl and proton-terminated end groups atroom temperature. In the case of the number-average molecular weight, M_n, less than ca. 4.0×10~4, the surface was in a glass-rubber transition state even though the bulk glass transition temperature, T_g was far above room temperature, meaning thatthe surface molecular motion was fairly active compared with that in the bulk. LFM measurements of the, monodisperse PSfilms at various scanning rates and temperatures revealed that the time-temperature superposition was applicable to thesurface mechanical relaxation behavior and also that the surface glass transition temperature, T_g~σ, was depressed incomparison with the bulk one even though the magnitude of M_n was fairly high at 1.40×10~5. The surface molecular motionof monodisperse PS with various chain end groups was investigated on the basis of temperature-dependent scanningviscoelasticity microscopy (TDSVM). The T_g~σs for the PS films with M_n of 4.9×10~6 to 1.45×10~6 measured by TDSVMwere smaller than those for the bulk one, with corresponding M_ns, and the T_g~σs for M_ns smaller than ca. 4.0×10~4 were lowerthan room temperature (293 K). The active thermal molecular motion at the polymeric solid surface can be interpreted interms of an excess free volume near the surface region induced by the surface localization of chain end groups. In the case ofM_n=ca. 5.0×10~4, the T_g~σs for the α, ω-diamino-terminated PS (α,ω-PS(NH_2)_2) and α, ω-dicarboxy-terminated PS (α, ω-PS(COOH)_2) films were higher than that of the PS film. The change of T_g~σ for the PS film with various chain end groups canbe explained in terms of the depth distribution of chain end groups at the surface region depending on the relativehydrophobicity.     

EPR studies of mechanically induced bond rupture in elastomers

Electron paramagnetic resonance (EPR) spectroscopy was used to compute the surface bond rupture density in polyurethane and to determine the phase experiencing fracture in styrene-butadiene block copolymers when these elastomers are subjected to mechanical degradation by grinding. The polyurethane grinding was done at temperatures above and below the glass transition T_g; 0.155 × 10¹³ radicals/cm² of fracture surface area were formed above the T_g and 4.42 × 10¹³ radicals/cm² for grinding below the T_g. These values are essentially equal to those found earlier for spherulitic polymers. In all cases the fracture appears able to progress along preferential paths so as to rupture significantly fewer molecular chains than one would expect on the basis of calculations of the number of chains passing through each square centimeter of cross section. Comparison of EPR spectra formed by grinding styrene-butadiene copolymer with those of styrene and butadiene above indicated that at cryogenic temperature, the fracture in the copolymer takes place in the butadiene phase.     

Comparison of the Plasma Temperature and Electron Number Density of the Pulsed Electrolyte Cathode Atmospheric Pressure Discharge and the Direct Current Solution Cathode Glow Discharge

A novel-pulsed electrolyte cathode atmospheric pressure discharge (pulsed-ECAD) plasma source driven by an alternating current (AC) power supply coupled with a high-voltage diode was generated under normal atmospheric pressure between a metal electrode and a small-sized flowing liquid cathode. The spatial distributions of the excitation, vibrational, and rotational plasma temperatures of the pulsed-ECAD were investigated. The electron excitation temperature of H T_exc(H), vibrational temperature of N₂ T_vib(N₂), and rotational temperature of OH T_rot(OH) were from 4900?±?36 to 6800?±?108 K, from 4600?±?86 to 5800?±?100 K, and from 1050?±?20 to 1140?±?10 K, respectively. The temperature characteristics of the dc solution cathode glow discharge (dc-SCGD) were also studied for the comparison with the pulsed-ECAD. The effects of operating parameters, including the discharge voltage and discharge frequency, on the plasma temperatures were investigated. The electron number densities determined in the discharge system and dc-SCGD were 3.8–18.9?×?10¹⁴?cm^–3 and 2.6?×?10¹⁴ to 17.2?×?10¹⁴?cm^–3, respectively.     

EFFECT OF IRRADIATION TEMPERATURE ON GENERAL EQUATION OF SOL FRACTION-DOSE RELATIONSHIP FOR FLUOROPOLYMERS

In this paper, the effect of irradiation temperature on sol fraction-dose relationship of tluoropolymers was studied. It was found that the increasing of irradiation temperature can result in the decreasing of βvalue of fluoropolymer, which increases the crosslinking probability of fluoropolymer. The relationship between crosslinking parameter βand irradiation temperature (T_i)of fluoropolymer is established as follows:β=2.2×10~(-3) T_g+4×10~(-4)(T_g-T_i)+0.206.values of some tluoropolymers calculated from the above expression are in agreement with the experimental values.     

Glass transition of crosslinked polystyrene shells formed on the surface of calcium carbonate whisker

Glass transition of core/shell capsules consisting of calcium carbonate whisker as a core and crosslinked polystyrene as a shell was studied by differential scanning calorimetry. The thickness of the crosslinked shell was in the range of 26–81 nm. The crosslinked shells were revealed to show higher glass transition temperatures (T_g) than the corresponding bulk values. It was revealed that a thicker shell exhibits a lower T_g than a thinner shell, and that capsules without core (hollow capsules) exhibit lower T_g's than the corresponding core/shell capsules. These results suggest that the interfacial molecular interaction plays a role in the segmental relaxation, which is responsible for the glass transition. The difference in T_g between the core/shell and hollow samples was reduced when a coupling agent, methacrylic acid 3‐(trimethoxysilyl)propyl ester, was not included. This also suggests the interfacial effect on T_g. However, the results still suggest that the enhancement of T_g for the present crosslinked shells is not only due to the interfacial effect but also to the effects of chain configuration and heterogeneous crosslink. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2475–2485, 2006     

Low-angle electron diffraction from high temperature polystyrene crazes

Low-angle electron diffraction (LAED) was used to study the microstructure of crazes produced at different temperatures T and strain rates in thin films of monodisperse polystyrene (PS). At a slow strain rate of 4.1 × 10^?6 s^?1 both the fibril diameter D and the fibril spacing D₀ of crazes in 1800k molecular weight PS remained constant with temperature up to T ≈ 70°C and then sharply increased as T approaches T_g. At a higher strain rate of ～ 10^?2 s^?1, both D and D₀ increase only slightly with T. The values of D and D₀ over a range of temperature are in very good agreement with those values obtained in bulk samples using small-angle x-ray scattering. The crazing stress was measured as a function of temperature in the thin films of the 1800k molecular weight PS strained at the same slow strain rate used for the LAED measurements. These measurements were analyzed using a simple model of craze growth to reveal the temperature and strain rate dependence of the craze surface energy Γ. At room temperature Γ ≈ 0.076 J/m² (versus Γ ≈ 0.087 J/m² predicted) and was observed to remain constant up to T ≈ 70°C and then decrease by approximately a factor of two at T = 90°C. This decrease in Γ is believed to result from chain disentanglement to form fibril surfaces at sufficiently high temperatures and occurs in the same temperature range in which the craze fibril extension ratio λ was observed to increase.     

Synthesis and characterization of novel alternating fluorinated copolymers bearing oligo(ethylene oxide) side chains

The synthesis and characterization of novel poly(CTFE‐g‐oligoEO) graft copolymers [chlorotrifluoroethylene (CTFE) and ethylene oxide (EO)] are presented. First, vinyl ether monomers bearing oligo(EO) were prepared by transetherification of ω‐hydroxyoligo(EO) with ethyl vinyl ether catalyzed by a palladium complex in 70–84% yields. Two vinyl ethers of different molecular weights (three and 10 EO units) were thus obtained. Then, radical copolymerization of the above vinyl ethers with CTFE led to alternating poly(CTFE‐alt‐VE) copolymers that bore oligo(OE) side chains in satisfactory yields (65%). These original poly(CTFE‐g‐oligoEO) graft copolymers were characterized by ¹H, ¹⁹F, and ¹³C NMR spectroscopy. Their molecular weights reached 19,000 g mol^?1, and their thermal properties were investigated while their glass transition temperatures ranged between ?42 and ?36 °C. Their thermogravimetric analyses under air showed decomposition temperatures of 270 °C with 10% weight loss (T_d,10%). These novel copolymers are of potential interest as polymer electrolytes in lithium ion batteries, showing room temperature conductivities ranging from 4.49 × 10^?7 to 1.45 × 10^?6 S cm^?1 for unplasticized material. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

New soybean oil–styrene–divinylbenzene thermosetting copolymers. II. Dynamic mechanical properties

A variety of new polymeric materials ranging from soft rubbers to hard, tough, and brittle plastics were prepared from the cationic copolymerization of regular soybean oil, low saturation soybean oil (LoSatSoy oil), or conjugated LoSatSoy oil with styrene and divinylbenzene initiated by boron trifluoride diethyl etherate (BF₃ · OEt₂) or related modified initiators. The relationship between the dynamic mechanical properties of the various polymers obtained and the stoichiometry, the types of soybean oils and crosslinking agents, and the different modified initiators was investigated. The room‐temperature storage moduli ranged from 6 × 10⁶ to 2 × 10⁹ Pa, whereas the single glass‐transition temperatures (T_g) varied from approximately 0 to 105 °C. These properties were comparable to those of commercially available rubbery materials and conventional plastics. The crosslinking densities of the new polymers were largely dependent on the concentration of the crosslinking agent and the type of soybean oil employed and varied from 74 to 4 × 10⁴ mol/m³. The T_g increased and the intensity of the loss factor decreased irregularly with an increase in the logarithmic crosslinking densities of the polymers. Empirical equations were established to describe the effect of crosslinking on the loss factor in these new polymeric materials. The polymers based on conjugated LoSatSoy oil, styrene, and divinylbenzene possessed the highest room‐temperature moduli and T_g 's. These new soybean oil polymers appear promising as replacements for petroleum‐based polymeric materials. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2721–2738, 2000     

Mechanical properties and transition temperatures of crosslinked-oriented gelatin

 This second part of a systematic study of the properties of crosslinked-oriented gelatin involves the effects of orientation and water content on the glass transition temperature T _g and on the melting behavior. The samples were the same as those in the preceding study, and their transition temperatures were determined by both differential scanning calorimetry and dynamic mechanical thermal analysis. The crosslinked gelatin which had been room-conditioned showed two transition temperatures: the lower one was attributed to T _g of the water-plasticized gelatin, and the higher one was interpreted as T _g of dried gelatin superimposed by melting. A rather unusual situation arose because of the fact that the T _g and melting temperatures T _m (217 and 230 ^°C, respectively) are so similar. Using water as plasticizer not only decreases T _g but produces imperfect crystallites which melt below the T _g of the system. The presence of the amorphous phase in the glassy state would presumably make it essentially impossible to define a melting point or crystallization temperature in the normal manner, as an equilibrium between crystalline and amorphous phases. Received: 8 October 1996 Accepted: 2 November 1995     

Proton mobility and copper coordination in polysaccharide- and gelatin-based bioblends and polyblends

Polysaccharide- and gelatin-based bioblends and polyblends were synthesized and characterized by complex impedance spectroscopy, proton nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). Higher ionic conductivities of 7.9 × 10^?5 S/cm at room temperature and 2.5 × 10^?3 S/cm at 80 °C were obtained for the agar-chitosan polyblends. For all samples, the activation energies, calculated from the Arrhenius plot of ionic conductivity and from the onset of NMR line narrowing, are in the range 0.30–0.86 and 0.38–0.57 eV, respectively. The glass transition temperatures (T _g ^NMR ) varied from 200 to 215 K, depending on the sample composition. The temperature dependence of the ¹H spin–lattice relaxation revealed two distinct proton dynamics. The EPR spectra are characteristic of Cu² ions in tetragonally distorted octahedral sites. Quantitative analysis of the EPR spin Hamiltonian g _|| and A _|| parameters revealed copper ions complexed by nitrogens and oxygens in the samples containing chitosan or gelatin and only by oxygens in agar-based ones. The in-plane π bonding is less covalent for the gelatin and chitosan blends. Results suggest that natural bioblends and polyblends are interesting systems to be used in materials science engineering.     

Theoretical interpretation of the kinetics and mechanisms of the HNO + HNO and HNO + 2NO reactions with a unified model

Previously measured decay rates of HNO in the presence of NO have been kinetically modeled on the basis of thermochemical data calculated with the BAC-MP4 technique. The results of this modeling, aided by TST-RRKM calculations for the association of HNO and the isomerization, decomposition, and stabilization of the many dimers of HNO, reveal that the decay of HNO under NO-lean conditions occurs primarily by association forming cis- and trans-(HNO)₂ at temperatures below 420 K. N₂O, which is a relatively minor product, is believed to be formed by H₂O elimination from cis-HON ? NOH, a product of succesive isomerization reactions: trans-(HNO)₂^? → HN(OH)NO^? → HN(O)NOH^? → cis-HON NOH^?. The calculated rate constants, which fit experimental data quantitatively, can be represented by k = 10^16.2 × T^?2.40e^?590/T cm³/mol sec for the HNO recombination reaction and k = 10^?2.44T^3.98e^?600/T cm³/mol sec for N₂O formation in the temperature range 80–420 K, at a total pressure of 710 torr H₂ or He. Under NO-rich conditions, HNO reacts predominantly by the exothermic termolecular reaction, HNO + 2NO → HN(NO)ONO → HN NO + NO₂, with a rate contant of (6 ± 1) × 10⁹ cm⁶/mol² sec at room temperature, based on both HNO decay and NO₂ production. All existing thermal kinetic data on HNO + HNO and HNO + 2NO processes can be satisfactorily rationalized with a unified model based on the thermochemical data obtained by BAC-MP4 calculations.     

Dissociation of 2,2′-substituted thioindigo whites,and recombination of their radicals in solution and in polymer matrix

The dissociation of 2,2′-disubstituted thioindigo whites into captodative radicals and the recombination of these radicals have been examined in solution and in polymeric matrix. For the methyl- and ethyl-substituted TIW the quantum yield of dissociation in solution is equal to 4 × 10^?4 and 5 × 10^?4, respectively. Using the iodine scavenging method the quantum yield of formation of free radicals was almost 3 to 4 × 10^?4, i.e. 20–25% radicals recombine in cage. For the isopropyl and aryl TIWs partial dissociation occurs already at room temperature. Their dissociation enthalpies have been evaluated in solution on the basis of the ESR signal surfaces at different temperatures. For the aromatic substituted Δ H_diss amounts to 88–95 kJ mol^?1, while for i-PrTIW ΔH_diss is 150 kJ mol^?1. The behavior of these compounds was studied in three different matrices: polymethyl methacrylate (PMMA), polypropyl methacrylate (PPMA), and polystyrene (PST). In the cases of the aryl substituted derivatives, cage dimensions of the TIW-radical pairs were measured at low temperature, and their apparent dissociation enthalpies above their glass transition temperatures were evaluated using ESR spectrometry; they are equal to 118 ± 3 kJ mol^?1 in PPMA and around 155 kJ in PMMA and PST. The decay kinetics of the radicals after photolysis of the TIWs below T_g were interpreted on the basis of Waite's equations for diffused controlled reactions. The great influence of steric effects in the cases of the 2-orthochlorophenyl and the 2,4-dichlorophenyl TIWs is stressed as well as the importance of the merostabilization of the captodative radicals on these kinetic characteristics. The nature of the polymeric matrix is also underlined; below T_g the diffusion rate constant is only one-third in PST compared to PMMA. The radicals generated from Ph TIW and its para-nitro and p-methoxy derivatives show a strong inhibiting effect toward the polymerization of methyl methacrylate, while the alkyl TIWs behave as free radical initiators.