Thermal analysis of poly(phenylene sulfide) polymers. I: Thermal characterization of PPS polymers of different molecular weights

Thermal properties of Fortron®

1 ®Registered trademark of Hoechst Celanese Corporation.

poly(phenylene sulfide) (PPS) polymers of different molecular weights were studied by DSC. Crystallization studies revealed that the ability of these polymers to crystallize decreases with increasing molecular weight. The Avrami equation poorly describes the isothermal crystallization of PPS. Lamellar crystallization was observed for the lowest molecular weight sample. For the other, higher molecular weight polymers the Avrami exponent is always between 2 and 3, suggesting development of distorted spherulites with heterogeneous nucleation. The temperature dependence of the solid and melt heat capacities have been determined. The solid specific heat capacity did not exhibit a molecular weight dependence. The heat capacity increase at the glass transition, T_g, has been calculated to be 28.1 J°C^?1 mole^?1. The equilibrium melting point of PPS has been estimated to be 348.5°C using the Hoffman–Weeks method. The T_g of PPS increases with molecular weight. The T_g of the highest molecular weight evaluated is 92.5°C. A DMA relaxation peak corresponding to the onset of the phenylene ring rotation occurs at ?92°C. Only the highest molecular weight could be quenched to a completely amorphous state.     

Thermomechanical properties of blends of pectin and poly(vinyl alcohol)

Blends of citrus pectin and several types of poly(vinyl alcohol) were investigated to determine the effects of compositional variables and polymer type on film properties. Some films were also plasticized with glycerol. Films were cast from water onto Lexan™ plates, dried, and removed. Thermomechanical properties were obtained using a dynamic mechanical analyzer, and thermodynamic transitions were also obtained using a differential scanning calorimeter. Increasing the amount of poly(vinyl alcohol) in the blends reduced the storage and loss modulus of the films above the glass transition temperature (T_g). The T_g values observed decreased as the amount of PVOH in the blend increased. Addition of glycerol depressed the PVOH T_g and merged it into the T_g of the pectin/glycerol blend. Changes in the molecular weight and degree of ester hydrolysis of poly(vinyl alcohol) exerted a rather small effect on the blends. © 1996 John Wiley & Sons, Inc.

1 Reference to a brand or firm name does not constitute an endorsement by the U.S. Department of Agriculture over others of a similar nature.

     

Influence of cure treatment on extent of reaction and glassy modulus for BADGE‐DDM epoxy resin

The extent of conversion of epoxy groups cured with diaminodiphenyl methane, a diamine, at 100°C was approximately 100%, and the glass‐transition temperature (T) was found to be an increasing function of cure time with very large increases with extended postcure treatments at 180°C. However, this considerable increase in the T_g with postcure at 180°C was not due to the reactions of epoxy and amine groups. The specific volume reduced with the T_g to a minimum at 103° for the cured samples but showed a very slight increase with the T_g for the postcured samples. It was also found that the glassy modulus (E_g) was a linear decreasing function of the T_g. There were two separate relationships between the E_g and the rubbery modulus that depended on the cure conditions and suggested that the “structure” formed due to cure at a temperature of 100°C was different than that at postcure, which was 180°C. The most sensitive structural parameter for these cured epoxy resins was their T. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1265–1276, 2001     

Thermal properties of poly(vinyl cyclohexane)

Isotactic poly(vinyl cyclohexane) (PVCH) was studied by thermal analysis. The deduced equilibrium melting point, T, is 405°C (678 K). The heat of fusion, Δ H was found to be 50.82 J/g (5.60 kJ/mol) and Δ C_p at T_g, is 0.273 J/(gK) [30.1 J/(molK)]. The glass transition temperature, T_g, of the amorphous PVCH is 80°C (353 K). In semicrystalline samples, T_g increases up to 165°C (438 K) for crystallinities > 40%. Beside crystalline and flexible amorphous, a rigid amorphous phase is postulated in the semicrystalline polymer.     

Studies in nonisothermal rheology: Behavior near the glass transition temperature and in the oriented glassy state

As part of a continuing study of nonisothermal rheology (meaning the simultaneous application of strain and temperature changes), we here consider the behavior of polystyrene near the glass transition temperature T_g. In particular, we measured the increase of the apparent T_g as the cooling rate is increased from 0.003 to 4.5°C/sec. This change (up to 16°C increase) has both practical and theoretical implications. For enhancing the mechanical properties of a glassy product, one desires maximum orientation (stress) just prior to quenching; the optimum deformation/temperature strategy for maximizing stress is affected by the level of T_g. By using a nonisothermal strategy we were able to produce higher frozen-in orientations, and thus higher mechanical properties, than have been previously reported. For a theoretical understanding of the rubbery state just prior to quenching, we used the generalized time-temperature superposition of our prior work; we found that a modified shift factor of the form a_T(T,T), where T refers to a rate-dependent T_g, gives an improved fit to data but is not by itself adequate.     

Characterization of mechanical properties of thermoplastic films by creep measurements

Plasticized poly(methyl methacrylate) and methyl methacrylate/acrylate copolymer films were examined by isothermal creep at low loads measured at several temperatures from ～T_g to T_g + 15°C. Viscosity calculated using η = σ/3\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} was plotted vs temperature giving precise values for T_g based on a viscosity criterion of η = 10¹³ poises. Creep fracture data at various temperatures below T_g were interpreted using the maximum apparent viscosity measured at the minima of strain rate vs strain curves. Plots of η_max VS stress at several temperatures gave values of ΔT_g/Δσ of ?1° to 2°C/10⁶ N/m² in agreement with treatment of ΔT_g/Δσ based on free volume. Fracture occurred at low elongations when η_max was ≥10¹³ poises, and at higher elongations when η_max was <10¹³ poises supporting the concept that fracture is related to the lowering of T_g under stress. Plots of log σ VS log ε_b (the elongation at fracture) had the same form as that for crosslinked elastomers above T_g reported by T. L. Smith. Plots of log \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}_b VS log ε_b also had the same form supporting proposals on the rate sensitivity of fracture.     

The Relationship Between the Microhardness and Glass Transition Temperature of Inorganic Glasses Compared with Polymeric Glasses

ABSTRACT

In this article an attempt is undertaken to verify the approach already successfully applied to polymeric glasses for deriving a simple analytic relationship between the glass transition temperature, T_g , and Vickers microhardness, H_v , (for polymers it is H_v  = 1.57 T_g –571, H_v in MPa, T_g in K). On the basis of previously reported data for H_v and T_g of 12 inorganic glasses (lead-silicate-, alkali-silicate-, alumosilacate, and quartz glasses) a linear relationship in the form H_v  = 5.87 T _g + 1740 (H_v in MPa, T_g in K) is derived. In addition, a critical analysis of the published attempt for theoretical deriving of the relationship between H_v and T_g is also offered.     

Parameters of the Fluctuation Free Volume Theory for Glasses in the Ge-As-Se System

The fraction of fluctuation free volume (f _g = V _f/V) frozen at the glass transition temperature T _g is determined from the temperature dependence of the viscosity in the glass transition range in terms of the Vogel-Fulcher-Tammann equation and the formula _f T _g T _g = f _gln(1/f _g). The fluctuation free volume fractions f _g obtained according to these two procedures for glasses in the Ge-As-Se system are in quite reasonable agreement. The energies E _h of formation of fluctuation microvoids and their volumes V _h are calculated. It is demonstrated that the quantities f _g, E _h, and V _h and the ratio of the microhardness H to T _g depend substantially on the glass structure and can serve as characteristics of the rigidity of the glass networks. It is noted that the fluctuation free volume fraction f _g is a nonmonotonic function of the mean coordination number Z _m and that it exhibits a specific dependence on the lattice Grüneisen parameter . The Poisson ratios are estimated from the fluctuation free volume fraction f _g with the use of the relationship f _gln(1/f _g) = . It is shown that the Poisson ratios thus obtained are close to those calculated from the data on the transverse (V _s) and longitudinal (V _l) velocities of ultrasound.     

Preparation and glass transition temperature of hyperbranched poly[allyl methyl maleate‐co‐N‐propyl maleimide]

The kinetics and molecular weight averages of the hyperbranched polymers formed by the alternating copolymerization of equimolar allyl methyl maleate (AMM) and N‐n‐propyl maleimide (PMI) were investigated. The yields, molecular weight averages, and polydispersity indices as well as the branching degrees of the produced copolymers increased with increasing initiator concentrations and prolonged polymerization time. The trends of the experimental molecular weights as determined by size exclusion chromatography were in good agreement with the theoretical predictions. The molecular weight distribution indices fit the curve given by M_w/M_n = 1/(1‐x_D), and the molecular weights fit the curve given by M_w = 4076/(1‐x_D)², where x_D was the conversion of vinyl groups. DSC studies demonstrated a nonlinear relation of T_g values to the reciprocal of molecular weight (M), and T_g values decreased with the increase of molecular weight. For the T_g values of highly branched polymers in high molecular weight range, a relation of T_g = T + k/M was obtained, where T was obtained by extrapolating to infinite molecular weight and k was a constant. T was 136°C, and k = 2.9 for this work. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1941–1947, 2005     

Dynamic mechanical properties of a TiO2-filled crosslinked epoxy resin from 20–90°C.

Dynamic mechanical measurements were made with a torsional pendulum of a TiO filled epoxy polymer (crosslinked with hexamethylene diamine) over a temperature range from 20–90°C., at filler concentrations of 0–40 wt.-%. The second-order transition temperature (T_g) was raised as the filler content increased. The behavior of TiO₂ filler results in a long-range immobilization of the highly crosslinked system with resultant increases in shear modulus (higher G′) as well as decreased capacity for energy dissipation (lower damping factor). The out-of-phase modulus (G″) increased with filler content as well. The magnitudes of the slope parameters H_r (representing G′ data above T_g) and H_g (representing G′ data below T_g) decreased with greater filler content. The possibility is set forth that the TiO₂ filler causes a different distribution of mobility around the nitrogen junction as well as a change in the effective number of CH₂ units between crosslinks.     

Fracture behavior of coated/uncoated graphite-epoxy composites

The static delamination behavior of graphite/epoxy composite specimens subjected to mode I tensile opening (using UDCB

1 Uniform double cantilever beam.

specimens), and pure mode II shear loading (using ENF

2 End-notched flexural.

specimens) were studied. The graphite epoxy composites for the study were made from commercially treated fibers, with and without an electropolymerized interlayer. The mode I fracture energy (G_IC) was found to be significantly higher (more than 50 percent) for the coated fibers. However, this improvement was accompanied by a high reduction (more than 3 times) in the mode II fracture energy (G_IIC). This effect is apparently related to poor adhesion between the interlayer and the epoxy resin, which may be corrected by use of a “top layer” of appropriate composition to form chemical bonds between the phases. The fracture toughness (K_IC) of composites made with commercially treated fibers was also evaluated, using double side-notched specimens.     

Chemical Bonding between Phenolic Resins and Polyhedral Oligomeric Silsesquioxanes (POSS) in Inorganic–Organic Hybrid Nanocomposites

Three classes of inorganic–organic hybrid phenolic resin/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were synthesized. Multifunctional dichloromethylsilylethylheptaisobutyl-POSS (POSS-1), trisilanolheptaphenyl-POSS (POSS-2), and poly(phenylsilsesquioxane) uncured POSS (POSS-3) were employed. Nonfunctional POSS-4 (octaisobuty1-POSS) was blended into the uncured phenolic resin and cured under the same conditions used for the other three nanocomposite classes. Weight ratios of 99/1, 97/3, 95/5 and 90/10 were prepared for the POSS-1, 2 and 4 series and 99/1, 97/3 and 95/5 ratios for the POSS-3 nanocomposites. POSS-1 incorporation into this phenolic resin network increases T _g and broadens the tan peak (DMTA) range. T _g and E′ values at T>T _g both increase with higher POSS-1 content. In contrast, incorporating 5 wt% of POSS-2 into the phenolic resin network lowers T _g to 193 from 213°C for the neat phenolic resin. All values of E′ for POSS-2 composites were higher, than those of the phenolic control in both glassy and rubbery regions. The T _g values of the 1 and 10% POSS-2 systems were higher. Incorporating 10 wt% of POSS-1 or POSS-2 improved the heat distorsion temperature and moduli (E′=123 and 201 GPa at 265°C, respectively, versus 56 GPa for the pure phenolic resin). Increases in E′ for T>T _g and T<T _g were also observed for all POSS-3 nanocomposites. However, the E′ at T>T _g and the T _g values of the POSS-4 composites were lower than those of the control resin. Octaisobutyl POSS-4 cannot form chemical bonds to the resin and could be extracted from its composites with THF. POSS derivatives were not present in residues extracted by THF from the phenolic resins containing POSS-1, 2 or 3, because each of these derivatives were chemically bound within the phenolic resin. Subsequent heating cycles produce much larger increases in T _g and E′ values in the rubbery region for the POSS-1, 2 and 3 composites than for the neat phenolic resin or for the POSS-4 systems. An erratum to this article can be found at     

A Study of Sodium–Copper and Sodium–Nickel Polyphosphate Glasses by Differential Scanning Calorimetry1

Sodium polyphosphate and sodium–copper and sodium–nickel copolyphosphate glasses (with the ratio Na : M = 9 : 1 and 8 : 2, where M is Cu or Ni) are studied. The glass transition (T _g) and melting (T _m) temperatures are determined by differential scanning calorimetry (DSC). It is revealed that the T _gand T _mtemperatures depend on the molecular weight M _t(determined from terminal groups) of polymeric glasses, the Na : M ratio, and the glass synthesis conditions. The activation energies are calculated, and the thermodynamic parameters H, S, and C _pare measured.     

Fine structures and fracture processes in plastic-rubber two-phase polymer systems III. Temperature dependence of Charpy impact strength

Notched Charpy impact strengths of a series of plasticrubber two-phase polymer systems were measured over a wide range of temperatures. Blends of polyvinylchloride and rubbers with varying chemical structures, and several ABS polymers were investigated. In all systems, Charpy impact strength began to increase near the T_g of the rubber component followed by a logarithmic increase with increasing temperature. The trend is expressed by the following empirical relation: where I is Charpy impact strength, A and B are constants, and T is the absolute temperature. This equation is applicable between the T_g's of the plastic and the rubber components. The increasing tendency of impact strength, i.e. the B value of the above equation, is depressed mainly by the decrease of the compatibility and/or the interfacial adhesive force between the two phases. Toughening mechanism and the ways of increasing toughness are discussed based on the craze formation mechanism.     

High-temperature elastomers: A systematic series of linear poly(carborane-siloxane)s containing icosahedral (?CB10H10C?) cages. I. Thermomechanical behavior in nitrogen

An extensive study of structure–bulk property relations for a systematic series of well-defined linear poly(carborane-siloxane)s is reported. These polymers form the backbone components of the most recently developed high-temperature elastomers. The basic structure is where (1) x = 1, 3, 4, 5, ∞; (2) A = endgroups (reactive and inert); (3) Z = meta-, para-carborane (for x = 3); (4) R = ? CH₃, R = ? C₂H₄CF₃ (for x = 3), one in five R = ? C₆H₅ with the remainder ～CH₃ (for x = 4, randomly and regularly substituted); (5) molecular weight = ～10,000, ～50,000 (for x = 3). Thermomechanical spectra (～1 cps) from ?180°C to 625°C to ?180°C in nitrogen at 3.6°C/min and thermogravimetric data from 25°C to 800°C in argon are presented. Physical transitions (T_g, T_m, T_crys, T_sec) are discussed, including a correlation of T_g data with structure (for x = 1, 2, 3, 4, 5, ∞) using a copolymer equation. Thermostability is also discussed in terms of structure.     

Inverse gas chromatography of poly(n-butyl methacrylate): Effect of flow rate on specific retention volume and detection of glass transition temperature

Flow-rate effect on specific retention volume (V) was studied by eluting aliphatic, aromatic, and chlorinated aliphatic probes at infinite dilution on poly(n-butyl methacrylate) stationary phase at different temperatures from ?10 to 150°C, encompassing both the glass transition (T_g) and the softening temperatures of the polymer. The effect became pronounced as the temperature was reduced below 100°C. V decreased with an increase in the flow rate: first linearly at temperatures between 70 and 100°C, and then nonlinearly at all temperatures below 70°C. The retention diagrams of n-pentane, isooctane, and cyclohexane alone enabled the detection of glass transition. Dichloromethane gave a linear retention diagram through T_g without showing the flow-rate effect.     

Preparation and characterization of bismaleimide-diamine prepolymers and their thermal-curing behavior

Various bismaleimide-diamine Michael addition type prepolymers were prepared through melt condensation and using acetone, dimethylformamide, and m-cresol as solvents in a molar ratio of 1 : 1. Structures of the prepolymers, such as terminal moieties and molecular weight of main chain, depended strongly on the preparation conditions used. More terminal double bonds were observed in the molecule of the prepolymer (sample 3) prepared in dimethylformamide solution without a catalyst. In contrast, the prepolymer produced in m-cresol solution had a polyaspartimide structure with a higher molecular weight. The differential scanning calorimetry and Fourier transform infrared spectra results demonstrated that the molecular structure of the prepolymer had a noticeable effect on their thermal-curing behavior. Thermal properties (T_g and T_d) of cured polymers were evaluated. The polyimide (sample 3b) from sample 3 exhibited the highest T_g and but still retained very good processing properties for film casting. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2471–2477, 1998     

Characterization of metal-ion containing polyesters

Summary The glass transition behavior of poly(diethylene glycol-co-succinic acid) (DEGSA) and its complexes obtained in the reaction with MgO have been investigated. The number average molar mass ( ) of the DEG-SA samples prior to complexation was determined by titration of the terminal COOH groups. The glass transition temperature (T_g) was measured as a function of molar mass and Mg²⁺ ion content. The dependence of T_g on obeyed the Fox-Flory relationship. Addition of increasing amounts of MgO to DEG-SA led to a gradual increase in T_g, and a decrease in the heat capacity change (c_p). This behavior is associated with complex formation between COO^-and Mg²⁺. The decrease in c_p is a result of ion-ion and to a lesser extent ion-dipole interactions which lower chain mobility. The common limiting T_g value for the three DEG-SA samples at an Mg²⁺/COO^- ratio of ca. 0.5 approaches T_g,, which is the corresponding T_g of a polymer of infinite molar mass.     

Sugar-based bicyclic monomers for aliphatic polyesters: a comparative appraisal of acetalized alditols and isosorbide

Three series of polyalkanoates (adipates, suberates and sebacates) were synthesized using as monomers three sugar-based bicyclic diols derived from D-glucose (Glux-diol and isosorbide) and D-mannose (Manx-diol). Polycondensations were conducted in the melt applying similar reaction conditions for all cases. The aim was to compare the three bicyclic diols regarding their suitability to render aliphatic polyesters with enhanced thermal and mechanical properties. The ensuing polyesters had molecular weights (M_w) in the 25,000–50,000 g mol^?1 range with highest values being attained for Glux-diol. All the polyesters started to decompose above 300 °C and most of them did not display perceivable crystallinity. On the contrary, they had glass transition temperatures much higher than usually found in homologous polyesters made of alkanediols, and showed a stress–strain behavior consistent with their T_g values. Glux-diol was particularly effective in increasing the T_g and to render therefore polyesters with high elastic modulus and considerable mechanical strength.     

Viscoelastic response of model epoxy networks in the glass transition region

Six epoxy networks with various structures built up from a diepoxy prepolymer, DGEBA, and three different diamines or mixtures of a monoamine and a diamine were studied by dynamic mechanical analysis in the glass transition region. The systems were designed in order to investigate the dependence of glass transition T_g on both crosslink density and network chain flexibility. The time (frequency)—temperature superposition principle (WLF equation) was used to determine the viscoelastic coefficients C^g₁ and C which are related to some free volume characteristics on the molecular scale. C^g₁, related to the free volume fraction available at T_g depends mainly on crosslink density, even though the product C^g₁C, related to the free volume expansion coefficient, is dependent on both chain flexibility and crosslink density. Thus, viscoelastic properties determined over large temperature and frequency ranges are shown to yield more precise information on epoxy network structure than the simple analysis of glass transition temperature.