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1.
The results of calculations of viscoelastic properties of filled polymers assuming “boundary layer” and the polymer matrix having their own and different glass transition temperatures are presented. The calculations have been made on the basis of the models in series and parallel coupling of viscoelastic bodies as well as Takayanagi's model. Using specified temperature, dependences of viscoelastic properties of the polymer and the “boundary layer” temperature dependences of the real part G′ of the complex shear modulus and tan δ for such a two-phase system with varied differences in glass transition temperatures and concentration of the components were derived. The degree of maxima shift observed experimentally for the filled polymer owing to variation of properties of the “boundary layer” (its concentration and glass transition temperature) were evaluated. Conditions for the appearance of two maxima tan δ for the respective glass transtion temperatures of the polymer and “boundary layer” on the curves tan δ = f(T) were determined. 相似文献
2.
Specific heat capacity measurements were made in a differential scanning calorimeter on a series of eight crosslinked epoxy/diamine polymers over a range of temperatures chosen, for each polymer, to include the glass transition. The tabular data at 5°C intervals was then fitted to a five-parameter empirical equation that represents the data with a deviation less than the experimental uncertainty of the measurements. The measured change in specific heat at the glass transition was an average of 1.9 cal/mol°C for each bead in the polymer repeat unit compared with 2.6 cal/mol°C bead found by Wunderlich for linear polymers. The measurements were then analyzed in terms of the molecular components of the polymers, assuming that the specific heat contribution of each component is independent of its neighbors, i.e., that specific heat is an additive property. In calculating empirical component values as a function of temperature, the polymer specific heats should be plotted as a function of T–Tg rather than T alone. In this manner, component specific heats as functions of T–Tg were determined over a range from the glassy to the rubbery state. 相似文献
3.
High‐pressure partition chromatography, a modification of the inverse gas chromatography technique, is presented as suitable technique for the study of the plasticization effect of carbon dioxide on the following polymers: poly(methyl methacrylate), polystyrene, and bisphenol A–polycarbonate. Polymers in the presence of a compressed gas or a supercritical fluid become plasticized; this means that their glass‐transition temperatures (Tg's) can be lowered by 10s of degrees, which causes changes in their mechanical and physical properties. CO2‐induced plasticization has an important impact on many polymer processing operations in which the Tg depressions of the polymers can be evaluated. The experimental results are discussed and compared with data available from literature for each polymer we considered. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2189–2193, 2003 相似文献
4.
The effect of monomer sequence on physical properties was investigated for butadienestyrene solution copolymers made by organolithium initiation. The polymers varied from random copolymers of uniform composition along the polymer chain to ideal block polymers of specific block sequence arrangement and included rubbers of intermediate degrees of randomness. Uniform composition random copolymers exhibit a single glass transition temperature and a very narrow dynamic loss peak corresponding to this transition. The glass transition can be predicted from the styrene content and the microstructure of the butadiene portion of the rubber. Random copolymers in which composition varies along the polymer chain, and to some extent between molecules, exhibit a single glass transition, but the dynamic loss peak is broadened. The extent of this broadening is shown to be compatible with the sequence distribution, polymer segments of various compositions losing mobility at different temperatures. This indicates a tendency for association between segments of different temperatures. This indicates a tendency for association between segments of different chains which are similar in composition. Block copolymers display two transitions, corresponding to Tg for each type of block. The position and width of the dynamic loss peaks are related to block length and compositional purity of the blocks. 相似文献
5.
Sumaya F. Kabir Kevin Adlington Andrew J. Parsons Ifty Ahmed Derek J. Irvine 《应用聚合物科学杂志》2020,137(15):48547
A range of polymer blends were prepared via a solvent-based film casting process using highly/hyperbranched (HB) polydivinylbenzenes (PDVB) polymers of two different molecular weights, linear functionalized (LF), hydrogenated hyperbranched (H-HB2) PDVB, and linear polystyrene (LP). The thermal, thermomechanical, and rheological properties of the pure polymers and blends were then investigated and the results related to the concentration of “branched” polymer in the blend and the level of branching/polymer end groups present in the “branched” polymers used. Differential scanning calorimetry (DSC) analysis revealed an increase of the glass transition temperature (Tg) for the blends containing the nonhydrogenated HBs (~108 °C compared to ~102 °C for LP), which was attributed to crosslinking via the unsaturated reactive chain end/pendant groups in the HB ( CHCH2). In contrast at the blends, containing the hydrogenated polymers H-HB2, exhibited the same Tg as LP (~102°C) due to absence of crosslinking from the (H-HB2) polymer. As the unsaturated HBs were found to be thermally curable, curing temperature rheology measurements were carried out employing a temperature ramp. No specific Tgel (the temperature at which HB gets crosslinked) was identified for LP-HB1 and LP-HB2 blends, which might be suggested to be due to the fact that both chain entanglement from linear polystyrene. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48547. 相似文献
6.
Srivatsan Srinivas Marvin Graham M. Heather Brink Slade Gardner Richey M. Davis James E. McGrath Garth L. Wilkes 《Polymer Engineering and Science》1996,36(14):1928-1940
Novel high performance semicrystalline polyimides, based on controlled molecular weight phthalic anhydride (PA) endcapped 1,4-bis(4-aminophenoxy)benzene (TPEQ diamine) and oxydiphthalic dianhydride (ODPA), were synthesized. They exhibited excellent thermal stability in nitrogen and air atmospheres as determined by thermogravimetric analysis (TGA). The glass transition temperatures (Tg) for these polymers ranged from 225°C for the 10,000 Mn (10K) polymer, to 238°C for the 30,000 (30K) Mn material. The observed melting temperatures for all the polymers were ∼420°C. The crystallization behavior of these polymers showed a strong molecular weight dependence, as illustrated by the observation that the 10K and 12.5K polymers crystallized with relative ease, whereas the 15K, 20K, and 30K polymers showed little or no ability to undergo thermal recrystallization. The thermal stability of these polymers above Tm was investigated by studying the effect of time and temperature in the melt on the cold crystallization and melting of these polymers. Increased time and temperature in the melt resulted in lower crystallinity because of melt state degradation, such as crosslinking and branching, as evidenced by an increase in melt viscosity, which was more prominent for the higher molecular weight polymers. 相似文献
7.
The effect of cure history on the dynamic thermomechanical properties of a high temperature curing epoxy resin has been studied using torsional braid analysis. In isothermal cures “full cure” is not possible except at temperatures above the maximum glass transition temperature (Tg) of the cured resin, hence the necessity of a “post-cure” after lower temperature isothermal cures. The highest Tg and maximum cross-linking in the cured resin was for a linear heating rate of 0.05°C/min from 30 to 200°C; higher heating rates lead to lower glass transition temperatures. 相似文献
8.
Blends of chlorinated polyethylene (CPE) elastomer and ethylene methacrylate copolymer (EMA) in various compositions were studied for their compatibility using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared (FTIR) spectroscopy techniques. Irrespective of measurement techniques used, all blends showed a single glass transition temperature (Tg) lying in between the Tg of control polymers in both DSC and DMA. Glass transition temperatures of blends obtained from DSC were in consistency with Couchman–Karasz equation. Also, the Tg obtained from both DSC and DMA are above the “rule of mixing” line of the two control polymers. These results from thermal analysis clearly indicate some compatibility between the two polymers. Furthermore, compatibility of CPE/EMA blends were also been investigated by FTIR spectroscopy and scanning electron microscopic analysis. A shifting of characteristic C? Cl stretching peak of CPE and C?O stretching peak of EMA toward lower wave number indicate the presence of specific interaction between the two polymers. Mechanical properties like tensile strength, modulus at 100% elongation, elongation at break, and hardness were observed above the line of additivity drawn between the two control polymers, which corroborate compatibility between CPE and EMA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40316. 相似文献
9.
The effects of polymer composition and penetrant molecular size on the solubility and diffusivity of alcohol vapors in a series of well characterized isoprene-methyl methacrylate copolymers and their corresponding homopolymers has been investigated at room temperature. The rate of sorption behavior changes progressively from Fickian to non-Fickian, to Case II to “Super Case II” transport with increasing methyl methacrylate (MMA) content in the polymers. The equilibrium solubility of the alcohols increases linearly with increasing penetrant molecular size for polymers which are above their glass transition temperature and decreases for polymers which are below their Tg. The solubility also initially increases as an approximately linear function of MMA content in the copolymers. At about 55 mole percent MMA, the sorbed concentration either levels off or passes through a maximum depending on the size of the penetrant. The apparent “diffusion coefficients” (D) decrease with increasing molecular volume of the penetrants. An exponential dependence was found between these two variables for PMMA. These “diffusion coefficients” also decrease exponentially with increasing MMA content in these polymers. However, at 55 mole percent MMA the copolymer undergoes a rubber to glass transition at the temperature of the experiments. On this basis, it is suggested that the hindered chain segmental motion contributes to the sorption process in addition to strictly thermodynamic considerations. Free volume theory can be used to explain the mechanism of diffusion through the rubbery polymers while the “hole” theory can be applied to explain the transport of the penetrants through the glassy polymers. 相似文献
10.
A method and apparatus for measuring the elastic and other properties of polymers in the melt state is presented. The recoverable strain magnitude and the rate of strain recovery have been measured as a function of: applied shear rate, applied shear magnitude, temperature and molecular weight. The elastic properties indicate that there is an abrupt change or “transition” in the response of polystyrene melts at temperatures well above the glass transition. This abrupt change is found to be molecular weight dependent. The results are interpreted qualitatively in terms of molecular structure and practical processing operations. The possible relationship of this “transition” to Tu, is briefly discussed. 相似文献
11.
Most structured latex particles are formed in the nonequilibrium state as a result of the reaction kinetics proceeding faster than the phase separation kinetics. Of the many factors controlling such morphologies, the polarity and glass transition temperature (Tg) of the seed polymer are important. In order to study the direct effect of the seed polymer Tg on morphology, we produced a series of poly(methyl methacrylate)/poly(methyl acrylate) seed copolymers having glass points between 52 and 98°C, and particle sizes between 320 and 390 nm. We then used styrene as a second‐stage monomer reacting in both the batch and semibatch process modes, and utilized reaction temperatures (Tr) between 50 and 70°C. Monomer feed rates were varied between flooded and starve‐fed conditions. The equilibrium morphology for these composite particles is an inverted core–shell structure, but all morphologies obtained in our experiments were nonequilibrium. Under monomer starved conditions only core–shell structures were formed when (Tr?Tg) < 0, but significant penetration of the polystyrene into the acrylic core occurs when (Tr?Tg) > 15°C. These results are reasonably well predicted using the “fractional penetration” model developed earlier. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 905–915, 2003 相似文献
12.
Ester or cyano substituted tetracyclo [4.4.0.12,5.17,10]dodec-3-enes (1) were synthesized and their metathesis ring-opening polymerization was examined. The tungsten-based ternary catalyst system polymerized them very well. The polymers showed high glass transition temperatures (Tg) and no evidence of crystallization (e.g., the Tg of the polymer derived from 8-methyl-8-methoxycarbonyl substituted monomer (1a) was 207°C, and colorless transparent films could be casted from the solution of the polymer). The stability of these high Tg polymers were too unstable, so practical thermal molding methods could not be applied to them. The hydrogenation of these polymers with a palladium catalyst decreased Tg and greatly increased thermal stability. The physical and thermal properties of the hydrogenated polymers were thoroughly investigated. Monomer 1 was successfully copolymerized with other cyclic olefins. The resultant copolymers were hydrogenated, giving thermally stable polymers. In all cases examined in this study, a decrease of Tg by hydrogenation was about 35°C, regardless of the monomer structure. These results indicate that the main-chain mobility is the major contribution to the decrease of Tg. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 367–375, 1997 相似文献
13.
The glass transition temperatures (Tg's) of several polystyrenes and styrene–alkyl methacrylate copolymers and terpolymers were measured using thermomechanical analysis (TMA) and differential scanning calorimetry (DSC). The polymers studied had number-average molecular weights from 3000 to 250,000 g/mole. The results indicate that the composition dependence of the Tg's for the copolymers and terpolymers can be satisfactorily described by a general Fox equation. In general, the measured Tg's of the copolymer and terpolymer samples depend more on the steric effects of the constituent pendent groups than on their molecular weights. The chain flexibility rather than the size of the pendent group is the determining factor in the glass transition properties of the styrene polymers. 相似文献
14.
Roberto Recio Ángel E. Lozano Pedro Prádanos Ángel Marcos Fernando Tejerina Antonio Hernández 《应用聚合物科学杂志》2008,107(2):1039-1046
The aim of this work is to study how the characteristics of the polymer used to manufacture gas separation membranes influence its permeability and selectivity. It has been shown that the gas diffusivity decreases with the kinetic diameter of the gas except for CO2, probably due to its high condensability. While solubility increases with the gas condensation temperature and clearly with the glass transition temperature of the polymer for each gas. The permeabilities of CO2, CH4, O2, N2 increase for increasing glass transition temperatures. Nevertheless only the selectivity of CO2 versus the other gases increases significantly when polymers with high glass transition are used. The Robeson limit in a selectivity‐versus‐permeability plot is approached for CO2/CH4 when Tg increases. This distance to the Robeson limit, for this pair of gases, results to decrease for increasing Tg. For the case of the O2/N2 selectivity remains approximately constant with an appreciable increase in permeability for polymers with increasing Tg. Permeability increases due to the corresponding increase in fractional free volume, FFV, that appears for increasing glass transition temperatures, Tg. This correlation of FFV with Tg has been confirmed by obtaining FFV by different methods. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献
15.
Most polymeric materials appear as complex mixtures of macromolecules characterized by distributions of specific properties that are essential to the quality of these products. Among such properties, the accurate determination of the glass transition temperature, and therefore, accurate representation of it, is a key issue. When analyzed using dynamic scanning calorimetry (DSC) techniques, many copolymers exhibit a wide range of temperature over which the glass transition takes place, and the width of the transition region is, therefore, not satisfactorily described by average Tg values, for example those computed from tangent curves drawn on thermograms. This article describes a method that allows us to characterize this spreading of the glass transition region by reconstructing weighted Tg distributions from DSC thermograms. As such an objective might appear as questionable from a strictly physical point of view, the significance of what is meant by “distribution” is specified in the text. A model is proposed that accounts for relaxation phenomena. The approach is validated by examining samples of BuA/Sty emulsion copolymers produced at different overall conversions and compositions, and examining the corresponding histograms of Tg were computed. The results show that accurate and consistent information on the glass transition behavior of the copolymer is obtained, and that the effective distribution is clearly connected with the composition drift in the polymer particles. The proposed algorithm allows one to obtain a maximum amount of information from DSC measurements, and provides a deeper insight into the “history” of complex polymer mixtures. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 357–367, 2000 相似文献
16.
Jean-Noël Gorce J. W. Hellgeth Thomas C. Ward 《Polymer Engineering and Science》1993,33(18):1170-1176
The mechanical hysteresis of a polyether polyurethane thermoplastic elastomer was studied as a function of temperature, percent strain, and deformation energy. Hysteresis values remained small at low temperatures when the extent of the sample deformation did not disrupt the glassy matrix. This was readily evident at temperatures below the glass transition temperature, Tg of the polymer where the material did not formally yield. At temperatures above the Tg of the polymer, hysteresis remained small even at substantial strains levels and demonstrated the capabilities of the hard segment domains to act as physical crosslinks. At elevated temperatures, percent hysteresis increased as the hydrogen-bonded hard segment domains weakened. When mechanical hysteresis was considered on the basis of constant deformation energies, hysteresis values reached a maximum in the vicinity of the Tg of the polymer. These maxima existed as a consequence of two opposing trends: the decreasing resiliency of the polymer as it becomes a glass and the increase in the resistance of that glass to undergo deformations sufficient to cause plastic flow. Finally, a hysteresis response surface constructed as a function of deformation energy and temperature was found to be sensitive to both the strain-induced crystallization of the rubbery soft segment matrix and to the strain-induced yielding of the glassy soft segment matrix. 相似文献
17.
Evidence is presented which justifies the use of the dyeing transition temperature (TD) instead of the glass transition temperature (Tg) as a reference temperature when using the WLF equation to describe the carrier dyeing of polyester film. Changes in the properties of the substrate caused by the effect of “carriers” on the molecular structure of the polymer have also been detected and a connection between the location of TD and chain folding is suggested from IR measurements. 相似文献
18.
One objective of this study was to measure the crystallization parameters for syndiotactic polystyrene (MW = 244,000) to support a computer simulation of this material in an injection molding application. A second objective was to introduce a new crystallization rate equation that adequately predicts crystallization rates over a broader temperature range than the Hoffman‐Lauritzen equation. A third objective was to establish a new clearly defined method for determining the true induction time of a semicrystalline polymer as a function of temperature. The new crystallization rate equation introduced in this study has been formulated to give appropriate crystallization rate constants for all the temperatures currently usable with the Hoffman‐Lauritzen equation. In addition, this new equation also predicts appropriate crystallization rate constants outside the range of the Hoffman‐Lauritzen equation from temperatures significantly below the glass transition temperature, Tg, to temperatures significantly above the melting point, Tm. Interestingly, the isolation of the true isothermal induction times from apparent induction times in this study nicely mirrored the isothermal crystallization rates at each specific temperature. Both the true induction time and the crystallization rate curves were found to be similarly unsymmetrical as a function of temperature. Also, the temperature at the minimum induction time and the temperature at the peak crystallization rate determined from nonisothermal crystallization rate measurements were found to be nearly identical. Consequently, the results from this study strongly suggest that there is a significant and potentially very useful relationship between induction time analysis and crystallization rate kinetics. 相似文献
19.
Ming Qiu Zhang Le Song Han Min Zeng Klaus Friedrich Jzsef Karger-Kocsis 《应用聚合物科学杂志》1997,63(5):589-593
Most semicrystalline polymers exhibit multiple melting peaks in the course of normal differential scanning calorimetry (DSC) measurements. When their amorphous versions are annealed above the glass transition temperatures, the lower endothermic temperatures (Tm1) appearing on the subsequent DSC heating traces are highly dependent on the annealing temperature (Ta). In consideration of the fact that temperature is the critical environmental factor controlling polymer crystallization, thermal history experienced by the material during annealing in the DSC cell is basically equivalent to that under frictional heating, and the surface temperature prevailing under sliding wear can be estimated from DSC scans taken on the worn surface. In this case, the lower melting peak temperature observed (which can be correlated with the annealing temperature) serves as an indicator for the flash temperature. In addition, this thermoanalytical method can also provide information about microstructural changes due to wearing. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 589–593, 1997 相似文献
20.
Following the approach of Kusumoto an equation is derived which relates the correlation time for the tumbling of a nitroxide spin probe in a polymer matrix with the parameter f, the ratio of the volumes of the probe and the polymer segment undergoing motion at T>Tg. For poly(vinyl acetate) probed with a series of nitroxides the correlation between f and the molecular volumes of the probes is poor, possibly because of wide variations in probe flexibility and polarity. An approximate version of the equation also permits evaluation of f from the parameter T50G. Values of f calculated in this manner for the probe 2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl-benzoate in nine different polymers suggest that polymers with high glass transition temperatures have relatively bulky segments. 相似文献