Depression of glass transition temperatures of polymer networks by diluents (original) (raw)
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The nature and determination of the dynamic glass transition temperature in polymeric liquids
2014
The physical properties of polymers are very much dictated by where the operating temperature lies with respect to the transition temperature between glassy and rubbery states. The precise identification of this glass transition temperature, Tg, is critical in assessing the feasibility of a polymer for a given application. In this book, the behavior of polymers near their Tg and the capability of predicting Tg using theoretical and empirical models is assessed. While all polymers undergo structural relaxation at various temperatures both nearly above and below Tg, practical assessment of a single consistent Tg is successfully performed through consideration of only immediate thermal history and thermodynamic properties. The determination of Tg for a wide variety of polymers of theoretically infinite chain length has been found to be accurately performed through the use of novel quantitative structure-property relationship (QSPR) models. The supplementation of such values to configur...
Glass transition temperatures in binary polymer blends
Journal of Polymer Science Part B: …, 2009
Knowledge of the glass transition temperatures (T g s) as function of composition reflects miscibility (or lack of it) and is decisive for virtually all properties of polymer-based materials. In this article, we analyze single blend-average and effective T g s of miscible polymer blends in full concentration ranges. Shortcomings of the extant equations are discussed to support the need for an alternative. Focusing on the deviation from a linear relationship, defined as DT g ¼ T g À u 1 T g,1 À u 2 T g,2 (where u i and T g,i are, respectively, the weight fraction and the T g of the i-th component), a recently proposed equation for the blend T g as a function of composition is tested extensively. This equation is simple; a quadratic polynomial centered around 2u 1 À 1 ¼ 0 is defined to represent deviations from linearity, and up to three parameters are used. The number of parameters needed to describe the experimental data, along with their magnitude and sign, provide a measure of the system complexity.
Glass transition in poly(propylene glycol) networks
Journal of Polymer Science: Polymer Physics Edition, 1983
Difficulty in controlling and determining the structural parameters of polymer networks has hindered experimental studies on the glass transition in crosslinked polymers. A series of wellcharacterized networks of poly(propy1ene glycol) having narrow network chain-length distributions and average molecular weight between crosslinks mc in the range of 425-3000 has been prepared.
The Glass Transition Temperature of Polymer Melts †
The Journal of Physical Chemistry B, 2005
We develop an analytic theory to estimate the glass transition temperature T g of polymer melts as a function of the relative rigidities of the chain backbone and side groups, the monomer structure, pressure, and polymer mass. Our computations are based on an extension of the semiempirical Lindemann criterion of melting to locate T g and on the use of the advanced mean field lattice cluster theory (LCT) for treating the themodynamics of systems containing structured monomer, semiflexible polymer chains. The Lindemann criterion is translated into a condition for T g by expressing this relation in terms of the specific volume, and this free volume condition is used to calculate T g from our thermodynamic theory. The mass dependence of T g is compared to that of other characteristic temperatures of glass-formation. These additional characteristic temperatures are determined from the temperature variation of the LCT configurational entropy, in conjunction with the Adam-Gibbs model for long wavelength structural relaxation. Our theory explains generally observed trends in the variation of T g with polymer microstructure, and we find that T g can be tuned either upward or downward by increasing the length of the side chains, depending on the relative rigidities of the side groups and the chain backbone. The elucidation of the molecular origins of T g in polymer liquids should be useful in designing and processing new synthetic materials and for understanding the dynamics and controlling the preservation of biological substances.
The glass transition temperature of nonstoichiometric epoxy–amine networks
Journal of Polymer Science Part B: Polymer Physics, 1991
Glass transition temperatures (T,) of nonstoichiometric epoxy-amine networks based on the diglycidylether of bisphenol A (DGEBA), are analyzed in terms of the network structure. In most cases reasonable predictions of T, can be made using an empirical equation reported by L. E. Nielsen together with the experimental Tg value of the stoichiometric network and statistical calculations of the concentration of elastic chains. It is stated that in these rigid networks the concentration of elastic chains is the main structural factor associated to the variation of Tg with stoichiometry. For flexible networks based on the diglycidylether of butanediol (DGEBD) , the effect of elastic chains on the T, value is much less significant. Keywords: glass transition of non-stoichiometric epoxy lamine networks epoxy/amine non-stoichiometric networks, Tg of networks of non-stoichiometric epoxy lamine, T, of * To whom all correspondence should be addressed.
Statistical thermodynamics of the glass transition and the glassy state of polymers
The Journal of Physical Chemistry, 1972
The hole theory of Simha and Somcynsky is applied to an analysis of the liquid-glass boundary and to the equation of state in the region between the glass transition and the 0-relaxation. Two systems already studied experimentally are considered, namely, polystyrene and poly (o-methylstyrene). The liquid-glass boundary relations are investigated under two sets of conditions corresponding to a low-(LPG) and a high-pressure glass (HPG). The former is formed by cooling the liquid a t atmospheric pressure, whereas the latter is obtained by pressurizing the liquid isothermally. The equation of state is analyzed for LPG only. The link between the conventional thermodynamic relations, experiment, and the statistical theory is formed by identifying the vacancy fraction 1y appearing in the latter with the ordering parameter 2 introduced in the thermodynamic theory. For LPG, ye, the value of y along the boundary, is indeed found to be constant for both polymers. For HPG, 1y, is a decreasing function of pressure, as should be expected. The equation dT,/dP = (bT,/W)z + (bT,/bZ)p X dZ/dP is tested by evaluating the product on the right-hand side by a combination of the statistical theory with experiment. An equation of state for LPG is first computed entirely from theory by assuming that a single constant parameter, y = yg, characterizes not only the liquid-glass boundary line, but the glassy region as well. This results in too low a thermal expansivity, as had been noted earlier by Somcynsky and Simha for several other polymers at atmospheric pressure. Hence, within the frame of the hole theory, y cannot remain constant in the glass but is a function of T and P. It differs, of course, from the function derived by maximization of the configurational partition function of the liquid and is obtained here from experiment. Thus, additional constants enter into the equation of state of the glass, which cannot be obtained solely from the properties of the liquid and the liquid-glass boundary line. On approaching this line, however, the above function reduces to a single constant, viz., yg.
Influence of Network Structure on Glass Transition Temperature of Elastomers
Materials, 2016
It is generally believed that only intermolecular, elastically-effective crosslinks influence elastomer properties. The role of the intramolecular modifications of the polymer chains is marginalized. The aim of our study was the characterization of the structural parameters of cured elastomers, and determination of their influence on the behavior of the polymer network. For this purpose, styrene-butadiene rubbers (SBR), cured with various curatives, such as DCP, TMTD, TBzTD, Vulcuren ® , DPG/S 8 , CBS/S 8 , MBTS/S 8 and ZDT/S 8 , were investigated. In every series of samples a broad range of crosslink density was obtained, in addition to diverse crosslink structures, as determined by equilibrium swelling and thiol-amine analysis. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to study the glass transition process, and positron annihilation lifetime spectroscopy (PALS) to investigate the size of the free volumes. For all samples, the values of the glass transition temperature (T g ) increased with a rise in crosslink density. At the same time, the free volume size proportionally decreased. The changes in T g and free volume size show significant differences between the series crosslinked with various curatives. These variations are explained on the basis of the curatives' structure effect. Furthermore, basic structure-property relationships are provided. They enable the prediction of the effect of curatives on the structural parameters of the network, and some of the resulting properties. It is proved that the applied techniques-DSC, DMA, and PALS-can serve to provide information about the modifications to the polymer chains. Moreover, on the basis of the obtained results and considering the diversified curatives available nowadays, the usability of "part per hundred rubber" (phr) unit is questioned. conceived and designed the experiments; Katarzyna Bandzierz performed the crosslink density and crosslink structure analyses, density measurements, DSC and DMA experiments; Jerzy Dryzek performed the PALS measurements; Katarzyna Bandzierz analyzed the data and wrote the paper, with contribution of Louis Reuvekamp and Dariusz Bielinski. All authors have given approval to the final version of the manuscript.
Relationship between dynamics and thermodynamics in glass-forming polymers
EPL (Europhysics Letters), 2005
We have tested the validity of the Adam-Gibbs (AG) equation to glass-forming polymers by means of dynamics data from dielectric relaxation and thermodynamic data. The AG equation holds for polymers with simple monomeric chemical structure, whereas it fails for more complex systems possessing secondary relaxation processes with some degree of intra-chain cooperativity. However, we found that the AG equation still works once the contribution to the excess entropy of intra-chain secondary relaxation processes uncoupled to the process is removed. This contribution results to be essentially temperature independent.
Polymer, 2002
The average specific volume of the model poly(3-aminopropyl methyl siloxane) as a function of temperature near the glass transition was computed from molecular dynamics simulations. The glass transition temperature was defined as the slop intersection around 210 K, a value similar to that of the experimental result. Globular polymer shaped chains were observed where the chain is closed upon itself. Three amino groups of amino propylene chains were located in the center and the rest of the amino groups were situated outside the main chain. The glass transition temperature of this low molecular weight polymer strongly depends on the binding energies between chains. The intersection of binding energy slopes defines a temperature of 213 K near the glass transition temperature. The most important contributions to the glass transition changes were the electrostatic binding contributions. The Van der Waals contributions in the volume changes were less important. The chain mobility was evaluated by the transition between angles for the states trans, g þ and g 2 . The glass transition temperature observed experimentally, 208^2 K, is due to cooperative movements of two different torsion angles, (O-Si) and (Si-C) of the main chain and the lateral chain, respectively, and its rotational mobility. Self-diffusion constant variation for all polymer atoms with the temperature is a probe that the polymer chain cooperative movement had started at temperatures around the glass transition temperature. q
Composition variation of glass-transition temperatures. 7. Copolymers
Macromolecules, 1982
A thermodynamic theory for the compositional variation of glass-transition temperatures is generalized to include copolymers, providing an equation with no adjustable parameters. Properties required for this relation are glass-transition temperatures and glass-transition incrementa of heat capacity for the two associated homopolymers and the fully alternating copolymer, and the monomer reactivity ratios. Formal conditions are obtained for the occurrence, nature, and values of absolute extrema in copolymer glass-transition temperatures and glass-transition incrementa of heat capacity. Previous expressions for the composition dependence of copolymer glass-transition temperatures are derived as secondary approximations to a central equation.