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Component glass transition

When the respective component glass transition temperatures are close, the blend Tg is not a useful measure of blend homogeneity. In fact, excess mixing volumes and specific interactions can cause anomalous behavior. The Tg of such a blend can be lower (as seen in polychloroprene/epoxidized polyisoprene blends (McGrath and Roland, 1994)) or higher (as seen in polylepichlorohydrin/polyvinylmethylether blends (Alegria et al., 1995)), than Tg of either neat component. In blends of polymers having nearly equivalent... [Pg.151]

Herrero and Acosta (80) investigated the microstmcture of poly(ethylene oxide)-poly[(octafluoropentoxy)(trifluoroethoxy)phosphazene] blends. Limited miscibility of both components was inferred, based on the observed shift of the components glass-transition temperatures. Wycisk and co-workers (81) prepared membranes from blends of sulfonated poly[bis(3-methylphenoxy)phosphazene] with polyimides, polyacrylonitrile, and Kynar FLEX PVDF. Morphology, electrochemical performance, and methanol permeabilities of the membranes were then evaluated as part of a program to investigate such blends in direct methanol fuel cells. The polymers were immiscible and a domain-type structure was observed. The best compatibility resulted when the tetrabutylammonium or sodium salt of the polyphosphazene was used (82). [Pg.6521]

Several polymer blends that are commercial products in the industry are partially miscible. Partially miscible polymer blends are those that exhibit some shift from their pure component glass transition temperatures. Thus, a binary miscible polymer blend will exhibit one glass transition temperature and a partially miscible polymer blend will exhibit two distinct glass transition temperatures different from their pure component glass transition temperatures. Some experimental systems that have been reported as partially miscible polymer blends are PET and poly(hydroxy butyrate) (PHB) and PC/SAN. Later on, in a separate chapter, a mathematical framework... [Pg.8]

Steady-state fluorescence spectroscopy has been used by Torkelson et al. [43,44] to determine the components glass transition temperature (Tg) in various blends, including blends of PS with poly(tert-butyl acrylate) (PtBA), PMMA, and poly(w-butyl methacrylate) (PnBMA) [43], as well as in miscible blends of pyrene-labeled PMMA (MPy-labeled PMMA) with poly(ethylene oxide) (PEO) or poly(vinyl chloride) (PVC) over a broad composition range [44]. In the particular case of this latter study [44], the blend Tg-values were measured upon heating by increasing the... [Pg.842]

Evans, C.M. and Torkelson, J.M. (2012) Determining multiple component glass transition temperatures in miscible polymer blends Comparison of fluorescence spectroscopy and differential scanning calorimetry. Polymer, 53 (26), 6118-6124. [Pg.847]

Homogeneous alloys have a single glass transition temperature which is determined by the ratio of the components. The physical properties of these alloys are averages based on the composition of the alloy. [Pg.1014]

Since successful commercialization of Kapton by Du Pont Company in the 1960s (10), numerous compositions of polyimide and various new methods of syntheses have been described in the Hterature (1—5). A successful result for each method depends on the nature of the chemical components involved in the system, including monomers, intermediates, solvents, and the polyimide products, as well as on physical conditions during the synthesis. Properties such as monomer reactivity and solubiHty, and the glass-transition temperature,T, crystallinity, T, and melt viscosity of the polyimide products ultimately determine the effectiveness of each process. Accordingly, proper selection of synthetic method is often critical for preparation of polyimides of a given chemical composition. [Pg.396]

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. [Pg.264]

The two-component urethane structural adhesives are among the most difficult to characterize, simply because of the widely varying properties that are possible. These adhesives may be rigid plastics similar in modulus to standard epoxy adhesives, with glass transition temperatures of the cured adhesive being approximately 60°C. [Pg.795]

Mixtures of monomers can be used to balance properties. This is possible due to the ease of copolymer formation via free-radical polymerization. The glass transition temperature of acrylic copolymers can be predicted from the weight fraction of the component monomers and the glass transition temperatures of the respective homopolymers [20]. Eq. 3 (commonly known as the Fox equation) is reported ... [Pg.830]

In a fundamental sense, the miscibility, adhesion, interfacial energies, and morphology developed are all thermodynamically interrelated in a complex way to the interaction forces between the polymers. Miscibility of a polymer blend containing two polymers depends on the mutual solubility of the polymeric components. The blend is termed compatible when the solubility parameter of the two components are close to each other and show a single-phase transition temperature. However, most polymer pairs tend to be immiscible due to differences in their viscoelastic properties, surface-tensions, and intermolecular interactions. According to the terminology, the polymer pairs are incompatible and show separate glass transitions. For many purposes, miscibility in polymer blends is neither required nor de-... [Pg.649]

DSC helps in determining the glass-transition temperature, vulcanization, and oxidative stability. TG mainly is applied for the quantitative determination of major components of a polymer sample. TMA or DLTMA (dynamic load thermomechanical analysis) measures the elastic properties viz. modulus. [Pg.655]


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Component glass transition temperatures

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