Glass transition parameters

The relationship between Tg and microbial stability is the least studied of all the stability areas. Based mainly on mold germination data, Slade and Levine (1991) postulated that glass transition parameters, specifically Tm/Ts ratio, T g and W g (related to C defined previously in Figure 32), could be useful for predicting the microbial stability of concentrated and... 

TABLE 16.1 Estimated Values of the Melting Point Tm and the Glass Transition Temperature Tg of Pure Substances of Various Molar Masses M, As Well As the Special Glass Transition Parameters (Tg and i]/w ) for Maximally Freeze-Concentrated Solutions... 

Figure 2 shows the d3mamic modulus (E ) and the loss tangent (tan 6) at 0% RH as a function of temperature for unoriented and oriented (5.5X) poly(ethylene terephthalate), (PET) fibers. The glass transition parameters (a peak temperature, tan 6 ax and... 

TABLE 2.2. Glass Transition Parameters of Poly(ethylene Terephthalate) (PET), Poly(ethyIene 2,6-NaphthalenedicarboxyIate) (PEN), and Poly(phenylene Snifide) (PPS)... 

In methacrylic ester polymers, the glass-transition temperature, is influenced primarily by the nature of the alcohol group as can be seen in Table 1. Below the the polymers are hard, brittle, and glass-like above the they are relatively soft, flexible, and mbbery. At even higher temperatures, depending on molecular weight, they flow and are tacky. Table 1 also contains typical values for the density, solubiHty parameter, and refractive index for various methacrylic homopolymers. 

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

Plasticizers and Processing Aids. Petroleum-based oils are commonly used as plasticizers. Compound viscosity is reduced, and mixing, processing, and low temperature properties are improved. Air permeabihty is increased by adding extender oils. Plasticizers are selected for their compatibihty and low temperature properties. Butyl mbber has a solubihty parameter of ca 15.3 (f /cm ) [7.5 (cal/cm ) ], similar to paraffinic and naphthenic oils. Polybutenes, paraffin waxes, and low mol wt polyethylene can also be used as plasticizers (qv). Alkyl adipates and sebacates reduce the glass-transition temperature and improve low temperature properties. Process aids, eg, mineral mbber and Stmktol 40 ms, improve filler dispersion and cured adhesion to high unsaturated mbber substrates. 

In emulsion polymerization, NBR with acrylonitrile content between 15 and 50% can be obtained. The increase in the acrylonitrile content in the NBR produces an increase in the polar nature and solubility parameter in the copolymer [12]. Furthermore, the increase in acrylonitrile content improves the resistance to oils and also increases the glass transition temperature of the copolymers from -60 to-lO C. 

In this approach, connectivity indices were used as the principle descriptor of the topology of the repeat unit of a polymer. The connectivity indices of various polymers were first correlated directly with the experimental data for six different physical properties. The six properties were Van der Waals volume (Vw), molar volume (V), heat capacity (Cp), solubility parameter (5), glass transition temperature Tfj, and cohesive energies ( coh) for the 45 different polymers. Available data were used to establish the dependence of these properties on the topological indices. All the experimental data for these properties were trained simultaneously in the proposed neural network model in order to develop an overall cause-effect relationship for all six properties. 

Experimental data for Van der Waals volumes Molar volumes Heat capacities Solubility parameter and glass transition temperature... 

Figure 25 ANN model (5-8-6) training and testing results for van der Waals volume, molar volume, heat capacity, solubility parameter, and glass transition temperature of 45 different polymers.

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-... 

In calculation the authors of the model assume that the cube material possesses the complex modulus EX and mechanical loss tangent tg dA which are functions of temperature T. The layer of thickness d is composed of material characterized by a complex modulus Eg = f(T + AT) and tg <5B = f(T + AT). The temperature dependences of Eg and tg SB are similar to those of EX and tg <5A, but are shifted towards higher or lower temperatures by a preset value AT which is equivalent to the change of the glass transition point. By prescibing the structural parameters a and d one simulates the dimensions of the inclusions and the interlayers, and by varying AT one can imitate the relationship between their respective mechanical parameters. 

Table 9. Effect of organic substituents on the solubility parameter and the glass transition temperature of an organosiloxane polymer...

FIGURE 13.2 Calculated relation between the solubility parameter and glass transition temperature (Jg) for a variety of ethylene-propylene copolymers (EPMs) grafted with polar monomers the window for rubbers with an oil resistance similar to or better than hydrogenated acrylonitrile-butadiene copolymer (NBR) (20 wt% acrylonitrile) is also shown. 

FIGURE 13.7 Calculated values for the solubility parameter and glass transition temperature (Tg) of a variety of designed ethylene-propylene graft copolymers. 

Calculated Degree of Maleic Anhydride Grafting Required to Obtain a Solubility Parameter of 18.0 (J/cm ) , Assuming Full Conversion of the Grafted Anhydride with the Amines Listed, and Corresponding Glass Transition Temperatures (Tg)... 

This statement can be proved very easily by considering four different types of general POP properties and their variability as a function of the side substituents on the polymer skeleton, i.e. glass transition temperature (Tg), morphology, solvent solubility and limiting oxygen index (LOI). The values of these parameters are reported in Tables 5-8. 

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