In glass transition

In cases where the copolymers have substantially lower glass-transition temperatures, the modulus decreases with increasing comonomer content. This results from a drop in crystallinity and in glass-transition temperature. The loss in modulus in these systems is therefore accompanied by an improvement in low temperature performance. However, at low acrylate levels (< 10 wt %), T increases with comonomer content. The brittle points in this range may therefore be higher than that of PVDC. 

MA Samus, G Rossi. Methanol absorption in ethylene-vinyl alcohol copolymers Relation between solvent diffusion and changes in glass transition temperature in glassy polymeric materials. Macromolecules 29 2275-2288, 1996. 

Chung, H.-J., Lee, E.-J., and Lim, S.-T. (2002). Comparison in glass transition and enthalpy relaxation between native and gelatinized rice starches. Carbohydr. Polym. 48, 287-298. 

The same extruder as in wire coating with PE can be used. However, since the cyclic olefin polymer composition has a higher in glass transition temperature than PE, the cylinder temperature of the extruder must be set to a somewhat higher temperature than used in the conventional method. 

Figure 2 shows the effect of two Aroclors on the glass transition temperatures. A very rapid decrease in transition temperatures of the polymers from bisphenols I and II took place when as much as 5 or 10% additive was in the films. When the antiplasticizer concentration was 5 to 30% in the bisphenol I polymer and 10 to 40% in the bisphenol II polymer, there was a linear relationship between the decrease in glass transition temperature and the antiplasticizer concentration. 

Her, L., Deras, M., Nail, S. Electrolyte-induced changes in glass transition temperatures of freeze-concentrated solutes. Pharm Res 12 768-772 (1995). 

For miscible blend phases, these parameters need to be described as a function of the blend composition. In a first approach to describe the behavior of the present PPE/PS and SAN/PMMA phases, these phases will be regarded as ideal, homogeneously mixed blends. It appears reasonable to assume that the heat capacity, the molar mass of the repeat unit, as well as the weight content of carbon dioxide scale linearly with the weight content of the respective blend phase. Moreover, a constant value of the lattice coordination number for PPE/PS and for SAN/PMMA can be anticipated. Thus, the glass transition temperature of the gas-saturated PPE/SAN/SBM blend can be predicted as a function of the blend composition (Fig. 17). Obviously, both the compatibilization by SBM triblock terpolymers and the plasticizing effect of the absorbed carbon dioxide help to reduce the difference in glass transition temperature between PPE and SAN. 

Figure 8.6 Variation in glass transition temperature of starch (DSC data) as a function of water content 1, 2 and 4 correspond to gelatinized potato, rice and wheat starch 3 and 5 correspond to amorphous amylopectin and granular wheat starch, respectively. Inset shows the DSC traces of native wheat starch at...

In fact, most polymers have a distinct temperature above which the chains become much more flexible. This temperature can be measured by a variety. of techniques and is called the glass transition temperature, or Tg. For PDMS it is -127°C, while for PS it is approximately 100°C. It is this tremendous difference in glass transition temperatures that makes PDMS and PS behave so differently (at room temperature). The physical properties of amorphous polymers are determined in large part by the freedom of the chains to move, and this determines the glass transition temperature. Although commercial... 

The main reason for the greater flexibility is due to long-chain difunctional materials that upon cure become part of the epoxy matrix. The result is a single-phase, flexible system. The disadvantage of this approach is a reduction in the crosslink density and consequently reductions in glass transition temperatures as well as the heat and chemical resistance of the system. 

Series I Acrylic Latex Emulsions. A series of four acrylic latex emulsions varying in glass transition temperature (Tg) (3) were applied first. Tg is the temperature at which the resin changes from a relatively flexible to a relatively stiff material. The acrylic latexes are made from water-insoluble monomers such as acrylates and alkyl acrylates polymerized in emulsion form to produce an aqueous dispersion or latex of the polymer. Upon drying, the emulsion is irreversibly broken so that the applied material becomes wash-fast. The application requires no catalyst or high temperature heating. 

Velasco Santos et al. (27) measured both the dynamic mechanical behavior and tensile mechanical properties of MWCNT-PMMA composites. They observed 1135% increase in storage modulus at 90°C and increase in glass transition temperature by 40°C over neat PMMA with only 1 wt% functionalized nanotubes. The tensile... 

The glass transition in a molecular system sets in at the moment the free volume (about 2.5% of the free volume in glass transition of polymers) disappears. Loss of fluidity ( glass transition ) in suspensions occurs when the free volume of suspensions tends to zero. 

Irradiation crosslinking of PVC-U, carried out using electron beam, has shown a marked increase in glass transition temperature in the presence of a triacrylate, with minimal thermal degradation (216). Electron beam irradiation has also been investigated on a PVC-P wire coating formulation in the presence of different reactive monomers (185). Flame retardancy has also been improved with the incorporation of appropriate flame retardants (118). The effect of UV irradiation on formulations, incorporating iron chloride or cobalt chloride, has also been studied (67). 

Figure 8. Dynamic mechanical spectroscopy on samptes II, 12, and 15 showing the increase in glass transition temperature with increased epoxy prereaction time...

Figure 5.6. Water plasticization and sorption behavior typical of dairy powder showing critical water content and water activity resulting in glass transition at a typical room temperature.

Another plausible explanation of the Stage IV effect is a high temperature reaction or molecular rearrangement that cuases a decrease in glass transition temperature. 

Table 5.2 Effect on physical properties of acrylics with increase in glass transition temperature...

It can be seen from the data presented in Table 9.2 that the parallelism of the decrease in permeability with the increase in glass transition temperature of the polymer is somewhat disrupted for He and CO2. Helium has the lowest solubility among the penetrants under study. However, the permeability of organosilicon polymers for helium is higher than could be expected from... 

In selective separation of hydrocarbons from their mixtures with air or from their aqueous solutions, it makes sense to use membranes based on rubbery polymers, whose permeability increases with the decrease in glass transition point. Permselectivity of rubbery polymers is dominated by the sorption component, which increases with condensability of the hydrocarbon penetrant. Higher activity of the component being separated in the feed mixture results in plasticization of the membrane and can make it swell. This can produce a non-monotonic dependance of selective properties of the membrane on activity of the component being separated. As a rule, permselectivity for mixtures of penetrants is significantly lower than their ideal values. Negative values of sorption heat of easily condensable hydrocarbons can result in existence of non-monotonic temperature dependencies of mass transfer coefficients. 

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