Glass transition temperature typical values

The TPX experimental product of Mitsubishi Petrochemical Ind. (221) is an amorphous, transparent polyolefin with very low water absorption (0.01%) and a glass-transition temperature comparable to that of BPA-PC (ca 150°C). Birefringence (<20 nm/mm), flexural modulus, and elongation at break are on the same level as PMMA (221). The vacuum time, the time in minutes to reach a pressure of 0.13 mPa (10 torr), is similarly short like that of cychc polyolefins. Typical values of TPX are fisted in Table 11. A commercial application of TPX is not known as of this writing. 

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. 

Alloys exhibit physical properties, the values of which are typically the weighted average of those of its constituents. In particular, the blend exhibits a single glass-transition temperature, often closely obeying semitheoretically derived equations. Blends of two compatibiLized immiscible polymers exhibit physical properties which depend on the physical arrangement of the constituents and thus maybe much closer to those of one of the parent resins. They will also typically exhibit the two glass-transition temperatures of their constituent resins. 

The effects of these different factors can be seen in the Tg values of some typical polymers. A number of these values are shown in Table 3.1, together with a brief note about what feature particularly contributes to the relative level of the glass transition temperature. 

For motion of entire molecular strands, consisting of n segments, to take place in 0.1 s, the frequency of segmental motion must be much faster than 0.1 s by a factor of or more. This rate is achieved only at a temperature well above Tg for typical values of n, of the order of 100. Thus, fully rubber-like response will not be achieved until the test temperature is Tg + 30°C, or even higher. (On the other hand, for sufficiently slow movements that take place over several hours or days, an elastomer would still be able to respond at temperatures below the conventionally dehned glass transition temperature.)... 

Since the Lindemann ratio dija 0.1 is empirically roughly the same for all substances, one expects the g value, as measured by sound attenuation, to be correlated with the glass transition temperature. Note that this relationship is independent of the details of the bead assignment. Equation (20), if rewritten as Tg di/a) g, is almost obvious, given the interaction of the form in Eq. (17) The typical lattice displacement, at Tg, is roughly A< ) j- dija. On the other hand, the typical structural excitations have the energy of about Tg, at the glass transition. 

Plasticixers arc low-molecular-weight liquids that lower the glass transition temperature of a polymer. A typical example is the use of dioctyl phthalate in poly(vinyl chloride) to convert the polymer from a rigid material to a soft, flexible one. It the glass transition of the two components A and B are known, an estimate can be made of the Tg value of the mixture by one or the other of the equations... 

Viscosity temperature dependence in ILs is more complicated than in most molecular solvents, because most of them do not follow the typical Arrhenius behavior. Most temperature studies fit the viscosity values into the Vogel-Tammarm-Fulcher (VTF) equation, which adds an additional adjustable parameter (glass transition temperature) to the exponential term. 

The glass transition temperature of PMTFPS is -75°C (-103°F). Moreover, it does not exhibit low-temperature crystallization at -40 C (-40°F) as PMDS does. Because of this and the low Tg, fluorosilicone elastomers remain very flexible at very low temperatures. For example, the brittleness temperature by impact (ASTM D 746B) of a commercial fluorosilicone vulcanizate was found to be -59°C (-74°F).62 This is considerably lower than the values typically measured on fluorocarbon elastomers. Fluorosilicones combine the superior fluid resistance of fluoropolymers with the very good low-temperature flexibility of silicones. 

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