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In the case of polymers, conformational changes of segments, typically consisting of 10–20 main-chain atoms, become infinitely slow below the glass transition temperature. In a partially crystalline polymer the glass transition occurs only in the amorphous parts of the material. The definition is different from that in ref. [9]
Figure 5: Scheme of regiospecific polymer synthesis Figure 6: Schematic description of two most common conformations of PVDF, the left one is tg + tg − and the right one is all trans, the yellow sphere represents fluorine atom, the white sphere represents hydrogen atom and the grey sphere represents the carbon atom.
The Flory–Fox equation relates the number-average molecular weight, M n, to the glass transition temperature, T g, as shown below: =, where T g,∞ is the maximum glass transition temperature that can be achieved at a theoretical infinite molecular weight and K is an empirical parameter that is related to the free volume present in the polymer sample.
A printer cartridge made of PPE and polystyrene; it is an example of a product which requires good dimensional stability and accuracy to fit.. PPE blends are used for structural parts, electronics, household and automotive items that depend on high heat resistance, dimensional stability and accuracy.
Because it achieves an unusually high degree of polymerization, chain entanglements can be relied upon as anchor points to achieve the thermally induced shape-memory effect. Therefore, this polymer relies solely on physical anchor points. When heated up to Tg, the material abruptly changes from a rigid state to a tapered state (softens).
These same authors have proposed the "universal constants" C g 1 and C g 2 for a given polymer system be collected in a table. These constants are approximately the same for a large number of polymers and can be written C g 1 ≈ 15 and C g 2 ≈ 50 K. Experimentally observed values deviate from the values in the table. These orders of ...
The miscibility of the hard and soft segments in TPU depends on the differences in their glass transition temperature (Tg) [1] which occurs at the onset of micro-Brownian segmental motion, identifiable by dynamic mechanical spectra. For an immiscible TPU, the loss modulus spectrum typically shows double peaks, each of which is assigned to the ...
For the polymer chemist, DSC is a handy tool for studying curing processes, which allows the fine tuning of polymer properties. The cross-linking of polymer molecules that occurs in the curing process is exothermic, resulting in a negative peak in the DSC curve that usually appears soon after the glass transition.