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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]
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.
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 ...
PTMC is a predominantly amorphous polymer in the relaxed state but it can present some crystallinity, particularly when the chains are stretched. [ 4 ] The polymer presents glass transition temperature ( T g {\displaystyle T_{g}} ) between -15 and -30 °C and melting temperature ( T m {\displaystyle T_{m}} ) ranging from 38 to 41°C.
Mixture of polymers and solvent on a lattice. Flory–Huggins solution theory is a lattice model of the thermodynamics of polymer solutions which takes account of the great dissimilarity in molecular sizes in adapting the usual expression for the entropy of mixing.
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 ...
On cooling, the hardness of the polymer increases in the neighborhood of T g by several orders of magnitude. This hardening follows the Williams-Landel-Ferry equation, not the Arrhenius equation. Organic polymers are thus called fragile glass formers. Silicon glass (e.g., window glass), is in contrast labelled as a strong glass former.
Shape-memory polymers (SMPs) are polymeric smart materials that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape when induced by an external stimulus (trigger), such as temperature change.