Glass transition molecular weight dependence

The Tg of linear polymers such as polyimides is heavily dependent on, and increases with, the molecular weight. The equivalent statement can also be said about crosslinked networks, where the glass transition temperature is dependent on the network crosslink density [111-117]. 

The concept of chain entanglement" was originally developed in order to explain the deformation of chemically uncrosslinked amorphous polymers above their glass transition temperature (see e.g. jhe increase in molecular weight dependence... 

To what extent do linear ionic polymers differ from thdr non-ionic counterparts Specifically are tte theories developed for organic polymers with regard to, for instance, the molecular weight dependence of the glass transition applicable also to ionic systems, and if not are the ionic systems qualitatively different from their non ionic counterparts or is the difference merely quantitative, implying only a higher d ree of intermolecular attraction ... 

The glass transition temperature is dependent on the structure of the polymer, and for the same polymer varies as a function of the polymer molecular weight. The increase in the molecular weight of the polymer is associated, as expected, with an increase in the... 

Because water plasticizes hydrophilic food components, their glass transition is strongly dependent on water content. The effect of water on the glass-transition temperature of several amorphous carbohydrates, calculated with the Gordon Taylor equation [B.79], is depicted in Fig. 6.4-6. Within the range of the materials shown, Tg decreases with lower average molecular weight and/or increased concentration of plasticizer (water). 

Figure 4. (a) Inherent viscosity dependence of the melting temperature (r ) and the clearing temperature (T ) of nematic poly(2-n-decyl-1,4-phenylene-terephthalate) [6] and (b) the molecular weight dependence of the glass transition temperature (Lg) of nematic poly(2,2 -dimethyl-4,4 -biphenylene-phenyltereph-thalate)[7]. 

Dalnoki-Veress, K., Forrest, J. A., Murray, C., Gigault, C., andDutcher, J. R., Molecular weight dependence of reductions in the glass transition temperature of thin freely standing polymer films, Phys. Rev. E, 63, 031801 (2001). 

Glass-Rubber Transition Detected by the Spin Label Method for Polystyrene (PS) Molecular Weight Dependence... 

The molecular motion of a segment at a chain end is more rapid than that in an inner chain site. The fact is clarified by the selective spin labeling in an amorphous polymer. The molecular weight dependencies of glass-rubber transitions at two kinds of sites, the chain end and inner chain sites give a free volume size of micro Brownian motion. 

The rubber-fluid transition is associated with the change in the global mobility of molecules. This transition is practically important to the molding of polymer materials, for it is a prerequisite condition of permanent deformation. In 1979-1981, Boyer suggested that corresponds to a dynamic transition called as Til (a liquid-liquid transition above Tg), reflecting the frozen and de-frozen of the whole polymer chain (Boyer 1979, 1980, 1981). From the molecular weight dependence curve illustrated in Fig. 6.3, one may see that Tf appears as an extrapolation from glass transition temperatures of small molecules. The properties of Til ate quite similar to Tg. 

Figure 10-6. Molecular weight dependence of the brittleness and the glass-transition temperatures Tg and Tq of poly(isobutylene) (after A. X. Schmidt and C. A. Marlies).

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