Polymer reviewGlass transition elevation by polymer entanglements
Review articleOpen access
Abstract:

AbstractFor some polymers a plot of glass transition temperature, Tg, versus reciprocal molecular weight can be taken to define two lines which intersect at a molecular weight which is designated as Mg. The value of Mg agrees, within a factor of two, with critical values of molecular weight reported for other properties which are generally attributed to incipient formation of a network of entanglements. Therefore, it is suggested that an increased elevation of Tg at molecular weights greater than Mg is due to an increasing concentration of entanglements.A more detailed analysis was made by extending the Fox-Flory theory of the glass transition to include negative contributions to the free volume from entanglements. This extension leads to revised estimates of the free volume per chain end which are much smaller (6–19 Å3 near Tg) than previous estimates which took no account of entanglements. These smaller values are interpreted to mean that the jump units are correspondingly small at Tg, such as envisaged in the Gibbs-diMarzio theory of the glass transition.

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