Dilatometric and viscometric data on fractionated polystyrenes containing diethylbenzene end groups are presented over wide temperature ranges. The second-order transition temperature, viscosity-temperature coefficient, and specific volume all change rapidly with increasing molecular weight toward asymptotic limits which are practically reached at M≅30,000. Empirical expressions are presented relating these properties to molecular weight and temperature. In each case the dependence on molecular weight is expressed as a simple function of M̄n−1. These observations are interpreted and correlated on the basis of the hypothesis that the local configurational order in a liquid polymer is disturbed by the introduction of end groups to a degree that is proportional to their number. The second-order transition does not represent an isoviscous state. The internal local configurational structure appears to be equivalent, and independent of temperature, in all polystyrenes below their second-order transition temperatures.

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On the basis of simple assumptions, equations are derived for predicting the specific volume‐temperature‐molecular weight (v‐T‐M) relationships for a homologous series of polymers from the v‐T curves for the monomer and the polymer of infinite molecular weight. Analogous v‐T‐ρ relationships (where ρ is the degree of crosslinking) are similarly obtained. The result, that v decreases linearly with decreasing 1/M and with increasing ρ, conforms with the picture that either the removal of two chain ends (as M increases) or the introduction of a crosslinkage involves, between two polymer segments, the exchange of a van der Waals bond for a shorter covalent bond. The validity of these equations is illustrated by comparison with the observed data for polymers covering a wide range in M, T, and chemical type. For several polymer series the extrapolated value of v at 0°K (v0) is the same for all members of the series, indicating that at this temperature the average length of the van der Waals and covalent bonds between polymer segments are the same. Assuming that the form of the linear relationship observed for polystyrene between the specific volume (vg) at the glass temperature and the value (Tg) of the latter is valid for other polymer series, equations are derived which predict Tg as a function of M from the limiting value of the glass temperature for a chain of infinite length, and from the v‐T curves in the liquid state for the monomer and for the polymer of M = ∞. Analogous Tg‐ρ relationships are similarly obtained. According to these equations, a linear relationship between 1/Tg and 1/M should be obtained, which reduces at high M to a linear dependence of Tg on 1/M. Similarly, a linear dependence of Tg on ρ is predicted at low ρ. These predictions are in satisfactory agreement with data on polystyrene fractions and on crosslinked copolymers of styrene with divinylbenzene. The conclusion that Tg for polystyrenes represent a state of iso‐free volume irrespective of M is shown to be an approximation that is valid, within experimental error, only for large values of M.

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An improved derivation is given for the relationship between the configurational dimensions of a polymer molecule in solution and the thermodynamic interaction between polymer segments and solvent molecules. The connection between intrinsic viscosity and molecular configuration is discussed in the light of recent theories, and general procedures for treating intrinsic viscosity data are given. The root-mean-square end-to-end distance for the polymer molecule when the net thermodynamic interaction between segments and solvent is zero may be computed from suitable viscosity measurements. The influence of hindrance to free rotation on the polymer configuration, unperturbed by thermodynamic interactions with the solvent medium, is obtained directly from this dimension. The influence of thermodynamic interactions on chain dimensions is considered separately. Parameters expressing the heat and entropy of dilution of polymer segments with solvent may be deduced from intrinsic viscosity measurements at different temperatures.