AbstractIn the course of studying the intrinsic viscosity–temperature relationship for polymethyl methacrylate in acetone, it was found that the intrinsic viscosities η of four samples of different molecular weights showed a maximum at about 30°C. This phenomenon can be interpreted according to the Flory‐Fox theory of intrinsic viscosities. An equation has been derived from their results that gives the condition for the existence of the temperatureTmat which the η vs. temperature curve shows a maximum. This equation indicates thatTmis lower for lower θ points (better solvents) and higher for more flexible chains and for higher molecular weights. It may thus be concluded that such behavior as was found here is in no way specific to polymethyl methacrylate in acetone but should be observed generally for polymer solutions when their intrinsic viscosities are measured over sufficiently wide ranges of temperature.Tmis important because it is a characteristic temperature of a given polymer‐solvent combination, just as is the θ temperature. Polymer molecules take the most expanded configurations at this temperature, whereas they take the most compact configurations at the θ temperature. Although the θ temperature depends upon only the thermodynamic properties of the solution,Tmis also affected by the chain flexibility. The measurement ofTmthus provides a method for estimating a parameter expressing the chain flexibility. The resulting equations can also be utilized to determine the sign of the temperature coefficient of η of a given polymer solution in a given temp
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