Effect of plasticizers on second‐order transition points of high polymers

This is a review article concerned with the effect of plasticizers on the second‐order transition point and related phenomena in high polymers. The second‐order transition temperature behavior of plasticized polymers can be described by a linear relationship between the square root of the weight fraction of polymer and the reciprocal transition temperature. For certain temperature regions and plasticizer contents, this is mathematically equivalent to the linear decrease of transition temperature with plasticizer content which is also observed experimentally. This latter result is in accord with Zhurkov's theory of the softening action of solvents, which predicts a linear decrease in softening temperature with solvent content, and no dependence on the nature of the solvent. Neither the second‐order transition approach nor Zhurkov's theory permits conclusions about the nature of the plasticizer. However, it is shown empirically that brittle temperature can be represented as a function of the solvent‐polymer interaction constant μ by a curve having a maximum at μ ≈ 0.4. Since μ is also the parameter which measures compatibility, it is seen that the efficiency and the compatibility of a plasticizer are intimately related. Moreover, correlation can be made with older observations showing the relation between efficiency and the temperature coefficient of viscosity of the plasticizer.