Dilute solution behaviour of polymers near the phase separation temperature

Light scattering and viscosity measurements performed in the temperature range between the θ-point and the temperature of phase separation with dilute solutions of polystyrene in cyclohexane and poly(acrylic acid) in dioxane have indicated a different mechanism of precipitation in the two systems. While polystyrene molecules give rise to progressively growing clusters the poly(acrylic acid) coils assume compact forms before precipitating. Phase separation is achieved in the former case by extensive clustering, in the latter by particle coalescence. The dimensions that the compact form of the poly(acrylic acid) molecule can reach before precipitation sets in correspond to a solid-like density inside the molecular domain. From the experimental data the temperatures characteristic for cluster formation (T_c) and for coil to globule transition (T_g) have been obtained.