Collapse and Aggregation of Polymers in Solvents with Varing Molecular Sizes below $\theta$-Temperatures

The collapse and interpenetration of polymer in various solvents were monitored by fluorescence below $\theta$-temperatures. Polystyrene was labeled with a donor and an acceptor groups respectively. Dilute and semidilute solutions in cyclohexane and DOP (dioctylphthalate) containing a mixture of the two polymers were monitored by nonradiative energy transfer. We found that PS collapsed to dis-entangled globules in DOP, while it collapsed and aggregated to interpenetrated particles in cyclohexane as the solutions were cooled from their $\theta$-temperatures. This can be attributed to the effect of viscoelasticity; namely, the diffusion coefficient of chain segments is very small in solvent with larger molar size due to the high viscosity, each chain becomes a tiny glassy ball before collision and association with other chains. The dis-entanglement of the glassy polymer was confirmed by a recently developed 1H solid state NMR.