Influence of Intermolecular Entanglements on the Glass Transition and Structural Relaxation Behaviors of Macromolecules. 2. Polystyrene and Phenolphthalein Poly(ether sulfone)

Abstract

The effect of entanglements on the glass transition and structural relaxation behaviors has been studied for polystyrene (PS) and phenolphthalein poly(ether sulfone) (PES-C) samples by fast evaporation of the solution of concentrations varying from above the overlapping concentration to far below it, and compared to the results we have studied previously in PC. It has been found that for all the polymers we have studied, in the concentrated solution region, the T g of the samples obtained from solution are independent of the change of concentration and are very close to that of normal bulk samples, whereas in the dilute solution region the T g of the samples decrease with the logarithm of decreasing concentration. The critical concentrations that divide the two distinct regions for the three polymers are 0.9% g/mL for PC, 0.1% g/mL for PS, and 1% g/mL for PES-C. The decrease of T g of the samples is interpreted by the decrease of intermolecular entanglements as the isolation of polymer chains, and the entanglement of polymer chains restrained the mobility of the segments. The structural relaxation behavior of the polymers is also found to be different from that of normal bulk samples. The enthalpies of single-chain samples are lower than that of the bulk ones, which correspond to the lower glass transition temperature; the peaks are lower and broader, and the relaxed enthalpy is much lower as compared to that of bulk samples. In the three polymers we have studied, the influence of change of entanglements on both the decrease in glass transition temperature and relaxed enthalpy is the most significant for PS and the least for PES-C. It is indicated that the interactions in the flexible polymers are weak; thus, the restraint of the entanglements on the mobility of the segments plays a more important role in the flexible polymers, and the change of entanglement in the flexible polymers has a more significant influence on the physical properties.

Effect of solution-blended poly(styrene-co-acrylonitrile) copolymer on crystallization of poly(vinylidene fluoride)

“…So with decreasing of SAN content, the ratio of incorporated PVDF increased and the T g,SAN increased. Besides, T g,SAN by solution casting was much lower than T g,SAN by melt molding, which might be attributed to the entanglement which has been intensively studied [33,34]. In Table 2, the addition of SAN did not show obvious effect on the melting temperatures of PVDF until SAN exceeded 20 wt%, which resulted in similar ΔT m = T m f -T m on .…”

Thickness dependence of structural relaxation in spin-cast, glassy polymer thin films

“…8 were adjusted by varying the concentration of the solution used for spin casting. It has been found recently that when glassy polymers are precipitated from dilute solutions, below the polymer overlap volume fraction *, their T g is reduced below the bulk value [22,23]. This result was attributed to a lower extent of entanglement in the polymers obtained from dilute solution.…”

Slow Relaxation of Spin-Cast Poly(methyl methacrylate) Confined in Thin Films

“…The phenomenon might not be the result of the effects of a free surface on molecular mobility per se, however, but it might instead be linked to the molecular conformation and the extent of entanglement in the spin-cast film. When a solvent is removed quickly from a polymer solution, it has been found elsewhere that the T g of the glass is reduced from the bulk value, and the magnitude of the reduction is inversely related to the original concentration [19]. One explanation for this result is that if the concentration of the solution is below the overlap concentration φ* where the chains come into contact with each other, they will be less able to entangle when the solvent is removed quickly.…”