Influence of intermolecular entanglements on the glass transition and structural relaxation behaviors of macromolecules. 2. Polystyrene and phenolphthalein poly(ether sulfone)

The effect of entanglements on the glass transition and structural relaxati on behaviors has been studied for polystyrene (PS) and phenolphthalein poly (ether sulfone) (PES-C) samples by fast evaporation of the solution of conc entrations 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 solut ion region, the T-g of the samples obtained from solution are independent o f the change of concentration and are very close to that of normal bulk sam ples, whereas in the dilute solution region the T-g of the samples decrease with the logarithm of decreasing concentration. The critical concentration s 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 th e samples is interpreted by the decrease of intermolecular entanglements as the isolation of polymer chains, and the entanglement of polymer chains re strained the mobility of the segments. The structural relaxation behavior o f the polymers is also found to be different from that of normal bulk sampl es. 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 influen ce of change of entanglements on both the decrease in glass transition temp erature and relaxed enthalpy is the most significant for PS and the least f or PES-C. It is indicated that the interactions in the flexible polymers ar e weak; thus, the restraint of the entanglements on the mobility of the seg ments plays a more important role in the flexible polymers, and the change of entanglement in the flexible polymers has a more significant influence o n the physical properties.