Transition phenomena in polystyrene near the theta condition

Abstract

In a recent paper') we have presented some preliminary results, which indicate that polystyrene exhibits a transition near its theta-conditions. In this communication we present some new results, obtained with a new polymer/solvent system. These observations corroborate our previous findings and suggest the idea that this transition must be a general phenomenon. Moreover, we show that any variation of the thetaconditions gives a corresponding variation of the transition point of the polymer.As already shown') a discontinuity in the variation of the intrinsic viscosity of polystyrene (PS) is observed at about 40 "C when the polymer is dissolved in cyclohexane. It is well known that this solvent is a theta-solvent for PS at 34°C. This transition is presented in Fig. 1 b. If now a little quantity of ethanol (precipitant of PS) is added, it will be evident that the theta-point must be observed at a higher temperature than 34 OC. As we can see in Fig. 1 a, the transition of PS is observed now at a temperature higher than in pure cyclohexane. On the contrary, if we add a little quantity of benzene (good solvent of PS) to the cyclohexane, the theta-conditions must be observed at a lower temperature than 34 "C and as we can see from Fig. 1 c the transition of PS is now observed at a temperature lower than 40°C. The above results clearly demonstrate that the PS transition is tightly related to the theta-conditions of this polymer. We must emphasize here that the observed transition phenomenon is beyond any doubt. Many of the experimental points given in this paper are the mean values of two or three independent measurements. The lowering of [ q ] above the theta-temperature is of the order of 6%.For a given polymer dissolved in a given solvent the theta-conditions can be changed, if the segment density of the polymer is changed. It is known that thetaconditions are displaced to a lower temperature as the segment density of the macromolecular coil is increased. This happens in case of star-polymers as well as in case of very low molecular weight polymers. For a star-shaped PS sample we have already shown') that the transition temperature is lower than the transition temperature of a linear PS sample, because the theta-temperature of the former sample is lower than that of the latter. In Fig. 2 the variation of [ q ] versus temperature of some PS samples in cyclohexane with very low molecular weights are given. The results show that the transition temperature becomes lower as the segment density of the sample becomes higher (transition points 38,s "C and 36°C for molecular weights 7700 and 3600, respectively). a) Part 1: cf.'). 0173-2803/84/$01 .OO

Effect of Comonomer Sequence Distribution on the Adsorption of Random Copolymers onto Impenetrable Flat Surfaces

“…Recall that whereas at 25 °C CH acts as a θ solvent, at 50 °C CH becomes a good solvent for PS. The θ temperature of PS in CH is ∼34 to 35 °C . In the latter case, PS chains prefer to stay solvated by CH more strongly relative to the case of the poor solvent conditions.…”

“…The θ temperature of PS in CH is ∼34 to 35 °C. 82 In the latter case, PS chains prefer to stay solvated by CH more strongly relative to the case of the poor solvent conditions.…”

Renormalization and the two-parameter theory. 2. Comparison with experiment and other two-parameter theories

“…T has been ascribed to a "conformational transition" due to side-group motion. 48 The location of the observed cusp is displaced by varying solvent and by studying polystyrene stars which, of course, have slightly shifted points. This cusp effect is unobserved in the data in Figure 12 which is for a high molecular weight sample,30,50 ~O(107).…”

Synthesis, characterization and conformational transitions in copolymers of 2‐(o‐chlorophenyl)‐4‐methylene‐1,3‐dioxolane with vinyl monomers

“…Tsitsilianis et al 18–20 showed that the transition detected near the theta conditions is a general phenomenon and is induced mainly by the rotation around the carbon–carbon bonds in the main chain.…”