Thermoreversible gelation of isotactic polystyrene: thermodynamics and phase diagrams

Abstract

The thermodynamics of thermoreversible gelation of isotactic polystyrene in cis-decalin, frans-decalin, and 1-chlorodecane was investigated by using differential scanning calorimetry. The gel formation and the gel melting were studied as a function of various parameters such as the cooling or heating rate and the polymer molecular weight. The temperature-concentration phase diagrams were established from both cooling and heating experiments. It is found that the shape of the phase diagram is the same in heating or in cooling, but that for cis-decalin differs from the one for tron.s-decalin. The phase diagrams correspond to various types of compound: congruently melting compound in cis-decalin and compound characterized by a singular point in trans-decalin. In addition, it is shown from optical microscopy experiments and X-ray diffraction experiments that the threefold helical form reappears beyond 50% polymer concentration in tnms-decalin but does not in cis-decalin.

Non‐Helical Chain Conformations of Isotactic Polymers in the Crystalline State

“…In agreement with the research of Guenet et al, [21][22][23][24][25][26]30] we hypothesize that the chain conformation in the nascent gel should not be very different from that in solution. [27] The chain conformation of i-PS in the stretched dry gels is, hence, derived from that one present in solution, in a rather straightforward manner.…”

“…[15] The sub-periodicity of 0.51 nm, indeed, would correspond to a repetition length of a dimeric unit in a vinyl polymer with the backbone in an almost fully extended (all-trans) conformation which, for isotactic vinyl polymers, is not energetically feasible. [13,[16][17][18] In agreement with more recent studies supporting the presence in the i-PS crystalline gels of chains in a nearly 3/1 -(TG) 3 -helical conformation in the crystalline phase [19][20][21][22][23][24][25][26] and based on simple considerations about the conformational statistics of polymer chains in solution, [27] we present a structural model of the conformation of i-PS chains in the crystalline gels here.…”

Crystallization of Poly(ethylene oxide) from Solutions of Different Solvents

“…4, 5 However, studies on the solvent effect have been done exclusively for single crystals from very dilute solutions, and the general characteristics of the solvent effect on solution crystallization have not yet been fully elucidated even from the phenomenological point of view. In some cases, strong interaction between a polymer and a solvent results in the formation of a polymersolvent compound 6, 7 or in physical gelation, [8][9][10][11] while in other cases, a liquid-liquid phase separation process may play a role in the crystallization. 10, 12, 13 However, the effects of liquid-liquid phase separation on kinetics and crystalline morphology have not been extensively studied.…”

Influence of chain structure and molecular weight of poly(vinylidene fluoride) on the morphology of its thermoreversible gels in acetophenone, ethyl benzoate, and glyceryl tributyrate

“…To explain this differences in morphology one has to consider that when a polymer solution is cooled from higher temperature, conformational changes occur from a random coil arrangement to an ordered conformer 16,17) . The ordered conformer may get solvated by the medium through compound formation and if no compound is formed, the solvation does not take place 18,19) . The solvation stabilizes the conformer from the chain folding process producing a fibrillar morphology, but where solvation is absent, the chain folding process produces a spheroidal morphology of the gel.…”