Polymorphism in melt crystallized syndiotactic polystyrene samples

Abstract

1539eters to being orthorhombic as observed for the planar form. It is difficult to know whether these calculated values for the kink and planar forms are close enough to permit polymorphism. They apply to the energy difference at 0 K as opposed to the free energy difference at somewhere in the region of room temperature. The energy difference of 13.4 kJ/(mol repeat) corresponds to -1 kJ/ (mol chain atom) and about 13% of the calculated lattice dissociation energy. In the case of 6-6 polyester, the calculations place the planar-2 form as 9 kJ/(mol repeat) more stable energetically than the kink structure, the latter representing the experimentally observed one. This amounts to -0.6 kJ/(mol chain atom) and about 8% of the lattice dissociation energy. This is probably near the level of reliability of the calculations.In summary, it can be concluded that the kink containing structures are stable because, in the appropriate examples, the energy penalty for forming them compared to the planar counterparts is modest and they pack competitively or better than the planar forms. By the time aliphatic lengths of those in 6-10 polyester are reached the packing in planar form is less perturbed by the ester groups, the packing is favored in the latter, and the intramolecular penalty for kink formation is apparent.

Non-isothermal crystallization kinetics of syndiotactic polystyrene polystyrene functionalized SWNTs nanocomposites

“…This phenomenon is due to the competition between melting and recrystallization processes during the heating step [47]. Furthermore, a WAXD study near the melting region of about 270°C showed that the double endothermic melting behavior of sPS was caused not by a change in the crystalline form but by a recrystallization to a more perfect crystal [48]. The normalized crystallinity of sPS in the composites, X c , is given by the Equation (1): (1) where ΔH f is the melting enthalpy of sPS in the composites, ΔH f 0 is the melting enthalpy of 100% crystalline sPS (ΔH f 0 = 53 J/g) [49] and w is the weight fraction of sPS in the composites.…”

Clathrate (δ) Form Crystal Transitions of Syndiotactic Polystyrene in Atactic Polystyrene Networks

“…38 Figure 1a shows a typical 3D WAXD pattern for samples heated from 70 to 230°C with a heating rate of 2°C/ min. The results show the characteristic WAXD pattern of the sPS δ, γ, and R form crystals appears sequentially during the gradually heating procedure, which indicates that the sPS δ form crystals transfer into γ form and then into R form crystals.…”

Influence of multi-walled carbon nanotubes on the β form crystallization of syndiotactic polystyrene at low temperature

“…In particular, the formations of an instable mesophase during the crystallization of sPS at lower temperature, was clearly observed in the literature [2,8]. Even if the conformational order of the chain sequences is not sufficient to give rise to discrete X-ray reflections, the presence of mesomorphic phase can be characterized by infrared spectroscopy as well as permeability tests [8].…”

“…For this reason, the sPS β form could represent a polymeric material of industrial interest due to its high melting temperature, fast crystallization rate, good chemical and thermal resistance [2,5]. However, in spite of its thermodynamic higher stability with respect to the α form, it can be obtained only at very low under-cooling (high crystallization temperature), whereas at crystallization temperatures lower than 230°C the α form is always obtained [8]. Many attempts to obtain the β form at lower temperatures failed so far.…”