Solidification of syndiotactic polystyrene by a continuous cooling transformation approach

Syndiotactic polystyrene (sPS) was solidified from the melt under drastic conditions according to a continuous cooling transformation methodology developed by the authors, which covered a cooling rate range spanning from approximately 0.03 to 3000 °C/s. The samples produced, structurally homogeneous across both their thickness and surface, were analyzed by macroscopic methods, such as density, wide-angle X-ray diffraction (WAXD), and microhardness (MH) measurements. The density was strictly related to the phase content, as confirmed by WAXD deconvolution. The peculiar behavior encountered (the density first decreasing and then increasing with the cooling rate) was attributed to the singularity of the phases formed in sPS; that is, one of the crystalline phases (α) was less dense than the amorphous phase, and the latter, in turn, was less dense than the other crystalline phase (β). With an increasing cooling rate, the thermodynamically stable phase (β) disappeared first, and it was followed by the α phase. On the other hand, the MH values remarkably depended on the amount of the β phase, the α-phase content influencing the mechanical properties only to a minor extent. The behavior of the crystallization kinetics was described through a modified multiphase Kolmogoroff–Avrami–Evans model for nonisothermal crystallization

Polymer-Slvent Compounds

+110hlm.;24c

Molecular blending by polymerisation of intercalated solvents in polymer/solvent gels

Recently, with the help of in-situ small- and wide-angle X-ray scattering experiments combined with Raman spectroscopy and thermal analysis we have investigated the phase behaviour of several polymer/solvent systems. Some examples of these systems are syndiotactic polystyrene/benzylmethacrylate (sPS/BzMA) and polybenzyl-L-glutamate/benzylmethacrylate (PBLG/BzMA). Benzylmethacrylate is chosen as the solvent because it contains a phenyl ring, which forms the basis for specific interactions between the polymer and the solvent and because of the presence of a polymerisable unit. When sPS solutions are quenched, gel formation occurs. In these gels sPS adopts a helical conformation. For the sPS/BzMA system, the solvent intercalates with the stereo-regular polymer and forms its own structure, giving rise to a solvent ordered peak in the X-ray pattern. For reference see, Macromolecules 1998, 31, 2983-2998. Also for the glutamate system intercalation of the solvent molecules within the helical conformation is observed, which results in a regular order in the intercalated solvent. For both systems it was found that even after polymerisation of the intercalated solvent the side chains of the polymerised solvent remained intercalated, thus stabilising the compound. This method can therefore be used as a novel route to obtain blending at the molecular level between the polymer and the polymerised solvent. Moreover, as the parent polymer is stereo-regular, at the right stochiometric ratios between the polymer and the solvent it may be anticipated that the polymerised solvent will have the same stereo-regularity as of the polymer

A study on the ordering of intercalated solvents in poly-benzyl-L-glutamate : in-situ Raman and X-ray scattering investigations

A polymer/solvent system can form a gel due to specific interactions between the polymer and the solvent. For poly-benzyl-L­glutamate/solvent systems, gelation can be based on carbonyl or phenyl ring interactions, depending on the solvent. The present paper describes X-ray scattering and Raman investigations on cast films of poly-benzyl-L-glutamate (PBLG) and benzylmethacrylate (BzMA). The studies indicate that in the cast samples separate zones of PBLG and BzMA are present. Upon heating, the system homogenises and the PBLG molecules pack in a pseudo hexagonal lattice. At approximately 150 "C a new reflection at I 1.4 A in the WAXS pattern arises. This reflection is attributed to structural ordering of the solvent, due to intercalation of the solvent molecules within the helices of PBLG. The observed changes in the WAXS pattern upon heating are supported by Raman experiments

Inverse melting in syndiotactic polystyrene

Syndiotactic polystyrene (sPS) is a semicrystalline polymer for which several crystalline structures can be obtained. Cold crystallization of an amorphous sPS sample results in the formation of the a-phase, for which a close packing of the chains is hindered by the phenyl rings. This results in the unusual situation that the density of the crystalline phase (1.03 g cm-3) is lower than that of amorphous sPS (1.04 g cm-3). It is shown that as a result a line where the difference in specific volume between the liquid and crystal is zero (¿V = 0 line) is observed in the p-T phase diagram (similar to P4MP1). At the point where this line intersects with the melting line the slope of the melting line becomes negative. Another remarkable phenomenon is that the crystalline a-phase disorders either with the application of pressure at room temperature (below Tg) or on cooling isobarically at high pressure. These observations, obtained via WAXD, SAXS, HP-DSC, and Raman spectroscopy experiments, give an indication for the existence of a reentrant phase behavior, first described by Tamman in 1903

Correlating molecular and crystallization dynamics to macroscopic fusion and thermodynamic stability in fused deposition modeling; a model study on polylactides

To define molecular parameters for fused deposition modeling of mechanically integral polylactide parts, the effect of intrinsic local heat fluctuations on morphology and structure evolution is studied. Macroscopic fusion during melt deposition is governed by molecular dynamics of solidification and positively affected by low print speed, low molar mass. However, low molar mass and high L-enantiomeric purity induces melt crystallization during deposition, limiting interfacial molecular diffusion. By increasing molar mass crystallization during melt deposition is suppressed, establishing interfacial molecular diffusion and mechanically effective interfaces. Further structure evolution via cold crystallization is timed in successive annealing cycles. Adding more layers entails a progressive decrease (i) in heat transfer to the build plate and (ii) number of annealing cycles per layer, inducing variations in crystallinity and thus thermodynamic instability. Consequently, macroscopic mechanics and geometrical stability of fused deposition modeled polylactides are compromised by judiciously timed crystallization and process design. (C) 2018 Elsevier Ltd. All rights reserved