Solvent induced crystallization

The experimental growth rate data of Fig. 11.32 are plotted against in Fig. 13.34. The shapes of the curves are now similar to one another and the data for several of the mixtures fall on the same curve. The maxima for all compositions occurs at = 0.57. From the data given, the ratio of is about 0.85 for the isotactic 

The crystallization process can he initiated, or accelerated, by interaction with appropriate solvents. Two different situations can be distinguished. In one case, 

The isotherms that represent crystallization that is solvent induced do not always give the typical sigmoidal shape found in conventional crystallization. (95,96,98-104) Examples are given in Fig. 13.35 for the solvent induced crystallization of poly(ethylene terephthalate) by either dioxane or nitromethane.(96) The isotherms in this figure do not resemble those of the Avrami type. It can be suspected that the penetration of the solvent and its diffusion through the sample is rate determining. This suspicion is confirmed by the plots in Fig. 13.36.(104) Here the crystallinity is 

The experimental results indicate that in solvent induced crystallization there is an interplay between the conventional Avrami type kinetics and the diffusion of the solvent through the polymer sample. There are many different factors involved. These include the type of diffusion, whether or not Pick s law is obeyed, the geometry and dimensions of the sample and the role of the solvent in reducing the glass and equilibrium melting temperature, and the solubility parameter among others. (104a) Complete analysis of this crystallization process is obviously 

in Integration of Fundamental Polymer Science and Technology, P. J. Lemstra and L. A. Kleitjens eds., Elsevier (1988) p. 346. 

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It was shown (8,9) that the pretreatment of PET yarns with certain strongly interacting solvents can lead not only to swelling but also to irreversible modifications of polymers structure. The basis of structural modification during the DMF treatment of PET is solvent-induced crystallization which occurs while the PET structure is swollen by DMF. At low treatment temperatures (i.e., 50-100°C, Table I), only small crystallites are formed and after removal of the solvent the swollen structure cannot be supported by the small crystallites and consequently collapses. 

These solvents include tetrahydrofuran (THF), 1,4-dioxane, chloroform, dichloromethane, and chlorobenzene. The relatively broad solubility characteristics of PSF have been key in the development of solution-based hollow-fiber spinning processes in the manufacture of polysulfone asymmetric membranes (see Hollow-fibermembranes). The solvent list for PES and PPSF is short because of the propensity of these polymers to undergo solvent-induced crystallization in many solvents. When the PES structure contains a small proportion of a second bisphenol comonomer, as in the case of RADEL A (Amoco Corp.) polyethersulfone, solution stability is much improved over that of PES homopolymer. 

Figure 18.5 8-Form of SPS solvent-induced crystallized form with incorporation of toluene in the lattice...

An illustrative example for solvent polymer interactions is the solvent induced crystallization of polycarbonate. Amorphous PC was reported to crystallize when in contact with butyl acetate vapor. Figure 4.35 shows a 2D spherulite grown almost to a fully round envelope. These spherulites resemble spherulites grown from the melt. With an AFM, the growth can be in principle followed in real time down to the nanometer level. 

Fig. 4.35 Contact mode AFM image of semicrystalline PC surrounded by an amorphous film. The solvent-induced crystallization process results in spherulitic growth. Reprinted with permission of John Wiley Sons, Inc. [66]. Copyright 1996. John Wiley Sons, Inc.

This report summarizes recent work on a process for the physical modification of polyester fiber surfaces via solvent Induced crystallization (SING). New experimental results show ... 

To be clear, the phenomenon of cleavage-induced crystallization should not be confused with solvent-induced crystallization, in which mobility is increased by the lowering of the glass transition temperature. We are also not referring to the well-known effect of molecular weight on mobility and hence crystallizability. Instead, it is based on removing a physical restraint of the molecular chain. 

Solvent induced crystallization [152] and fracture toughness [153] have been studied. 

Nelson KM, Seferis JC, Zachmann HG, Solvent-induced crystallization in polyetherimide thermoplastics and their carbon-fiber composites, J Appl Polym Sci, 42(5), 1289-1296, 1991. 

Vittoria V, De Candia F, lanelli P, Immirizi A (1988) Solvent-induced crystallization of glassy syndiotactic polystyrene. Makromol. Chem. Rapid. Commun. 9 765-769. 

An understanding of the solubility of polysulfones is important for applications in which the polymer must be dissolved, such as in coatings and membrane applications. Solubility of the three commercial polysulfones follows the order PSF > PES > PPSE All three polysulfones can be dissolved in a small number of highly polar solvents to form stable solutions at room temperature. NMP, DMAc, pyridine, and aniline are suitable solvents for polysulfones. Also 1,1,2-trichlorethane and 1,1,2,2-tetrachloroethane are suitable but are unattractive for health reasons. Because of the lower solubility parameter of PSF, it can also be dissolved in several less polar solvents such as tetrahydrofuran (THF), 1,4-dioxane, chloroform, dichloromethane, and chlorobenzene. Solvent choices for PES and PPSF are fewer because these polymers have a propensity to undergo solvent-induced crystallization in many solvents. 

The good solubility of amorphous PC in contrast to the high stability of crystalline PC in THF at ambient temperatures enables separation and isolation of PC-sphe-rulites prepared by solvent induced crystallization. 

The solvent induced crystallization effect is very evident in the room temperature blend spectra shown in figure 8 which displays the PC carbonyl stretching region. 

McGrath, Robeson, and Matzner investigated block copolymers and homopolymer-copolymer blends of bisphenol-A polysulfone and nylon-6 (7). They found improved ESCR as the content of the crystalline nylon-6 block increased. Similarly, Viswanathan, al. prepared random block copolymers of bisphenol-A pFTysulfone and the partially crystalline hydroquinone polysulfone (8). ESCR improved markedly as the hydroquinone content increased. However, while the copolymers "as made" are semicrystalline, the compression molded specimens used for ESCR studies are amorphous. Hence, recrystallization from the melt was quite slow. The improvement of ESCR is attributed to solvent-induced crystallization of the surface layers, which was presumed to restrict diffusion of the liquid into the bulk. 

Another example of this class is solvent-induced crystallization (142). The effects of crystallization kinetics and rate of movement of the boundary between penetrated and impenetrated regions have been treated. Moreover, effects of increasing impediments to diffusion caused by the increasing crystalline fraction during the same time scale as that of the solvent transport are included in the model of the system. Such models become exceedingly complex and fall outside the domain of the present discussion however, they clearly require the input of information related to transport properties and their dependence on local conditions. 

The mechanism for the development of Perclene resistance is not known. It is believed that solvent induced crystallization of chain segments is responsible. It has also been suggested that since the heat treatment takes place in air that surface oxidation or cross linking may be responsible. To test this hypothesis equipment was assembled to heat treat yarn in an oven in a reasonably controlled environment of air, argon, or nitrogen. 

As-received LDPE resins exhibited crystallinities (Xc) around 45%, but the two LDPEs with lower MI had similar levels of Xc. This is presumably due to differences in branch point defects and topological constraints such as entanglements both disrupt the crystallization process. During DDC foaming, the polymers appeared to undergo thermomechanical and solvent-induced crystallization that further increased their crystallinities. The DDC foams were... 

Study of solvent diffusion and solvent-induced crystallization in syndiotactic polystyrene using FT-IR spectroscopy and imaging. Macromolecules, 38 (6), 2327-2332. 

Tashiro, K., Yoshioka, A. Molecular mechanism of solvent-induced crystallization of syndiotactic polystyrene glass. 2. Detection of enhanced motion of the amorphous chains in the induction period of crystallization. Macromolecules, 35(2), 410-414 (2002). 

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