Polymer-Controlled Crystallization

Among the various possible additives for the control of crystallization events, polymers as a class of siuTactants , stabilizers, fimctional additives or a soft template have been foimd to play key roles in bio-inspired approaches for mimicking the biomineraUzation process. The most important role of hydrophilic polymers in that respect is certainly that of a novel surfactant or particle stabilizer. Such surfactants are not always siuTace-active in a classical sense (i.e., hydrophilic-hydrophobic being attracted by the air/water or oil/water interface), but can also become selectively attracted by mineral or metallic surfaces, only in aqueous solution [146,147]. 

Biopolymers are often a natural soluble additive choice for morphogenesis of complex crystalline superstructiues [148] due to their role in biomineralization, even though it is still difficult to reproduce complex biomineral shapes because an insoluble matrix strongly influences the crystallization lo- 

In the following sections, recent advances in the area of bio-inspired mineralization via morphosynthesis of various inorganic minerals by use of biopolymers, various synthetic polymers, and block and graft copolymers will be discussed with a clear focus on recent developments in this rapidly emerging field. Some recent reviews at least partially covering the focus of the present overview exist and shall be mentioned here to allow the reader to find further detail [26,34-36,40,43-45,57,105,113,149-152]. 

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Wang, T. An-Wu Xu and H. CoRen, Ermnation of self-organized dynamic structure patterns of barium carbonate crystals in polymer controlled crystallization. Angew. Chem. hrt Ed. 45, 4451 (2006)... 

Reflection on the above points already indicates that an even further increased scientific interest into polymer-controlled crystallization can be expected. This field is mifltidisdplinary because it is of interest for mifltiple scientific disciplines. Bio-inspired minerahzation is straight at the heart of several key development fields for futme technological benefit. Therefore, it will be of importance that multidisciplinary teams of researchers share their ideas and results in this complex field. 

In the following sections, we will discuss recent advances in the area of polymer controlled crystal growth and morphogenesis of various inorganic minerals by the use of biopolymers, various synthetic polymers, and non-... 

The latest results of a controlled crystallization of macromolecules are the polymer fibrids which are a completely new modification of synthetic polymers as far as the micro- and macro-structure is concerned. They exist of small fibers having a length of up to some millimeters, which are highly oriented, and which have a macro-morphology similar to that of cellulose pulp. 

Thus, it is concluded that as far as possible experiments should be made on single crystal samples using guard ring techniques under conditions where the ambient atmosphere may be rigorously controlled. In the case of polymers single crystal samples of any size are virtually impossible to obtain. 

The exact make-up and architecture of the polymer backbone will determine the ability of the polymer to crystallize. Figure 15.7 shows the different types of microstructure that can be obtained for a vinyl polymer. Isotactic and syndiotactic structures are considered stereospecific polymers, and their highly regular backbone structure allows them to crystallize. The atactic form is irregular and would produce an amorphous material. This nature of the polymer microstructure can be controlled by using different synthetic methods. As will be discussed below, the Ziegler-Natta catalysts are capable of controlling the microstructure to produce different types of stereospecific polymers. 

SSP [Solid State Polymerization] Also called UOP Sinco SSP. A process for making articles from PET (polyethylene terephthalate) and related polymers. The key step is controlled crystallization of the polymer under optimum conditions. Developed jointly by UOP (United States) and Sinco (Italy) and widely adopted since 1986. 

The extent to which this polymer can crystallize under given conditions is controlled by the butene concentration. 

Y. Onogi, T. Hayashi, Y. Mizushima, and M. Yamamoto, Liquid crystal formation control of polymer liquid crystal mixtures by photoirradiation of azobenzene moiety, Nippon Kagaku Kaishi 1990, 815-819. 

T. Ikeda, O. Zushi, T. Sasaki, K. Ichimura, H. Takezoe, A. Fukuda, and K. A. W. Skarp, Photochemical control of switching behaviors of ferroelectric polymer liquid crystals Poly[2-methylbutyl4 -(l(0-acryloyloxydecyloxy)-biphenyl-4-carboxylate)], Mol. Cryst. Liq. Cryst. 225, 67-79 (1993). 

This article describes the solid state polymerization of 1,i-disubstituted butadiene derivatives in perovskite-type layer structures, in layered structures of organic ammonium halide salts, and in lipid layer structures. Recent investigations by spectroscopic methods and x-ray structure analyses are described. The studies clearly indicate that the photolysis in the crystalline state leads to the formation of 1,i-trans-polymers exclusively. Crystal structure analyses of monomeric and polymeric layer perovskites demonstrate that upon y-irradiation a stereoregular polymer is obtained in a lattice controlled polymerization. 

Much work has been reported on studying the structure of thermoset resins via SAXS, especially focussing on interpenetrating network polymers (IPNs), thermoset nanocomposites, rubber-modified thermosets and thermoset-thermoplastic blends. Most recently Guo et al, (2003) have examined the use of SAXS to monitor the nanostructure and crystalline phase structure of epoxy-poly(ethylene-ethylene oxide) thermoset-thermoplastic blends. This work proposes novel controlled crystallization due to nanoscale confinements. 

Interesting supramolecular structures can furthermore be obtained by the controlled crystallization of polymers hke polyethylene or nylon-6,6 on carbon nanotubes. The latter serve both as template and as nucleus of crystallization. There are in principle three modes of how a polymer crystal might grow on a nanotube surface (a) Phase separation may occur in the course of the crystallization so the initially dispersed carbon nanotubes rea omerate and precipitate, (b) The polymer coils around the individual tubes whose solubility increases in the sequel,... 

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