Solution and Melt Processes

Solution and Melt Processes 2.1 Solution Spinning and Drawing... 

Figure 1.41 Schematic representation of steps involved in the formation of ICP-based blends/composites via solution and melt-processing techniques.

In an attempt to improve solution and melt processability of polythiophene, researchers [96] recently prepared thiophene-dimethylsiloxane homopolymers. First, 3-allythiophene and a dimethylsiloxane oligomer containing 4 siloxane units are reacted in the presence of a platinum catalyst. Next, the thiophene ring is oxidized by ferric chloride in chloroform for 24 hours. 

Moore RB et al (2005) Alteration of membrane properties of perfluorosulfonate ionomers using solution and melt processing procedures. Abstracts of Papers of the American Chemical Society. 230 p 756-POLY... 

What are the properties of the sulfonate group that make it so popular for use in modification of CP systems for enhanced solution and melt processibility ... 

ABSTRACT. The poly(3-alkylthiophenes) represent a new generation of conducting polymers, that exhibit both solution and melt processability. These properties open new possibilities for the utilization of conducting polymers in practical applications. Fur eimore, the solubility of these polymers enables the characterization of the physical and chemical structure in greater detail than hitherto have been possible. In this chq)ter we give a brief review of the synthetic routes to the poly(3-alkylthiophenes) as well as an overview of some of the recent results on the physical and chemical characterization of this class of materials. In diis overview we include results on stability properties, transport properties, thermo- and solvatochromism. We also discuss some aspects of the utilization of the poly(3-dkyltiiiophenes) in plications. 

Another class of polymer that has received attention is based on PPP, e,g, poly(l,3-phenylene), poly(thio-l,4-phenylene) (11 poly(p-phenylene sulfide), PPS), etc A major advantage of PPP and PPS is that the undoped polymers are solution- and melt-processable. PPS is also available commercially. The physical properties of these polymers, undoped and doped, have been interpreted in terms of the bipolar on model. The validity of this approach has been questioned by chemical analysis, which has shown that these materials are complex mixtures of dissimilar oligomers rather... 

This monograph compiles the latest research on the chemistry of complex fluorides and oxyfluorides of tantalum and niobium, and covers synthesis and fluorination processes, crystal structure peculiarities and crystal chemical classification, as well as the behavior of complex ions in fluorine solutions and melts. 

Development of several new siloxane-imide copolymers for commercial applications have also been reported by Lee 181) and Berger58). Although no information was given in terms of the chemical compositions of these materials, most of these polymers were reported to be processable by solution or melt processing techniques, most probably due to their high siloxane contents. However, due to the presence of low (—20 to —120 °C) and high (>230 °C) temperature Tg s, it was clear that multiphase copolymers have been synthesized. Molecular weights and thermal stabilities, etc, were not reported. 

AIChESymp. Ser. (a) 65 (1969) no. 95, Crystallization from solutions and melts (b) 67 (1971) no. 110, Factors affecting size distribution (c) 68 (1972) no. 121, Crystallization from solutions Nucleation phenomena in growing crystal systems (d) 72 (1976) no. 153, Analysis and design of crystallisation processes (e) 76 (1980) no. 193, Design, control and analysis of crystallisation processes (f) 78 (1982) no. 215, Nucleation, growth and impurity effects in crystallisation process engineering (g) 80 (1984) no. 240, Advances in crystallisation from solutions. 

Knowledge of the molecular weight and of the molecular-weight distribution of a polymeric material is indispensable for scientific studies as well as for many technical applications of polymers. They effect the solution and melt viscosity, the processability, and the resulting mechanical properties tremendously. Therefore, we will give a short introduction into methods that allow us to determine the required information. Roughly, the methods developed for the determination of molecular weights are subdivided into absolute and relative methods ... 

In contrast to solid state crystallization, crystallization from vapor, solution, and melt phases, which correspond to ambient phases having random structures, may be further classified into condensed and dilute phases. Vapor and solution phases are dilute phases, in which the condensation process of mass transfer plays an essential role in crystal growth. In the condensed melt phase, however, heat transfer plays the essential role. In addition to heat and mass transfer, an additional factor, solute-solvent interaction, should be taken into account. 

Of the various synthetic processes that are available, two are of most relevance in the present context - precipitation from aqueous solution and melt forming. These methods are used where it is not possible to produce adequate products directly from natural sources. This will be because there is no suitable mineral, due to the chemical nature of the product, of particle size and shape requirements, or to purity considerations. The other principal synthetic method in use for filler production is pyrolysis/combustion. This type of process in which the particles are formed in the gas phase is used where very small particles are required, such as with carbon blacks and some silicas. This type of filler is not widely used in thermoplastics and so these processes are not discussed in any detail here, although some information specific to the production of antimony oxide will be found later. 

The concept of free-volume appeared to be very useful and was applied for the theoretical description of many processes in liquids, including polymeric solutions and melts. Taking the free-volume concept as a basis, theories were developed for the diffusion of low-molecular-weight compounds into polymers14,1S, thermal conductivity16, solution and solubility of polymers17, etc. 

In application to very concentrated solutions, the optical anisotropy provides the important means for the investigation of slow relaxation processes. It is important to confirm whether or not there is any deviations from the stress-optical law in the low-frequency region for a polymer melt with different lengths of macromolecules. In fact, this is the most important thing to understand the details of the slow relaxation behaviour of macromolecules in concentrated solutions and melts. The evidence can be decisive for understanding the mechanism of the relaxation. 

De Gennes scaling concepts for polymer solutions and melts and the concept of reptation movement of polymer chains in melts Pennings discovery of chain extension and shish-kebab formation in stirred solutions of very high MW polyethylene this eventually led to the ultra-high modulus gel-spinning process of polyethylene... 

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