Polyamide polymers description

Fluorinated diacids offer a convenient method for introducing a perfluoro moiety into organic molecules. They are of potential interest in the preparation of polyamides and other fluorinated polymers. A detailed description of the perfluorocarboxyUc acids and their derivatives has been pubflshed (1), and a review article on polyfluorinated linear biflmctional compounds has appeared (35). 

Most of the available commercial microporous membranes such as polysulfone, polyethersulfone, polyamide, cellulose, polyethylene, polypropylene, and polyvinylidene difluoride are prepared by phase inversion processes. The concept of phase inversion in membrane formation was introduced by Resting [75] and can be defined as follows a homogeneous polymer solution is transformed into a two-phase system in which a solidified polymer-rich phase forms the continuous membrane matrix and the polymer lean phase fills the pores. A detailed description of the phase inversion process is beyond the scope of this section as it was widely discussed in Chapters 1 and 2 nevertheless a short introduction of this process will be presented. 

General Description Nylon is a generic name for a family of long-chain polyamide engineering thermoplastics which have recurring amide groups [-CO-NH-] as an integral part of the main polymer chain. The nylon family members are identified by the number of carbon atoms in the monomers. Where two monomers are involved, the polymer will carry two numbers (e.g., nylon 66). Commercial nylons are as follows nylon 4, nylon 6, nylon 66, nylon 6/10,nylon 6/12, nylon 11,and nylon 12. 

General Description Elf Atochem Pebax Resins, breathable resins, are polyether block amides (PEBAs), thermoplastic elastomers made of a flexible polymer and a rigid polyamide. Extruded films made with Pebax are compact, thoroughly waterproof, and breathable. 

The connection between liquid crystallinity (mesomorphism) and polymers can arguably be dated from 1950 with Elliott and Ambrose s description of birefringent chloroform solutions of the synthetic polypeptide polyCybenzyl-L-glutamate). Robinson s reports, begun in 19562, on careful studies of such solutions, firmly established the phenomenon of lyotropic (solvent induced) liquid crystallinity in polymers. In the 1960 s industrial research into what later proved to be thermotropic liquid crystalline polymers - linear para-substituted aromatic polyesters - was actively pursued. The now famous discovery in 1965 by Kwolek at du Pont of lyotropic liquid crystallinity in aromatic polyamides led to the highly successful Kevlar materials. 

CH1 Cheng, L.-P., Dwan, A.-H., and Giyte, C.C., Membrane formation by isothermal precipitation in polyamide-formic acid-water systems 1. Description of membrane morphology, J. Polym. ScL PartB Polym. Phys., 33, 211, 1995. 

On the basis of the results obtained so far using the three methods mentioned above, a relevant conclusion can be drawn the accurate temperature control (S 170 ° C) permits to mn polymerizations of CL in quasi-isothermal conditions and very efficiently contribute to the minimization of side reactions, the other relevant factor in this respect being the use of very fast activator/initiator pairs. Only the simultaneous effect of both factors, that is, temperature control and very fast catalytic systems, allows to reach both optimum process conditions and excellent polymer properties. The use of slow activators, such as N-acetyl-CL, on the contrary, strongly limits possible advantages of the method. Moreover, it should be taken into account that in general, solution polymerizations (methods 1 and 3) ate characterized by lower reaction rates as compared to suspension processes (method 2). On the other hand, these latter methods have to face more difficult and expensive purification procedures of the polyamide from the reaction mixture. The only other lactam-based polyamide synthesized in powder form in laboratory by a suspension process is poly(2-pyrrolidone). A description of its synthesis is given in Section 4.14.11.1. 

This brief description of the appearance of the liquid-crystalline state in solutions concerned rigid-chain polymers, PEG in particular (in coiling solvents), aromatic polyamides with phenyl units in the para position, and some... 

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