Polymer modification polyacrylonitriles

Recently, nitrilases have been applied to polymer modification, specifically to the modification of polyacrylonitrile (PAN). Nearly 3 x 106 tons of PAN are produced per annum and used in the textile industry. However, there is a great need to improve moisture uptake, dyeability with ionic dyes, and feel of this acrylic fiber. The cyano moieties of PAN have been successfully modified to carboxylates with the commercial Cyanovacta nitrilase, thus enhancing the aforementioned properties of PAN [98]. Nitrilase action on the acrylic fabric was improved... 

Perhaps the most thoroughly investigated approach is the modification of preformed polymers in particular poly(vinyl isocyanate) and polyacrylonitrile Figure 29.21). 

Among the various types of polymers the problem of chemical modification of polyacrylonitrile8 (PAN) and polyacrylonitrile fibres attracts the ever growing attention of numerous investigators. 

Perhaps one of the best known syntheses of a heterocyclic polymer via the modification method is the generation of nitrogen-containing ladder polymers by pyrolysis of polyacrylonitrile) (77MI11109). The thermolysis is known to take place in discrete steps. The first step in the sequence, which can take place with explosive violence if the heating rate is not sufficiently slow, occurs at about 150 °C and can be detected by the onset of intense color formation. The product of this reaction (Scheme 101) is the cyclic tetrahydropyridine ladder structure (209). The next step, which is conducted in the presence of air at ca. 250 °C, involves the thermooxidation of polymer (209) to form what is best described as terpolymer (210) containing dihydropyridine, pyridone and pyridine units. 

Belfort, G. and Ulbricht, M., Surface modification of ultrafiltration membranes by low temperature plasma. I. Treatment of polyacrylonitrile, J. Appl. Polym. Sci., 56, 325, 1995. 

Apart from natural materials, oxidoreducates have been used to modify synthetic polymers. For example, using peroxidase, poly(4-hydroxystyrene) has been functionalized with aniline while poly(p-phenylene-2,6-benzobisthiazole) has been rendered more hydrophilic [22, 23]. Other authors have demonstrated that phenolics can be covalently bound to amino-functionalized polymers by using laccase resulting in increased fire resistance [13]A large number of scientific reports are available on enzymatic functionalization of poly(alkyleneterephthalate)s. Polyester fibers account for 73% of all synthetic fibers on the market with an annual production of approx. 27 million tons [24]. Similarly, polyamides and polyacrylonitriles have significant market shares. In contrast to natural polymers discussed above, hydrolases have shown higher potential for modification of these synthetic materials than oxidoreducates. 

Ghosh P, Ganguly PK (1994) Polyacrylonitrile (PAN)-grafted jute fibers some physical and chemical properties and morphology. J Appl Polym Sci 52 77-84 Goyal P (2008) Chemical modification of tamarind kernel powder. Ph. D. thesis. Forest Research Institute, Deemed University, Dehradun, India... 

A modification of bulk polymerization that is a heterogeneous system is one in which the polymer product precipitates. Typical polymers that can be produced by this technique are polyacrylonitrile and polyvinyl chloride. The polymerization rate for polyvinyl chloride is given by... 

Modification of polyurethanes as a blood contacting material is achieved by coating the polymer surface with heparin as the most suitable biomolecule that avoids thrombogenesis. The immobilization needs a functionalized surface that may offer sites for the heparin bonding. It is observed that helium plasma treatment of polyacrylonitrile and polysulfone followed by exposure to air leads to peroxide species of the order of 10 nmol/cm which are available for decomposition... 

HoUow fibers are widely used for filtration, utilizing the semipermeable nature of their capillary walls. In the medical industry, hollow fiber bioreactors are often made from cellulose and synthetic polymers. Cellulose acetate and cuprammonium rayon are the widely used ceUulose-based hollow fibers, while synthetic hollow fibers are often made from polysulfone, polyamide, and polyacrylonitrile. Modifications can be made to these materials to improve their functions by using polymers based on phospholipid, a substance found in the human cell membrane. 2-methaCTyloyloxyethyl phosphoryl-choline (MPC) is a methacrylate monomer with a phospholipid polar group. When MPC-based copolymers are used as additives for polysulfone, protein adsorption and platelet adhesion can be effectively reduced, thereby improving blood compatibility. Cellulose acetate hollow fiber membranes can also be modified with MPC-based copolymers by means of blending or surface coating to obtain improved permeability. 

Shahinpoor [930], working at the "Artificial Muscles Research Institute", University of New Mexico, Albuquerque, NM, USA, fabricated devices for a wide variety of applications based on electrochemomechanical principles, from ion conducting polymers (not CPs). These polymers included poly(acrylic acid-bisacrylamide) (PAAM), poly(2-acrylamido-2-methylpropanesulfonic acid (Poly(AMPS)), and polyacrylonitrile (PAN). While these are not CPs, Shahinpoor also indicated that similar action could be expected, with minor modifications, from CPs such as poly (ary lene vinylenes) and poly(thienylene vinylenes). Shahinpoor typically used a metal (e.g. Pt) + ion conductive polymer composite in place of the customary bilayers. Some of the applications envisioned, or demonstrated for ion conductive polymers, included microactuators, motion sensors, accelerometers, oscillating artificial muscles, inchworms, cardiac>circulation assistants, noiseless propulsion swimming robots for military applications, fully constituted contractile artificial muscles, miniature flying machines, and electrically controllable adaptive optical lenses (Fig. 21-51. The potential military applications of these have fueled much interest recently [931]. 

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