Nylon system monomers

Third, the gel times of nylon systems are much longer than those of urethanes, typically on cue order of 45 to 120 seconds, versus 5 to 30 seconds for urethanes. There are several reasons for this. First, the polymer is soluble in the monomer until very high molecular weights are attained. Second, the reactants are typically held at temperatures 30 to 90°F lower than the mold temperatures for reasons of energy conservation and product stability. At these temperatures, polymerization rate is low and pot life of the mixed stream is on the order of 5-10 minutes. For optimum physical property generation, part surface quality and release from the tool, nylon RIM molds are normally run at temperatures between 250 and 325°F. At these temperatures, gel times are typically 30 to 60 seconds for parts of about 1/8-inch thickness. Thus, part of the gel time difference is the time reauired for the reactants to rise to mold temperature by conductive heating. 

Nylon 12 first beeame available on a semieommercial scale in 1963. The monomer, dodecanelactam, is prepared from butadiene by a multistaged reaction. In one proeess butadiene is treated with a Ziegler-type eatalyst system to yield the cyclic trimer, cyclododeca-1, 5, 9-triene. This may then be hydrogenated to give cyelododeeane, which is then subjeeted to direct air oxidation to give a mixture of cyclododecanol and cyclododecanone. Treatment of the mixture with... 

The basic RIM process is illustrated in Fig. 4.47. A range of plastics lend themselves to the type of fast polymerisation reaction which is required in this process - polyesters, epoxies, nylons and vinyl monomers. However, by far the most commonly used material is polyurethane. The components A and B are an isocyanate and a polyol and these are kept circulating in their separate systems until an injection shot is required. At this point the two reactants are brought together in the mixing head and injected into the mould. 

FIRE RETARDANT FILLERS. The next major fire retardant development resulted from the need for an acceptable fire retardant system for such new thermoplastics as polyethylene, polypropylene and nylon. The plasticizer approach of CP or the use of a reactive monomer were not applicable to these polymers because the crystallinity upon which their desirable properties were dependent were reduced or destroyed in the process of adding the fire retardant. Additionally, most halogen additives, such as CP, were thermally unstable at the high molding temperatures required. The introduction of inert fire retardant fillers in 1965 defined two novel approaches to fire retardant polymers. 

Most addition polymers are formed from polymerizations exhibiting chain-growth kinetics. This includes the typical polymerizations, via free radical or some ionic mode, of the vast majority of vinyl monomers such as vinyl chloride, ethylene, styrene, propylene, methyl methacrylate, and vinyl acetate. By comparison, most condensation polymers are formed from systems exhibiting stepwise kinetics. Industrially this includes the formation of polyesters and polyamides (nylons). Thus, there exists a large overlap between the terms stepwise kinetics and condensation polymers, and chainwise kinetics and addition (or vinyl) polymers. A comparison of the two types of systems is given in Table 4.1. 

Conversion of polymers and biomass to chemical intermediates and monomers by using subcritical and supercritical water as the reaction solvent is probable. Reactions of cellulose in supercritical water are rapid (< 50 ms) and proceed to 100% conversion with no char formation. This shows a remarkable increase in hydrolysis products and lower pyrolysis products when compared with reactions in subcritical water. There is a jump in the reaction rate of cellulose at the critical temperature of water. If the methods used for cellulose are applied to synthetic polymers, such as PET, nylon or others, high liquid yields can be achieved although the reactions require about 10 min for complete conversion. The reason is the heterogeneous nature of the reaction system (Arai, 1998). 

The last of the direct methods for graft initiation in liquid phase presented in this review involves chemical additives. Either free radical or ionic initiators can be chosen. Benzoyl peroxide is reported for grafting styrene on Nylon fibers in methanol media (71,105-107), as well as vinyl acetate (106). Azoisobutyro-nitrile has been employed in systems where the graft monomer is styrene (71,106) or vinyl acetate (106). Redox systems involving hydrogen peroxide and monomers like styrene (106,108,109). vinyl acetate (106), acrylic acid (108,109), methyl... 

Hydroperoxide groups can be generated previously on the Nylon monomer, e.g. oxidizing the tertiary carbon atom of the isopropyl group of the 5-isopropyl phthaloyl chloride with potassium permanganate. The corresponding polyamide can be grafted with styrene in a redox system (151). 

There are various types of multiphase processes that are widely used in the mass production of polymers. The two phases can both be liquids, as in suspension and emulsion polymerization, or can be a gas/solid, gas/melt (liquid) or liquid/solid system. In the interfacial polymerization of nylon 6,6, for example, the two monomers are initially dissolved in different solvents, hexameth-... 

This technique can be used effectively to prepare polyesters, polyamides, and polycarbonates. The process of interfacial polymerization can best be illustrated by the reaction between a diamine and a diacid chloride to produce polyamide. The word Nykm is used to represent synthetic polyamides. The various nylons are described by a numbering system that indicates the number of carbon atoms in the monomer chains. Nylons from diamines and dibasic acids are designated by two numbers the first representing the diamine and the second the dibasic acid. Thus, nylon-6,10 is formed by the reaction of hexam-ethylenediamine and sebacoyl chloride ... 

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