Nylon-MXD6 (PA-MXD6)Lum disclosed in 1956 that PA-MXD6 is a semicrystalline polymer in spite of the meta configuration of the MXDA (m-xylylenediamine) [1, 2]. Carothers had described in 1940 the preparation of a nylon using a xylylenediamine, but it was the para-isomer. PA-MXD6 attracted study by textile fiber manufacturers; its unit cell [3] and rate of crystallization [4] were determined. The unit cell is triclinic with dimensions of a=1.201 nm, b=0.483 nm, c=2.98 nm, and fiber axis angles of PA-MXD6 can be prepared in much the same manner as PA-66 Lum used a low steam pressure of 400 to 700kPa (58 to 100psi) in the early stages of polymerization to depress the melting point and avoid decomposition of the diamine [5]. Subsequent work [6] showed that the low volatility of MXDA voids the need for water so the early stages can proceed under atmospheric pressure. MXDA can be added continuously to molten adipic acid (m.p. 153°C) until the NH2/COOH ratio approaches 1 and the condensation has produced high molecular mass oligomers with a corresponding increase in the freezing point. The required mole ratio of unity can be obtained with sufficient accuracy by gravimetric or volumetric feeders and strict control of diamine loss. Isolation of the MXD6 salt (m.p. 189°C) and pH measurement of an aqueous solution are unnecessary. The combination of the relatively high boiling point (274°C) of MXDA, the relatively low melting point (243°C) of the polymer and the depression of the freezing temperature by water of condensation allows preparation of resin of reasonably high molecular mass. Exposure to a vacuum or solid phase polymerization can be used to achieve higher levels. MGC makes several grades of
PA-MXD6 crystallizes slowly when dry even at the optimum temperature of 170 °C (see Fig. 2.1). As shown, its crystallization behavior differs from that of the aliphatic nylons and is more like that of PET, poly(ethylene terephthalate). If unstretched it gives an opaque product with large spherulites. An amorphous resin is easily obtained by quenching the melt, but the absorption of water accelerates crystallization. The dry Tg of PA-MXD6, which is 31% to 33% crystalline, is 102°C in a dynamic mechanical test and 85°C by DSC at 10°C/min. The Tg by DSC decreases linearly with RH and is about 52°C, 40°C, and 15°C at 50%, 65%, and 100%RH respectively. The rate of crystallization under "standard" conditions depends on the accepted standard. It is faster at the Japanese conditions of 20°C and 65%RH than at the United States practice of 23°C and 50% RH. Unstretched, amorphous PA-MXD6 is unstable; crystallinity in shaped articles should be assured by adequately high mold temperatures (120 °C to 150 °C) or by annealing (1 h at 130 °C is recommended) .
PA-MXD6 is processed at 250 °C to 290 °C. A resin with a
Property data for injection molded, neat PA-MXD6 and resin with 50% glass fiber are provided in Table 2.1. PA-MXD6 is marketed as a molding resin by MGC under the Reny trade name [7 to 12] and by Solvay as Ixef [13, 14]. The PA-MXD6/PXD6 copolymer has similar mechanical properties to the homopolymer, but it has a higher melting point (258 °C versus 243 °C), a higher Tg by about 10 °C, and a higher deflection temperature under a 1.8 MPa (264 psi) load (244 °C versus 234 °C). The copolymer also crystallizes significantly faster. The need for precise control of composition and rate of crystallization, particularly to exploit potential utility as a fiber, was the incentive for homopolymer development. The water absorption of the neat resin with 31% to 33% crystallinity is 1.9, 3.1, and 5.8 wt% at 50%, 65%, and 100% RH, respectively. High mechanical strength, modulus, and heat resistance make the reinforced polymer suitable as a metal substitute. Its good flow, low moisture absorption, and chemical resistance enhance its usefulness. Almost all of the molding materials developed by MGC contain glass fiber. Other modifiers that are used, often in combination with the glass fiber, include carbon fibers, whiskers, minerals, and flame retardants. The common additives such as nucleating agents, mold release agents, and colorants are also used. All help to account for the development of over 30 grades that are used to make parts for the automotive, machine, electrical/electronic, civil engineering, sports, and miscellaneous other industries. Examples are car mirror stays, car door handles, watch gears, opera glass cylinders, nails, bolts, fishing reels, scissors, reel hubs, pulleys, screws, bobbins, connectors, etc.
Extrusion applications, especially as a barrier material, are important. The physical properties of biaxially oriented film are shown in Table 2.2. Toyo Boseki found excellent gas barrier properties (particularly, low oxygen permeation) in the biaxially oriented film of PA-MXD6 and developed packaging materials such as flexible film [15] and multilayer, stretch-blown bottles [16]. The oxygen permeability of PA-MXD6 is much lower than that of PA-6 or PET. It is a minimum at 60% to 70% RH, but its dependence on % RH is less than that of ethylene/vinyl alcohol copolymer (EVOH) in the 80% to 100% RH region. Furthermore, the barrier to oxygen is better than that of poly(vinylidene chloride) (PVDC) in the 40% to 80% RH range. This behavior at low and high % RH makes application practical both at atmospheric conditions and in wet food packaging. In the late 1980's, CMB found the incorporation of small amounts of cobalt compounds produce an oxygen scavenging system and enhances performance as an oxygen barrier [17]. The availability of grades with different molecular masses permits use as components of polymer blends or multilayer films for retortable pouches, cup lids, flexible tubing, rigid bottles, etc. [18 to 20]. Packaged materials include soup, jelly, curryroux, ham sausage, printing ink, cleanser, cosmetics, wine, beer, soft drinks, seasoning, etc. PA-MXD6 blends are also used in applications where barrier properties are not important; these include buttons, fishing line, paper coating, and nonwoven fabrics. References1. Lum, F.G.; Carlston, E.F.; Butler, J.C. U.S. Patent 2 766 211, 1956. [BACK]
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=75.0°,
=26.0°, and 
=65.0°. The conformation differs from a planar zigzag arrangement by inclination of the planes to the c axis by a few degrees. Research, however, was limited to the laboratory because MXDA was not a commercial product although mixtures of PXDA and MXDA (30:70) were available. m-Xylene, which was essentially free of p-xylene did not become available until 1968 when the Mitsubishi Gas Chemical (MGC) began its production. PXDA-free MXDA followed in 1971. This made possible the commercial production of PA-MXD6 that was free of sizable quantities of the para-isomer.
=16,000 to 40,000 and has developed the following expression based on end group analysis.
-1.10) where 1.4 < 
