Aliphatic nylons

Whilst the aliphatic nylons are generally classified as being impact resistant, they are affected by stress concentrators like sharp comers which may lead to brittle failures. Incorporation of mbbers which are not soluble in the nylons and hence form dispersions of rubber droplets in the polyamide matrix but which nevertheless can have some interaction between mbber and polyamide can be most effective. Materials described in the literature include the ethylene-propylene rubbers, ionomers (q.v.), polyurethanes, acrylates and methacrylates, ABS polymers and polyamides from dimer acid. 

Compared with aliphatic nylons it also shows greater rigidity and hardness, lower water absorption, low temperature coefficient of expansion, good resistance to heat and moisture, better electrical insulation properties, particularly under hot and damp condition, and of course transparency. 

In the absence of fire retardants the material has a limiting oxygen index of 27.5 and may bum slowly. Only some grades will achieve a UL 94 V-1 rating. The Underwriters Laboratories continuous use temperature index is also somewhat low and similar to the polyarylates with ratings of 135-140°C (electrical) and 105°C (mechanical with impact). Initial marketing has emphasised comparisons with the aliphatic nylons for the reasons given in the previous... 

The general structure for aliphatic nylons for naming purposes is... 

TABLE 4.7 Melting Point of Selected Polyamides Aliphatic Nylons ... 

The glass transition temperature Tt of aliphatic nylons is low (40 to 70 C) and is not affected to any great extent by composition. However, the Tm is inversely related to the number of methylene groups present In the... 

S. Levchik and E. Weil, Combustion and fire retardancy of aliphatic nylons. Polym. Int., 49, 1033-1076... 

The Py-GC/MS results for a poly(phenylene isophthalimide) or Nomex sample are shown in Figure 13.3.9. The pyrolysis was done at 850° C in He, with the rest of the conditions similar to those used for other examples previously discussed (see Table 4.2.2). Higher temperature was necessary for the sample since Nomex decomposes more slowly at temperatures used, for example, for the pyrolysis of aliphatic nylons. 

These contributions to chain geometry and order confer both a much higher melting point to the resin and much higher tensile strength to spun fiber than is possible with the aliphatic nylons. 

The irregular structure of the polymer indicates that it will be amorphous and glass-like. The presence of the p-phenylene group in the main chain and the lone methyl group leads to a high Tg of about 150°C. There is, somewhat surprisingly, a further transition in the range 220-228°C, the nature of which is not really understood. The polymer is more soluble than the crystalline aliphatic nylons. For example it will dissolve in 80/20 chloroform/methanol mixtures. 

Kuhn model, Equation (1.1). Data for several polymers in addition to polyethylene are given, including a rigid-rod aromatic nylon polymer, poly(p-phenylene terephthalamide) (Kevlar ), as well as the aliphatic nylon polymer poly(hexamethylene adipamide) (nylon-6,6). 

Besides the eight well documented condis phases of flexible, carbon-backbone macro-molecules described in Sects. 4.1 to 4.5, ttere is evidence of an even larger abxmdance of condis crystals as stable phase, intermediate in crystallization, and possibly also on large scale deformation. In this section some indication of the existence of condis phases for aliphatic nylons, polyallene and pofy[(S)-3-methyl-pentene-1] will be reviewed. Lateral and longitudinal disorder was noted much earlier for a larger series of polymers but little is known about the dynamic nature, i.e. if these macromolecules must be considered CD glasses or if they are stable condis crystals at any temperature. 

The discussion of the behavior of eondis crystals of flexibte linear macromolecules and some of the homolc ous oUgcaners covers a witte range of cdisorder-effects and accompanying motion. For many of the macromolecules in the eondis phase chain-extension afto- erystallization with chain folding is possible [polyethylene, polytetrafluOToethylene, poly(vinylidene fluoride), polydilorotrifluoro-ethylene, some aliphatic nylons and polyphosphazenes]. Stx h extended ehain crystals are exceptionally stable and elose to equlibrium. 

For the aliphatic nylons there is an indfcation of a non-cooperative introdwtion of conformational disOTdOT. For the polyplK>sphazenes the transition from the condis phase to the isotropic melt has an exceptionally small entropy gain vriiite retaining normal volume ehan. Both observations are still in need of further investigation. 

PE s studied had diflFerent degrees of crystallinity, molecular weights, and morphology. Copolymers of ethylene with propylene or vinyl acetate and aliphatic nylons were also investigated in efforts to separate morphological effects from the basic processes of the isolated methylene sequences. 

Polyamide 12 Poly (amide imide) Polyamides, aliphatic Nylon 3 Nylon 4,6 Nylon 6... 

Straight-chain aliphatic nylons are commonly identified either as nylon X,Y or nylon Z, where X, Y, and Z signify the number of carbon atoms in the respective monomeric units. The pair X,Y refers to the AABB-type nylons, where the first number X is equal to the number of carbon atoms in the diamine unit and the second number Y represents the number of carbon atoms in the corresponding diacid unit. The number Z refers to the AB-type nylons and is equal to the number of carbon atoms in the amino acid unit. A few examples are ... 

Describe the Nylon family, and discuss advantages and disadvantages. Compare aromatic to aliphatic Nylons. 

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