Aliphatic polyamides crystals

CrystaUizable polyester compositions contain an aliphatic polyamide crystallization nucleator. " They exhibit controUable and adjustable crystaUization rates upon cooling from the melt and are thermoformable in melt to mold processes. Typical amormt of aliphatic polyamide is 5 wt% and it achieves 30% crystalhnity in only 5 to 6 seconds. ... 

Taking into account the crystalline character of the aliphatic polyamides, the second peak is given not only hy the polymerization s heat but also contains the amount of heat corresponding to the crystallization of the separated polymer. It is very difficult to discern between heat of propagation and crystallization, respectively, since the two processes occur almost concomitantly. Consequently, additional off-line data, i.e., gravimetric and DSC were used in order to bring about the deconvolution of the overall heat. Figure 5. 

In addition, conformational disorder in polymer crystals may give rise to point and line defects which are tolerated in the crystal lattice at a low cost of free energy as kinks [104,105], jogs [106,107] and dislocations [108,109]. Such crystallographic defects arise whenever portions of chain adopt conformations different from the conformation assiuned by the chains in the crystal state [99], and have been widely discussed in the literature, in the case of polyethylene [108,109] and some aliphatic polyamides [99,106]. Point and... 

Quite early solution blend work by Takayanagi et al. [83] of rigid aromatic polyamides (poly(p-phenylene terephthalate)) (PPTA) and flexible aliphatic polyamides, nylon 66 and nylon 6 (the latter will be discussed here) has been instrumental in developing the concept of molecular composites and although this lies more in the realm of lyotropic blends, it is often cited in the literature with regard to the effect of the PLC on the crystallization of other components in blends. PPTA has the structure... 

Flexible chain molecules can be spun by the melt, dry- or wet-spinning processes from the melt or from sufficiently concentrated solutions. Examples are poly(ethylene), it-poly(propylene), poly(acrylonitrile), poly(oxymethyl-ene), and aliphatic polyamides. All of these chain molecules have only low potential energy barriers for conformation transitions in addition, they crystallize readily to lamellar structures with chain folding. Crystallization, however, is not a precondition for filament formation since, for example. 

Aliphatic polyamide is linear and easy to crystallize but crystallinity varies widely with conditions. Crystalline content may be 50-60% by slow cooling and 10% by fast cooling. High interchain attraction in the crystalline zones and flexibility in the amorphous zones leads to polymers which are tough above their apparent glass transition temperatures (Brydson, 1982). 

Polymer chains in semicrystalline polymers such as polyolefines, aliphatic polyamides (nylons), and aliphatic polyesters crystallize in the form of lamellae of folded chains that are organized to form lamellar stacks (Fig. 2.14a). The spaces between the lamellae and between the stacks are occupied by... 

Packing Effects on the Conformation of Polymer Chains in the Crystals The case of Aliphatic Polyamides, 50... 

In the 1980s Keith and Padden proposed that chain tilt itself (not screw dislocations) results in axial twisting of growing lamellae that is manifested as banded spherulites. The reviews of Keith and Padden [44] and Lotz and Cheng [23] may be consulted for original references. Chain tilt is almost always found for chains crystallized in an extended (not helical) conformation. For orthorhombic polyethylene and a-poly(vinylidene fluoride), the chains are inclined to the basal lamellar surfaces to provide more volume for chain folding (Section 3.2.1). On the other hand, those aliphatic polyamides (nylons) and polyesters that crystallize with monoclinic... 

Alcohols, reaction of isocyanates with, 224-225 Alcoholysis, 69 Alicyclic dianhydrides, 297 Alignment coating, for liquid crystal devices, 269-270 Aliphatic AA-BB-type polyamides, synthesis of, 164-173 Aliphatic AB-type polyamides, 173-180 Aliphatic acids, 60... 

While aliphatic-containing polyamides are given the name nylons, those in which at least 85% of the amide groups are attached to an aromatic are called aramids. Aramids are stronger and tougher than nylons but they are also more difficult to solubilize and fabricate. Because the presence of the aromatic groups causes the aramids to be stiff, they often form liquid crystals (LCs) that are present in a nematic EC state in concentrated solution. 

Many properties of polyamides are attributable to the formation of hydrogen bonds between the NH and CO groups of neighboring macromolecules. This is evidenced by their solubility in special solvents (sulfuric acid, formic acid, m-cresol), their high melting points (even when made from aliphatic components), and their resistance to hydrolysis. In addition, polyamides with a regular chain structure crystallize very readily. 

Figure 6.27. Predicted maximum possible crystalline fraction (xC)lllax) under isothermal quiescent crystallization, for aliphatic polyesters -[(CH2)k-COO-]n and polyamides -[(CH2)k-CON(H)-]n.

The synthesis of 1,6-diamino-l,6-dideoxy-2,3,4,5-tetra-0-methyl-D-mannitol and its L-iditol analogue from D-mannitol has been described [100], These diamines, containing a two-fold axis, gave stereoregular AABB polyamides on polycondensation with terephthaloyl dichloride and dipentachlorophenyl esters, or dichlorides of aliphatic dicarboxylic acids, in solution or under interfacial polycondensation conditions [99, 109]. In spite of the regioregularity present in the polymeric chains, these optically active polyamides could not be crystallized. 

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