Polyamides molecular structure

Diamantane-based polymers are synthesized to take advantage of their stiffness, chemical and thermal stability, high glass transition temperature, improved solubility in organic solvents, and retention of their physical properties at high temperatures. All these special properties result from their diamantane-based molecular structure [90]. Polyamides are high-temperature polymers with a broad range of applications in different scientific and industrial fields. However, their process is very difficult because of poor solubility and lack of adequate thermal stability retention [90]. Incorporation of 1,6- or... 

Solutions of the aromatic polyamides (PpBA, PpPTA and PmPTA), the polybenzazoles (PBT and PBO), poly(benzyl glutamate) (PBG) and hydroxypropylcellulose (HPC) are the most studied main chain lyotropic systems and our understanding of the behaviour of lyotropics is based on investigations of this relatively small number of materials (Moldenaers, 1996). They form main chain liquid crystals because of their rigid molecular structure in the appropriate solvents. Two kinds of solvents are used (Collyer, 1996) ... 

Figure 5.1. Molecular structures of the chemical repeat units for common polymers. Shown are (a) polyethylene (PE), (b) poly(vinyl chloride) (PVC), (c) polytetrafluoroethylene (PTFE), (d) polypropylene (PP), (e) polyisobutylene (PIB), (f) polybutadiene (PBD), (g) c/5-polyisoprene (natural rubber), (h) traw5-polychloroprene (Neoprene rubber), (i) polystyrene (PS), (j) poly(vinyl acetate) (PVAc), (k) poly(methyl methacrylate) (PMMA), ( ) polycaprolactam (polyamide - nylon 6), (m) nylon 6,6, (n) poly(ethylene teraphthalate), (o) poly(dimethyl siloxane) (PDMS).

Lee and Char [93] studied the reinforcement of the interface between an amorphous polyamide (PA) and polystyrene with the addition of thin layers of a random copolymer of styrene-maleic anhydride (with 8% MA) sandwiched at the interface. After annealing above the Tg of PS, they found significantly higher values of Qc for samples prepared with thinner layers of SMA than for the thicker ones. They initially rationalized their results by invoking the competition between the reaction rate at the interface and the diffusion rate of the SMA away from the interface. For very thick layers, and therefore also for pure SMA, the reaction rate was much faster than the diffusion rate away from the interface and favored therefore a multiple stitching architecture, as shown schematically in Fig. 50. Such an interfacial molecular structure does not favor good entanglements with the homopolymer and is mechanically weak. 

Used for polyurethane, polypropylene, polyester and polyamide fibers where it provides gas fading resistance at low load levels. In addition, the molecular structure and the relatively high molecular weight results in a high extraction resistance in demanding applications like hot water conducting polypropylene pipes. 

Thermoplastic polymers are synthetic polymers that become plastic on heating and harden on cooling. PE, iPP, PET, and polyamides, among others, are typical examples of this type of polymers. Depending on the chemical and molecular structure and processing variables, they may or may not crystallize. Thermoplastic polymers that are able to crystallize have a significant amount of amorphous material, and therefore they are known as semicrystalline thermoplastic polymers. 

Gao, ]., Liu, D.G., Sansi Ena, J.M., Wang, H.L., 2004. Synthesis and characterization of electrochromic polyamides with well-defined molecular structures and redox properties. Adv. Funct. Mater. 14, 537-543. 

Information on physical parameters of the molecular structure of polyamide fibers are usually obtained by x-ray diffraction methods, electron and light microscopies, infrared spectroscopy, thermal analyses such as differential thermal analysis, differential scanning calorimetry, and thermomechanical analysis, electron spin resonance, and nuclear magnetic resonance (NMR) spectroscopy. X-ray diffraction provides detailed information on the molecular and fine structures of polyamide fibers. Although the diffraction patterns of polyamide fibers show wide variation, they exhibit usually three distinct regions ... 

Figure 34.23 Self-healing polymer blend, as described by Hayes et al. (a) Molecular structures of the pyrene-terminated polyamide and the polyimide reported in Ref. [95] (b) Schematic representation of...

High molecular weight polyamides are commonly known as nylon. Polyamides are crystalline polymers typically produced hy the condensation of a diacid and a diamine. There are several types and each type is often descrihed hy a number, such as Nylon 66 or Polyamide 66 (PA66). The numeric suffixes refer to the number of carbon atoms present in the molecular structures of the amine and acid respectively (or a single suffix if the amine and acid groups are part of the same molecule). 

The catalyst or add source can consist of ammonium phosphate or polyphosphate salts, phosphoric add-derived amides or alkyl or halo-alkyl phosphates. Charring agents are based on molecular structures that can form cross-linked networks such as pentaerythritol, sorbitol, melamine, and phenol-formaldehyde resins. Other polymeric systems capable of intumescence are some polyamides and polyurethanes. Blowing agents help form a porous structure in the char and can fadlitate its formation. Common blowing agents are based on urea and urea-formaldehyde resins, melamines, and polyamides that can liberate moisture. 

Based on extensive research into the relationships between molecular structure and bulk physical properties, scientists at DuPont reasoned that a polyamide containing aromatic rings would be stiffer and stronger than either nylon 66 or nylon 6. In early 1960, DuPont introduced Kevlar, a polyaromatic amide (aramid) fiber synthesized from tere-phthalic acid and p-phenylenediamine ... 

Tensile specimens of polypropylene, polycarbonate. Mylar (polyester), Nomex (nylon paper), and Kapton (polyimide) had dimensions of 3 mm in width and 10 mm in guage length. The specimen thicknesses were 65 ym for polypropylene, 75 ]lm for polycarbonate, 85 ym for Mylar, 200 ym for Nomex, and 50 ym for Kapton. Their tensile axes were perpendicular to the rolling direction of the sheets. The molecular structures of these specimens are shown in Table I. Epoxy resins were tested by compression. The specimens of epoxy resin were made of Epikote 828 (bisphenol A type) hardened by K61B (tridimethylaminophenol) or polyamide in a teflon mold of 2 mm in diameter and about 6 mm in height. 

The greatest increase in synthetic fiber materials has been an increase in the polyesters, which now account for almost two-thirds of total synthetic fiber production. It must be remembered that terms such as polyester and polyamide refer to broad classes of compounds and not to specific materials. Each class contains untold thousands of possible variations in molecular structure, both from the chemical identity of the monomers used and from the order in which they react during polymerization. 

---