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Tham khảo tài liệu 'plastics technology handbook 2011 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TABLE 1.3 Continued Polymer Type and Polycondensation Reaction Comments Poly p-phenylene terephthalamide O u n Cl-C 2n-1 NaCl High modulus fibers as strong as steel but have one-fifth of weight ideally suited as tire cord materials and for ballistic vests e.g. Kevlar Twaron. Polyimide n H2N nh2 N 2n-1 H2O Films coatings adhesives laminates outstanding in heat resistance flame resistance abrasion resistance electrical insulation resistance resistance to oxidative degradation high energy radiation and most chemicals except strong bases used in specialist applications e.g. Kapton Vespel. 1-20 Plastics Technology Handbook 2006 by Taylor Francis Group LLC Characteristics of Polymers 1-21 a b FIGURE 1.8 Schematic representation of a a covalent polymer and b a supramolecular polymer. After Brunsveld L. Folmer B. J. B. Meijer E. W. and Sijbesma R. P. 2001. Chem. Rev. 101 4071. With permission. A difunctional UPy compound 4 in Figure 1.10 possessing two UPy units can be easily made in a one step procedure from commercially available compounds methylisocytosine R CH3 and hexyldiisocyanate R C6H12 . The compound forms very stable and long polymer chains 5 in Figure 1.10 in solution as well as in the bulk 9 11 . Dissolving a small amount of the compound in chloroform gives solutions with high viscosities while calculations show that polymers with molecular weights of the order of 106 can be formed. Deliberate addition of small amounts of monofunctional compounds 1 in Figure 1.9 results in a sharp drop in viscosity proving that linkages between the building blocks are reversible and unidirectional and that the monofunctional compounds act as chain stoppers. For the same reason the supramolecular polymers show polymer-like viscoelastic behavior in bulk and solution whereas at elevated temperatures they exhibit liquid-like properties 9 . N O H R NH2 O C N - R H H N N N R Solvent UPy R R 2 gg FIGURE 1.9 Synthesis of a monofunctional 2-ureido-4 1H -pyrimidinone UPy 1 and .
