Long-Aliphatic-Segment Polyamides: Salt Preparation and Subsequent Anhydrous Polymerization Anastasia C. Boussia, Stamatina N. Vouyiouka, Athanasios D. Porfiris, Constantine D. Papaspyrides* Introduction Linear polyamides, commonly referred to as nylons, are an important category of condensation polymers, reflecting 4 wt.-% of plastics global production. [1] They are semi- crystalline materials that usually exhibit a relatively high modulus, toughness and strength, low creep and good temperature resistance, that allow their widespread use as fibers and engineering resins. Their attractive set of properties, such as the high melting points (T m ) and mechanical strength, originates in the strong intermole- cular hydrogen bonds (dissociation energy ¼ 35 kJ  mol 1 ). They are formed between the amide groups of adjacent chains, resulting in well-defined, two-dimensional H-bonded sheets that are held together in a three- dimensional lattice. [2–4] The density of the H-bonds, and thus the polyamide properties, is firstly analog to the amide linkages (CONH) content, also referred to as the hetero- chain index (h ¼ CONH:CH 2 ). A linear correlation between the T m (8C) of even/even polyamides and h (%) has been proposed and verified by Korshak and Frunze: [2] T m ¼ 7h þ 110 (1) Secondly, the pattern of hydrogen bonds that develops is a function of the stereochemistry of each polyamide. [5,6] A characteristic example is that of PA 6.6 and PA 6, which have the same density of amide groups (h ¼ 20%), but exhibit different melting points, with PA 6.6 having the higher value. In PA 6.6, the repeating unit has a center of symmetry: the amide linkages easily align to form hydrogen bonds when the fully extended zigzag-like chains Full Paper A. C. Boussia, S. N. Vouyiouka, A. D. Porfiris, C. D. Papaspyrides Laboratory of Polymer Technology, School of Chemical Engineering, National Technical University of Athens, Zographou, Athens 157 80, Greece Fax: þ30 210 772 3180; E-mail: kp@softlab.ece.ntua.gr Long-aliphatic-segment polyamides were prepared based on hexamethylenediamine and a,v-(CH 2 ) x biosynthetic diacids (x ¼ 10, 11, 12). The pertinent monomers (salts) were isolated as solids, thoroughly characterized for the first time, and then submitted to an anhydrous melt prepolymerization technique. The obtained prepolymers exhibited M n in the range of 5 100–11 800 g  mol 1 , and the molecular weight was further increased by up to 55% through solid-state finishing. The suggested over- all polyamidation cycle was conducted at short melt-reaction times, so as to avoid any thermal degradation, and was proved efficient, indicating similar reactants polymerizability independently of the methylene content. 812 Macromol. Mater. Eng. 2010, 295, 812–821 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com DOI: 10.1002/mame.201000057