Solid-state polymerization has long been an important tool in the preparation and study of oriented polymers'). In recent years, most of the research in this field has been devoted to the study of addition polymerization') or polymerization of cyclic monomers3), while little work has been done on solid-state polyesterification and related processes.We have now been able to prepare highly crystalline, biaxially oriented specimens of Nylon 11 by means of solid-state synthesis4! The reaction was camed out with single crystals of Il-aminoundecanoic acid (m. p. 187-188 " C ) sealed in evacuated ampoules mbar) and heated at 160 0,5 "C for several days. Under these conditions, the transparent, needle-shaped, single crystals of monomer were converted into biaxially oriented, polycrystalline aggregates of polyamide 11. After 188 h of reaction, for example, the number-average degree of polymerization of the sample reached values of43-48 as determined by conductimetric titrations of the amino end groups'). The product was also investigated by IR spectroscopy, whereby the presence of the amide 1(1640 cm-') and amide I1 bands (1 535 cm-') fully confirmed its chemical nature. The position of the amide V (675 cm-I)") and amide VI bands (575 cm-1)7,8), moreover, pointed to the fully-extended, planar conformation, triclinic variety of the polyamide generally known as alphaas opposed to the non-planar, pleated sheet conformation known as gamma-form''.'*'. This observation was later substantiated by X-ray diffraction evidence.The crystallographic analysis was carried out on rotation (flat-plate) and Weissenberg photographs taken from water-leached, needle-shaped, polycrystalline aggregates of Nylon 1 1. The needles were mounted with the a direction of the polymer crystallites parallel to the rotation axis. The Weissenberg plates were registered with a zero-layer type of setting, spanning the equatorial (001) and (010) reflections of the polymer. Some faint (100) streaks also present in the Weissenberg plates are due to the finite value of the orientation distribution function all over the reciprocal space. The four strong arcs in Fig. (la) at 4,41,3,75,3,70, and 11,95 A could be immediately indexed according to the triclinic unit cell of Nylon Il9.'O) (Tab. 1). The high, biaxial orientation of a ) Mailing address: Instituto de Investigaciones Fisicoquimicas, San Martin 683,1004 Buenos Aires, Argentina.

X-ray and electron diffraction studies were made on the two phases of l l-aminoundecanoic acid, C1~H21NO2. Origin of specimensSamples of 11-aminoundecanoic acid (11-AUA) from different origins (Aldrich Chem. Co., m.p. 459-460 K; and Ato Chimi., m.p. 460-461 K) were purified by recrystallization in mixtures of 100 ml 95% ethanol/24 ml water per gram of amino acid, reaching a final melting point of 461 K. Single crystals of the monomer, adequate for X-ray studies, were as well obtained from the same solvent system or from mixtures of 1-butanol and water. Under these conditions, the monomer crystallized with two molecules of water per molecule of amino acid (phase I), and all attempts to obtain anhydrous crystals (phase II) by direct crystallization from solutions were unsuccessful. The anhydrous phase could only be prepared by a solid-state dehydration reaction which transformed the hydrated single crystals into polycrystalline aggregates of the anhydrous specimen (phase II). The reaction proceeded with such a high retention of crystallographic order and orientation that the polycrystalline specimens of phase II were just adequate for single-crystal work.

In a recent communication ') we have reported on chemical and crystallographic results concerning the conversion of 1 I-aminoundecanoic acid (m.p. 187 -180'C) to three-dimensionally oriented, polycrystalline aggregates of Nylon-I I . Since the process was carried out at temperatures between 30 and 40°C below the monomer's melting point it has been described as taking place in the crystalline, solid state. Subsequent experimental evidence2), however, showed that the reaction only proceeded when heated in a closed, evacuated system where the monomer vapor pressure had the opportunity to build up to equilibrium values. Heating in a continuously pumped vessel, on the other hand, resulted in sublimation of the monomer into the cool regions of the system without any conversion to polymer; and, reactions carried out in the presence of inert gases took place at substantially lower rates. The process, therefore, as in the case with 6-aminocaproic acid/Nylon-6 3, must have proceeded from the monomer vapor phase by a polymerization-during-crystallization mechanism.