Abstract
Copolyamides derived from even 1,4-butanediamine and different mixtures of odd dicarboxylic acids with a great difference in the number of methylene groups (i.e., glutaric and azelaic acids with 3 and 7 groups, respectively) have been synthesized, characterized and structurally studied. Calorimetric analyses revealed a complex behavior with multiple melting peaks associated to lamellar reordering and the presence of defective crystals. Equilibrium melting temperatures were evaluated and showed a eutectic behavior with composition. Copolymers were able to crystallize even for samples with comonomer percentages close to 50%. Negative and ringed spherulites from the melt state and small lath-like lamellar crystals from dilute solution crystallizations were attained. Furthermore, calorimetric data pointed out the exclusion of the less abundant monomer from the lattice of the predominant structure. All samples at room temperature showed a similar crystalline structure (form I) defined by two predominant reflections at spacings close to 0.430 and 0.380 nm, which has been related for even-odd nylons with a two-hydrogen bonded structure. Real time synchrotron experiments showed that melt crystallized samples have two polymorphic transitions on heating, which were practically reversible and consequently were also detected during cooling from the melt state. Interestingly, a different behavior was detected among solution crystallized samples and specifically the transition to the intermediate structure (form II) was not detected during heating for samples enriched on the azelate component or more precisely when they were exclusively crystallized in the form I.
Highlights
Aliphatic polyamides constitute a group of semi-crystalline polymers that could cover a wide range of properties, depending in general on their amide/methylene ratio [1,2,3]
Nylons derived from preferences and the optimization of hydrogen bonding interactions/geometry [1]
Materials and Synthesis of Copolyamides Based on 1,4-Diaminobutane and Glutaric and Azelaic Acids
Summary
Aliphatic polyamides (nylons) constitute a group of semi-crystalline polymers that could cover a wide range of properties (e.g., specific gravity, melting point and moisture content), depending in general on their amide/methylene ratio [1,2,3]. A to deviation of the molecular conformation skew torsional angles bonds carbon in order to improve intermolecular bonding interactions This case, vicinal atoms to the amide groups has been postulated forhydrogen nylons having units with an oddInnumber of amide carbon groups respectintermolecular to the plane hydrogen defined by the methylene carbon atoms to atoms inrotate orderwith to improve bonding interactions. Nylons having peculiar units where only one methylene group is placed between two amide groups displayed different molecular arrangements that varied from one [27], two [28,29] and three H-bonding directions [30,31]. Phase transitions induced by temperature will be firstly studied due to the peculiar structure (i.e., two hydrogen-bonding directions) of such even–odd nylons, and secondly the crystallization behavior of such copolymers having units with well-differentiated lengths will be evaluated
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