Exchange Reactions Occurring through Active Chain Ends. MALDI−TOF Characterization of Copolymers from Nylon 6,6 and Nylon 6,10

Abstract

A study on the sequence and composition of copolyamides formed by activated exchange reactions occurring in the melt mixing of Ny6,10 and Ny6,6 is reported. Equimolar mixtures of Ny6,10, Ny6,6, and carboxyl-terminated Ny6,6 (Ny6,6-COOH) samples were melt mixed at different temperatures (290−310 °C) for different times (10−180 min). The determination of copolyamides formation, sequence, and composition proved to be unfeasible with 13C NMR spectroscopy. On the other hand, matrix-assisted laser desorption ionization−time-of-flight (MALDI−TOF) mass spectra allowed the detection of the copolyamides formation and the determination of their sequence and composition. The results can be reconciled within the overall scheme of exchange reaction occurring through active chain ends. In fact, the composition of the copolyamides formed by the exchange of Ny6,6-COOH/Ny6,10 mixtures showed a higher amount of Ny6,6 units, with respect to the initial blends composition, and a higher value of the Ny6,6 average block length, at the beginning of the reaction (10 min). The composition of the copolyamides was found to be equal to the feed composition (50/50), after 30 min of heating, with a random distribution of sequences. The composition and the sequence distributions of the copolyamides remained unaffected even at a higher heating time (180 min) although some degradation reactions also occurred. Instead, the exchange reaction of a mixture of high molar mass Ny6,6 and Ny6,10 both containing a very low amount of carboxylic chain ends produced a segmented copolyamides even at high heating time (150 min). The Ny6,6/Ny6,10 copolyamides were also characterized by differential scanning calorimetry (DSC) and by wide-angle X-ray spectroscopy (WAXS).