Essential Role of Chain Ends in the Ny6/PBT Exchange. A Combined NMR and MALDI Approach

Abstract

A combination of NMR and MALDI was found to be a suitable tool to study the exchange reactions that occur during the melt mixing of Nylon-6 and poly(butylene terephthalate) (Ny6/PBT) blends. The results reveal the essential role of carboxyl end groups in the exchange reaction, and allow drawing a detailed mechanism for this reaction. Using Ny6 and PBT samples bearing specific reactive end groups, it was demonstrated that only the carboxyl end groups of PBT and of Ny6 are able to react in the initially biphasic Ny6/PBT blends, so that an outer-inner exchange takes place (Scheme 3). The composition of the copoly(esteramide) obtained at 260 °C in the exchange of Ny6/PBT shows a higher amount of Ny6 units with respect to the initial blend composition and a high value of the Ny6 average sequence length. However, the composition of the copoly(esteramide) obtained at 280 °C was instead found to be equal to the feed composition (50/50), with a random distribution of average sequence lengths. The results obtained in the present work can be reconciled within the overall model of exchange reaction occurring through active chain ends.

When medical evidence alone is simply not enough

“…This result suggest that, as well as in the PET/Ny6 5 and PBT/Ny6 6 blends, the direct ester–amide exchange reaction [Scheme (A)] does not occurs in incompatible PET/MXD6 blends, confirming also the studies of Prattipati et al 35. Therefore, because the PET and MXD6 samples used in this study are essentially terminated with hydroxyl and aliphatic carboxylic acid end groups, the outer–inner reactions schematized in Scheme (routes B‐E) do not occur in the incompatible polyeter/polyamide melt blend, as already observed for PET/Ny6 5 and PBT/Ny6 blends 6 . 1 H NMR spectra of PET/MXD6 blends melt mixed in presence the of TA (1 wt %; referred thereafter as PET/MXD6–(1 wt %)TA) for 30, 45, 75, and 120 min are displayed in Figure 3; the peaks present are assigned as in Table 2 and in accordance with the chemical shifts of the homopolymers models (PET,MXD6, PEA, and MXDT).…”

“…However, the surprising presence of the E‐A sequences in the copolymer formed at shorter reaction time (15 min) is diagnostic of the exchange reaction due to the attack of aliphatic carboxyl ends of MXD6 at the inner ester groups of PET chains [Scheme (C)]. Therefore, although MXD6 chains with aliphatic carboxyl groups are unreactive in the initial incompatible PET/MXD6 blends, as discussed before and as already observed for Ny6/polyester blends,5, 6 when the blend become partial or totally compatible, the aliphatic carboxylic may promote the exchange reactions determining their progress.…”

“…The progress of the exchange reactions can be followed by 1 H and 13 C NMR analyses and also by investigation of thermal properties of the melt‐mixed materials. In accordance with our previous studies on the polyester/polyamide5, 6 and polyamide/polyamide2, 7 incompatible blends, here we have performed the melt mixing of equimolar mixtures of PET and MXD6 at 285 °C for different times, ranging from 15 to 120 min, with TA (1 wt %) and from 5 to 60 min without TA, under N 2 flow. All melt‐mixed materials were studied without any purification or removal of possibility nonaffected homopolymers, by 1 H and 13 C NMR, DSC, and viscosity tools.…”

Essential role of chain ends in the nylon‐6/poly(ethylene terephthalate) exchange

“…Blends of polyamides and polyesters as poly-(ethylene terephthalate)/nylon-6 (PET/Ny6), poly-(butylene terephthalate) (PBT)/Ny6, and PET nylon-66 (Ny66) have been investigated. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Several literature reports assert that exchange reactions in the preceding polyester/polyamide blends can be induced with an appropriate catalyst. 6,13,15,16,19 Some researchers 13,15,16 have stated that p-toluene sulfonic acid (TsOH) is the most efficient catalyst for amide-ester exchange reactions in PET/Ny6 and PET/Ny66 blends, but Brown 18 has suggested that TsOH catalyzes the outer-inner exchange reaction of an amino end group with an inner ester group of PET.…”

Mechanical behavior of electrospun Nylon66 fibers reinforced with pristine and treated multi-walled carbon nanotube fillers

“…Alternatively, the mechanical integrity of the fibers can be significantly improved by incorporating high strength and high aspect ratio nano-fillers to obtain novel composite nanofibers such that they possess remarkably superior mechanical strength [7,8]. Furthermore, it is demonstrated that electrospinning polymer solutions dispersed with filler materials is a unique technique to efficiently disperse, align and orientate the particles [7][8][9]. The fillers are self-assembled and carried by the spun fibers and possess improved strength and stiffness than the filler-dispersed composites that are obtained using the conventional extrusion techniques [1,7,8].…”