Conversion of polyester into heat‐resistant polyamide by reacting with aromatic diamine compound

Abstract

ABSTRACT:The ester-amide exchange reaction between poly(ethylene terephthalate) and p-phenylenediamine in ndodecylbenzene as a solvent in the absence of catalyst was carried out to obtain heat-resistant polyamide. The observation of the amide group generated in the reaction product was made by FTIR analysis and the relative extent of reaction was estimated by the amidation ratio from FTIR and the nitrogen content determined from elemental analysis. The effect of chemical structure in the homologous series of aliphatic and aromatic diamines on the reactivity of esteramide exchange reaction was studied. How reaction variables such as time, temperature, and the amount of diamine used affected the extent of reaction and the heat-resistant property of polyamide obtained was thoroughly studied. Finally, a search for an efficient catalyst among metal acetates was attempted.

Conversion of polyester into heat‐resistant polyamide by reacting with aromatic diamine compound II. Semibatch reaction by nitrogen gas sweeping process

“…Amidation ratio (AR) was used as a relative indicator for the extent of reaction and it was estimated using the FTIR spectrum as follows:5, 6 Here λ 1510 and λ 1710 are the IR absorbency of the characteristic peaks at 1,510 cm −1 (CONH group) and 1,710 cm −1 (COO group), respectively. Figure 1 shows the FTIR spectrum in the wave number of 1,400 to 2,000 cm −1 for the virgin PET and the semibatch reaction product (210°C, 5 h, 0.25 mL/g/min, catalyzed starting material).…”

“…Recently, it has been reported that a polymer(I) could be chemically converted into another value‐added polymer(II) 3–6. Nakano3 claimed that PET could be converted into various polyamides by reacting with aliphatic or aromatic diamines in the presence of organic solvent.…”

“…Nakano and Kato4 also reported a novel batch reaction process used to obtain poly(hexamethylene terephthalamide) (polyamide 6T) from PET by reacting PET with hexamethylenediamine in the presence of organic solvent. In our previous report,5, 6 we reported that the ester–amide exchange reaction between PET and p ‐phenylenediamine (PDA) produced a heat‐resistant polyamide in the batch reactor and also the reaction could be expedited with the addition of lead(IV) acetate as a catalyst without losing the heat‐resistant property of the product. Effects of batch reaction variables such as time, temperature, and the amount of PDA used upon the extent of reaction and the heat‐resistant property of polyamide were reported 6…”

“…The ester–amide exchange reaction between PET and PDA in organic solvent could produce poly( p ‐phenylene terephthalamide) in the complete conversion according to the following reaction route5, 6 and thus the increase of reaction conversion during the whole reaction process is desirable to obtain the more heat‐resistant polyamide product. Since the ester–amide exchange reaction is reversible, it is necessary to remove a low molecular weight reaction byproduct (e.g., ethylene glycol) from the reaction mixture to promote the forward reaction, which highly increases the extent of reaction relative to the batch reaction (Scheme ).…”

“…A promotion of the forward reaction in the reversible condensation reaction process is achieved in general by applying a vacuum in the reactor to facilitate the removal of reaction byproduct. The ester–amide exchange reaction between PET and PDA was carried out in the batch reactor5, 6 and the reaction mixture represented the slurry state in the presence of n ‐dodecylbenzene (NDDB). However, the semibatch reaction to remove a reaction byproduct from the reaction mixture needs to be carried out in the solid state.…”