Synthesis And Properties Of Long Chain Semiaromatic Polyamides Containing Naphthalene-ring

Up to now, the mainly commercially semiaromatic polyamides are polyhexamethylene terephthalamide (PA6T) and polynonamethylene terephthalamide (PA9T). However, PA6T can not be processed by melting method because of its high-melting temperature and relatively lower decomposition temperatures, and the high cost of PA9T limited its applications. Therefore, the researches of new semiaromatic polyamides have important theoretical and practical values. In this work, for increasing processing ability and decreasing the cost of semiaromatic polyamides, naphthalene ring and long flexible aliphatic chains were introduced into the backbones of the semiaromatic polyamides. The long chain semiaromatic nylons containing naphthalene ring with excellent performance are near to PA9T, and the synthetic process is simple. Therefore, the long chain semiaromatic nylons containing naphthalene ring are promising commercial application.In this paper, four new long chain semiaromatic nylons containing naphthalene ring have been synthesized via the reaction of 2,6-naphthalene dicarboxylic acid and four distinct long flexible aliphatic diamines through a three-step procedure, respectively. The polymerization conditions of the long chain semiaromatic polyamides containing naphthalene ring have been investigated. The physical and mechanical properties have also been investigated. The thermal behaviors, non-isothermal melt crystallization kinetics, pyrolysis products and pyrolysis mechanisms of the long chain semiaromatic nylons containing naphthalene ring have also been discussed in this contribution. The main results of this contribution are summarized as follows:1. The long chain semiaromatic nylons containing naphthalene ring poly(decamethylene 2,6-naphthalamide) (PA10N), poly(undecamethylene 2,6-naphthalamide) (PA11N), poly(dodecamethylene 2,6-naphthalamide) (PA12N) and poly(tridecamethylene 2,6-naphthalamide) (PA13N) were prepared from the reaction of 2,6-naphthalene dicarboxylic acid and four distinct cheap long flexible aliphatic diamines(1,10-decanediamine,1,11-undecanediamine,1,12-dodecaediamine and 1,13-tridecanediamine) through a three-step procedure:salt formation, prepolymerization and solid-state polymerization, respectively. The optimal reaction conditions have been investigated. The molecular weight of the long chain semiaromatic nylons containing naphthalene ring changing upon the polymeric reaction conditions and technical conditions have been studied. The suitable pH value of the nylon salt solutions should be controlled in the range of 7.4～7.6. The suitable prepolymerization temperatures of PA10N, PA11N, PA12N and PA13N should be 260℃,250℃,250℃and 240℃, respectively, with the reaction time about 3 h. The solid state polymerization temperatures of PA10N, PA11N, PA12N and PA13N should be 280℃,250℃,260℃and 260℃, and reaction times were 20 h,15 h,15 h and 20 h, respectively, with the vacuum value of 10 Pa.2. The structures of the synthesized long chain semiaromatic nylons containing naphthalene ring were characterized by elemental analysis, Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR). The water absorption of PA10N, PA11N, PA12N and PA13N are 0.14%,0.12%,0.10% and 0.07%, respectively. The low water absorption, close to that of PA9T, is conducive to maintain dimensional and mechanical stability of products. The relationship of the melting temperatures (Tm) and the structure of the long chain semiaromatic nylons containing naphthalene ring were analysised by DSC. Tm of PA10N, PA11N, PA12N and PA13N are 320℃,294℃,299℃and 288℃, and the glass transition temperatures (Tg) are 130℃,124℃,120℃and115℃, respectively.3. The dynamic mechanical thermal properties of the long chain semiaromatic nylons containing naphthalene ring were investigated by dynamic mechanical thermal analysis (DMTA). Tgof PA10N, PA11N, PA12N and PA13N analysised by DMTA are 173℃,161℃,140℃and 129℃, respectively. The relaxation activation energy of the long chain semiaromatic nylons containing naphthalene ring were calculated by Arrhenius equation. The relaxation activation energies of PA10N respective are Eα=67.7 kJ/mol, Eβ=1.10 kJ/mol and Eγ=28.4 kJ/mol. The relaxation activation energies of PA11N respective are Eα=74.7 kJ/mol, Ep=2.90 kJ/mol and Eγ=34.4 kJ/mol. The relaxation activation energies of PA12N respective are Eα=63.2 kJ/mol, Eβ=2.80 kJ/mol and Eγ=33.7 kJ/mol. The relaxation activation energies of PA13N respective are Eα=73.0 kJ/mol, Eβ=2.20 kJ/mol/and Eγ=35.3 kJ/mol. 4. The mechanical properties, electrical properties, solubility, thermal properties and physical parameters of the synthesized semiaromatic long chain nylons containing naphthalene ring were investigated according to China standard. The relationship between structures and properties of semiaromatic nylons containing naphthalene ring was studied. The results show that the synthesized semiaromatic nylons containing naphthalene ring display good physical and mechanical properties, good solubility property, good electrical properties, excellent heat-resisting and well processable property closed to those of PA9T. Compared with PA9T, the low-cost and good performance of semiaromatic nylons containing naphthalene ring demonstrate it could be a promising, heat-resisting and well processable engineering plastic, and it can be a candidate nylon for the industrial production.5. Nonisothermal crystallization processes and kinetics of semiaromatic nylons containing naphthalene ring were studied by DSC. The results show that the peak temperatures of the DSC curves gradually decrease with cooling rate increasing. Half-crystallization time (tl/2) decreased by exponentially with the increase of cooling rate and thus the crystallization rate was enhanced with the increasing of cooling rate. The crystallization rate decreased with the relative crystallinity increasing. The commonly used Avrami equation and that modified by Jeziorny were used to fit the primary stage of nonisothermal crystallization of semiaromatic nylons containing naphthalene ring, and the Avrami index n was evaluated. The Avrami index n of PA10N, PA11N, PA12N and PA13N was in the range of 2.6 to 3.6,3.1 to 4.8,3.1 to 4.6 and 2.2 to 3.3, respectively. The non-isothermal crystallization activation energies (△E) of PA10N, PA11N, PA12N and PA13N were determined to be-45.7 kJ/mol,-88.1 kJ/mol,-44.0 kJ/mol and-62.3 kJ/mol/by Kissinger's methods, respectively.6. The pyrolysis products of the long chain semiaromatic nylons containing naphthalene ring were investigated by flash pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and the pyrolysis mechanisms have been studied. Long chain semiaromatic nylons containing naphthalene ring decomposed viaβ-CH hydrogen transfering with the formation of 2,6-naphthalene dicarbonitrile, olefins, diolefins and alkanes. The C-C bond of long chain semiaromatic nylons containing naphthalene ring homolytic cleavaged with the generation of naphthalenecarbonitrile, alkyl nitriles, naphthalene and naphthalene compounds. CO2 were mainly generated from the hydrolysis of long chain semiaromatic nylons containing naphthalene ring at high temperature.