Chaoyi Guo,Jie Jiang,Zhihua Zhu,Jinjin Li,Ling Zhao,Zhenhao Xi
Semi-aromatic nylon MXD6 shows superior mechanical strength and gas barrier properties. To improve its toughness and get sight into its excellent properties, a series of poly( m -xylylene adipamide-co-isophthalamide) (MXD6/I) random copolyamides were synthesized using adipic acid, isophthalic acid (IPA) and m -xylylene diamine as monomers via direct melt polycondensation. The effect of IPA content on the thermal, crystallization, heat resistant, mechanical, and barrier properties of the copolyamides were systematically investigated. The results showed that the increase of IPA content from 0 to 12 mol% resulted in a decrease in the melting point of the copolyamides from 238 to 217°C but the glass transition temperature ( T g ) increased from 88 to 105°C. Correspondingly, the Vicat softening temperature decreased from 199.2 to 172.5°C. The crystallization rate of the copolyamides significantly decreased with the increase of the IPA content. The copolyamides had improved elongation and rupture energy and decent oxygen barrier properties with the introduction of IPA. It is expected that this study would guide design of MXD6 macromolecular chain structure to prepare high-performance MXD6 materials.
Li Hongjiao,Cao Xiuling,Tan Yufeng,Li Lingyu,Tan Zhenzhen,Zhong Jiachun,Pu Zejun
MXD6 (poly(m-xylylene adipamide)), as a semi-aromatic polyamide, is extensively utilized in packaging, automotive, and unmanned aerial vehicle fields. High strength and heat resistance are very important properties for an engineering plastic. To enhance the thermal and mechanical properties of MXD6, in this study, we investigated the influence of aromatic dicarboxylic acids on its copolymerization. MXD6 and its copolymer derivatives were synthesized via a one-pot synthesis method, which only takes six and a half hours, and the chemical structures of the resulting copolymers were characterized using Fourier transform infrared (FTIR) spectroscopy. X-ray diffraction (XRD) test results indicated that the crystallinity gradually decreased with the introduction of MXDT and MXDI segments. Differential scanning calorimetry (DSC) results demonstrated that the incorporation of copoly(aromatic dicarboxylic acid) segments led to an increase in the glass transition temperature (Tg). Specifically, the Tg of the samples containing 10% MXDT and MXDI segments rose from 77.6 °C to 91.4 °C and 82.4 °C, respectively. Thermogravimetric analysis (TGA) results indicated that the copolymer aromatic dicarboxylic acid would lower the initial decomposition temperature, but expand the decomposition temperature range. The results of the heat distortion temperature (HDT) test showed that the introduction of MXDT and MXDI segments would increase the heat distortion temperature of MXD6, and the increase was more obvious when MXDT segments were introduced compared to MXDI segments. Specifically, when the content of MXDT segments reaches 20%, the heat deflection temperature of MXD6‑T reaches 80.5 °C, which represents an increase of 13.3 °C relative to that of the pristine MXD6 sample. The mechanical property test results indicated that the tensile and flexural properties presented a trend of increasing first and then decreasing, and the introduction of 10% aromatic dicarboxylic acid was the best, while the impact performance decreased. The findings confirm that the inclusion of aromatic dicarboxylic acid segments enhances the heat resistance performance of MXD6. The copolymer with 10% aromatic dicarboxylic acid content shows optimal mechanical performance, establishing this formulation as the most effective. Owing to the fact that this study involved only two types of aromatic dicarboxylic acids in the copolymerization, the aforementioned conclusions are consequently of a relative and context-dependent nature.
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