Yingwei Zhang,Chunhua Wang,Yong Yi,Wenzhi Wang,Jun Yang
In order to adjust the properties of polyamide 6 (PA6) and expand its application, a new strategy of introducing an aromatic imide structure into the PA6 chain through the random copolymerization method is reported. The diimide diacid monomer was first synthesized by the dehydration and cyclization of pyromellitic dianhydride and 6-aminocaproic acid before it reacted with 1,6-hexamethylene diamine to form poly(amide imide) (PAI) salt, and finally synthesized PA6/PAI random copolymers containing an aromatic imide structure by the random copolymerization of ε-caprolactam and PAI salt. The introduction of an aromatic imide structural unit into the PA6 chain could have a great influence on its properties. As the content of PAI increases, the crystallinity (Xc) and melting temperature (Tm) of the PA6/PAI random copolymer gradually decrease, but its glass transition temperature (Tg) increases obviously. When the PAI content is 20 wt%, the copolymer PA6/PAI-20 has the best comprehensive performance and not only has high thermal stabilities but also excellent mechanical properties (high strength, high modulus, and good toughness) and dielectric properties (low dielectric constant and dielectric loss). Moreover, these properties are significantly superior to those of PA6. Such high-performance PA6 random copolymers can provide great promise for the wider applications of PA6 materials.Keywords:polyamide 6;poly(amide imide);random copolymerization
A series of epoxy resins containing aromatic imine are synthesized via the Duff reaction by using various bisphenols, which show significantly reduced heat release capacity (HRC) and total heat release (THR) after curing. Compared to diglycidyl ether bisphenol A/4,4-diaminodiphenyl methane (DGEBA/DDM), the HRC and THR of phenolphthalein-based epoxy resin containing aromatic imine/DDM (BPP-E/DDM) are reduced by 87% (464 J/g K vs 58 J/g K) and 62% (30.2 kJ/g vs 11.4 kJ/g), respectively. Furthermore, the BPP-E/DDM exhibits a UL-94 V-0 rating (1.6 mm) and a limiting oxygen index of 48% (3.2 mm). Compared to DGEBA/DDM in the cone calorimeter test, the peak heat release rate, THR, peak smoke produce rate, and total smoke production of BPP-E/DDM were reduced by 91% (1006 kW/m2vs 87 kW/m2), 51% (89 MJ/m2vs 44 MJ/m2), 89% (0.36 m2/s vs 0.09 m2/s), and 79% (38 m2vs 8 m2), respectively. The influences of aromatic imine and the chemical structures between two benzene rings in the bisphenols on HRC and THR of the resultant epoxy thermosets are investigated. The mechanism studies show that the presence of aromatic imine in the epoxy resins completely changes the decomposition process to generate the products containing aromatic N-heterocycle, which contributes greatly to the improved char-forming ability and flame retardancy. Meanwhile the thermosets bearing carbonyl, 3-phthalidylene, and sulfonyl between two benzene rings in the bisphenols show better char-forming ability and flame retardancy among the resultant epoxy resins containing aromatic imine, due to more polycyclic aromatic hydrocarbons produced in the condensed phase.
Covalent adaptable networks (CANs) relying on dynamic cross-links have been developed to make the cross-linked polymeric materials and composites degradable. However, due to the reversibility of dynamic bonds, the CANs and composites suffer accidental degradation and failure upon a certain stimulus (moisture, acid/base, reductant/oxidant, etc.) in the application environment. Herein, inspired by parallel circuits, interlocked covalent adaptable networks (ICANs) were prepared by one-pot reactions from epoxy monomers and two curing agents that contained different dynamic bonds of aromatic disulfide and aromatic imine bonds, resulting in dual dynamic parallel cross-links in homogeneous epoxy networks. The ICANs exhibited outstanding mechanical properties and improved stability, relying on the topological interlocking structure. The ICANs could be unlocked and became degradable only when two stimuli were both applied to completely break the cross-links of disulfide bonds and imine bonds. When applying ICANs as a matrix to form carbon fiber-reinforced polymer (CFRP) composites, the resulted CFRP inherited the interlocking properties from the ICANs, exhibiting improved stability and nondestructive recyclability. Maintaining the degradable properties, the interlocking structure of networks provided a facile way to optimize the stability of CANs and their composites.
危险品化学品经营许可证（带存储）