Carbon black filled natural rubber (CB/NR) is a paradigm of nanocomposite materials with high performances. However, the mechanism for the nonlinear Payne effect is still not fully clear. CB gel (CBG) network embedded in the entanglement rubber matrix is supposed to be crucial for the reinforcement and viscoelastic nonlinearity. In this paper, we report for the first time the preparation of bulk CBGs by extracting the highly filled compounds in toluene and the systematic study of their viscoelastic behaviors. The CBG obtained from highly filled compounds with CB loadings from 40 to 70 phr has almost identical microstructure and composition, containing 40 wt % inextractable rubber fractions, among which ∼12 wt % is glassy. Dynamic rheological studies show that the Payne effect of the CBG network is frequencyindependent and highly resilient, exhibiting an unjamming characteristic. On the other hand, the Payne effect of highly filled compounds is determined by the coupling between the breakdown of CBG network and the frequency-dependent chain disentanglement of extractable rubber fractions. This work provides new insights into the Payne effect of CB filled NR and should merit designing other rubbery nanocomposites with high performances and functions.

In this paper, diamine monomers with ether bonds in the main chain are selected for molecular structure design, and four polyamide-imide (PAI) materials are prepared by the acyl chloride method. A diamine monomer containing an ether group can reduce the friction coefficient and improve the wear performance of PAI material. The wear mechanism of PAI material can also change due to ether linkages. PAI synthesized using m-phenylenediamine without an ether bond has the highest friction coefficient and abrasion loss, and the wear mechanism is mainly adhesive wear. With the increase of the number of ether bonds in the diamine monomer structure, the friction coefficient of the material decreases from 0.5445 to 0.4216 (22.57 %). The abrasion loss of the PAI material synthesized using 4,4′-diaminodiphenyl ether is the smallest, which is 84.4 % lower than m-phenylenediamine. The wear mechanism is abrasive wear and slight adhesion wear. With the increase of the number of ether bonds, the heat r esistance of PAI decreases slightly, while the hydrophobic property increases and the water absorption decreases. To summarise, PAI material synthesized using 4,4′-diaminodiphenyl ether has a low friction coefficient, the best wear resistance, the highest tensile strength and elongation at break, and the best comprehensive properties of the materials reported here.

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In this paper,4,4′-diaminodiphenyl ether and 2,2′-bis (trifluoromethyl)-4,4′-diaminophenyl ether are selected for molecular structure design, and PAI materials are synthesized by acyl chloride method. 2,2′-bis (trifluoromethyl)-4,4′-diaminophenyl ether has the same main chain structure as 4,4′-diaminodiphenyl ether, but the side chain contains two trifluoromethyl groups, which has high fluorine content. PAI terpolymerswere prepared by compounding two diamine monomers, and the effects of trifluoromethyl on heat resistance, friction and wear properties, hydrophobic properties and mechanical properties of PAI materials were studied. The results showed that with the increase of trifluoromethyl content, the Tg of PAI material first increased and then changed little, and the Td5% would decrease and the tensile properties would also decrease. The wear mechanism of PAI varied with the content of trifluoromethyl. With the increase of the amount of fluorinated diamine monomer, the adhesive wear degree of PAI materials gradually increased, and reached the maximum when the molar ratio of the two monomers was 5:5, and then decreased gradually. Different trifluoromethyl content had little effect on friction coefficient, and the friction coefficient increased slightly when the molar ratio of 4,4′-diaminodiphenyl ether to 2,2′-bis (trifluoromethyl)-4,4′-diaminophenyl ether is 1:9. With the increase of trifluoromethyl content, the wear of PAI material would increase. With the increase of the amount of trifluoromethyl, the water absorption of PAI material decreased and the water contact angle increased, which indicated that the hydrophobic property of PAI material was improved. To sum up, the results of this study showed that the introduction of trifluoromethyl into the side chain provided an effective way to prepare PAI materials with low water absorption. Considering the comprehensive properties such as heat resistance, friction and wear, tensile properties, etc., the appropriate addition amount is 10–30%.