515 ISSN 1068-3666, Journal of Friction and Wear, 2019, Vol. 40, No. 6, pp. 515–520. © Allerton Press, Inc., 2019. Russian Text © The Author(s), 2019, published in Trenie i Iznos, 2019, Vol. 40, No. 6, pp. 678–686. The Antifriction Properties of Amorphous Poly(Arylene Ether Ketone) Copolymers with a Low Content of Cardo Groups M. V. Goroshkov a , A. P. Krasnov a, *, V. V. Shaposhnikova a , S. N. Salazkin a , A. S. Lyubimova a , A. V. Naumkin a , S. V. Polunin a , and A. V. Bykov b a Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, 119991 Russia b Tver State Technical University, Tver, 170026 Russia *e-mail: krasnov@ineos.ac.ru Received October 9, 2018; revised September 4, 2019; accepted September 5, 2019 Abstract—The causes of an abrupt decrease in the wear and in the friction coefficient from 0.6 to 0.24 for poly(arylene ether ketone) copolymers containing 10, 15, and 25 mol % of cardo bisphenol moieties in the main chain have been investigated. The presence of cardo groups in the copolymers promotes an increase in the microhardness from 12 to 22 kgf/mm 2 and maintains a high antifrictionality as a parameter that charac- terizes the dispersion interaction energy contribution to the total energy of the intermolecular interaction. The XPS examination of the copolymers has shown that only in the case of poly(arylene ether ketone) copo- lymer containing 10 mol % cardo groups, wear products do not undergo any considerable structural changes in the friction process. The studies demonstrated that a significant improvement of friction-and-wear param- eters in the case of a poly(arylene ether ketone) copolymer containing a 10 mol % of cardo groups is caused by an optimal combination of increasing microhardness, formation of a discrete surface, and by maintaining a high antifrictionality. With increasing cardo group content in the copolymers to 15 and 25%, a gradual increase in the friction coefficient to 0.5 and 0.75, respectively, was observed. Keywords: polyarylene ether ketones, cardo copolymers, friction coefficient, wear, microhardness, XPS anal- ysis, antifrictionality DOI: 10.3103/S1068366619060102 INTRODUCTION The synthesis of copolymers offers wide potential for adjusting the properties of polyarylene ether ketones (PAEKs) by changing their chemical structure. Research works devoted to synthesizing homo- and co-PAEKs, as well as to studying their properties, have not lost their relevance [1–3]. The prospect of studies concerning the antifriction properties of amorphous cardo PAEKs and partially crystalline co-PAEKs is caused by the development of modern equipment [4‒7]. The achievement of improved frictional parame- ters is of particular interest due to the introduction of small amounts of one of the copolymeric compo- nents into a complex composition. Thus, the intro- duction of a small amount of thermoplastic PAEK containing a phthalide group into the composition of a complex composition results in high-strength mul- tifunctional nanocomposites due to a 5% additive of nanoparticles [8]. To achieve a targeted effect, for example, to improve solubility and strength properties, a phtha- lide-containing PAEK was combined with polyether based on bisphenol A. It is has been shown that the combination is characterized by the presence of the only glass transition temperature in various mixtures of these polymers. Studies have shown that hydrogen bonds are formed between these two polymeric compo- nents. It has been revealed that phthalide-containing PAEKs are compatible with polysulfone, as well [9]. In the study of the friction of cardo co-PAEKs, it has been demonstrated that the best frictional proper- ties are exhibited by flexible-chain cardo copolymers. They combine the rigidity inherent in cardo moieties and the flexibility inherent in the moieties of bisphe- nol A [5]. Amorphous cardo co-PAEKs with reduced viscos- ity η red = 0.5–0.8 dL/g are used to produce molding materials. At a processing temperature lower than 300°C, they maintain a margin of heat resistance at approximately 100°C, which protects the product from a significant change in molar mass. This work was aimed at studying the antifriction properties of amorphous copolymeric PAEKs with cardo groups (with the contents of these groups from 10 to 25 mol %).