Preparation and Tribological Property of Poly (Phthalazinone Ether) Composite Thin Films

Poly（phthalazinone ether ketone）（PPEK）and Poly（phthalazinone ether nitrile）（PPEN） are both high performance thermoplastics with good mechanical performance,high glass-transition temperature,good solubility and well film-forming ability.In this work,we synthesized functionalized PPEK and PPEN.Then utilizing the activity functional groups along the backbone,we preparaed organic/inorganic poly（phthalazinone ether）hybrid films via the sol-gel process and self-assembled films on the glass substrate surface,respectively. The characterization and tribological property of these films were investigated.PPEK can be hydroxylated by using a solution of NaBH₄ in NMP.The effects of the reaction time and temperature,the concentration of the polymer and NaBH₄ and the solvent were studied on the rate of reduction,respectively.The kinetics of the reaction was also discussed.The result indicates that the reduction rate of carbonyl group increase with the increasing reaction temperature or prolonging the reaction time.The properties of reductive PPEK（HPPEK）were determined by measuring water contact angle,glass transition temperature（T_g）and solubility in different solvents.The results indicate that the present of hydroxyl groups significantly enhance the wettability of HPPEK film and its T_g is higher than PPEK’s.PKCS and PKGS were synthesized with HPPEK and isocyanatopropyltriethoxysilane （ICPTES）and 3-glycidoxypropyltrimethoxysilane（GPTMS）,respectively.The properties of PKCS and PKGS were measured with water contact angle,glass transition temperature（T_g） and solubility in different solvents.The results indicate that the present of alkoxysilyl groups significantly enhance the thermal stability.As for the cross linking reaction among the alkoxysilyl groups,PKCS and PKGS are both insoluble in the solvents.PPEN was modified in a hydrolysis reaction in order to preparing functional polymer. The CN groups of PPEN were successfully converted into hydrophilic groups（-COOH）.By studying the effect of different co-solvents,reaction temperature and KOH concentration on the hydrolysis reaction,the optimal synthetic technique could be determined.With the nitrile group conversion ratio increasing,glass transition temperature（T_g）of hydrolyzates（HPPEN） increases slightly as hydrolysis reaction time prolonging.The water contact angle of HPPEN decreases greatly owing to the hydrophilicity of HPPEN is improved.After the acylation reaction of HPPEN,it was then modified by aminopropyltriethoxysilane（the product was called PNAS）.The thermostability and solubility of PNAS are similar as PKCS and PKGS.Organic-inorganic poly（phthalazinone ether）（PKCS,PKGS and PNAS）/SiO₂ hybrid composite thin films were prepared by the dip-coating method on pre-cleaned glass substrates. The covalent bonds between organic and inorganic phases were introduced by the in situ reaction of silane coupling agents（ICPTES,GPTMS,APTES）with HPPEK and HPPEN forming a polymer bearing triethoxysilyl groups.Theses groups subsequently were hydrolyzed with tetraethoxysilane（TEOS）and allowed to form a network via a sol-gel process.The polymer hybrid composites exhibite good thermal stability and a high glass transition temperature as compared with the pure resin.Atomic force microscope,water contact angle and scanning electron microscope were used to characterize the polymer hybrid thin films.The tribological properties of the prepared films were investigated using a UMT-2 friction precision measurement apparatus.The tribological experiments show that the films have very low friction coefficient（about 0.1）and good anti-wear properties,with a lack of failure even after sliding 18000 s under modest loads.The functionalization of poly（phthalazinone ether）makes them（HPPK,HPPEN,PKCS, PKGS and PNAS）easier assemble on the hydroxylated glass substrate surface.The self-assembly behavior on the glass substrate of the obtained polymer films were studied by measuring the water contact angle,film thickness and characterized by FTIR.Investigations show that the film thickness and the film formation can be almost completed in 1 h.The nano-scale morphology of the films was investigated by atomic force microscopy（AFM）.The friction coefficients of self-assembled polymer films against steel ball at a load of 100 mN are about 0.1 which is much lower than that for the bare glass substrate in the same experiment conditions（friction coefficient of bare glass is about 0.8）.Self-assembled poly（phthalazinone ether）film modified glass substrate exhibit excellent friction reduction and good anti-wear behavior comparing with their bare counterparts.According to this investigation, organic/inorganic poly（phthalazinone ether）/SiO₂ hybrid films and self-assembled polymer films have the prospect for the boundary lubricant application in Micro-electro-mechanical-system（MEMS）.