Study On Synthesis Of High Molecular Weight Linear Polyphenylene Sulfide With Soluble Polyfluorene Cation As Precursor

Polyphenylene sulfide?PPS?is a semi-crystalline organic polymer engineering plastic.Because of its good heat resistance,chemical resistance,flame retardancy,outstanding electrical properties,dimensional stability,and ease of processing,it is widely used in many industries such as automobile,electrical,chemical,textile.At present,the consumption of PPS resin in the world is increasing,and the domestic demand for PPS is increasing.Although the domestic PPS-related enterprises are increasing and the production scale is gradually expanding,it still cannot meet the demand of high-quality PPS in the domestic market.Domestically,the industrial production of PPS is mainly carried out by the sodium sulfide method,and the characteristic sulfur method is also introduced into the industrial production line.However,due to the insolubility of PPS products,these conventional methods require high temperature and high pressure in the polymerization process to promote the forward progress of the reaction,so that the side reactions are more,the product yield is low,and the by-product NaCl which is formed is difficult to remove.In view of the shortcomings in the traditional PPS synthesis process,this paper synthesized the high molecular weight and high purity linear PPS by relying on the previous method and bypassing the problem of PPS solubility.Using benzyl sulfide and diphenyl disulfide as starting materials,the intermediate intermediate 4-?thiophenyl?phenyl sulfide?MPS?was electrophilically substituted at room temperature,and then polymermonomer was synthesized by oxidation reaction.4-?Thiophenyl?benzyl sulfoxide?PSO?,and the effects of oxidant selection,reaction temperature and material ratio on the reaction in the two-step reaction were investigated,and the optimal synthesis method of PSO was determined.Cationic polymerization produces a soluble polyfluorene cation precursor with a high degree of polymerization,poly[methyl[4-?phenylthio?-phenyl]indole trifluoromethanesulfonate]?PPST?,and finally depolymerized to PPS.The reaction time,the choice of protonic acid and the amount of water absorbing agent in the polymerization process were investigated.The optimum conditions for PPS synthesis were determined.The characterization and performance analysis of PPS synthesized under optimal conditions were compared with commercial PPS.The main conclusions are as follows:?1?Intermediate MPS was synthesized by reacting thioanisole and diphenyl disulfide with oxidant and reacting under acidic conditions of TFA.The product was qualitatively analyzed by means of appearance properties,¹H NMR,and its structure was determined.By investigating the effects of oxidant selection,raw material ratio and reaction temperature on the reaction,the optimal synthesis conditions were determined as follows:K₂S₂O₈ is the best oxidant;the best molar ratio of raw material diphenyl disulfide,thioanisole and K₂S₂O₈ is 1:2.1:1.5;The reaction was carried out at room temperature at 25°C for 12 h,the yield of MPS was 80%,and the purity was 99.8%.?2?Using MPS as raw material,acetonitrile as solvent,adding oxidant,selective oxidation to synthesize product PSO.The product was qualitatively analyzed by appearance traits,¹H NMR,DSC melting point and other means to determine its structure.By examining the effects of oxidant selection,reaction temperature and raw material ratio on the reaction,the optimal synthesis conditions were determined:20%diluted HNO₃ was used as the best oxidant;the molar ratio of raw materials MPS and HNO₃ was 1:3;the reaction was carried out at room temperature at25°C for 1 h;the yield of PSO was 91%,and the purity was 99.9%.?3?The precursor polyfluorene cation PPST was synthesized from the polymerization of monomer PSO as a raw material under protonic acid conditions.The polymer structure was determined by qualitative analysis using ¹H NMR and FT-IR.After the nucleophilic reagent pyridine,the precursor was demethylated to synthesize PPS.The structure was preliminarily determined by infrared spectroscopy.Compared with PPST,the change of functional group indicated that the conversion of PPST to PPS was complete.The final synthesized PPS product was tested by changing the polymerization conditions and keeping the reaction conditions of the demethylation unchanged.The selection of protonic acid,polymerization time and the effect of the addition of dehydrating agent P₂O₅ on the reaction were investigated.The optimal synthesis conditions were determined:trifluoromethanesulfonic acid was used as protonic acid,0.33 equivalent of water absorbing agent P₂O₅ was added,and the reaction was polymerized into PPST for 20 h.The precursor was then dephosphorylated with pyridine as a nucleophile to obtain a self-made PPS.The mechanism of synthesis is explained.?4?Under the optimal conditions,the self-made PPS was characterized by FT-IR,elemental analysis,Raman,XRD and other means to determine its chemical structure.The thermodynamic properties were characterized by DSC,TG and DTG,and the average weight was measured.The molecular weight M_w is 1.98×10⁵,the ash content is 0.06%,and compared with the commercial PPS,indicating that the self-made PPS product has excellent thermodynamic properties and is a high molecular weight and high purity linear PPS.