A Study On Solution Behaviors And Applications Of Polyarylene Sulfide Sulfone

Polyarylene sulfide sulfone (PASS) belongs to a new generation ofheat-resistant engineering thermoplastics of the polyarylene sulfide (PAS) typeand has already been used as a structural polymer. It differs from its predecessor,polyphenylene sulfide (PPS), with an amorphous structure and higher glasstransition temperature (T_g=218℃, compared to 88～90℃for PPS). Also, it issoluble in some organic solvent at room temperature, whereas PPS is soluble onlyat 200℃. Solubility of PASS suggests new possibilities for processing this film-and fiber-forming polymer from solution.Up to now, research on PASS is mostly limited to either the patent orcommercial trade literature. Therefore, exploration of the nature of PASSsolutions and application research of PASS is unquestionably important in bothaspect of science and industry. Under this direction, here the main work andconclusions come as follows:1. Solution of PASS in N-methylpyrrolidone (NMP) was found to beunstable and showed a tendency to precipitation. The precipitation is a kind ofcrystal solvate formed by PASS and NMP and is relatively unstable at raisedtemperatures and washing out with acetone or drying at high temperature leads tothe separation of the solvent. From DSC investigations, phase diagram of PASS/NMP system was determined and an arylene sulfide sulfone/NMP molarratio of 7/3 was deduced. The dependence of T_m on volume fraction of solventconforms rather well with polymer melting theory, which yields 4.59cal. g^-1 or1139cal per mole PASS segment for the heat of fusion of the crystal solvate. Theearly stage of crystalline process of PASS/NMP crystal solvate is satisfied withAvrami equation. An Avrami exponent n=1.1 and Avrami rate constants k₂₀=2.77×10^-4, k₄₀=1.06×10^-2 were determined from the analysis of the isothermalcrystallization kinetic analysis of the crystal solvate. Moreover, the thermaldegradation activation energy of PASS alters from 214.24KJ/mol of pure PASS to174.18KJ/mol of PASS/NMP crystal solvate due to the present of NMP accordingto the thermal degradation kinetic analysis.2. It was found that nodular structure emerges during annealing process ofthe PASS denser film. PASS denser films were gained through solution castingmethod under different processing parameters. From these experiments, a numberof empirical rules are found to describe the resulting morphology of the top layer.Then, the film formation process is analyzed and a new mechanism for theformation of a nodular structure on PASS film is proposed. This nodular structureis formed by a certain amount of solvent remained in the bulk of the film due toglass transition of surface layer. The remainder solvent molecules and PASSmolecule chains can form paracrystallines with high surface energy. Duringannealing process, the paracrystallines aggregate on the surface of the film andform the nodules. According to the mechanism, a reasonable explaination of theexperimental phenomenon was obtained.3. The preparation of PASS separation membrane by means of immersionprecipitation method (L-S method) and the performance of the PASS membranewere systematically studied. Liquid-liquid phase separation phenomena wereinvestigated adopting ternary Flory-Huggins theory. The experimental data ofincipient phase separation of the ternary systems were obtained by application ofthe cloud composition titration. The miscibility gaps are fairly good agreement between the calculated and measured data by the theory and experimentsrespectively. The non-solvent plays the most important role in the membraneforming system. Solubility order of the solvents to PASS according to ternaryphase diagrams is NMP＞phenol/tetrachloroethane＞DMF. Precipitating ability ofnon-solvent is H₂O＞glycerine＞glycol＞isopropanol＞grain alcohol＞1,2-propanediolin order. The prepared membranes have unsymmetrical structure which contains athin porous layer and a thick support layer with finger like bores. The formationmechanism of the finger like bores is attributed to delay phase separation of thecast solution. Polyethylene glycol (PEG) was added into the cast solution toimprove permeability of PASS membrane. According to the experimental results,evaporating time should be about 60s and amount of PEG should be less than5wt% to obtain a PASS membrane with good permeability. Furthermore,precipitating bath with higher precipitating ability will lead to a higher separationproperty and lower permeability of PASS membrane.4. PASS nanofibers were successfully prepared by means of electrospinning.Environment temperature controller was firstly introduced in the electrospinningprocess to promote evaporation of solvent with high boiling point.Electrospinbilities of several kinds of PASS solution were discussed. PASS/NMPsolution can not be electrospined at room temperature but can be electrospined ata higher temperature, while PASS/ phenol/ tetrachloroethane solution can beelectrospined at room temperature. PASS solution has a minimum electrospinableconcentration, and the concentration turns lower with increasing molecular weightof PASS. Molecular chain entanglements and effective solvent evaporation areproved to be two necessary conditions of polymer solution electrospinable. Sinceprocessing parameter of electrospinning is various, orthogonal experiments weredesigned and performed to determine effects of solution concentration,environment temperature, voltage, receiving distance and flux on diameter ofPASS nanofiber. From the orthogonal experiments results, solution concentrationis found to be the most influential parameter to PASS nanofiber, whereas environment temperature to be the least one. Therefore, solution concentration,voltage and flux should be controlled to define the diameter of PASS nanofiber inthe electrospinning process.