High molecular weight poly(phenylene sulfide sulfone) (PPSS) homo- and statistical copolymers have been reproducably synthesized using a known, but complex procedure utilizing 4,4'-dichlorodiphenyl sulfone (DCDPS), sodium hydrosulfide, sodium hydroxide, sodium acetate, and deionized water, in NMP at elevated reaction temperatures and pressure. The effect of these variations, e.g., reaction temperatures and times, molar ratios of H2O-to-NaSH, NMP-to-H2O, etc. were investigated. Optimized conditions were defined, which produced Tg as high as 222°C, very high refractive index (1.70), and tough/solvent resistant films could be prepared by melt fabrication. A two-stage decomposition mechanism in air was demonstrated by dynamic thermal gravimetric analysis.

The melt stability of PPSS was improved by incorporating thermally stable endgroups, such as diphenyl sulfone, 4-chlorophenylphenyl sulfone, and t-butylphenoxide. The chemical structures of the endgroups were confirmed by 13C and 1H NMR spectra. Compared with mercaptide endcapped PPSS, the new systems showed higher initial degradation temperatures (2% and 5% weight loss), higher char yield at 650°C in air and a more stable melt viscosity at 300°C.

A greatly simplified synthesis of both homo and copolymers has been successfully developed using the new A-A or A-B type thiol-functional monomers, such as bis-(4-mercaptophenyl) sulfone, 4-chloro-4'-mercaptodiphenyl sulfone and 4-chloro-4'-mercapto benzophenone, instead of sodium hydrosulfide. A series of high molecular weight triphenyl phosphine oxide and/or diphenyl ketone containing PPSS copolymers were subsequently synthesized from the bis-(4-mercaptophenyl) sulfone by reaction with 4,4'-dichlorodiphenyl sulfone, bis-(4-fluorophenyl) phenyl phosphine oxide, and 4,4'-difluorobenzophenone in DMAc in the presence of K2CO3 at 160°C. The new phosphine oxide containing PPSS copolymers were completely amorphous, showed improved solubility in common organic solvents and exhibited very high char yields in air at 750°C. Surface (XPS) analysis results suggested that the phosphorus moieties in the polymer backbone can form phosphate-like layers on the polymer surface which protects the inner materials from further decomposition in air at high temperatures. The diphenyl ketone containing PPSS copolymers showed very high char yields at 750°C in a nitrogen atmosphere, compared to sulfide sulfone homopolymer and phosphine oxide containing copolymers, possibly because of higher bond energies.

Semi-crystalline poly(phenylene sulfide ketone) homopolymers and sulfone containing copolymers with sulfone/ketone mole ratio (S : K) < 25 : 75 were synthesized by a novel base catalyzed self-polycondensation of 4-chloro-4'-mercaptodiphenyl sulfone and/or 4-chloro-4'-mercapto benzophenone in N-cyclohexyl-2-pyrrolidinone (CHP) at 290°C. Amorphous copolymers with S : K ratios > 25 : 75 were prepared in DMAc at 160°C. These materials exhibited an increase in glass transition temperature with increasing sulfone content. TGA and micro cone calorimetry analyses showed that the semi-crystalline materials with high ketone content had much higher char yields and significantly lower heat release rate and total heat release, compared to the poly(phenylene sulfide sulfone) and poly(pheylene sulfide) controls.