（a） Identity. For the purpose of this section, polyphenylene sulfone resins consist of basic resin produced by reacting polyphenylene sulfide with peracetic acid such that the finished resins meet the specifications set forth in paragraph （c） of this section. The polyphenylene sulfide used to manufacture polyphenylene sulfone is prepared by the reaction of sodium sulfide and p -dichlorobenzene, and has a minimum weight average molecular weight of 5,000 Daltons.

（b） Optional adjuvant substances. The basic polyphenylene sulfone resins identified in paragraph （a） of this section may contain optional adjuvant substances required in the production of such basic resins. These optional adjuvant substances may include substances permitted for such use by regulations in parts 170 through 189 of this chapter, substances generally recognized as safe in food, or substances used in accordance with a prior sanction or approval.

（c） Specifications. The glass transition temperature of the polymer is 360±5 °C as determined by the use of differential scanning calorimetry.