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Nucleophilic aromatic substitution (SNAr) reactions are exploited to prepare poly(arylene sulfide)s (PAS's) via the reaction of bis‐thiolates and dibrominated pyromellitic diimide (PMDI) derivatives. Small‐molecule model studies reveal the reaction is well‐defined and proceeds in quantitative yield in practical times at room temperature. Variation in comonomer feed ratios allowed some control over target polymer molecular weights in the step polymerization, but control was likely limited by the relatively poor polymer solubility in the dipolar aprotic solvents typically employed to promote SNAr reactions. One substitution pattern produces a steric “pocket” around the PMDI units, inducing a peculiar solubility trend in halogenated solvents; that is, greatly reduced solubility in CHCl3relative to CH2Cl2and C2H2Cl4. One example small‐molecule readily dissolves in CHCl3at room temperature, then rapidly grows poorly soluble crystals revealed by single‐crystal XRD to contain CHCl3molecules in the steric pockets. Finally, the recently demonstrated depolymerization of phthalonitrile‐based PAS's via ipsosubstitution with monothiolates as chain scission agents yields quantitative molecular weight reduction to monomeric species from the polymers reported here.