Selective monochlorination of hydroquinone by SO2Cl2 is a preferred synthetic route to chlorohydroquinone. The product mixture, without purification, may be polymerized with terephthalic acid and other comonomers, such as 6-hydroxy-2-naphthoic acid, to provide high-strength fibers. Successive in situ chlorination, acetylation, and polymerization constitute a simple, single-reactor process with an inexpensive starting material. Chlorination by SO2Cl2 took place almost exclusively in the para position of monoaryl- or alkyl-substituted hydroquinones. Polymers therefrom, e.g., the polyterephthalates of 2-chloro-5-phenylhydroquinone or its tert-butyl analog, melted significantly lower and had T(g), higher than in the absence of chlorine. They provided crystalline, high-strength fibers, with a tenacity of 20-26 gpd and good strength retention at high temperatures. A prime cause of these effects is electronic dissymmetry across the hydroquinone moiety, optimally enhanced by steric dissymmetry.