A polymerization process for producing a copolymer of tetrafluoroethylene and perfluorobutylethylene, prepared by an aqueous dispersion polymerization technique, and the resin produced thereby, are provided. This copolymer contains a relatively small amount, between about 0.02 weight percent and about 0.6 weight percent, of comonomer polymerization units. The copolymer is believed to be comprised of a core-shell structure wherein the polymerized comonomer units reside primarily within the core. The primary particle size of the copolymer ranges from 0.175 microns to and including 0.203 microns and the standard specific gravity is less than 2.143. This copolymer possesses a unique combination of very small particle size coupled with high molecular weight, a combination not heretofore achieved in tetra-fluoroethylene polymers of the dispersion or fine powder type. The process of this invention is characterized by permanganate initiation and the entire reaction is carried out in the absence of zinc chloride or other ionic strength enhancer. The addition of initiator must be stopped well before completion of the reaction, preferably at or before the mid-point of the complete reaction.