Flash spinning process

A process for the production of flash-spun plexifilamentary film-fibril strands of a high molecular weight alternating copolymer of ethylene and carbon monoxide or a high molecular weight alternating copolymer having alternating polymerized units of carbon monoxide and at least two different olefin units one of which is ethylene, and the remainder are selected from the group consisting of propylene, butene, pentene, hexene, heptene, octene, nonene, decene, dodecene, styrene, methyl acrylate, methyl methacrylate, vinyl acetate, undecenoic acid, undecenol, 6-chlorohexene, N-vinylpyrrolidone, and the diesters of vinylphosphonic acid in which a majority of the olefin units are ethylene units which comprises forming a spin solution of said alternating copolymer in a solvent having an atmospheric boiling point between 0.degree. C. and 210.degree. C., and selected from the group consisting of alcohols and halogenated hydrocarbons having 1 to 3 carbon atoms and spinning said spin solution at a pressure that is greater than the autogenous pressure of the spin solution into a region of substantially lower pressure and at a temperature at least 50.degree. C. higher than the atmospheric boiling point of the solvent to form plexifilamentary film-fibril strands of said alternating copolymer.