A novel arsonium ylide, ω-2-methylallylarsonium ylide, was synthesized and used as monomer for polyhomologation with triethyborane as initiator. It was found that the terminal methyl group leads to C3 polymerization. Furthermore, the copolyhomologation of arsonium ylide with dimethylsulfoxonium methylide is reported for the first time. (Chemical Equation Presented). © 2016 American Chemical Society.