A number of vinyl ethers investigated were found to undergo violent polymerization reactions on the addition of free iodine. With very small amounts of the catalyst, considerable differences in polymerizability are disclosed, the phenyl ether being least sensitive to its action. The alkyl ethers, but not the phenyl ether, are very slowly converted into polymeric forms under the influence of heat and ultra-violet light. The orders of polymerization of the products range from 18 to 82. The "mer" refractivities of some of the polymers have been determined and shown to agree with the theoretical values calculated on simple assumptions. A closed-ring chain structure, with the structural units arranged in regular order and joined by normal, single bonds, is proposed.