1.Polymerizability has been investigated in the halogen-substituted ethylene series, tetra- and di-haloethylenes being taken as examples.2.It has been established that steric hindrance to polymerization in the substituted-ethylene series is determined by the number and sizes of the substituents on the doubly bound carbon atoms.3.It has been found that the “limiting steric radius” for a substituent, is about 1.4–1.7 A in the case of tetra-substituted ethylenes.4.It has been shown that in the case of the asymmetrical dihaloethylenes polymerization is possible whatever the halogen may be.5.The polymerization of 1,1-dibromoethylene has been investigated.6.It has been shown that tetrabromo-, tetrachloro-, and tetratodoethylenes are not able to polym