1, 1,3,3-Tetramethylbutyl peroxyneodecanoate (1), t-butyl peroxyneodecanoate (II), t-butyl peroxyneoheptanoate, and di(ethylhexyl) peroxycarbonate (III) were used, each 40 or 50 dry wt.% emulsified in water, to initiate polymn. of vinyl chloride in 1.5, 10-liter and 135 m(3) reactors at 53degreesC (K-PVC = 70), 57degreesC (K = 67), and 62degreesC (K = 61). In 3-h and 4-h polymns., II (40%) converted vinyl chloride in 70 and 74%, and III (50%) did so in 71 and 77%, resp. Mixts. of initiators, I + II or I + III, gave best com. results at 57degreesC (K = 67) and 54degreesC (K = 70).