A comparative study of the tack of Butyl and natural rubbers was made by contacting freshly cut surfaces of the compounds under various time-temperature-pressure conditions and measuring the force required to separate the splice. The temperature of the knife used to cut the samples was found to be of primary importance. The tack of Butyl compounded with 50 parts of semireën-forcing carbon black (no curatives) decreases regularly with increasing knife temperature. Both longer time and higher pressure of contact favor better splicing. Data are presented on the effect of various plasticizers and carbon blacks on the tack of Butyl compounds.

I tie iporitaneous f o r m a t i o n of a n i n s o~i~e , infii-il>lv 1,utacliene popcorn pol?;mer ha$ been encountered i n c o~i i t . o f Lhe commercial clibtillation u n i t s w h i c h are ic-etl t o purify butadiene for the s?;nthetir r u b b e r proprani. On( t' initiated, the p o l > m e r Shows a logarithmic pro\+ t h i t i b u t a d i e n e monomer and has caused fouling and etet] hurstiiig of large scale distillation e q u i p m e n t i n relatit el? short times. h l t h o u g h it can be initiated in n %ariety of w a y s , iron and a c t i t e oxygen play a11 i m p o r t a n t p a r t i r i its formation. Its growth is retarded b u t n o t t e r m i n a t e d by ~ulcanization accelerators, n hereas c.on\eritional ' i n t ioxidants have little effect.