AbstractFree‐radical polymerizations of five 2‐silyl‐substituted 1,3‐butadienes, 2‐trimethoxysilyl‐1,3‐butadiene(1), 2‐triisopropoxysilyl‐1,3‐butadiene(2a), 2‐[diisopropoxy(methyl)silyl]‐1,3‐buta‐diene(2b), 2‐[isopropoxy(dimethyl)silyl]‐1,3‐butadiene(2c), and 2‐trimethylsilyl‐1,3‐butadiene(3), were carried out in bulk. Considerable amounts of Diels‐Alder dimers as well as polymers were obtained at 80°C with AIBN as an initiator. Formation of the dimer was suppressed completely at 15°C with a redox type initiator, a combination of benzoyl peroxide andN,N‐dimethylaniline. In these cases, the polymerization rates were extremely low, resulting in low polymer yield, at most 50%. The microstructures of the resulting polymers were predominantlyE‐1,4, regardless of the polymerization conditions and the substituents at the silicon atom. The results of copolymerizations of silyl‐butadienes (M1) and styrene (M2) show that the former monomers have higher reactivity than the latter (r1= 4,1 − 2,2;r2= 0,4 − 0,5). Ther1values decrease with an increa