α,ω‐dichloropoly(2‐methylpropene) as an inifer: A modification to the Kennedy‐Smith mechanism

Experimental details are given of attempts to enumerate the binary ionogenic equilibria (B.I.E.) of 1‐chloro‐1‐methylethylbenzene (1)/BCl3, 1,4‐bis(1‐chloro‐1‐methylethyl)benzene (2)/BCl3 and 1,3,5‐tris(1‐chloro‐1‐methylethyl)benzene (3)/BCl3 in CH2Cl2. Due to chemical reaction (dimerisation or polymerisation) no experimental values for the B.I.E. constants could be obtained. A Born‐Haber cycle is constructed to estimate the relative sequence of the overall B.I.E. constants. A similar treatment for 2‐chloro‐2methylpropane as a thermodynamic model for α,ω‐dichloropoly(2‐methylpropene) (4) suggests that the overall B.I.E. constant for these polymers is somewhat smaller than those for 1 and 2 but greater than that for 3. Using 2/BCl3 as initiator for the polymerisation of 2‐methylpropene (IB) it is shown, that the degree of polymerisation of 4 can be controlled within the limits 10 < DP < 100. It is shown that 4 can also act as an initiator for the polymerisation of IB, that these polymerisations involve only free ion propagation and, from a kinetic analysis of these polymerisations, that: (k )2/k = 12 1 · mol−1 · s−1, k = 1,2 · 10−3 l · mol−1 · s−1, k [P ] = 1,7 · 10−3 s−1, and k /(k K ) = 102. The same analysis demonstrates that the self‐ionisation of BCl3 can be neglected in terms of any influence on the molar mass of the products. Experiments are also described which show that 2‐chloro‐2‐methylpropane is not suitable as a substitute initiator for IB, but that 2‐chloro‐2,4,4‐trimethylpentane is a useful model for 4 as an initiator for the polymerisation of IB.