Structural analysis of regular copolymers of butadiene and methylene with repeat unit [But—(Ch 2) n—But] by the use of model compounds—I. The effect of changing “ n” on the microstructure of the copolymers prepared using lithium

Abstract

A method is described for the preparation of regular copolymers containing butadiene and having the repeat unit —[But—R—But]— where R is an alkyl ligand. The process involves reaction between the monomer, alkyl dihalide and alkali metal. A new technique is presented for determining the 1,2 to 1,4 ratios in the polymers by preparing model compounds of structures HR—But—But—RH under identical experimental conditions, separating by preparative GLC, and analysing by 1H NMR. Results indicate that, when lithium is used as the alkali metal and R = (CH 2) n , the probability of 1,2 placement at a polymerization temperature of -15° is about 0·4 and is independent of n at values of n > 2. The reasons for deviations at n = 1 are discussed.