Determination of compositional heterogeneity of styrene‐methyl methacrylate block copolymers

Determinations of compositional heterogeneity of anionically prepared block copolymers of styrene (S) and methyl methacrylate (M) were attempted by three different methods: thin‐layer chromatography (TLC), cross‐fractionation, and by a computer simulation method. To this end the TLC elution behavior of diblock and triblock copolymers of SM‐ and MSM‐type were compared with those of their statistical copolymers. A new TLC method was devised which does not require any reference samples as TLC elution standards. The compositional distributions determined by the three methods were in good agreement with one another, and found to be unexpectedly broad. The implication of such a result was discussed on the basis of the polymerization mechanism of the block copolymers.