Recently, we reported that dimethylsilanolate-initiated anionic ring opening polymerization of dimethylsiloxy- and diphenylsiloxy-cyclic siloxanes results in polymer chain branching by dimethylsilanolate-induced cleavage of only one Si-C-Ar side bond in diphenylsiloxy repeat units, leading to formation of Ph-T-branches, and not extending to the cleavage of the second phenyl group. We attributed this behavior to electronic structures of the participating dimethylsiloxy-, diphenylsiloxy and Ph-T-branch silicons and predicted that copolymers prepared by this synthetic route from dimethylsiloxy- and methylphenylsiloxy-cyclics should not undergo branching at all but should have perfect linear chain configuration. Here, we describe results of a study of two such dimethylsilanolate-initiated ring opening polymerizations of dimethylsiloxy- and methyphenylsiloxy-cyclic tetramers and characterization of the resulting polymers by SEC-MALS-VIS, Mark-Houwink-Sakurada relationship and Si-29 NMR. The results obtained clearly confirmed our prediction of expected linearity of these polymer chains and also indicated that the resulting polymers were completely amorphous even at as low methylphenylsiloxy-content as 3.9mol %. (c) 2019 Wiley Periodicals, Inc.