Poly[(S)-(+)-2-methylbutyl]pentylsiloxane has been synthesized by anionic ring opening polymerization of the corresponding strained cyclic trisiloxane (D-3(MeBu,Pe)) With cryptated lithium (Li+/[211]) as counterion. The polymer did not show the low and high temperature crystalline phases, that are generally found for poly(di-n-alkylsiloxane)s. Instead, the material formed a hexagonal columnar mesophase until it melted around 400 degrees C. MAS and solution C-13- and Si-29-NMR, polarizing microscopy and WAXS indicated an unexpectedly regular chain structure. It was tentatively concluded that the steric interaction of the (S)-(+) -2-methylbutyl side chains introduces sufficient regularity of the tacticity and that the chains tend to adopt a defect helix conformation. On the other hand, DSC showed the presence of a glass transition at -113 degrees C, indicating a high flexibility of the backbone.