Liquid crystalline polymers containing heterocycloalkanediyl groups as mesogens. 7. Molecular weight and composition effects on the phase transitions of poly(methylsiloxane)s and poly(methylsiloxane-co-dimethylsiloxane)s containing 2-4-(2(S)-methyl-1-butoxy)phenyl-5-(11-undecanyl)-1,3,2-dioxaborinane side groups