New poly(silylenemethylene)s with long n-alkyl side chains, namely, poly(di-n-butylsilylenemethylene) (PDBSM), poly(di-n-pentylsilylenemethylene) (PDPeSM), and poly(di-n-hexylsilylenemethylene) (PDHSM), have been prepared by means of catalytic ring-opening polymerization of the corresponding tetraalkyl-substituted 1,3-disilacyclobutanes. Polymerization yielded high molecular weight poly(silylenemethylene)s with a strictly alternating SiR(2)/CH2 backbone structure. Longer polymerization times were necessary for 1,3-disilacyclobutanes substituted with longer n-alkyl chains than for the polymerization of monomers with methyl groups. High molecular weight fractions of the materials were characterized by calorimetry with respect to their thermal behavior. Considerably higher glass transition temperatures evidenced lower backbone flexibility than for the analogous poly(di-n-alkylsiloxane)s. Surprisingly, all homologues including poly(di-n-propylsilylenemethylene) (PDPSM) displayed similar phase behavior, showing a small endotherm a few degrees below isotropization, but no broad mesophases as observed in the case of the poly(di-n-alkylsiloxane)s.