Isotactic and syndiotactic polyketones were synthesized by the alternating copolymerizations of a mesogenic vinylarene, 4-cyano-4'-[8-(4-vinylphenyl)octy]-1-oxylbiphenyl, with carbon monoxide, and this revealed the influence of backbone tacticity on their thermal properties. The isotactic polyketone was an amorphous polymer that did not show any mesophase, whereas the syndiotactic polyketone exhibited liquid crystallinity. (C) 2003 Wiley Periodicals, Inc.