--M--L.sup.4 --Y, where Y is a polymerizable group selected from the groupconsisting of acryloxy, methacryloxy, vinyloxy and epoxy,--L.sup.3 -- and --L.sup.4 -- are linker units which are independently selected and represent a direct bond or --CH.sub.2 --, --M-- is a mesogenic unit selected from the group consisting of --M.sup.1 --M.sup.2 --, --M.sup.1 --M.sup.3 --M.sup.2--, --M.sup.1 --COO--M.su