Anionic polymerisations of p-methoxystyrene, p-methylstyrene, p-chlorostyrene and p-cyanostyrene were carried out in tetrahydrofuran (THF) and methylcyclohexane. The block copolymers poly(styrene-b-p-methoxystyrene-b-styrene), poly(styrene-b-p-methylstyrene-b-styrene) and poly(styrene-b-p-cyanostyrene) were also polymerised by using THF as solvent. The initiators included n-butyllithium (n-BuLi) and sodium naphthalenide. The use of both n-BuLi and sodium naphthalenide usually produced higher values of <(M)over bar (n)> than were calculated. In the former case this could be explained by the lower reactivity of the initiator, which has been found to aggregate in THF. The molar masses were determined by thermal field-flow fractionation (ThFFF), size exclusion chromatography (s.e.c.) and light scattering (LS). ThFFF and the s.e.c. were used for determining the molar mass distributions. The agreement between the three methods was satisfactory.