Methacrylic acid was photopolymerised using CdS and composite, CdS/HgS
and CdS/TiO2, Colloidal semiconductor particles as initiators. The pr
eviously proposed photoinitiation mechanism involving the photogenerat
ed positive hole in the valence band of the CdS colloid was confirmed
by the electron scavenging action of TiO2. The effect of pH on the cou
rse of the polymerisation was investigated and is discussed.