A novel silicon(IV) phthalocyanine with two axial poly(sebacic anhydride) chains has been synthesized by melt condensation of silicon phthalocyanine dihydroxide and oligo(sebacic anhydride). The polymer has been spectroscopically characterized and its molecular weights have been determined by gel permeation chromatography. (GPC) and H-1 NMR spectroscopy. Nanoparticles with an intensity-average apparent hydrodynamic radius of 65 +/- 1 nm have been prepared from this polymer via a microphase inversion method with sodium dodecyl sulfate as the Surfactant. The spherical nanoparticles contain loosely aggregated polymer chains, trapping about 90% of the water. On treatment with NaOH, these nanoparticles under-go degradation that has been monitored by laser light scattering and fluorescence Spectroscopy. Because, of the axial substitution, the change in the aggregation state of the phthalocyanine core of this polymer during nanoparticle formation and degradation is relatively Small compared with that of the zinc(II) phthalocyanine, danalogue reported earlier. in which poly(sebacic anhydride) chains are linked to the periphery of the phthalocyanine ring. (C) 2005 Wiley Periodicals, Inc.