The H-shaped block copolymers (PTMSPMA)2-PEG(PMPSTMSPMA)2 with two compositions, (EG)91-b-(TMSPMA)92 and (EG)455-b-(TMSPMA)176 have been successfully synthesized by atom transfer radical polymer-ization (ATRP) of tri(methoxylsilyl)propyl methacrylate (TMSPMA) at room temperature in methanol. The ini-tiation system applied was composed of 2,2-bis(methylene α-bromoisobutyrate)propionyl terminated poly(ethylene glycol) (Br2PEGBr2) with Mn= 4000 or 20000, CuBr and 2,2’-bipyridine. The macroinitiator, Br2PEGBr2, was pre-pared by the reaction of two hydroxyl groups terminated PEG with 2,2-bis(methylene α-bromoisobutyrate)propionyl chloride. The NMR spectroscopy and GPC measurements were used to characterize the structure and molecular weight and molecular weight distribution of the resultant copolymers. The H-shaped block copolymers Sam 1 and Sam 2 were self-assembled in DMF/water mixtures and then the trimethoxysilyl groups in PTMSPMA were cross-linked by condensation reaction in the presence of triethylamine. Stable large-compound vesicles with 10 nm diameter of cavities were formed for Sam 1 which contains a short PEG chain. However, the self-assembling of the Sam 2 in the selective solvents resulted in big vesicles aggre-gates. These two different morphologies of aggregates are attributed to their relative chain length of water soluble PEG. The vesicles formed from Saml with short PEG chains have big surface energy which will lead them to self-assemble further, forming large-compound vesicles.