Synthesis and self-assembly of reactive H-shaped block copolymers

Abstract

The H-shaped block copolymers (PTMSPMA)₂PEG(PMPSTMSPMA)₂ with two compositions, (EG)₉₁-b-(TMSPMA)₉₂ and (EG)₄₅₅-b-(TMSPMA)₁₇₆ have been successfully synthesized by atom transfer radical polymerization (ATRP) of tri(methoxylsilyl)propyl methacrylate (TMSPMA) at room temperature in methanol. The initiation system applied was composed of 2,2-bis(methylene ?-bromoisobutyrate)propionyl terminated poly(ethylene glycol) (Br₂PEGBr₂) with M_n = 4000 or 20000, CuBr and 2,2′-bipyridine. The macroinitiator, Br₂PEGBr_2, was prepared by the reaction of two hydroxyl groups terminated PEG with 2,2-bis(methylene ?-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 aggregates. These two different morphologies of aggregates are attributed to their relative chain length of water soluble PEG. The vesicles formed from Sam1 with short PEG chains have big surface energy which will lead them to self-assemble further, forming large-compound vesicles.

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