SYNTHESIS AND SELF-ASSEMBLY OF AMPHIPHILIC ABA TRIBLOCK COPOLYMER via COMBINATION OF ROMP AND ATRP

Ring-opening metathesis polymerization (ROMP) with functionalized chain transfer agent (CTA) for the preparation of telechelic polymers has the ability to control the polymer molecular weights through varying the ratio of monomer to CTA. The bromo-terminated telechelic polymer (Br-PNBEDE-Br) was prepared via ROMP of norbornene derivative, in conjunction with a CTA in[bmim] [BF4]. The obtained polymer was characterized by H-1-NMR spectroscopy. The alkene proton signals of the norbornene ring appeared approximately at delta = 6.24. Upon ring-opening and subsequent polymerization, these proton signals shifted upfield to approximately delta = 5.64 similar to 5.16, this indicated the polymerization had occurred. The resonances of methylene protons adjacent to the ester bond (CH = CHCH2 OCO) shift from delta = 4.82 in the CTA to delta = 4.56 in the polymer. These characteristic H-1-NMR resonances indicated that the CTA have been incorporated into the polymer chain. Furthermore, other types of end-groups were not observed in their expected regions of the H-1-NMR spectroscopy. Thus, the polymer should be a difunctionalized telechelic polymer with a high degree of bromine end functionalization. Based on using of the bromo-terminated telechelic polymer as macroinitiator, amphiphilic ABA triblock copolymer was synthesized by atom transfer radical polymerization (ATRP) of 2-(dimethylamino) ethyl methacrylate (DMAEMA) in [bmim] [BF4]. The formation of the copolymer was verified through the characteristic resonances of OCH2 CH2N and N(CH3)(2) protons from the block of PDMAEMA at delta = 2.63 similar to 2.52(H-p) and delta = 2.35 similar to 2.24(H-q), respectively, and resonances of methyl protons of C (CH3) from the same block at delta = 1.12 similar to 0.80 (H-k). The integration area ratios of these characteristic resonances of 2.00:5.96:2.92 were well agreed with the ratios of corresponding protons of 2:6:3. The molecular weights of the copolymers were calculated by comparing the integral intensity of the methylene protons (H-p) of PDMAEMA at delta = 2.56 to the combined integral intensities of the methylene protons from both PNBEDE and PDMAEMA at delta = 4 05 (H-e and H-1). The GPC curve showed a monomodal molecular weight distribution of the triblock copolymer prepared from ROMP macroinitiator. After polymerization, the molecular weight of the copolymer is shifted to high molecular weight position, and no peak attributed to the starting macroinitiator was observed, which means the ROMP macroinitiator used has been completely converted to the ABA triblock copolymer. The molecular weight of the triblock copolymer obtained by GPC analysis (M-n,M-GPC) was slightly lower than that estimated by NMR (M-n,M-NMR), and the triblock copolymer has reasonable low molecular weight distribution with a PDI of less than 1.40. The prepared triblock copolymer PDMAEMA(90)-PNBEDE8-PDMAEMA(90) (M-n,M-NMR = 33100) can self-assemble spontaneously in H2O to form polymeric micelles, which were characterized by DLS I AFM, and TEM techniques. DLS measurements were used to estimate the hydrodynamic diameters of the micelles in aqueous solutions. The hydrodynamic diameter of the micelles was in the range of 183 similar to 236 nm with the increasing of pH value from 4 to 9. The morphology of copolymer was examined in preliminary investigations b AFM An the AFM image, one can see many separate and densely deposited particles as spherical morphology on the mica surface, the spherical particles appear to be comparatively uniform in size, i. e., they are essentially monodisperse with an average diameter of 600 rim, while these nanoparticles exhibited collapsed shapes on the mica surface with average height of 35 nm. Further evidence for the formation of triblock copolymer was obtained by TEM analysis. The projection of the micelles is circular, and the micelles must be spherical with the overall diameter of around 50,30 and 100 nm at pH 4,7 and 9, respectively.