Synthesis of ionic hybrid polymers with polyhedral oligomeric silsesquioxane pendant by acyclic diene metathesis polymerization and characterization

On the basis of nucleophilic substitution of aminopropyl heptaisobutyl-polyhedral oligomeric silsesquioxane (POSS-NH₂) with 4-bromo-1-butene or 11-bromo-1-undecene, two types of α, ω-diene monomers N,N'-bis(butenyl)-aminopropyl-POSS (M1) and N,N'-bis(10-undecenyl)-aminopropyl-POSS (M2) with POSS pendant were synthesized by one-step reaction, respectively. Acyclic diene metathesis (ADMET) polymerization has proven to be a versatile tool for the production of novel polymeric materials. Using tricyclohexylphosphine[1,3-bis(2,4,6-trimethylphenyl)-4, 5-dihydroimidazol-2-ylidene]benzylidine ruthenium (IV) dichloride (second generation Grubbs catalyst, Ru-II) as the catalyst, ADMET polymerization behaviors of monomers M1 and M2 were investigated in toluene, and the results showed that no polymerization occurred for M1, which may be caused by the steric hindrance of the POSS units and the strong complexation between N of the monomer and Ru of Grubbs catalyst, while polymerization of M2 was well conducted to give the POSS-containing hybrid polymer P2 with moderate molecular weight (M_n) of 29.4 kDa and large polydispersed index (PDI) of 2.21 at the time point of 24 h. After ionization of N in M2 with methyl iodide, the methylated ionic α,ω-diene monomer M3 was obtained. M3 displayed a good performance of ADMET polymerization catalyzed by Ru-II, and the corresponding polymers P3 (a~d) have the M_nvalues of 37.1, 43.9, 86.4 and 108.2 kDa under different reaction time of 24, 48, 96 and 144 h, respectively, and also their PDIs become narrower from 1.94 to 1.63 as the reaction time prolonged. The unsaturated hybrid polymer P3d with the highest M _n was further hydrogenated by p-toluenesulfonhydrazide and converted into the saturated hybrid polymer P4 with polyethylene backbone and POSS pendant at the precise position of main chain, and the hydrogenation degree was reasonably high with virtually little remaining unsaturation as monitored by ¹H NMR spectroscopy. P4 demonstrated an obviously crystallinity for both POSS group and polyethylene backbone, showing strong reflections at 2θ of 7.9°, 8.0°, 8.8°, 11.8°, 19.9° and 21.2° in X-ray diffraction patterns. The morphology of this hybrid polyethylene was investigated by atom force microscopy, and exhibited a spherical morphology with different diameter of 200, 500 and 1000 nm, which being in accordance with the size of unimolecular polymer containing about 100 POSS units in each hybrid polyethylene and their congregates.