Preparation and Characterization of POSS-based Seven-arm Star-shaped Polymers via Living Anionic Polymerization

The preparation of star-shaped polymers using incorporation of living anionic polymerization with polyhedral oligomeric silsesquioxane (POSS) is rarely reported. In this study, two types of POSS-cored star-shaped polymers were obtained by one-step addition reaction. Firstly, the living (polyisopryl)lithium (PI-Li) and living polystyrene-block-polyisoprene block copolymer chain (PS-PI-Li) were synthesized by high-vacuum living anionic polymerization. Meanwhile, a POSS derivative with one hydroxyl and seven vinyl groups (VPOSS-OH) was prepared by the addition of triflic acid to commercial octavinyl POSS with eight vinyl groups (V8T8). Subsequently, the mono-hydroxyl functionalized seven-arm star polymers were prepared by directly adding living PI-Li or PS-PI-Li to VPOSS-OH in benzene. The purified star-shaped polyisoprene 7PI-POSS-OH and star-block copolymer 7(PS-PI)-POSS-OH were obtained after fractionation precipitation, and then characterized by nuclear magnetic resonance (H-1- and C-13-NMR), gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy, respectively. By changing the feed ratio of the monomer to initiator, the polymers with different degree of polymerizations were synthesized. The compositions of the polymers were calculated by comparison of the integrals of the characteristic signals from H-1-NMR spectra. GPC analysis indicated that the trace of the crude products showed an apparent shift to smaller retention time compared with that of the base PI or PS-PI. The fractionated samples had symmetric peaks and relatively narrow polydispersity. MALDI-TOF MS tests demonstrated that the base PS gave a single molecular weight distribution, and the observed molecular weight was in good agreement with the calculated value. The similar result was also found for the base PS-PI. However, the MALDI-TOF MS spectra were not obtained for the fractionated star-shaped polymers, possibly because of their high molecular weights. TGA analysis showed that the thermal decomposition temperature of 7PI-POSS-OH and 7(PS-PI)-POSS-OH was higher than the base PI and the block copolymer PS-PI. In addition, it was also found that about 6% of residue left at 600 degrees C, which may be due to the incorporation of POSS segment. The process reported here may serve as an alternative approach to produce functional star-shaped polymers by changing the structure of the initiators and the monomers.