Structural Design And Synthesis Of Functionalized Hyperbranched Polyethylenes And Surface Modification Of Ordered Mesoporous Silica With Functionalized Hyperbranched

Functionalization of hyperbranched polyethylene (HBPE) with specific second polymer block is of great importance for its successful applications in various fields. In this paper, a new strategy has been explored for the functionalization of HBPE via introducing polyketone (PK) block into the structure of HBPE. A series of HBPE-b-PK block copolymers and core-shell HBPE-g-PK multiarm star copolymers were successfully synthesized by means of Pd-a-diimine catalysts, a type of late transition metal catalysts, based on an unique ligand exchange mechanism.(1) A series of HBPE-b-PK block copolymers were synthesized via one-pot sequential polymerization process based on ligand exchange mechanism. In this process, ethylene polymerization was first performed at25℃and ethylene pressure of1atm with a Pd-diimine catalyst bearing an ATRP initiating group to give an living HBPE chain, then bipyridine of equal molar ratio relative to catalyst was added to further catalyze subsequent tert-butyl styrene (TBS)/CO alternating copolymeri-zation, thus rendering the HBPE-b-PK block copolymer. Structural characterizations on various as-synthesized block copolymers were carried out by means of Fourier-transformed infare spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1H NMR), differential scanning calorimetry (DSC), dynamic light scattering (DLS) and state light scattering (SLS) technologies. It is well confirmed that well-defined HBPE-b-PK block copolymers can be achieved via the ligand exchange strategy by means of the Pd-diimine catalyst, with controllable polymer block length conveniently adjusted by changing polymerization time for ethylene polymerization and TBS/CO alternating copolymerization stage, respectively. Also, the HBPE block was found to possess hyperbranched chain topology with higher total branching density (79-93/1000C).(2) To synthesize core-shell HBPE-g-PK multiarm star copolymers, a HBPE bearing multiple pendant acryloyl groups was first prepared via chain walking copolymerization of ethylene and1,4-butanediol diacrylate (BDA) with Pd-diimine catalyst at25℃and ethylene pressure of1atm. Then a multinuclear Pd-diimine catalyst was obtained by reacting the acryloyl-functionalized HBPE and acetonitrile Pd-diimine catalyst, and TBS/CO alternating copolymerization was performed with the as-synthesized multinuclear catalyst at25℃to render the HBPE-g-PK multiarm star copolymers via the ligand exchange mechanism. Structural characterizations on the synthesized star polymers were performed by FT-IR, DSC,1H NMR and DLS technologies and it is testified that the resulting HBPE-b-PK copolymer exhibits core-shell structure with multiple PK arms. The PK arm number and length can be effectively adjusted by changing polymerization time.(3) The SBA15was first surface modified with a coupling agent to give the acryloyl-functionalized SBA15silica, then Pd-diimine catalyst was covalently immobilized onto the surface of SBA15to give a SBA15-supported Pd-diimine catalyst. TBS/CO alternating copolymeri-zations were further performed with the synthesized SBA15-supported Pd-diimine catalyst, giving the hybrid SBA15silica covalently tethered with PK within mesopores. One-pot sequential copolymerization of ethylene/TBS/CO was also performed with the SBA15-supported Pd-diimine catalyst and HBPE-b-PK grafted SBA15silica was obtained. It is confirmed by the results, from thermogravimetry analysis (TGA), FT-IR, X-ray diffraction (XRD) and high-resolution transmittance electron microscopy (HRTEM), that PK and HBPE-b-PK have been grafted within the mesopores of SBA15silica. The polymer-modified SBA15silica was found to exhibit well-remained mesoporous structures with controllable polymer grafting ratio by changing polymerization time.