Study on branching structure, melting, and crystallization of polyethylene prepared by nickel a-diimine catalyst covalently intercalated inside OapPOSS-modified laponite clay gallery

Ethylene polymerization was catalyzed by using nickel α-diimine covalently supported inside the octaaminopropyl polyhedral oligometric silsesquioxane (OapPOSS)-modified Laponite clay layers. The branching structure, melting, and crystallization of the polyethylene (PE) matrix of PE/OapPOSS-clay nanocomposites were investigated by X-ray diffraction analysis (XRD), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR). The results showed that the PE matrix of PE/OapPOSS-clay nanocomposites has lower branching density and higher melting point and degree of crystallinity when compared with those of PE prepared by unsupported catalyst. It is proposed that the chain walking rate of the ethylene polymerization was reduced greatly, resulting in a lower degree of branching because the catalyst has been intercalated into the clay galleries. In order to further investigate the chain branching distribution of the PE matrix of PE/OapPOSS-clay nanocomposites, a DSC technique termed successive self-nucleation and annealing was applied. It was found that the PE matrix of PE/OapPOSS-clay nanocomposites has a larger high melting point fraction, thicker lamella and longer L¯n and L¯w than PE obtained with unsupported catalyst.