In situ copolymerization of ethylene to linear low-density polyethylene (LLDPE) with calcosilicate (CAS-1) supported dual-functional catalytic system

Calcosilicate (CAS-1) was used for the first time as an effective carrier for simultaneous immobilization of a dual-functional catalytic system consisted of iron-based bis(imino) pyridyl complex (O) and zirconocene compound (C) to form heterogeneous catalyst precursor (CAS-1/O/C). The α-olefins formed form O-catalyzed ethylene oligomerization copolymerized in situ with ethylene to linear low-density polyethylene (LLDPE) under the catalysis of C in CAS-1/O/C upon addition of cocatalysts as described hereafter. Instead of methylaluminoxane (MAO), triethylaluminum (TEA) was employed to activate the copolymerization reaction with high catalytic activities and smooth kinetic process. Experimental results reflected that the selectivity for lower α-olefins was improved due to the confinement effect of the layered structures of CAS-1, hence greatly increasing the incorporation rate of α-olefins into LLDPE main chains and the branching degree accordingly during the in situ copolymerization of α-olefins and ethylene. The layered structure of CAS-1 endowed the resultant LLDPE with improved thermal stability in addition to higher molecular weights (Mn).