Functionalization of polyolefins : entrapment of functionalized ethylene oligomers in polyethylene

Abstract

Functionalization of polyethylene by entrapment of functionalized ethylene oligomers in precipitates of polyethylene is described. The details of this entrapment process, which is an alternative to harsh, unselective existing methods for derivatizing polyolefins, have been studied using ethylene oligomers containing nitroxyl spin labels as reporter groups. The degree of mobility of these entrapped ethylene oligomers in the presence of various solvents and the reactivity of the terminal functional groups of these entrapped functionalized ethylene oligomers toward reducing agents were evaluated by ESR spectroscopy. The results show that 12% ethyl branched ethylene oligomers containing about 200 carbon atoms can be quantitatively and reproducibly entrapped in polyethylene powders by this entrapment process. The polar functional groups of these ethylene oligomers entrapped in polyethylene are near the polyethylene/solution interface when a high-density polyethylene is used as a host polymer. Studies of the mobility and reactivity of the polar spin labels entrapped in polyethylene demonstrate that the dimensions of the interfacial region of polyethylene (i.e., the effective surface dimensions of polyethylene in contact with a solution) are dependent on the parameters of the particular experiment being conducted. Examinations of the effects of changing experimental variables on the topological selectivity of entrapment of the polar functional groups in polyethylene have also been studied. These variables were focused on the nature of host polyethylene (e.g., high-density polyethylene or low-density polyethylene), the polarity of the terminal functional groups of the functionalized ethylene oligomers, the microstructure of ethylene oligomers (e.g., linear ethylene oligomers or branched ethylene oligomers), the nature of precipitation process (e.g., thermal precipitation, or solvent precipitation), and the use of various precipitation solvents (e.g., methanol or hexane). The results indicate that different extents of surface functionalization of polyethylene can be achieved by altering these experimental variables in the entrapment process.