Characterization of a polyurethane copolymer covalently linked to graphite and the influence of graphite on electric conductivity

Abstract

Polyurethane was linked to graphite modified with a phenol or 4-phenylethanol group on its surface, and the composite polymer was characterized regarding its thermal, spectroscopic, mechanical, and shape-memory properties as well as its electric conductivity. Graphite as a filler was covalently linked to a polyurethane backbone composed of 4,4′-methylenebis(phenylisocyanate) and 1,4-butanediol as hard segments and poly(tetramethyleneglycol) as a soft segment. The two different polyurethane series, differing in their modifying spacer, show similar structural characteristics and exhibit a small degree of cross-linking due to the agent used for the covalent linking of graphite to the polyurethane frame. The tensile mechanical strength and shape-recovery characteristics remain high as the graphite content is increased when compared to the linear polyurethane polymer without the linked graphite. Regarding the tensile mechanical properties, the maximum stress increases up to 436% compared to the linear polyurethane, and the maximum strain goes up to 1744%. Shape recovery reaches values as high as 93%, and shape retention gradually decreases as the graphite content increases. The electric conductivity of graphite-linked polyurethane exhibits a sharp increase as the graphite content increases, but the blended graphite polyurethane has very poor electric conductivity at higher graphite contents. The implication of this finding is discussed, and the synthesized polymers are compared with other conductive polymer composite.