Synthesis and applications of functionalized polyolefins using organometallic complexes

Abstract

The copolymerization of ethylene with triphenylamine (TPA)-containing $\alpha$-olefin monomer 4-(7-Octen-1-yl)-N,N-diphenylaniline (\bf{1}) using a \emph{rac}-$Et(Ind)_2ZrCl_2$ (EBIZr)/MAO catalytic system was investigated to prepare polyethylene with pendent TPA groups. Despite the presence of a large excess of TPA moieties, the polymerization reactions efficiently produce copolymers of high-molecular-weight with the comonomer incorporation up to 6.1 mol % upon varying the comonomer concentration in the feed. Inspection of the aliphatic region of the $^{13}C$ NMR spectrum and the estimated copolymerization parameters ($\emph{r_1}\approx 0$ for 1 and $\emph{r_E}\approx43$ for ethylene) reveal the presence of isolated comonomer units in the polymer chain. While UV-vis absorption measurements of the copolymers show an invariant absorption feature, PL spectra exhibit a slightly red-shifted emission with increasing content of $\bf{1}$ in the polymer chain. All the copolymers show high thermal stability ($T_{d5} > 436^\circC$) and the electrochemical stability toward oxidation is also observed. Particularly the copolymer displays hole-transporting ability for the stable green emission of $Alq_{3}$ when incorporated into the hole-transporting layer of an electroluminescence device. Single-site group 4 metallocene catalytic systems have enabled us to produce polyolefins with the tailored polymer architecture in terms of molecular weight, functionalities, and degree of functionalization, which in turn may lead to intriguing properties. Particularly, polyolefins bearing triarylamine (TAA) functionality could be of great interest in display applications like OLEDs since they can possess hole-transporting properties. In this regard, we recently reported that polyethylene bearing triphenylamine group can act as hole-transporting layer materials in OLEDs. As part of our continuous contributions to this area, we have investigated the effects of catalyst structure and tria...