High-pressure synthesis of polyphenylacetylene

Abstract

Polyacetylene is an insoluble conjugated polymer that can be obtained by using conventional ZieglerNatta catalysts [1-3]. Substituted acetylenes, having bulky phenyl groups such as phenylacetylene, produce oligomers not exceeding the number-average molecular weight of 7500 and insoluble polymers by the use of the Ziegler-Natta catalyst [4, 5]. Masuda et al. found in 1974 that group 5 and 6 transition metal catalysts (W and Mo based catalysts) are effective for phenylacetylene polymerization [4, 6]. These polyacetylenes with substituents have attracted much attention as electrical and non-linear optical materials [7-9]. The application of pressure is well known to influence the structure, properties and reactions of substances [10-15]. Acetylene was polymerized at room temperature by a reaction-induced high pressure [11]. A previous paper reported the synthesis of a phenylacetylene oligomer under high pressure (0.11-0.92 GPa) and high temperature (100-200 °C) [16]. In the study reported here, the polymerization of phenylacetylene was carried out at room temperature under high pressure (1.5 GPa). Visible absorption spectroscopy and gel permeation chromatography (GPC) were utilized to characterize the structure of the product. Phenylacetylene (molecular weight 102.14, liquid) in the form H--C=--C--CoH 5 (Wako Pure Chemical Industries Ltd, Japan) was used for the reaction without further purification [purity >99% (gas chromatography)]. The reaction of phenylacetylene under high pressure was performed with a specially designed super high hydrostatic pressure reactor (Hikari High Pressure Machinery Co., Japan). The block diagram of the reactor is schematically illustrated in Fig. 1. Paraffin was used as a pressure transmitting medium. The pressure in the super high pressure vessel was increased ten times compared with that in the high pressure vessel through the hydraulic intensifier. Pressure was measured using a Bourdon gauge (Heise gauge) and a manganin coil gauge. The pressure was displayed on a digital manometer and was recorded on a recorder. The specimen (about 2 g) was packed into a polytetrafluoroethylene cell (inside diameter 8 mm, length 40 mm). After closing the cell, it was introduced into the super high pressure vessel. The specimen was compressed at 1.5 GPa by a motor driven oil pump and substantially reacted at room temperature (2225 °C) for constant times of 1-300 h. After reaction under high pressure, the product was decompressed and removed from the cell. Visible absorption spectra of the products in a quartz cell (specimen path length 10mm) were recorded on an Ultraviolet (UV)-visible recording spectrophotometer (Shimadzu UV-2100). The spectrum was measured in the 400-800 nm region. The molecular weight of the product was determined using a liquid chromatograph (Japan Analytical Industry Co., Ltd, LC-08) consisting of a UV absorption detector (wavelength 254nm) and a column. Chloroform was used as a mobile phase at