Synthesis and crystalline structure of poly(p-phenylene alkylene)s and poly(p-phenylene co-alkylenes)s by Kumada coupling reaction of α,ω-dibromoalkane and p-dichlorobenzene

Poly(p-phenylene alkylene)s were synthesized by Kumada coupling reaction of α,ω-dibromoalkane (BR) (1,6-dibromohexane (BH), 1,8-dibromooctane (BO), 1,10-dibromodecane (BD), 1,12-dibromododecane (BDD)), and p-dichlorobenzene (CB). The corresponding poly(p-phenylene alkylene)s (PPPRs) with low molecular weight were obtained in moderate yields. Polymer chain ends of methyl group was detected in ¹³CNMR spectroscopy, indicating preferential termination of BR. Wide angle X-ray diffraction (WAXD) profile of the poly(p-phenylene hexylene) (PPPH) showed a diffraction peak at 2θ = 20.4°. Poly(p-phenylene octylene) (PPPO), poly(p-phenylene decylene) PPPD, and poly(p-phenylene dodecylene) PPPDD showed the different WAXD profiles from that of PPPH, and the diffraction peaks at around 2θ = 18° and 24° were detected in their WAXD profiles. PPPD and PPPDD also showed a diffraction peak at 2θ = 21.6°, which was not detected in the WAXD profile of PPPO. FT-IR spectra in the frequency region, 710–740 cm⁻¹, of methylene rocking vibration of the PPPRs indicated hexagonal crystal in PPPH and triclinic-based crystal in PPPO, PPPD, and PPPDD. All the PPPRs showed melting point, which decreased with increasing of methylene length of the BR used as following, PPPH: 131.2 °C, PPPO: 91.1 °C, PPPD: 84.6 °C, PPPDD: 80.1 °C,. Poly(p-phenylene co-alkylenes)s (PPPCRs) were newly prepared by polymerizations of two kinds of BRs, BH/BO, BH/BD, or BO/BD, with CB. The PPPCRs showed the lower melting temperatures than those of the corresponding PPPRs. The WAXD profiles of the PPPCRs showed the diffraction peaks derived from both the corresponding PPPRs, and their intensities were depended on the feed ratios of the BRs.