Polycondensation of di- and tetrasubstituted dibromobenzenes for synthesis of poly(p-phenylene)s having alkoxy groups and gas permeability of membranes

Abstract

Polymerizations of di-substituted p-dibromobenzenes αwith the following substituents: linear alkoxy groups (1a-d), branched alkoxy groups (1e and 1f), and methoxyethoxy (1g) and tetrasubstituted p-dibromobenzenes αwith the following substituents: butoxy (1h) as well as butoxy and methyl (1i) were investigated with a Ni catalyst. Monomers having linear alkoxy groups polymerized to give relatively high molecular weight polymers (M n =40 300-49 600) in good yields. However, the molecular weights and yields of the polymers having branched alkoxy groups were relatively low because of the steric effect of branched alkoxy chains. The methoxyethoxy group-containing monomer afforded an oligomer with an M n of 666. The coupling reaction of tetrasubstituted p-dibromobenzenes occurred at a very-low level because of the steric hindrance of the tetra substituents. Polymers 2a-f exhibited high thermal stability, and the decomposition temperatures were higher than 350 °C. From the differential scanning calorimetry thermograms, 2b-d and 2f showed melting of crystallites (T m: 120 °C for 2b, 95 °C for 2c, 100 °C for 2d and 16 °C for 2f), and 2a and 2e showed glass transitions (T g: 155 °C for 2a, 65 °C for 2e). The freestanding membranes could be prepared by the hot-press method from the crystalline polymers (2b-d). These membranes exhibited relatively high gas permeability, and the oxygen permeability coefficients were 14.8-27.8 barrer, higher than those previously reported for poly(p-phenylene)s having ester substituents.