Preparation and solubility of a partial ladder copolymer from p-phenylenediamine and o-phenetidine

A series of copolymers were synthesized by chemically oxidative polymerization of p-phenylenediamine (PPD) and o-phenetidine (PHT) in acidic aqueous media. The polymerization yield, intrinsic viscosity, and solubility of the copolymers were comprehensively studied by changing the comonomer ratio, polymerization time and temperature, oxidant, monomer/oxidant ratio, and acidic medium. As-prepared fine powder of the PPD/PHT copolymers was characterized by FT-IR, UV–vis, high-resolution 1H-NMR, and DSC techniques. A circular dichroism technique was firstly used to characterize the macromolecular structure of the copolymers. The results showed that the oxidative copolymerization from PPD and PHT is exothermic and the resulting copolymers exhibit an enhanced solubility in most of the organic solvents as compared with poly(p-phenylenediamine), sometimes also with poly(o-phenetidine). The polymer obtained is a real copolymer containing PPD and PHT units, and the actual PPD/PHT ratio calculated by 1H-NMR spectra of the polymers is very close to the feed ratio. The DSC measurement indicates that the copolymers are amorphous and chemically instable at elevated temperature.