Preparation of well-oriented poly(p-phenylene pyromelliteimide) fiber via shear-induced orientation of poly(amic ethyl ester) precursor during polymerization

The orientation of poly(p-phenylene pyromelliteimide) (PPPI) molecules was examined by means of shearing during the gelation of poly(amic ethyl ester) (PAEE) precursor and thermal imidization. The polymerization of 1,4-phenylene diamine (PPDA) and 2,5-diethoxycarbonyl-1,4-benzenedicarbonyl chloride (DEBC), and that of N,N′-bis(trimethylsilyl)-1,4-phenylenediamine (N-silyl-PPDA) and DEBC yielded the PAEE gel during polymerization. With respect to the polymerization of PPDA and DEBC, 0.44 mol L^-1 gave the highest DPn of PAEE at the gelation point, and the strong shear during gelation made the PAEE and ultimately PPPI molecular chains oriented in the planar mode. In contrast to this, the polymerization of N-silyl-PPDA and DEBC gave a higher DPn of PAEE at the gelation point than that of PPDA and DEBC. The strong shear stress applied to the PAEE gel, prepared at 0.50 mol L^-1, induced the uni-axial orientation of the molecular chains, but the relaxation of the orientation occurred gradually with time. The addition of ethyl acetate to the gel prevented the relaxation of the chain orientation and accelerated the crystallization. As a result, uni-axial orientation of the PAEE molecular chains was induced along the shear direction in the gel rather than the planar mode, and ultimately the PPPI molecular chains were well-oriented.