Morphology of a phase‐separated and a molecular composite PBT/ABPBI polymer blend

Abstract

The structure and morphology of homopolymers and blends of rigid‐rod poly(p‐phenylene benzobisthiazole) (PBT) and semiflexible coil poly[2,5(6)benzimidazole] (ABPBI) were examined by wide‐angle x‐ray diffraction and scanning and transmission electron microscopy. When samples were processed from a solution where the total polymer concentration of 30% PBT/70% ABPBI blend was greater than a critical concentration, large‐scale phase separation occurred and 0.1–4 μm ellipsoidal particles were present in a ductile matrix. The ellipsoids were chiefly composed of aggregates of well‐oriented 10‐nm PBT crystallites, while the matrix material was chiefly ABPBI. When the concentration was less than a critical concentration, the solution was optically homogeneous. In processing of fiber and film samples from the homogeneous solution, large‐scale phase separation was inhibited by rapid coagulation in a water bath. After heat treatment, these samples were found to contain crystallites of both PBT and ABPBI with lateral dimensions of ordered regions no larger than 3 nm. The PBT homopolymer was dispersed in the matrix at the molecular level in ordered regions at a scale no larger than 3 nm, resulting in a rigid‐rod molecular composite. In the rigid‐rod molecular composite fiber both the molecular‐level dispersion and high orientation contributed to higher values of strength and modulus compared to the properties of a phase‐separated fiber. The strength and modulus of highly oriented fiber were only 25% higher than those of planar isotropically oriented film, suggesting that the level of dispersion of rod molecules is more important than orientation of the reinforcing phase in rigid‐rod molecular composites.

Extractive Bioconversion of 2‐Phenylethanol from l‐Phenylalanine by Saccharomycescerevisiae

“…ABPBI has been shown to be crystalline,14–16 but the X‐ray data contain relatively few Bragg reflections. Wereta et al14 reported that films of ABPBI prepared from FAMC and MSA solutions had uniplanar orientation.…”

“…Wereta et al14 reported that films of ABPBI prepared from FAMC and MSA solutions had uniplanar orientation. Hwang et al15 prepared oriented fibers from MSA/chlorosulfonic acid solutions and interpreted the X‐ray data in terms of a 2 1 chain conformation with a fiber repeat of c = 11.5 Å. Krause et al16 observed off‐axis layer line reflections pointing to the existence of three‐dimensional order and proposed an orthorhombic unit cell for ABPBI, with the dimensions a = 7.16 Å, b = 3.49 Å, and c = 11.7 Å, by analogy to the structures of poly(2,5‐benzoxazole) (ABPBO) and poly(2,6‐benzothiaole) (ABPBT) 17…”

“…Recently, a new method of preparing films of ABPBI with high orientation has been developed in this laboratory:18 the films are cast from ethanol/sodium hydroxide solutions and stretched after doping with phosphoric acid. These stretched films have higher modulus (47 GPa) than pristine ABPBI fibers (36 GPa) 16. This article describes the X‐ray analysis and molecular modeling of the crystal structure of ABPBI films doped with phosphoric acid.…”

Dielectric relaxations in phosphoric acid‐doped poly(2,5‐benzimidazole) and its composite membranes

“…The samples were heat‐treated at a temperature of 100 and 250 °C (5 h each) prior to recording the XRD patterns; the tests were carried out on the same sample in each case, and after the annealing at 250 °C, the XRD pattern was again recorded at 30 °C (30 °C—after HT, Figure ). The undoped samples [Figure (a,b)] show distinct peaks at 2θ values of 10 and 26.5° attributed to the orthorhombic unit cell of ABPBI . The broad shoulder peak observed at 2θ value of 18.5° can be attributed to short‐range order in the polymer.…”

Miscibility, Structure, and Property of Poly(biphenyl dianhydride perfluoromethylbenzidine)—Poly(ether imide) Molecular Composites

“…The incorporation of a small amount of flexible coil molecules into the rigid-rod matrix has been sought as a route for improving the compressive strength of the highly oriented rigid-rod materials (2)(3)(4)(5)(6)(7)(8)(9). On the other hand, a minor amount of rigid-rod polymer molecules may be dispersed in the matrix of flexible coils in order to reinforce the matrix (7). This concept is similar to the principle of the chopped fiber reinforced composites (10,11), except that reinforcement is expected to occur at a molecular level or a nanometer-scale.…”