The morphology of rigid‐rod polymers and molecular composites resulting from coagulation processing

Abstract

The effects of processing conditions on the morphology of molecular composite films are examined by optical and electron microscopy. During coagulation processing from solutions in methanesulfonic acid (MSA), rigid‐rod polymer, such as poly(p‐phenylenebenzobisoxazole) (PBO), phase separates into undesirable aggregates. The coagulant and the method of its introduction have been found to exert a strong impact on the final film morphology. A quench of a PBO solution in MSA into a water bath results in a three dimensional interconnected network of PBO, while a slower introduction of water results in a more amorphous material. A computer simulation program of the coagulation process has been developed to better understand the different structures emerging from coagulation processing of molecular composites. The simulation results are in qualitative agreement with the experimental observations.

In-Situ Synchrotron WAXD/SAXS Studies of Structural Development during PBO/PPA Solution Spinning

“…The PBO crystal structure has been studied quite extensively over the past two decades using different methods. [12][13][14][15][16][17][18][19][20][21][22][23][24][25] It has been determined that PBO chains crystallize into a monoclinic unit cell with parameters a ) 11.20 Å, b ) 3.5 Å, c ) 12.0 Å, and γ ) 101.3°, 17 where the c-axis represents the chain axis. In the crystal structure, the neighboring chains exhibit axial shifts of +c/4 or -c/4 distance.…”

“…To understand the intermediate structure during spinning, prior knowledge about the PBO crystal structure is essential. The PBO crystal structure has been studied quite extensively over the past two decades using different methods. − It has been determined that PBO chains crystallize into a monoclinic unit cell with parameters a = 11.20 Å, b = 3.5 Å, c = 12.0 Å, and γ = 101.3°, where the c -axis represents the chain axis. In the crystal structure, the neighboring chains exhibit axial shifts of + c /4 or − c /4 distance. , In addition, a translational disorder along the chain axis can cause distinct streaking in the layer lines of the X-ray diffraction patterns. ,, Several groups have considered this translational disorder in the analysis of the diffraction data. , It has been noted that the aromatic rings can be twisted, producing another kind of defect in the crystal structure .…”

Rigid‐Rod Polymers

“…Different coagulants can lead to different morphologies of the PBO fibers. A quench of a PBO/MSA solution into a water bath results in a (3D) interconnected network, whereas a slower introduction of water results in a more amorphous material (152). Under some extreme conditions during coagulation, the heterocyclic rings of the PBO structure suffer cleavage and some chains are even broken completely.…”

Structure Formation Phenomena During Phase Inversion. II. Semiflexible Polymers and Liquid Crystallinity

“…A review by Papkov [6] appears to come closest to a discussion of simultaneous liquid crystallinity and phase inversion for CA. On the experimental side, semirigidity (semiflexibility) instead of rigidity, different strengths of kinetic effects (including the possibility of formation of various types of gels), and the absence of an orienting field are the reasons why the consequences of liquid crystalline equilibria have not been noticed so far during PI processing of CA-based dopes [1], while such consequences are well known in the case of rod polymer solution fiber spinning [7][8][9][10][11][12][13].…”