Structure and hydrodynamics of polyamic acid chains in solutions. Effect of “pin-joint” oxygen atom |
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Authors: | OV Kallistov JuE Svetlov IG Silinskaya VP Sklizkova VV Kudriavtsev MM Koton |
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Institution: | Institute of Macromolecular Compounds, Academy of Sciences of U.S.S.R. Bolshoi 31, Leningrad 199004, U.S.S.R. |
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Abstract: | The hydrodynamic characteristics and weight-average molecular weights of some samples of poly-(4,4′-oxydiphenylene) pyromellitamic acid (I) and poly (4,4′-phenylene) pyromellitamic acid (II) in DMF have been obtained by sedimentation, viscometry and light scattering. For (I) the dependence of S0 on M was obtained and it was found that the hydrodynamic parameters depend on M up to M = 105. The experimental results were treated by using two models, viz. a Yamakawa-Fujii persistent chain and a rotational isomeric chain with free rotation about valence bonds. It was shown that the hydrodynamic behaviour of macromolecules of (I) with a pin-joint oxygen atom in the main chain is satisfactorily described by the rotational isomeric chain model with free rotation about valence bonds. The dependence of η] on M was obtained and the constants K and a in an equation of the Mark-Kuhn-Houwink type were determined for (II). The flexibility of the chain was estimated and the Kuhn segment was found to be 200 Å using the Yamakawa-Fujii theory. The flexibilities of the chains of (I) and (II) are compared; it is shown that the rigidity of the chain of (II) without a pin-joint oxygen atom in the monomer unit is much higher than that of the chain of (I). The dependence of S0 on M obtained for (II) suggests that its macromolecules show a more pronounced tendency for formation of aggregates than those of (I). |
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