The polymer chain configuration, molecular relaxation, and the dipole moment of poly(nhyphen;butyl isocyanate), (sngbnd;COsngbnd;NRsngbnd;)n, where Rthinsp;equals;thinsp;C4H9, have been studied by dielectric measurements of the polymer in dilute solution. The complex dielectric constant,egr;*thinsp;equals;thinsp;egr;prime;thinsp;minus;thinsp;jegr;Prime;, was measured at room temperature over a frequency range 10minus;1ndash;1thinsp;times;thinsp;106Hz for fractionated samples whose molecular weights cover a very broad range, 20thinsp;times;thinsp;103ndash;10thinsp;times;thinsp;106. From observation of the dielectric relaxation time as a function of molecular weight we deduce that the lowhyphen;molecularhyphen;weight molecule,Mwthinsp;thinsp;80thinsp;times;thinsp;103, is rodlike and helical. Upon increasing the molecular weight, this rodlike conformation can not be sustained and chain flexibility accumulates with the addition of each monomer unit to the chain. Finally at high molecular weight,Mwthinsp;thinsp;106, the polymer chain configuration can be described as random coil. The relaxation time and dipolehyphen;moment measurements indicate that there is a onehyphen;tohyphen;one correspondence between the endhyphen;tohyphen;end distance and the dipole moment of the poly(nhyphen;butyl isocyanate) (PBIC) molecule. Using the dipolehyphen;moment data alone, we are able to show that the PBIC chain configuration as a function of molecular weight can be described by the Kratkyndash;Porod wormlike model. The relationship between PBIC and biological molecules, especially the polypeptides, is discussed.
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