CONFORMATION OF STAR POLYMERS WITHOUT EXCLUDED VOLUME

Nonideal behavior in the vicinity of the point where chains are attached together can significantly affect the dimensions of branched polymers. Several features of the branch point are considered, and their effect on the radius of gyration of star-shaped molecules is calculated. Two classes of behavior are found according to whether the description treats only specific geometrical properties of the monomers close to the junction or perceives the branch point more generally, as a region of reduced accessibility to more distant parts of the molecule. A new model is introduced within the latter category in which a repulsive potential surrounds the branch point and acts on all the monomers. For the special case of a hardsphere potential an exact solution is found, from which a general relationship, (S2)1/2 - (S2)01/2 ≈ c, is derived, linking the mean squared radius of gyration, (S2), to its value in the unperturbed state, (S2)0, and to a length, c, characteristic of the range of the potential. It is shown how the effect of the repulsive potential can be distinguished experimentally from local, geometrical properties of the branch point, and from the available data it is concluded that this repulsive nature of the branch-point region is the more important factor in determining the size of star-branched polymers. © 1990, American Chemical Society. All rights reserved.