ON THE ORIGINS OF ENTANGLEMENT CONSTRAINTS

We have studied the dynamic structure factors of poly(ethylene-propylene) alternating copolymer (PEP) and saturated polybutadiene (PEB-2). To investigate different models of entanglement formation, we varied the polymer volume fraction (PEB-2) and temperature (PEB-2 and PEP) and, thereby, systematically changed the two length scales considered to be important for the buildup of entanglements: namely, the contour length density and the random walk step length. In the framework of the scaling ansatz, our result is in the range of the binary contact models and excludes the packing model. Quantitatively, however, the scaling ansatz is not confirmed. Also, qualitative agreement is found with respect to the topological calculations by Iwata and Edwards. Our results are at variance with one of the basic relations of the Doi-Edwards theory of viscoelasticity, which relates the elastic response of a polymer melt with molecular chain parameters and the entanglement distance.