Abstract
The unperturbed chain dimensions (〈R2〉0/M) of cis/trans-1,4-polyisoprene, a near-atactic poly(methyl methacrylate), and atactic polyolefins were measured as a function of temperature in the melt state via small-angle neutron scattering (SANS). The polyolefinic materials were derived from polydienes or polystyrene via hydrogenation or deuteration and represent structures not encountered commercially. The parent polymers were prepared via lithium-based anionic polymerizations in cyclohexane with, in some cases, a polymer microstructure modifier present. The polyolefins retained the near-monodisperse molecular weight distributions exhibited by the precursor materials. The melt SANS-based chain dimension data allowed the evaluation of the temperature coefficients [dln 〈R2〉0/dT(κ)] for these polymers. The evaluated polymers obeyed the packing length (p)-based expressions of the plateau modulus, GNo = kT/nt2p3 (MPa), and the entanglement molecular weight, Me = ρNant2p3 (g mol-1), where nt denotes the number (∼21) of entanglement strands in a cube with the dimensions of the reptation tube diameter (dt) and Ρ is the chain density. The product nt2p3 is the displaced volume (Ve) of an entanglement that is also expressible as pdt2 or kT/GNo. © 2002 Wiley Periodicals, Inc. J. Polym. Sci. Part. B: Polym. Phys.