Intrinsic viscosities of four homopolymers and one copolymer in nonpolar solvents. I. Effect of correlations of molecular orientations

Intrinsic viscosities η] of four homopolymers, polyisobutylene (PIB), polypentene-1 (PP-1), polypentenamer (PPmer), and polydimethylsiloxane (PDMS), and of an ethylene-propylene copolymer containing 81% ethylene (81% E) have been measured at 25°C in seven linear alkanes ranging from n-C₆ to n-C₁₆ and three highly branched alkanes, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane, and 2,2,4,4,6,8,8-heptamethylnonane. Correlation of molecular orientations (CMO) in the polymers was investigated. The difference Δη] = η](lin) ? η](br) is used as a test of CMO with the supporting assumption that CMO lowers the free energy and the destruction of CMO raises it. The positive value of Δη], which varies from 20% to 40% for PPmer and 81% E, is indicative of orientational order in these two polymers. The negative value of Δη] for PDMS results from the disordering of linear alkanes by the nonordered PDMS. δη] is near zero for PP-1 and small for PIB implying that these two polymers are indifferent to solvent molecular shape. The variation of η] with alkane chain length of the linear alkanes gives additional information about size and solvent quality. The dependence is small for ordered polymers due to the short range of CMO. η] diminishes rapidly with n for PDMS probably because of the increased difference of cohesive energy between polymer and solvent. The dependence is small for PIB but very large for PP-1. The much better quality of small-molecule solvents for PP-1 may be an indication of a helicoidal conformation of this polymer in solution.