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This paper represents the first comprehensive report of the molecular weight dependence of the dynamics of polyfarnesene (PF), utilizing oscillatory shear rheology and broadband dielectric spectroscopy. Extended PF chain conformations arising from tightly packed C11/C13 pendant groups reduce the probability of chain entanglements and lead to Rouse-like melt dynamics up to a critical molecular weight ∼105 g/mol. At higher molecular weights, PF behaves as an entangled polymer melt. Dielectric spectroscopy measurements establish PF as a type-A polymer, whose normal mode relaxation is strongly dependent on molecular weight, providing a compliment to melt rheology for the exploration of PF global chain dynamics.

A bio-based route to the production of trans-β-farnesene has recently been commercialized. Trans-β-farnesene is capable of being polymerized by both anionic and cationic pathways, creating low molecular weight polymers with structure–property relationships unique within the diene class of monomers. Trans-β-farnesene is produced through fermentation of sugar feedstocks. The pathway offers an alternative to petroleum-based feedstocks derived as by-products of naphtha or ethane cracking. Anionic polymerization of the monomer produces a highly branched “bottlebrush” structure, with rheological properties that are markedly different than those of linear diene polymers. Specifically, a lack of entanglements is observed even at relatively high molar masses. For hydroxyl-terminated oligomers, Tg as a function of molar mass follows a trend opposite non-functional materials. The synthesis and characterization of trans-β-farnesene–based polymers will be presented, including anionically prepared low molecular weight diols and monols.

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Values of the bulk thermodynamic interaction parameter, χeff, for blends of anionically polymerized star (number of arms ) 4, 6, 8, 12) and linear polybutadienes (PB) of well-defined architecture and molecular weight were measured as a function of temperature using small-angle neutron scattering. Comparison of these measured values of χeff with results from comparable polystyrene (PS) blends suggests the existence of nonuniversal aspects in the thermodynamic interaction due to entropic contributions, χ , arising from architectural differences in chains. While the value of χ for PS star/linear blends increases monotonically with number of arms in the star, the value of χ in the PB star/linear blends does not, a result which cannot be anticipated by the Gaussian field theory (GFT) of Fredrickson et al. 1 An important discrepancy between theory and experiment is also found for the variation of χ with linear chain length. Theory anticipates the value of χ should decrease with increasing linear chain size, but in fact it increases. Qualitative agreement with the GFT is found on two counts: χ decreases with increasing concentration of star (when assuming χisotopic for linear/linear blends is constant with concentration), and χ decreases with increasing length of the star arm. In general, the value of χ for a PB blend of star and linear components is larger than the value of χ for a comparable PS blend. Indeed, phase separation is observed in one particular PB blend of a six-arm star with a sufficiently large linear chain.