Nonuniversal Behavior of the Thermodynamic Interaction Parameter in Blends of Star and Linear Polybutadiene

Abstract

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.

Enthalpy and Volume Relaxation of Core‐Crosslinked Star Polystyrene/Poly(methyl methacrylate) Blends

“…[11] The advantage of CCS polymers over other types of filler/ crosslink is the excellent compatibility and interfacial interaction that occurs, in particular when the polymer matrix and the arms on the CCS polymer are the same material. Several authors have calculated the interaction parameter (x eff ) for linear/star polymer blends, [12][13][14] observing a decrease in x eff with increasing star polymer concentration. This indicates an increase in miscibility, encouraging sufficient interaction between the linear and star polymer components.…”

Branched Versus Linear Polyisoprene: Flory–Huggins Interaction Parameters for their Solutions in Cyclohexane

“…[10][11][12][13][14][15][16] Comparatively many basic studies concern the behavior of star shaped polymers as compared with their linear analogs. [10,12,[17][18][19][20][21][22][23][24][25] Here it is interesting to note that the application of the blob theory predicts a decrease in the solubility of a nonlinear polymer as compared to the corresponding linear polymer. [26] Despite the abundant literature (the above compilation is far from being complete) a comparison of the Flory-Huggins interaction parameters for a linear and a branched polymer homolog with a given, thermodynamically favorable solvent is still missing to the best of our knowledge.…”

Effective interaction parameter of linear/star polymer blends and comparison with that of linear/linear and star/star blends

“…[2][3][4] The dependence of on these parameters is included only in complex polymer theories 5 The interactions between the chain units play a crucial role for the stability of polymer mixtures.…”