Linear Viscoelastic Behavior of Symmetric and Asymmetric Star Polymer Solutions

Abstract

Linear viscoelastic properties of linear and star-branched polymer solutions are investigated experimentally and theoretically. Two series of high molar mass 1,4-polyisoprene linear and three-arm star polymers blended with marginally unentangled linear chains of the same chemistry form the focus of this study. We find that, irrespective of polymer architecture, unentangled linear molecules dilate the entanglement environment in the blends in a manner consistent with expectations for a Θ-solvent. A tube model analysis used in an earlier study [Lee, J. H.; Fetters, L. J.; Archer, L. A. Macromolecules 2005, 38, 4484], for predicting linear viscoelastic properties of branched melts, is extended to describe relaxation dynamics of entangled star-branched polymer solutions. We find that, by simply rescaling the model parameters to account for Θ-solvent dilution effects, this model quantitatively describes relaxation dynamics in concentrated star and linear polymer solutions, without adjustable parameters. At lower polymer concentrations, however, the tube model systematically overestimates the effect of solvent dilution on the dynamic moduli. These observations are discussed in terms of the universality of the dilution exponent and breakdown of dynamic dilution at low degrees of arm entanglement.

Newtonian Viscosity of Dilute, Semidilute, and Concentrated Polymer Solutions

“…(1.114)]. Such an expectation has been confirmed experimentally for the melt [Kraus and Gruver, 1965] and for solutions [Lee et al 2006], and is illustrated in Figure 1.13, which compares shear viscosity data [Lee et al, 2006] for solutions of a linear 1,4-polyisoprene (PIP; M n = 256.9 kg/mol) versus a three-arm star PIP (M n = 299.8 kg/mol), each dissolved in a low-molar-mass linear PIP (M n = 3.22 kg/mol). The latter M n is smaller than the entanglement molecular weight for PIP (M e = 4.2 kg/mol) [Lee et al, 2006].…”

Chain Architecture as an Orthogonal Parameter To Influence Block Copolymer Morphology. Synthesis and Characterization of Hyperbranched Block Copolymers: HyperBlocks

“…Predominantly these studies have been aimed at understanding the impact of chain branching upon the melt rheology of such polymers. Commonly studied branched architectures include the simplest branched structure, star polymers [1][2][3][4][5] , and increasingly complex architectures such as miktoarm stars 6,7 , graft/comb polymers [8][9][10][11][12][13] , H-shaped polymers [14][15][16][17] and dendritically long-chain branched polymers [18][19][20][21][22][23][24][25][26][27][28] . Chain-branching in block copolymers has also been explored with a view to understand the influence of architecture upon phase separation.…”

Synthesis and temperature gradient interaction chromatography of model asymmetric star polymers by the “macromonomer” approach

“…Star polymers with varying numbers of arms have been widely produced and studied [1][2][3][4][5][6][7][8] and branched polymers of increasing complexity and diverse structures have evolved. These include H-shaped polymers [9][10][11][12][13][14][15], comb-shaped polymers [16][17][18][19][20][21][22][23][24][25][26][27][28] and more recently dendritically branched polymers [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48].…”