Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Abstract

In the preceding publication, we showed that the hyperbranched polystyrenes (HBPS) synthesized as part of this study may be viewed as starlike molecules with a high branch density, which are either unentangled or weakly entangled. In this paper, the role of architecture, especially the branch density, on the rheological and orientation behavior is investigated using simultaneous, quantitative stress and flow birefringence measurements in the melt state. Linear PS and eight-arm symmetric PS stars follow the stress-optical rule (SOR) over a wide dynamic range, with the stress-optical coefficient (C) governed by the arm molecular weight. When the branch density is "moderate" (greater than ∼20 arms), there is only a hint of nonterminal behavior in the viscoelastic moduli, while the C drops by 30% compared to a star with eight arms of comparable length. When the branch density is "high" (∼50 arms), and the arms are unentangled, the nonterminal behavior in G* is clearly apparent, and there is a dramatic breakdown in the stress-optical rule in these homopolymer melts. The quantitative birefringence measurements suggest that the "excess" birefringence may be due to the "form" contributions from the core-shell structure. Such a structure may be formed by the preferential radial stretching of the chain segments near the core, as suggested by other studies on hyperstars. For comparable chain density, the core would be bigger than the shell when the arm length is smaller. Therefore, the 5K-HBPS exhibits a more severe breakdown compared to the 10K-HBPS.

Highly Branched Poly(arylene ether)s via Oligomeric A2 + B3 Strategies

“…Contraction factors were used as previously described to characterize the change in dimension of a coil of a given molar mass: [18,23] g 0 ¼ ½Z br =½Z l ð5Þ…”

“…[1,[18][19][20][21][22] However, there has been less progress in the control of branch length in step-growth Summary: Branched poly(arylene ether)s were prepared in an oligomeric A 2 þ B 3 polymerization of phenol endcapped telechelic poly(arylene ether sulfone) oligomers as A 2 and TFPPO as trifunctional monomer B 3 . The molar mass of the A 2 oligomer significantly influenced the onset of gelation and the DB.…”

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 2. Linear Viscoelasticity and Flow Birefringence

“…In the preceding paper (part 1), 3 we established the differences in molecular architecture of HBP in comparison to linear and symmetric star polymers by studying dilute solution properties of these materials. Our HBPS materials appear to be "starlike" polymers with high branch density.…”

Shear-induced effects in hyperbranched-linear polyelectrolyte complexes

“…Since the main effect of electrostatic interactions is expected when the Debye length exceeds the complexes' size, we have adopted a sufficiently large value of r D = k −1 = 8.96l which corresponds to low aqueous salt concentration, 17 as was used in past studies in charged dendrimer systems 42 and in complexes with linear polyelectrolytes. 34,36 For complexes like the ones studied in this work, where the HP charge is fully compensated by the charge of the linear chain, counterion condensation is expected to be only of minor importance, and therefore the presence of counterions is not taken into account.…”

“…If such systems are, e.g., intravenously administered, they can be subjected to shear stresses of the order of 10 3 -10 4 s −1 in blood flow, 16 which may induce severe shape deformation and/or disruption of the complexes, rendering them inappropriate for the desired usage. 17,18 The response of HPs under an applied strain as well as several key properties of their complexes with other charged moieties has been found to depend on molecular weight ͑size͒ and on a number of structural characteristics such as shape, branch flexibility, and local density.…”