Rheological and Dielectric Behavior of Dipole-Inverted (SIS)_p-Type Multiblock Copolymers:  Estimates of Bridge/Loop Fractions for Respective I Blocks and Effect of Loops on High Extensibility of Bridges

Abstract

A series of symmetric styrene− (S−) cis-isoprene (I) multiblock copolymers of (SIS) p -type (p = 1, 2, 3, and 5 corresponding to tri-, penta-, hepta-, and undecablock) was synthesized with an anion-coupling method and their rheological and dielectric behavior was examined in n-tetradecane (C14), a solvent dissolving the I block and precipitating the S block. The molecular weights of the constituent blocks were almost identical for these copolymers, and a particular I block(s) of respective copolymers had symmetrically once-inverted type-A dipole while the remaining I blocks had noninverted dipoles. At 20 °C, the (SIS) p /C14 systems with the (SIS) p concentration of 40 wt % formed a bcc lattice of glassy, spherical S domains (as confirmed from SAXS) and exhibited the gel-like elasticity. This elasticity was sustained mainly by the bridge-type I blocks connecting the S domains and partly by the coexisting loop-type I blocks. The dielectric loss (ε‘ ‘) data exclusively detected the fluctuation of the midpoint of the dipole-inverted I block having either bridge or loop conformation. (Since the ends of the I blocks were immobilized on the surface of the glassy S domains, the motion of the I blocks having noninverted dipoles was dielectrically inert.) A moderate difference was noted for the ε‘ ‘ data of the (SIS) p copolymers normalized by the volume fractions of respective dipole-inverted I blocks. This difference unequivocally indicated that the bridge- and loop-type I blocks exhibited different dielectric responses and that the bridge fraction φbridge moderately changed with the location of the dipole-inverted I block in the (SIS) p copolymer backbone as well as the number of repeating SIS units, p. On the basis of a hypothesis of dielectric similarity between the loop and its half-fragment tail under an osmotic constraint, φbridge was estimated from the ε‘ ‘ data of the (SIS) p copolymers and their precursor SI diblock copolymer (having the tail-type I block). φbridge was a little larger for the I block located at the center of the copolymer backbone than for the off-center I block and φbridge of the center I block decreased slightly with increasing p. The (SIS)5 undecablock system was extensible up to the stretch ratio of λ ≅ 30, and the loops therein appeared to osmotically stretch the bridges thereby helping the bridges bear such a high extensibility.

Competitive Supramolecular Associations Mediate the Viscoelasticity of Binary Hydrogels

“…In this case, at a concentration similar to the one used for rheological measurements (∼5 wt %), many spherical micelles are observed (5–10 nm in size, Figure 3 f) along with some elongated objects that are most likely due to bridging between the spherical micelles ( Figure 3 e). This is similar to what has been reported for amphiphilic triblock copolymer solutions 36 − 38 as well as for similar supramolecular systems. 25 , 34 The contrast in these images originates from the (aggregated) hydrophobic parts of the BTA-PEG-BTA, because the electron density of the hydrated PEG-chain is very similar to the surrounding water.…”

Nonlinear Mechanical Behavior of Scarcely Crosslinked Poly(dimethyl siloxane) Gel: Effect of Strand Length Polydispersity

“…17 This E can be re-written as a function of , the number density ratio ¼ N S =N C , , , and the equilibrium shear modulus G e . 29 The explicit form of this function is shown in Appendix B.…”

A New Strategy to Synthesize α,ω‐Dihydroxy Multiblock Copolymers via [CpRu(CH3CN)3]PF6/Quinaldic Acid Catalyst

“…Currently, major sy nthesis methods to get MBCs relying on polycondensation can be divided into two categories, that is, click chemistry and coupling chemistry of α,ω‐dihydroxy to form urethane, ester, or amide bonds . Although some of the MBCs have been successfully prepared and got some applications, those MBCs were mainly focused on thermoplastic materials with superior performance . Therefore, having a special terminal groups of MBCs which can be used as thermosetting material were not yet received much attention and research.…”