Synthesis and Rheology of Tailored Poly(dimethylsiloxane) Zinc and Sodium Ionomers

Abstract

We describe a synthesis scheme for the preparation of "model" poly(dimethylsiloxane) ionomers with tailored number of monomers between ions and number of ions per chain. Melts of low ion concentration (0.3-1.3 mol %) model zinc and cobalt ionomers, and their unneutralized COOH precursors are found to precipitate as polymers that flow and exhibit a zero-shear viscosity but equilibrate to physical gels. The gel time follows an Arrhenius relationship and is used to predict and verify physical gel formation at room temperature over a time scale from several months to years. The gel time depends chiefly on the ion concentration (calculated here as the average number of ions per monomer units (×100)) and functionality (defined as the average number of ions per chain); for ionomers with comparable overall molar mass, the ion concentration and functionality act counter to each other. Unlike traditional hydrocarbon ionomers, gel formation in these polysiloxane ionomers is favored by high temperature, and the gel moduli are comparable to moduli of end-linked PDMS networks. We propose this is due to transformation of intramolecular interactions to intermolecular interactions at high temperatures. Sodium ionomers form critical gels immediately after precipitation which we attribute to the more ionic nature of sodium relative to the transition-metal ionomers.

Precision Ionomers: Synthesis and Thermal/Mechanical Characterization

“…1−17 Countless studies have been and continue to be conducted in efforts to understand and control ionomer morphology. With some exceptions, such as regularly sequenced polyurethane, 18−20 polysiloxane, 21,22 and poly(ethylene oxide) 23,24 based ionomers, most current synthetic approaches yield a random (or pseudorandom) distribution of ionic groups along a polymer backbone (type A of Figure 1); thus, the impact of perfect regioregularity on ionomer morphology and performance in various applications remains largely unexplored due to a lack of synthetic methodology. 1,25 We recently reported the synthesis of an ionomer and an ionene (in which the ionic group is in the main chain of the polymer) by acyclic diene metathesis polymerization (ADMET) of α,ω-diene-functionalized ionic liquids.…”

“…Ionic polymers are often prepared via polymerization of acryloyl- or vinyl-functionalized ionic liquids or by ionization of electrically neutral polymers. − Countless studies have been and continue to be conducted in efforts to understand and control ionomer morphology. With some exceptions, such as regularly sequenced polyurethane, − polysiloxane, , and poly(ethylene oxide) , based ionomers, most current synthetic approaches yield a random (or pseudorandom) distribution of ionic groups along a polymer backbone (type A of Figure ); thus, the impact of perfect regioregularity on ionomer morphology and performance in various applications remains largely unexplored due to a lack of synthetic methodology. , …”

Inorganic and organometallic polymers

“…Poly(dimethylsiloxane) zinc and sodium ionomers (0.3-1.3 mol% of metal) have been prepared and their gel formation has been described. 38 Chojnowski and coworkers have completed oligomerization reactions of 9 in the presence of B(C 6 F 5 ) 3 to form oligosilicone 10 (m = 1, 2, etc.). 39 The formation of 10 was accompanied by hexamethylcyclotrisiloxane (D 3 ), octamethylcyclotetrasiloxane (D 4 ) and dimethylsilane.…”

Scaling Behavior of the Viscosity of Poly(dimethylsiloxane) Ionomer Solutions

“…The final step is a fractionation in a good/bad solvent mixture to yield fractions with moderate polydispersity. The details of the synthesis scheme are reported elsewhere 1 Molar Mass and Polydispersity of OH-Terminated PDMS Precursors Used in the Synthesis of Ionomers precursor chains M n (kg/mol) M peak (kg/mol)PDI 6K 6.0 5.6 1.28 11K 12.5 11.2 1.32 15K 16.4 14.7 1.37 18Ka 17.8 18.0 1.32 18Kb 19.6 18.1 1.40 27K 29.5 27.2 1.32 …”

“…Solutions of associating polymers have found an increasing number of applications. , Considerable theoretical − and experimental − effort has been devoted to understanding the rheology of these materials. Most associative polymer systems studied in the literature are hydrophobically modified water-soluble polymers. − As discussed in a previous paper, we have developed a strategy to synthesize poly(dimethylsiloxane) (PDMS)-based ionomers with tailored number of monomers between ions, ions per chain, and cation. This allows us to synthesize ionomers with structures systematically varied to examine the viscosity vs polymer volume fraction for this highly flexible hydrophobic polysiloxane backbone.…”