Halato-Telechelic Polymers. 5. A Theoretical Approach to Gel Formation in Nonpolar Solvents

Ion aggregation in halato-telechelic polymers (HTP) is treated from a theoretical point of view. When diluted in media of low dielectric constant, HTP would easily form ionic multiplets up to sextets whereas the energy gained in the formation of higher multiplets would decrease rapidly. This expectation is qualitatively confirmed by the very early gelation of HTP in nonpolar solvents. At high concentration, the ionic multiplets can possibly aggregate and form periodic structures, as evidenced in barium α,ω-carboxylato-polybutadiene. A theoretical relationship is proposed between the critical concentration of gelation (Cgel) and the molecular weight of the telechelic prepolymer (M̄n) for a given ion pair, solvent, and temperature: Cgel = kM̄n −1/2. This relation is largely confirmed by experience. The proportionality constant k depends on the lability of the ionic bonds and on the conformational state of the polymeric carrier: [〈r2〉/M]1/2. The longer the distance between the ion pairs, the earlier the gelation. © 1982, American Chemical Society. All rights reserved.