Supramolecular polymers from linear telechelic siloxanes with quadruple-hydrogen-bonded units

Telechelic oligo- and poly(dimethylsiloxanes) 1 and 2, with two ureidopyrim idone (UPy) functional groups, have been prepared via a hydrosilylation rea ction. The compounds have been characterized in solution by H-1 NMR and vis cometry and in the solid state by H-1 NMR and C-13 NMR, FTIR, and rheology measurements. The measurements show that the UPy groups of 1 and 2 are asso ciated via quadruple hydrogen bonds in a donor-donor-acceptor-acceptor (DDA A) array. In many aspects, the materials behave like entangled, high molecu lar weight polymers. Compound 2 has a T-g at -119 degrees C and shows melti ng of microcrystalline domains of associated UPy units at -25 degrees C. Co mpound 1 has a crystalline form (T-m = 112 degrees C) and an amorphous modi fication with a T-g of 25 degrees C. Solid-state NMR was used to investigat e the mobility of these phases. WISE spectra show a higher mobility of the UPy groups in the amorphous phase than in the crystals of 1. Amorphous 1 an d 2 behave like entangled polymers. Their mechanical behavior is characteri zed by a rubbery plateau and a relatively high activation enthalpy for stre ss relaxation (Delta H 127 kJ/mol for 1; Delta H 54 kJ/mol for 2), which wa s derived from the temperature dependence of the zero-shear viscosity. Esti mates for the degree of polymerization (DP) of 1 and 2, based on the mechan ical properties, give DP > 100 for 1 and approximately 20 for 2. Like in co ndensation polymerization, the DP's of reversible supramolecular polymers a re presumably limited by the presence of small amounts of monofunctional im purities.