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

Telechelic oligo- and poly(dimethylsiloxanes) with two ureidopyrimidone (UPy) functional groups and 2 (I) and 100 (II) dimethylsiloxy repeating units, were prepd. via hydrosilylation reaction of poly(dimethylsiloxane). The compds. were characterized in soln. by 1H NMR and viscometry and in the solid state by 1H NMR and 13C NMR, FTIR, and rheol. measurements. The measurements show that the UPy groups of the polymers are assocd. via quadruple hydrogen bonds in a donor-donor-acceptor-acceptor (DDAA) array. In many aspects, the materials behave like entangled, high mol. wt. polymers. Compd. II has a Tg of -119 Deg and shows melting of microcryst. domains of assocd. UPy units at -25 Deg. Compd. I has a cryst. form (Tm = 112 Deg) and an amorphous modification with a Tg of 25 Deg. Solid-state NMR was used to study the mobility of these phases; wide-line sepn. [WISE] spectra show a higher mobility of the UPy groups in the amorphous phase than in the crystals of I. Amorphous I and II behave like entangled polymers. The mech. behavior is characterized by a rubbery plateau and a relatively high activation enthalpy for stress relaxation (DH = 127 kJ/mol for I; DH = 54 kJ/mol for II), which was derived from the temp. dependence of the zero-shear viscosity. Ests. for the d.p. of I and II, based on the mech. properties, give DP > 100 for I and approx. 20 for I. Like in condensation polymn., the DP of reversible supramol. polymers is presumably limited by the presence of small amts. of monofunctional impurities