Molecular View on Supramolecular Chain and Association Dynamics

The chain and association dynamics of supramolecular polymer ensembles decisively determines their properties. Using neutron spin echo (NSE) spectroscopy we present molecular insight into the space and time evolution of this dynamics. Studying a well characterized ensemble of linearly associating telechelic poly(ethylene glycol) melts carrying triple H-bonding end groups, we show that H-bond breaking significantly impacts the mode spectrum of the associates. The breaking affects the mode contributions and not the relaxation times as was assumed previously. NSE spectra directly reveal the so far intangible H-bond lifetimes in the supramolecular melt and demonstrate that for both the microscopic and the macroscopic dynamics of the supramolecular ensemble the instantaneous average of the $M_w$ distribution governs the system response at least as long as the Rouse picture applies.

Figure 1

NSE data at 373 K compared to $S(Q,t{)}_{\text{diff}}$, the pure diffusion contribution in part (a), and in part (b) the prediction of the unmodified (unbreakable chain) as described in the text.

Figure 2

NSE data for three different temperatures. The solid lines represent the result of the model fitting, where only one parameter, the bond breaking time ${\tau }_b$, was fitted.

Figure 3

Temperature dependencies of the bond breaking time ${\tau }_b$ (circles) and the lifetime of an average aggregate ${\tau }_c^{\prime }(M_{\mathrm{agg},n})$ (triangles). The inset in the upper left illustrates the sticker groups with the H-bond pairing.