Association Behavior, Diffusion, and Viscosity of End-Functionalized Supramolecular Poly(ethylene glycol) in the Melt State

Abstract

In this work we present a combined analysis of small-angle neutron scattering, linear rheology and pulsed field gradient nuclear magnetic resonance spectroscopy experiments on the supramolecular association and chain structure of well-defined telechelically modified poly­(ethylene glycol) (PEG) in the bulk. Oligomeric PEG was functionalized with directed heterocomplementary hydrogen-bonding end-groups, thymine (Thy) and diaminotriazine (DAT). The polarity of the backbone polymer is comparable to the end groups and avoids clustering of the groups basing on energetic arguments. Their linear association behavior in the ideal melt state was investigated on the microscopic/molecular level as a function of temperature. By means of a selective labeling scheme, which should ideally lead to the formation of alternating hydrogeneous-deuterated building block sequences if the hydrogen bonding reaction is exclusively heterocomplementary, we showed that the Thy–DAT association is dominant and a Thy–Thy homoassociation is approximately three times less probable. Latter nondirected association gives rise to a considerable amount of random-copolymerization without affecting seriously neither the macroscopic melt viscosity nor the diffusivity of the supramolecular associates. From the q-dependence of a multiblock RPA structure factor, the linear association in the melt is confirmed. Furthermore, this diffusion and viscosity study reveals simple Rouse dynamics of supramolecular polymer chains with molecular weight much larger than the entanglement mass M e. The Rouse-like dynamics of long supramolecular chains indicates short lifetime hydrogen bonds of the end groups. Our results are in excellent agreement with the related polycondensation theory.

Supramolecular Dimerization in a Polymer Melt from Small-Angle X-ray Scattering and Rheology: A Miscible Model System

“…The absence of it or the size of a measurable χ interaction parameter between A and B moieties is typically obtained from SAXS or SANS experiments. The estimation was good in the case of PEO [34], and we will assume further that it will be approximately correct also for PBO.…”

“…Some comments regarding the sensitivity of calculation are important here: For the thy and DAT groups an average solubility parameter δ~24 is derived [27,34]. Referring to [34], the estimated δ parameter for PEO is 20.8, i.e., lower than the experimental literature value situated between 22 and 25 by roughly 2-3 MPa 1/2 [39]. Nevertheless, from SANS, the mixture was found ideal with negligible Flory-Huggins parameter.…”

“…Secondly, the question of the competitive homo-association of thy and DAT groups still stands. In the PEO case of [34], the probability for pure thy-thy or DAT-DAT homo-complexes was estimated to be roughly 1:3 when they are compared to the thy-DAT hetero-association. Figure 1 presents absolute SAXS intensity patterns of an equimolar monofunctional thy-DAT mixture as a function of temperature.…”

“…Recently, Kruteva et al identified a suitable model system for advanced bulk applications. It ideally combined electronic and thermodynamic properties of the active H-bonding entities and the polymeric backbone [34]. The pronounced compatibility of the matrix polymer and the functional groups is a significant aspect, as it may allow a further step to arrive at bulk materials with better and increased damage resistance [9].…”

“…For both systems, a microphase separation was reported. In combination with PEO and with equimolar amounts of difunctional unentangled oligomers, labeled by hydrogen and deuterium, small-angle neutron scattering (SANS) experiments in the melt state could identify uniquely linear -(HD) n -multiblock copolymers similar to polycondensation in the bulk [34]. The length of the dynamic chains was observed to be polydisperse and T-dependent.…”