| Two homologous series of dendronized polymers (DPs) of the second and third generations, with different degrees of polymerization of the backbone, were synthesized combining two previously reported approaches. First, methacrylate-based DPs of the first generation were prepared via radical polymerization of the corresponding methacrylate macromonomers. As the side branches of such first-generation DPs can form hydrogen bonds and π-π stacks, they are referred to as 'classic' (intermolecularly interacting) DPs. Second, the first-generation DPs so prepared were grafted with branched oligoethylene glycol groups to increase the size of the dendrons up to the second and third generations. Because of the different chemical structures of the outermost generations with respect to the inner one, these DPs are termed 'hybrid' DPs. The glycol-based generations do not form intermolecular supramolecular associations, which so strongly control the aging dynamics and viscoelastic properties of the interacting DPs. Therefore, the series of hybrid DPs allow for investigating the dynamics of DPs for which synergistic effects because of supramolecular interactions and topology are reduced or absent. We find, at first glance surprisingly, that the loss of intermolecular peripheral interactions increases the equilibration time dramatically. Concerning the viscoelastic behavior of the hybrids of the second generation, the onset of global relaxation is observed at low frequencies. This is in contrast with supramolecular DPs having the same generation and the same backbone degree of polymerization, for which a clear plateau region was previously demonstrated. In addition, the low-frequency plateau of the elastic modulus increases upon increase of the degree of polymerization of the backbone, suggesting that one oligoethylene generation does not suffice to completely shield supramolecular interactions between the branches. Such a scenario is also supported by atomistic simulations. The hybrid DPs of the third generation display two distinct plateau regions of the storage modulus. The first one (at higher frequencies) is of the order of 106 Pa, and attributed to the interpenetration of the side branches, the second is of the order of 103 Pa. In contrast with the behavior of second-generation hybrid DPs, the degree of polymerization of the backbone has no effect on the low-frequency plateau of third-generation hybrid DPs. This suggests that supramolecular interactions do not contribute to the elastic plateau. Hence, we ascribe it to the entanglements of the entire hybrid DPs. The reported results are summarized in a table, which compares the properties of different DPs and provides the needed ingredients for tailoring the rheology of such hyperbranched polymers.
for LaTeX users @article{SCostanzo2019-52,
author = {S. Costanzo and L. Scherz and G. Floudas and R. Pasquino and M. Kr\"oger and A. D. Schl\"uter and D. Vlassopoulos},
title = {Hybrid dendronized polymers as molecular objects: viscoelastic properties in the melt},
journal = {Macromolecules},
volume = {52},
pages = {7331-7342},
year = {2019}
}
\bibitem{SCostanzo2019-52} S. Costanzo, L. Scherz, G. Floudas, R. Pasquino, M. Kr\"oger, A.D. Schl\"uter, D. Vlassopoulos,
Hybrid dendronized polymers as molecular objects: viscoelastic properties in the melt,
Macromolecules {\bf 52} (2019) 7331-7342.SCostanzo2019-52
S. Costanzo, L. Scherz, G. Floudas, R. Pasquino, M. Kr\"oger, A.D. Schl\"uter, D. Vlassopoulos
Hybrid dendronized polymers as molecular objects: viscoelastic properties in the melt
Macromolecules,52,2019,7331-7342 |
mk@mat.ethz.ch
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