Effects of Branching and Crystallization on Rheology of Polycaprolactone Supramolecular Polymers with Ureidopyrimidinone End Groups

Abstract

The rheology of supramolecular polycaprolactone polymers with two ureidopyrimidinone (UPy) end groups and unimer molecular weights between 600 and 4000 was compared with that of branched tri- and tetrafunctional analogs. Above the melting point of polycaprolactone, the previously observed low-frequency plateau in storage and loss moduli during oscillatory frequency sweep of lower molecular weight bifunctional unimers was shown to persist up to 130−170 °C, where it gradually disappeared but reappeared upon slow cooling. Even though they are supramolecularly cross-linked, the tri- and tetrafunctional materials showed no plateau. This counterintuitive behavior was further investigated with optical microscopy, WAXS, and DSC experiments, which indicated that the plateau is closely connected to the presence of crystalline domains in the lower molecular weight fraction of bifunctionalized unimers. Because the formation of crystallites is prevented by branching, and because the network formed by the tri- and tetrafunctional unimers has a short lifetime, the branched materials do not show a low-frequency plateau.

Supramolecular Polymer Networks: Preparation, Properties, and Potential

“…Similar clustering and micellization of heterocomplementary hydrogenbonding motifs has also been observed by Binder and coworkers, who studied telechelic polyisobutylenes with thymine and diaminotriazine end groups [104]. Clustering and stacking of supramolecular cross-links often enforces supramolecular networks rather than making them weaker [14,88,[104][105][106][107], which stands in marked contrast to covalently cross-linked networks, wherein nanostructural network heterogeneity is assumed to entail weaker materials [108][109][110][111][112][113].…”

Effect of Supramolecular Interchain Sticking on the Low‐Frequency Relaxation of Transient Polymer Networks

“…As an addendum to the preceding argument based on primary polydispersity of the precursor‐polymer length and substitution, several previous studies have found evidence for cluster formation within supramolecular polymer networks, typically caused by secondary interactions between the supramolecular crosslinking motifs . Such clusters are likely to be another or additional cause for complex relaxation of these systems .…”

Structure and Rheological Behavior of Thermoreversible Supramolecular Polymers with Weak Multiple Hydrogen Bonds

“…Supramolecular polymers based on two, three, four, or more hydrogen bonds have been reported to form stable physical networks with very interesting prospects for applications 15–18. For example, Meijer and coworkers 19–21. employed self‐complementary multiple hydrogen‐bonding groups with high dimerization constants to the chain‐ends of polymers, such as poly(ethylene oxide ‐co‐ propylene oxide)s, polycaprolactone, and telechelic poly(ethylene/butylene) with 2‐ureido‐4[1 H ]‐pyrimidone (UPy) that have complementary quadruple hydrogen/bonding interactions.…”