The Influence of Hydrogen Bonding Side-Groups on Viscoelastic Behavior of Linear and Network Polymers

Polymers containing hydrogen-bonding side groups (HBGs) can form transient supramolecular networks that exhibit technologically useful viscoelastic properties. Here, we investigate how dynamic behavior of functional poly(n-butyl acrylate) melts and cross-linked networks is influenced by different HBGs. Random copolymers containing weak and strong HBGs were synthesized and subjected to thermal and dynamic mechanical analysis. The glass transition temperature (Tg) increased nearly linearly with the HBG concentration, and this effect was similar for both weak and strong binding groups. Copolymers containing weak HBGs behaved as unentangled melts and exhibited higher storage and loss modulus with increasing amounts of binding group. In contrast, copolymers containing strong HBGs behaved like entangled networks. Flow activation energies increased linearly with comonomer content; and, for weak hydrogen-bonding groups, they depended only on the departure from Tg. Similar behavior was observed in cross-linked films. Differences between weak and strong HBGs were also apparent from shape memory cycles.