Mediating the slow dynamics of polyacrylates by small molecule-bridged hydrogen bonds

Abstract

This report studied changes in slow dynamics of polyacrylate by adding a hindered phenol (CA) capable of forming three intermolecular hydrogen bonds (inter-HBs) per molecule with the polymer chain. The...

Hydrogen Bonding-Induced Alleviation of Topological Constraints in Acrylic Polymers Mixed with Small Molecules

“…The long-chain connectivity arises from the mutual interpenetration and entanglement between nonbonded polymer chains, especially above the critical molecular weight of entanglement ( M c ). In general, chain connectivity restricts the motion of molecular chains in the viscous regime, and consequently, the chain-scale slow dynamics (i.e., sub-Rouse and Rouse modes) containing dozens of monomer units must be activated at temperatures high above T g . − For phenol-loaded polyacrylate hybrids, as the immobile phenolic additives transform to plasticizers with the dissociation of inter-HBs above T g , the hybrids typically exhibit a diminishing slow mode with lower activation temperatures that gradually merges with the α-peak . Moreover, since chain segments must push its way through the crowded surroundings built by entangled chains or segments, the chain connectivity also restricts the segmental dynamics at the length scale of several monomer units. ,, Compared with nonbonded molecular glasses, the presence of chain connectivity in polymers typically increases the chain rigidity and retards and constrains the segmental motion.…”

“…In the isochronal storage modulus ( E ′) curves of polymers, the plateau region at the rubbery state is referred to as the entanglement plateau . Based on the entropic elasticity theory, entangled polymers usually have a high entanglement plateau modulus ( E ′ R ) due to the chain connectivity.…”

“…112−115 For phenol-loaded polyacrylate hybrids, as the immobile phenolic additives transform to plasticizers with the dissociation of inter-HBs above T g , the hybrids typically exhibit a diminishing slow mode with lower activation temperatures that gradually merges with the α-peak. 4 Moreover, since chain segments must push its way through the crowded surroundings built by entangled chains or segments, the chain connectivity also restricts the segmental dynamics at the length scale of several monomer units. 36,116,117 Compared with nonbonded molecular glasses, the presence of chain connectivity in polymers typically increases the chain rigidity and retards and constrains the segmental motion.…”

“…36−38 In the isochronal storage modulus (E′) curves of polymers, the plateau region at the rubbery state is referred to as the entanglement plateau. 4 Based on the entropic elasticity theory, 9 entangled polymers usually have a high entanglement plateau modulus (E′ R ) due to the chain connectivity. To elucidate the effect of AO300 additives on the E′ R values of the P(St-EA) matrix, the viscoelastic properties of P(St-EA)/ AO300 hybrids are further examined.…”

“…Due to the unavailability of free volume and severe topological constraints during the glass–rubber transition (GRT), segments must move cooperatively to complete the whole vitrification process, so segmental motion near glass transition temperature ( T g ) reveals the structural evolutions of condensed matter in real time . Unlike the weakly interacting secondary or slow modes with homogeneous relaxation dynamics, − segmental (or α-) relaxations subjected to strong intermolecular constraints are typically dynamically heterogeneous with nonlinear, nonexponential, and non-Arrhenius features . The enthalpic effects associated with the vitrification process can be probed by most relaxation spectroscopies, such as enthalpy, dielectric, and mechanical relaxations. , Among them, enthalpy relaxation directly traces the free energy of configurational transitions; it not only captures the pure segmental dynamics − but also quantifies all three dynamically heterogeneous features of α-relaxation .…”