Hydrogen bonding exchange and supramolecular dynamics of monohydroxy alcohols

This Letter unravels hydrogen bonding dynamics and their relationship with supramolecular relaxations of monohydroxy alcohols (MAs) at intermediate times. Rheological modulus of MAs exhibit Rouse scaling relaxation of G(t) ~ t^(-1/2) switching to G(t) ~ t^(-1) at time tau_m before their terminal time. Meanwhile, dielectric spectroscopy reveals clear signatures of new supramolecular dynamics matching with tau_m from rheology. Interestingly, the characteristic time, tau_m, follows an Arrhenius-like temperature dependence over exceptionally wide temperatures and agrees well with the hydrogen bonding exchange time from nuclear magnetic resonance measurements. These observations demonstrate the presence of collective Rouse-like sub-chain motions and the active chain-swapping of MAs at intermediate times. Moreover, detailed theoretical analyses point out explicitly that the hydrogen bonding exchange truncates the Rouse-type supramolecular dynamics and triggers the chain-swapping processes, supporting a recently proposed living polymer model.Comment: 15 pages, 4 figure

Dynamics of Associative Polymers with High Density of Reversible Bonds

We design and synthesize unentangled associative polymers carrying unprecedented high fractions of stickers, up to eight per Kuhn segment, that can form strong pairwise hydrogen bonding of $\sim20k_BT$ without microphase separation. The reversible bonds significantly slow down the polymer dynamics but nearly do not change the shape of linear viscoelastic spectra. Moreover, the structural relaxation time of associative polymers increases exponentially with the fraction of stickers and exhibits a universal yet non-Arrhenius dependence on the distance from polymer glass transition temperature. These results cannot be understood within the framework of the classic sticky-Rouse model but are rationalized by a renormalized Rouse model, which highlights an unexpected influence of reversible bonds on the structural relaxation rather than the shape of viscoelastic spectra for associative polymers with high concentrations of stickers.Comment: 4 figure

Polymeric Dynamic Crosslinker for Upcycling of Fragile Low-Molecular-Weight Polypropylene

While tremendous progress has been made in the dynamic crosslinking of polypropylene (PP) for plastic upcycling, the efficacy in addressing low-molecular-weight (MW) PP waste remains untapped. In this work, we demonstrate a simple and scalable method to convert brittle low-MW PP to vitrimer materials with enhanced thermal and mechanical properties, enabling their use in circular upcycling. Different from most previous work employing small-molecule crosslinkers, we prepare PP vitrimers (PPv) using polymeric crosslinkers, containing polyethylene glycol segments, which leads to altered crystalline structures and network formation. Importantly, by increasing the MW of crosslinkers from 200 to 1000 Da, the PPv exhibit more than 50 times increase in their fracture energy with strong ductility, which can be attributed to combined effects of strengthened amorphous regions of semi-crystalline PP domains and the phase separation between soft polyethylene glycol segments and the PP matrix. Moreover, when blending the PPv with high MW PP (PPh), the PPh/PPv blends show comparable elastic modulus, yield strength, and stretchability to that of the PPh, in sharp contrast to the widely known embrittlement of low-MW PP/PPh blends. These results demonstrate the use of polymeric dynamic crosslinkers as an important strategy for upcycling low-MW PP waste to value-added products