The composition of low-T g n-butylacrylate-block-(acetoxyaceto)ethyl acrylate block polymers is investigated as a strategy to tune the properties of dynamically cross-linked vinylogous urethane vitrimers. As the proportion of the cross-linkable block is increased, the thermorheological properties, structure, and stress relaxation evolve in ways that cannot be explained by increasing cross-link density alone. Evidence is presented that network connectivity defects such as loops and dangling ends are increased by microphase separation. The thermomechanical and viscoelastic properties of block copolymer-derived vitrimers arise from the subtle interplay of microphase separation and network defects.File list (3) download file view on ChemRxiv Ishibashi MS revision.pdf (6.10 MiB) download file view on ChemRxiv Ishibashi SI revision.pdf (5.78 MiB)

Graft block copolymers (BCPs) with poly­(4-methyl caprolactone)-block-poly­(±-lactide) (P4MCL-PLA) side chains containing 80–100% PLA content were synthesized with the aim of producing tough and sustainable plastics. These graft BCPs experience physical aging and become brittle over time. For short aging times, t a, the samples are ductile and shear yielding is the primary deformation mechanism. A double-yield phenomenon emerges at intermediate t a where the materials deform by stress whitening followed by shear yielding. At long t a, the samples become brittle and fail after crazing. PLA content strongly governs the time to brittle failure, where a 100% PLA graft polymer embrittles in 1 day, an 86% PLA graft BCP embrittles in 35 days, and at 80% PLA, the material remains ductile after 210 days. Molecular architecture is also a factor in increasing the persistence of ductility with time; a linear triblock ages three times faster than a graft BCP with the same PLA content. Small-angle X-ray scattering and transmission electron microscopy analysis suggest that the rubbery P4MCL domains play a role in initiating crazing by cavitation. Prestraining the graft BCPs also significantly toughens these glassy materials. Physical aging-induced embrittlement is eliminated in all of the prestrained polymers, which remain ductile after aging 60 days. The prestrained graft BCPs also demonstrate shape memory properties. When heated above the glass-transition temperature (T g), the stretched polymer within seconds returns to its original shape and recovers the original mechanical properties of the unstrained material. These results demonstrate that graft BCPs can be used to make tough, durable, and sustainable plastics and highlight the importance of understanding the mechanical performance of sustainable plastics over extended periods of time following processing.

Commercially available surgical sealants for internal use either lack sufficient adhesion or produce cytotoxicity. This work describes a surgical sealant based on a polymer blend of poly(lactic-coglycolic acid) (PLGA) and poly(ethylene glycol) (PEG) that increases wet tissue adherence by incorporation of nano-to-microscale silica particles, without significantly affecting cell viability, biodegradation rate, or local inflammation. In functional studies, PLGA/PEG/silica composite sealants produce intestinal burst pressures that are comparable to cyanoacrylate glue (160 mmHg), ~2 times greater than the non-composite sealant (59 mmHg), and ~3 times greater than fibrin glue (49 mmHg). The addition of silica to PLGA/PEG is compatible with a sprayable in situ deposition method called solution blow spinning and decreases coagulation time in vitro and in vivo. These improvements are biocompatible and cause minimal additional inflammation, demonstrating the potential of a simple composite design to increase adhesion to wet tissue through physical, noncovalent mechanisms and enable use in procedures requiring simultaneous occlusion and hemostasis.

Graft polymers are useful in a versatile range of material applications. Understanding how changes to the grafted architecture, such as the grafting density (z), the side-chain degree of polymerization (N sc), and the backbone degree of polymerization (N bb), affect polymer properties is critical for accurately tuning material performance. For graft-through copolymerizations, changes to N sc and z are controlled by the macromonomer degree of polymerization (N MM) and the initial fraction of the macromonomer in the feed (f MM 0), respectively. We show that changes to these parameters can influence the copolymerization reactivity ratios and, in turn, impact the side-chain distribution along a graft polymer backbone. Poly((±)-lactide) macromonomers with N MM values as low as ca. 1 and as high as 72 were copolymerized with a small-molecule dimethyl ester norbornene comonomer over a range of f MM 0 values (0.1 ≤ f MM 0 ≤ 0.8) using ring-opening metathesis polymerization (ROMP). Monomer conversion was determined using 1H nuclear magnetic resonance spectroscopy, and the data were fit with terminal and nonterminal copolymerization models. The results from this work provide essential information for manipulating N sc and z while maintaining synthetic control over the side-chain distribution for graft-through copolymerizations.

The order−disorder transitions of diblock copolymers grafted to a common backbone were examined by oscillatory shear rheology and small-angle X-ray scattering. The effect of grafting density, graft molecular weight, number of grafts, and backbone dispersity were studied using poly[(styrene-alt-N-hydroxyethylmaleimide)-random-(styrene-alt-N-ethylmaleimide)]-graf t-poly(4-methylcaprolactone-block-D,Llactide) [PSHE-g-(P4MCL-PLA)] as a model graft block copolymer. At high grafting densities (25−50%), the order−disorder temperature (T ODT ) of the graft polymers was nearly identical to the analogous linear diblock. At lower grafting densities (<25%), the T ODT was found to systematically decrease. The number of grafts did not significantly change the value of the T ODT ; however, increasing the number of grafts resulted in broad, ill-defined transitions. Backbone dispersity was found to have little impact on the T ODT . Ordered morphologies were imaged by transmission electron microscopy. Long-range order was observed in polymers with at least 10 grafts/chain.