Molecular Bottlebrushes as Novel Materials.

Form-stable phase change composites: Preparation, performance, and applications for thermal energy conversion, storage and management

Transforming how plastics are made, unmade, and remade through innovative research and diverse partnerships that together foster environmental stewardship is critically important to a sustainable future. Designing, preparing, and implementing polymers derived from renewable resources for a wide range of advanced applications that promote future economic development, energy efficiency, and environmental sustainability are all central to these efforts. In this Chemical Reviews contribution, we take a comprehensive, integrated approach to summarize important and impactful contributions to this broad research arena. The Review highlights signature accomplishments across a broad research portfolio and is organized into four wide-ranging research themes that address the topic in a comprehensive manner: Feedstocks, Polymerization Processes and Techniques, Intended Use, and End of Use. We emphasize those successes that benefitted from collaborative engagements across disciplinary lines.

Defining the Macromolecules of Tomorrow through Synergistic Sustainable Polymer Research.

Super-ductile, injectable, fast self-healing collagen-based hydrogels with multi-responsive and accelerated wound-repair properties

We report a straightforward and scalable method for the generation of polystyrene-based vinylogous urethane vitrimers using conventional radical polymerization. The copolymerization of the commerci...

Polystyrene-Based Vitrimers: Inexpensive and RecyclableThermosets

The composition of low-Tg 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.

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Mechanical and Structural Consequences of Associative Dynamic Cross-Linking in Acrylic Diblock Copolymers

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 sust...

Physical Aging of Polylactide-Based Graft Block Polymers

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)]-graft-poly(4-methylcaprolactone-block-d,l-lactide) [PSHE-g-(P4MCL-PLA)] as a model graft block copolymer. At high grafting densities (25–50%), the order–disorder temperature (TODT) of the graft polymers was nearly identical to the analogous linear diblock. At lower grafting densities (<25%), the TODT was found to systematically decrease. The number of grafts did not significantly change the value of the TODT; however, increasing the number of grafts resulted in broad, ill-defined transitions. Backbone dispersity was found to have little impact on the TODT. Ordered morphologies were imaged by transmission electron microscopy. Long-range order was observe...

The Order–Disorder Transition in Graft Block Copolymers

A series of model poly((±)-lactide) (PLA) graft copolymers was synthesized by ring-opening metathesis polymerization and used to probe the star-to-bottlebrush transition in shear and extensional flows. Ten samples with backbone degrees of polymerization 11 ≤ Nbb ≤ 420 were investigated using small-amplitude oscillatory shear (SAOS) and extensional rheometry measurements. Each contained one PLA side chain of length Nsc = 72 per two backbone repeating units on average (graft density of z = 0.5). The star-like to bottlebrush transition was identified at Nbb = 50–69 using SAOS. In extension, melt strain hardening is absent in the star-like melts (Nbb ≤ 50) but is prominent in the bottlebrush limit (Nbb > 69). The onset of melt strain hardening occurs at a time scale equivalent to the Rouse time of the backbone. A molecular interpretation of these results builds upon recent conjectures related to strain-induced increases in interchain friction in bottlebrush polymers. These findings will be useful in designing bottlebrush melts that strain harden, which is critical in various types of processing methods involving extensional flows, including foaming, 3D printing, and film-blowing. 

Aristotelis Zografos

Papers

Mechanical and Structural Consequences of Associative Dynamic Cross-Linking in Acrylic Diblock Copolymers

Physical Aging of Polylactide-Based Graft Block Polymers

The Order–Disorder Transition in Graft Block Copolymers

Star-to-Bottlebrush Transition in Extensional and Shear Deformation of Unentangled Polymer Melts