24 research outputs found
A General Approach to Sequence-Controlled Polymers Using Macrocyclic Ring Opening Metathesis Polymerization
A General Approach to Sequence-Controlled Polymers Using Macrocyclic Ring Opening Metathesis Polymerization
A new and general
strategy for the synthesis of sequence-defined
polymers is described that employs relay metathesis to promote the
ring opening polymerization of unstrained macrocyclic structures.
Central to this approach is the development of a small molecule “polymerization
trigger” which when coupled with a diverse range of sequence-defined
units allows for the controlled, directional synthesis of sequence
controlled polymers
Applications of C–H Functionalization Logic to Cyclobutane Synthesis
The
application of C–H functionalization logic to target-oriented
synthesis provides an exciting new venue for the development of new
and useful strategies in organic chemistry. In this article, C–H
functionalization reactions are explored as an alternative approach
to access pseudodimeric cyclobutane natural products, such as the
dictazole and the piperarborenine families. The use of these strategies
in a variety of complex settings highlights the subtle geometric,
steric, and electronic effects at play in the auxiliary guided C–H
functionalization of cyclobutanes
Modular Approach to Degradable Acetal Polymers Using Cascade Enyne Metathesis Polymerization
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Tuning of protease resistance in oligopeptides through N-alkylation
N-Methylation of amino acids is an effective way to create protease resistance in both natural and synthetic peptides. However, alkyl substituents other than N-methyl have not been extensively studied. Here, we prepare and examine a series of N-substituted peptides in which the size and length of the alkyl group is modulated. These design insights provide a unique and modular handle for tuning proteolysis in oligopeptides
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Established and Emerging Strategies for Polymer Chain-End Modification
Informatics-Driven Design of Superhard B–C–O Compounds
Materials containing
B, C, and O, due to the advantages of forming
strong covalent bonds, may lead to materials that are superhard, i.e.,
those with a Vicker’s hardness larger than 40 GPa. However,
the exploration of this vast chemical, compositional, and configurational
space is nontrivial. Here, we leverage a combination of machine learning
(ML) and first-principles calculations to enable and accelerate such
a targeted search. The ML models first screen for potentially superhard
B–C–O compositions from a large hypothetical B–C–O
candidate space. Atomic-level structure search using density functional
theory (DFT) within those identified compositions, followed by further
detailed analyses, unravels on four potentially superhard B–C–O
phases exhibiting thermodynamic, mechanical, and dynamic stability
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Direct access to functional (Meth)acrylate copolymers through transesterification with lithium alkoxides
A straightforward and efficient synthetic method that transforms poly(methyl methacrylate) (PMMA) into value-added materials is presented. Specifically, PMMA is modified by transesterification to produce a variety of functional copolymers from a single starting material. Key to the reaction is the use of lithium alkoxides, prepared by treatment of primary alcohols with LDA, to displace the methyl esters. Under optimized conditions, up to 65% functionalization was achieved and copolymers containing alkyl, alkene, alkyne, benzyl, and (poly)ether side groups could be prepared. The versatility of this protocol was further demonstrated through the functionalization of both PMMA homo and block copolymers obtained through either radical polymerization (traditional and controlled) or anionic procedures. The scope of this strategy was illustrated by extension to a range of architectures and polymer backbones
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Efficient Synthesis of Asymmetric Miktoarm Star Polymers
Asymmetric miktoarm star polymers comprising an unequal number of chemically-distinct blocks connected at a common junction produce unique material properties, yet existing synthetic strategies are beleaguered by complicated reaction schemes that are restricted in both monomer scope and yield. Here, we introduce a new synthetic approach coined "ÎĽSTAR" - Miktoarm Synthesis by Termination After Ring-opening metathesis polymerization - that circumvents these traditional synthetic limitations by constructing the block-block junction in a scalable, one-pot process involving (1) grafting-through polymerization of a macromonomer followed by (2) in-situ enyne-mediated termination to install a single mikto-arm with exceptional efficiency. This modular ÎĽSTAR platform cleanly generates AB n and A(BA') n miktoarm star polymers with unprecedented versatility in the selection of A and B chemistries as demonstrated using many common polymer building blocks: poly(siloxane), poly(acrylate), poly(methacrylate), poly(ether), poly(ester), and poly(styrene). The average number of B or BA' arms (n) is easily controlled by the molar equivalents of macromonomer relative to Grubbs catalyst in the initial ring-opening metathesis polymerization step. While these materials are characterized by dispersity in n that arises from polymerization statistics, they self-assemble into mesophases that are identical to those predicted for precise miktoarm stars as evidenced by small-angle X-ray scattering experiments and self-consistent field theory simulations. In summary, the ÎĽSTAR technique provides a significant boost in design flexibility and synthetic simplicity while retaining the salient phase behavior of precise miktoarm star materials