- Degradable Polyacetals/Ketals from Alternating Ring-Opening Metathesis Polymerization ACS MACRO LETTERS 2020; 9 (2): 180–84
- Precise Placement of Single Monomer Units in Living Ring-Opening Metathesis Polymerization CHEM 2019; 5 (10): 2691–2701
Tuning the Reactivity of Cyclopropenes from Living ROMP to Single Addition and AROMP via Simple Substituents.
Angewandte Chemie (International ed. in English)
Ring-opening metathesis polymerization (ROMP) has become one of the most important living polymerizations. Despite being the most strained cyclic olefin, cyclopropenes (CPEs) remain underexplored for ROMP. We discovered that the simple swap of 1-methyl to 1-phenyl on 1-(benzoyloxymethyl)-CPEs elicited strikingly different modes of reactivity, switching from living polymerization to selective single addition and living alternating ROMP, respectively, to yield well-controlled polymers in both cases. This pronounced difference in reactivity stemmed from differences in steric repulsions at the Ru alkylidene after CPE ring-opening. Possible olefin or oxygen chelation from ring-opened CPE substituents was also observed to significantly affect the rate of propagation. These results demonstrate the versatility of CPEs as a new class of monomers for ROMP, provide mechanistic insights for designing new monomers with rare single addition reactivity, and generate a new functionalizable alternating copolymer scaffold with controlled molecular weight and low dispersity.
View details for DOI 10.1002/anie.201909688
View details for PubMedID 31571344
Synthesis and Mechanochemical Activation of Ladderene-Norbornene Block Copolymers.
Journal of the American Chemical Society
2018; 140 (39): 12388–91
We have recently reported a polymechanophore system, polyladderene (PLDE), which dramatically transforms into polyacetylene (PA) upon mechanical stimulation. Herein, we optimized conditions to synthesize unprecedented block copolymers (BCPs) containing a force-responsive block by sequential ring-opening metathesis polymerization of different norbornenes and bromoladderene. Successful extension from PLDE to other blocks required careful timing and low temperatures to preserve the reactivity of the PLDE-appended catalyst. The PLDE-containing BCPs were sonochemically activated into visually soluble PA with a maximum absorption lambda ≥ 600 nm and unique absorption patterns corresponding to noncontinuous activation of ladderene units. Access to polymechanophore BCPs paves the way for new stress-responsive materials with solution and solid state self-assembly behaviors and incorporation of polymechanophores into other materials.
View details for PubMedID 30229652
A bright organic NIR-II nanofluorophore for three-dimensional imaging into biological tissues
2018; 9: 1171
Fluorescence imaging of biological systems in the second near-infrared (NIR-II, 1000-1700 nm) window has shown promise of high spatial resolution, low background, and deep tissue penetration owing to low autofluorescence and suppressed scattering of long wavelength photons. Here we develop a bright organic nanofluorophore (named p-FE) for high-performance biological imaging in the NIR-II window. The bright NIR-II >1100 nm fluorescence emission from p-FE affords non-invasive in vivo tracking of blood flow in mouse brain vessels. Excitingly, p-FE enables one-photon based, three-dimensional (3D) confocal imaging of vasculatures in fixed mouse brain tissue with a layer-by-layer imaging depth up to ~1.3 mm and sub-10 µm high spatial resolution. We also perform in vivo two-color fluorescence imaging in the NIR-II window by utilizing p-FE as a vasculature imaging agent emitting between 1100 and 1300 nm and single-walled carbon nanotubes (CNTs) emitting above 1500 nm to highlight tumors in mice.
View details for PubMedID 29563581
Ring-opening metathesis polymerization of 1,2-disubstituted cyclopropenes
2016; 52 (58): 9097-9100
The ring-opening metathesis polymerization (ROMP) of 1,2-disubstituted cyclopropenes (CPs) has been explored for the first time using Grubbs 3rd generation catalyst. A range of 1,2-CPs yielded polymers with controllable MWs and low dispersitities, and allowed the synthesis of block copolymers, absent from secondary metathesis. However, there existed a competing intramolecular termination pathway for these monomers, limiting the timescale for their ROMP to stay living.
View details for DOI 10.1039/c6cc00466k
View details for Web of Science ID 000379431000029
View details for PubMedID 26947899