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Photoredox-mediated metal-free ring-opening metathesis polymerization (MF-ROMP) is a convenient metal-free method to produce a variety of ROMP polymers. Transitioning MF-ROMP from a batch to a continuous flow process has yet to be demonstrated and could potentially benefit production efficiency, safety, and modularity of reaction conditions. We designed and evaluated continuous flow and droplet flow setups and compared the results for MF-ROMP across a short series of common monomers. By using the droplet flow reactor setup, we achieved flow conversions comparable to that of batch, and circumvented issues with diffusion-limited mixing and air exposure. 

We have developed a highly efficient synthesis of linear polydicyclopentadiene (pDCPD)viaphotoredox mediated metal-free ring-opening metathesis polymerization (MF-ROMP) and investigated theT_g–M_ndependence of linear pDCPD.

 

Post‐polymerization modification (PPM) via direct C−H functionalization is a powerful synthetic strategy to convert polymer feed‐stocks into value‐added products. We found that a metal‐free, Se‐catalyzed allylic C−H amination provided an efficient method for PPM of polynorbornenes (PNBs) produced via ring‐opening metathesis polymerization. Inherent to the mechanism of the allylic amination, PPM on PNBs preserved the alkene functional groups along the polymer backbone, while also avoiding transposition of the double bonds. Amination using a series of aryl sulfonamides led to good control over the degree of functionalization, access to a range of functionalities, and tunable thermal properties from the resulting polymers.

 

Post‐polymerization modification (PPM) via direct C−H functionalization is a powerful synthetic strategy to convert polymer feed‐stocks into value‐added products. We found that a metal‐free, Se‐catalyzed allylic C−H amination provided an efficient method for PPM of polynorbornenes (PNBs) produced via ring‐opening metathesis polymerization. Inherent to the mechanism of the allylic amination, PPM on PNBs preserved the alkene functional groups along the polymer backbone, while also avoiding transposition of the double bonds. Amination using a series of aryl sulfonamides led to good control over the degree of functionalization, access to a range of functionalities, and tunable thermal properties from the resulting polymers.

 

We report the synthesis of a new class of strained macrocycle that performs well in ring-opening metathesis polymerization (ROMP). The polymerization displays chain growth characteristics with evidence of secondary metathesis in the form of chain transfer. The unique structure enables access to stilbene-based polymers that are traditionally prepared via uncontrolled polymerizations. 

Stereochemistry can have a profound impact on polymer and materials properties. Unfortunately, straightforward methods for realizing high levels of stereocontrolled polymerizations are often challenging to achieve. In a departure from traditional metal‐mediated ring‐opening metathesis polymerization (ROMP), we discovered a remarkably simple method for controlling alkene stereochemistry in photoredox mediated metal‐free ROMP. Ion‐pairing, initiator sterics, and solvation effects each had profound impact on the stereochemistry of polynorbornene (PNB). Simple modifications to the reaction conditions produced PNB withtransalkene content of 25 to >98 %. Highciscontent was obtained from relatively larger counterions, toluene as solvent, low temperatures (−78 °C), and initiators with low Charton values. Conversely, smaller counterions, dichloromethane as solvent, and enol ethers with higher Charton values enabled production of PNB with hightranscontent. Data from a combined experimental and computational investigation are consistent with the stereocontrolling step of the radical cationic mechanism proceeding under thermodynamic control.

 

Stereochemistry can have a profound impact on polymer and materials properties. Unfortunately, straightforward methods for realizing high levels of stereocontrolled polymerizations are often challenging to achieve. In a departure from traditional metal‐mediated ring‐opening metathesis polymerization (ROMP), we discovered a remarkably simple method for controlling alkene stereochemistry in photoredox mediated metal‐free ROMP. Ion‐pairing, initiator sterics, and solvation effects each had profound impact on the stereochemistry of polynorbornene (PNB). Simple modifications to the reaction conditions produced PNB withtransalkene content of 25 to >98 %. Highciscontent was obtained from relatively larger counterions, toluene as solvent, low temperatures (−78 °C), and initiators with low Charton values. Conversely, smaller counterions, dichloromethane as solvent, and enol ethers with higher Charton values enabled production of PNB with hightranscontent. Data from a combined experimental and computational investigation are consistent with the stereocontrolling step of the radical cationic mechanism proceeding under thermodynamic control.