Recent advances in frontal ring-opening metathesis polymerization (FROMP) have enabled the rapid and energy-efficient fabrication of high-performance and thermoset materials. The second-generation Grubbs complex [(SIMes)­RuCl2(PCy3)] is the most exploited FROMP catalyst to date despite the availability of several other commercial variants. Changes in the nature of the catalytic species may provide potential advantages for controlling FROMP conditions, polymer microstructure, and monomer selectivities. Herein, nine catalysts are employed for the FROMP of dicyclopentadiene and ethylidene norbornene mixtures to generate copolymers, and the associated polymerization process parameters (front temperatures and velocities) are measured for each system. Dynamic mechanical analysis, differential scanning calorimetry, and quasistatic tensile testing reveal significant differences in the mechanical and material properties of the resultant polymers.

No abstract

In this work, a simple method is reported for control over initiation in frontal ring-opening metathesis polymerization (FROMP). This noncontact approach uses 375 nm light to excite Grubbs’ second-generation catalyst in the presence of a phosphite inhibitor. Photoinitiated FROMP of dicylcopentadiene (DCPD) displays a similar cure profile to that of its thermally initiated counterpart, yielding a robust polymer with high glass transition temperature. Furthermore, this system is applied to enhance reaction rates in conventional ring-closing metathesis reactions.

Frontal ring-opening metathesis polymerization (FROMP) catalyzed by Grubbs-type Ru complexes enables new, rapid, and energy-efficient syntheses of high-performance, structural plastics. Ideal catalysts survive the extended time periods associated with resin preparation, storage, and transportation. Current catalysts, however, induce premature polymerization within hours to days under ambient conditions. In this work, a thermally latent bis-N-heterocyclic carbene complex provides exceedingly robust resins, which are viable for 8 weeks. When mixed with CuI coreagents, precatalyst activation primes the system for rapid reactivity after thermal initiation. In this study, more than 40 dual-component formulations successfully catalyzed FROMP of dicyclopentadiene. The polymerization process parameters (front temperatures and velocities), resin storability, and resultant polymer properties (e.g., T g) were determined for each composition. Intriguingly, the Cu to Ru ratio dramatically impacts the observed frontal velocity and temperature, as well as the polymer glass-transition temperature; slower, colder reaction fronts result from formulations with large Cu to Ru ratios. The resultant polymers display lower T g values. Mechanistic analysis of a related model system demonstrated that an excess Cu reagent decreases the activation and polymerization rates.

Frontal ring-opening metathesis polymerization (FROMP) is a rapid, low-energy manufacturing reaction that is useful for curing thermosetting materials. FROMP of dicyclopentadiene (DCPD) results in poly­(dicyclopentadiene) (p­(DCPD)), a tough thermoset with excellent mechanical performance and chemical stability. Like most thermosets, p­(DCPD) cannot be reprocessed and is therefore difficult to recycle. Previous work demonstrated that the incorporation of a small quantity of cleavable units in the strand segments of p­(DCPD) networks enables their deconstruction. Here, we report that a commercially available multifunctional comonomer, 2,3-dihydrofuran (DHF), both acts as a potent Grubbs catalyst inhibitor during FROMP and introduces acid cleavable units. The resulting materials retain high performance characteristics, including glass-transition temperatures ranging from 115 to 165 °C and ultimate strength ranging from 35 to 40 MPa. The addition of DHF above critical loading levels enables deconstructable thermosets. We further demonstrate freeform three-dimensional (3D) printing of deconstructable thermosets via frontal polymerization.

Tunable molecular weight and well-defined polydispersity are the hallmarks of a controlled polymerization. This process relies on vanishingly small termination rates, minimal chain transfer, and initiation rates faster than propagation rates. Ring-opening metathesis polymerization (ROMP) is a well-known controlled polymerization based on the opening of strained cyclic olefins. The exothermic nature of ROMP allows rapid conversion of neat monomers to polymers through frontal ROMP (FROMP). Unlike traditional ROMP, FROMP uses the exothermic heat from the opening of strained cyclic olefins to thermally activate the initiator that sustains the propagation of a cascading reaction front. Although the reaction mechanisms for ROMP and FROMP are the same, the reaction conditions differ greatly, especially in the temperature and monomer concentration. The ability to control the polymerization under FROMP conditions has yet to be investigated, as well as its potential in the synthesis of well-defined polymers without the use of solvents and with minimal energy input. Here, we show that FROMP rapidly transforms monomers into polymers of high-molecular weight (M n ) with good fidelity and low dispersity (Đ). Specifically, the synthesis of polymers with M n up to 700 kg/mol and Đ of 1.5 was achieved with a rapid, solvent-free, and oxygen-tolerant frontal polymerization technique. Further control of the polymerization was possible with the addition of a phosphite ligand that lowered the Đ to 1.2. We anticipate that controlled FROMP will become a valuable macromolecular synthetic tool due to its reliability, speed, scalability, and simplicity.

Two frontal polymerization (FP) mechanisms, frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene and frontal radical polymerization (FRaP) of benzyl acrylate and hexanediol diacrylate, were combined for rapid manufacturing of welded thermoset materials. Leveraging the immiscibility of the two different FP resins, welded thermosets and gradient foams of varying composition were achieved by switching of FP mechanisms. The adhesion strength of the welded thermoset materials differed depending on the originating mechanism. Finally, welded thermoset foams of varying porosity and homogeneity were generated through initiation from the bottom of the two resins.Letter pubs.acs.org/macroletters

No abstract