Cross-Linking Agents for Enhanced Performance of Thermosets Prepared via Frontal Ring-Opening Metathesis Polymerization

Abstract

Frontal polymerization (FP) is a self-propagating reaction in which the reactive zone propagates through a monomer solution at a steady velocity. Using FP, polymeric materials are cured rapidly with minimal energy input. Here, we produce high-glass-transitiontemperature thermosets via frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) with norbornene-based cross-linkable co-monomers that enable tuning of the cross-link density. The glass-transition temperatures of poly(DCPD) systems are systematically varied from 138 to 219 °C by altering the amount of cross-linking co-monomers in the resin. Front velocities exceeding 5 cm•min −1 enable rapid, solvent-free production of thermoset materials with a 99% degree of cure and yield strength of 57 MPa. The DCPD-norbornene co-monomer resins are cured with 6 orders of magnitude less energy than a traditional oven cure and have a T g nearly 90 °C higher than reported thermosets of DCPD prepared via FROMP.

Molecularly Designed Additives for Chemically Deconstructable Thermosets without Compromised Thermomechanical Properties

“…30 mol %). 23 Other reports have noted similar increases in T g with increased crosslinking density or polar functionalization of DCPD itself. 24−26 The addition of cleavable crosslinks to thermosets with permanent, noncleavable crosslinks, however, cannot facilitate chemical deconstruction into soluble products (Figure 1C).…”

“…Increasing crosslink density can enhance the thermomechanical properties of thermosets for high-performance applications. , For example, Sottos, Moore, and co-workers reported that the T g of pDCPD prepared by frontal ring-opening metathesis polymerization could be increased by ∼90 °C compared to virgin pDCPD when multifunctional norbornene crosslinkers were doped in at modest levels (ca. 30 mol %) . Other reports have noted similar increases in T g with increased crosslinking density or polar functionalization of DCPD itself. − The addition of cleavable crosslinks to thermosets with permanent, noncleavable crosslinks, however, cannot facilitate chemical deconstruction into soluble products (Figure C) .…”

“…Finally, to determine the effective change in crosslink density in the resins due to the introduction of NbMeSi and CyMeSi , the average molecular weight between crosslinks ( M c ), which is inversely related to the crosslink density, of each sample was estimated using the ideal rubber elasticity relation: ,− Here, ρ represents the density of virgin pDCPD at room temperature (assumed to be 1.00 g cm –3 ); R is the universal gas constant (8.314 J K –1 mol –1 ); and T is the temperature in K at T g + ∼50 °C (Note: for NbMeSi at 0, 10, and 20 v/v %, E′ values obtained at T g + 48, 48, and 42 °C, respectively, were used to avoid operating temperatures above 220 °C). When bimodal tan­(δ) curves were observed (e.g., for CyMeSi samples at high loading), E′ was taken at 50 °C above the highest-temperature maximum.…”

Analytical estimates of front velocity in the frontal polymerization of thermoset polymers and composites

“…[4][5][6][7][8] Recently motivated by the substantial energy and time savings offered by the FP-based approach compared to conventional manufacturing methods, more advances have been made in the development of this technique for thermoset polymers and fiber-reinforced polymer composites (FRPC). 9,10 Simultaneously, theoretical and computational advances have been achieved in the modeling of this process. 11,12 These advances together have enabled a more energy-and timeefficient manufacturing of these materials with mechanical properties comparable to the traditionally manufactured materials used in many industrial applications.…”

“…Research in various aspects of FP‐based manufacturing initiated in the 70s 1–3 and has continued since 4–8 . Recently motivated by the substantial energy and time savings offered by the FP‐based approach compared to conventional manufacturing methods, more advances have been made in the development of this technique for thermoset polymers and fiber‐reinforced polymer composites (FRPC) 9,10 . Simultaneously, theoretical and computational advances have been achieved in the modeling of this process 11,12 .…”