Synthesis and Characterization of a High-Temperature Thermoset Network Derived from a Multicyclic Cage Compound Functionalized with Exocyclic Allylidene Groups

Abstract

A heptacyclo[6.6.0.0 2,6 .0 3,13 .0 4,11 .0 5,9 .0 10,14 ]tetradecane (HCTD) complex with terminal allylidene groups at the 7-and 12-positions (HCTD-7,12-diallylidene, 2) was generated at the multigram scale from norbornadiene via an efficient six-step synthesis. Thermal polymerization of 2 at temperatures ranging from 160 to 240 °C yielded a robust crosslinked material with thermal stability up to 488 °C in air, a glass transition temperature of 377 °C, and a char yield (600 °C) of 56% in air. This degree of thermal stability is remarkable for a nonaromatic hydrocarbon polymer and is likely due to the rigid multicyclic cages that make up the bulk of the material. To elucidate the polymerization mechanism, a model compound, 7allylidenenorbornane (4), was synthesized and thermally cured. This resulted in the formation of polymeric material, suggesting that the cross-linking reaction of 2 proceeds via a free-radical reaction and not through Diels−Alder cycloaddition. Addition of dibutylhydroxytoluene (BHT) to compound 2 delayed the onset of cure, providing further support for a radical mechanism. On the basis of these results, it can be concluded that exocyclic allylidene groups represent a new class of thermosetting end-cap capable of generating highly cross-linked materials with thermal stabilities that rival those of high temperature polyimides. Applications include heat resistant composites utilized in the aerospace, electronic, automotive, and textile industries.

Generation and Capture of Both Sides of the 7-Norbornylidene — Bicyclo[2.2.2]oct-2-yne Fritsch–Buttenberg–Wiechell Rearrangement

“…13 Bicyclo[2.2.2]oct-2-yne (13) has been previously considered to be thermodynamically less stable than the corresponding 7-norbornylidenecarbene 12 based on trapping experiments with norbornadiene. 19 Precursor 11, from which 7-norbornylidenecarbene can be photochemically generated, was synthesized from 7-norbornanone ( 22) [47][48][49] and dichlorocyclopropyl phenanthrene derivative 23 50 (Scheme 4). The synthesis of 7-norbornanone (22) was achieved in four steps starting from norbornadiene (18) following previously reported procedures.…”

“…The suspension was then ltered, and the ltered solid was washed with methanol (150 mL). The combined ltrates were concentrated in vacuo, then suspended in 10% aqueous sodium thiosulfate (185 mL) and stirred 1 h. The mixture was then extracted with diethyl ether (3 x 100 mL), and the combined organic phases were dried (Na 2 SO 4 ), ltered, and concentrated in vacuo to afford 7-norbornol (21) as an orange waxy solid (2.20 g, 98%): 1 7-norbornone (22): Following the procedure of Rosenkoetter et al, 49 to a suspension of pyridinium chlorochromate (5.39 g, 25 mmol) in dichloromethane (300 mL) was added a solution of 7-norbornol (21, 1.12 g, 10.0 mmol) in dichloromethane (150 mL). The reaction mixture was stirred until 7-norbornol (21) was completely consumed, as determined by GC-MS. Diethyl ether (150 mL) was then added and the mixture was stirred 30 min, then transferred to a separatory funnel and extracted with diethyl ether (150 mL).…”

Photocatalytic Functionalization of Heptacyclo[6.6.0.02,6.03,13.04,11.05,9.010,14]Tetradecane

“…Classical syntheses typically delivered difficult to separate mixtures of products and low conversions; [5] in fact, selective procedures able to deliver HCTD in gram‐scale have only recently been reported [6] . Considering the potential utility of HCTD derivatives, for example in the design of thermally robust polymers, [6b] it seems timely to design effective routes for the selective incorporation of substituents on this cage compound.…”

Two‐Step Synthesis of Heptacyclo[6.6.0.02,6.03,13.04,11.05,9.010,14] tetradecane from Norbornadiene: Mechanism of the Cage Assembly and Post‐synthetic Functionalization

“…This synthetic route has finally paved the way to use the rigid HCTD cage as building block. [19] On the other hand, the efficient post-synthetic functionalization of the naked HCTD skeleton still remains unsolved. Only ahandful of methods are reported, and most of them are characterized by exiguous yields or cleavage of the HCTD cage.…”