Four Stereoisomeric Norbornadiene Dimers Containing a Cyclopropane Ring: ROMP, Polymer Properties, and Post-Polymerization Modification

Abstract

The efficient and selective introduction of functional groups to hydrocarbon polymers enables facile access to new polymer materials with various physical properties. In the present study, we have focused on cyclopropane-containing norbornadiene dimers (NBDDs) as bifunctional monomers and post-polymerization modification (PPM) for the synthesis of functionalized cyclic olefin polymers (COPs). The ring-opening metathesis polymerization (ROMP) of the four NBDD stereoisomers (exo-exo, exo-endo, endo-exo, and endo-endo) and the subsequent hydrogenation proceeded selectively to give the corresponding COPs (H-poly­(NBDD)­s) with reactive cyclopropane moieties. There are distinct differences between the four isomers in terms of polymerization rate and the physical properties of the resultant polymers. The endo-exo- and endo-endo-NBDDs show lower ROMP reactivities than the exo-exo- and exo-endo-NBDDs due to steric hindrance. All of the polymers before and after hydrogenation are amorphous, regardless of annealing (with the exception for the unannealed H-poly­(exo-endo-NBDD)). Compared with the polymers of the exo-norbornenyl isomers, their endo-counterparts show lower solubilities, higher glass transition temperatures, sharper X-ray diffraction peaks, and larger d-spacings. The highly soluble H-poly­(exo-exo-NBDD) was employed for the PPM via protic acid-catalyzed cyclopropane ring-opening to produce six new COPs bearing acyloxy, alkoxy, or aryl groups. Although rearrangements occur during ring-opening presumably through nonclassical carbocations, the polymer structures were determined with reference to the reactions of their corresponding monomeric model compounds. The PPM with m-xylene, for example, proceeds regioselectively while maintaining a narrow molecular weight distribution to produce a xylyl-substituted COP with good solubility and high thermal stability.

Spiro-Fluorene-Containing Cyclic Olefin Polymers

“…The XRD patterns of all obtained polymers, (H-)­poly­( 1 )­s and (H-)­poly­( 1 - co -NB)­s (except for the block copolymers), exhibit amorphous halos without crystalline peaks (Figures and S8–S15). They are significantly broader than those of previously reported COPs, (H-)­poly­(NBL), (H-)­poly­(MNBL), and (H-)­poly­(NBDD) . This finding indicates that polymer chains containing 1 are difficult to arrange regularly.…”

“…The design of the monomer structure and the copolymer sequence are critical for the resulting COP properties, and polycyclic polymer structures are required to obtain a high glass-transition temperature ( T g ) of around 150 °C. Various COPs have been produced from polycyclic NB derivatives, including conventional hydrocarbons (dicyclopentadienes, − tetracyclododecenes, − and others), ester-, , imide-, epoxy-substituted NBs, anthracene-derived NBs, NB lactones (NBL), , and cyclopropane-containing norbornadiene dimers (NBDDs) …”

“…Endo -/ exo -isomerism practically affects the polymerization rate as well as T g , and thus, this is also an important factor for the precise control of the properties of (co)­polymers. Endo -isomers are polymerized slower than exo -isomers because of the steric hindrance and/or chelation to the metal catalyst at the polymer terminals. − Endo -isomeric polymers show higher T g values than exo -isomers; − ,, however, it is unclear how the structural difference affects their physical properties. In this context, we previously proposed that the higher T g and lower solubility of endo -isomers are due to more regularly arranged structures of endo -isomers, as indicated by sharper X-ray diffraction (XRD) patterns based on the analysis of the polymers derived from the four isomers ( exo - exo -, exo - endo -, endo - exo -, and endo - endo -) of NBDDs …”

Synthesis and properties of cyclic olefin polymers by ring-opening metathesis (co)polymerization of α-methyl-substituted norbornene lactones

“…The polymer should be amorphous, with high glass transition (T g ) temperatures ranging from 120 °C to 170 °C but with possible deformation processing for optical transparency material application. ROMP has an advantage over coordination polymerization in the applicability to various NB monomers; however, to synthesize high T g polymers, polycyclic NB monomers, such as dicyclopentadienes, [5][6][7][8][9] tetracyclododecenes, [10][11][12] and others, [13][14][15][16][17][18][19] should be employed. Optical properties, including refractive indexes and birefringence, are also important factors.…”

Unraveling the Compounded Interplay of Weakly and Strongly Coordinating Ligands in G3-Catalyzed Living Metathesis Polymerization: toward Well-Defined Polynorbornene at Ambient Temperature

“…So far, strategies for enhancing metathesis polymerization control include lowering the temperature, , enlarging steric hindrance, – and adding extra ligands, – as shown in Figure b. Lowering temperature regulates the reaction rates through the physical modulation of external conditions.…”