Ru-Catalyzed, cis-Selective Living Ring-Opening Metathesis Polymerization of Various Monomers, Including a Dendronized Macromonomer, and Implications to Enhanced Shear Stability

Abstract

An unsaturated polymer’s cis/trans-olefin content has a significant influence on its properties. For polymers obtained by ring-opening metathesis polymerization (ROMP), the cis/trans-olefin content can be tuned by using specific catalysts. However, cis-selective ROMP has suffered from narrow monomer scope and lack of control over the polymerization (giving polymers with broad molecular weight distributions and prohibiting the synthesis of block copolymers). Herein, we report the versatile cis-selective controlled living ROMP of various endo-tricyclo­[4.2.2.02,5]­deca-3,9-diene and various norbornene derivatives using a fast-initiating dithiolate-chelated Ru catalyst. Polymers with cis-olefin content as high as 99% could be obtained with high molecular weight (up to M n of 105.1 kDa) and narrow dispersity (<1.4). The living nature of the polymerization was also exploited to prepare block copolymers with high cis-olefin content for the first time. Furthermore, owing to the successful control over the stereochemistry and narrow dispersity, we could compare cis- and trans-rich polynorbornene and found the former to have enhanced resistance to shear degradation.

Mechanochemical Reactivity of Bottlebrush and Dendronized Polymers: Solid vs. Solution States

“…[1][2][3][4][5][6][7][8][9] Mechanoresponsive polymers have been targeted for diverse solution-and solid-state applications,i ncluding catalysis, [10,11] drug-delivery, [12,13] force sensors, [14,15] and self-healing/strengthening materials. [16,17] Va rious design principles influence mechanochemical reactivity including the location of mechanophores, [18] regio-and stereochemistry, [19][20][21][22][23] linkers, [24][25][26] polymer composition, [27,28] and polymer topology. [29] In regard to topology,i ntramolecularly cross-linked, [30][31][32][33][34] cyclic, [35] dendritic, [36,37] star, [38][39][40][41][42][43] bottlebrush, [44][45][46] and dendronized polymers, [47] have been utilized to tune mechanochemi...…”

Stereoretentive Olefin Metathesis: A New Avenue for the Synthesis of All-cis Poly(p-phenylene vinylene)s and Stereo­defined Polyalkenamers

“…16 Choi and coworkers recently expanded the scope of the stereoretentive ROMP using Ru-2e with several norbornene (1c-1g) and endo-tricyclo[4.2.2.0 2,5 ] deca-3,9-diene derivatives (5a and 5b) to access a series of high cis-content polymers (Figure 6). 28 The living characteristics of the process were clearly confirmed by narrow dispersities, predictable molar masses, and efficient chain-extension. The narrower dispersities observed with Ru-2e compared to Ru-2a-d were attributed to the increased dissociation rate of the ether chelating group as a result of the steric influence of the bulkier NHC ligand with larger diisopropyl phenyl substituents than the NHC ligand of Ru-2a-d. Impressively, the polymers were observed to have virtually no trans olefins within the polymer backbone, further highlighting the high stereoselectivity of Ru-2e.…”

Recent Developments in Z‐Selective Olefin Metathesis Reactions by Molybdenum, Tungsten, Ruthenium, and Vanadium Catalysts

“…The reaction was conducted in anhydrous THF at 60 °C and stirred for 24 h in the dark under nitrogen to avoid photoisomerization of poly‐all‐ cis into poly‐all‐trans isomers (Scheme 87). [138] …”