Copolymerization of Norbornene and Norbornadiene Using a cis-Selective Bimetallic W-Based Catalytic System

Abstract

Abstract:The bimetallic cluster Na 3 Cl 4 (THF) 2 ]·(THF) 3 ({W 2 }, {W 3 W} 6+ , a 2 e 4 ), which features a triple metal-metal bond, is a highly efficient room-temperature initiator for ring opening metathesis polymerization (ROMP) of norbornene (NBE) and norbornadiene (NBD), providing high-cis polymers. In this work, {W 2 } was used for the copolymerization of the aforementioned monomers, yielding statistical poly(norbornene)/poly(norbornadiene) PNBE/PNBD copolymers of high molecular weight and high-cis content. The composition of the polymer chain was estimated by 13 C CPMAS NMR data and it was found that the ratio of PNBE/PNBD segments in the polymer chain was relative to the monomer molar ratio in the reaction mixture. The thermal properties of all copolymers were similar, resembled the properties of PNBD homopolymer and indicated a high degree of cross-linking. The morphology of all materials in this study was smooth and non-porous; copolymers with higher PNBE content featured a corrugated morphology. Glass transition temperatures were lower for the copolymers than for the homopolymers, providing a strong indication that those materials featured a branched-shaped structure. This conclusion was further supported by viscosity measurements of copolymers solutions in THF. The molecular structure of those materials can be controlled, potentially leading to well-defined star polymers via the "core-first" synthesis method. Therefore, {W 2 } is not only a cost-efficient, practical, highly active, and cis-stereoselective ROMP-initiator, but it can also be used for the synthesis of more complex macromolecular structures.

Large, Rapid Swelling of High-cis Polydicyclopentadiene Aerogels Suitable for Solvent-Responsive Actuators

“…Therefore, the characterization data for PDCPD aerogels are presented below, along with SEM and N2 sorption data, which provided information about the porous network of the aerogels. As expected, the chemical characterization showed that the PDCPD aerogels of this study were very similar with PDCPD xerogels obtained previously with W2/PA [75], following the characteristic features of reactivity of W2 [75][76][77][78][79], and confirmed the highcis content of the polymer chain. For comparison purposes, figures showing the spectra of PDCPD materials obtained with catalytic systems W2/NBD, W2/PA (which provides mostly-trans PDCPD), and Ru-I (which provides mostly-trans PDCPD) [63,75] are given in the Supporting Information (Figure S1 and Figure S2).…”

“…Although less widely known, bimetallic clusters with metal-metal bonds have also been employed as ROMP catalysts. For example, both Na[W 2 (µ-Cl) 3 Cl 4 (THF) 2 ]•(THF) 3 (W 2 ; (W 3 W) 6+ , a 2 e 4 ) [75][76][77][78][79] and (Ph 4 P) 2 [W 2 (µ-Br) 3 Br 6 ] (W 2 -Br; (W 2.5 W) 7+ , a 2 e 3 ) [80] show high catalytic activity towards the metathesis polymerization of alkynes, as well as the polymerization of many cycloolefins. W 2 , in particular, yields polymers with a high-cis double bond content [75][76][77][78][79].…”

“…For example, both Na[W 2 (µ-Cl) 3 Cl 4 (THF) 2 ]•(THF) 3 (W 2 ; (W 3 W) 6+ , a 2 e 4 ) [75][76][77][78][79] and (Ph 4 P) 2 [W 2 (µ-Br) 3 Br 6 ] (W 2 -Br; (W 2.5 W) 7+ , a 2 e 3 ) [80] show high catalytic activity towards the metathesis polymerization of alkynes, as well as the polymerization of many cycloolefins. W 2 , in particular, yields polymers with a high-cis double bond content [75][76][77][78][79]. The addition of phenylacetylene (PA) as a co-initiator improves the catalytic activity, while the high-cis stereoselectivity is retained [75,78].…”

“…In contrast to PA, however, NBD has the advantage of yielding crosslinked polymers, while the W 2 /PA system yields polymer chains that contain linear polyphenylacetylene segments. Thus, for example, W 2 /NBD catalyzes the ROMP of norbornene yielding materials with a controlled molecular structure (star-shaped structure) via the "core-first" synthesis method [79], which is not possible with the W 2 /PA system. Another advantage of the higher degree of crosslinking obtained with the W 2 /NBD catalytic system is expected to be some rubber-like elasticity that would hold the resulting polymer together after solvent swelling, which in turn would increase reversibility in applications such as sensors and actuators (see next paragraph).…”

Trends in Polymers 2017/2018: Polymer Synthesis

“…The catalyst showed considerable solubility in the polymerization mixture and might be a metal-free alternative for benzoxazine resin formation for future applications. Paraskevopoulou and coworkers investigated the ROMP of norbornene and norbornadiene [34]. Therefore, a cis-selective bimetallic W-catalyst was utilized.…”