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

Grigorios Raptopoulos,Alice Scarpellini,Marinos Pitsikalis,Gregor Mali,George Anyfantis,Thomas Mavromoustakos,Patrina Paraskevopoulou,Katerina Kyriakou

doi:10.3390/polym9040141

Abstract

The bimetallic cluster Na[W2(μ-Cl)3Cl4(THF)2]·(THF)3 ({W2}, {W 3 W}6+, a′2e′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, {W2} 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 13C 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, {W2} 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.

Highlights

The ring opening metathesis polymerization (ROMP) reaction belongs to the big family of metathesis, which induces the cleavage/formation of carbon–carbon double and triple bonds, allowingPolymers 2017, 9, 141; doi:10.3390/polym9040141 www.mdpi.com/journal/polymersPolymers 2017, 9, 141 for the one-step synthesis of complex functional molecules
The composition of the polymer that the ratio of PNBE/PNBD segments in the polymer chain is relative to the monomer molar chainin was not quantitatively, by 13C CPMAS
Homopolymers high-cis the ratio of segments in the polymer chain is relative to the monomer molar ratio in the structures and that the only cross-linking mechanism operating for PNBD was the metathetic one

Summary

Introduction

The ring opening metathesis polymerization (ROMP) reaction belongs to the big family of metathesis, which induces the cleavage/formation of carbon–carbon double and triple bonds, allowingPolymers 2017, 9, 141; doi:10.3390/polym9040141 www.mdpi.com/journal/polymersPolymers 2017, 9, 141 for the one-step synthesis of complex functional molecules. Because of the properties and the applications of the unsaturated polymer materials, ROMP has been extensively studied and numerous catalytic systems have been developed. Those are mostly based on mononuclear complexes of various transition metals [4,5], which can be catalytically active per se, or after activation by a co-initiator. The active catalytic species for metathesis polymerization reactions is a metal carbene, which is either generated in situ, in which case its exact composition may remain unknown (ill-defined catalytic systems), or it has been previously synthesized and isolated, such as the Katz (W-based) [6,7,8], Schrock (Mo- or W-based) [9], and Grubbs (Ru-based) [10] alkylidenes and their numerous variations (well-defined catalytic systems). Apart from homogeneous systems, immobilized (on polymeric or inorganic support) and recyclable catalysts have been developed [11,12]

Methods

Results

Conclusion