Polynorbornenes are a multipurpose class of materials used for a variety of important applications, such as gas separation membranes and lithographic photoresists. This versatility is due in part to the ability of norbornene-based monomers to be readily functionalized, and that they may be polymerized via multiple distinct polymerization mechanisms – the most notable of which are ring-opening metathesis polymerization (ROMP) and vinyl-addition (VA) polymerization. While ROMP has numerous advantages, such as catalyst compatibility with a numerous functional groups, accessing related materials via VA polymerization can often prove problematic due to catalyst-functionalized monomer incompatibility. This is frequently attributed to the sterically uninhibited nature of commonly employed VA catalysts and their strong Lewis acidity, both of which may lead to undesirable chelates and other non-productive intermediates. Motivated to find catalysts capable of polymerizing alkoxysilane-substituted norbornenes via VA, we performed an extensive catalyst search that ultimately identified the catalyst trans-[Ni(C6F5)2(SbPh3)2] as a suitable candidate. This catalyst propagates via a neutral Ni-based active site, as opposed to most other catalysts that propagate via more Lewis acidic, cationic Ni and Pd reactive centers. We will show that this catalyst is capable of producing VAPNBs bearing a variety of polar functionalities, such as alkoxysilane groups, and to achieve high yields (66-74%) and high molecular weights (120-167 kg/mol) after only short polymerization times. Using this methodology, we have synthesized a variety of alkoxysilane-bearing VA polynorbornenes that have been investigated for a variety of applications ranging from engineering materials to gas separation membranes. Of particular interest, we have discovered that many of these polymers exhibit exceptional CO2/N2 gas separation performance, and though they are in fact high Tg glassy materials (Tg = 300-375 °C), they actually exhibit gas transport phenomena more commonly associated with low Tg rubbery polymers.

Synthesis of alkoxysilane-functionalized polynorbornenes: High Tg polymers with unusual gas transport behavior

ACS Spring Meeting 2021

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