Toward Taming the Chemical Reversibility of Perfluoropyridine through Molecular Design with Applications to Pre- and Postmodifiable Polymer Architectures

Abstract

Polymer functionality greatly determines many of the key properties of these materials, such as glass-transition temperature, electrical and thermal conductivity, thermal stability, mechanical strength, and processability. Despite the importance of polymer functionality in determining material properties, the synthesis of functional polymers, with well-defined molecular weights and compositions, can still present a significant challenge, with many of the methods related to pre- or postpolymerization modification lacking synthetic scope, or requiring harsh functionalization conditions or transition-metal coupling reactions to install the desired functionality. Perfluoroaromatic systems are promising for the preparation of novel polymer architectures given that they can be readily functionalized using simple nucleophilic chemistries under very mild basic conditions. While promising, these systems have displayed some drawbacks. Previous work has shown that perfluoroaromatics, such as perfluoropyridine, can demonstrate a high degree of chemical reversibility with heteroatom nucleophiles. If the synthetic potential of these systems is to be realized, then a strategy for the rational design of stable monomers must be developed. Herein, we report the design, synthesis, and characterization of a series of unexplored heteroatom-based ring-opening metathesis polymerization (ROMP)-active monomers containing a reactive perfluoropyridine pendent group, which can be used to readily prepare a wide variety of aryl ether-functionalized polymers, using both pre- and postpolymerization modification strategies. We also establish a direct connection between the dihedral angle of the monomer and its propensity to undergo reversible addition reactions, establishing functional criteria for the design of pre- and postmodifiable systems.

Perfluoropyridine: Discovery, Chemistry, and Applications in Polymers and Material Science

“…The reversibility was also seen when attempts to post-functionalize poly38 with the various ROH nucleophiles resulted in densely cross-linked polymer. DFT calculations, along with the experimental observations on the monomers utilized in this study, support that the reversibility of 38 could be attributed to having a small dihedral angle [75]. By reacting the terminal alkenes of these monomers with hydride-terminated polydimethylsiloxanes (H-PDMSs), linear silicon-based elastomers and oils were obtained.…”

“…Later, in 2021, Houck et al demonstrated the ability to prepare a variety of aryl ether-functionalized polymers using both pre- and post-functionalized approaches [ 75 ]. In order to accomplish this, the authors initially prepared three monomers capable of undergoing ring-opening metathesis polymerization (ROMP) ( Scheme 26 ) [ 75 ]. Compounds 37 and 38 had been previously reported [ 76 ].…”

“…Interestingly, this is the first known report of chain growth polymers containing PFPy as a pendant group. Polymers prepared from 36 and 37 were characterized by GPC, TGA, and DSC ( Table 10 ) [ 75 ].…”

“…Selected characterization data for the polymers prepared by the pre-and [post-] functionalization methods developed by Houck et al[75].…”

Theoretical Prediction and Explanation of Reaction Site Selectivity in the Addition of a Phenoxy Group to Perfluoropyrimidine, Perfluoropyridazine, and Perfluoropyrazine

“…Perfluoroaromatics are a privileged scaffold in organofluorine chemistry, often used in the production of various drugs, agrochemicals, and high-performance fluoropolymers [1][2][3]. Fluoropolymers, particularly those with fluoroaromatics in their architectures, are widely known for their desirable properties such as chemical resistance, thermal stability, and solution and melt processability [3][4][5][6]. Fluoroaromatics have also shown great promise for use in biomedical applications [7][8][9][10], including as substituents to allow medications to more easily cross the blood brain barrier [11,12] and penetrate cells [13].…”