Changing up BN-Polystyrene: Effect of Substitution Pattern on the Free-Radical Polymerization and Polymer Properties

Abstract

Azaborinine-substituted polymers are poised to dramatically expand the diversity and functionality of polystyrenes via BN for CC substitution, but this new class of materials remains underexplored. Although formally isosteric to the respective all-carbon polystyrene derivatives, polarization due to the difference in electronegativity between B and N can have a distinct effect on polymerizability and the resulting polymer properties. Discussed herein is the successful preparation of a series of new isomeric azaborinine-substituted polymers via standard free-radical polymerization. We investigate the effects of the substitution pattern of vinylated B-mesityl azaborinines, that is, the position of the vinyl group relative to the BN moiety, on the polymerization reactivity and physical properties of the respective polymers. Copolymerization experiments with the parent styrene, as well as meta-and para-mesitylstyrene as direct all-carbon analogues of the azaborinine monomers, reveal that depending on the substitution pattern the more polarized azaborinines are incorporated to a lesser (B-Mes in para-position) or larger extent (B-Mes in meta-position) than the all-carbon analogues. Computational studies offer insights into the subtle electronic effects that result in this differential reactivity. We also compare the polymer properties to those of the all-carbon polystyrene analogues.

One tool to bring them all: Au-catalyzed synthesis of B,O- and B,N-doped PAHs from boronic and borinic acids

“…105 In the 1 H NMR spectra of 4a,b-6a,b and 8a-c, the successful cyclization reactions are indicated by the presence of singlet resonances in the aromatic regions, which are due to the newly generated H β protons (see Schemes 3 and 4 for the position labels). The 13 δ(C γ ) = 128.9 ppm). These differences can be explained by different conformations of the tBuC6H4 substituents with respect to the heterocyclic cores in 4a,b-6a,b: the small O atom allows an essentially coplanar arrangement in solution, whereas the larger NMe group enforces a twist between the two moieties (the bulky Mes rings are consistently orthogonally positioned).…”

“…This promotes a coplanar conformation between the respective B,O heterocycle and, e.g., B-bonded phenyl substituents and can thus contribute to the increase of conjugation lengths and the extension of the frontier orbitals from the oxaborin moiety to the phenyl ring. 38,47,52,[58][59][60] If one proceeds further from B,E-PAHs to (B,E)n-PAHs with E = N or O and n > 1, the available information again becomes dramatically less, 9,11,13,30,32,39,54,55,[61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78] which is unfortunate, because some evidence has already been gathered that the number n of embedded -B=E + units significantly influences the chemical and physical properties of corresponding compounds. 30,54,68,72,79 Thus, new atom-economic strategies for the construction of (B,E)n-PAHs, which ideally avoid the use of sensitive boron halides, sophisticated organometallic reagents, or forcing reaction conditions, are still in demand.…”

“…2 By varying the positions, 3 orientations, and number of -B=N + units within the molecular framework, a greatly expanded structural and chemical space becomes accessible. [4][5][6][7][8][9][10][11][12][13][14][15] In addition, breaking the symmetry of a molecular scaffold through the introduction of a -B=N + unit often allows late-stage functionalizations with higher regioselectivities than in the case of the parent PAH. 16 Because of these appealing features, considerable research efforts are currently being made to develop novel B,N-PAHs.…”

Stereoselective Polymerization of an Aromatic Vinyl Monomer to Access Highly Syndiotactic Poly(vinyl alcohol)

“…A series of BN containing monomers such as BN‐styrene and BN‐vinylbiphenyl are reported to polymerize via RAFT mechanism. [ 21,22 ] 2‐Vinyl‐2,1‐borazanaphthalene (BN2VN) can be homo‐ and copolymerized with 2‐vinylnaphthalene via radical catalysts to give high molecular weight polymers while it can only be homopolymerized in moderate syndioselectivity by titanium catalysts. Noted that, in all the above cases long reaction times are required.…”

A BN‐Doped Cycloparaphenylene Debuts

“…[2,4] While significant advances have been made in the area of BNdoped conjugated polycyclic aromatic hydrocarbons, the development of BN-doped materials derived from monocyclic aromatic building blocks has remained underexplored. [5] Cycloparaphenylenes (CPPs), [6] cyclic strings of benzene rings that constitute the thinnest slices of arm-chaired singlewalled carbon nanotubes (SWCNTs), [7] are examples of carbonaceous materials derived from monocyclic aromatic building blocks that can benefit from the expanded chemical space provided by BN/CC isosterism. In the past decade, CPPs with varying diameters have been successfully prepared via methodologies developed by Jasti, [8] Itami, [9] and Yamago [10] research groups.…”