Systematic Studies on (Co)Polymerization of Polar Styrene Monomers with Palladium Catalysts

Experimental and theoretical insights into palladium-mediated polymerization of para-N,N-disubstituted aminostyrene

Experimental and theoretical insights into polymerization of para-N,N-disubstituted aminostyrene monomers (St-4-NR2, R = Me, Et, Ph) using cationic α-diimine palladium complexes have been initially reported. The effects of the catalyst structure and monomer substituent were studied systematically. Polymerization turnover frequency (TOF) was shown to decrease in the order of monomer substituents Me > Et > Ph, whereas the molecular weight of the produced polymers showed an opposite trend (Me < Et < Ph). Methanol-mediated polymerization of para-N,N-dimethylaminostyrene (DMAS), along with polymer chain-end analysis, and palladium intermediate isolation proved that palladium-initiated DMAS polymerization obeyed a cationic mechanism. Comprehensive theoretical calculations further revealed that the carbocation was generated from the insertion of DMAS into the palladium center rather than the polarization of the methyl palladium intermediate with a coordinated DMAS. The produced amine-functionalized amorphous polystyrenes have low stereoregularity and exhibit good hydrophilic properties. The poly(para-N,N-disphenylaminostyrene) is a luminescent polymer and shows fluorescence properties, rendering this material a promising candidate for versatile potential applications.

Polar-Functionalized Polyethylenes Enabled by Palladium-Catalyzed Copolymerization of Ethylene and Butadiene/Bio-Based Alcohol-Derived Monomers

Polar-functionalized polyolefins are high-value materials with improved properties. However, their feedstocks generally come from non-renewable fossil products; thus, it requires the development of renewable bio-based monomers to produce functionalized polyolefins. In this contribution, via the Pd-catalyzed telomerization of 1,3-butadiene and three types of bio-based alcohols (furfuryl alcohol, tetrahydrofurfuryl alcohol, and solketal), 2,7-octadienyl ether monomers including OC8-FUR, OC8-THF, and OC8-SOL were synthesized and characterized, respectively. The copolymerization of these monomers with ethylene catalyzed by phosphine-sulfonate palladium catalysts was further investigated. Microstructures of the resultant copolymers were analyzed by NMR and ATR-IR spectroscopy, revealing linear structures with incorporations of difunctionalized side chains bearing both allyl ether units and polar cyclic groups. Mechanical property studies exhibited better strain-at-break of these copolymers compared to the non-polar polyethylene, among which the copolymer E-FUR with the incorporation of 0.3 mol% displayed the highest strain-at-break and stress-at-break values of 940% and 35.9 MPa, respectively.

Isospecific Polymerization of Halide- and Amino-Substituted Styrenes Using a Bis(phenolate) Titanium Catalyst

Isospecific polymerization of polar styrenes is a challenge of polymer science. Particularly challenging are monomers bearing electron-withdrawing substituents or bulky substituents. Here, we report the coordination polymerization of halide- and amino-functionalized styrenes including para-fluorostyrene (pFS), para-chlorostyrene (pClS), para-bromostyrene (pBrS), and para-(N,N-diethylamino)styrene (DMAS) using 2,2′-sulfur-bridged bis(phenolate) titanium precursor (1). The combination of 1 and [Ph3C][B(C6F5)4] and AliBu3 provides crystalline poly(pFS)s with perfect isotacticity (mmmm > 95%) and high molecular weights (≤16.0 × 104 g mol−1). Upon activation with a large excess of DMAO, 1 reaches polymerization activity of 5.58 × 105 g molTi−1 h−1 producing isotactic poly(pFS)s featuring higher molecular weights (≤39.6 × 104 g mol−1). The distinguished performance of the 1/DMAO system has been extended to the polymerization of pClS and pBrS, both usually involve halogen abstraction during the polymerization, to produce isotactic and high molecular weight (Mn = 32.2 × 104 vs. 13.7 × 104 g mol−1) polymers in good activities (2.18 × 105 vs. 1.31 × 105 g molTi−1 h−1). Surprisingly, 1/DMAO is nearly inactive for DMAS polymerization, on contrary, the system 1/[Ph3C][B(C6F5)4]/AliBu3 displays isoselectivity (mmmm > 95%) albeit in a moderate activity.

Interrupted Intramolecular Hydroaminomethylation of N-Protected-2-vinyl Anilines: Novel Access to 3-Substitued Indoles or Indoline-2-ols

A new synthetic alternative to the synthesis of 3-methyl indoles and 3-methyl indoline-2-ols with an excellent atomic economy is presented in this study. It is demonstrated that the intramolecular interrupted hydroaminomethylation (HAM) reaction is a powerful tool for the formation of these compounds, which exhibit wide-ranging biological activity. Several N-Protected-2-vinyl anilines were synthesized and involved in the reaction producing the corresponding 3-methylindole or 3-methyl indoline-2-ol depending on the nature of the N-protecting groups.

The synthesis and properties research of functionalized polyolefins

This work demonstrated a tandem ROMP/hydrogenation approach for the preparation of functionalized polyolefins and their properties were investigated.

Scandium-catalyzed stereoselective block and alternating copolymerization of diphenylphosphinostyrenes and isoprene

The coordination copolymerization of polar diphenylphosphinostyrenes (StPPh2) and isoprene (IP) by a half-sandwich scandium catalyst (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2 afforded a new series of phosphine-functionalized alternating and block isoprene-styrene copolymers. In the copolymerization...

Functionalization of Biphenylcarbazole (CBP) with Siloxane-Hybrid Chains for Solvent-Free Liquid Materials

We report herein the synthesis of siloxane-functionalized CBP molecules (4,4′-bis(carbazole)-1,1′-biphenyl) for liquid optoelectronic applications. The room-temperature liquid state is obtained through a convenient functionalization of the molecules with heptamethyltrisiloxane chains via hydrosilylation of alkenyl spacers. The synthesis comprises screening of metal-catalyzed methodologies to introduce alkenyl linkers into carbazoles (Stille and Suzuki Miyaura cross-couplings), incorporate the alkenylcarbazoles to dihalobiphenyls (Ullmann coupling), and finally introduce the siloxane chains. The used conditions allowed the synthesis of the target compounds, despite the high reactivity of the alkenyl moieties bound to π-conjugated systems toward undesired side reactions such as polymerization, isomerization, and hydrogenation. The features of these solvent-free liquid CBP derivatives make them potentially interesting for fluidic optoelectronic applications.

The yttrium-catalyzed heteroatom-assisted terpolymerization of ortho-alkoxystyrene, isoprene and butadiene with high regio- and stereoselectivity

The use of coordination polymerization to synthesize functional styrene-isoprene-butadiene rubber (SIBR) is a theoretical challenge in the field of polymer science. This paper reports great progress in this area.

Custom-made polar monomers utilized in nickel and palladium promoted olefin copolymerization

In this review, the functions of custom-made polar monomers are insightfully emphasized in the preparation of functional polyolefins.

Palladium-catalyzed ortho-halogen-induced deoxygenative approach of alkyl aryl ketones to 2-vinylbenzoic acids

The 2-vinylbenzoic acids have wide applications in the field of polymer chemistry and are key precursors for the synthesis of important bioactive molecules. Herein, an ortho-halogen-induced deoxygenative approach for the generation of 2-vinylbenzoic acids from alkyl aryl ketones by palladium catalysis is discovered and explored. This approach requires no base or stoichiometric additives and can be carried out through a simple one-step process. Furthermore, the present reaction is scalable up to one-gram scale. The commercially available palladium on carbon (5 wt%) was used as a heterogeneous catalyst and showed excellent recyclability (<5 times) without significant loss in catalytic activity. Pleasingly, under our optimized conditions, the alpha alkyl substituted 2-iodoacetophenones exhibit good diastereoselectivity and predominantly (E)-2-vinylbenzoic acids were obtained with good to excellent yields.

A tripodal heptadentate Schiff base as an active ligand for atom transfer radical polymerization

The use of a tripodal heptadentate Schiff base, tris[N-(2-pyridylmethyl)-2-iminoethyl]amine (Py₃Tren), as an active ligand for atom transfer radical polymerization (ATRP) is reported.