Synthesis and Stereospecific Polymerization of a Novel Bulky Styrene Derivative

Abstract

A novel vinylbiphenyl monomer, 2-methoxy-5-phenyl­styrene (MOPS), was designed and efficiently synthesized to investigate the stereospecific polymerization of bulky and polar styrenic derivative. Regardless of its large side group and electron-donating o-methoxy substituent, this compound showed a high polymerizability and was readily converted to the corresponding polymers with moderate to high molecular mass through radical, anionic, and coordination polymerizations. The resultant polymers were characterized by a combination of 1H/13C NMR spectrometry, thermal analysis, and wide-angle X-ray diffraction. Radical polymerization initiated by AIBN in toluene at 60 °C produced a syndiotactic-rich (rr = 0.37) polymer as most bulky vinyl monomers, whereas anionic polymerizations induced by n-BuLi yielded only isotactic-rich polymers no matter if polar tetrahydrofuran (−78 °C, mm = 0.54) or apolar toluene (−40 °C, mm = 0.78) was employed as the solvent. The isotactic-rich microstructure obtained by anionic polymerization in polar solvent at low temperature, the condition that usually leads to syndiotactic-rich polymer, manifested the strong interactions between the o-methoxy groups of the growing chain end and the penultimate unit with the lithium counterion. Highly isotactic (mm = 0.95) and perfect syndiotactic (rr > 0.99) polymers were obtained via coordination polymerizations in toluene at ambient temperature with the β-diketiminato­yttrium precursor (I) and the heterocyclic-fused cyclo­pentadienyl­scandium complex (III) as the catalytic precursor, respectively. All the polymers were thermally stable with 5% weight loss temperatures above 360 °C. They underwent glass transitions in the temperature range of 124–140 °C depending on the tacticity, much higher than polystyrene, implying the dominant role of congestion effect of large side groups on the segment movement restriction of polymer chain. Both isotactic and syndiotactic polymers were crystalline and had melting points higher than 300 °C, although the atactic and less stereoregular polymers were amorphous. The facile synthesis in conjunction with stereostructure tailorability, high thermal stability, glass transition temperature, and melting point makes the polymer a promising candidate for not only helical functional material but also engineering plastics.

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

“…As a significant breakthrough, Cui and Hou respectively reported the homopolymerization of polar methoxystyrene with a perfect stereoselectivity using Group 3 (rare-earth metal) catalysts for the first time. − Mechanistic insights revealed that the chelation of polar methoxy group of monomer to the metal center does not poison the active species but unexpectedly lowers the coordination and insertion energies of the methoxystyrene monomer, thus, facilitating its polymerization. This milestone finding opened the mysterious box of homopolymerization of a broad scope of polar styrenes. − Furthermore, this approach has been extended to the copolymerization of ethylene and polar styrenes using Group 3 and 4 catalysts. − However, it is noteworthy that functional groups on polar styrenes applied to ethylene copolymerization are generally limited to the alkyloxy, alkylthio, amino, phosphine, and halide moieties at meta- and para-positions. In contrast, the utilization of more challenging ortho-substituted (closer to the reactive double bond) polar styrenes with a broader scope of functional groups is still an open research area.…”

Syndioselective Polymerization of Vinylnaphthalene

“…Since then, extensive studies have been devoted to develop efficient “single‐site” catalytic systems for stereospecific polymerization of styrene and its derivatives, and various homogeneous metallocene, half‐metallocene, and non‐metallocene group 3 and 4 metal‐based catalysts have been invented . In the meantime, syndiotactic polystyrene derivatives bearing polar groups such as halogen, alkoxyl, aminoalkyl, and methylthio etc., that provide polymers with improved surface properties, adhesive properties, affinity for dyes, and compatibility with other polar polymers, have been successfully prepared …”

“…Recently, we found that rare‐earth metal catalysts supported by pyridyl methyl fluorenyl ligand demonstrated their superiority on selective and controlled coordination polymerization of styrene derivatives bearing various electron‐donating/withdrawing substituents . With the help of these powerful constrained geometry configuration (CGC) catalysts, we successfully synthesized a series of high syndiotactic polystyrene derivatives such as poly(methoxystyrene), poly(4‐Methylthiostyrene), poly(4‐fluorostyrene) etc . In this contribution, we report that coordination polymerizations of 1VN, 2VN, and MVN were carried out by using the half‐sandwich scandium precursor 1 and the CGC rare‐earth metal precursors 2a ‐ 2c ( Figure ).…”

Syndiospecific Polymerization of o-Methoxystyrene and Its Silyloxy or Fluorine-Substituted Derivatives by HNC-Ligated Scandium Catalysts: Synthesis of Ultrahigh-Molecular-Weight Functionalized Polymers

“…The coordination (co)­polymerization of polar olefins to prepare high functional polyolefins having superior surface properties, adhesion properties, and compatibility with other types of materials has always been a challenging and high-profile issue in academia and industry. − The most serious difficulty lies in the fact that the high oxyphilic early transition metal catalysts can be easily poisoned by polar olefins because the stronger Lewis basic heteroatom groups of polar olefins have more preferential coordination ability than the weaker Lewis basic double bond to the strong Lewis acidic metal centers. − Subsequently, the low oxyphilic late transition metal catalysts, which are more tolerant of heteroatom functionalities in the monomer and the polymer, have ascended on the history stage and gradually began to open up new areas for the coordination (co)­polymerization of polar olefins such as polar norbornene, acrylates, vinyl ethers, vinyl acetate, vinyl halides, acrylonitrile, CO, etc. − Recently, a significant breakthrough in the coordination (co)­polymerization of polar olefins has been made by the high oxyphilic rare-earth metal catalysts. − Activated by a catalytically equimolar amount of cocatalyst borate and/or an excess of AlR 3 , rare-earth metal alkyl cations [LLnR] + generated from a series of rare-earth metal dialkyl complexes LLnR 2 L' n (Ln is a rare earth metal center, L is a negative monovalent multi-dentate supporting ligand, R is a negative monovalent alkyl ligand, L' n is a neutral ligand like tetrahydrofuran (THF) solvent molecules with a number in the range of 0–2) exhibit high activities and stereoselectivities in the coordination (co)...…”