Syndiospecific Copolymerization of Styrene with para-Methoxystyrene Catalyzed by Functionalized Fluorenyl-Ligated Rare-Earth Metal Complexes

Abstract

The development of efficient catalysts for the copolymerization of nonpolar monomers with polar monomers remains a great challenging task in polymer synthesis. A one-pot reaction of anhydrous LnCl 3 with pyridyl-methylene-functionalized octamethylfluorenyl lithium OctFlu-CH 2 PyLi in a 1:1 molar ratio, followed by alkylation with 2 equiv of LiCH 2 SiMe 3 in THF afforded the fluorenyl-ligated rare-earth metal bis(alkyl) complexes (OctFlu-CH 2 Py)Ln(CH 2 SiMe 3 ) 2 (THF) [Ln = Sc (1), Y (2)]. Both complexes were isolated as neutral species and were characterized by NMR spectrum and elemental analysis. Complex 2 was subjected to single-crystal X-ray diffraction, which showed that the whole modified fluorenyl ligand was coordinated to Y 3+ in the η 5 /κ 1 mode to form a constrained geometry configuration. In the presence of excess Al i Bu 3 , and on activation with 1 equiv of [Ph 3 C][B(C 6 F 5 ) 4 ] in toluene, complexes 1 and 2 became active for both styrene (St) and para-methoxystyrene (pMOS) polymerization, giving polymers with high syndiotacticity (rrrr > 99%) without solvent extraction. Moreover, the ternary catalyst system composed of complex 2/Al i Bu 3 /[Ph 3 C][B(C 6 F 5 ) 4 ] was highly effective for the syndiospecific copolymerization of styrene with pMOS, producing random copolymers with high molecular weights and narrow molecular weight distributions. The contents of pMOS in the copolymers could be easily tuned in a wide range (11−93 mol %) by simply changing the pMOS-to-St feed ratios.

Mechanistic Insights into Rare-Earth-Catalyzed Alternating Copolymerization through C–H Polyaddition of Functionalized Organic Compounds to Unconjugated Dienes

“…Notably, among various approaches, the coordination copolymerization of polar and nonpolar olefins has been extensively investigated by using various transition metal catalysts since it is a straightforward and atom-efficient strategy for synthesis of functional polyolefin materials . In this content, it is noteworthy that rare-earth alkyl catalysts have emerged as a new class of highly efficient catalysts for the copolymerization of a wide range of polar and nonpolar olefins in the past decade. − As we know, precise control of monomer sequence in the primary structure of functional polyolefins is crucial, as it will dictate subsequent secondary and tertiary structures, as well as final properties . Despite considerable efforts, most reported rare-earth-catalyzed coordination copolymerizations of polar and nonpolar olefins have resulted in block or random copolymers.…”

Polar comonomers regulate and control the copolymerization of conjugated dienes and methoxystyrenes catalyzed by a CGC-type rare-earth metal catalyst

“…3,20 Recently, high oxyphilic rare-earth catalysts having a high coordination number exhibit both high activities and high regio-/stereo-selectivities in the polymerization of POs such as polar styrenes, polar α-olefins, or polar dienes and copolymerization with non-polar olefins, affording regio-/ stereo-regular poly(PO)s with the adjustable content of POs. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] The mechanism of heteroatom-assisted synergistic coordination mode or heteroatom dynamic reversion coordination mode explains that instead of occupying all the empty coordination sites to cause deactivation, the preferential coordination of heteroatoms toward the metal center reduces the oxophilicity of the metal center and facilitates the coordination and insertion of CvC bonds to finally afford poly(PO)s (Fig. 1a).…”

Syndiotactic (Co)polymerization of 4-Vinylbenzocyclobutene Catalyzed by Rare-Earth Metal Complex

“…In the last two decades, precisely controlled polymerization of styrene and its derivatives had made significant progress by using rare-earth metal catalysts. − A variety of well-defined rare-earth metal catalysts sprung up, which showed high activity and perfect regioselectivity in both the homo- and copolymerization of styrene monomers. − The first examples of highly syndiospecific styrene polymerization mediated by rare-earth metal was reported almost simultaneously by the groups of Hou and Carpentier. , Cui’s group designed a series of constrained-geometry-configuration (CGC) type rare-earth metal complexes, which behaved well in styrene polymerization. ,− More interestingly, these complexes exhibited excellent performances in the polymerization of polar styrene monomers. ,− Isotactic polymerization of styrene monomers can be achieved by rare-earth metal catalysts as well. Carpentier et al first reported the highly isotactic polymerization of styrene initiated by rare-earth metal complexes in 2007 .…”