One-Pot Synthesis of Hyperbranched and Star Polyketones by Palladium-Catalyzed Terpolymerization of 4-tert-Butylstyrene, Divinylbenzene, and Carbon Monoxide

Abstract

We demonstrate in this article the first synthesis of a class of hyperbranched and star polyketones by Pd-catalyzed terpolymerization of 4-tertbutylstyrene (TBS), divinylbenzene (DVB), and carbon monoxide (CO), where TBS/DVB undergoes alternating copolymerization with CO. Hyperbranched polyketones are first synthesized by direct one-pot terpolymerization, where difunctional DVB monomer serves as the branching agent. A simple variation of the feed ratio of TBS and DVB facilitates the efficient tuning of the branching density in the hyperbranched polymers. The success of the terpolymerization enables the subsequent one-pot synthesis of star polyketones by both "core-first" and "arm-first" strategies. In the "core-first" strategy, multinuclear Pdcontaining hyperbranched cross-linked polyketone cores are first formed by TBS/DVB/CO terpolymerization and serve as multifunctional initiating cores for subsequent multidirectional arm growth upon TBS addition. In the "arm-first" strategy, "living" TBS/CO alternating copolymerization is first carried out to grow linear polyketone arms, followed by the addition of DVB for star formation by cross-linking the linear arms. Tuning the polymerization parameters in both strategies allows the efficient design of star polyketones of varying arm lengths and average arm numbers.

Alternating copolymerization of carbon monoxide and vinyl arenes using [N,N] bidentate palladium catalysts

“…127 Previous documents have mainly focused on 4-substituted styrene (4-R-St, R═Me, t Bu, NO 2 , CN, CF 3 ) used as comonomers and addressed the electronic effect of 4-substituents on the productivity and the molecular weight of polyketones. 69,73,[127][128][129][130] Copolymerization results clearly showed electron-donating 4-Me and 4-t Bu enhanced copolymerization productivity, while electron-withdrawing 4-NO 2 , 4-CN, and 4-CF 3 groups decreased copolymerization performance.…”

“…On the contrary, the introduction of the electron‐withdrawing groups on the comonomer leads to a decrease in copolymerization productivity and copolymer molecular weight (Scheme 7). 127 Previous documents have mainly focused on 4‐substituted styrene (4‐R‐St, R═Me, t Bu, NO 2 , CN, CF 3 ) used as comonomers and addressed the electronic effect of 4‐substituents on the productivity and the molecular weight of polyketones 69,73,127–130 . Copolymerization results clearly showed electron‐donating 4‐Me and 4‐ t Bu enhanced copolymerization productivity, while electron‐withdrawing 4‐NO 2 , 4‐CN, and 4‐CF 3 groups decreased copolymerization performance.…”

Unprecedented Steric and Positioning Effects of Comonomer Substituents on α-Diimine Palladium-Catalyzed Vinyl Arene/CO Copolymerization

“…Aromatic polyketones generated by vinyl arene/carbon monoxide (CO) alternating copolymerization have attracted much academic and industrial interest due to their unusual properties and wide range of applications as engineering resins. − Additionally, introduction of functional groups on the aryl ring of the polymer chain can further improve the properties of aromatic polyketones, thereby expanding their potential applications. − In comparison with the postfunctionalization approach, , the direct coordination–insertion copolymerization of substituted styrene monomers with functional groups and CO by α-diimine palladium catalysts is a more straightforward and efficient method. However, the coordination–insertion copolymerization normally suffers from the heavily reduced activity and copolymer molecular weight because of the possible “poison” effects of the polar groups on the active metal center. − Therefore, palladium-catalyzed copolymerization of polar styrenic monomers and CO is highly challenging until now.…”

“…Previous documents have mainly focused on 4-substituted styrenes (4-X-St, X = Me, t Bu, NO 2 , CN, CF 3 ) used as comonomers and addressed the electronic effect of 4-substituents on the productivity and the molecular weight of polyketones. − For palladium-catalyzed alternating copolymerization of vinyl arene and CO, the resting state is the palladium-acyl-carbonyl species and the rate-limiting step is the coordination of the vinyl arene monomer. − On the basis of the widely acceptable mechanistic model, the electron-rich styrenic comonomers more easily coordinate the palladium metal center, thereby enhancing copolymerization productivity and copolymer molecular weight. , On the contrary, the introduction of electron-withdrawing groups on the comonomer leads to a decrease in copolymerization productivity and copolymer molecular weight …”

“…Despite these contributions, copolymerization of polar styrenic monomers and CO has been far from successful. On the one hand, a few comonomers were used in the synthesis of aromatic polyketones, and styrenic comonomers were only limited to 4-substituted styrenes. − 2- and 3-Substituted styrene derivatives have never been used as comonomers in vinyl arene/CO copolymerization, and the positioning effects of comonomer substituents on vinyl arene/CO copolymerization remain unexplored until now. In α-diimine palladium-catalyzed (co)­polymerization of substituted styrene monomers and ethylene, substituents and their locations have been found to significantly affect the polymerization reaction .…”