Organic Brønsted Acid-Catalyzed Stereoselective Cationic RAFT Polymerization:The Effect of RAFT Agents

The tacticity of vinyl polymers is a key factor affecting the properties of materials.Recently,organic Brønsted acids have been demonstrated as effective catalysts for the development of highly stereoselective cationic reversible addition-fragmentation chain transfer(RAFT)polymerizations of vinyl ethers,in which the use of RAFT agents could allow the control the molecular weight and tacticity of polymer products simultaneously.However,the effect of RAFT agents on the tacticity-regulation remains elusive and lacks of investigation.In this study,we synthesized four types of RAFT agents and evaluated their influence in the stereoselective cationic polymerization of isobutyl vinyl ether in the presence of PADI as a Brønsted acid catalyst,which unveils that the Z group of RAFT agents could not only affect the polydispersity of the products,but also exert a profound effect on the stereoselectivity.After extensive screening of the RAFT agents,high stereoregularity(isotacticity,90%m)was obtained when using dithiocarbonate ester-type RAFT agents with a benzyloxy Z group.

Synthesis of pyrrolidinyl-ethylene fluorenyl rare-earth metal complexes and catalysis for 2-vinylpyridine polymerization

The metathesis reaction between pyrrolidinyl-ethylene fluorenyl lithium salts with in situ prepared cationic rare-earth metal dialkyl species[Ln(CH_(2)SiMe_(3))_(2)(THF)_(x)][BPh_(4)]afford efficiently the corresponding constrained-geometry complexes L^(1)Ln(CH_(2)SiMe_(3))_(2)(L^(1)=FluCH_(2)CH_(2)NC_(4)H_(8),Ln=Y(1a),Lu(1b),Sc(1c))and L^(2)Ln(CH_(2)SiMe_(3))_(2)(L^(2)=(2,7-di-tert-butyl)FluCH_(2)CH_(2)NC_(4)H_(8),Ln=Y(2a),Lu(2b),Sc(2c))in good yields.All these complexes were characterized by NMR spectroscopy,and the solid-state molecular structure of yttrium complex 1a was defined with single-crystal X-ray diffraction analysis.The catalytic performance of these complexes towards 2-vinylpyridine polymerization was investigated,where these complexes alone can efficiently promote the polymerization of 2-vinylpyridine giving isotactic poly(2-vinylpyridine).Upon the activation with[Ph_(3)C][B(C_(6)F_(5))_(4)],the yttrium and lutetium complexes also afford isotactic poly(2-vinylpyridine),while the scandium complexes produce syndiotactic poly(2-vinylpyridine).

Organocatalytic stereoselective cationic polymerization of vinyl ethers by employing a confined BrΦnsted acid as the catalyst

The properties of poly(vinyl ether)s(PVEs)are highly dependent on their tacticity,and the appealing thermoplastics features of isotactic PVEs have drawn considerable efforts to develop stereoselective cationic polymerization methods to access this class of polymers.However,reported methods that could achieve a high degree of tacticity control are limited to process employing metal-based Lewis acids,and with various limitations on catalyst loading,monomer scope,etc.Here,we introduce a metal-free stereoselective cationic polymerization of vinyl ethers by employing a class of chiral confined Br?nsted acids,imidodiphosphorimidates(IDPis),as the catalyst.This organocatalytic approach features its metal-free conditions,high efficiency,high stereoselectivity,single catalyst system,operation simplicity,etc.