Liu Bo,Liu Dong-tao,Li Shi-hui,Sun Guang-ping,Cui Dong-mei
β -Iminophosphonamide ligated lanthanum bis(benzyl) complex (NPN Dipp )La(CH 2 Ph-4-Me) 2 (THF) (NPN Dipp = Ph 2 P(NC 6 H 3
i Pr 2 -2,6) 2 ), upon activation of AlEt 3 and [Ph 3 C][B(C 6 F 5 ) 4 ], exhibited high catalytic activity and high trans -1,4 stereoselectivity for the polymerization of bio-sourced β -myrcene (MY). Based on which, a series of novel trans -1,4 regulated elastomers could be generated by random/block copolymerization of MY and isoprene (IP).
A convenient synthetic route has been developed for preparing the novel rigid 4,5-(PR2)2–2,7,9,9-tetramethylacridane-based pincer ligands (acri-RPNP; R = iPr and Ph), and the first rare-earth (Ln = Y, Lu) alkyl complexes bearing the acri-RPNP ligands were synthesized by a salt metathesis reaction (for the isopropyl-substituent acri-iPrPNP complexes, 1-Ln) or direct alkylation (for the phenyl-substituent acri-PhPNP complexes, 2-Ln). For both 1-Ln and 2-Ln, the NMR spectroscopy and X-ray diffraction study confirmed the successful coordination of the acri-RPNP ligand to the central metal ion in a tridentate manner via the two phosphine and the nitrogen donors. In contrast to 1-Ln that are solvent-free complexes, the metal centers in 2-Ln are each coordinated with one tetrahydrofuran molecule. Upon activation by [Ph3C][B(C6F5)4], 1-Y and 2-Lu could catalyze the living polymerization of isoprene and β-myrcene with high catalytic activity and high cis-1,4-selectivity (up to 92.3% for isoprene and 98.5% for β-myrcene). Moreover, the 1-Y/[Ph3C][B(C6F5)4] catalytic system also could promote the polymerization of butadiene and its copolymerization with isoprene to produce copolymers with high cis-1,4-selectivity and narrow polydispersity.
Qingtao Niu,Aihua He,Chongdian Si,Guodong Liu,Mingxuan Xiao,Guifan Chen,Manman Jin
Four TiCl 4 /MgCl 2 Ziegler-Natta catalysts (Cat-1∼Cat-4) with titanium contents in the range of 0.038–0.578 wt% were synthesized by the chemical rout and used for isoprene polymerizations. Four catalysts had similar possessed rod-like morphologies and their surface areas gradually increased as Ti contents increased. Cat-1 with the lowest Ti content (0.038 wt%) had the highest catalytic activity (28039.6 g∙P/(g∙Ti∙h)). To our knowledge, this was the highest activity achieved for isoprene polymerization using the heterogeneous TiCl 4 /MgCl 2 Ziegler-Natta catalyst. With the increasing Ti content, the catalyst activity gradually decreased in the order of Cat-1 < Cat-2 < Cat-3 < Cat-4, whereas the trans -1,4 stereoselectivity increased. Cat-4 with the highest Ti content (0.578 wt %) gave highest trans -1,4 units (97.7 mol%). The polymers were mainly composed of fraction C, D and G. C and D had high trans -1,4 structure while G fraction had low trans -1,4 structure. The plausible stereospecific transformation models of MgCl 2 -supported Ziegler-Natta catalyst with different Ti contents were discussed.
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