Copolymers of ethylene and butadiene were prepared using the ansa-bisfluorenyl complex Me2Si-(C1(3)H(8))(2)NdR in combination with dialkylmagnesium as a chain transfer agent. Thorough kinetic studies and computational mechanistic investigations of this copolymerization reaction were performed. In combination with detailed analyses of the polymer microstructure and chain ends, these studies demonstrate that the title copolymerization operates according to a living coordinative chain transfer copolymerization of ethylene and butadiene. In addition to the formation of the previously described 1,2-cyclohexane inner chain cyclic motif, the presence of bicyclic 1,5-decalin units via the formation of transient (vinylcyclohexyl)methyl chain ends is discussed in the present communication. The nonaccumulation of the vinylcyclohexane motif within the chains is explained by the reversibility of its formation, as interpreted with the help of DFT calculations, or by its rapid conversion into decalin motif after one ethylene insertion. Finally, this study also illustrates the ability of the fluorenyl ligand to adjust its binding mode on demand in order to avoid inhibition of the catalyst.

Fourier transform infrared spectroscopy by attenuated total reflection (ATR-FTIR), combined with the partial least square (PLS) method provides a fast characterization of ethylene/butadiene copolymers' intricate composition. The PLS regression method is constructed to quantify ethylene, 1,2-butadiene (vinyl), trans-1,4-butadiene, and 1,2-cyclohexane units in the copolymer. These rings are formed by intramolecular cyclization during polymerization. The performance of PLS models is evaluated by comparing the result obtained by C-13 NMR and the model for three unknown samples. It is shown that the proposed method allows to accurately estimate the chemical composition of ethylene/butadiene copolymers in a much shorter time than NMR.

Zr(CH 2 Ph) 4 ( 1 ) was grafted onto a recently disclosed hybrid material based on amorphous silica that features unique phenol grafting sites {[(≡SiO) 2 (AlOC 6 H 4 OH)(Et 2 O)] ( H )}. A monopodal tribenzyl surface species, structurally similar to the silica-supported species previously disclosed [≡SiOZr(CH 2 Ph) 3 ] ( 2 ), was obtained and fully characterized as [(≡SiO) 2 (AlOC 6 H 4 OZr(CH 2 Ph) 3 )(Et 2 O)] ( 3 ). The activation of both these species by B(C 6 F 5 ) 3 proceeded by benzyl abstraction to yield the inner-sphere ion pairs [≡SiOZr(CH 2 Ph) 2 ] + [(PhCH 2 )B(C 6 F 5 ) 3 ] – ( 4 ) and [(≡SiO) 2 (AlOC 6 H 4 OZr(CH 2 Ph) 2 )(Et 2 O)] + [(PhCH 2 )B(C 6 F 5 ) 3 ] – ( 5 ), respectively. These surface species were fully characterized by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, elemental analyses, and 1 H, 13 C, 11 B, and 19 F solid-state NMR spectroscopy. These isolated cationic catalysts displayed increased ethylene polymerization activity compared to the neutral species. Most importantly, the heterogenization of the cationic complex with the phenol spacer ( 5 ) led to a fourfold increase in productivity compared to that of the silica counterpart 4 , in agreement with reduced surface interactions and improved electrophilicity.

Homoleptic benzyl derivatives of titanium and zirconium have been grafted onto silica that was dehydroxylated at 200 and 700 °C, thereby affording bi-grafted and mono-grafted single-site species, respectively, as shown by a combination of experimental techniques (IR, MAS NMR, EXAFS, and elemental analysis) and theoretical calculations. Marked differences between these compounds and their neopentyl analogues are discussed and rationalized by using DFT. These differences were assigned to the selectivity of the grafting process, which, depending on the structure of the molecular precursors, led to different outcomes in terms of the mono- versus bi-grafted species for the same surface concentration of silanol species. The benzylzirconium derivatives were active towards ethylene polymerization in the absence of an activator and the bi-grafted species displayed higher activity than their mono-grafted analogues. In contrast, the benzyltitanium and neopentylzirconium counterparts were not active under similar reaction conditions.