Coordinative Chain Transfer Polymerization Research Articles

Syndio‐ and Isoselective Coordinative Chain Transfer Polymerization of Styrene Promoted by ansa‐Lanthanidocene/ Dialkylmagnesium Systems

AbstractCombinations of the discrete neutral allyl ansa‐lanthanidocenes {Me2C(Cp)(Flu)}Nd[1,3‐ (SiMe3)2C3H3] and rac‐{Me2C(Ind)2}Y[1,3‐ (SiMe3)2C3H3] with di(n‐butyl)magnesium constitute efficient binary catalytic systems for the stereocontrolled coordinative chain transfer polymerization of styrene, yielding near‐perfect syndio‐ and isospecific polystyrenes, respectively, with high activities and productivities. By adjusting the amount of di(n‐butyl)magnesium, up to 200 polymer chains can be generated per lanthabide center, and good control of the molecular weight features enables the tailoring of low to medium molecular weight polymers.

Isoselective Styrene Polymerization Catalyzed by ansa-Bis(indenyl) Allyl Rare Earth Complexes. Stereochemical and Mechanistic Aspects

Mechanistic features of the isoselective polymerization of styrene promoted by racemic allyl ansa-lanthanidocene complexes rac-{CMe2(Ind)2}Ln(allyl)(THF)n (Ind =5-indenyl; allyl = C3H5, n = 1, Ln = Y (1), Nd (2); allyl =1,3-(SiMe3)2C3H3, n = 0, Ln = Y (3), Nd (4)), which act as unique single-component catalysts, have been investigated by experimental and theoretical methods. Combined 1H NMR and MALDI−ToF−MS analyses conducted on low molecular weights isotactic polystyrene (iPS) produced by compounds 1 or 2 established the presence of allyl end-groups and therefore that polymerization is initiated by insertion of styrene into Ln−C(allyl). 1H, 2D, and 13C NMR analyses performed on H(D)-iPS-nBu polymers, selectively produced by coordinative chain transfer polymerization (CCTP) of styrene with the binary system 3/Mg(nBu)2 (1:10), evidenced that the polymerization is highly regioselective and proceeds in a secondary insertion mode, both in the initiation and propagation steps. Microstructural analyses of the backbone of crude (unfractionated) polymers produced with 1−4 evidenced a virtually perfect isoselective (mmmmmm > 0.99) polymerization up to 120 °C. Stereoerrors observed in the 13C{1H} NMR spectra of the iPS produced at 130 °C with 1−4 are consistent with an enantiomorphic site control operative during the polymerization. DFT computations of the first and second insertions of styrene in 3 confirmed the above features and the overall mechanistic scenario.

Rare earths/main group metal alkyls catalytic systems for the 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene

AbstractA series of lanthanum and neodymium complexes comprising the half‐lanthanidocenes Cp*La(BH4)2(THF)2 (Cp* = C5Me5) (1) and Cp*Nd(BH4)2(THF)2 (2), the trisborohydrides La(BH4)3(THF)3 (3) and Nd(BH4)3(THF)3 (4), the trichlorides LaCl3(THF)3 (5) and NdCl3(THF)3 (6), the triisopropoxides La(OiPr)3 (7) and Nd(OiPr)3 (8), and the triaryloxide Nd(OC6H3‐tBu2‐2,6)3 (9) has been assessed for the chain transfer polymerization of isoprene. A transmetalation process is occurring efficiently with the borohydride complexes in the presence of magnesium dialkyl. A gradual decrease of the 1,4‐trans stereoselectivity of the reaction is observed at the benefit of 3,4‐selectivity with increasing quantities of magnesium dialkyl. This can be at least partially attributed to the growth of 3,4 polyisoprene units onto the magnesium atom. By combining dialkylmagnesium and trialkylaluminum, a 1,4‐trans stereospecific reversible coordinative chain transfer polymerization of isoprene is reached using the half‐lanthanocene Cp*La(BH4)2(THF)2. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Preparation of highcis‐1,4 polyisoprene with narrow molecular weight distribution via coordinative chain transfer polymerization

AbstractHighcis‐1,4 polyisoprene with narrow molecular weight distribution has been prepared via coordinative chain transfer polymerization (CCTP) using a homogeneous rare earth catalyst composed of neodymium versatate (Nd(vers)3), dimethyldichlorosilane (Me2SiCl2), and diisobutylaluminum hydride (Al(i‐Bu)2H) which has strong chain transfer affinity is used as both cocatalyst and chain transfer agent (CTA). Differentiating from the typical chain shuttling polymerization where dual‐catalysts/CSA system has been used, one catalyst/CTA system is used in this work, and the growing chain swapping between the identical active sites leads to the formation of highcis‐1,4 polyisoprene with narrowly distributed molecular weight. Sequential polymerization proves that irreversible chain termination reactions are negligible. Much smaller molecular weight of polymer obtained than that of stoichiometrically calculated illuminates that, differentiating from the typical living polymerization, several polymer chains can be produced by one neodymium atom. The effectiveness of Al(i‐Bu)2H as a CTA is further testified by much broad molecular weight distribution of polymer when triisobutylaluminum (Al(i‐Bu)3), a much weaker chain transfer agent, is used as cocatalyst instead of Al(i‐Bu)2H. Finally, CCTP polymerization mechanism is validated by continuously decreasedMw/Mnvalue of polymer when increasing concentration of Al(i‐Bu)2H extra added in the Nd(ver)3/Me2SiCl2/Al(i‐Bu)3catalyst system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Crystallization in Ordered Polydisperse Polyolefin Diblock Copolymers

The morphologies of polydisperse ethylene−octene diblock copolymers, synthesized via a novel coordinative chain transfer polymerization process, are examined using two-dimensional synchrotron small...

Reversible coordinative chain transfer polymerization of styrene by rare earth borohydrides, chlorides/dialkylmagnesium systems

AbstractThe ability of various rare earth borohydride and chloride complexes/n‐butylethylmagnesium systems to operate styrene chain transfer polymerization in mild conditions has been assessed. Thirteen precatalysts have been considered: the rare earth trisborohydrides Ln(BH4)3(THF)x (x = 3, Ln = Nd (1), La (2), Sm (3), x = 2, Ln = Y (4), Sc (5)), the rare earth chlorides LnCl3(THF)x (x = 3, Ln = Nd (6), La (7), Sm (8), Y (9), x = 2, Ln = Sc (10)), the mixed La(BH4)2Cl(THF)2.6 (11) and the half‐lanthanidocenes Cp*Ln(BH4)2(THF)2 (Ln = Nd (12), La (13)). Six systems were found to be active precatalysts for the polymerization of styrene. 1, 2, and 11 led to an efficient transmetalation of the growing polystyrene chain with the simultaneous occurrence of βH elimination, whereas 7, 12, and 13 led to catalyzed chain growth behavior. It is noteworthy that the catalyzed chain growth obtained with 12 and 13 occurs with significant stereoselectivity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 802–814, 2010

Synthesis and Structure of Aminopyridinato‐Stabilized Yttrium and Lanthanum Amides and Their Reactivity towards Alkylaluminium Compounds

AbstractA series of aminopyridinato‐stabilized (amido)lanthanide complexes has been synthesized and characterized. The bulky aminopyridines (2,6‐diisopropylphenyl)[6‐(2,4,6‐triisopropylphenyl)pyridin‐2‐yl]amine (1a) and [6‐(2,4,6‐triisopropylphenyl)pyridin‐2‐yl](2,4,6‐trimethylphenyl)amine (1b) were introduced by amine elimination reaction with [Ln{N(SiHMe2)2}3(thf)2] (Ln = Y, La, thf = tetrahydrofuran, Me = methyl) to obtain the corresponding mono(aminopyridinato) complexes. Single‐crystal X‐ray analyses were carried out for the yttrium derivatives. The complexes are not able to undergo coordinative chain transfer polymerization with ethylene in the presence of alkylaluminium compounds as the corresponding dialkyl complexes do. Investigations of the reactions of the lanthanide aminopyridinato complexes with triethylaluminium or diisobutylaluminium hydride reveal a fast transfer of the aminopyridinato ligand to the aluminium atom. The products of this transfer reaction are aminopyridinato‐stabilized dialkylaluminium compounds. One example of these aluminium complexes was characterized by X‐ray crystal structure analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Living Coordinative Chain-Transfer Polymerization and Copolymerization of Ethene, α-Olefins, and α,ω-Nonconjugated Dienes using Dialkylzinc as “Surrogate” Chain-Growth Sites

Highly efficient, rapid, and reversible chain transfer between active transition-metal-based propagating centers derived from {Cp*Hf(Me)[N(Et)C(Me)N(Et)]}[B(C6F5)4] (Cp* = η5-C5Me5) (1a) or {Cp*Hf(Me)[N(Et)C(Me)N(Et)]}[B(C6F5)3Me] (1b) and multiple equivalents of dialkylzinc (ZnR2) acting as “surrogate” chain-growth sites has been achieved for establishing the living coordinative chain-transfer polymerization (CCTP) of ethene, α-olefins, and α,ω-nonconjugated dienes and living CCTP copolymerization of ethene with α-olefins and α,ω-nonconjugated dienes. These living CCTP processes not only provide a work-around solution to the “one chain per metal” cap on product yield currently limiting traditional living coordination polymerization of ethene and α-olefins but, in addition, provide access to practical volumes of a variety of unique new classes of precision polyolefins of tunable molecular weights and very narrow polydispersity (Mw/Mn ≤ 1.1).

Highly Efficient, Living Coordinative Chain-Transfer Polymerization of Propene with ZnEt2: Practical Production of Ultrahigh to Very Low Molecular Weight Amorphous Atactic Polypropenes of Extremely Narrow Polydispersity

Highly efficient, living coordinative chain-transfer polymerization (CCTP) of propene can be conducted with the highly active catalyst derived from equimolar amounts of (η5-C5Me5)Hf(Me)2[N(Et)C(Me)N(Et)] (2), and the borate, [PhNMe2H][B(C6F5)4] (3), in toluene at 0 °C, in the presence of varying molar equivalents of ZnEt2 to provide practical quantities (vis-a-vis, living Ziegler−Natta polymerization) of a series of amorphous atactic polypropene (a-PP) samples. These samples are distinguished by having tunable molecular weights ranging from ultrahigh, in the absence of CCTP, to very high to very low when CCTP is conducted with increasing initial equivalents of ZnEt2all the while maintaining extremely narrow polydispersities.

Continuous Production of Ethylene-Based Diblock Copolymers Using Coordinative Chain Transfer Polymerization

Continuous Production of Ethylene-Based Diblock Copolymers Using Coordinative Chain Transfer Polymerization

Dynamical model of forest

Incorporating polar segment or polar block to non-polar polybutadiene is eye-catching as they can modify the interfacial energy and adhesion between polybutadiene matrix and polar materials. Herein, we report the in-situ preparation of well-defined polybutadiene-based block copolymers (poly(1,3-butadiene)-b-poly(cyclohexene oxide) and poly(1,3-butadiene)-b-poly(trimethylene carbonate)) using a commercially available neodymium-based catalytic system Nd(vers)3/AliBu2H/Me2SiCl2. First, the polybutadiene block was conveniently and highly efficiently synthesized via Coordinative Chain Transfer Polymerization (CCTP), yielding 5–11 polymer chains per catalyst molecule. This system revealed a high catalytic efficiency and well-controlled fashion, narrowly distributed together with well-regulated molecular weights were also resulted. Then, taking advantage of the living metal-capped polybutadienyl chain that were produced during the CCTP reaction in the first step, in-situ Ring Opening Polymerization of cyclohexene oxide, trimethylene carbonate were assessed. All the products were carefully characterized by combination of GPC, FTIR, 1H NMR, 2D DOSY NMR and DSC analysis, providing advantages and limitations for this method to prepare nonpolar-polar block copolymers.