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A synthetic method for the production of polyethylene (PE) chains carrying alkoxyamine end‐group has been proposed first by successfully reacting the well‐known 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) and N‐(2‐methyl‐2‐propyl)‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl)‐N‐oxyl (commonly called SG1) stable radicals with dipolyethylenylmagnesium compounds to give PE‐TEMPO and PE‐SG1. Since the homolytic cleavage of these two macroalkoxyamines for the production of block copolymers using controlled radical polymerization would require temperatures higher than 160 °C, two original new nitroxides (4‐[(2,2‐dimethyl‐4‐(N‐tert‐Butyl‐N‐(1‐diethoxyphosphoryl‐2,2‐dimethylpropyl)aminoxy)‐4‐n‐butoxycarbonyl)butanoyloxyl]‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy, DD1) and 4‐[(2,2‐dimethyl‐4‐(N‐tert‐Butyl‐N‐(1‐diethoxyphosphoryl‐2,2‐dimethylpropyl)aminoxy)‐4‐phenyl) butanoyloxyl]‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy, DD2) containing a TEMPO moiety and incorporating an SG1‐based alkoxyamine (cleavage temperature: 60 °C) were then synthesized. NMR analyses showed that the resulting PE‐DD1 and PE‐DD2 were obtained using this functionalization strategy though with low to moderate yields (from 17% to 40%). PE‐DD2 (40% functionalization) was used under controlled radical polymerization conditions of n‐butyl acrylate. SEC analyses together with 1H NMR analysis showed that a poly(ethylene‐b‐n‐butyl acrylate) block copolymer was produced and that the polymerization proceeded under control. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2705–2718, 2007 [ABSTRACT FROM AUTHOR]

Well-defined,crystalline, low molar mass polyethylene PEx(where xis the molar mass 1300and 2200 g mol–1) bearing thymine (Thy) or 2,6-diaminotriazine(DAT) end groups have been synthesized from amino-terminated PE. Eitherdouble-layer or monolayer solid-state morphologies were attained dependingon the nature of the end-group(s). PE1300-NH2, PE1300-DAT, and the equimolar blend PE1300-Thy/DAT-PE1300all organized into double-layer structurescomposed of extended PE chains sandwiched between H-bonding chain-ends.The double-layered morphology arose from the microphase separationof the polar end-groups and the nonpolar PE chains and was frozenby the crystallization of the PE domains. The regularity of the PElamellar stacking was higher for the stronger and more directionalassociated pair Thy/DAT compared with samples of either PE-NH2or PE-DAT. For PE1300-Thy, the mesoscopic organizationwas driven by the crystallization of Thy domains prior to crystallizationof the PE chains, forcing the small proportion of nonfunctionalizedPE chains to segregate and crystallize separately to the PE-Thy chains.The confinement of PE chains between Thy domains lead to a conventionalmonolayer form in which extended PE chains were interdigitated. Thevolume fraction of Thy or DAT end-groups was a key parameter in theorganization in all these systems: the PE crystallinity was higherwith longer PE chains (i.e., a low volume fraction of Thy or DAT units),but the mesoscopic organization of the supramolecular PE was lessregular. [ABSTRACT FROM AUTHOR]

Metallocene borohydride complexes {(Me2Si(C13H8)2)Nd(μ-BH4)[(μ-BH4)Li(THF)]}2(1) and (Me2Si(2,7-tBu2C13H6)2)Nd(BH4)(μ-BH4)Li(ether)3(2) were prepared by reaction of the dilithium salts of silylene-bridged bis(fluorenyl) ligands with the borohydride precursor Nd(BH4)3(THF)3. The solid state structures of dimeric 1and monomeric 2ate complexes were established by X-ray diffraction studies. We showed that these complexes used in combination with (nBu)(nOct)Mg are highly efficient for cyclocopolymerization of ethylene with butadiene leading to a new class of elastomers. Catalyst 1/(nBu)(nOct)Mg provided elastomers with a polyethylene skeleton incorporating unsaturated groups (trans double bond and pendant vinyl units) and 1,2-cyclohexane rings. These rings are formed via an intramolecular cyclization which occurs with a high transselectivity. The investigation of catalyst 2/(nBu)(nOct)Mg has revealed that the tertio-butyl substitution in positions 2 and 7 of fluorenyl ligands influenced the microstructure of copolymers since in addition to 1,2-cyclohexane rings, 1,4-cyclohexane rings were formed. This original microstructure was characterized using 2D NMR 1H−1H and 1H−13C with direct and long-range correlations. Mechanisms of stereoselective formation of trans-1,2-cyclohexane and trans-1,4-cyclohexane rings were fully investigated. [ABSTRACT FROM AUTHOR]