A means to an end: Polyethylene chains obtained by catalyzed chain growth on magnesium and exhibiting molar masses up to 5000 g mol−1 have been end‐functionalized in high yield with iodide, azide, and amine reactive end groups (see scheme). The functionalized polyethylenes can be used to generate a range of reactive polyolefins; for example, the azide‐functionalized chain can undergo “click” reactions to afford macromonomers.
The reactions between two polyisocyanates, 4,4'-methylenebis(phenyl isocyanate) (MDI) and trimer of isophorone diisocyanate (tIPDI) and a model aryl-alkyl diurethane were carried out at high temperature (≥ 170°C) and several NCO/urethane ratios. A combination of 1 H & 13 C NMR and MALDI-TOF spectroscopies was used and allows the identification of reaction products. When MDI or tIPDI is reacted with a diurethane at high temperature and after cooled, allophanates are formed but no isocyanurates. 13 C NMR was used to quantify the different reaction products obtained under different experimental conditions. Only a few allophanates (≤ 10%) are obtained after 1h of reaction.
International audienceLow-molecular-weight poly(acrylic acid) (PAA) was synthesized by reversible addition fragmentation chain transfer polymerization with a trithiocarbonate as chain-transfer agent (CTA). With a combination of NMR spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, the PAA end-groups of the polymer were analyzed before and after neutralization by sodium hydroxide. The polymer prior to neutralization is made up of the expected trithiocarbonate chain-ends and of the H-terminated chains issued from a reaction of transfer to solvent. After neutralization, the trithiocarbonates are transformed into thiols, disulfides, thiolactones, and additional H-terminated chains. By quantifying the different end-groups, it was possible to demonstrate that fragmentation is the rate limiting step in the transfer reaction
Metallocene borohydride complexes {(Me 2 Si(C 13 H 8 ) 2 )Nd(µ-BH 4 )[(µ-BH 4 )Li(THF)]} 2 (1) and (Me 2 Si(2,7-tBu 2 C 13 H 6 ) 2 )Nd(BH 4 )(µ-BH 4 )Li(ether) 3 (2) were prepared by reaction of the dilithium salts of silylenebridged bis(fluorenyl) ligands with the borohydride precursor Nd(BH 4 ) 3 (THF) 3 . The solid state structures of dimeric 1 and monomeric 2 ate 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 trans selectivity. 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 1 H-1 H and 1 H-13 C with direct and long-range correlations. Mechanisms of stereoselective formation of trans-1,2-cyclohexane and trans-1,4cyclohexane rings were fully investigated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.