Die Sammlung Simone Collinet. Simone Breton als leidenschaftliche Sammlerin des Surrealismus

A series of highly active yttrium phosphasalen initiators for the heteroselective ring-opening polymerization of <i>rac</i>-lactide are reported. The initiators are yttrium alkoxide complexes ligated by iminophosphorane analogues of the popular “salen” ligand, termed “phosphasalens”. A series of novel phosphasalens have been synthesized, with varying substituents on the phenoxide rings and ethylene, propylene, <i>rac</i>-cyclohexylene, <i>R</i>,<i>R</i>-cyclohexylene, phenylene, and 2,2-dimethylpropylene groups linking the iminophosphorane moieties. Changing the substituents on the phosphasalen ligands results in changes to the rates of polymerization (<i>k</i>_obs) and to the PLA heterotacticity (<i>P</i>_s = 0.87). Generally, the initiators have high rates, excellent polymerization control, and a tolerance to low loadings

The word as a unit of meaning. The role of context in words meaning

A unit of meaning is a word plus all those words within its contextual context that are needed to disambiguate this word to make it monosemous. A lot of research were made to study the influence of the context. They testify that there is usually in each word a hard core of relatively stable meaning and can be modified by the context within certain limits

8‑Quinolinolato Gallium Complexes: Iso-selective Initiators for <i>rac</i>-Lactide Polymerization

The synthesis and characterization of a series of 8-quinolinolato gallium complexes is presented, and the complexes are analogous to a series of aluminum complexes previously reported. The complexes have been shown to be active initiators for the ring-opening polymerization of <i>rac</i>-lactide. High degrees of polymerization control are demonstrated, as exemplified by the linear evolution of molecular weight as the polymerization progresses, narrow polydispersity indices, and molecular weights corresponding to those predicted on the basis of initiator concentration. Some of the initiators show iso-selective polymerization of <i>rac</i>-lactide, with <i>P</i>_i = 0.70. The polymerization rates have been monitored, and the pseudo first-order rate constants are compared to those of analogous aluminum compounds. The 8-quinolinolato gallium initiators show rates approximately 3 times higher than those of the series of aluminum compounds, while maintaining equivalently high iso-selectivity (<i>P</i>_i = 0.70) and polymerization control

Scandium and Yttrium Phosphasalen Complexes as Initiators for Ring-Opening Polymerization of Cyclic Esters

The synthesis and characterization of novel scandium and yttrium phosphasalen complexes is reported, where phosphasalen refers to two different bis­(iminophosphorane) derivatives of the more ubiquitous salen ligands. The activity of the complexes as initiators for the ring-opening polymerization of cyclic esters is presented. The scandium complexes are inactive for lactide polymerization but slow and controlled initiators for ε-caprolactone polymerization. The lack of activity toward lactide exhibited by these compounds is probed, and a rare example of single-monomer insertion product, unable to undergo further reactions with lactide, is identified. In contrast, the analogous yttrium phosphasalen complex is a very active initiator for the ring-opening polymerization of <i>rac</i>-lactide (<i>k</i>_obs = 1.5 × 10^–3 s^–1 at 1:500 [yttrium initiator]:[<i>rac</i>-lactide], 1 M overall concentration of lactide in THF at 298 K). In addition to being a very fast initiator, the yttrium complex also maintains excellent levels of polymerization control and a high degree of isoselectivity, with the probability of isotactic enchainment being <i>P</i>_i = 0.78 at 298 K

Yttrium Phosphasalen Initiators for <i>rac</i>-Lactide Polymerization: Excellent Rates and High Iso-Selectivities

Highly active yttrium phosphasalen initiators for the stereocontrolled ring-opening polymerization of <i>rac</i>-lactide are reported. The initiators are coordinated by a new class of ancillary ligand: an iminophosphorane derivative of the popular “salen” ligand, termed “phosphasalen”. Changing the phosphasalen structure enables access to high iso-selectivities (<i>P</i>_i = 0.84) or hetero-selectivities (<i>P</i>_s = 0.87). The initiators also show very high rates, excellent polymerization control, and tolerance to low loadings; furthermore, no chiral auxiliaries/ligands are needed for the stereocontrol. The combination of such high rates with high iso-selectivities is very unusual

Yttrium Phosphasalen Initiators for <i>rac</i>-Lactide Polymerization: Excellent Rates and High Iso-Selectivities

Highly active yttrium phosphasalen initiators for the stereocontrolled ring-opening polymerization of <i>rac</i>-lactide are reported. The initiators are coordinated by a new class of ancillary ligand: an iminophosphorane derivative of the popular “salen” ligand, termed “phosphasalen”. Changing the phosphasalen structure enables access to high iso-selectivities (<i>P</i>_i = 0.84) or hetero-selectivities (<i>P</i>_s = 0.87). The initiators also show very high rates, excellent polymerization control, and tolerance to low loadings; furthermore, no chiral auxiliaries/ligands are needed for the stereocontrol. The combination of such high rates with high iso-selectivities is very unusual