A series of rare earth phenolates substituted by alkyl groups for D,L-lactide ring-opening polymerization

Abstract

Single component rare earth phenolates substituted by various alkyl groups have been prepared and the correlation between the aryloxides' structure and catalytic activity in the ring-opening polymerization of D, L-lactide has also been investigated. The catalytic activity of all rare earth aryloxides, characteristics of the ring-opening polymerization as well as polymerization kinetics and mechanism were investigated. The results showed that both phenolates' catalytic activities and polymerization characteristics changed regularly, keeping in good concordance with variations in substitutents' number on phenol and structure of aryloxide ligands. The stronger ability of electron-donation of alkyl groups, the higher catalytic activity. Moreover, the more numbers of substituted alkyl on phenyl ring, the higher catalytic activity. The analyses of polymer ends revealed that the polymerization proceeded via a coordination-acyl-oxygen bond cleavage-insertion mechanism.

Mechanism of ring‐opening polymerization of l‐lactide by lanthanide aryloxide: A theoretical study on the effect of the aryloxide ligands on the process

“…The La∙∙∙arene interaction observed at ~2.8 Å in 3b I is consistent with the same distances (2.73–2.93 Å) reported in solid state structures of lanthanum complexes containing π‐bounded arene fragments [43–45]. Note that this La∙∙∙OAr species 3b I has not been reported in previous experiments on similar ROP process with rare earth aryloxide catalyst [6, 15–17, 19, 21, 25, 26, 46, 47]. This structural arrangement of the sterically bulky ligand prior to ring opening has also been found in other relevant studies on lactide ROP [48–50].…”

“…More polar solvents can decrease the activation energies significantly (Table S3). The results also suggest that La(OTMP) 3 is a low-active initiator for LLA ROP, which support experimental observations for the broadening of molecular weight distribution in the lactide ROP mediated by La(OAr) 3 -type initiators [6,26,38,46].…”

“…The homopolymerization of 1-methyltrimethylene carbonate and copolymerization of 2,2-dimethyltrimethylene carbonate and ε-caprolactone initiated by highly active single-component rare earth tris (2,6-di-tert-butyl-4-methylphenolate)s [Ln(OAr) 3 , Ln = La, Dy, Y] have also been reported in 2010 [19,25]. Recently, six kinds of lanthanum phenolates substituted by various alkyl groups have succeeded in the ROP of LLA [26]. The authors of this work discussed the relationship between the aryloxides' catalytic activities and their polymerizability.…”

Contemporary approaches to reducing weld induced residual stress

“…Most researchers have concentrated on the martensitic transformation, using additional carbon and/or a combination of nickel and chromium (in quantities up to y15 wt-% each) to reduce the temperature at which martensite begins to form. [156][157][158] Unfortunately, the increased carbon content and presence of brittle martensite can give low-transformation-temperature weld material reduced impact toughness. 155 Therefore, while the effectiveness of this approach for reducing residual stresses has been demonstrated in several studies, 155,157 further research is needed to simultaneously achieve excellent mechanical properties.…”

Multi-aircraft Rerouting Method Under Dangerous Weather

“…Yang Shuangshuang [2] adopted a geometric method to reroute under static dangerous weather. Wang Fei and Wang Lili [3][4][5] aim at minimizing the cost of rerouting, and established a rerouting model based on genetic algorithm, which improves the accuracy of rerouting planning. Meng Linghang [6] considered the dynamic characteristics of dangerous weather and designed a heuristic algorithm for the specific weather conditions.…”