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International audience; Poly(lactic acid)/poly(lactide) (PLA) is an aliphatic polyester nowadays emerging as the most popular and promising bio-based, sustainable, (bio)degradable, biocompatible and ecological/environmentally friendly "plastic" candidate. PLA is a commercialized viable alternative to the traditional petrochemically derived polymeric materials in many short-time commodity and engineering applications. Whereas polycondensation of lactic acid gives PLA, ring-opening polymerization (ROP) of lactide (LA) is the preferred route towards well-defined PLA. Following the traditional metal-catalyzed ROP, the organocatalyzed ROP (OROP) of LA, enables, under mild and highly selective polymerization conditions, to prepare PLA with predictable/tunable molar mass values and extremely narrow dispersities. Organic activators most typically used in the ROP of LA, most commonly based on commercially available molecules, revolve around single organic initiators, Brønsted/Lewis acids or bases featuring different functional groups including amines and pyridine derivatives, amidines and guanidines, N-heterocyclic carbenes (NHCs), as well as phosphines and phosphazenes, and mono- or multi-component dual catalytic systems involving hydrogen-bond interactions. Recent advances in LA OROP developed over the past decade are thus accordingly addressed, emphasizing polymerization mechanism aspects and monomer activation modes, catalyst development, methodologies, stereocontrol/stereoselectivity, and functional group incorporation. The OROP of O-carboxy anhydrides (OCAs), which similarly to LA produce poly(α-hydroxy acid)s, thus enabling the introduction of functional groups along the polyester backbone, is also covered. © The Royal Society of Chemistry 2019.

International audience; Telechelic polymers have garnered a great deal of scientific interest due to their reactive chain-end functions. This comprehensive book compiles and details the basic principles of and cutting-edge research in telechelic polyesters, polycarbonates, and polyethers, ranging from synthesis to applications. It discusses general strategies toward telechelic polymers, centered on the fundamental aspects of polycondensation reactions, of cationic, anionic, coordination-insertion, and activated monomer mechanisms of the metal-, enzyme-, or otherwise organocatalyzed ring-opening polymerization of cyclic monomers, and of postpolymerization chemical modification methods of polymer precursors. All main classes of polymers are covered separately, comprising polyhydroxyalkanoates, poly(ε-caprolactone)s, poly(lactic acid)s, polylactides, polycarobnates, and polyethers, including synthetic approaches as well as some illustrative, up-to-date examples and uses. The book also addresses applications of hydroxyl, thiol, amino, or acrylate/methacrylate end-capped polymers as starting materials for the preparation of diverse polymer architectures ranging from block, graft, and star-shaped polymers and micelles to precursors for ATRP macroinitiators, polyurethane copolymers, shape-memory polymers, or nanosized drug delivery systems. The book will appeal to advanced undergraduate- and graduate-level students of polymer science; researchers in macromolecular science, especially those with an interest in functional and reactive polymers; and polymer chemists in academia and industry.

Bis(phosphinimino)methanide bisborohydride complexes of lanthanum, yttrium and lutetium, [{CH(PPh2NSiMe3)2}La(BH4)2(THF)] (1) and [{CH(PPh2NSiMe3)2}Ln(BH4)2] (Ln = Y (2), Lu (3)), have been investigated in the ring-opening polymerization (ROP) of trimethylene carbonate (TMC). All three initiators afforded linear poly(trimethylene carbonate)s (PTMCs) in toluene at 23 °C. 1H NMR analyses of the polycarbonates revealed the formation of α-hydroxy,ω-formate telechelic PTMCs, as previously observed in the ROP of TMC initiated by [Sm(BH4)3(THF)3]. This suggested the non-reduction of the carbonyl of the carbonate group in the active species by the BH3 moiety, as hinted by this same prior experimental work. Formation of α,ω-dihydroxy PTMCs, resulting from the reduction of the carbonyl, is also likely and cannot be ruled out from experimental data. DFT investigations, focused on the initiation step, supported two energetically (thermodynamically and kinetically) favorable and similar reaction pathways leading to two distinct end-functionalized PTMCs. Depending on whether reduction of the carbonyl occurred or not, α,ω-dihydroxy or α-hydroxy,ω-formate telechelic PTMCs were predicted, respectively. Although these two calculated feasible approaches are very close in energy, the formation of the latter heterofunctionalized α-hydroxy,ω-formate telechelic PTMCs is slightly preferred computationally. This first in silico study on the mechanism of the ROP of a cyclic carbonate revealed several features without any precedent in the ROP of a cyclic ester (e-caprolactone or lactide). An easily accessible (no activation barrier) intermediate in which BH3 is trapped by the intracyclic oxygen of a non-opened TMC ring has been located for the first time. The low activation barrier for the opening of the TMC ring that proceeds without B–H activation is predicted to be competitive, affording the thermodynamically less stable BH3 adduct. Finally, trapping of BH3 by the nitrogen of the {CH(PPh2NSiMe3)2}− ligand, in agreement with previous findings, highlights again the valuable role of this bisphosphiniminomethanide ligand.