Lactides cationic catalysts

Apart from the development of lithium initiators for the facile polymerization of L-lactide, mainly by our group, there are only a limited number of Na and K initiators known in the literature. Sodium and potassium cations are nontoxic and are essential to life, and we reported the first EDBP-Na complex as efficient initiator for the preparation of PLA [41]. Similarly, potassium EDBP complex [EDBPH-K-(THE)2] 18 has been demonstrated to be an efficient catalyst for the ROP of L-lactide in a controlled fashion, yielding PLAs with expected molecular weights and moderate PDIs (1.29-1.58) [42],... 

Early-on it was discovered that these Salen compounds, and the related six-coordinate cations [6], were useful as catalysts for the polymerization of oxiranes. These applications were anticipated in the efforts of Spassky [7] and in the substantial work of Inoue [8]. Subsequently, applications of these compounds in organic synthesis have been developed [9]. Additional applications include their use in catalytic lactide polymerization [10], lactone oligomerization [11], the phospho-aldol reaction [12], and as an initiator in methyl methacrylate polymerization [13]. 

Abstract. This paper reviews ring-opening polymerization of lactones and lactides with different types of initiators and catalysts as well as their use in the synthesis of macromolecules with advanced architecture. The purpose of this paper is to review the latest developments within the coordination-insertion mechanism, and to describe the mechanisms and typical kinetic features. Cationic and anionic ring-opening polymerizations are mentioned only briefly. 

Although increasing the catalyst concentration results in the faster overall reaction rate, enhanced rate of racemization, which is unwanted in the production of optically pure lactide may also occur. Higher synthesis temperatures, longer reaction times and presence of some metal cations such as sodium and potassium have the same effect on the stereochemical purity of the crude lactide [14, 15, 19]. Released metals through corrosion and carboxylic acid impurities formed during lactic acid fermentation are other sources of impurities [10,14, 20-22]. 

PREPARATIVE TECHNIQUES Practically useful high molecular weight PLA can be synthesized by a cationic ring opening polymerization of lactide using antimony, zinc, lead, or tin as catalyst and alcohol as molecular weight and reaction rate... 

Depending on the employed initiator/catalyst system, the ROP of 8-capro-lactone can proceed via anionic, cationic or coordination-insertion mechanisms (Scheme 6.6). The reaction can be performed in bulk, solution or as an emulsion or dispersion polymerization, and is in many respects similar to the ROP of the six-membered cyclic diester lactide. ... 

Lactide, once formed, can be polymerized by three general mechanisms anionic, (33,59-61) cationic, (33,62,63). and coordination insertion (see below). Of these, coordination-insertation is the most prevalent and industrially most important. Polymerization reactions may be performed in bulk or in solution. The type of lactide, reaction temperature, and catalyst system determine the stereochemistry at each carbon-carbon bond along the backbone of PLA, in turn determining the properties of the resulting material, while impurities present in the lactide such as water, lactic acid, and lactyl-lactic acid decrease the molecular weight of the end polymer (64,65). 

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