Polymeric metal complexes polyesters

The incorporation of a rigid metal complex in a polymer chain reduces the solubility and processibility as is known for aromatic polyamides or polyesters. Polymeric metal complexes with aliphatic alkylene moieties between the chelate units or bulky groups as substituents are easier to handle. Cross-linked polymeric metal complexes are, of course, more difficult to analyze. 

Polymeric metal complexes with polyester macroligands have been generated by initiation from hydroxyl functionalized ligand and metal complex reagents. Ligand initiators lead to macroligands which can be combined with metal precursors in coordination reactions to produce PMCs (51). Metalloinitiators, on the other hand, produce PMCs directly (2). 

Enzymatic, surface-initiated polymerizations of aliphatic polyesters was reported for wider clinical use of aliphatic polyesters 84). The hydroxyl terminated SAM acted as an initiation site for lipase B catalyzed ROP of aliphatic polyesters, such as poly(e-caprolactone) and poly (p-dioxanone) (Scheme 3). Another example of enzymatic SIP is the polymerization of poly (3-hydroxybutyrate) (PHB), where PHB synthase, fused with a His-tag at the N-terminus, was immobilized onto solid substrates through transition-metal complexes, Ni (II)-NTA, and the immobilized PHB synthase catalyzed the polymerization of 3-R-hydroxybutyry 1-coenzyme A (3HB-CoA) to PHB 85). 

MA copolymerization kinetics, 281, 282 MA copolymerization mechanism, 281, 282 MA-metal complex polymerization, 213 MA reactivity ratios, 301 permaleic acid eypoxidation, 78 polyester reactive diluent, 485, 489, 495, 505 styrene-MA CTC initiated polymerization, 371 1 -Methyl-2-(p-methoxypheny)ethylene, MA copolymerization, 373, 374 Methyl p-methoxyphenylpropiolate, MA Diels-Alder reaction, 138 Methyl methoxysuccinate, sodium salt, 46 Methyl 2-methyl-2-butenoate, 197... 

In this chapter we present an overview of this increasingly active research field. The first section focuses on coordination polymerization with metal complexes, classified by the nature of their ancillary ligands. The spectacular achievements reported recently in organocatalyzed and stereocontrolled ROP are then presented. The third section concerns the macromolecular engineering of poly(a-hydroxyac-ids) by varying both their substitution pattern (with alternative monomers to lactide and glycolide) and their architecture (via block, star and dendritic copolymers). The well-established and rapidly emerging applications of these synthetic polyesters are discussed briefly in the last section. 

The concept of using group I metal initiators was applied in order to minimize the toxicity generated by heavy metal residues in the end product PLAs when using metals like aluminum, tin, and lanthanides as initiators. In recent years, dinuclear lithium and macro-aggregates with phenolate ligands have attracted substantial interest, mainly due to uncommon strucmral feamres and their ability to catalyze formation of polyester and various other polymeric materials via ROP [28]. A series of lithium complexes supported with 2, 2-ethylidene-bis (4, 6-di-tert-butylphenol) (EDBP-H2) 2-6, (Scheme 6) are excellent initiators for the ROP of L-lactide in CH2CI2 at 0 °C and 25 °C [33-35]. In this case, the PDIs of the obtained PLAs were quite narrow (1.04—1.14) and a Unear relationship between and the monomer-to-initiator ratio ([M]o/[I]o) existed at 0 °C. Dimeric complexes 4 and 6 were the... 

Such alkali metal ion pairs are capable of two electron transfer from the potassium anion towards a suitable substrate, e.g. p-butyrolactone with formation of a respective carbanion. The strong tendency to two electrons transfer is due to the unusual oxidation state of potassium anion bearing on its outer s orbital a labile electron doublet shielded from the positive potassium nucleus by inner orbitals. Using 5 -enantiometr of P-butyrolactone as a monomer and potassium supramolecular complex as catalyst, enolate carbanion is formed as the first reactive intermediate which induces polymerization, yielding poly-(R)-3-hydroxybutanoate. The resulting biomimetic polyester has the structure similar to native PHB produced in nature, except for acetoxy-end-groups, which are formed instead of the hydroxyl ones typical for natural PHB. 

These aliphatic polyesters can be obtained by catalyzed dehydration of hydroxyacids and, more efficiently, by ring opening polymerization of the cyclic esters of hydroxyacids (equations (1) and (2)). Catalysts are generally used to facilitate the polymerization. Among the effective catalysts are Lewis acids in the form of metal salts of Sn, Zn, Ti, Al, and rare earth metals [17-23] alkali metal alkoxides and super-molecular complexes [20,24,25] and acids [26]. 

Then, the resulting tin(II) mono- and/or dialkoxide initiates polymerization in the same manner as the other metal alkox-ides. However, there was, at that time, no direct proof of such a mechanism and several other mechanisms have been pro-posed. " The most often cited was the trimolecular mechanism in which first the catalyst-monomer complex is formed. This mechanism has conclusively been shown not to operate since it excludes the presence of Sn atoms covalently bonded to the growing macromolecules. The matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectral measurements of the cyclic ester/ROH/Sn(Oct)2 system revealed the presence of tin(II) alkoxides in the growing polyester chains. Moreover, the kinetic studies also clearly supported this sequence of the exchange reactions. ... 

Recently, a new polymeric electrolyte consisting of polyester-substituted polyphosphazene [71] has been developed. This polymer, which is designated MEEP, forms complexes with a large number of metallic salts, the complexes having a higher conductivity at room temperature than earlier polymer electrolytes. For example, MEEP-LiF3S03 has a conductivity of 10 ohm -cm, which is sufficient... 

The citrate method, also called polymerizable complex method, was first developed by Pechini [26], The process uses citric acid (CA) to chelate metal ions and ethylene glycol (EG) as a solvent for the polymerization to form an intermediate of polyester-type resin. According to Popa and Kakihana [27] the process consists of three major steps (i) complexation of metal ions with citric acid in water (ii) polymerization, where the formed chelates undergo polyesterification with ethylene glycol and (iii) decomposition of the organic network to obtain the powder precursor. These steps can be seen on Figure 4. 

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