Functionalization aliphatic polyesters

Lipase is an enzyme which catalyzes the hydrolysis of fatty acid esters normally in an aqueous environment in living systems. However, hpases are sometimes stable in organic solvents and can be used as catalyst for esterifications and transesterifications. By utihzing such catalytic specificities of lipase, functional aliphatic polyesters have been synthesized by various polymerization modes. Typical reaction types of hpase-catalyzed polymerization leading to polyesters are summarized in Scheme 1. Lipase-catalyzed polymerizations also produced polycarbonates and polyphosphates. 

The use of aliphatic monomers for hyperbranched polyesters has been debated because aliphatic monomers are said to be prone to thermal degradation reactions such as decarboxylation, cyclization, or dehydration [77]. The only commercial hyperbranched polymer is a hydroxy-functional aliphatic polyester, Boltorn, available from Perstorp AB, Sweden. 

The most direct route towards functionalized aliphatic polyesters is based on the functionalization of polyester chains. This approach is a very appealing because a wide range of functionalized aliphatic polyesters could then be made available from a single precursor. This approach was implemented by Vert and coworkers using a two-step process. Eirst, PCL was metallated by lithium diisopropylamide with formation of a poly(enolate). Second, the poly(enolate) was reacted with an electrophile such as naphthoyl chloride [101], benzylchloroformate [101] acetophenone [101], benzaldehyde [101], carbon dioxide [102] tritiated water [103], ot-bromoacetoxy-co-methoxy-poly(ethylene oxide) [104], or iodine [105] (Fig. 26). The implementation of this strategy is, however, difficult because of a severe competition between chain metallation and chain degradation. Moreover, the content of functionalization is quite low (<30%), even under optimized conditions. 

Detrembleur C, Mazza M, Halleux O, Lecomte P, Mecerreyes D, Hedrick JL, Jerome R (2000) Ring-opening polymerization of y-Bromo-E-caprolactone a novel route to functionalized aliphatic polyesters. Macromolecules 33 14-18... 

El Habnouni HS, Darcos V, Coudane J (2009) Synthesis and ring-opening polymerization of a new functional lactone, a-iodo- -caprolactone a novel route to functionalized aliphatic polyesters. Macromol Rapid Commun 30 165-169... 

Malberg S, Plikk P, Fiime-Wistrand A, Albertsson A-C (2010) Design of elastomeric homo-and copolymer networks of functional aliphatic polyester for use in biomedical applications. Chem Mater 22 3009-3014... 

Also, 10,11-undecanoic acid in the presence of a quaternary ammonium or phosphonium bromide as initiator undergoes polymerization via ring opening of the epoxide group with the carboxylic acid moiety to yield a hydroxyl-functionalized aliphatic polyester [33]. 

H. Seyednejad, et al., Functional aliphatic polyesters for biomedical and pharmaceutical applications, J. Control. Release 152 (1) (2011) 168-176. 

Functional aliphatic polyesters derived from malic acids... 

Although, normally, in the aqueous environment associated with a living system, Hpase wiU catalyze the hydrolysis of fatty acid esters, certain isolated lipases have been found to be stable in organic solvents and capable of serving as a catalyst for the reverse reaction [1, 2]. Hence, by employing a lipase-mediated catalysis of esterifications and transesterifications in an organic medium, functional aliphatic polyesters have been created with a variety of polymerization modes (Scheme 23.7). 

PAR Parrott, M.C., Valliant, J.F., and Adronov, A., Thermally induced phase separation of carborane functionalized aliphatic polyester dendrimers in aqueous media,... 

A recent publication described preparation of dendrimers from functional aliphatic polyesters that are based on 2,2-bis(hydroxymethyl)propionic acid [249]. A, Al -dicyclohexylcarbodiimide was used as the coupling agent in a double-stage convergent approach that reduced the number of synthetic and Uquid chromatographic steps required in the preparations and purifications. The hydroxyl functional dendrimers were then subjected to a variety of surface modifications by reactions with different acid chlorides [249]. 

Seyednejad FI, et al. (2011) Functional Aliphatic Polyesters for Biomedical and Pharmaceutical Applications. J. controlled release. 152 p. 168-76. 

Functionalized aliphatic polyesters based on lactones have been extensively investigated. The synthesized functionalized lactones include four-membered, six-membered and seven-membered lactones, and among them, substituted caprolactone (CL) is the most commonly used. Lou" has given a detailed review on these functionalized lactones and so we will not discuss them here. 

Versatile functional aliphatic polyesters have been prepared by copolymerization with the above mentioned functional monomers. The introduction of reactive groups along the chains is highly desirable for fine tuning the polymer properties, such as chemical reactivity, biocompatibility, biodegradability and... 

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