Poly Hydroxy Acid s

Aliphatic polyesters may be classified into two groups, depending on the bond constitution of the monomCTs poly(hydroxy acid)s i.e. polyhydroxyalkanoates (PHAs)) and polyfalkylene dicarboxylate)s [68]. The former are polymers of hydroxy acids (a, p,...(i)-hydroxy acids), obtained by ring-opening polymerization or polycondensation reactions. The latter are S3uithesized by the polycondensation reaction of diols with dicarboxylic acids. Aldonic and aldaric acids can be used to prepare both groups of polyesters. 

Poly(hydroxy acid)s are an important class of degradable polymers for biomedical applications due to their biocompatibility and physiologically tolerable degradation products 886302. Poly(L-lactic acid) or poly(L-lactide) (PLLA) has been used as a biomaterial for tissue engineering, bone fracture fixation and controlled drug delivery... 

Aliphatic polyesters are low-melting (40-80°C) semicrystalline polymers or viscous fluids and present inferior mechanical properties. Notable exceptions are poly (a-hydroxy acid)s and poly (ft -hydroxy acid)s. 

Poly(lactic acid) (PL A) is a renewable resource-based bioplastic with many advantages, compared to other synthetic polymers. PL A is eco-friendly, because, apart from being derived from renewable resources such as corn, wheat, or rice, it is recyclable and compostable [1, 2]. PLA is biocompatible, as it has been approved by the Food and Drug Administration (FDA) for direct contact with biological fluids [3] and has better thermal processability compared to other biopolymers such as poly(hydroxy alkanoate)s (PHAs), poly(ethylene glycol) (PEG), or poly(e-caprolactone) (PCL) [4]. Moreover, PLA requires 25-55% less energy to be produced than petroleum-based polymers, and estimations show that this can be further reduced by 10% [5]. 

Biomedical Applications of Poly (a-hydroxy acid)s Hydroxy acids derived from natural resources such as lactic and glycolic acid have been employed to synthesize a wide variety of useful biodegradable polymers for large number and type of biomedical product applications. As an example, bioresorbable surgical sutures made form poly(a-hydroxy acid)s have been in clinical use since 1970. 

These are the best known examples of the poly(a-hydroxy acid)s, of general formula -(-OCHRCO- , which are degradable in the body, with R = H in poly(glycolic acid) (PGA) and R = Me in poly(lactic acid) (PLA). For well over 20 years these materials, either as homopolymers or copolymers, have been used in clinical situations by virtue of their degradability. " ... 

RAFT polymerization has been used to prepare poly(ethylene oxide)-/ /wA-PS from commercially available hydroxy end-functional polyethylene oxide).4 5 449 Other block copolymers that have been prepared using similar strategies include poly(ethylene-co-butylene)-6/oci-poly(S-eo-MAH), jl poly(ethylene oxide)-block-poly(MMA),440 polyethylene oxide)-Moe -poly(N-vinyl formamide),651 poly(ethylene oxide)-Wot A-poly(NlPAM),651 polyfethylene ox de)-b ock-polyfl,1,2,2-tetrahydroperfluorodecyl acrylate),653 poly(lactic acid)-block-poly(MMA)440 and poly( actic acid)-6focA-poly(NIPAM),4 8-<>54... 

Copolymers of a-hydroxy acids and a-amino acids are one type of poly(ester-amide)s and are called polydepsipeptides (PDPs) [17]. Since some of natural occurring a-amino acids, typically Asp, Glu, lysine (Lys), cysteine (Cys), serine (Ser), and threonine (Thr), possess reactive (hydrophilic) side-chain groups, PDPs... 

Working with a solution is needed for polymers which above their melting point would degrade (example aromatic polyamide fibres such as Kevlar and Twaron). For fibres the removal of the solvent is not too problematic. In e.g. injection moulding applications solvents caimot be used here thermotropic LCP s have to be used. Since these would degrade during processing, they are diluted by copolymerisation (example poly-hydroxy-benzoic acid - co - PETP)... 

Ferrocene has been reported to be very effective as a soot reducing agent in combustion [42 — 44]. Thus, when ferrocene compounds are incorporated in a fire retardant polymer, such as a phenolphthalein-based polymer and poly(phosphate ester)s, they have shown added advantages in that they promote extinction and reduce smoke formation by accelerated char reduction [45, 46]. The synthesis of such ferrocene-containing poly(phosphate ester)s was achieved by interfacial polycondensation using a phase transfer catalyst [47]. Accordingly, l,l -bis(p-hydroxy-phenylamido)ferrocene and l,l -bis(p-hydroxyphenylcarbonyl)ferrocene underwent condensation with various aryl phosphoroic acid dichlorides to yield two series of ferrocene-containing polymers, i.e., poly (amide-phosphate ester)s 38a and poly(ester-phosphate ester)s 38b respectively, as shown in Scheme 10-17. 

Li, S.M. Garreau, H. Vert, M. Structure-property relationships in the case of the degradation of massive poly-(a-hydroxy acids) in aqueous media, part 1. poly(oL-lactic acid). J. Mater. Sci. Mater, in Med. 1990, i, 123-130. 

The reaction of trimellitic anhydride (7) with ethanolamine (9) giving the hydroxy acid (10) and with 4,4 -diaminodiphenylmethane (8) giving the diacid (11) has been published in the first poly(ester-imide) patent [l].The second one is nowadays the predominant reaction for making poly(ester-imide)s. Trimellitic anhydride is the basic dianhydride for introducing the imide structure into the polyesters. Nearly every example in patents is based on trimellitic anhydride alone or mixtures with other anhydrides, e.g., tetrahydrophthalic anhydride [59]. The imides made from aromatic anhydrides are thermally more stable than the ones resulting from aliphatic structures (Fig. 4). Both types have been protected by patents, and products made from them are on the market. 

Another possibility for obtaining imide modified thermoplastic polyesters was to use as a monomer the hydroxy acid made from trimellitic anhydride and aminoethanol. Such a poly(ester-imide) was claimed for injection molding [240]. For the same use, poly(ester-imide)s containing aminophenol/trimellitic anhydride [241],imidised polyfbutylene terephthalate) [242] and a wholly aromatic poly(ester-imide) made from trimellitic anhydride, p-aminobenzoic acid, p-acetoxybenzoic acid, diacetoxybiphenyl and terephthalic and isophthalic acids are known, which showing optical anisotropy [243]. 

Sawhney, A. S., Pathlak, C. P. and Hubbel, J. A., Bioerodible hydrogels based on photo-polymerized PEG-co-poly(x-hydroxy acid) diacrylate macromers. Macromolecules, 26, 581, 1993. 

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