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  • 1. IntroductionChiral phenomena play significant roles in nature.The synthesis and application of optically activepolymers are topics currently attracting much con-sideration in recent times, due to the wealthy andmultifaceted architecture of macromolecular chiral-ity as compared to that of small molecules. Becauseof unique chiral arrays, nature produces numeroussmaller chiral, optically active compounds. Most ofthe naturally occurring molecules/macromolecules,such as nucleic acids, proteins, and polysaccharidesare chiral and optically active. Chirality is essentialfor life. This situation can be very obviously seen ifwe look at the chirality of nearly 800 drugs (about97%) derived from natural sources. Only 2% areracemates and only 1% is achiral. In the past

    30 years, the development of chiral drugs with asingle enantiomer (optical isomer) has attractedgreat attention in drug industries, and the market forchiral drugs has tremendously grown. We areundoubtedly living in a chiral world, because of thisfact that our life results from homochiral biosub-stances [13]. Deoxyribonucleic acid (DNA) is atypical example of a homochiral biopolymer whosechirality derives from two features: (i) the incorpo-ration of enantiopure chiral sugars connecting theachiral chromophoric bases such as adenine, gua-nine, cytosine and thymine and (ii) the double-stranded, stiff helical conformation arising fromcomplementary base pairing and base stacking inwater [4]. Optically active polymers often playimportant functions as key basic materials for well-

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    Advances in synthetic optically active condensationpolymers A reviewS. Mallakpour*1,2, A. Zadehnazari1

    1Organic Polymer Chemistry Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan,84156-83111, I. R. Iran

    2Nanotechnology and Advanced Materials Institute, Isfahan University of Technology, Isfahan, 84156-83111, I. R. Iran

    Received 19 August 2010; accepted in revised form 12 October 2010

    Abstract. The study of optically active polymers is a very active research field, and these materials have exhibited a num-ber of interesting properties. Much of the attention in chiral polymers results from the potential of these materials for sev-eral specialized utilizations that are chiral matrices for asymmetric synthesis, chiral stationary phases for the separation ofracemic mixtures, synthetic molecular receptors and chiral liquid crystals for ferroelectric and nonlinear optical applica-tions. Recently, highly efficient methodologies and catalysts have been developed to synthesize various kinds of opticallyactive compounds. Some of them can be applied to chiral polymer synthesis. In a few synthetic approaches for opticallyactive polymers, chiral monomer polymerization has essential advantages in applicability of monomer, apart from bothasymmetric polymerization of achiral or prochiral monomers and enantioselective polymerization of a racemic monomermixture. The following are the up to date successful approaches to the chiral synthetic polymers by condensation polymer-ization reaction of chiral monomers.

    Keywords: biodegradable polymers, optically active polymers, polycondensation reaction, amino acids, chiral monomer

    eXPRESS Polymer Letters Vol.5, No.2 (2011) 142181Available online at www.expresspolymlett.comDOI: 10.3144/expresspolymlett.2011.15

    *Corresponding author, e-mail: mallak@cc.iut.ac.ir BME-PT

  • defined high-performance polymers [5]. Recentadvances in asymmetric reactions and catalysis aswell as in chiral separations have afforded a rapidincrease in the number of commercially availableoptically active compounds and reagents. Both nat-urally occurring and synthetic chiral polymers andsupramolecules have found prosperous applicationsin chiral chromatographic separations and shownpotential uses in chiral catalytic systems, liquidcrystals in ferroelectric and nonlinear optical (NLO)devices, electrodes for enantioselective recognitionfor performing bioelectro synthesis, microwaveabsorbents, membrane separation technology, opti-cal switches, biomedical equipments and optoelec-tronics application. A direct and efficient approachfor synthesizing chiral polymers is to introduce chi-ral elements into the macromolecule backbone orthe side chains [614].In the history of synthetic polymer chemistry, itseems that one of the most challenging tasks is toconstruct functional polymeric systems and opti-cally active synthetic polymers that will be as effec-tive as those in living systems [1518]. Specially,the synthesis of chiral polymers containing aminoacids is a subject of much interest, since a highdegree of amino acid functionality can lead to poly-mers with increased solubility and the ability toform secondary structures. The synthetic chiralpolymers that have been reported may be catego-rized into two parts: the first category representspolymers that adopt helical conformations. Suchpolymers do not contain any chiral center in themain chain or side chain. If a right-handed or left-handed helical conformation is generated in excess,the polymer can show chiroptical properties. How-ever, the helical conformation is responsible fortheir optical activity. Helical polymers existing ingenes, proteins (!-helix), DNA (double helices),collagen (triple helices), enzymes, and polypeptidesare frequently found in nature. They are easilydenaturalized by certain physical factors such asheat, ultraviolet irradiation, and high pressure andby other chemical factors such as organic solvents.In contrast, synthetic polymers represent much bet-ter stability. Various helical polymers have beensynthesized, which include polyisocyanates, poly-isocyanides, polychloral, polymethacrylates, poly-silanes, polythiophenes, poly(p-phenylene)s, poly(1-methylpropargyl-ester)s, poly(phenylacetylene)s

    and poly(!,"-unsaturated ketone) [1930]. The sec-ond one is polymers whose optical activity is derivedfrom main chain or side chain chirality such as:amino-acid-based polymers. Because the aminoacids are naturally occurring compounds, syntheticpolymers based on amino acids are anticipated to benontoxic, biocompatible, and biodegradable. On theother hand, synthetic polymers containing aminoacid residues in the main chain or in the side chaincan be employed for biomedical applications. Pos-sible applications include dentistry, temporary arti-ficial skin substrates, polymer carriers for proteinconjugates, drug delivery, gene therapy, tissue engi-neering, chiral recognition stationary phases, asym-metric catalysts, metal ion absorbents, and biomate-rials [3133]. Chiral recognition of optically activepolymers has been utilized in various forms of cat-alytic and separation chemistry. For example, oneof the generally function of chiral polymers is theuse as chiral stationary phase in high-performanceliquid chromatography (HPLC) for the separationof racemic mixtures [2, 3438].Optically active polymers were divided to threetypes: biopolymers, polymers prepared by almostcompletely isotactic polymerization by modifica-tion of naturally occurring polymer backbones suchas polysaccharides and synthetic polymers [2]. Chi-ral synthetic polymers can be classified as: additionpolymers, condensation polymers and cross-linkedgels. Addition polymers are including vinyl, alde-hyde, isocyanide and acetylene polymers that wereprepared via addition polymerization reaction suchas poly(acryl amide)s, polyolephynes, polystyrenederivatives, polyazulenes, poly(vinyl ether)s, poly-methacrylate, polymethacryloylamine, polychloral,polyisocyanides, polyisocyanates, polyacethyleneand polyethers [3945]. Condensation polymeriza-tion continues to receive intense academic andindustrial attention for the preparation of polymericmaterials used in a vast array of applications [46].One of application is synthesis of chiral polymers.For this purpose, monomer must be optically active.Cross-linked gels possessing chiral cavities havebeen prepared and their chiral recognition abilityhas been studied. The synthesis of gels is based onmolecular imprinting technique. Two distinctivemethods have been independently developed, thatis, (i) polymerizing a monomer having a removablechiral template moiety with a cross-linking agent

    Mallakpour and Zadehnazari eXPRESS Polymer Letters Vol.5, No.2 (2011) 142181

    143

  • and removing the template groups from the prod-ucts or (ii) polymerizing a monomer with a cross-linking agent in the presence of a non-polymeriz-able template molecule and removing the template[2]. This article reviews the synthesis of opticallyactive polymers via polycondensation reaction ofchiral monomers.

    2. Synthetic optically active condensationpolymers

    2.1. PolyamidesHistorically, the first study of optically active poly-mers has been of those available i.e. natural poly-mers such as proteins, polypeptides, polynu-cleotides and so on. These polymers are remarkablefor their high structural regularity, their ability totake on secondary ordered structures, even in solu-tion, and to undergo order disorder conformationaltransitions by changes in external conditions (sol-vent, temperature, pH, etc.). Progress in polymerchemistry has allowed the synthesis of entirely dif-ferent condensation polymers which one of them isoptically active polyamides (PA)s [47].Many studies concerned with the synthesis andcharacterization of optically active PAs have beenundertaken [4855], mainly polypeptides and pro-teins which have been extensively investigated.Synthesis and optical properties of asymmetric PAsderived from composed of optically active cyclicdicarboxylic acids, (+)-(S)- and ()-(R)-trans-1,2-cyclopr

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