Optically Active Polymers

Optically combat-ready PolymersOptically supple polymers play very eventful role in our modern society. The speciality of optically active polymers atomic number 18 known with its diverse characteristics as occurred earthyly in mimicry. The present review describes the monomers and synthesis of optically active polymers from its helicity, internal compounds disposition, dendronization, co polymerisation, side chromophoric groups, chiral, metal convoluted and stereo- particular(prenominal) behaviour. The various properties compar competent nonlinear optical properties of azo-polymers, thermal analysis, chiroptical properties, vapochromic behaviour, assiduousness and emission properties, thermosensitivity, chiral separation, fabrication and photochromic property argon explained with details. This review is expected to be of interesting and useful to the researchers and pains personnel who be actively engaged in research on optically active polymers for versatile covering s.Optically active materials are those which give the axe able-bodied to rotate the plane of polarization of a beam of transmitted plane-polarized light containing unequal amounts of corresponding enantiomers. The optical natural process originates from the presence of chiral elements in a polymer such as chiral centres or chiral axes due to long-range conformational order in a macromolecule. In fact, most naturally occurring macromolecules take in the ability to organize to more than complex high structure rather than single one and manifest their functions.Optically active polymers are related to problems of the charged and reactive polymers, since optical exertion is an inherent property of two natural macromolecules as tumefy as a heavy(p) variety of polymers synthesized. Chiral compounds are optically active and essential for flavor such as proteins, polysaccharides, nucleic acids, etc. and chirality is most important for existence. About 97% drugs are formed from na tural sources, 2% are recemates and only 1% is achiral, in looking of chirality of nearly 800 drugs. Optically active polymers today stand also become of great interest and thus play an important role in molecular arrangement and assembly, which is critical for optoelectronics super molecular structure 1-4. The synthetic optically active polymers may also play important role like mimicry of naturally occurring polymers and thats why the extensive studies are required on their synthesis, conformations and properties. Various kinds of optically active polymers e.g., from its helicity, internal compounds nature, dendronization, copolymerization, side chromophoric groups, chiral, metal complex and stereo-specific behaviour are reported, however, those are not placed in a systematic manner. In the present review an effort has been made to collect most of those works in one place for better understanding in the subject with detailed explanation of properties like nonlinear optical proper ties of azo-polymers, thermal analysis, chiroptical properties, vapochromic behaviour, absorption and emission properties, thermosensitivity, chiral separation, fabrication and photochromism.-Classification of optically active polymersOptically active polymers are divided into three typesBiopolymers as obtained from nature.Polymers nimble by almost completely isotactic polymerization by qualifying of naturally occurring polymer moxies such as polysaccharides.Synthetic polymers as per the requirement with proper tailoring of functional groups.-Speciality of optically active polymerOptical properties of polymers are not so different of opposite substances, excepting those characteristics related to the chain dimension and structure or conformational changes. Optically active polymers shoot found interesting applications because of their specific properties. The optical properties of these materials lie at the basis of many applications, for example in chromatographic methods for enantiomeric separations or creating complex optical devices. The dispersion of the specific rotation offers instruction regarding the conformational changes or Cotton effect. Optically active polymers characteristics as followsOptically active polymers with configurational chirality the optical activity is given by the presence of an asymmetric snow atom in the backbone or in the side chain of the monomerOptically active polymers with conformational chirality the optical activity is related to the conformational changesOptically active polymers with both configurational and conformational chirality the optical activity is given by macromolecular asymmetry and by the presence of the unsymmetric centers.-Monomers of optically active polymersSome biological polymers are composed of a variety of different but structurally related monomer residues for example, poly substructures such as DNA are composed of a variety of nucleotide subwholes. The solid-state structures of polystyrene poly(Z-L-lysine) stymy copolymers were examined with respect to the polymer architecture and the secondary structure of the polypeptide using circular dichroism, quantitative subatomic and wide-angle X-ray scattering, and electron microscopy 5.Synthesis of optically active polymersThe optically active compounds are synthesized by highly efficient methodologies and catalysts. The various synthetic approaches for optically active polymers are described below verticillated polymer Helicity is one of the subtlest aspects of polymer chain where the polymer chain spiral structure along the chain axis acts like a spring. Helical polymers are frequently occurring in nature in single, double or triple helices form in genes, proteins, DNA, collagen, enzymes, and polypeptides. The spiraling conformations increase the stability of the natural polypeptides.Preparation of artificial turbinate polymers is a great challenge to the researchers. So far, only limited success has been achieved in c onstructing microscale particles using helical polymers, despite the great number of analogous microparticles created from vinyl polymers and even from other conjugated polymers like poly(thiophene), poly(phenylene ethynylene), and poly(fluorene) and polyacetylenes. Meckings et al has performed extensive investigations on preparing nanoparticles from polyacetylenes, which have shown interesting potential in inkjet printing. Later on, various group of researchers have successfully prepared both nano and microparticles consisting of optically active helical substituted polyacetylenes 6. Such nano- and microarchitectures demonstrated remarkable optical activity and signifi chamberpott potential applications ranging from asymmetric catalysis, chiral recognition/resolution, and enantiomer-selective crystallization to enantio-selective red ink 7-9.Synthetic helical polymers may be categorize as either static or dynamic helical polymers, depending on the inversion barrier of the helical conformation 10-11. Static helical polymers have a relatively high energy barrier for helix inversion and are stable in solution, plot dynamic helical polymers have a relatively low energy barrier for helix inversion and exist as a mixture of right- and remaining handed helical domains that are separated by rarely occurring helix reversals. Even a slight incorporation of optically active repeat units can shift the equilibrium to excess one-handed helicity.The chiral recognition properties of biopolymers with skilled emulating of synthetic helical polymers are currently a focus of much interest. Enantioseparation, catalysis, and sensing are among the more promising applications of molecular recognition based on responsive three-dimensional intramolecular or intermolecular superchiral structures. Optically active conjugated polymers represent an kind class of chiral macromolecules adaptable to this purpose because their chiral behaviour can be augmented by nonlinear electrically co nductive or optical properties arising from conjugation along the backbone. The first example of optically active polycarbazoles, polyN-(R)- or (S)-3,7-dimethyloctyl-3,6-carbazoles (R- or S-PDOC) were synthesized in 60-70% yield using modified nickel coupling method 12.Helical polymers are easily denaturalized by certain physical factors e.g. heat, ultraviolet irradiation, and high pressure and by other chemic factors such as organic solvents. Various helical polymers have been synthesized, which include polyisocyanates, polyisocyanides, polychloral, polymethacrylates, polysilanes, polythiophenes, poly(p-phenylene)s, poly(1-methylpropargyl-ester)s, poly(phenylacetylene)s and poly(-unsaturated ketone) 13-19 (Fig. 1). Other polymers are whose optical activity is main chain or side chain chirality dependent e.g. amino-acid-based polymers are nontoxic, biocompatible and perishable.Optically Active PolymersOptically Active PolymersIntroductionOptically active polymers are related to pr oblems of the charged and reactive polymers, since optical activity is an inherent property of both natural macromolecules as well as a great variety of polymers synthesized. Most of the naturally occurring molecules/macromolecules, such as nucleic acids, proteins, and polysaccharides are chiral and optically active. Chirality is essential for life. This situation can be very obviously seen ifwe look at the chirality of nearly 800 drugs (about 97%) derived from natural sources. Only 2% are racemates and only 1% is achiral. Synthetic optically active polymers are of great interests, since they might mimic the fascinating functions of naturally occurring polymers, leading extensive studies being conducted on their synthesis, conformations and functions. In fact, most naturally occurring macromolecules possess the ability to organize to more complex high structure rather than single one and manifest their functions. Optical activity is a physical phantasmal property of chiral matter c aused by asymmetric configuration, confirmations and structures which have no plane and no centre of symmetry and consequently have two mirror mountain range enantiomeric forms of inverse optical rotation. The recemic mixture of chiral enantiomers is optically inactive.The great majority of natural molecules contain chiral centres and are optically active. This is the case because living systems and their extracts as enzymes are able to produce completely stereoselective asymmetrical synthesis or transformations. This led Pasteur to say that life is asymmetrical at the molecular level. The majority of food and drug molecules of physiologic activity are chiral 1. Xi et al. 2-8 investigated about chirality of optically active compounds. Optically active polymers today have also become of great interest owe to their chiral structure which may play an important role in molecular arrangement and assembly, which is critical for optoelectronics super molecular structure 9-12. Chiral polym ers with helical chain backbone have received increasing heed due to their helicity generating from secondary interactions such as hydrogen bonds and van der Waals forces. These chiral helical polymers undergo conformational change as well as helical reversal easily. The concept of the optically active aromatic chromophore as conformational probe in isotactic polymers can be further extended by the use of optically active monomers 13. Optically active polymers have exhibited a number of interesting properties in several highly specialized areas such as chromatographic resolution of steroregular 14, chiral 15-16, asymmetric catalysis and phase of the separation of racemic mixtures 17, thermosensitivity 18, synthesis molecular receptors and chiral liquid crystals for ferroelectric and nonlinear optical applications 20.In the last year 52, Angiolini and co-workers have synthesized and investigated methacrylic polymers bearing in the side chain the chiral cyclic (S)-3- hydroxypyrrolidi ne moiety interposed between the main chain and the trans azoaromatic chromophore, substituted or not in the 4 position by an electron withdrawing group. In these materials, the presence of a rigid chiral moiety of oneprevailing absolute configuration favours the establishment of a chiral conformation of one prevailing helical handedness, at least within chain segments of the macromolecules, which can be observed by circular dichroism (CD). The simultaneous presence of the azoaromatic and chiral functionalities allows the polymers to display both the properties typical of dissymmetric systems (optical activity, exciton splitting of dichroic absorptions), as well as the features typical of photochromic materials (photorefractivity, photoresponsiveness, NLO properties).Recently, highly efficient methodologies and catalysts have been developed to synthesize various kinds of optically active compounds. Some of them can be use to chiral polymer synthesis and in a few syntheses for optica lly active polymers chiral monomer polymerization has essential advantages in pertinency of monomer, apart from both asymmetric polymerization of achiral or prochiral monomers and enantioselective polymerization of a recemic monomer mixture. Optically active chiral polymers are not only fundamentally interesting, due to the rich and complex architecture of macromolecular chirality as compared to that of small molecules, but also technologically important because their unique chiral arrays give rise to a number of potential, and in some cases commercially implemented.Classification of Optically active polymersOptically active polymers are divided into three typesBiopolymers Biopolymers are the main type of biomaterials. According to their degradation properties, biopolymers can be further classified into biodegradable and non-biodegradable biopolymers. Many implants, such as bone substitution materials, some bone fixing materials, and dental materials, should possess long term stabl e performance in the body. Recently biopolymers acts as developments in bone tissue engineering, vascular tissue engineering, nerve tissue engineering, genitourinary tissue engineering, regenerative medicine, gene therapy, and controlled drug delivery have promoted the need of new properties of biomaterials with biodegradability. Biologically derived and synthetic biodegradable biopolymers have attracted considerable aid 21.Polymers prepared by almost completely isotactic polymerization by modification of naturally occurring polymer backbones such as polysaccharides.Synthetic polymers Polymers synthesized from low molecular weight compounds are called synthetic polymers, e.g., polyethylene, PVC, nylon and terylene 7. This polymer is also divided into three types(a) Addition polymers Addition polymers are including vinyl, aldehyde, isocyanide and acetylene polymers that were prepared via addition polymerization reaction such as poly(acryl amide)s, polyolephynes, polystyrene derivati ves, polyazulenes, poly(vinyl ether)s, polymethacrylate, polymethacryloylamine, polychloral, polyisocyanides, polyisocyanates, polyacethylene and polyethers 2232.(b) Condensation polymers Condensation polymerization continues to receive intense academic and industrial attention for the preparation of polymeric materials used in a vast array of applications 28. One of application is synthesis of chiral polymers. For this purpose, monomer must be optically active.(c) Cross-linked gels One of application is synthesis of chiral polymers. For this purpose, monomer must be optically active. One of application is synthesis of chiral polymers. For this purpose, monomer must be optically active.Why optically active polymers are important?orSpeciality of optically active polymerOptical properties of polymers are not so different of other substances, excepting those characteristics related to the chain dimension and structure or conformational changes. Optically active polymers have found inte resting applications because of their specific properties. The optical properties of these materials lie at the basis of many applications, forexample in chromatographic methods for enantiomeric separations or creating complex optical devices. The dispersion of the specific rotation offers information regarding the conformational changes or Cotton effect. Optically active polymers characteristics as follows-Optically active polymers with configurational chirality the optical activity is given by the presence of an asymmetric carbon atom in the backbone or in the side chain of the monomer Optically active polymers with conformational chirality the optical activity is related to the conformational changes Optically active polymers with both configurational and conformational chirality the optical activity is given by macromolecular asymmetry and by the presence of the asymmetrical centers.Monomers of Optically active polymersPolymerization is the process of combining many small molecu les known as monomers into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester. The monomers are terephthalic acid (HOOC-C6H4-COOH) and ethylene glycol (HO-CH2-CH2-OH) but the repeating unit is -OC-C6H4-COO-CH2-CH2-O-, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue.The identity of the monomer residues (repeat units) comprising a polymer is its first and most important attribute. Polymer nomenclature is generally based upon the type of monomer residues comprising the polymer. Polymers that contain only a single type of repeat unit are known as homopolymers, while polymers containing a mixture of repeat units are known as copolymers. Poly(styrene) is composed only of styrene mono mer residues, and is therefore classified as a homopolymer. Ethylene-vinyl acetate, on the other hand, contains more than one variety of repeat units and is thus a copolymer. Some biological polymers are composed of a variety of different but structurally related monomer residues for example, polynucleotides such as DNA are composed of a variety of nucleotide subunits. The solid-state structures of polystyrene poly(Z-L-lysine) block copolymers were examined with respect to the polymer architecture and the secondary structure of the polypeptide using circular dichroism, quantitative small- and wide-angle X-ray scattering, and electron microscopy 33.Synthesis of optically active polymersMuch of the attention in chiral polymers results from the potential of these materials for several specialized utilizations that are chiral matrices for asymmetric synthesis, chiral stationary phases for the separation of racemic mixtures, synthetic molecular receptors and chiral liquid crystals for f erroelectric and nonlinear optical applications. Presently optically active compounds are synthesized by highly efficient methodologies and catalysts. In a few synthetic approaches for optically active polymers, chiral monomer polymerization has essential advantages in applicability of monomer, apart from both asymmetric polymerization of achiral or prochiral monomers and enantioselective polymerization of a racemic monomer mixture 17.