Showing papers in "Advances in Polymer Science in 2002"

Aliphatic Polyesters: Synthesis, Properties and Applications

Abstract: The synthesis of aliphatic polyesters by polycondensation and ring-opening polymerization is reviewed. This includes homopolyesters, random, block, graft, star, and hyper-branched (co)polyesters. Recent progress in the synthesis of high molecular weight aliphatic polyesters is described. Specific properties of these polymers are also given. The biomedical and ecological applications of these biodegradable polymers show their technological importance and relevance.

Recent Advances in the Theory of Filler Networking in Elastomers

Abstract: The viscoelastic properties of (mostly carbon black) filled elastomers are reviewed with emphasis on the strain-dependence of the complex dynamic modulus (Payne effect) Considerable progress has been made in the past in relating the typical dynamical behavior at low strain amplitudes to a cyclic breakdown and reagglomeration of physical filler-filler bonds in typical clusters of varying size, including the infinite filler network Common features between the phenomenological agglomeration/deagglomeration Kraus approach and very recent semi-microscopical networking approaches (two aggregate VTG model, links-nodes-blobs model, kinetical cluster-cluster aggregation) are discussed All semi-microscopical models contain the assumption of geometrical arrangements of sub-units (aggregates) in particular filler network structures, resulting for example from percolation or kinetical cluster-cluster aggregation These concepts predict some features of the Payne effect that are independent of the specific types of filler These features are in good agreement with experimental studies For example, the shape exponent m of the storage modulus, G′, drop with increasing deformation is determined by the structure of the cluster network Another example is a scaling relation predicting a specific power law behavior of the elastic modulus as a function of the filler volume fraction The exponent reflects the characteristic structure of the fractal filler clusters and of the corresponding filler network The existing concepts of the filler network breakdown and reformation appear to be adequate in describing the deformation-dependence of dynamic mechanical properties of filled rubbers The different approaches suggest in a common manner that there is a change of filler structure with increasing dynamic strain However, in all cases additional assumptions are made about the accompanying energy dissipation process, imparting higher hysteresis to the filled rubber This process may be slippage of entanglements (slip-links) in the transition layer between bound rubber layer and mobile rubber phase, and/or partially release of elastically ‘dead’ immobilized rubber trapped within the filler network or agglomerates

Degradable polymer microspheres for controlled drug delivery

Abstract: Controlled drug delivery technology is concerned with the systematic release of a pharmaceutical agent to maintain a therapeutic level of the drug in the body for a sustained period of time. This may be achieved by incorporating the therapeutic agent into a degradable polymer vehicle, releasing the agent continuously as the matrix erodes. This review is concerned with degradable polymers for use in controlled drug delivery with emphasis on the preparation, applications, biocompatibility, and stability of microspheres from hydrolytically degradable polymers.

Controlled Ring-Opening Polymerization: Polymers with designed Macromolecular Architecture

Abstract: This paper reviews ring-opening polymerization of lactones and lactides with different types of initiators and catalysts as well as their use in the synthesis of macromolecules with advanced architecture. The purpose of this paper is to review the latest developments within the coordination-insertion mechanism, and to describe the mechanisms and typical kinetic features. Cationic and anionic ring-opening polymerizations are mentioned only briefly.

Nonlinear Optical Polymeric Materials: From Chromophore Design to Commercial Applications

Abstract: Polymeric electro-optic materials have recently been developed that, when fabricated into devices such as Mach-Zehnder interferometers, permit drive ( Vπ) voltages of less than 1 V to be realized at the telecommunications wavelength of 1.3 and 1.55 microns. Operation of polymeric electro-optic modulators to frequencies (bandwidths) of greater than 100 GHz has been demonstrated. The total insertion loss of polymeric electro-optic modulators has been reduced to values as low as 5 dB, which is competitive with values obtained for lithium niobate modulators and is much lower than that obtained for gallium arsenide electro-absorptive modulators. Polymeric electro-optic modulators can be operated for long periods of time at temperatures on the order of 100 °C. Techniques have been developed for seamlessly integrating polymeric electro-optic circuitry with passive low loss optical circuitry (e.g., silica long-haul transmission fiber and medium-range fluoropolymer fibers) and with very large scale integration (VLSI) semiconductor electronics. These advances have created a considerable interest in the commercialization of polymeric electrooptic materials. Polymeric electro-optic materials are now being evaluated for applications such as phased array radar, satellite and fiber telecommunications, cable television (CATV), optical gyroscopes, electronic counter measure (ECM) systems, backplane interconnects for high-speed computers, ultrafast (100 Gbit/s) analog-to-digital (A/D) converters, land mine detection, radio frequency (rf) photonics, and spatial light modulators. This review discusses the structure-function relationships that had to be defined and the synthesis and processing advances achieved before materials appropriate for commercialization could be produced. Topics discussed include the design and synthesis of chromophores that simultaneously exhibit large molecular hyperpolarizability, low optical absorption, processability (e.g., solubility in various processing media), and the prerequisite (thermal, chemical, electrochemical, and photochemical) stability to survive conditions encountered in the fabrication and operation of polymeric electro-optic devices. Chromophore-chromophore intermolecular electrostatic interactions have been shown to be the most serious problem impeding the optimization of electro-optic activity in organic materials. The quantitative theoretical treatment of such interactions by equilibrium and Monte Carlo statistical mechanical methods is discussed. Rules for designing chromophores with shapes leading to maximum obtainable electro-optic activity are discussed and the synthetic realization of such structures is reviewed. The role of electrostatic interactions in influencing the choice of processing conditions is also discussed. A number of processing steps, including spin casting, electric-field poling, lattice hardening, fabrication of buried channel waveguides (including deposition of cladding layers), electrode deposition and connection with electronic circuitry, and integration of active and passive optical circuitry, are required. Each of these steps can affect device performance (e.g., influence optical loss, electro-optic activity, and stability). The systematic optimization of each of these steps is reviewed. Finally, device design and operation are reviewed and speculation on the future of the field is expressed.

Aliphatic polyesters : Abiotic and biotic degradation and degradation products

Abstract: This paper reviews the degradation behavior of aliphatic polyesters of current interest, including polylactide, polycaprolactone, poly(3-hydroxybutyrate) and their copolymers. Special focus is given to degradation products formed in different abiotic and biotic environments. The influence of processing and processing additives on the properties and degradation behavior is also briefly discussed.

Polymers from Renewable Resources

Abstract: From the point of view of making novel polymers with inherent environment-favorable properties such as renewability and degradability, a series of interesting monomers are found in the metabolisms and cycles of nature. This review presents and discusses a number of aliphatic polyesters which show interesting applications as biomedical materials and degradable packages. Available from nature are amino acids, microbial metabolites from the conversion of glucose and other monosaccharides (e.g., acetic acid, acetone, 2,3-butanediol, butyric acid, isopropanol, propionic acid), lactic acid, ethanol and fatty acids. A series of biodegradable polymers with different properties and different potential industrial uses were made starting with succinic acid and/or 1,3-propanediol. There were two routes for making the polyester-based materials; the direct ring-opening polymerization of lactones (cyclic esters) synthesized from 1,3-propanediol, and the chain-extension of α,ω-dihydroxy-terminated oligomeric polyesters produced by thermal polycondensation of 1,3-propanediol and succinic acid (oligo(propylene succinate)s).

Pharmaceutical Polymeric Controlled Drug Delivery Systems

Abstract: Drug delivery systems have taken a great impetus to deliver a drug to the diseased lesions. Although this concept is not new great progress has recently been made in the treatment of a variety of diseases. A suitable carrier is needed to deliver a suitable and sufficient amount of the drug to a targeted point, hence, various kinds of formulations are being constantly developed. This paper reviews the present state of art regarding the synthetic methods and characterization of nanoparticles, the suitability of polymeric systems for various drugs, drug loading and drug release properties of various systems such as nanoparticles, hydrogels, microspheres, film and membranes, tablets, etc. The purpose of this review is to summarize the available information so that it will be helpful to beginners and serve as a useful tool for active researchers involved in this area.

Light-Emitting Characteristics of Conjugated Polymers

Abstract: This article reviews mainly the results of our recent research on the relationship between the structure and the luminescence properties of PPV derivatives. PPV derivatives are particularly useful in an effort toward the establishment of such relationship because their chemical structures can be manipulated very systematically. Attachment of a wide variety of substituents, inclusion of kinky structural units, modification of main chain structures by inclusion of hole- and/or electron-transferring structures, and blending of polymers having different optical and electronic properties are representative approaches. The device characteristics of the light-emitting diodes (LEDs) fabricated from these polymers are discussed in relation to their structures. In certain cases, their photoluminescence (PL) properties are compared with their electroluminescence (EL) properties.

Molecular Design for Third-Order Nonlinear Optics

Abstract: We discuss recent developments in the design of molecules for applications in third-order nonlinear optics with emphasis on all-optical signal processing and two-photon absorption We especially concentrate on functional substitution patterns and conjugation length expansion We show that low molecular symmetry with regard to the conjugation path of the delocalized electrons was found to be a good guideline towards linearly conjugated molecules with large second-order hyperpolarizabilities γ We show that this guideline is also valid for two-dimensionally conjugated systems and that the observed effects can be explained by the symmetry of the electronic wavefunctions We present scaling laws and critical conjugation lengths of rod-like molecules with electrons delocalized over a one-dimensional path and show that the exponent tends to be constant for various polymers in the transparency range and that the values presented here are of similar magnitude for various organic materials systems Finally, we discuss different materials systems with regard to the figures of merit relevant for all-optical signal processing

Hydrogel-Based Colloidal Polymeric System for Protein and Drug Delivery: Physical and Chemical Characterization, Permeability Control and Applications

Abstract: The use of polymeric nanoparticles as drug carriers is receiving an increasing amount of attention both in academia and industry. The development of suitable delivery systems for protein drugs with high molecular weights and short half-lives is of current interest. In addition, nanoparticles have a number of potential applications in drug and vaccine delivery as well as gene therapy applications. This article features a new production technology for nanoparticles comprised of multicomponent polymeric complexes that are candidates for delivery vehicles of biological molecules such as proteins and drugs. Materials science theory and practice provide the basis for the development of highly compacted structures that are insoluble in water and buffered media. Biocompatible and mostly natural polymers are fabricated into thermodynamically stable nanoparticles, in the absence of organic solvents, using two types of processing: batch and continuous. Careful choice of construction materials and the superposition of several interacting principles during their production allow for the customization of the physicochemical properties of the structures. Among the typical polymers used to assemble nanoparticles, different polysaccharides, natural amines and polyamines were investigated. The entrapped substances tested included proteins, antigens and small drug molecules. The size and charge of nanoparticles is considered to be of primary importance for application in biological systems. Detailed experiments in batch and continuous systems allowed time-dependent stoichiometric characterization of the production process and an understanding of fundamental assembly principles of such supramolecular structures. Continuous-flow production is shown to provide more consistent data in terms of product quality and consistency, with further possibilities of process development and commercialization. To control permeability, polydextran aldehyde, incorporated into the particle core, was used to enable physiologic cross-linking and long-term retention of substances that would otherwise rapidly leak out of the nanoparticles. Results of cross-linking experiments clearly demonstrated that the release rate could be substantially reduced, depending on the degree of cross-linking. For vaccine antigen delivery tests we measured an antibody production following subcutaneous and oral administration. The data indicated that only the cross-linked antigen was immunogenic when the oral route of administration was used. The data presented in this paper address primarily the utility of nanoparticulates for oral delivery of vaccine antigen. This novel technology is extensively discussed in contrast to other technologies, primarily water- and organic solvent-based. The usefulness is demonstrated using several examples, evaluating protein and small drug delivery.

Recent Progress in Gel Theory: Ring, Excluded Volume, and Dimension

Abstract: Recent developments in gel research are reviewed with emphasis on the gel point problem. We will describe in due course how the gel point equation can be deduced from first principles. First we review briefly the industrial development of gel science in Japan (Sect. 1) and a central aspect of the classical theory of gelation (Sect. 2). In Sect. 3, we survey the progress on the excluded volume problem from the author’s point of view. In all respects, this theme is, now, too biased to physics and hence beyond the scope of this review; while it is an essential subject to understand the nature of the gel point. Regarding the excluded volume problem, a recent interesting idea is the screening effect. This notion of screening is a different interpretation of the Flory excluded volume theory, but takes us into advanced physics. For instance, the behavior of a branched molecule in the melt becomes comprehensible in a natural fashion. In Sect. 4, we mention cyclization in branching media. Like the problem of volume exclusion, the cyclization problem has not been solved rigorously. The most troublesome aspect with cyclization is that there is no way to enumerate the combinatorial number of branched molecules with rings. On the other hand, the mathematical framework for the general solution has already been given. In this article we will mention the limiting solutions of C→∞ for real systems and of d→∞ for the lattice model. What is important is that these limiting solutions are by no means useless, fictitious entities, but have real meanings. By analogy with the f = 2 case, we can put forward the general relation, [Γ]|≅constant for gelation conditions, where [Γ] represents the total ring concentration; this is the basic premise of the gel point theory developed in Sect. 6. Through these analyses, essential differences between real gelations and the percolation model are brought into sharp relief (Sect. 5). The gel point theory starts from the obvious equality: D c = D(inter)+D(ring), where D c represents the gel point, D(inter) the extent of the intermolecular reaction alone at the gel point and D(ring) the corresponding quantity of cyclization. Then, according to some definitions, fundamental equalities for gel points can be deduced for all the models of real systems and the percolation model. The problem of seeking a gel point for a given system thus reduces to the problem of finding a solution for the corresponding fundamental equality. To solve the equalities, we introduce two main assumptions: (1) random distribution of cyclic bonds, and (2) that the ring distribution functions can be expanded about D c =D co , where D co is the gel point for the ideal tree model. Under these assumptions, we can derive analytical expressions for gel points as functions of γ (= 1/C: the reciprocal of an initial monomer concentration), κ (mole ratio of B-type functional units to A-type functional units), and d (space dimension); that is, D c = G(γ, κ,d). In Sect. 7, the theoretical equations thus obtained are compared with experiments. The result shows that the theory recovers well the points observed by Flory, Weil, and Gordon in all the regimes of κ = 1 ~ 2. The corresponding expression for the percolation model is found to agree well with simulation experiments in high dimensions, but fails in low dimensions. The discrepancy in low dimensions is analyzed in light of the critical dimension concept. One possible explanation is that the above-mentioned assumptions (1) and (2) do not work below. d c = 8.

Quadratic Parametric Interactions in Organic Waveguides

Abstract: This chapter addresses issues related to quadratic parametric interactions in organic waveguides. It attempts to give an overview of the field, especially emphasizing the initial experimental milestones together with the most recent results.

Molecular Simulation Approaches for Multiphase Polymer Systems

Abstract: Computer simulation has recently attracted much attention from both academia and industry because it provides much useful information on polymers, particularly multiphase polymer systems, which are not easily obtained by experiment. The computer simulation approaches for multiphase polymer systems may be classified into three modeling methods according to their levels of approximation, i.e., atomistic, coarse-grained, and atomistic-continuum modeling. In this article the three methods are applied to miscibility of polymer blends, compatibilizing effect of block copolymers, and mechanical properties of semicrystalline polymers, respectively, and their results are compared with experimental ones.