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Polymer Architectures (polymer + architecture)
Selected Abstracts(Mini)emulsion Polymerization: Effect of the Segregation Degree on Polymer ArchitectureMACROMOLECULAR REACTION ENGINEERING, Issue 6 2007Iker González Abstract A continuous loop reactor was used for the production of 2-ethylhexyl acrylate (2-EHA), methyl methacrylate (MMA) and acrylic acid (AA) pressure sensitive adhesive by both emulsion and miniemulsion polymerization. Similar high monomer conversions were achieved in both processes, but striking differences in polymer architecture were found. A mathematical model was used to analyze these differences concluding that because the costabilizer suppressed monomer diffusion from miniemulsion droplets, the average polymer concentration in the polymerization loci was lower in the miniemulsion process. This resulted in less chain transfer to polymer, and hence in lower sol molecular weight and gel content. [source] Effects of Polymer Architecture and Composition on the Adhesion of Poly(tetrafluoroethylene)CHEMPHYSCHEM, Issue 6 2006Chen-Yuan Tu Dr. Abstract Poly(glycidyl methacrylate), PGMA, chains in linear and arborescent structures were incorporated onto surfaces of poly(tetrafluoroethylene), PTFE, films by hydrogen plasma and ozone treatment and atom transfer radical polymerization. The epoxide groups of the PGMA chains were further reacted with acetic acid (AAc), oxalic acid (XAc), allyl amine (AA), and ethylenediamine (EDN) to introduce hydroxyl and amine groups to the surfaces of the PTFE films. Surface characterizations performed by Fourier Transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the surface modification and the chemical structure. The PGMA chains in arborescent structures show a high effectiveness for the enhancement of the adhesion of PTFE films. The adhesion of PTFE films was also significantly enhanced by ring-opening reactions of the PGMA epoxide groups with acetic acid and amine compounds. A high value of 9.5 N,cm,1 in the optimum 180° peel strength test was observed with PTFE/copper assemblies. [source] Synthetic Strategies for Controlling the Morphology of Proton Conducting Polymer Membranes,,FUEL CELLS, Issue 2 2005Y. Yang Abstract The nanostructure and morphology of proton conducting polymers is of considerable interest in the search for next generation materials and optimization of existing ones. Synthetic methodologies for tailoring molecular structures that promote nanoscopic phase separation of ionic and non-ionic domains, and the effect of phase separation on parameters such as proton conductivity, are considered. Rather than distinguish proton conducting polymers according to chemical class, they are categorized under sub-headings of random, block, and graft copolymers. The synthetic methodology available to access archetypal polymer structures is dependent on the nature of the monomers and restrictive compared to conventional non-ionic polymer systems. Irrespective of the methodology, ionic aggregation and phase separation are consistently found to play an important role in the proton conductivity of low ion exchange capacity,(IEC) membranes, but less of a role in high IEC membranes. Significant research is required to further develop relationships between polymer architecture, morphology, and electrolytic properties. [source] Influence of the copolymer architecture and composition on the response and mechanical properties of pH-sensitive fibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Anasuya Sahoo Abstract A series of copolymers based on acrylonitrile (AN) and acrylic acid (AA) with varying architecture and composition were synthesized using free radical polymerization. The distribution of monomers in the copolymer chains could be successfully controlled by regulating the addition of more reactive monomer (AA). Copolymers having nearly random distribution of comonomer moieties to block type distribution with different composition (10,50 mol % AA) were synthesized to investigate the effect of polymer architecture and composition on pH response and mechanical properties of resultant structures. These copolymers were solution spun from dimethylformamide-water system, drawn in coagulation bath, and annealed at 120°C for 2 h to make pH-sensitive fibers which were structurally stable without the need of chemical crosslinking. The fibers from block copolymers showed significantly better tensile strength (34.3 MPa), higher retractive forces (0.26 MPa), and enhanced pH response (swelling 3890%) in comparison with fibers from random copolymer (13.55 MPa, 0.058 MPa, and 1723%, respectively). The tensile strength and retractive forces could be further improved to a value of 72 MPa and 0.36 MPa, respectively, by changing the composition of the block copolymer while retaining the swelling percentage similar to the random copolymer mentioned above. It is proposed that on processing to fibers, the block copolymers could form a segregated domain structure with separate domains of AA and AN, where AN domains were responsible for high structural integrity by providing connectivity among polymer chains, while AA domains showed improved response to changing pH of the environment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Formation of honeycomb-structured, porous films via breath figures with different polymer architecturesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2006Martina H. Stenzel Abstract Honeycomb-structured, porous films with pore sizes ranging from 200 nm to 7 ,m were prepared with breath figures. The regularity of the hexagonal array and the pore size was influenced by the polymer architecture and the casting conditions. A nanoscaled suborder next to the microarray was obtained with amphiphilic block copolymers. These films were shown to be suitable as surfaces for cell growth. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2363,2375, 2006 [source] (Mini)emulsion Polymerization: Effect of the Segregation Degree on Polymer ArchitectureMACROMOLECULAR REACTION ENGINEERING, Issue 6 2007Iker González Abstract A continuous loop reactor was used for the production of 2-ethylhexyl acrylate (2-EHA), methyl methacrylate (MMA) and acrylic acid (AA) pressure sensitive adhesive by both emulsion and miniemulsion polymerization. Similar high monomer conversions were achieved in both processes, but striking differences in polymer architecture were found. A mathematical model was used to analyze these differences concluding that because the costabilizer suppressed monomer diffusion from miniemulsion droplets, the average polymer concentration in the polymerization loci was lower in the miniemulsion process. This resulted in less chain transfer to polymer, and hence in lower sol molecular weight and gel content. [source] Polymeric Photosensitizer Prodrugs for Photodynamic TherapyPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2007Marino A. Campo ABSTRACT A targeting strategy based on the selective enzyme-mediated activation of polymeric photosensitizer prodrugs (PPP) within pathological tissue has led to the development of agents with the dual ability to detect and treat cancer. Herein, a detailed study of a simple model system for these prodrugs is described. We prepared "first-generation" PPP by directly tethering the photosensitizer (PS) pheophorbide a to poly-(l)-lysine via epsilon amide links and observed that by increasing the number of PS on a polymer chain, energy transfer between PS units improved leading to better quenching efficiency. Fragmentation of the PPP backbone by trypsin digestion gave rise to a pronounced fluorescence increase and to more efficient generation of reactive oxygen species upon light irradiation. In vitro tests using the T-24 bladder carcinoma cell line and ex vivo experiments using mouse intestines illustrated the remarkable and selective ability of these PPP to fluoresce and induce phototoxicity upon enzymatic activation. This work elucidated the basic physicochemical parameters, such as water solubility and quenching/activation behavior, required for the future elaboration of more adaptable "second-generation" PPP, in which the PS is tethered to a proteolytically stable polymer backbone via enzyme-specific peptide linkers. This polymer architecture offers great flexibility to tailor make the PPP to target any pathological tissue known to over-express a specific enzyme. [source] Polymers Move in Response to LightADVANCED MATERIALS, Issue 11 2006Y. Jiang Abstract Significant advances have recently been made in the development of functional polymers that are able to undergo light-induced shape changes. The main challenge in the development of such polymer systems is the conversion of photoinduced effects at the molecular level to macroscopic movement of working pieces. This article highlights some selected polymer architectures and their tailored functionalization processes. Examples include the contraction and bending of azobenzene-containing liquid-crystal elastomers and volume changes in gels. We focus especially on light-induced shape-memory polymers. These materials can be deformed and temporarily fixed in a new shape. They only recover their original, permanent shape when irradiated with light of appropriate wavelengths. Using light as a trigger for the shape-memory effect will extend the applications of shape-memory polymers, especially in the field of medical devices where triggers other than heat are highly desirable. [source] The identification of synthetic homopolymer end groups and verification of their transformations using MALDI-TOF mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2010Yejia Li Abstract Recent advances in the resolving power of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) enable the detailed characterization of linear homopolymers, and in particular provide invaluable data for the determination of their end-group functionalities. With the growing importance of macromolecular coupling reactions in building complex polymer architectures, the ability to accurately monitor end-group transformations is becoming increasingly important for synthetic polymer chemists. This tutorial demonstrates the application of MALDI-TOF MS in determining both end-group functionalities and their transformations for linear homopolymers. Examples of both polycaprolactone and polystyrene are examined, and the strengths and weaknesses of various approaches to data analysis are given. Copyright © 2010 John Wiley & Sons, Ltd. [source] Synthesis of well-defined polymeric activated estersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2008Patrick Theato Abstract Monomers bearing an activated ester group can be polymerized under various controlled polymerization techniques, such as ATRP, NMP, RAFT polymerization, or ROMP. Combining the functionalization of polymers via polymeric activated esters with these controlled polymerization techniques generate possibilities to realize highly functionalized polymer architectures. Within this highlight two different research areas of activated esters in polymer science will be discussed: (i) the preparation of defined reactive polymer architectures by controlled polymerization techniques and (ii) the preparation of defined reactive thin films. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6677,6687, 2008 [source] Formation of honeycomb-structured, porous films via breath figures with different polymer architecturesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2006Martina H. Stenzel Abstract Honeycomb-structured, porous films with pore sizes ranging from 200 nm to 7 ,m were prepared with breath figures. The regularity of the hexagonal array and the pore size was influenced by the polymer architecture and the casting conditions. A nanoscaled suborder next to the microarray was obtained with amphiphilic block copolymers. These films were shown to be suitable as surfaces for cell growth. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2363,2375, 2006 [source] Design strategies for controlling the molecular weight and rate using reversible addition,fragmentation chain transfer mediated living radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2005Michael J. Monteiro Abstract Living radical polymerization has allowed complex polymer architectures to be synthesized in bulk, solution, and water. The most versatile of these techniques is reversible addition,fragmentation chain transfer (RAFT), which allows a wide range of functional and nonfunctional polymers to be made with predictable molecular weight distributions (MWDs), ranging from very narrow to quite broad. The great complexity of the RAFT mechanism and how the kinetic parameters affect the rate of polymerization and MWD are not obvious. Therefore, the aim of this article is to provide useful insights into the important kinetic parameters that control the rate of polymerization and the evolution of the MWD with conversion. We discuss how a change in the chain-transfer constant can affect the evolution of the MWD. It is shown how we can, in principle, use only one RAFT agent to obtain a polymer with any MWD. Retardation and inhibition are discussed in terms of (1) the leaving R group reactivity and (2) the intermediate radical termination model versus the slow fragmentation model. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3189,3204, 2005 [source] New Polymeric Materials with Interferential Optical PropertiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 13 2007Leďla Ghannam Abstract Nature provides a wide pallet of colors but also a wide number of fascinating optical phenomena such as nacre or interferential effects, which can be observed in insect wings and shellfish. The origin of such effects is attributed to the presence of highly ordered arrangements in Nature's materials. The aim of this paper is to focus some new approaches and advances for creating interferential optical phenomena as observed in nature by tuning or modeling the polymer architectures or organization. A relatively simple method is described to prepare organic/inorganic hybrid pigments constituted of mica platelets and adsorbed polymer layers. It is shown that the color of mica is changed upon polymer adsorption, and when one of the copolymer sequences includes a dye, its color is influenced by the chemical properties of the mica surface. Moreover, a new facile route is presented to obtain highly ordered surfaces using ionomer macromolecular designs synthesized in one step by controlled radical polymerization. The preparation of films with very regular pore size and spatial organization is successfully realized by using ionomer solutions. An original property of these films with an iridescent color obtained by light diffraction as a result of the optical interferences of sunlight with the periodic honeycomb structures is presented. All these new materials based on polymeric controlled structures can reproduce nature by creating an optical interferential and iridescent material, which offers new fascinating applications as original bio-mimetic materials on inorganic surfaces. [source] | |||||||||||||