69,496 research outputs found
Characterization of block copolyesters and block copolyamides, 1984
No full textThe thermal characterization of block copolyesters and block copolyamides and the solution viscosity of block copolyamides containing Kevlar blocks are discussed. The thermal analysis techniques differential scanning calorimetry (DSC) and thermogravimetry were employed to obtain the glass transition temperature (T^), melting temperature (Tm), and the decomposition temperature (T^) of the following polymers and block copolymers: poly[oxy(2-methyl-l,3-phenylene)oxy- terephthaloyl], poly [ oxy(2-methyl-l,3-phenylene)oxyisophthaloyl ], poly [oxy- (cis,trans)-l,4-cyclohexyleneoxycarbonyl-trans-l,4-cyclohexylenecarbonyl] , poly [ oxy(cis,trans)-l,4-cyclohexyleneoxycarbonyl-trans-l,4-cyclohexylenecarbonyl- b-oxy(2-methyl-l,3-phenylene)oxyterephthaloyl ], poly [oxy(2-methyl-l,3-pheny-lene)oxyisophthaloyl-b-oxy(2-methyl-l,3-phenylene)oxyterephthaloyl ], poly [ imi- no(2-methyl-l,3-phenylene)iminoterephthaloyl] , poly[ imino-trans-1,4-cyclohexy- leneiminocarbonyl-(cis,trans)-l,4-cyclohexylenecarbonyl ], poly(imino-trans-l,2- cyclohexyleneiminocarbonyl-trans-l,4-cyclohexylenecarbonyl), poly(imino-trans- l,4-cyclohexyIeneiminocarbonyl-trans-l,4-cyclohexylenecarbonyl-b-imino-l,4- phenyleneiminoterephthaloyl), poly [imino-trans-l,4-cyclohexyleneiminocarbonyl- trans-l,4-cyclohexylenecarbonyl-b-imino(2-methyl-l,3-phenylene) iminoterephth- aloyl ], poly [ imino-trans-l,4-cyclohexyleneiminocarbonyl-(cis,trans)-l,4-cyclohexy- lenecarbonyl -b-imino(2-methyl-l ,3-phenylene)iminoterephthaloyl ], poly [ imino- trans-l,2-cyclohexyleneiminocarbonyl-trans-l,4-cyclohexylenecarbonyl-b-imino-l,4- phenyJeneiminoterephthaloyl] and poly [imino(2-methyl-l,3-phenylene)iminotere- phthaloyl-b-imino-l,4-phenyleneiminoterephthaloyl]. Using the intrinsic viscosities of solutions of poly(imino-l,4-phenylene- iminoterephthaloyl) and the published values of K and a in the Mark-Houwink equation, molecular weights were calculated for several samples
Space-Time Block Coded Adaptive Modulation Aided OFDM
No full textSpace-time block codes provide substantial diversity advantages for multiple transmit antenna systems at a low decoding complexity. In this contribution, we investigate the achievable diversity advantages in the context of adaptive modulation aided turbo coded OFDM. The two-transmitter, one-receiver block space-time coded scheme using no channel coding or gradually increasing rate turbo coding strikes the best trade-off in terms of its overall performance and complexity. Adaptive OFDM performs impressively, when the extra complexity of space-time coding is not affordable, but no adaptive modulation is necessary in conjunction with the more complex multiple transmit and receive antenna associated scenario
Concatenated Space Time Block Codes and TCM, Turbo TCM Convolutional as well as Turbo Codes
No full textSpace-time block codes provide substantial diversity advantages for multiple transmit antenna systems at a low decoding complexity. In this paper, we concatenate space-time codes with Convolutional Codes (CC), Turbo Convolutional codes (TC), Turbo BCH codes (TBCH), Trellis Coded Modulation (TCM) and Turbo Trellis Coded Modulation (TTCM) schemes for achieving a high coding gain. The associated performance and complexity of the coding schemes is compared
The synthesis and characterization of poly(trans-l,4-cyclohexylene-trans-l,4-cy clohex anedic arbox amide-b-1,3-phenyleneisophthalamide), 1982
No full textThe synthesis and characterization of oligomeric homopolyamides and block copolyamide are discussed. The homopolymers, poly(trans-l,4-cyclohexylene-trans-l,4-cyclohexane- dicarboxamide) and poly(l,3-phenyleneisophthaIamide), and the block copoly�amide, poly(trans-l,4-cyclohexylene-trans-l,4-cyclohexanedicarboxamide-b-l,3- phenyleneisophthalamide), were prepared by low-temperature polycondensation techniques. The aliphatic oligomer was prepared from trans-l,4-cyc!ohexanediamine and cyclohexanedicarboxyl chloride using a 10 mole percent excess of diamine. The aromatic oligomer was prepared from m-phenylenediamine and isophthaloyl chloride, using a 10 mole percent excess of acid chloride. The block copolymer was prepared by reacting the above aliphatic and aromatic prepolymers having amino and acid chloride end groups respectively. The characterization of these prepolymers and block copolymer was accomplished using spectroscopic techniques (infrared, proton and carbon-13 nuclear magnetic resonances), solution viscosity and differential scanning calorimetry
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Synthesis and characterization of liquid crystalline block copolyamides, 1983
No full textThe synthesis and characterization of aliphatic polyamides, aromatic poly�amides and block copolyamides are discussed. The following aliphatic polyamides were synthesized: poly(trans l,4 cyclo hexylene trans l,4 cyclohexanedicarboxamide), poly(trans 1, 4 cyclohexy lene cis,trans l,4 cyclohexanedicarboxamide), and poly(trans 1, 2 cyclohexy lene tr ans 1,4 cyclohexanedicarboxamide). The following aromatic polyamides were synthe�sized: poly(1, 4 phenyleneterephthalamide) and poly(2 methyl l,3 phenylenetere phthalamide). The following block copolyamides were synthesized: poly(trans l,4 cyclohexylene trans 1,4 cyclohexanedicarboxamide b 1,4 phenyleneterephthalam ide), poly(trans l,4 cyclohexy lene cis,trans l,4 cyclohexanedicarboxamide b l,4 phenyleneterephthalamide), poly(trans 1, 4 cyclohexy lene trans 1,4 cyclohexanedi carboxamide b 2 methyl l,3 phenyleneterephthalamide), poly(trans l,4 cyclohexy lene cis,trans l,4 cyclohexanedicarboxamide b 2 methyl l,3 phenyleneterephthal amide), poly(trans l,2 cyclohexylene trans l,4 cyclohexanedicarboxamide b l,4 phenyleneterephthalamide) and poly(2 methyl l,3 phenyleneterephthalamide b l,4 phenyieneterephthalamide). The polymers were prepared by low temperature solution polycondensation, ambient temperature interfacial polycondensation and combinations of solution and interfacial polycondensations. Aliphatic oligomers were prepared from trans l,4 cyclohexanediamine,trans 1,2 cyclohexanediamine, trans l,4 cyclohexanedicarbonyl chloride, and cis,trans 1,4 cyclohexanedicarbony 1 chloride using a 10 percent excess of diamine. Aromatic oligomers were prepared from 1,4 phenylenediamine, 2,6 diaminotoluene and terephthaloyl chloride using a 10 percent excess of acid chloride. Block copolymers were prepared by reacting the aliphatic blocks having amino end groups with the aromatic blocks having acid chloride end groups. Characterization of the aliphatic and aromatic blocks and the block copolymers was accomplished by spectroscopic analysis (infrared, proton and carbon 13 nuclear magnetic resonance) and solution viscosity
Amphiphilic block copolymers : synthesis, self-assembly and applications
No full textSelf-assembly of amphiphilic block copolymers in aqueous solution is one of the most important nanotechnological methods to prepare nanocarriers for
different applications, such as drug delivery, biosensor, nanoreactor and so on. Synthesis of new types of amphiphilic block copolymers with novel
functionality and detailed characterization of self-assembly, influenced by self-assembly methods and different other parameters (molecular weight,
hydrophilic to hydrophobic ratio), are important. Especially, building up the relationship between the self-assembled nanomorphologies and molecule
constitution are helpful to understand amphiphilic block copolymer self-assemble theroy.
In this thesis, I present to you the influence of different parameters on the self-assembly nanostructures for the poly(dimethylsiloxane)-
block-poly(2-methyl-2-oxazoline) (PDMS-b-PMOXA) amphiphilic block copolymers.3D phase diagram clearly shows in which domain the PDMS-b-PMOXA
self-assemble into polymersome. The polymersome are possible for us to constribute the nano-sized based nanoreactor.
In addition, in order to develop more functional amphiphilic block copolymers and enlarge the potential application areas, another two types of
copolymers, grafted poly(2-methyl-2-oxazoline)-graft(ss)-poly(e-caprolactone) (PMOXA-graft(ss)-PCL) and linear poly(2-ethyl-2-oxazoline)-block-
poly(e-caprolactone)-ss-poly(L-lysine) (PEtOXA-b-PCL-ss-PLL), were designed and synthesized with reduction responsiveness, utilizing different
polymerization techniques, including ring openning polymerization and "graft-to" technology. Due to the amphiphilicity of these two types of
copolymers, nanoparticles are formed by them in aqueous solution. The primary evaluation of these two new type amphiphilic block copolymers
demonstrated that they can be promising candidates as smart nanocarries for the application of drug delivery.
In this dissertation, the result of our research have been comprehensivly compared with other publications and results from different groups.
We have new findingS. We find one new nano-object with 80-100 nm diameter, but without hollow aqueous cavity.
We also realize that basing on poly(2-ethyl-2-oxazoline)-block-poly(e-caprolactone)-ss-poly(L-lysine) (PEtOXA-b-PCL-ss-PLL) copolymer, it is possible
to synthesize more functional copolymer, for example introducing the pH-cleavable linker between PEtOXA and PCL, to mimic more closely the virus delivery
gene into cells
Self-assembled nanoparticles of ribozymes with poly(ethylene glycol)-b-poly(L-lysine) block copolymers
No full textComplex nanoparticle formation of poly(ethylene glycol)-b-poly(L-lysine) (PEG-b-PLL) block copolymers with ribozyme (Rzs) in an aqueous solution was studied. Nanoparticles formed from PEG-b-PLL and Rzs have about 100 nm in an effective diameter with the hydrophilic PEG segments stabilizing and surrounding the core of complexes formed between the PLL segments and Rzs. The block copolymer having a higher positive charge formed relatively smaller complex nanoparticles. The profile of the ethidum bromide (EtBr) displacement assay and images of agarose gel electrophoresis revealed the condensation of Rzs to form complex nanoparticles above a critical weight ratio, r (r: 4.0 for PEG(5000)-b-PLL1920 and 3.0 for PEG(5000)-b-PLL3840). Furthermore, the PEG-b-PLL/Rz complex nanoparticle showed high resistance against RNase attack in biological fluids
Solid-supported biomimetic membranes based on amphiphilic block copolymers
No full textPlanar artificial membranes based on amphiphilic block copolymers are of high interest due to their potential applications in catalysis, drug screening, sensing, etc. Such polymeric membranes can successfully mimic biological membranes, providing high robustness and stability, which makes them good candidates to be developed in direction of applications. Even though solid-supported polymer membranes have been already investigated to a certain extent, it is still an emerging area. This thesis presents a new generation of biomimetic solid-supported membranes and hybrid polymer-lipid materials, based on amphiphilic block copolymers: poly(dimethylsiloxane)-block-poly(2-methyl-2-oxazoline) (PDMS-b-PMOXA) and poly(ethylene glycol)-block-poly(γ-methyl-ε-caprolactone)-block-poly[(2-dimethylamino) ethyl methacrylate] (PEG-b-PMCL-b-PDMAEMA). The scope was preparation of stable solid-supported membranes and development of different strategies for insertion/attachment of biomolecules into such membranes. Block copolymers were firstly investigated in respect of behavior at the air-water interface. Deposition of the films on different solid supports (silica wafers, glass and gold slides) was achieved by performing transfers of Langmuir monolayers, which provide formation of defect-free films with good reproducibility. Further, deposited films were functionalized by introduction of membrane proteins and enzymes. To get the insights into morphology and thickness, the obtained systems were analyzed by surface-sensitive techniques, such as atomic force microscopy, ellipsometry, and contact angle measurements. Activity of inserted biomolecules was evaluated by electrical conductance measurements and activity assays. This thesis provides valuable impact in the preparation of membranes in a controllable and reproducible way. Furthermore, it presents different strategies for introduction of biomolecules into such systems, in order to obtain tailored functionality and properties. This work impact fundamental understanding and development of functional membranes. Such artificial membranes and hybrid materials can be further adapted for potential applications
The Synthesis, Self-Assembly and Self-Organisation of Polysilane Block Copolymers
No full textBlock copolymers containing polysilane blocks are unique in that the polysilane components possess electro-active properties and are readily photodegradable. This review will discuss and assess the two major approaches to the synthesis of polysilane block copolymers via pre-formed polymer chain coupling and living polymerisation techniques. The self-organisation of polysilane block copolymers and the morphologies adopted in thin films are reviewed. Amphiphilic polysilane-containing block copolymers self-assemble in solvents selective for one block and a number of examples are highlighted. The versatility of these materials is highlighted by recent significant applications including the preparation of hollow crosslinked micellar aggregates in aqueous solutions and in patterned thin film generation subsequently employed as templates for the growth of cell cultures and CaCO (3.
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