A Bipedal Silica-Immobilized Azo-Initiator for Surface-Confined Radical Polymerizations

2009 ◽  
Vol 62 (11) ◽  
pp. 1473 ◽  
Author(s):  
Robert Rotzoll ◽  
Philipp Vana
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Methyl Acrylate ◽  
Chain Transfer ◽  
Molecular Weights ◽  
Surface Initiated Polymerization ◽  
Reversible Addition ◽  
Azo Initiator ◽  
Scanning Electron

The present study introduces the silica-anchored azo-initiator 4,4′-azobis(4-cyano-N-(3″-triethoxysilylpropyl)-valeric amide) (ACTA) for the surface-initiated polymerization of methyl acrylate (MA) with and without additional grafted reversible addition–fragmentation chain transfer (RAFT) agents 1,4-bis(3′-trimethoxysilylpropyltrithiocarbonylmethyl)benzene and 1,6-bis(o,p-2′-trimethoxysilylethylbenzyltrithiocarbonyl)hexane. While the sole use of silica-linked ACTA produced grafted poly(methyl acrylate) (pMA) of high molecular weight, due to a 2D Trommsdorff effect, the polymerization in combination with the fixed RAFT agents exhibited living behaviour with increasing molecular weights during polymerization. Silica-pMA hybrids were further analyzed via thermogravimetric analysis and scanning electron microscopy, which revealed significant differences between the three approaches.

scholarly journals Scanning Electron Microscopy Analysis of Changes of Hydroxiapatite/Poly-L-Lactide with Different Molecular Weight of PLLAaAfter Intraperitoneal Implantation

2016 ◽  
Vol 66 (2) ◽  
pp. 234-244
Author(s):  
Ljubiša Đorđević ◽  
Stevo Najman ◽  
Perica Vasiljević ◽  
Miroslav Miljković ◽  
Nenad Ignjatović ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Bone Tissue ◽  
Tissue Loss ◽  
Practical Applications ◽  
Molecular Weights ◽  
Significant Difference ◽  
Tissue Reactions ◽  
Scanning Electron

Abstract Implantation of a biomaterial is one of the important trends in solving the problem of bone tissue loss. Calcium hydroxiapatite (HAp), as the most representative bone component is a serious candidate for such implantations. The synthetic polymer poly-L-lactide (PLLA) in HAp/PLLA is often used as a polymeric material, with a role in the substitution of bone tissue collagen fibers. Fibers of PLLA may strengthen HAp and its good bioresorption provides space for tissue remodeling. Differences in porosity, microstructure, compressive consistency as well as bioresorbility of HAp/ PLLA may be achieved by using PLLA with different molecular weights. In this study HAp/PLLA composites with PLLA of different molecular weights (50,000; 160,000 and 430,000) were implanted in mouse peritoneum in order to examine the influence of the molecular weight of PLLA on morphology changes. Microstructural changes of biomaterial (HAp/PLLA) surface were analyzed one week, three weeks and four months after their implantation using Scanning Electron Microscopy. The results showed a significant difference in tissue reactions on the applied biocomposites, depending on their molecular weight. The most intense proliferation of cells was induced by HAp/PLLA 50,000 compared to HAp/PLLA 430,000 and HAp/PLLA 160,000. In the vicinity of HAp/PLLA 430,000 abundant erythrocytes were observed. The differences in biological reactions on the examined biocomposites are significant for their practical applications. HAp/PLLA composite biomaterials of different types and resorption rates require specific designing and programming to become suitable for particular purposes in an organism.

scholarly journals Effect of the molecular weight of polyvinylpyrrolidone on the structure and morphology of materials based on substituted hydroxyapatite for bone implants

2018 ◽  
Vol 226 ◽  
pp. 03012
Author(s):  
Elizaveta A. Mukhanova ◽  
Inna A. Suprunova ◽  
Yana A. Suprunova ◽  
Igor Yu. Zabiyaka
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Thermodynamic Stability ◽  
Structural Transformations ◽  
Experimental Results ◽  
Molecular Weights ◽  
Structure And Morphology ◽  
Size And Morphology ◽  
Scanning Electron

In this work, we study the influence of various molecular weights of polyvinylpyrrolidone (PVP) on synthesis substituted hydroxyapatite. Using the scanning electron microscopy we estimated the size and morphology of the particle. We studied the structural transformations of phosphates and the effect of polymer sizes on the structure and morphology. We revealed the thermodynamic stability of the structure of hydroxyapatite due to experimental results.

scholarly journals Molecular spectroscopy analysis of the substitution of bone tissue by HAp/PLLA composite biomaterial

2004 ◽  
Vol 18 (4) ◽  
pp. 553-565 ◽  
Author(s):  
Nenad Ignjatovic ◽  
Dragan Uskokovic
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Ir Spectroscopy ◽  
Molecular Spectroscopy ◽  
Absorption Bands ◽  
Molecular Weights ◽  
Ft Ir ◽  
Scanning Electron ◽  
Ft Ir Spectroscopy

Due to its pronounced osteoinductive properties, calcium hydroxyapatite (HAp) has been widely used in medicine. Bioresorptive poly-L-lactide (PLLA) as a polymer biomaterial has been also used extensively in medicine for its non-toxicity and biocompatibility. To combine the advantages exhibited by each of these materials, a HAp/PLLA composite biomaterial has been synthesized and used for reconstruction and repair of bone defects. Hydroxyapatite/poly-L-lactide (HAp/PLLA) composite biomaterial with PLLA of 50,000 and 430,000 g/mole molecular weight was studiedin vivo. The biocomposite with PLLA of both molecular weights was implanted into mice, then removed from their organisms and analyzed by the Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and histopathologic analysis. Characteristic absorption bands, registered and defined by FT-IR spectroscopy, confirm the formation of new functional groups and compounds during the bone repair process using HAp/PLLA biocomposite with PLLA of 50,000 and 430,000 molecular weights. Analysis of the microstructures of the sample surfaces by scanning electron microscopy (SEM) before and after implantation revealed bioresorption of the PLLA polymer phase in the system with PLLA of lower molecular weight and generation of collagen fibers at the sites of implanted bioresorptive PLLA. As the studied synthetic materials behave as the natural bone, i.e., they are phagocytosed and resorpable, they can be considered as biocompatible.

scholarly journals Cinnamyl-Imine-Chitosan Hydrogels. Morphology Control

2018 ◽  
Vol 26 (2) ◽  
pp. 221-232
Author(s):  
Anda M. Craciun
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Functional Groups ◽  
Molar Ratio ◽  
Crosslinking Degree ◽  
Molecular Weights ◽  
Amine Groups ◽  
Chitosan Hydrogels ◽  
Scanning Electron

Abstract The study deals with the exploration of the possibilities to control the morphology of cinnamyl-imine-chitosan hydrogels in view of their bio-application. Three series of hydrogels were synthetized from chitosan of three different molecular weights and cinnamaldehyde, varying the molar ratio between the amine groups on chitosan and aldehyde functional groups. The hydrogel morphology has been monitored by scanning electron microscopy. The variation of the hydrogel morphology as a function of chitosan molecular weight, crosslinking degree, and incubation conditions has been monitored. It was concluded that there are multiple possibilities of tuning the morphology of these hydrogels in function of the targeted application.

scholarly journals Effect of the dispersion of the chromophore on the optical performances of polarizers from polyethylene and 5”-thio- (3-butyl)nonyl-2,2’:5’,2”-terthiophene

e-Polymers ◽  
2002 ◽  
Vol 2 (1) ◽  
Author(s):  
Andrea Pucci ◽  
Letizia Moretto ◽  
Giacomo Ruggeri ◽  
Francesco Ciardelli
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Differential Scanning Calorimetry ◽  
Melting Point ◽  
Drawing Ratio ◽  
Scanning Calorimetry ◽  
Affine Deformation ◽  
Ultra High Molecular Weight ◽  
Scanning Electron

AbstractA new polyethylene-compatible terthiophene chromophore, 5”-thio-(3- butyl)nonyl-2,2’:5’,2”-terthiophene, with melting point lower than 0°C was prepared and used for linear polarizers based on ultra-high-molecular-weight polyethylene (UHMWPE). Differential scanning calorimetry and scanning electron microscopy indicate that the new chromophore is dispersed uniformly in films of UHMWPE obtained by casting from solution. The films show excellent dichroic properties (dichroic ratio 30) at rather low drawing ratio (≈ 20) . Moreover, qualitative agreement is observed with the Ward pseudo-affine deformation scheme.

Preparation of Polyacrylamide Nanofibers by Electrospinning

2009 ◽  
Vol 87-88 ◽  
pp. 433-438 ◽  
Author(s):  
Li Liu ◽  
Wei Wei Gu ◽  
Wen Ting Xv ◽  
Chang Fa Xiao
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Applied Voltage ◽  
Diameter Distribution ◽  
Uniform Thickness ◽  
Technological Parameters ◽  
Glutaraldehyde Solution ◽  
Scanning Electron

Polyacrylamide (PAM) nanofibers was spun by electrospinning. In order to increase the molecular weight of the PAM, It has been cross linked by Glutaraldehyde solution. By means of scanning electron microscopy (SEM), the effect of electrospun technological parameters on the fibers’ morphology were researched. The parameters include the concentration of PAM spinning solution, the applied voltage and tip-collector distance (TCD). The PAM nanofibers of uniform thickness with the fibers’ diameter distribution of 80 ~ 160nm were got under the conditions as followers: the concentration of 16 wt.%, applied voltage of 23 kV, the TCD of 13cm.

Fracture of Polymers Under Repetitive Loading

1986 ◽  
Vol 79 ◽  
Author(s):  
J. A. Sauer ◽  
C. C. Chen
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Fracture Surface ◽  
Surface Morphology ◽  
Thermal Effects ◽  
Second Phase ◽  
Fracture Surface Morphology ◽  
Repetitive Loading ◽  
Scanning Electron

AbstractThe fracture surface morphology of various polymer specimens, fractured under alternating loading, has been examined by scanning electron microscopy. Illustrations are given of both typical and unusual fracture surfaces and the influence of such variables as composition, molecular weight, presence of a dispersed second phase and induced thermal effects is discussed.

The Effects of Organic Solvent on the Electrospinning of Water-Soluble Polyacrylamide with Ultrahigh Molecular Weight

2007 ◽  
Vol 121-123 ◽  
pp. 113-116
Author(s):  
Yi Yang Zhao ◽  
X. Li ◽  
C. Wang ◽  
L.J. Li
Keyword(s):  
Electron Microscopy ◽  
Aqueous Solution ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Organic Solvent ◽  
Colloidal Particles ◽  
Water Soluble ◽  
Ultrahigh Molecular Weight ◽  
Scanning Electron

The effects of an organic solvent on the electrospinning of water-soluble polyacrylamide with ultrahigh molecular weight were investigated. An organic solvent, DMF, was introduced to the polyacrylamide aqueous solution and subsequently, transparent spinning solutions were obtained. The spinning solution was electrospun at the voltage of 10 kV and the electrospun products were examined by scanning electron microscopy (SEM). Results indicated that all the electrospinning products including colloidal particles, beaded fibers and smooth fibers were fabricated in the DMF/H2O bi-component solvent and the morphology of electrospun products changed from smooth fiber to beaded fiber with the increasing amount of DMF used.

scholarly journals Changes in the Molecular Characteristics of Bovine and Marine Collagen in the Presence of Proteolytic Enzymes as a Stage Used in Scaffold Formation

Marine Drugs ◽  
2021 ◽  
Vol 19 (9) ◽  
pp. 502
Author(s):  
Marfa N. Egorikhina ◽  
Ludmila L. Semenycheva ◽  
Victoria O. Chasova ◽  
Irina I. Bronnikova ◽  
Yulia P. Rubtsova ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Scanning Electron Microscopy ◽  
Proteolytic Enzymes ◽  
Molecular Characteristics ◽  
Species Origin ◽  
Bovine Collagen ◽  
Hydrolyzed Collagen ◽  
Source Materials ◽  
Scanning Electron

Biopolymers, in particular collagen and fibrinogen, are the leading materials for use in tissue engineering. When developing technology for scaffold formation, it is important to understand the properties of the source materials as well as the mechanisms that determine the formation of the scaffold structures. Both factors influence the properties of scaffolds to a great extent. Our present work aimed to identify the features of the molecular characteristics of collagens of different species origin and the changes they undergo during the enzymatic hydrolysis used for the process of scaffold formation. For this study, we used the methods of gel-penetrating chromatography, dynamic light scattering, reading IR spectra, and scanning electron microscopy. It was found that cod collagen (CC) and bovine collagen (BC) have different initial molecular weight parameters, and that, during hydrolysis, the majority of either type of protein is hydrolyzed by the proteolytic enzymes within the first minute. The differently sourced collagen samples were also hydrolyzed with the formation of two low molecular fractions: Mw ~ 10 kDa and ~20 kDa. In the case of CC, the microstructure of the final scaffolds contained denser, closely spaced fibrillar areas, while the BC-sourced scaffolds had narrow, short fibrils composed of unbound fibers of hydrolyzed collagen in their structure.

scholarly journals Role of Lewis Acids in Preventing the Degradation of Dithioester-Dormant Species in the RAFT Polymerization of Acrylamides in Methanol to Enable the Successful Dual Control of Molecular Weight and Tacticity

2021 ◽  
Author(s):  
Yuji Imamura ◽  
Shigeru Yamago
Keyword(s):  
Molecular Weight ◽  
Lewis Acids ◽  
Chain Transfer ◽  
Raft Polymerization ◽  
Degradation Mechanism ◽  
Earth Metal ◽  
Nucleophilic Attack ◽  
Molecular Weights ◽  
Reversible Addition ◽  
Metal Triflates

Reversible addition-fragmentation chain transfer (RAFT) polymerization of acrylamide in methanol using dithioester RAFT chain-transfer agents was unsuccessful due to degradation of the end group. However, this degradation was completely suppressed by the addition of rare-earth metal triflates (RMTs). As RMTs are effective for the stereoselective polymerization of acrylamides, RAFT polymerization in the presence of RMTs afforded the corresponding poly(acrylamide)s with controlled molecular weight and tacticity. The conditions allowed the synthesis of high-molecular-weight polyacrylamides with molecular weights up to 168,000, low dispersity (<1.5) and high tacticity (90% <i>meso</i> diad selectivity). The degradation mechanism initiated by nucleophilic attack of acrylamide on the dithioester group was experimentally clarified for the first time. As RMT is a Lewis acid, its coordination to the amide group of acrylamide reduces its nucleophilicity.

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