Free-radical-induced chain scission and cross-linking of polymers in aqueous solution—an overview

2003 ◽  
Vol 67 (3-4) ◽  
pp. 353-359 ◽  
Author(s):  
Clemens von Sonntag
Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1706
Author(s):  
Elena Olăreț ◽  
Brîndușa Bălănucă ◽  
Andra Mihaela Onaș ◽  
Jana Ghițman ◽  
Horia Iovu ◽  
...  

Mucin is a glycoprotein with proven potential in the biomaterials field, but its use is still underexploited for such applications. The present work aims to produce a synthesis of methacryloyl mucin single-network (SN) hydrogels and their double-cross-linked-network (DCN) counterparts. Following the synthesis of the mucin methacryloyl derivative, various SN hydrogels are prepared through the photopolymerization of methacrylate bonds, using reaction media with different pH values. The SN hydrogels are converted into DCN systems via supplementary cross-linking in tannic acid aqueous solution. The chemical modification of mucin is described, and the obtained product is characterized; the structural modification of mucin is assessed through FTIR spectroscopy, and the circular dichroism and the isoelectric point of methacryloyl mucin is evaluated. The affinity for aqueous media of both SN and DCN hydrogels is estimated, and the mechanical properties of the systems are assessed, both at macroscale through uniaxial compression and rheology tests and also at microscale through nanoindentation tests.


2016 ◽  
Vol 89 (4) ◽  
pp. 671-688 ◽  
Author(s):  
M. A. L. Verbruggen ◽  
L. van der Does ◽  
W. K. Dierkes ◽  
J. W. M. Noordermeer

ABSTRACT The theoretical model developed by Charlesby to quantify the balance between cross-links creation of polymers and chain scission during radiation cross-linking and further modifications by Horikx to describe network breakdown from aging were merged to characterize the balance of both types of scission on the development of the sol content during de-vulcanization of rubber networks. There are, however, disturbing factors in these theoretical considerations vis-à-vis practical reality. Sulfur- and peroxide-cured NR and EPDM vulcanizates were de-vulcanized under conditions of selective cross-link and random main-chain scissions. Cross-link scission was obtained using thiol-amine reagents for selective cleavage of sulfur cross-links. Random main-chain scission was achieved by heating peroxide vulcanizates of NR with diphenyldisulfide, a method commonly employed for NR reclaiming. An important factor in the analyses of these experiments is the cross-linking index. Its value must be calculated using the sol fraction of the cross-linked network before de-vulcanization to obtain reliable results. The values for the cross-linking index calculated with sol-gel data before de-vulcanization appear to fit the experimentally determined modes of network scission during de-vulcanization very well. This study confirms that the treatment of de-vulcanization data with the merged Charlesby and Horikx models can be used satisfactorily to characterize the de-vulcanization of NR and EPDM vulcanizates.


Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1992 ◽  
Author(s):  
Alexey Kondyurin ◽  
Anastasia Eliseeva ◽  
Alexander Svistkov

A model of rubber with a cross-linked rubber layer on a carbon black filler has been proposed. The cross-links are the result of free radical reactions generated by carbon atoms with unpaired electrons at the edge of graphitic sheets in a carbon black filler. The experimental study of the cross-linking reactions in polyisoprene was done on a flat carbonized surface after ion beam implantation. The cross-linking process in the polyisoprene macromolecules between two particles was simulated. The model with a cross-linked rubber layer on a carbon filler as a “glassy layer” explains the mechanical properties of the rubber materials.


2018 ◽  
Vol 76 (7) ◽  
pp. 3535-3554 ◽  
Author(s):  
Akila Merakchi ◽  
Souhila Bettayeb ◽  
Nadjib Drouiche ◽  
Lydia Adour ◽  
Hakim Lounici

2017 ◽  
Vol 50 (4) ◽  
pp. 1482-1493 ◽  
Author(s):  
Sarah J. Byard ◽  
Mark Williams ◽  
Beulah E. McKenzie ◽  
Adam Blanazs ◽  
Steven P. Armes

Author(s):  
Mirvari Hasanova Mirvari Hasanova

The separation and purification of antibiotics with sorption by ion-exchange materials, as well as their delivery in biological processes by immobilization, are now widely used in biotechnology. There are many scientific studies in the literature on the sorption of antibiotics by polymer-based sorbents and inorganic materials, as well as the study of thermodynamics and kinetics of the process. In the literature, the acquisition of biologically active systems from the sorption of antibiotics by ion-exchange fibers based on various polymers and inorganic substances was carried out. However, the synthesis of selective gels for the effective separation of doxycycline and its delivery in different pH mediums by sorption with biodegradable, biocompatible polysaccharide-containing composites is one of the topical issues. Gel was synthesized from the cross-linking of N,N-diethyl N-methyl derivative of a natural polyaminosaccharide of chitosan by glutaric aldehyde. Also, pH-sensitive hydrogels that can swollen in water were synthesized from the cross-linking of a graft copolymer of cherry source gummiarabic with N-vinylpyrrolidone, as well as synthetic polymer polyacrylic acid with N,N-methylene-bis-acrylamide. The structure of the gels were identified by FTIR and NMR spectroscopy, and the sorption of doxycycline antibiotic from an aqueous solution was investigated. According to the values of zeta potential, the protonation of functional groups in the main macromolecule in an acidic medium leads to a value of zeta potential of 40÷80 mV on the surface of chitosan-based gel and others. Although the chemical structure is different, the isoelectric point is set around pH=6÷8 for all three hydrogels. The dependences of the sorption process on the amount of gels, antibiotic concentration, temperature, and pH medium were studied. The experimental data were analyzed using two adsorption models, Langmuir and Freundlich, with the later system providing the best fit. Doxycycline is adsorbed on the surface of chitosan, gummiarabic and polyacrylic acid based hydrogel composite through by physical interactions. Also, the results of thermodynamic parameters ΔG40 kJ/mol show that the nature of the adsorption process is physical, and spontaneous, too. Keywords: Chitosan, Gummiarabic-arabinogalactane, polyacrylic acid, hydrogel, sorption isoterms, doxycycline, thermodynamica.


2012 ◽  
Vol 506 ◽  
pp. 315-318 ◽  
Author(s):  
C. Witthayaprapakorn ◽  
Robert Molloy

Design and preparation of synthetic hydrogels for biomedical use as wound dressings were studied. A partially hydrated hydrogel of sodium salt of 2-acrylamido-2-methylpropanesulfonic acid (Na-AMPS) was prepared by redox initiation via free radical polymerisation in aqueous solution. In this reaction, of 40% w/v Na-AMPS aqueous solution was prepared, with 1.0% by mole of monomer ethylene glycol dimethacrylate (EGDM) as crosslinker, and potassium persulfate (K2S2O8) as the free radical initiator at a concentration of 0.5% mol monomer with potassium metabisulfite (K2S2O5) and ferrous sulphate (FeSO4) as coinitiator. The results showed that the hydrogel sheets gave good coherency, transparency, flexibility, high oxygen permeability, good skin adhesion and were non-toxic. The water properties of the hydrogel sheets (absorption, retention, water vapour transmission rate) were balanced which can maintain the moist environment of the wound. It is concluded that Na-AMPS hydrogels have properties which show potential for biomedical use as a wound dressing for second degree burn.


1997 ◽  
Vol 37 (8) ◽  
pp. 1331-1338 ◽  
Author(s):  
S. G. Kulichikhin ◽  
A. Ya. Malkin ◽  
O. M. Polushkina ◽  
V. G. Kulichikhin

Sign in / Sign up

Export Citation Format

Share Document