scholarly journals THE MECHANISM OF POPCORN POLYMER FORMATION

1948 ◽  
Vol 26b (3) ◽  
pp. 356-377
Author(s):  
C. A. Winkler ◽  
J. C. Devins
Keyword(s):  
Nitric Oxide ◽  
Growth Rate ◽  
Free Radicals ◽  
Kinetic Study ◽  
Proliferative Activity ◽  
Molar Ratio ◽  
Double Bonds ◽  
Polymer Formation ◽  
Quantitative Treatment ◽  
Butadiene Styrene

A kinetic study of popcorn formation in solutions of butadiene in styrene indicates that the free radicals necessary for the polymerization are produced initially on the seed by decomposition of hydroperoxides. A further reaction involving opening of double bonds in reacting chains leads also to radical formation. The function of butadiene is to supply double bonds to the chain and thus enable branching to occur. The growth rate varies with the molar ratio of butadiene: styrene in the seed, showing an optimum value at 0.27 M/M. Benzoyl peroxide inhibits the reaction somewhat, at the same time catalyzing the normal formation of soluble polymer. Popcorn initiation in unseeded samples is catalyzed by small concentrations of peroxides, larger concentrations producing no further effect. An optimum butadiene: styrene ratio of 0.1 M/M exists in popcorn initiation. The reaction apparently does not take place on the surface of the vessel. Traces of nitric oxide strongly inhibit popcorn formation in seeded and unseeded samples. The proliferative activity of popcorn seed is reduced by treating it with nitric oxide. A quantitative treatment of the mechanism is given.

Oxidation of Photoexcited Elastomers

1972 ◽  
Vol 45 (2) ◽  
pp. 481-518 ◽  
Author(s):  
Mme J. L. Morand
Keyword(s):  
Free Radicals ◽  
Linear Function ◽  
Initial Rate ◽  
Incident Light ◽  
Double Bonds ◽  
Photophysical Process ◽  
Vulcanized Rubber ◽  
The One ◽  
Limiting Value ◽  
Butadiene Styrene

Abstract The sensitivity spectrum of elastomers to sunlight (λ≽300 nm), determined by the variation at 30° C of the initial rate of oxidation or chain scissions as a function of the wavelength of incident light, shows several maxima in the near UV. These maxima are approximately equidistant and the space between them differs only slightly (10 to 11.5 nm) according to the polydienes (polyisoprene, polybutadiene, copolymer butadiene-styrene) in the crude or the vulcanized state, whatever may be the curing system. The identified maxima, existing also under vacuum (10−4 Torr), can be due to the presence of some chromophores in the chains. The latter, in absorbing the light during the primary photophysical process, would initiate the degradation. Among different possibilities, an S0→T1 transition of the isolated double bonds, producing free radicals, seems to be the one likely to explain the results. After the initiation, the photoxidation at 30° C and 5 mW/cm2 proceeds like the thermoxidation near 150° C. For a peroxide vulcanized rubber, the kinetics are similar and the rates of oxidation are somewhat faster under the most harmful sunrays than those observed by Bevilacqua at 120° C. Moreover, the chain scissions are a linear function of the oxygen consumed and their ratio is close to the limiting value of about 6 moles of O2 per broken bond, obtained by this author at 140–150° C.

NITRIC OXIDE, FREE RADICALS AND CELL SIGNALLING IN CARDIOVASCULAR DISEASE

1997 ◽  
Vol 25 (3) ◽  
pp. 384S-384S
Author(s):  
Victor M. Darley-Usmar ◽  
Joanne McAndrew ◽  
Roger White ◽  
Rakesh Patel ◽  
Doug Moellering ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Cardiovascular Disease ◽  
Free Radicals ◽  
Cell Signalling

Mastication of Rubber. II. Interpolymerization of Natural Rubber and Neoprene on Cold Milling

1956 ◽  
Vol 29 (2) ◽  
pp. 427-437
Author(s):  
D. J. Angier ◽  
W. F. Watson
Keyword(s):  
Free Radicals ◽  
Natural Rubber ◽  
Small Molecules ◽  
The Other ◽  
Polymer Molecules ◽  
Commercially Important ◽  
The Individual ◽  
Cold Mill ◽  
General Method ◽  
Butadiene Styrene

Abstract The softening of elastomers on cold milling results from scission of the polymer molecules by the applied shearing forces. The ruptured chains are free radicals, which can undergo mutual combination, interaction with oxygen and various additives, and branching (grafting) on to other polymer molecules. A general method of producing graft and block interpolymers between elstomers is therefore indicated, namely, to cold-mill the polymers together in the absence of small molecules which can terminate the polymeric radicals in order that the radicals may cross-terminate or graft onto the polymer molecules of the other type. A survey of several pairs of the commercially important elastomers, natural rubber, butadiene-styrene, Neoprene, and butadiene-acrylonitrile, has shown that cold milling does effect interlinking. Detailed results for the rubber-Neoprene system are reported in this communication. Experimental verification of polymer interlinking was obtained from the solubility properties of the milled elastomers. Cold milling of Neoprene under nitrogen produces gel, whereas of natural rubber does not, but the milling of mixtures gives gels containing natural rubber. Also, the solubilities and precipitation of the milled mixtures cannot be accounted for by these properties of the individual polymers. Finally, Neoprene-natural rubber mixtures, after and not before cold-milling, can be cross-linked by magnesium oxide, with rubber bound into the vulcanizate.

Kinetic study of the nitric oxide oxidation between 288 and 323 K, under pressure, focus on the oxygen influence on the reaction rate constant

2020 ◽  
Vol 52 (5) ◽  
pp. 329-340 ◽  
Author(s):  
Esther Neyrolles ◽  
José Lara Cruz ◽  
Georgio Bassil ◽  
François Contamine ◽  
Pierre Cezac ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Kinetic Study ◽  
Rate Constant ◽  
Reaction Rate ◽  
Reaction Rate Constant

The Role of Oxygen-Derived Free Radicals and Nitric Oxide in Cytokine-Induced Antiproliferation of Pancreatic Cancer Cells

Pancreas ◽  
2002 ◽  
Vol 24 (2) ◽  
pp. 161-168 ◽  
Author(s):  
William J. Thomas ◽  
Deborah L. Thomas ◽  
Joseph A. Knezetic ◽  
Thomas E. Adrian
Keyword(s):  
Nitric Oxide ◽  
Pancreatic Cancer ◽  
Free Radicals ◽  
Cancer Cells ◽  
Pancreatic Cancer Cells ◽  
Oxygen Derived Free Radicals

Temporal effect of alcohol consumption on reactivity of pial arterioles: role of oxygen radicals

2001 ◽  
Vol 280 (3) ◽  
pp. H992-H1001 ◽  
Author(s):  
Hong Sun ◽  
William G. Mayhan
Keyword(s):  
Nitric Oxide ◽  
Free Radicals ◽  
Alcohol Consumption ◽  
Nitric Oxide Synthase ◽  
Chronic Alcohol ◽  
Chronic Alcohol Consumption ◽  
Oxygen Derived Free Radicals ◽  
Pial Arterioles ◽  
Oxide Synthase

Chronic alcohol consumption reduces nitric oxide synthase-dependent responses of pial arterioles via mechanisms that remain uncertain. In addition, the temporal effects of alcohol on pial arterioles is unclear. Thus our goals were to examine the role of oxygen-derived free radicals in alcohol-induced impairment of cerebrovascular reactivity and the temporal effect of alcohol on reactivity of pial arterioles. Sprague-Dawley rats were pair-fed a liquid diet with or without alcohol for 2–3 wk, 2–3 mo, or 5–6 mo. We measured the in vivo diameter of pial arterioles in response to nitric oxide synthase-dependent dilators acetylcholine and ADP and the nitric oxide synthase-independent dilator nitroglycerin. In nonalcohol-fed rats, acetylcholine (1.0 and 10 μM) and ADP (10 and 100 μM) produced dose-related dilatation of pial arterioles. Whereas there was no difference in reactivity of arterioles to the agonists in rats fed the nonalcohol and alcohol diets for a period of 2–3 wk, there was a significant impairment in reactivity of arterioles to acetylcholine and ADP, but not nitroglycerin, in rats fed the alcohol diet for longer durations. We then found that treatment with superoxide dismutase did not alter baseline diameter of pial arterioles in nonalcohol-fed or alcohol-fed rats, but significantly improved impaired nitric oxide synthase-dependent dilatation of pial arterioles in alcohol-fed rats. Thus our findings suggest a temporal relationship in the effects of alcohol on reactivity of pial arterioles and that impaired nitric oxide synthase-dependent cerebral vasodilatation during chronic alcohol consumption may be related, in part, to enhanced release of oxygen-derived free radicals.

Responses of Free Radicals to Subcutaneous Implantation of Alginate-Chitosan-Alginate (ACA) Microcapsules in Mice

2009 ◽  
Vol 32 (4) ◽  
pp. 224-231 ◽  
Author(s):  
Haibao Zhu ◽  
Zhaofang Xi ◽  
Shijin Yang ◽  
Yanhong Zhang ◽  
Hong Wang ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Superoxide Dismutase ◽  
Free Radicals ◽  
Cell Viability ◽  
Cellular Damage ◽  
Specific Response ◽  
Saline Injection ◽  
Encapsulated Cells ◽  
Post Implantation

The objective of this study was to characterize the levels of free radicals in serum and antioxidase activity after microcapsules were implanted into the subcutaneous space of mice. Cell viability was evaluated using AO/EB staining. Serum free radicals, malondialdehyde and superoxide dismutase levels were evaluated by colorimetry analysis. The mice were divided into three groups: saline injection group (n=15), empty microcapsules injected group (n=21), encapsulated cells injected group (n=21). Cell viability and serum analysis were executed at 1, 4 and 7 days post-implantation. Hydrogen peroxide and malondialdehyde levels initially increased in the recipients of the empty microcapsules, before decreasing to the basal level. However, in mice receiving the encapsulated cells, the levels were higher at the end of study. Nitric oxide and superoxide dismutase increased after the implantation of microcapsules with or without the BHK-21 cells, but were not changed in response to the saline injection. The viability of the encapsulated cells was high in vivo, although some microcapsules had broken by 7 days post-implantation. These results suggest that nitric oxide plays a role in the specific response to microcapsules. The levels of free radicals rapidly increased immediately following microcapsule transplantation, but they caused only slight cellular damage before the microencapsulated cells were exposed.

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