Photochemistry of Ketone Polymers. X. Chain Scission Reaction in the Solid State

1973 ◽  
Vol 6 (2) ◽  
pp. 230-235 ◽  
Author(s):  
E. Dan ◽  
J. E. Guillet
Keyword(s):  
Solid State ◽  
Chain Scission ◽  
Chain Scission Reaction

Solid-State C-13 NMR Studies of Vulcanized Elastomers X. N-t-Butyl-2-Benzothiazole Sulfenamide Accelerated Sulfur Vulcanization of cis-Polyisoprene at 75.5 MHz

1992 ◽  
Vol 65 (2) ◽  
pp. 427-443 ◽  
Author(s):  
M. R. Krejsa ◽  
J. L. Koenig
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Chain Scission ◽  
Sulfur Concentration ◽  
Nmr Studies ◽  
Double Bond Migration ◽  
Sulfur Vulcanization ◽  
Equilibrium Swelling ◽  
Cis And Trans ◽  
Good Agreement

Abstract Accelerated sulfur vulcanized cis-polyisoprene was analyzed using C-13 solid-state NMR to determine the chemical microstructure of the network. Three formulations were analyzed consisting of varying accelerator/sulfur ratios. All formulations yielded similar network structures, but the amount of sulfurization varied with sulfur concentration. At low percent cure, only polysulfidic A-type cis-structures were found. For longer cure times, the A-type structures shortened to monosulfldic, and B-type polysulfidic structures, both cis and trans, were formed. The amount of trans-sulfurized product was constant with cure once this resonance appeared. No isomerization, chain scission, saturation, or double bond migration was detected. The NMR measurements appeared to show fairly good agreement with equilibrium swelling measurements.

Solid-State 13C NMR Characterization of Irradiation-Cross-Linked Natural Rubber

1987 ◽  
Vol 41 (3) ◽  
pp. 441-446 ◽  
Author(s):  
Dwight J. Patterson ◽  
Jack L. Koenig
Keyword(s):  
Solid State ◽  
Natural Rubber ◽  
Mobile Phase ◽  
Chain Scission ◽  
Structure Changes ◽  
Nmr Characterization ◽  
Cross Links ◽  
Gamma Irradiated ◽  
Trans Structure

Solid-state 13C NMR was used to characterize the structure changes produced in gamma irradiation in natural rubber. The structure of the irradiated natural rubber was found to be heterogeneous, consisting of a mobile phase and a semi-rigid phase. Cis-trans chain isomerization was detected in the mobile phase of the gamma-irradiated samples. The CP/MAS spectra of the more rigid phase contained resonances due to quaternary carbons arising from cross-links and vinyl end groups caused by main chain scission. The calculated values of β and G( X) agreed with earlier published results. Peroxide-cured natural rubber of an equivalent amount of network density showed a higher amount of trans structure than did the gamma-irradiated natural rubber.

Different Curing Systems for Ethylene-Propylene Elastomers

1992 ◽  
Vol 65 (5) ◽  
pp. 869-878 ◽  
Author(s):  
Luis González Hernández ◽  
Andrés Rodríguez Díaz ◽  
Juan Luis de Benito González
Keyword(s):  
Physical Properties ◽  
Dynamic Mechanical Analysis ◽  
Chain Scission ◽  
Mechanical Analysis ◽  
Curing Agent ◽  
Ethylene Propylene ◽  
Dynamic Mechanical ◽  
Peroxide Curing ◽  
Chain Scission Reaction ◽  
Curing Systems

Abstract The scope of this paper is to review peroxide curing of ethylene-propylene elastomers, where apart from crosslinking, other reactions occur, such as chain scission, which account for the drop in physical properties. The results are compared with an alternative crosslinking system which is being assessed in our laboratory. With the new curing agent the chain-scission reaction is not present and the physical properties of the vulcanizates are improved. The effects of the different crosslinking systems on the reaction transitions are studied with the aid of dynamic mechanical analysis.

PHOTOLYSIS OF POLYACRYLONITRILE

1961 ◽  
Vol 39 (10) ◽  
pp. 2056-2068 ◽  
Author(s):  
H. H. G. Jellinek ◽  
I. J. Bastien
Keyword(s):  
Double Bond ◽  
Ethylene Carbonate ◽  
Bond Formation ◽  
Chain Scission ◽  
Photochemical Reactions ◽  
Polymer Chains ◽  
Small Quantum ◽  
Model Substance ◽  
Cross Links ◽  
Chain Scission Reaction

The photolysis of polyacrylonitrile has been investigated in solution (80:20 by weight of ethylene carbonate to propylene carbonate), in powder form, and as a film. Experiments have been carried out in vacuum and in the presence of oxygen. All polymer samples were exposed to ultraviolet light of wavelength 2537 Å. In solution a random chain-scission reaction with a small quantum yield (ca. 10−4 main chain bonds broken/quantum absorbed) takes place; at the same time, photochemical reactions occur involving side groups of the polymer chains, as evidenced by the change in the ultraviolet spectra of the polymer solutions. It seems likely that double-bond formation, both conjugated and isolated, and cyclization are responsible for the change in spectra. Infrared spectra do not show any change. Exposed polymer films become cross-linked and exposed powder also cross-links and evolves small molecules, such as nitriles, particularly HCN. Degradation in oxygen suppresses what is believed to be double-bond formation as evidenced by ultraviolet absorption spectra. The photolysis of glutaronitrile as a model substance has also been studied.

Chain Scission Efficiency in the Oxidation of Natural Rubber Vulcanizates

1957 ◽  
Vol 30 (4) ◽  
pp. 1146-1161
Author(s):  
A. G. Veith
Keyword(s):  
Natural Rubber ◽  
Elevated Temperatures ◽  
Density Ratio ◽  
Direct Consequence ◽  
Chain Scission ◽  
Polymer Chains ◽  
Published Report ◽  
Relaxation Measurements ◽  
A Chain ◽  
Chain Scission Reaction

Abstract Natural rubber when it degrades under the action of oxygen does so primarily by a chain scission reaction. A technique has been developed by Tobolsky and coworkers for assessing the magnitude of this chain scission reaction in vulcanizates by means of continuous stress relaxation measurements. Since the result of the oxygen attack on the rubber is a chain scission reaction, the question of the efficiency of the reaction comes to mind. The influence of antioxidants is of importance in this regard as is the type of vulcanizate or network structure. This paper describes some measurements of the chain scission efficiency of a simple benzothiazolyl disulfide (MBTS) vulcanizate and the effect of several antioxidants on this chain scission reaction. Some of the complications inherent in this type of measurement are discussed. The first published report on the efficiency of the chain scission reaction in vulcanizates was given by Tobolsky, Metz, and Mesrobian in 1950. A more recent publication is that of Baxter, Potts, and Vodden in 1955. Tobolsky has interpreted the stress decay of gum vulcanizates at elevated temperatures as a direct consequence of the cutting of polymer chains of the network. The reduced stress is postulated as being equal to the chain density ratio:

scholarly journals Preparation and characterization of liquid natural rubber through oxidative degradation with phenyl hydrazine and benzoyl peroxide-oxygen

2021 ◽  
Vol 912 (1) ◽  
pp. 012098
Author(s):  
Tamrin ◽  
S Leny ◽  
Eddiyanto
Keyword(s):  
Natural Rubber ◽  
Benzoyl Peroxide ◽  
Oxidative Degradation ◽  
Chain Scission ◽  
Phenyl Hydrazine ◽  
Vacuum Oven ◽  
Liquid Natural Rubber ◽  
Chain Scission Reaction ◽  
Rubber Product

Abstract The aim of this research was to synthesize liquid natural rubber (LNR) from Natural rubber (SIR-20) by chain scission method in the presence of oxygen gas and difference of peroxides, phenyl hydrazine and benzoyl peroxide. The chain scission reaction was conducted in solution of xylene in close system. SIR-20 was diluted xylene before flushing with oxygen and the addition of the peroxide. The degradation oxidation by the oxygen and the peroxides was processed at 60°C for 24 hours. The degradative oxidation product was re-precipitated by adding the excess of methanol and filtrated before dried in vacuum oven 60°C for 24 hours. The dried product was characterized by Fourier Transform Infra Red (FTIR). It was found that the liquid natural rubber product successfully degraded by chain scission process as shown the change of the peak area intensity of infrared absorption. It was showed the peaks area intensity of O-H and carbonyl group of liquid natural rubber spectra increased.

Solid-State C-13 NMR Studies of Vulcanized Elastomers XIII. TBBS Accelerated, Sulfur-Vulcanization of Carbon Black Filled Natural Rubber

1995 ◽  
Vol 68 (4) ◽  
pp. 551-562 ◽  
Author(s):  
Makio Mori ◽  
Jack L. Koenig
Keyword(s):  
Double Bond ◽  
Solid State ◽  
Carbon Black ◽  
Natural Rubber ◽  
Main Chain ◽  
Chain Scission ◽  
Nmr Studies ◽  
Double Bond Migration ◽  
Sulfur Vulcanization ◽  
Basic Network

Abstract Solid state C-13 NMR has been used to compare the chemistry of accelerated vulcanization of natural rubber using N-t-butyl-2-benzothiazole sulfenamide in the presence and absence of carbon black. The carbon black filler has an influence on the vulcanization chemistry in addition to its accepted role in reinforcment and stabilization. The basic network structure formation is modified to the extent that crosslink desulfurization from poly to monosulflde structures occurs earlier in the cure in the presence of carbon black. No main chain scission or double bond migration was detected.

Study of Vulcanization and Degradation Chemistry in Natural Rubber by Solid-State 13C NMR and Physical Property Measurements

2003 ◽  
Vol 76 (5) ◽  
pp. 1259-1275 ◽  
Author(s):  
Makio Mori
Keyword(s):  
Solid State ◽  
Natural Rubber ◽  
13C Nmr ◽  
Physical Property ◽  
Small Strain ◽  
Chain Scission ◽  
Curing Temperature ◽  
Physical Strength ◽  
Physical Measurements ◽  
Solid State 13C Nmr

Abstract Sulfur-vulcanization and heat aging of natural rubber was investigated by solid-state 13C NMR along with the measurements of physical properties. 13C NMR detects all of the sulfurization occurring in natural rubber network including inter- and intra-molecular crosslink and pendant linkages, while physical measurements such as modulus at small strain and equilibrium swelling postulate detect only an amount of physically effective crosslinks. By comparing those two approaches, the efficiency of sulfur bonding in contributing to physical strength can be determined. It was found that the efficiency became lower for the samples with higher curing temperature, longer cure time, and also at higher sulfur level. It was assumed by 13C chemical shift analysis that all of the sulfurized isoprene units were cis-to-trans isomerized during the vulcanization and heat aging, even for ineffective sulfurization. Furthermore, it was found that the configuration of those units remained in the trans-1,4 form after the desulfurization at either reversion or heat aging. The nature of the trans-1,4 form in the isoprene series was assumed to be more rigid compared to that of a cis-1,4 form. This resulted in an introduction of chain scission at large deformation for the rubber with higher trans-1,4 content. Comparing several samples with different cure temperatures, cure degrees, and sulfur levels, it was postulated that such cis-to-trans isomerization is a main factor governing a degradation chemistry at elevated cure temperature, overcuring and heat aging.

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