Solid State Carbon-13 NMR Studies of Vulcanized Elastomers. III, Accelerated Sulfur Vulcanization of Natural Rubber

1987 ◽  
Vol 60 (2) ◽  
pp. 278-297 ◽  
Author(s):  
A. M. Zaper ◽  
J. L. Koenig
Keyword(s):  
Solid State ◽  
Natural Rubber ◽  
Nmr Spectra ◽  
Structural Modification ◽  
Main Chain ◽  
Nmr Studies ◽  
Structural Modifications ◽  
Sulfur Vulcanization ◽  
Chain Isomerization ◽  
Cyclic Sulfide

Abstract In summary, the solid state C-13 NMR technique has proven to be a significant method for the detection of crosslinks and other structural modifications in accelerated sulfur-vulcanized NR systems. When the amount of accelerator is high in proportion to the amount of sulfur used, the network structure appears to be simpler with less crosslinking, less main chain structural modification, and fewer cyclic sulfide structures as observed in the C-13 NMR spectra. Polysulfidic crosslinks have been detected in addition to polysulfides terminated by accelerator residues. Cis-to-trans chain isomerization is also evident in these vulcanizates.

Solid State Carbon-13 NMR Studies of Vulcanized Elastomers. II, Sulfur Vulcanization of Natural Rubber

1987 ◽  
Vol 60 (2) ◽  
pp. 252-277 ◽  
Author(s):  
A. M. Zaper ◽  
J. L. Koenig
Keyword(s):  
Solid State ◽  
Nmr Spectra ◽  
Molecular Motion ◽  
Main Chain ◽  
Repeat Unit ◽  
Crosslinking Agent ◽  
Nmr Studies ◽  
Structural Modifications ◽  
Chain Isomerization ◽  
Cyclic Sulfide

Abstract In summary, the solid-state C-13 NMR technique has proven to be a significant method for the detection of crosslinks and other structural modifications in sulfur-vulcanized NR systems. The use of sulfur as a crosslinking agent by itself generates a considerable amount of main-chain structural modifications. Cyclic sulfide structures and cis-to-trans chain isomerization are detected in addition to polysulfidic crosslinks which are found attached to different carbons of the NR repeat unit. The phenomenon of reversion has also been detected in this study. The nature of the spectral broadening in the NMR spectra of the highly cured vulcanizates has two origins. The broadening arises from lack of molecular motion in the system and from an increase in chemical shift dispersion due to the new structures formed with crosslinking.

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.

Thermosetting Mechanism Study of Organosilicon Polymer Containing Carborane by Solid-State NMR Spectroscopy

1999 ◽  
Vol 576 ◽  
Author(s):  
H. Kimura ◽  
K. Okita ◽  
M. Ichitani ◽  
M. Yonezawa ◽  
T. Sugimoto
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Nmr Spectra ◽  
Main Chain ◽  
Addition Reaction ◽  
Side Chain ◽  
Mechanism Study ◽  
Nmr Method ◽  
Organosilicon Polymer ◽  
Thermal Stable

ABSTRACTThe thermosetting mechanism of an organosilicon polymer containing carborane has been studied utilizing the 13and 29Si solid-state NMR method. The polymer having C≡C bonds in the main chain and CH═CH2, Si-H bonds, and carborane in the bulky side chain, shows a very highly thermal stability in air by curing. From 13C and 29Si NMR spectra of the polymer, it was found that the intermolecular cross-linking reactions of the polymer was due to (1) the diene reaction between Ph-C≡C and C≡C and (2) the addition reaction between side chain terminal and Ph-C≡C and between CH═CH2 and Si–H, and a very highly thermal stable structure is formed.

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 C-13 NMR Studies of Vulcanized Elastomers XVII. Effect of Carbon Black Grade on the Network Structure in Natural Rubber Vulcanizates

1997 ◽  
Vol 70 (4) ◽  
pp. 671-680 ◽  
Author(s):  
Makio Mori ◽  
Jack L. Koenig
Keyword(s):  
Solid State ◽  
Carbon Black ◽  
Natural Rubber ◽  
Network Formation ◽  
Physical Adsorption ◽  
Nmr Studies ◽  
Carbon Black Concentration ◽  
Effective Level ◽  
The Individual ◽  
Natural Rubber Vulcanizates

Abstract The vulcanization chemistry and network formation of carbon black filled natural rubber vulcanized with sulfur and TBBS were studied using solid-state C-13 NMR and equilibrium swelling measurements. A reduction in the sulfur rank of the A1 type sulfide and increased production of B1 type polysulfide are observed when the carbon black concentration increases in natural rubber. At the same loading level, the structural property or grade of carbon black does not affect qualitatively the type of sulfide formation. The efficiency of the intermolecular crosslinking over the whole range of sulfurizations is 45.7% for the unfilled vulcanizate. The extent of the chemical sulfurization reactions (NMR result) is constant with black incorporation, while the total network (swelling result) increases with increases in the black loading. The amount of physical entanglements, estimated from the comparison of the NMR and swelling results, is found to increase linearly with the carbon black concentration. The entanglements increase as a function of the 300% modulus, which suggests that the effective level of reinforcement depends on the nature of the individual carbon black. It is assumed that physical adsorption plays a major role in the polymer-filler interactions in the natural rubber/carbon black system.

Solid State Carbon-13 NMR Studies of Elastomers. XL N-t-Butyl Benzothiazole Sulfenimide Accelerated Sulfur Vulcanization of cis-Polyisoprene at 75 MHz

1993 ◽  
Vol 66 (1) ◽  
pp. 73-82 ◽  
Author(s):  
M. R. Krejsa ◽  
J. L. Koenig
Keyword(s):  
Solid State ◽  
Network Structure ◽  
Solid State Nmr ◽  
Cyclic Structure ◽  
Sulfur Concentration ◽  
Nmr Studies ◽  
Maturation Period ◽  
Sulfur Vulcanization

Abstract The network structure of TBSI-accelerated vulcanization of cis-polyisoprene was studied using C-13 solid-state NMR. The initial crosslink products consisted of A1c (cis) and A2c (cis) polysulfides. As the percent cure is increased, the A1c and A2c structures reduce in rank to monosulfides, and polysulfidic B1c (cis) and B1t (trans) structures are formed. During the maturation period C1c (cis) polysulfidic structures are also formed. The percent of sulfurization was shown to vary directly with sulfur concentration, while the efficiency of sulfurization (crosslink/cyclic-structure ratio) was shown to vary with accelerator content. TBSI-accelerated vulcanization was found to be more inefficient (lower crosslink/cyclic-structure ratio) than TBBS-accelerated vulcanization during the initial cure region. However, this results in shorter sulfur chains, which decreases the reactivity of TBSI vulcanizates as compared to TBBS vulcanizates during the reversion regime.

CURE CHARACTERISTICS OF DEVULCANIZED RUBBER:THE ISSUE OF LOW SCORCH

2017 ◽  
Vol 90 (3) ◽  
pp. 536-549 ◽  
Author(s):  
Anu Mary Joseph ◽  
Benny George ◽  
K. N. Madhusoodanan ◽  
Rosamma Alex
Keyword(s):  
Solvent Extraction ◽  
Natural Rubber ◽  
Main Chain ◽  
Process Safety ◽  
Original Sample ◽  
Vulcanized Rubber ◽  
Sulfur Vulcanization ◽  
Natural Rubber Vulcanizates ◽  
Devulcanized Rubber

ABSTRACT We investigate the reasons behind the observed low scorch during the revulcanization of devulcanized rubber. Mechanically devulcanized carbon black filled natural rubber vulcanizates originally cured by conventional vulcanization (CV), semiefficient vulcanization (semi EV), efficient vulcanization (EV), and peroxide systems as well as buffing dust obtained from pre-cured tread with known formulation were used. Revulcanization of these devulcanized samples using sulfur/sulfonamide system led to the following observations; irrespective of the type of sulfur cure system used for the initial vulcanization of the rubber, (i) the devulcanized samples cured without pre-vulcanization induction time and (ii) devulcanized samples prepared from peroxide vulcanized rubber cured with scorch safety. Based on the earlier reports that solvent extraction of devulcanized rubber did not improve the scorch time during revulcanization, the role of zinc bound non-extractable moieties was investigated using devulcanized rubber prepared from activator-free vulcanizates, which disproved the role of such moieties. This confirmed that the scorch reducing moieties should be attached to the rubber main chain, which can be unreacted crosslink precursors and cyclic sulfides left after the initial accelerated sulfur vulcanization of the original sample. The ability of pre-vulcanization inhibitor to induce scorch safety when devulcanized rubber is revulcanized as such, without adding any virgin rubber, proved that mercaptobenzothiazole (MBT) generated from crosslink precursors is the cause of low scorch. Acetone extracted devulcanized rubber samples prepared from tetramethyl thiuramdisulfide (TMTD) cured natural rubber, which does not follow the MBT pathway when revulcanized, cured with scorch safety, which further proved the role of MBT. Based on the previous reports and our results, it is obvious that powdering of rubber vulcanizate and devulcanization processes have no role on the low process safety of these materials, but it is inherent to the initial accelerated sulfur vulcanization chemistry undergone by these materials.

Solid State 13C NMR Analysis of Vulcanized Rubbers XVI. The Competitive Vulcanization of Natural Rubber and Polybutadiene Blends

1997 ◽  
Vol 70 (2) ◽  
pp. 231-242 ◽  
Author(s):  
B. Klei ◽  
J. L. Koenig
Keyword(s):  
Solid State ◽  
Natural Rubber ◽  
13C Nmr ◽  
Nmr Spectra ◽  
Sampling Technique ◽  
Nmr Analysis ◽  
Trans Isomerization ◽  
13C Nmr Analysis ◽  
Elastomer Blend ◽  
Solid State 13C Nmr

Abstract Solid state 13C NMR was used to study the competitive vulcanization of blends of natural rubber and high cis polybutadiene. A NMR sampling technique utilizing the stacked homopolymers was developed that helps to determine the spectral differences occurring due to competitively vulcanizing an elastomer blend. The small amount of interfacial crosslinking was expected to be undetectable but has been tentatively observed. Concentration of crosslinks at the interface may occur from limited solubility of curative species in both rubbers. The NMR spectra also showed inhibition of cis-trans isomerization in natural rubber with addition of polybutadiene.

51V NMR: A New Probe of Structure and Bonding in Catalysts

1987 ◽  
Vol 111 ◽  
Author(s):  
Hellmut Eckert ◽  
Israel E. Wacjs
Keyword(s):  
Solid State ◽  
Nmr Spectra ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Model Compounds ◽  
Nmr Studies ◽  
Vanadium Concentration ◽  
Structure And Bonding ◽  
Angle Spinning ◽  
Vanadium Species

AbstractSolid State 51V NMR spectra are sensitive to changes In the surface structure of V2O5 dispersed on Al2O3 and TiO2 supports. For V2O5 supported on alumina, wideline and magic-angle spinning experiments at 4.7 and 7.0 T reveal the presence of two vanadium species with different bonding environments. The relative proportions of these species change monotonically as a function of the vanadium concentration. In contrast, supported vanadium oxide on TiO2 substrates show a much more V2O5-like environment. Structural inferences are discussed In connection with solid state 51V NMR studies on model compounds with known crystal structures and site symmetries.

Solid-State 29Si VACP/MAS NMR Studies of Silicon-Accumulating Plants: Structural Characterization of Biosilica Deposits

2000 ◽  
Vol 55 (6) ◽  
pp. 459-461 ◽  
Author(s):  
Rüdiger Bertermann ◽  
Reinhold Tacke
Keyword(s):  
Solid State ◽  
Nmr Spectroscopy ◽  
Nmr Spectra ◽  
Mas Nmr ◽  
Typical Pattern ◽  
Nmr Studies ◽  
Polysilicic Acid ◽  
Freeze Dried ◽  
Pattern Characteristic

A series of silicon-accumulating plants [different Equisetum (horse tail) species, Echium vulgare, and Symphytum officinale] were studied by solid-state 29Si NMR experiments. For this purpose, selected parts of these plants were freeze-dried and then investigated by solid-state 29Si VACP/MAS NMR spectroscopy. The 29Si NMR spectra of these plants are quite similar and exhibit the typical pattern characteristic of polysilicic acid (amorphous silica).

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