Isoprene and Rubber. Part 30. Hydromethylrubber

1932 ◽  
Vol 5 (2) ◽  
pp. 141-145
Author(s):  
H. Staudinger ◽  
M. Brunner ◽  
E. Geiger
Keyword(s):  
Molecular Weight ◽  
High Pressure ◽  
Average Molecular Weight ◽  
Degree Of Polymerization ◽  
Methyl Groups ◽  
Butadiene Rubber ◽  
Double Bonds ◽  
Molecular Product ◽  
Unsaturated Rubber ◽  
Rubber Part

Abstract When rubber is reduced at 270° under high pressure, a hemi-colloidal hydrorubber is obtained, and it was proved by Geiger and Huber that the product has a higher molecular weight and is less cyclicized if a good catalyst is used in large quantity (for example, active nickel produced by the method of Kelber), while according to the original experiments of Fritschi, who carried out the hydrogenation in the presence of very little platinum, a more degraded and somewhat cyclicized hydrorubber is obtained. The saturated hydrorubber is much more stable than the unsaturated rubber since the loosening action of the double bonds is lacking. A hydrorubber of the average molecular weight of 10,000 is still relatively stable at 270°, while a hemi-colloidal rubber with this molecular weight will he cracked to still smaller fragments at this temperature, and these fragments are then changed by cyclicization. This behavior can be clearly seen in methylrubber. The following reduction proves that it is even more easily decomposed than rubber itself. With nickel as catalyst, Geiger obtained from methylrubber by reduction at 270° and 100 atmospheres a hemi-colloidal hydromethylrubber which had an average molecular weight of 1600 and therefore had a degree of polymerization of about 20. If rubber is reduced under the same conditions a higher molecular product is obtained with an average molecular weight of 3000 to 10,000. Judged by reduction experiments, the chain of butadiene rubber is still more stable, since the hydrobutadiene rubber prepared under the same conditions had the highest average molecular weight. The cleavage of the chains, as in the following formula, is therefore favored by the methyl groups:

The Use of Novel F-RAFT Agents in High Temperature and High Pressure Ethene Polymerization: Can Control be Achieved?

2007 ◽  
Vol 60 (10) ◽  
pp. 788 ◽  
Author(s):  
Markus Busch ◽  
Marion Roth ◽  
Martina H. Stenzel ◽  
Thomas P. Davis ◽  
Christopher Barner-Kowollik
Keyword(s):  
Molecular Weight ◽  
High Pressure ◽  
High Temperature ◽  
Degree Of Polymerization ◽  
Molecular Weight Distributions ◽  
High Pressure High Temperature ◽  
Reversible Addition ◽  
Weight Distributions ◽  
Raft Agent ◽  
Initial Results

Simulations are employed to establish the feasibility of achieving controlled/living ethene polymerizations. Such simulations indicate that reversible addition–fragmentation chain transfer (RAFT) agents carrying a fluorine Z group may be suitable to establish control in high-pressure high-temperature ethene polymerizations. Based on these simulations, specific fluorine (F-RAFT) agents have been designed and tested. The initial results are promising and indicate that it may indeed be possible to achieve molecular weight distributions with a polydispersity being significantly lower than that observed in the conventional free radical process. In our initial trials presented here (using the F-RAFT agent isopropylfluorodithioformate), a correlation between the degree of polymerization and conversion can indeed be observed. Both the lowered polydispersity and the linear correlation between molecular weight and conversion indicate that control may in principle be possible.

Isoprene and Rubber. Part 29. High Molecular Hydrorubbers

1932 ◽  
Vol 5 (2) ◽  
pp. 136-140
Author(s):  
H. Staudinger ◽  
W. Feisst
Keyword(s):  
Molecular Weight ◽  
Catalytic Reduction ◽  
Molecular Form ◽  
Average Molecular Weight ◽  
Molecular Size ◽  
Decomposition Products ◽  
Molecular Weights ◽  
Rubber Part ◽  
Derivatives Of ◽  
Suitable Process

Abstract The molecular concept in organic chemistry is based upon the fact that the molecules, whose existence is proved by vapor density determinations, enter into chemical reactions as the smallest particles. If now it is assumed that organic molecular colloids like rubber are dissolved in dilute solution in molecular form then it must be proved that in the chemical transposition of macromolecules as well no change in the size of the macromolecules occurs. In the case of hemicolloids, therefore for molecular colloids with an average molecular weight of 1000 to 10,000, this has been proved by the reduction of polyindenes, especially of polysterenes, to hydroproducts with the same average molecular weight, and also by the fact that cyclorubbers do not change their molecular weight upon autoöxidation. The molecular weights of hemi-colloidal hydrocarbons are therefore invariable. This is much more difficult to prove in the case of rubber, although there are many more ways in which unsaturated rubber can be transposed than the stable polysterenes, polyindenes, and poly cyclorubbers. In most of the reactions with rubber, as in its action with nitrosobenzene, oxidizing agents, hydrogen halides, and halogens, an extensive decomposition takes place as a result of the instability of the molecule, which is referred to in another work. Therefore derivatives of rubber are not formed, but derivatives of hemi-colloidal decomposition products. The catalytic reduction of rubber in the cold appears to be the most suitable process of making it react without changing its molecular size in order to prove that in a chemical transposition its molecular weight remains the same.

The Structure of Elastomers and Their Reactivity

1951 ◽  
Vol 24 (1) ◽  
pp. 95-98
Author(s):  
A. S. Kuz'minskii ◽  
N. N. Lezhnev
Keyword(s):  
Molecular Weight ◽  
Methyl Groups ◽  
Side Chains ◽  
Double Bonds ◽  
Gutta Percha ◽  
Different Temperatures ◽  
Spatial Configurations ◽  
The Mean ◽  
Kinetics Of ◽  
Mean Molecular Weight

Abstract It has not yet been ascertained what constituent parts within the structure of various elastomers have the greatest influence on the reactivity of the elastomers. There are indications that the side chains, the presence of methyl groups acting as substitutes, and differences in spatial configurations, etc., all have definite effects. The present authors have investigated the oxidation of several different elastomers at different temperatures. The experiments were carried out both in the presence and in the absence of an inhibitor (phenyl-β-naphthylamine). The elastomers and the inhibitor were first carefully purified. The kinetics of autoxidations were studied volumetrically by means of an apparatus already described by one of the authors. A chainless molecular introduction of oxygen into the double bonds of the elastomer in the presence of the inhibitor was studied with the aid of our own previously described inhibitor methods. The study included the oxidation of butadiene elastomers containing different distributions of double bonds in the main and side chains, divinylstyrene rubber, and the hydrocarbons of natural rubber and gutta-percha. These products are distinguished by their different degrees of unsaturation, the number of side chains, the number of double bonds in both their main and side chains, the length of their molecular chains (the mean molecular weight), and their spatial configurations.

Exploring the formaldehyde reactivity of tannins with different molecular weight distributions: bayberry tannins and larch tannins

Holzforschung ◽  
2020 ◽  
Vol 74 (7) ◽  
pp. 673-682 ◽  
Author(s):  
Tao Yang ◽  
Mengqi Dong ◽  
Juqing Cui ◽  
Lu Gan ◽  
Shuguang Han
Keyword(s):  
Molecular Weight ◽  
High Performance ◽  
Average Molecular Weight ◽  
Degree Of Polymerization ◽  
Standard Curve ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Curve Method ◽  
Standard Curve Method ◽  
Tannin Degradation

AbstractIn recent years, tannin degradation has been used to obtain tannin materials with an optimal molecular weight distribution (MWD) for synthesizing tannin-formaldehyde (TF) resin with high performance, but the optimal MWD of tannins is still unknown. The excellent formaldehyde reactivity of tannins is the basis for the synthesis of high-performance TF resin. Based on the formaldehyde reactivity of tannins, bayberry tannins and larch tannins were used to explore the optimal MWD of tannins for TF resin synthesis. Progressive solvent precipitation (PSP) was used to obtain tannin fractions with different MWDs. The formaldehyde reactivity of tannins was determined using the modified Stiansy method combined with the standard curve method (GB/T 17657-2013). The bayberry tannin fraction [weight-average molecular weight (Mw) of acetylated tannin: 4115, mean degree of polymerization (mDP): 6.64] and the larch tannin fraction (Mw of acetylated tannin: 3906, mDP: 5.84) had the best formaldehyde reactivity. Furthermore, significant differences in the formaldehyde reactivity of condensed tannins (CTs) with different MWDs were observed. The obtained results can be used to purposefully degrade tannins to achieve an optimal MWD, which is beneficial for the production of TF adhesives with high performance.

Isoprene and Rubber. Part 23. Cryoscopic Measurements of Rubber Solutions

1931 ◽  
Vol 4 (2) ◽  
pp. 201-205
Author(s):  
H. Staudinger ◽  
H. F. Bondy
Keyword(s):  
Molecular Weight ◽  
Double Bonds ◽  
Chain Cleavage ◽  
Rubber Part

Abstract Pummerer, Andriessen, and Gündel published a work with this title which contains a number of remarks about the communication of Staudinger, Asano, Bondy, and Signer. The following discussion deals with this subject. 1. Molecular Weight Determinations of Rubber in Camphor according to East Determinations of the molecular weight of rubber in camphor cannot explain the constitution of rubber because, as has been explained before, when rubber is heated in melted camphor, at 170°-180°, a very pronounced decomposition of the rubber to semi-colloidal cleavage products takes place. The rubber molecule is very unstable as a consequence of the peculiar position of the double bonds in the chain; cleavage takes place with extraordinary ease, and attention has already been called to the fact that the cleavage of hexaphenylethane into triphenylmethyl, of dicyclopentadiene into cyclopentadiene, as well as the migration of the ally group, e. g., in phenylallyl ethers, the mobility of the substituents in allyl residues and finally the extremely easy depolymerization of rubber, all have one and the same cause: namely, that a substituent in the ally! group is very loosely combined. These facts, which are of such importance in the chemistry of rubber, should not be ignored as happens in most works on rubber. In order to study the decomposition, we carried out viscosity determinations. As the following experiments show, the viscosity of rubber is much less after melting in camphor than before. There occurred a very great decomposition at 170°, as was to be expected, and the relation t1/t2 which characterizes the decomposition is about 15. If pure rubber is decomposed in boiling tetralin the relation t1/t2 = 6.2. The decomposition in camphor is, therefore, surprisingly great, possibly because of the greater concentration of the dissolved rubber. The camphor solution used was 10 per cent, that of tetralin on the contrary was only 1 per cent.

Effect of Molecular Weight on Dynamic Mechanical Properties of SKD cis-1,4-Butadiene Rubber

1967 ◽  
Vol 40 (2) ◽  
pp. 517-521
Author(s):  
A. I. Marei ◽  
E. A. Sidorovich
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
Average Molecular Weight ◽  
Dynamic Mechanical Properties ◽  
Considerable Effect ◽  
Butadiene Rubber ◽  
Dynamic Mechanical ◽  
Temperature Range ◽  
Molecular Weights ◽  
Dynamic Mechanical Behavior

Abstract In the high-elastic temperature range the molecular weight has a considerable effect on the dynamic mechanical properties of linear (uncrosslinked) SKD cis-1, 4-butadiene rubber. In this temperature range an unequivocal correlation exists between the rebound resilience at a given temperature and the viscosity average molecular weight, and the determination of the resilience can therefore be recommended as a rapid method of finding the molecular weight of SKD. A similarity is found in the dynamic mechanical behavior of rubbers of different molecular weights in the high-elastic temperature range. In the low-temperature range an increase in the molecular weight of crystalline polymers of SKD is accompanied by an impairment of their elastic properties.

Molecular Weight Defined in Sol-Gel Analysis and Its Application to Evaluate Branching

1995 ◽  
Vol 68 (2) ◽  
pp. 287-296 ◽  
Author(s):  
Asahiro Ahagon
Keyword(s):  
Molecular Weight ◽  
Crosslink Density ◽  
Sol Gel ◽  
Average Molecular Weight ◽  
Degree Of Polymerization ◽  
Gel Point ◽  
Linear Polymers ◽  
Molecular Parameter ◽  
Branch Points ◽  
Number Average Molecular Weight

Abstract It is considered that many “linear” polymers are actually branched; however, it is difficult to show this with ordinary methods for an arbitrarily chosen polymer. Branching can be regarded as premature crosslinking below the gel point. Attention is then paid to the well-established Charlesby-Pinner Equation used for sol-gel analysis in crosslinking studies. It contains the number average degree of polymerization before crosslinking as a parameter. The molecular parameter is considered here to be that of the virtual linear polymer which would be obtained by unlinking any branch points contained in the polymer. Evidence is shown to support this. It is then possible to estimate the total number of linear components on an average molecule of a branched polymer by taking the ratio of the number average molecular weight measured by two methods, i.e., sol-gel analysis and an ordinary method like GPC. Further information about the branching structure can be obtained by additional measurements of effective crosslink density for a series of polymers obtained from similar polymerization processes.

scholarly journals Modeling and optimization of ethylene copoplymerization in high pressure reactor using difunctional initiators

2021 ◽  
Author(s):  
Pegah Khazraei Karimi Fard
Keyword(s):  
Molecular Weight ◽  
High Pressure ◽  
Free Radical ◽  
Average Molecular Weight ◽  
Tubular Reactor ◽  
Monomer Conversion ◽  
Optimization Method ◽  
Reactivity Ratio ◽  
Reactor Model ◽  
Control Variables

Free radical (co-)polymerization of low-density polyethylene (LDPE) is carried out commonly in high pressure autoclaves or tubular reactors. The severe thermodynamic conditions of the process hinder ethylene from going to full conversion. One remedy to improve the monomer conversion is to investigate the effectiveness of initiators, such as difunctional organic peroxides. In the present work, a kinetic model based on a postulated reaction mechanism for free radical ethylene (co-) polymerization initiated by difunctional initiators is applied to analyze the dynamic behavior of a continuous LDPE isothermal autoclave reactor and a non-isothermal tubular reactor. The model describes the rates of initiation, propagation and the population balance equations. It predicts variations of the initiator and monomer concentrations and reaction temperature as well as molecular weight distribution of reactive macromolecular species. Variations of the pressure, velocity and transport/physical properties of the reacting mixture were accounted for in the tubular reactor. Model predictions are compared to experimental data collected from literatures for one monofunctional (dioctanoyl) and two difunctional initiators namely, (2,2-bis(tert-butylperoxy)-butane and 2.5-dimetyl hexane-2t-butylperoxy-5perpivalate). In comparison with dioctanoyl peroxide, polymerization with difunctional initiators requires a lesser amount of initiators and gives higher ethylene conversion in a shorter time. The modeling of LSPE with difunctional initiators was then extended to ethylene copolymerization with vinyl acetate and butyl acrylate. The model helps to determine the influence of reactivity ratio on the end-use product properties. Details of modeling a multiple feed LSPE tubular reactor are included for both homo- and co-polymerization reactions. The effect of monomer and initiator injections on the productivity and (co)polymer rheology and composition are investigated as well. Finally, an optimization method was applied to determine the optimal values of control variables via maximization of an objective function expressed in terms of monomer conversion, number average molecular weight, polydispersity and final desired composition of copolymer product. The results show that we can obtain a polymer with desired characteristics by proper manipulation of the control variables.

Simulation for Polymerization Process of Styrene Butadiene Rubber (SBR)

2010 ◽  
Vol 148-149 ◽  
pp. 1661-1667
Author(s):  
Kai Gu ◽  
Xiao Di Xu ◽  
Ming Zhao
Keyword(s):  
Molecular Weight ◽  
Process Model ◽  
Average Molecular Weight ◽  
Polymerization Process ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Weight Average Molecular Weight ◽  
Sensitivity Analysis Method ◽  
Increasing Temperature ◽  
Styrene Butadiene

In this paper, Polymer Plus of Aspen Tech Inc. is used to establish a styrene-butadiene rubber (SBR) polymerization process model; the sensitivity analysis method is used to analyze concentration of the initiator, reaction temperature and other factors which influence production and molecular weight of product. It is concluded that increasing amount of initiator can improve production, while the molecular weight would increase at first and then decline; and along with the increasing temperature, weight-average molecular weight would lower and production of polymer PBS would increase; molecular weight of polymer and production of polymer would magnify along with increase of amount of emulsifier and volume of the reactor.

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