Continuous Ultrasonic Treatment of Uncured and Sulfur Cured SBR: Effect of Styrene Content

2005 ◽  
Vol 78 (4) ◽  
pp. 606-619 ◽  
Author(s):  
A. I. Isayev ◽  
S. H. Kim ◽  
Wenlai Feng
Keyword(s):  
Molecular Weight ◽  
Ultrasonic Treatment ◽  
Crosslink Density ◽  
Main Chain ◽  
Structural Characteristics ◽  
Average Molecular Weight ◽  
Chain Scission ◽  
Gel Fraction ◽  
Styrene Content ◽  
Good Agreement

Abstract Unvulcanized and vulcanized SBR samples with styrene content of 18 and 23.5% were used to investigate the effect of ultrasound treatment on their structural characteristics. Gel fraction and crosslink density of gel are measured. Molecular weight and molecular weight distribution of sol are studied to determine the level of degradation of the macromolecular chain in ultrasonically treated unvulcanized and vulcanized rubbers. It is shown that the weight and number average molecular weight of sol in devulcanized SBR is, respectively, lower and higher in the samples having higher styrene content. Ultrasonic treatment of virgin unvulcanized SBR causes generation of gel along with its main chain modification due to the competition between chain scission and crosslinking. The competitive reactions taking place during this treatment are discussed. It was found that the intermolecular bonds in SBR vulcanizates containing higher styrene content are easier to break. The structural characteristics of devulcanized SBR rubber were simulated using the Dobson-Gordon theory of rubber network statistics. A fairly good agreement between experimental data and theoretical prediction on normalized gel fraction vs. normalized crosslink density was achieved. The simulation of devulcanized SBR rubber indicated that the rate of crosslink rupture is much higher than that of main chain. The styrene content in SBR rubber does not affect kp/kα substantially.

scholarly journals Self-Stable Precipitation Polymerization Molecular Entanglement Effect and Molecular Weight Simulations and Experiments

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2243
Author(s):  
Jiali Qu ◽  
Yi Gao ◽  
Wantai Yang
Keyword(s):  
Molecular Weight ◽  
Maleic Anhydride ◽  
Molecular Conformation ◽  
Average Molecular Weight ◽  
Precipitation Polymerization ◽  
Radius Of Gyration ◽  
Propagation Mechanism ◽  
Reactive Molecular Dynamics ◽  
End Distance ◽  
Good Agreement

In this paper, we developed a reactive molecular dynamics (RMD) scheme to simulate the Self-Stable Precipitation (SP) polymerization of 1-pentene and cyclopentene (C5) with maleic anhydride (MAn) in an all-atom resolution. We studied the chain propagation mechanism by tracking the changes in molecular conformation and analyzing end-to-end distance and radius of gyration. The results show that the main reason of chain termination in the reaction process was due to intramolecular cyclic entanglement, which made the active center wrapped in the center of the globular chain. After conducting the experiment in the same condition with the simulation, we found that the distribution trend and peak value of the molecular-weight-distribution curve in the simulation were consistent with experimental results. The simulated number average molecular weight (Mn) and weight average molecular weight (Mw) were in good agreement with the experiment. Moreover, the simulated molecular polydispersity index (PDI) for cyclopentene reaction with maleic anhydride was accurate, differing by 0.04 from the experimental value. These show that this model is suitable for C5–maleic anhydride self-stable precipitation polymerization and is expected to be used as a molecular weight prediction tool for other maleic anhydride self-stable precipitation polymerization system.

Molecular Structure and Macroscopic Properties of Synthetic Cis-Poly(Isoprene)

1974 ◽  
Vol 47 (2) ◽  
pp. 342-356 ◽  
Author(s):  
V. A. Grechanovskii ◽  
I. Ya Poddubnyi ◽  
L. S. Ivanova
Keyword(s):  
Molecular Weight ◽  
Functional Groups ◽  
Chemical Structure ◽  
Sol Gel ◽  
Average Molecular Weight ◽  
Dense Network ◽  
Green Strength ◽  
Gel Fraction ◽  
Rubber Compounds ◽  
Processing Properties

Abstract By changing the sol-gel ratio and the structure of the gel fraction it is possible to obtain various grades of synthetic cis-poly(isoprene) which show promise for different applications in the tire and mechanical rubber goods industries. The processability of commercial SKI-3 rubber (at a given average molecular weight of sol) depends mainly on the structure of the gel fraction. Thus, for example, inferior processing properties of rubber compounds is associated primarily with the presence of tight gel. The content and structure of the gel fraction also significantly affect plasto-elastic properties of raw rubbers, e.g. a low plasticity of raw rubbers owes to the increased content of gel fraction. The reduced green strength of compounds based on SKI—3 rubber is accounted for by its chemical structure. Conventional methods used to change the properties of rubbers (including the variation in molecular weight, molecular weight distribution, branching degree, and variation in the content and structure of gel fraction) cannot be considered to be adequate to tackle the problem of the green strength of SKI—3 black stocks. The way to solve the problem appears to be the introduction of functional groups into the polymer chain at the stage of synthesis or processing. These functional groups should be active as to the formation of labile rubber—carbon black—rubber and/or rubber—rubber bonds. High purity of microstructure is necessary but not sufficient for obtaining the required level of green strength of compounded SKI—3. The gel fractions of SKI—3 rubber yield vulcanizates with a more dense network than the corresponding sol vulcanizates. The temperature dependence of the tensile strength is controlled by the network density of vulcanizates from high cis-1,4 poly(isoprene).

Synthesis of Smart Biodegradable Hydrogels Cellulose-Acrylamide Using Radiation as Controlled Release Fertilizers

2014 ◽  
Vol 896 ◽  
pp. 296-299 ◽  
Author(s):  
Deni Swantomo ◽  
Rochmadi ◽  
Kris Tri Basuki ◽  
Rahman Sudiyo
Keyword(s):  
Molecular Weight ◽  
Controlled Release ◽  
Crosslink Density ◽  
Graft Copolymerization ◽  
Young Modulus ◽  
Fickian Diffusion ◽  
Grafting Efficiency ◽  
Swelling Degree ◽  
Gel Fraction ◽  
Controlled Release Fertilizers

Smart biopolymer-based hydrogels was synthesized by graft copolymerization of acrylamide onto the rice straw cellulose backbones using simultaneous graft copolymerization by gamma radiation as initiator. Evidence of grafting was obtained from comparison of FTIR of the cellulose and grafted cellulose. The effect of acrylamide monomer concentration on grafting efficiency, gel fraction, swelling degree, crosslink density, molecular weight between crosslink (Mc), network mesh size (ξ) and Young Modulus were examined. It was found that grafting efficiency, gel fraction, crosslink density, and Young Modulus increases with increasing acrylamide concentration. Swelling degree, molecular weight between crosslink, and network mesh sizes decreases with the increasing acrylamide concentration. Furthermore, controlled release fertilizers from loaded hydrogels was analyzed in water. The urea fertilizer release mechanism from the hydrogels were Fickian diffusion. The diffusion coefficient of urea closely related to its crosslink density and network mesh sizes.

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.

First GPC results of terpyridine based chain extended supramolecular polymers: comparison with viscosity and analytical ultracentrifugation

e-Polymers ◽  
2006 ◽  
Vol 6 (1) ◽  
Author(s):  
Michael A. R. Meier ◽  
Harald Hofmeier ◽  
Caroline H. Abeln ◽  
Christos Tziatzios ◽  
Mircea Rasa ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Analytical Ultracentrifugation ◽  
Average Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Supramolecular Polymers ◽  
Supramolecular Polymer ◽  
Poly Ethylene ◽  
A Chain ◽  
First Time ◽  
Good Agreement

AbstractThe molecular weight of an extended metallo-supramolecular polymer, based on a α,ω-bis-terpyridine-poly(ethylene glycol) polymer linked via ruthenium(II) ions, was determined by gel permeation chromatography, viscosimetry as well as analytical ultracentrifugation. An optimized GPC method was applied for the first time to this kind of chain extended supramolecular polymers and the obtained results showed a good agreement with viscosimetry and analytical ultracentrifugation. A chain extended polymer with an average molecular weight of around 140 000 was found. These results clearly demonstrate that well-soluble high-molecular-weight metal-containing coordination polymers that are based on well-defined telechelics can be synthesized and fully characterized.

scholarly journals Kinetics and Thermodynamics of Ultrasound-Assisted Depolymerization of κ-Carrageenan

2016 ◽  
Vol 11 (1) ◽  
pp. 48 ◽  
Author(s):  
Ratnawati Ratnawati ◽  
Aji Prasetyaningrum ◽  
Dyah Hesti Wardhani
Keyword(s):  
Molecular Weight ◽  
Average Molecular Weight ◽  
Chain Scission ◽  
Number Average Molecular Weight ◽  
Covalent Bonds ◽  
Exponential Factor ◽  
Kinetics And Thermodynamics ◽  
Thermal Depolymerization ◽  
Ultrasound Assisted ◽  
Kinetics Of

<p>The ultrasound-assisted depolymerization of κ-carrageenan has been studied at various temperatures and times. The κ-carrageenan with initial molecular weight of 545 kDa was dispersed in water to form a 5 g/L solution, which was then depolymerized in an ultrasound device at various temperatures and times. The viscosity of the solution was measured using Brookfield viscometer, which was then used to find the number-average molecular weight by Mark-Houwink equation. To obtain the kinetics of κ-carrageenan depolymerization, the number-average molecular weight data was treated using midpoint-chain scission kinetics model. The pre-exponential factor and activation energies for the reaction are 2.683×10<sup>-7</sup> mol g<sup>-1</sup> min<sup>-1</sup> and 6.43 kJ mol<sup>-1</sup>, respectively. The limiting molecular weight varies from 160 kDa to 240 kDa, and it is linearly correlated to temperature. The results are compared to the result of thermal depolymerization by calculating the half life. It is revealed that ultrasound assisted depolymerization of κ-carrageenan is faster than thermal depolymerization at temperatures below 72.2°C. Compared to thermal depolymerization, the ultrasound-assisted process has lower values of E<sub>a</sub>, ΔG<sup>‡</sup>, ΔH<sup>‡</sup>, and ΔS<sup>‡</sup>, which can be attributed to the ultrasonically induced breakage of non-covalent bonds in κ-carrageenan molecules. Copyright © 2016 BCREC GROUP. All rights reserved</p><p><em>Received: 10<sup>th</sup> November 2015; Revised: 18<sup>th</sup> January 2016; Accepted: 19<sup>th</sup> January 2016</em></p><p><strong>How to Cite</strong>: Ratnawati, R., Prasetyaningrum, A., Wardhani, D.H. (2016). Kinetics and Thermodynamics of Ultrasound-Assisted Depolymerization of κ-Carrageenan. <em>Bulletin of Chemical Reaction Engineering &amp; Catalysis</em>, 11(1): 48-58. (doi:10.9767/bcrec.11.1.415.48-58)</p><p><strong>Permalink/DOI</strong>:<a href="/index.php/bcrec/editor/viewMetadata/%20http:/dx.doi.org/10.9767/bcrec.11.1.415.48-58"> http://dx.doi.org/10.9767/bcrec.11.1.415.48-58</a></p><p> </p>

The Course of Autoöxidation Reactions in Polyisoprenes and Allied Compounds. II. Hydroperoxidic Structure and Chain Scission in Low-Molecular Polyisoprenes

1943 ◽  
Vol 16 (1) ◽  
pp. 45-57
Author(s):  
Ernest Harold Farmer ◽  
Donald A. Sutton
Keyword(s):  
Molecular Weight ◽  
Average Molecular Weight ◽  
Substantial Reduction ◽  
Quantitative Relationship ◽  
Chain Scission ◽  
Side Reactions ◽  
Hydrocarbon Solvents ◽  
Hydrocarbon Chains ◽  
The Moment ◽  
Inverse Proportionality

Abstract One of the most astonishing phenomena connected with the chemistry of rubber is the ease with which it absorbs progressively very small percentages of oxygen, and suffers as a result drastic and progressive reduction of its molecular weight. The natural conclusion to be drawn is that the polyisoprene chains of the rubber are undergoing oxidative scission at one after another of their unsaturated centers, so that the original long hydrocarbon chains become divided into smaller and smaller fragments possessing oxygenated ends. Recent estimates of the molecular weight of rubber by viscosity and osmotic methods range from 240,000 to 360,000 for fractions of decreasing solubility in hydrocarbon solvents. If we accept these figures and assume for the moment that two atoms of oxygen are sufficient to sever the hydrocarbon chains at a double bond, then an absorption of only 0.009–0.013 per cent of oxygen (applied, of course, exclusively to scission reactions) should suffice to reduce the average molecular weight to one-half. If the observed reductions of molecular weight are to be ascribed solely to oxidative scission of the chains, then, provided oxygen-consuming side reactions are few, a fairly exact inverse proportionality may be expected to hold between the uptake of oxygen and the average molecular weight of the degraded rubber. The most striking reductions in the molecular weight per unit of oxygen absorbed must, of course, occur at the very early stages of oxidative fission, while the hydrocarbon chains are still very long, and to be able to follow effectively the quantitative relationship between these important reductions and the oxygen uptake, it is necessary to make experimental provision for the absorption, even distribution, and measurement of very minute quantities of oxygen. Minute though the overall proportion of oxygen necessary to produce a substantial reduction in molecular weight appears in practice to be, however, there is no evidence to indicate that the scission reaction ever follows the course most economical in oxygen, i.e.,

Gel formation by main-chain fracture of long-chain polymers

1955 ◽  
Vol 231 (1187) ◽  
pp. 521-534 ◽  
Keyword(s):  
Molecular Weight ◽  
Random Distribution ◽  
Main Chain ◽  
Average Molecular Weight ◽  
Gel Formation ◽  
Fracture Density ◽  
Chain Polymer ◽  
Infinite Extent ◽  
Limiting Value ◽  
Long Chain

The conditions are examined under which the fracture of main-chain bonds in a long-chain polymer, which would normally result in a decrease in average molecular weight, can nevertheless result in formation of a network of infinite extent (gel). It is assumed that the two end-groups produced at a fractured site can attack neighbouring molecules, and link them ­ selves to them. For an initially random distribution it is shown that gel formation will first occur when one molecule in three is thus fractured. The sol fraction is found to equal ( i /3 r ) 2 , where r/i is the average number of fractures per molecule; with increasing fracture density the sol therefore tends to zero. Where only a proportion of the fractures result in linking, the sol fraction decreases to a limiting value. Expressions are derived for many of the parameters of the sol and gel fractions and for the swelling. The results obtained are compared with those for crosslinking of polymers with a similar molecular weight distribution. To distinguish the process considered in this paper from that usually referred to as crosslinking, the term endlinking is proposed.

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