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).

scholarly journals Characterisation of Sequential Solvent Fractionation and Base-catalysed Depolymerisation of Treated Alkali Lignin

BioResources ◽  
2015 ◽  
Vol 10 (3) ◽  
pp. 4137-4151 ◽  
Author(s):  
Aikfei Ang ◽  
Zaidon Ashaari ◽  
Edi Suhaimi Bakar ◽  
Nor Azowa Ibrahim
Keyword(s):  
Molecular Weight ◽  
Chemical Structure ◽  
Average Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Solubility Parameters ◽  
Low Molecular Weight ◽  
Sequential Fractionation ◽  
Weight Average Molecular Weight ◽  
Solvent Fractionation ◽  
Alkali Lignin

An alkali lignin (OL) with a weight-average molecular weight (Mw) of 11646 g/mol was used to prepare low-molecular weight lignin for resin synthesis. The low-molecular weight lignin feedstock was obtained via base-catalysed depolymerisation (BCD) treatments at different combined severity factors. Sequential fractionation of the OL and BCD-treated lignins using organic solvents with different Hildebrand solubility parameters were used to alter the homogeneity of the OL. The yield and properties of OL itself and OL and BCD-treated OL dissolved in propan-1-ol (F1), ethanol (F2), and methanol (F3) were determined. Regardless of the treatment applied, a small amount of OL was dissolved in F1 and F2. The BCD treatment did not increase the yield of F1 but did increase the yields of F2 and F3. Gel permeation chromatography (GPC) showed that the repolymerization reaction occurred in F3 for all BCD-treated OL, so these lignins were not suitable for use as feedstocks for resin production. The GPC, 13Carbon-nuclear magnetic resonance, and Fourier transform infrared spectroscopy analyses confirmed that the F3 in OL exhibited the optimum yield, molecular weight distribution, and chemical structure suitable for use as feedstocks for resin synthesis.

Growth of PLZT Thick Films by Polymer Modified Sol-Gel Processing for Optical Shutting

2008 ◽  
Vol 136 ◽  
pp. 67-74 ◽  
Author(s):  
Z.H. Du ◽  
T.S. Zhang ◽  
H.M. Shang ◽  
X.L. Chen ◽  
Jan Ma
Keyword(s):  
Molecular Weight ◽  
Critical Thickness ◽  
Thick Films ◽  
Sol Gel ◽  
Average Molecular Weight ◽  
Liquid Phase Sintering ◽  
Optical And Electrical Properties ◽  
Densification Behavior ◽  
Free Films ◽  
Gel Processing

PLZT9/65/35 thick films were prepared from the solution containing PVP360 (polyvinylpyrrolidone, with average molecular weight of 360000). With the solutions, the critical thickness of a single PLZT layer could increase to ~624nm compared with 77nm-thick films prepared without PVP360. Furthermore, by adding 20~35% excess of Pb to the precursor solutions, the nano-porous rosette-like structures and a small amount of pyrochlore remnant, which were found very common in the PVP-modified films, could be eliminated. 35% Pb excess was also found to initiate liquid-phase sintering, leading to dense and crack-free films. The effect of Pb excess on the rosette removal and densification behavior of the films was discussed. Moreover, the optical and electrical properties of the PLZT films with 35% Pb excess were also studied.

scholarly journals Synthesis of hydroxyl terminated liquid natural rubber by oxidative depolymerization of deproteinized natural rubber

2016 ◽  
Vol 54 (3) ◽  
pp. 340 ◽  
Author(s):  
Le Duc Giang ◽  
Dinh Long Mong Thao ◽  
Hoang Thi Huong ◽  
Le Thi Thu Hiep
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Chemical Structure ◽  
Spectroscopic Analysis ◽  
Average Molecular Weight ◽  
Analytical Data ◽  
Ammonium Persulfate ◽  
Weight Average Molecular Weight ◽  
Liquid Natural Rubber ◽  
Deproteinized Natural Rubber

Hydroxyl terminated liquid natural rubber (HTLNR) was prepared by the depolymerization of deproteinized natural rubber (DPNR) in mixture of toluene and water at 60oC for 24 hours in the presence of ammonium persulfate as an initiator and tetrahydrofuran (THF) as a homogenizing agent. GPC analysis revealed that the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of HTLNR were found to be 4.334×103 g/mol and 11.702×103 g/mol, respectively, with polydispersity index (PDI) of  2.7. The chemical structure of HTLNR was determined by FTIR and 1H-NMR and 13C-NMR spectroscopic analysis. The mechanism of depolymerization and hydroxylation of NR to form HTNR based on the analytical data is also suggested in this study.

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.

On the structure alteration of crosslinkable gelatin coupled with methacrylic acid and its hydrogel

e-Polymers ◽  
2012 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiaohong Hu ◽  
Dan Li ◽  
Feng Zhou ◽  
Changyou Gao
Keyword(s):  
Molecular Weight ◽  
Triple Helix ◽  
Sol Gel ◽  
Average Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Apparent Molecular Weight ◽  
Small Range ◽  
Scanning Calorimetry ◽  
Physical Chemical ◽  
Substitution Degree

AbstractPhysical structures of a crosslinkable gelatin derivative (GM) were studied in terms of alteration of apparent molecular weight, triple helix content and mechanical strength. The GM with a substitution degree (DS) of 49% and 79% was prepared by grafting mechacrylic acid (MA), which was able to form injectable hydrogel by photoinitiating polymerization. The zeta potential was increased along the increase of DS. After modification, the apparent number-average molecular weight (Mn) detected by gel permeation chromatography was decreased to about 2/3 of gelatin, while the apparent weight-average molecular weight (Mw) was changed within a small range. Differential scanning calorimetry and circular dichroism (CD) revealed that ability of triple-helix formation of GM was decreased along with the increase of DS and decrease of GM concentration. After photocrosslinking, the sol-gel transition of GM49 physical-chemical hydrogel still existed, but completely disappeared for its chemical hydrogel. The physical-chemical hydrogel showed a larger storage modulus at 20°C than at 37°C as a result of additional physical crosslinking.

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.

Terpenes, Phenylpropanoids, Sulfur and Other Essential Oil Constituents as Inhibitors of Cholinesterases

2020 ◽  
Vol 27 (26) ◽  
pp. 4297-4343 ◽  
Author(s):  
Franko Burčul ◽  
Ivica Blažević ◽  
Mila Radan ◽  
Olivera Politeo
Keyword(s):  
Molecular Weight ◽  
Biological Activity ◽  
Essential Oils ◽  
Functional Groups ◽  
Organic Compounds ◽  
Chemical Structure ◽  
Low Molecular Weight ◽  
Active Compounds ◽  
Oxygenated Compounds ◽  
Nitrogen Containing Compounds

: Essential oils constituents are a diverse family of low molecular weight organic compounds with comprehensive biological activity. According to their chemical structure, these active compounds can be divided into four major groups: terpenes, terpenoids, phenylpropenes, and "others". In addition, they may contain diverse functional groups according to which they can be classified as hydrocarbons (monoterpenes, sesquiterpenes, and aliphatic hydrocarbons); oxygenated compounds (monoterpene and sesquiterpene alcohols, aldehydes, ketones, esters, and other oxygenated compounds); and sulfur and/or nitrogen containing compounds (thioesters, sulfides, isothiocyanates, nitriles, and others). : Compounds that act as cholinesterase inhibitors still represent the only pharmacological treatment of Alzheimer´s disease. Numerous in vitro studies showed that some compounds, found in essential oils, have a promising cholinesterase inhibitory activity, such as α-pinene, δ-3-carene, 1,8-cineole, carvacrol, thymohydroquinone, α- and β-asarone, anethole, etc. : Essential oils constituents are a diverse family of low molecular weight organic compounds with comprehensive biological activity. According to their chemical structure, these active compounds can be divided into four major groups: terpenes, terpenoids, phenylpropenes, and "others". In addition, they may contain diverse functional groups according to which they can be classified as hydrocarbons (monoterpenes, sesquiterpenes, and aliphatic hydrocarbons); oxygenated compounds (monoterpene and sesquiterpene alcohols, aldehydes, ketones, esters, and other oxygenated compounds); and sulfur and/or nitrogen containing compounds (thioesters, sulfides, isothiocyanates, nitriles, and others).

scholarly journals Preparation and Characterization of Low-Molecular-Weight Natural Rubber Latex via Photodegradation Catalyzed by Nano TiO2

Polymers ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1216 ◽  
Author(s):  
Suhawati Ibrahim ◽  
Nadras Othman ◽  
Srimala Sreekantan ◽  
Kim Tan ◽  
Zairossani Mohd Nor ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Titanium Dioxide ◽  
Natural Rubber ◽  
Chemical Structure ◽  
Sol Gel ◽  
Natural Rubber Latex ◽  
Low Molecular Weight ◽  
Rubber Latex ◽  
Liquid Natural Rubber ◽  
New Applications

Natural rubber is one of the most important renewable biopolymers used in many applications due to its special properties that cannot be easily mimicked by synthetic polymers. To sustain the existence of natural rubber in industries, modifications have been made to its chemical structure from time to time in order to obtain new properties and to enable it to be employed in new applications. The chemical structure of natural rubber can be modified by exposure to ultraviolet light to reduce its molecular weight. Under controlled conditions, the natural rubber chains will be broken by photodegradation to yield low-molecular-weight natural rubber. The aim of this work was to obtain what is known as liquid natural rubber via photodegradation, with titanium dioxide nanocrystals as the catalyst. Titanium dioxide, which was firstly synthesized using the sol–gel method, was confirmed to be in the form of an anatase, with a size of about 10 nm. In this work, the photodegradation was carried out in latex state and yielded low-molecular-weight natural rubber latex of less than 10,000 g/mol. The presence of hydroxyl and carbonyl groups on the liquid natural rubber (LNR) chains was observed, resulting from the breaking of the chains. Scanning electron microscopy of the NR latex particles showed that titanium dioxide nanocrystals were embedded on the latex surface, but then detached during the degradation reaction.

The Cross-Linking of Rubber by Pile Radiation

1955 ◽  
Vol 28 (1) ◽  
pp. 1-11
Author(s):  
Arthur Charlesby
Keyword(s):  
Molecular Weight ◽  
Radiation Dose ◽  
Average Molecular Weight ◽  
High Energy ◽  
Cross Linking ◽  
Gel Formation ◽  
Gel Fraction ◽  
Cross Links ◽  
The Cross ◽  
The Relationship

Abstract The degree of cross-linking produced in a rubber by high-energy radiation is proportional to the radiation dose. Unit radiation, as defined in the text, links 1.1 per cent of the isoprene units. The distribution of molecular weight prior to cross-linking agrees with a Poisson distribution. Gel formation begins for γ=0.5. From the radiation dose required to initiate gel formation, the initial average molecular weight can be deduced. The increase of gel fraction with radiation dose follows the relationship deduced theoretically in the first part of the article. Measurement of gel fraction gives an alternative method of calculating the initial average molecular weight. Where some cross-linking is present in the rubber prior to cross-linking, this may be evaluated. In accordance with the theory presented in the article, the viscosity of the sol fraction rises initially, then decreases as the radiation dose increases. This provides a third method of measuring molecular weight, or of relating viscosity to molecular weight, which can be deduced from measurement of gel fraction. The swelling of very lightly cross-linked gel has been compared with the Flory-Huggins relationship, which is found to hold down to very lightly cross-linked gels for which the cross-linking index is only 0.2. To obtain this agreement, it is necessary to consider the swelling of the dry gel, rather than the whole specimen, and to ignore the cross-links required to form the gel itself.

Synthesis and characteristic applications of silicon resins for the modifying agent in heat conduction

2021 ◽  
pp. 004051752110342
Author(s):  
Chung-Feng Jeffrey Kuo ◽  
Naveed Ahmad ◽  
Sheng-Yu Lin ◽  
Garuda Raka Satria Dewangga ◽  
Min-Yan Dong
Keyword(s):  
Molecular Weight ◽  
Heat Tolerance ◽  
Pyrolysis Temperature ◽  
Sol Gel ◽  
Average Molecular Weight ◽  
Silicone Resin ◽  
Modifying Agent ◽  
Sol Gel Process ◽  
Energy Retention ◽  
Silicon Resin

Heat energy retention and dissipation have become key points of global smart textiles in recent years. This study describes the designing of silicon resin by using a sol–gel process, which acts as the modifying agent for siloxane substrate. The modifying agent was effectively blocked by silicon resin mixed with the ethylene or aluminum bond group, to control the molecular weight. Advanced polymer chromatography confirmed that the number average molecular weight (Mn) of silicon resin is 41,301 g mol−1, the weight average molecular weight (Mw) is 47,982 g mol−1, and the molecular weight distribution is 1.1617, which is relatively narrow. When the addition of vinyl groups is 5%, the silicone resin Mn decreases to 18,906 g mol−1 and Mw decreases to 28,641 g mol−1. When the addition of aluminum bond groups is 5%, the silicone resin Mn decreases to 17,497 g mol−1 and Mw decreases to 27,114 g mol−1. The result of thermogravimetric analysis shows that the pyrolysis temperature rises from 265.43°C to 266.17°C after the ethylene is added to the silicon resin, and the index of heat tolerance increases from 179.14°C to 191.38°C. After the addition of aluminum bond groups, the pyrolysis temperature rises from 265.43°C to 309.37°C, and the index of heat tolerance increases from 179.14°C to 193.09°C, meaning the silicone resin has higher thermal stability.

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