scholarly journals Identity of Low-Molecular-Weight Species Formed in End-To-End Cyclization Reactions Performed in THF

Polymers ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 844 ◽  
Author(s):  
Ching Pan ◽  
Katherine Xia ◽  
Samantha Parker ◽  
Eric Tillman
Keyword(s):  
Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Cyclization Reaction ◽  
Low Molecular Weight ◽  
Linear Polymers ◽  
End Joining ◽  
Cyclization Reactions ◽  
Molar Ratios ◽  
End To End ◽  
Material Forming

Cyclic polymers were produced by end-to-end coupling of telechelic linear polymers under dilute conditions in THF, using intramolecular atom transfer radical coupling or click chemistry. In addition to the expected shift to longer elution times on gel permeation chromatography (GPC) indicative of the formation of cyclic product, lower molecular weight species were consistently observed upon analysis of the unpurified cyclization reaction mixture. By systematically removing or altering single reaction components in the highly dilute cyclization reaction, it was found that THF itself was responsible for the low-molecular-weight material, forming oligomeric chains of poly(THF) regardless of the other reaction components. When the reactions were performed at higher concentrations and for shorter time intervals, conducive to intermolecular chain-end-joining reactions, the low-molecular-weight peaks were absent. Isolation of the material and analysis by 1H NMR confirmed that poly(THF) was being formed in the highly dilute conditions required for cyclization by end-to-end coupling. When a series of mock cyclization reactions were performed with molar ratios of the reactants held constant, but concentrations changed, it was found that lower concentrations of reactants led to higher amounts of poly(THF) side product.

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.

scholarly journals Fractionation of lignosulphonates released during the early stages of delignification

1983 ◽  
Vol 61 (2) ◽  
pp. 416-420 ◽  
Author(s):  
Norman G. Lewis ◽  
David A. I. Goring ◽  
Alfred Wong
Keyword(s):  
Molecular Weight ◽  
High Performance ◽  
Black Spruce ◽  
Gel Permeation Chromatography ◽  
Bimodal Distribution ◽  
High Yield ◽  
Low Molecular Weight ◽  
Lower Yield ◽  
Spruce Wood ◽  
Gel Permeation

High-yield spent bisulphite liquor (HY-SBL) from sulphonated black spruce wood (Piceamariana) was fractionated by gel permeation chromatography (GPC) and by high-performance liquid chromatography (HPLC). The GPC fractionation gave a wide bimodal distribution, whereas with HPLC, a more detailed resolution was seen with the bulk of the fraction giving several clearly defined peaks. The paucidisperse material was further concentrated by a bulk fractionation of the crude SBL which included complexing the lignosulphonates with dicyclohexylamine. The isolated paucidisperse material was found to be dialyzable and to constitute 90% of the lignosulphonate in the sample of SBL. If the bisulphite pulp obtained was recooked in fresh acid sulphite liquor to a lower yield, most of the lignosulphonate dissolved was widely polydisperse with no indication of the discrete components resolvable by HPLC. However, 25% of the lignin made soluble was in the form of the paucidisperse fractions. In all, we were able to obtain about 50% of the lignin in spruce wood as a relatively low molecular weight lignosulphonate resolvable into discrete fractions by HPLC.

The Research of Silane Oligomer with Lower Valatilization Rate for Protecting Concrete

2013 ◽  
Vol 357-360 ◽  
pp. 1318-1322 ◽  
Author(s):  
Hong Yao Sun ◽  
Zheng Yang ◽  
Gao Xia Sun ◽  
Xue Feng Xu
Keyword(s):  
Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Chloride Ions ◽  
Polymerization Reaction ◽  
Low Molecular Weight ◽  
Construction Process ◽  
Reaction Conditions ◽  
Hydrophobic Agent ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

As one of the measures to improve the durability of concrete, silane penetrating hydrophobic agents can preserve the properties of respiratory function of concrete and can prevent the penetration from harmful medium such as chloride ions. Because of low molecular weight of the silane penetrating hydrophobic agent such as isobutyl triethoxysilane, high volatilization rate of silane can result in waste of material in construction process. The silane oligomer was obtained by radical polymerization reaction with suitable monomers, initiators and reaction conditions. Furthermore, we verified the structure of the silane oligomer by FT-IR spectroscopy and got its molecular weight by GPC(Gel Permeation Chromatography). The silane oligomer with lower volatilization rate has excellent properties of hydrophobicity, higher penetration depth and resistance to chloride ions penetration.

scholarly journals Determining the Dilution Exponent for Entangled 1,4-Polybutadienes Using Blends of Near-Monodisperse Star with Unentangled, Low Molecular Weight Linear Polymers

2019 ◽  
Vol 52 (4) ◽  
pp. 1757-1771 ◽  
Author(s):  
Ryan Hall ◽  
Beom-Goo Kang ◽  
Sanghoon Lee ◽  
Taihyun Chang ◽  
David C. Venerus ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Low Molecular Weight ◽  
Linear Polymers

Study of the fractional composition of wheat proteins and macaroni products during storage

2021 ◽  
pp. 776-783
Author(s):  
I.A. Tarasova ◽  
K.B. Gurieva ◽  
E.A. Tarasova ◽  
S.L. Beletskiy ◽  
N.A. Khaba
Keyword(s):  
Molecular Weight ◽  
Fractional Composition ◽  
Gel Permeation Chromatography ◽  
Weight Fraction ◽  
Protein Fractions ◽  
Low Molecular Weight ◽  
English Version ◽  
Wheat Proteins ◽  
Photometric Detection ◽  
Main Protein

The results of the molecular weight distribution of wheat proteins and macaroni products are presented. The fractional composition of proteins was determined by gel permeation chromatography on a Knauer Smartline chromatograph; preliminary hydrolysis was carried out using a thermostable bacterium α-Amylase, then it was centrifuged, filtered through a Teflon filter, and the size of protein molecules was determined by photometric detection at a wavelength of 280 nm. It has been shown that the main protein fraction in both wheat and macaroni products is a low molecular weight fraction up to 3 kD (up to 79.4% of all protein fractions). The fraction with low and medium molecular weight from 3 to 10 kD accounted for 2.7 to 48.2%, while the fraction with a molecular weight of more than 10 kD accounted for up to 15.2%. During storage, a redistribution of protein fractions and their enlargement were noted. English version of the article is available at URL: https://panor.ru/articles/study-of-the-fractional-composition-of-wheat-proteins-and-pasta-products-during-storage/74321.html

Autohydrolysis of aspen milled wood lignin

1980 ◽  
Vol 58 (7) ◽  
pp. 669-676 ◽  
Author(s):  
Jairo H. Lora ◽  
Morris Wayman
Keyword(s):  
Molecular Weight ◽  
Populus Tremuloides ◽  
Soluble Fraction ◽  
Gel Permeation Chromatography ◽  
Insoluble Fraction ◽  
Low Molecular Weight ◽  
Milled Wood Lignin ◽  
Insoluble Material ◽  
Initial Generation ◽  
Insoluble Product

In order to obtain further understanding of the nature of lignin reactions during autocatalysed hydrolysis (autohydrolysis) of wood, milled wood lignin (MWL) was isolated from aspen (Populus tremuloides) and treated under autohydrolysis conditions. By this means reactions of the lignin itself could be distinguished from those taking place between lignin and the carbohydrate or other components of the wood. The material after the reaction was separated into a dioxane insoluble fraction (DI), a dioxane soluble but ether insoluble fraction (DSEI), and an ether soluble fraction (ES). Studies were carried out on the DI and DSEI fractions; no direct study was made of the small ES fraction.The formation of DI material increased linearly during the first 7.5 min at 170 °C and then levelled off. At the same time DSEI decreased and then levelled off. Gel permeation chromatography of the DSEI fraction suggested that during autohydrolysis there is an initial generation of low molecular weight fragments which recombine to form first a high molecular weight soluble fraction and from this the insoluble product. The DSEI fraction contained increased conjugated and unconjugated keto groups. Carboxylic acids were also detected; they have been attributed to the reincorporation of low molecular weight aromatic acids generated by the hydrolysis of the corresponding esters. The dioxane insoluble (DI) fraction had fewer unconjugated keto groups than the DSEI fraction, indicating that these groups participated in the condensation reactions leading to the formation of insoluble material. These probably involve position 6 of the aromatic ring.

Study of the Carbohydrate Content of Mucus Glycoproteins from Normal and Diseased Colons

1981 ◽  
Vol 61 (2) ◽  
pp. 229-234 ◽  
Author(s):  
J. R. Clamp ◽  
G. Fraser ◽  
A. E. Read
Keyword(s):  
Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Weight Fraction ◽  
Carbohydrate Content ◽  
Low Molecular Weight ◽  
High Molecular Weight Fraction ◽  
Mucus Glycoprotein ◽  
Active Colitis ◽  
High Mannose ◽  
Mucus Glycoproteins

1. Mucus samples obtained from colectomy colons from 10 patients with ulcerative colitis and four patients with Crohn's disease of the colon, together with samples from 10 normal postmortem colons, have been studied. 2. Two glycoprotein fractions were isolated from mucosal scrapings by gel-permeation chromatography. The high-molecular-weight fraction consisted largely of mucus glycoproteins and was further purified to the glycopolypeptides. The low-molecular-weight fraction contained a glycoprotein with a high mannose content. The carbohydrate content of both the mucus glycoprotein and glycopolypeptide fractions were significantly reduced in active colitis. 3. Oligosaccharides were prepared from the mucus glycoprotein material. In the normal material more than half the units contained eight or more monosaccharide residues, whereas in the disease material the bulk of the units were smaller than this.

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