Dehydrochlorination of Poly(vinyl chloride) in Isotactic Systems

1993 ◽  
Vol 58 (2) ◽  
pp. 343-353 ◽  
Author(s):  
Jaroslav Burda ◽  
Rudolf Lukáš
Keyword(s):  
Molecular Weight ◽  
Point Of View ◽  
Low Molecular Weight ◽  
Ionic Mechanism ◽  
Polyene Chain ◽  
Subsequent Growth ◽  
Reaction Conditions ◽  
Poly Vinyl Chloride ◽  
Semiempirical Mndo ◽  
Thermodynamic Factors

The dehydrochlorination of isotactic, low-molecular-weight models of PVC, dimers to pentamers, was studied using the semiempirical MNDO method. The results obtained lead to the conclusion that the thermal dehydrochlorination of PVC can occur through either a radical or an ionic mechanism, depending on the reaction conditions. The arising conjugated polyene structures do not grow by the generally accepted "zip" mechanism, but rather through the "alternating growth" mechanism. A comparison was also made to the reactivity of isotactic and syndiotactic sequences from the point of view of kinetic and thermodynamic factors. It follows from the computations that the splitting off of the first HCl molecule is easier in the isotactic sequence, but that subsequent growth of the polyene chain occurs more readily in syndiotactic systems.

Thermal Dehydrochlorination of Poly(vinyl chloride) in Syndiotactic Systems

1992 ◽  
Vol 57 (1) ◽  
pp. 93-106 ◽  
Author(s):  
Jaroslav Burda ◽  
Rudolf Lukáš
Keyword(s):  
Molecular Weight ◽  
Reaction Mechanism ◽  
Hydrogen Chloride ◽  
Vinyl Chloride ◽  
Quantum Chemical ◽  
Low Molecular Weight ◽  
Ionic Mechanism ◽  
Reaction Conditions ◽  
Poly Vinyl Chloride ◽  
Ionic Intermediates

The thermal dehydrochlorination of syndiotactic poly(vinyl chloride) sequences has been studied theoretically on low-molecular weight models ranging from vinyl chloride dimer to pentamer using the semiempirical quantum chemical MNDO method. Parameters obtained with saturated systems and their change caused by the proceeding elimination of hydrogen chloride accompanied by the formation of the corresponding unsaturated structures are discussed with respect to the repeated chloroallyl or α-chloropolyene activation of the dehydrochlorination process. The study of the assumed radical and ionic intermediates is used in discussing the reaction mechanism of dehydrochlorination, and the radical or ionic mechanism is supposed to be operative depending on the reaction conditions.

SYNTHESIS OF ISOTOPICALLY LABELLED OLEFINS VIA THE WITTIG REACTION

1965 ◽  
Vol 43 (5) ◽  
pp. 1614-1624 ◽  
Author(s):  
J. G. Atkinson ◽  
M. H. Fisher ◽  
D. Horley ◽  
A. T. Morse ◽  
R. S. Stuart ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Dimethyl Sulfoxide ◽  
Wittig Reaction ◽  
Low Molecular Weight ◽  
Phosphonium Salts ◽  
Reaction Conditions ◽  
Selective Labelling ◽  
Wittig Reactions

A new application of the Wittig reaction to the preparation of olefins of low molecular weight which allows selective labelling in the vinyl or allyl positions with isotopes of hydrogen and carbon has been developed. Using the modification of the Wittig reaction introduced by E. J. Corey, in which a solution of the methylsulfinyl carbanion in dimethyl sulfoxide serves as the base, a series of olefins from C2 to C8 were synthesized. The synthesis was applied to the preparation of the following labelled compounds: 5-methylene-14C-bicyclo[2.2.1]hept-2-ene; propene-1-14C; 1-butene-1-14C; propene-1-d1; 2-methylpropene-1,1-d2; 2-methyl-d3-propene-3,3,3-d3; 2-methyl-2-butene-4,4,4-d3; 2-methyl-d3-2-butene-1,1,1-d3; methylene-d2-cyclohexane. For the synthesis of carbon-labelled olefins the reaction has few limitations since the intermediates and products are isotopically stable under the reaction conditions. Deuterium-labelled olefins can be obtained from deuterated formaldehyde or β-deuterated phosphonium salts, but α-deuteroketones and aldehydes and α-deuterophosphonium salts lose the isotope to the solvent.In all the Wittig reactions, benzene was formed as a by-product in 10–15% yield. The mechanism of benzene formation is probably analogous to that proposed by Seyferth involving the decomposition of a pentacovalent phosphorous intermediate.

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.

Low-molecular-weight glycerol esters as plasticizers for poly(vinyl chloride)

2014 ◽  
Vol 20 (2) ◽  
pp. 65-71 ◽  
Author(s):  
Oscar Yesid Suárez Palacios ◽  
Paulo César Narváez Rincón ◽  
Jean-Pierre Corriou ◽  
Mauricio Camargo Pardo ◽  
Christian Fonteix
Keyword(s):  
Molecular Weight ◽  
Vinyl Chloride ◽  
Low Molecular Weight ◽  
Poly Vinyl Chloride

scholarly journals COVID-19 PNEUMONIA: THE POINT OF VIEW OF VASCULAR SPECIALIST

2020 ◽  
pp. 21-27
Author(s):  
Luca Costanzo ◽  
Simona Antonina Grasso ◽  
Francesco Paolo Palumbo ◽  
Giorgio Ardita ◽  
Luigi Di Pino ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Low Molecular Weight Heparin ◽  
Antiviral Effect ◽  
Protein Product ◽  
Point Of View ◽  
Low Molecular Weight ◽  
Potential Mechanism ◽  
Therapeutic Dosage ◽  
Prognostic Features ◽  
D Dimer

The development of coagulopathy is emerging as one of the most significant poor prognostic features in COVID-19 pneumopathy. Thromboembolic manifestations such as pulmonary embolism and disseminated intravascular coagulation (DIC) have been reported and resulted in poor prognosis for the patient. Starting from the evidence in the literature, the purpose of this paper is to analyze potential mechanism involved in coagulation impairment following COVID-19 infection and identify possible vascular therapeutic strategies. D-dimer, a protein product of fibrin degradation, has been found elevated in the most severe cases and correlated to mortality. Potentially involved factors in the impairment of coagulation caused by viral infection include the dysregulated inflammatory response, platelet and endothelial dysfunction with impaired fibrinolysis. Heparin is an anticoagulant molecule that also showed anti-inflammatory properties and a potential antiviral effect. A favorable outcome was highlighted with the use of LMWH in severe patients with COVID-19 who meet the SIC criteria (sepsis-induced coagulopathy) or with markedly high D-dimer. The use of low molecular weight heparin could prevent thromboembolic complications in COVID-19 pneumopathy. However, the correct timing of prophylaxis according to the stage of COVID-19 disease and the appropriate therapeutic dosage to use in severe cases need further researches. Keywords: COVID-19, pneumonia, thrombosis, coagulopathy, D-dimer, low molecular weight heparin. Одним из наиболее неблагоприятных прогностических признаков пневмопатии при COVID-19 является развитие коагулопатии. У пациентов с COVID-19 наблюдались признаки тромбоэмболии, например тромбоэмболия легочной артерии и ДВС-синдром, что негативно сказывалось на здоровье пациента. Целью исследования является анализ потенциального механизма нарушения свертывания крови у пациентов, перенесших COVID-19, и определение возможных терапевтических стратегий. Было обнаружено, что у пациентов с тяжелой формой заболевания уровень D-димера, белкового продукта распада фибрина, повышен и напрямую взаимосвязан со смертностью. К факторам, влияющим на нарушение коагуляции, вызванной вирусной инфекцией, относятся неуправляемый воспалительный процесс, тромбоцитарная и эндотелиальная дисфункция с нарушением фибринолиза. Гепарин, являясь прямым антикоагулянтом, также обладает противовоспалительными свойствами и выраженным противовирусным эффектом. Благоприятный исход наблюдался при использовании низкомолекулярного гепарина у тяжелых пациентов с COVID-19 с коагулопатией, вызванной сепсисом, или высоким уровнем D-димера. Использование низкомолекулярного гепарина может предотвратить тромбоэмболические осложнения пневмопатии у пациентов с COVID-19. Тем не менее точное время профилактики в зависимости от стадии заболевания COVID-19 и соответствующая терапевтическая дозировка, которая может быть использована в тяжелых случаях, требуют дальнейших исследований. Ключевые слова: COVID-19, пневмония, тромбоз, коагулопатия, D-димер, низкомолекулярный гепарин.

scholarly journals Aerobic Epoxidation of Low-Molecular-Weight and Polymeric Olefins by a Supramolecular Manganese Porphyrin Catalyst

Catalysts ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 195 ◽  
Author(s):  
Ivan Bernar ◽  
Floris Rutjes ◽  
Johannes Elemans ◽  
Roeland Nolte
Keyword(s):  
Molecular Weight ◽  
Ambient Temperature ◽  
High Activity ◽  
Molecular Oxygen ◽  
Low Molecular Weight ◽  
Mechanistic Studies ◽  
Manganese Porphyrin ◽  
Reaction Conditions ◽  
Porphyrin Complex ◽  
Epoxidation Reaction

We report on the highly efficient epoxidation of low-molecular-weight and polymeric olefins catalyzed by a supramolecular manganese porphyrin complex using molecular oxygen as an oxidant and an aldehyde as a co-reductant. At ambient temperature and under optimized reaction conditions, the catalyst showed high activity and stereoselectivity. The efficiency of the supramolecular manganese porphyrin was higher than that of a reference porphyrin catalyst, possibly because it was more stable under the applied reaction conditions. Mechanistic studies suggest that a manganese oxo porphyrin complex may be an intermediate in the epoxidation reaction.

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