From Stereospecific Polymerization to Asymmetric Autocatalytic Synthesis of Macromolecules

1965 ◽  
Vol 38 (1) ◽  
pp. 37-60 ◽  
Author(s):  
Giulio Natta
Keyword(s):  
Heterogeneous Catalysts ◽  
Regular Structure ◽  
Scientific Basis ◽  
Point Of View ◽  
Crystalline Polymers ◽  
Molecular Weights ◽  
Macromolecular Chemistry ◽  
Stereospecific Polymerization ◽  
Synthetic Macromolecules ◽  
Very High

Abstract Macromolecular chemistry is a relatively young science. Though natural and synthetic macromolecular substances had long been known, it was only between 1920 and 1930 that Hermann Staudinger placed our knowledge of the chemical structure of several macromolecular substances on a scientific basis. In the wake of Staudinger's discoveries and hypotheses, macromolecular chemistry has made considerable progress. Very many synthetic macromolecular substances were prepared both by polymerization and by polycondensation; methods were found for the regulation of the value and distribution of molecular weights; attempts were made to clarify the relationships existing among structure, chemical regularity, molecular weight, and physical and technological properties of the macromolecular substances. It was far more difficult to obtain synthetic macromolecules having a regular structure both from the chemical and steric point of view. An early result in this field, which aroused a certain interest in relation to elastomers, was the preparation of a polybutadiene having a very high content of trans-1,4 monomeric units, in the presence of heterogeneous catalysts. A wider development of this field was made possible by the recent discovery of stereospecific polymerization. This led to the synthesis of sterically regular polymers as well as to that of new classes of crystalline polymers.

scholarly journals IL 50° ANNIVERSARIO DEL NOBEL A GIULIO NATTA

2016 ◽  
Author(s):  
Italo Pasquon
Keyword(s):  
Economic Value ◽  
Nobel Laureate ◽  
Point Of View ◽  
Industrial Chemistry ◽  
Natural Polymers ◽  
Scientific Publications ◽  
Macromolecular Chemistry ◽  
Worldwide Production ◽  
The World ◽  
Stereospecific Polymerization

On March 11, 1954 Giulio Natta synthetized isotactic polypropylene. It was the first synthesis, in laboratory, of a polymer having a sterically ordered structure, similar to those found in some natural polymers like, for instance, natural rubber and cellulose. This meaningful aspect was emphasized by Prof. Fredga of the Swedish Academy in his speech at the customary ceremony of Nobel Prize on December 10, 1963, when he stated “Natta has broken the monopoly of nature”. With the polypropylene synthesis Natta discovered the “stereospecific polymerization” defined by Toblosky (Princeton University) and by Flory, one of the most eminent scientist in the macromolecular chemistry and future Nobel laureate in Chemistry (1974), a “revolution” in the macromolecular field. Natta was recognized as the “father” of stereospecific polymerization. The Journal of Polymer Science, vol. 51 (1961), dedicated to Natta, reports “Seldom a scientific contribution aroused such a deep and fundamental interest and was followed by such a rapid technical development as the series of publications by Professor Natta and his coworkers on the stereospecific polymerization. Yet Professor Natta has succeeded in maintaining undisputed leadership in this field of polymer chemistry and continues to surprise his colleagues with new and unexpected results”. The revolution brought by Natta in the field of macromolecular chemistry involved the entire scientific and industrial world specialized in that area. Soon after 1954-55 a lot of universities and industrial laboratories around the world started to work on activities concerning the novel stereospecific polymerization. The results of these studies are reported in about a thousand scientific publications and some hundreds of patents issued from the Milan Polytechnic Institute of Industrial Chemistry between 1955 and 1977 (concentrated in 1955-57). The importance of polypropylene from the commercial point of view is evident from the fact that the world production of various types of polypropylene now stands at about 60 million tons/year. It is estimated that the related global economic value approaches the second place over all synthetic products, after polyethylene, together with ammonia, and before other products such as urea, polymers of styrene and vinyl chloride, nylons, etc. For their part 1,4-cis polybutadiene and copolymers based on ethylene and propylene occupy respectively the second and the third place in terms of worldwide production and market value among synthetic elastomers, after styrene-butadiene rubbers (SBR). More information concerning the personality and the scientific and didactic activities of Giulio Natta and his relations with the scientific and industrial world are reported on the internet site www.giulionatta.it containing the “Giulio Natta Archive” (more than 40.000 pages).

Der Sommer und Herbst 2003 aus phänologischer Sicht | Summer and autumn 2003 from a phenological point of view

2004 ◽  
Vol 155 (5) ◽  
pp. 142-145 ◽  
Author(s):  
Claudio Defila
Keyword(s):  
Time Series ◽  
New Record ◽  
Point Of View ◽  
Late Spring ◽  
Mean Deviation ◽  
Leaf Shedding ◽  
The Mean ◽  
Very High ◽  
Selection Of

The record-breaking heatwave of 2003 also had an impact on the vegetation in Switzerland. To examine its influences seven phenological late spring and summer phases were evaluated together with six phases in the autumn from a selection of stations. 30% of the 122 chosen phenological time series in late spring and summer phases set a new record (earliest arrival). The proportion of very early arrivals is very high and the mean deviation from the norm is between 10 and 20 days. The situation was less extreme in autumn, where 20% of the 103 time series chosen set a new record. The majority of the phenological arrivals were found in the class «normal» but the class«very early» is still well represented. The mean precocity lies between five and twenty days. As far as the leaf shedding of the beech is concerned, there was even a slight delay of around six days. The evaluation serves to show that the heatwave of 2003 strongly influenced the phenological events of summer and spring.

scholarly journals FEBID 3D-Nanoprinting at Low Substrate Temperatures: Pushing the Speed While Keeping the Quality

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1527
Author(s):  
Jakob Hinum-Wagner ◽  
David Kuhness ◽  
Gerald Kothleitner ◽  
Robert Winkler ◽  
Harald Plank
Keyword(s):  
Volume Growth ◽  
Point Of View ◽  
High Fidelity ◽  
Direct Write ◽  
General Picture ◽  
3D Space ◽  
Design Flexibility ◽  
Substrate Temperatures ◽  
Very High ◽  
Comprehensive Discussion

High-fidelity 3D printing of nanoscale objects is an increasing relevant but challenging task. Among the few fabrication techniques, focused electron beam induced deposition (FEBID) has demonstrated its high potential due to its direct-write character, nanoscale capabilities in 3D space and a very high design flexibility. A limitation, however, is the low fabrication speed, which often restricts 3D-FEBID for the fabrication of single objects. In this study, we approach that challenge by reducing the substrate temperatures with a homemade Peltier stage and investigate the effects on Pt based 3D deposits in a temperature range of 5–30 °C. The findings reveal a volume growth rate boost up to a factor of 5.6, while the shape fidelity in 3D space is maintained. From a materials point of view, the internal nanogranular composition is practically unaffected down to 10 °C, followed by a slight grain size increase for even lower temperatures. The study is complemented by a comprehensive discussion about the growth mechanism for a more general picture. The combined findings demonstrate that FEBID on low substrate temperatures is not only much faster, but practically free of drawbacks during high fidelity 3D nanofabrication.

scholarly journals Inducible overexpression and secretion of int-1 protein.

1989 ◽  
Vol 9 (8) ◽  
pp. 3377-3384 ◽  
Author(s):  
J Papkoff
Keyword(s):  
Molecular Weight ◽  
Cho Cells ◽  
Secretory Pathway ◽  
Mammary Tissue ◽  
Neural Tubes ◽  
Molecular Weights ◽  
Activation Of Transcription ◽  
Mouse Mammary Tumor ◽  
Tumor Virus ◽  
Very High

The int-1 proto-oncogene is a target for insertional activation of transcription by mouse mammary tumor virus in many murine mammary tumors. Whereas no expression of int-1 is seen in normal mammary tissue, int-1 RNA can be detected in normal mice in the neural tubes of midgestation embryos and in postmeiotic spermatocytes from adult testes. I report here the results of a study in which several different antibodies against synthetic peptides were produced and used to characterize the processing and secretion of int-1 protein. CHO cells were transfected with an inducible int-1 expression vector that was subsequently amplified to generate cell lines expressing very high levels of int-1 protein. Immunoprecipitation of [35S]cysteine-labeled cell lysates from these CHO cells yielded large amounts of four immature forms of int-1 glycoprotein (molecular weights of 36,000, 38,000, 40,000, and 42,000). A significant fraction of these int-1 species formed disulfide-linked multimers. Pulse-chase and glycosidase digestion studies demonstrated that some of the immature species of int-1 protein move through the secretory pathway and are processed to a mature heterogeneous glycoprotein with a molecular weight of about 44,000. Suramin treatment of the CHO cells during pulse-chase experiments increased the amount of 44,000-molecular-weight int-1 protein in the culture medium.

Revolving cards: A financial analysis of the credit repayment and legal implications

2021 ◽  
Vol 39 (2) ◽  
Author(s):  
Salvador Cruz Rambaud ◽  
Salvador Cruz Vargas
Keyword(s):  
Interest Rate ◽  
Credit Card ◽  
Financial Analysis ◽  
Point Of View ◽  
Excessive Amount ◽  
Nominal Interest Rate ◽  
Legal Implications ◽  
Long Duration ◽  
Very High

The framework of this paper is credit card holding by users and consumers, more specifically, the so-called revolving cards. In most cases, the true interest rate applied to a credit is much higher than its nominal interest rate. Usually, this is due to the existence of some fees to be paid by the holder, and to the process of splitting the periods of interest. However, the contracted annual interest rate of revolving cards is very high which, together with the peculiar amortization system, gives rise to an excessive amount of interests. The objective of this paper is to describe and analyze, from a legal and financial point of view, the main characteristics of the credit repayment in revolving cards. We conclude that the complete amortization of the principal needs a long duration and the payment of a high amount of interests.

scholarly journals Molecular weight control in organochromium olefin polymerization catalysis by hemilabile ligand–metal interactions

2016 ◽  
Vol 12 ◽  
pp. 1372-1379 ◽  
Author(s):  
Stefan Mark ◽  
Hubert Wadepohl ◽  
Markus Enders
Keyword(s):  
Ethylene Polymerization ◽  
Weight Control ◽  
Transfer Reactions ◽  
High Catalytic Activity ◽  
Co Catalyst ◽  
Metal Centers ◽  
Molecular Weights ◽  
Metal Interactions ◽  
Polymerization Catalysis ◽  
Very High

A series of Cr(III) complexes based on quinoline-cyclopentadienyl ligands with additional hemilabile side arms were prepared and used as single-site catalyst precursors for ethylene polymerization. The additional donor functions interact with the metal centers only after activation with the co-catalyst. Evidence for this comes from DFT-calculations and from the differing behavior of the complexes in ethylene polymerization. All complexes investigated show very high catalytic activity and the additional side arm minimizes chain-transfer reactions, leading to increase of molecular weights of the resulting polymers.

scholarly journals Back to the Future: Very High-Energy Electrons (VHEEs) and Their Potential Application in Radiation Therapy

Cancers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 4942
Author(s):  
Maria Grazia Ronga ◽  
Marco Cavallone ◽  
Annalisa Patriarca ◽  
Amelia Maia Leite ◽  
Pierre Loap ◽  
...  
Keyword(s):  
Radiation Therapy ◽  
Current Knowledge ◽  
High Energy ◽  
High Dose Rate ◽  
Point Of View ◽  
High Dose ◽  
Dose Rates ◽  
High Energy Electrons ◽  
Very High Energy ◽  
Very High

The development of innovative approaches that would reduce the sensitivity of healthy tissues to irradiation while maintaining the efficacy of the treatment on the tumor is of crucial importance for the progress of the efficacy of radiotherapy. Recent methodological developments and innovations, such as scanned beams, ultra-high dose rates, and very high-energy electrons, which may be simultaneously available on new accelerators, would allow for possible radiobiological advantages of very short pulses of ultra-high dose rate (FLASH) therapy for radiation therapy to be considered. In particular, very high-energy electron (VHEE) radiotherapy, in the energy range of 100 to 250 MeV, first proposed in the 2000s, would be particularly interesting both from a ballistic and biological point of view for the establishment of this new type of irradiation technique. In this review, we examine and summarize the current knowledge on VHEE radiotherapy and provide a synthesis of the studies that have been published on various experimental and simulation works. We will also consider the potential for VHEE therapy to be translated into clinical contexts.

scholarly journals Common Birds of Chitwan National Park, Nepal

2017 ◽  
Vol 1 (2) ◽  
pp. 19-26
Author(s):  
Parveen Kumar Jha
Keyword(s):  
Protected Area ◽  
National Park ◽  
Bird Species ◽  
Point Of View ◽  
Central Nepal ◽  
South Central ◽  
Tropical Vegetation ◽  
Chitwan National Park ◽  
Common Birds ◽  
Very High

 This research paper gives checklist of common birds of Chitwan National Park, which is a wild-life protected area in south-central Nepal. It covers tropical and sub-tropical vegetation. It is first protected area and includes 932 sq. km. Common birds observed are about 170 belonging to 48 Avian families during 2013-2014. Present investigator has very minutely observed birds in habitat conditions. Bird species were recognized by very high binocular. Birds were thoroughly studied from point of view of Taxonomy. Machans were also erected for observing birds.

scholarly journals Prophetism and Enigma in Zviad Gamsakhurdia’s poetry

2021 ◽  
Author(s):  
Nana Qiria
Keyword(s):  
Point Of View ◽  
The Veil ◽  
Very High

Even a glance at Zviad Gamsakhurdia's work shows that he has experienced a long creative burn, he is extremely strong in worldviews and eternal, unchanging, even strangely calm, but thematically changeable.In his work, the arousal of feelings and the veil of thought are harmoniously combined. When the register of such harmony is very high, elements of prophethood appear in Zviad Gamsakhurdia's work and it must be said that his prophecy is infallible and skillfully placed in the artistic mold. In his poetry there is a skillfully blended vague allegory conveyed with a premeditated intent, something between mediocre openness and obscure, transparent and obscure. It can be boldly said that Zviad Gamsakhurdia is a master of enigmatic poetry.The aim of the research is to critically analyze the poetry of the great Georgian figure, thinker and writer Zviad Gamsakhurdia (from a prophetic and enigmatic point of view).The method is comparative. The merits and weaknesses of Zviad Gamsakhurdia's works can be seen in comparison, more - the first.Research result - Prophecy by Zviad Gamsakhurdia is the biggest secret of life. Both his enigma and prophecy stem from bottomless freedom.

The Air-to-air Missile Matra 530

1969 ◽  
Vol 73 (701) ◽  
pp. 449-452
Author(s):  
J. E. Cadoux
Keyword(s):  
Air Force ◽  
High Performance ◽  
First Generation ◽  
Second Generation ◽  
Point Of View ◽  
Ground Control ◽  
Close Link ◽  
Pure Pursuit ◽  
Very High ◽  
Pursuit Curve

The Matra 530 is currently called a second generation air-to-air missile. Indeed the first generation of air-to-air missiles was represented in France by the Nord 5103 which was command-guided, or the Matra 511 which was a semi-active, pure pursuit curve missile. In the second part of the 1950's the requirement was obvious for a sophisticated interception system capable of coping with the high and medium altitude threat represented by heavy and medium bombers. The destruction of this threat required a close link with an interception system composed of ground radars, ground control equipment, sophisticated high performance interceptor aircraft and, as a last link, a very high performance missile. From the French Air Force point of view, the two main characteristics of this missile as the last link of an interceptor system, were first its flexibility in different weather environment and counter measure environment; second, its capability to decrease to the maximum the penetration of the enemy bomber, which meant that the missile should be capable of attacking not only in the rear sector but also in frontal attack and in fact in all sectors around the attacking bomber.

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