Lecture 16 - 11/18/2010
Lecture 16
Breast cancer
Rashanda Chandler ELA 8th grade
Die Deutschen in Toulouse
Dans le cadre des interviews allemandes pour la rubrique VO sur Canal U, nous jetons aujourd'hui un regard sur « les Allemands à Toulouse ». Ils sont environ 10.000 à vivre dans l’agglomération toulousaine, la plupart d’entre eux à Pibrac, Blagnac, Colomiers et Tournefeuille.
Lorsqu’on parle de la « présence allemande » à Toulouse, on pense surtout à des entreprises telles que Airbus et EADS. Mais depuis les années 1960 un réseau allemand particulièrement dense et
GSF - Accueil en France des victimes : experience du Comede (video)
2ème journée humanitaire sur la santé des femmes dans le monde
Vendredi 6 mars 2009, Palais du Luxembourg, 15 rue de Vaugirard 75006 Paris. Journée organisée à l’occasion de la journée mondiale de la femme 2009
Sous la présidence de Mme Simone Veil, membre de l’Académie Française. Marrainage de Mme Michèle André, sénatrice du Puy-de-Dôme, présidente de la délégation du Sénat aux Droits des femmes et à l’égalité des chances entre les hom
Telling the time
This unit helps you to acquire the basic language to find your way around a French town. You will learn how to understand and give directions, ask about accommodation, book a hotel room at the tourist information office and get information about what to see and do in the local area. You will visit some museums in Avignon and buy a film for your camera. This unit also deals with telling the time and making liaisons in speech. By the end of the unit, you will feel more confident understanding and
Une brochure de détails d'hôtel
This unit helps you to acquire the basic language to find your way around a French town. You will learn how to understand and give directions, ask about accommodation, book a hotel room at the tourist information office and get information about what to see and do in the local area. You will visit some museums in Avignon and buy a film for your camera. This unit also deals with telling the time and making liaisons in speech. By the end of the unit, you will feel more confident understanding and
Activités 26 et 27
This unit helps you to acquire the basic language to find your way around a French town. You will learn how to understand and give directions, ask about accommodation, book a hotel room at the tourist information office and get information about what to see and do in the local area. You will visit some museums in Avignon and buy a film for your camera. This unit also deals with telling the time and making liaisons in speech. By the end of the unit, you will feel more confident understanding and
4.5.1 The copolymer equation It can be shown that the rate of change of monomer concentration in any copolymerization is given by the equation where [M1] and [M2] are the concentrations of monomers 1 and 2 at any instant and r1
and r2., are reactivity ratios. The reactivity ratios represent the rate at which one type of gr
4.5 Copolymerization The alloying of metals to improve their properties is widespread and although many polymers used today are relatively pure (e.g. polystyrene, nylon), an increasing number are mixtures of two or more polymers. As with metals, one reason for doing this is to increase the range of properties. The major practical problem, however, is that homopolymers blend together with difficulty and even where blends are possible, as in some thermoplastics, phase separation can occur readily. This proble
4.4 Step growth polymerization 4.3.5 Co-ordination polymerization While most free radical and ionic polymerizations are carried out homogeneously, there is another important class of reaction which is often performed with solid catalysts. These reactions, discovered in the mid-fifties, have revolutionized polymer manufacture by permitting much less severe polymerization conditions than with other systems and by allowing a greater degree of control of polymer structure. Ziegler-Natta catalysts, as they are called, will convert vinyl and diene monomers 4.3.4 Ionic polymerization Free radicals are indiscriminate in the compounds they attack, and their non-selective nature in polymerization reactions leads to problems such as chain branching and transfer which affect the structure of the polymer produced. Anionic polymerization overcomes many of these problems. A typical commercial (but also see Box 8) anionic reaction is the polymerization of styrene using butyllithium, C4H9 4.3.3 Termination and transfer There are basically three ways in which chains terminate. The first is known as coupling and occurs when two free radicals join together. This can be represented by the general equation Such a mechanism significantly increases molecular mass, if it results in two polymer chains joining. This is the main mechanism which terminates the po 4.3.2 Propagation Once a small number of chains have been started, propagation involves successive addition of monomer units to achieve chain growth. At each step the free radical is regenerated as it reacts with the double bond. So in the case of styrene the propagation step is
The free radical can also add on in a different way to produce
4.3.1 Initiation Initiation is the mechanism which starts the polymerization process. Vinyl monomers are quite easily polymerized by a variety of activating methods. Styrene, for example, can be converted to solid polymer simply by heating, and ultraviolet light can have exactly the same effect. Usually, however, an activating agent is used. This is an unstable chemical which produces active species that attack the monomer. A good example is benzoyl peroxide which splits up when heated:
Author(s): 4.3 Chain growth polymerization Chain growth polymerization is basically a three-stage process, involving initiation of active molecules, their propagation and termination of the active chain ends. Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Crea 4.2 Chain and step growth There are two basic ways of making chains. The first is to activate a small number of monomer units M which then successively consume other monomers. This mechanism is known as chain growth and is shown schematically in Figure 36 (a), where a monomer unit is activated by initiator I and forms a chain very quickly. After 75 per cent of the monomer molecules have reacted in this case the degree of polymerization n = 4.1 Understanding the polymerization process Converting monomer to long chain polymer is the final step in the polymer manufacturing sequence. Polymerization is usually highly favourable in thermodynamic terms, mainly on energetic grounds because ordering molecules into linked chains is a process where the entropy is decreased. Heat is always given out during polymerization owing to the very favourable energetics of reaction, a point you may have noticed if you have ever made GRP parts for your car, for example! Advances in cataly 3.4 The petrochemical industry The four-fold increase in the price of oil in 1973–4, together with associated political events, proved a powerful stimulus in the development and exploitation of North Sea crude oil. Increasing the price of oil does not mean that the price of the final plastic moulding increases by the same amount. For example if oil prices were doubled again then naphtha prices would typically increase by about 80 per cent, although there is no simple and fixed gearing mechanism between the two prices. Th 3.3.3 Higher aromatics Benzene rings can be fused in various ways to create component parts for some of the complex aromatic repeat units shown in Table 5. One of the most important is bisphenol A, made by fusing two phenol rings with acetone:
This intermediate is important for a number of speciality polymers, for example, polycarbonate and epoxy resi
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