Polysiloxanes Synthesis and Structure

Polysiloxanes Synthesis and Structure Abstract Silicones (polysiloxanes) are widely used inorganic polymers containing silicon atoms. This category includes many other kinds of polymers such as: polysilanes, polysilazanes, polycarbosilanes and polysiphenylenes [1]. In this project we will focus on polysiloxanes: synthesis and structure properties relationships. First, a brief reference on the history of these materials will be made. Organosilicon compounds were synthesized for the first time in the 1860s, while the first polysiloxanes were made on the 20th century by F.S.Kipping [2]. Then, the ways to synthesize and produce them will be analyzed. This is not a simple synthetic route, while many different procedures take place. These procedures include the reduction of SiO2 into an active reduced form of silicon, hydrolysis/methanolysis and polycondensation or cyclization and polymerization [3]. A more comprehensive study will be made regarding the structure properties relationships. Different cross linking densities create silicones with different properties. Silicones can be categorized by their cross linking density into: silicone oils, elastomers and silicone resins. Silicone oils are linear polymers synthesized by ring opening polymerization. They are thermally stable and thus they can be used as heat transfer fluids. Elastomer silicones are cross linked polysiloxanes via vulcanization and can find application in cars and food containers. On the other hand, silicone resins have high cross linking density and as a result they have high thermal stability. For this reason they are used in colors applied in outdoor surfaces while they are also largely used as water repellants [3], [4]. Introduction Many different silicon containing polymers had been synthesized in the past (figure 1). The most important category of these polymers is the one of polysiloxanes or else silicones. Figure 1: Silicon containing polymers. The synthesis of organo silicon materials started in the 1860s. After 1900s the Grignard reagents became available and as a result major progress occurred. The first polysiloxanes were synthesized by F. S. Kipping in the beginning of the twentieth century. Kipping synthesized diorgano dichloro silanes, R2SiCl2, that could be hydrolyzed into R2Si(OH)2. He was expecting that if these compounds got dehydrated they would produce compounds similar to ketones, R2Si = O. For that reason they were named silic-ones. Soon he realized that, the products were actually polymers that contained Si-O-Si and not Si=O [2]. Polysiloxanes are considered as inorganic organic hybrid materials. The main chain is comprised of atoms of Si and O, whereas the side groups are comprised of alkyl groups (figure 2). Figure 2: Structure of a polysiloxane. This structure is enough to grant them with excessive properties, thus they can be used in many different applications in our everyday life. These polymers can be found as silicone oils, elastomers and resins. Silicone oils are linear polymers synthesized by ring opening polymerization. They are thermally stable and as a result they can be used as heat transfer fluids. Elastomer silicones are cross linked polysiloxanes via vulcanization and can be used in cars and food containers. On the other hand, silicone resins have high cross linking density and as a result they have high thermal stability. For this reason they are used in colors applied in outdoor surfaces while they are also largely used as water repellants [3], [4]. Synthesis The first step of the synthesis of silicones is the reduction of SiO2 into Si. Usually the reduction is done electro thermally with carbon (1) and then silicon is converted into SiCl4 with chlorination (2). Otherwise hydro chloro silanes can be produced by its reaction with HCl (3). Really important for the industry is the direct reaction of methyl chloride with silicon, something that was discovered E. G. Rochow and R. Mà ¼ller in 1940. Copper is used as a catalyst in the form of CuO, as shown in the reactions (4), (5), (6) and (7). The main and most important product from this direct reaction is the dimethyl dichloro silane, (CH3)2SiCl2. The rest products of these reactions are shown above in table 1. Table 1: Main products of the direct reaction MeCl with Si. Hydrolysis The next step is the hydrolysis of the dimethyl dichloro silane, which results into the formation of HCl and a mix of cyclic and linear oligomers of polysiloxanes. The hydrolysis is contacted in the liquid phase with 22 % HCl. The industrial process of the hydrolysis is shown in figure 3. Figure 3: Flow chart of hydrolysis, where a) Cooler; b) Exhaust; c) Phase  separation; d) Settling vessel; e) Water separator; f ) Neutralization and g) Pump Whereas, in diagram 4 there is a synopsis of the whole procedure including the step of hydrolysis. Figure 4: Hydrolysis Methanolysis During this process a direct recovery of Cl with the form of chloro methane from the methyl chloro silanes takes place. Silanes react with methanol in order to produce oligomers of dimethyl siloxanes and chloro methane. Methanolysis occurs according to the reactions: The process of methanolysis is shown above with a flow chart: ΄ Figure 5: Synthesis with methanolysis. And the reactions that take place are: 3. Cyclization Cyclization needs to take place in order for cyclic siloxanes to be produced. This process is done with the heating of the mixture that was produced during the previous steps with KOH. Figure 6:Flow chart of the synthesis of polysiloxanes. 4. Polymerization The usual method of producing linear polysiloxanes is the ring opening polymerization of cyclic polysiloxanes. A polymerization like that can occur under acidic or basic conditions. In general basic conditions are preferable. Anionic Consists a really important procedure for the industry and alkali metal hydroxide catalysts are used. The usual catalyst is potassium hydroxide, whereas other catalysts can be used according to their catalytic activity: Cs > Rb > K > Na > Li. The polymerization occurs rapidly with the addition of only a few ppm of potassium hydroxide at a temperature above 140 ÃŽÂ ¿C. The mechanism is: This reaction leads to the formation of mixture of linear silicones with approximately 15 to 18 per cent of cyclic silicones. In the end, the catalyst needs to get deactivated, usually with the addition of phosphoric acids. Cationic: Cationic polymerization can occur with the use of strong protic acids or Lewis. The mechanism of this reaction is yet unknown. Polycondensation: Another way to synthesize polysiloxanes is by polycondensation reactions of siloxanediols. Hydroxy oligomers of siloxanes can be condensated into polymers with higher molecular weight with the loss of water: Structure Properties Relationships Polysiloxanes can be categorized according to their cross linking density into: silicone fluids, elastomers and resins. Silicone fluids Silicon oils are linear polymers that can be produced by ring -opening polymerization, as described earlier. The flow chart of their industrial production is shown in figure 7. Figure 7: Flow chart of silicone fluids production. Silicon fluids posses a variety of useful properties, such as: Thermal stability ( Temperatures: 150 250 ÃŽÂ ¿C ) High hydrophobicity Dielectric properties Good damping behavior Resistance to radiation These exceptional properties is the reason why silicones oils are used so widely. For example because of their high thermal stability they can be used as a heat transfer media in the industry and not only. Moreover, their strong hydrophobicity enables their use as coatings. Figure 8: Silicone oil used as a heat transfer media. Silicone elastomers Silicones can easily be converted into rubbers through vulcanization. The initial material is a polysiloxane of high molecular weight produced by ring opening polymerization. Cross linking is essential. This can happen with radicals from the decomposition of organic hyper oxides. The hydrogen atoms are removed from the methyl functional groups and the silixane chains connect with each other with Si CH2 CH2 Si bonds. In an alternative version of the vulcanization polysiloxanes that contain a small quantity of methyl vinyl siloxane groups constitute the raw materials. In order for the vulcanization to begin alkyl-hyper oxides are being used but this time the mechanism is different as shown above: The ultimate tensile strength of these elastomers is low, but it can be improved with the addition of fillers. Except from the above, there are also silicone elastomers that the vulcanization occurs at room temperature. There are two types of different systems for this, with one component and with two components. For the systems of one component air exposure is necessary. A typical example of this type is being composed by di -hydroxy siloxane oligomers. The product of this reaction can be placed into a mold in order to attain the appropriate shape. Silicone elastomers attain a really high strength at high temperatures. This makes them one of the elastomers that are used in application that require strength into extreme environmental conditions. Moreover, they are and as a result they do not react with many chemicals. For this reason they are being used in biomedical applications, including medical implants. Figure 9: Silicone elastomers used in catheters. Products made from silicone rubbers can be found in our everyday life. They are being used into cars, food containers, clothes, electronics and in many other applications. Figure 10: Different applications of silicone elastomers in our everyday life. Silicone Resins They are cross linked compounds containing tri functional (T) and tetra functional (Q) silicon units (Q). The simplest silicone resins are produced from methyl chloro silanes with hydrolysis, either directly or indirectly (after the intermediate conversion into methyl trialkoxy silanes). Figure 11: Characteristic structures of silicone resins. Silicone resins can be used as additives paints especially for use in high temperatures. They can also be used as coatings on pharmaceutical pills and as encapsulants for electronic components. Figure 12: Silicone resins used in paints and electronic components. References [1] H.-H. Morreto, M. Schultze and G. Wagner, Silicones, Ullmanns Encyclopedia Of Industrial Chemistry, John Wiley Sons, 2012 [2] A. Mitra and D. A. Atwood, Polysiloxanes and Polylanes Encyclopedia of Inorganic Chemistry, John Wiley Sons, 2006 [3] R. G. Jones, W. Ando, and J. Chojnowski, Silicon Containing Polymers, Kluwer Academic Publishers, Dordrecht, 2000 [4] F. S. Kipping, Proc. R. Soc. London, A159, 139, 1937 [5] J. Heiner, B. Stenberg, M. Persson, Material Behaviour: Crosslinking of siloxane elastomers, Polymer Testing 22, 253-257, 2003 [6] R. drake, I. MacKinnon and R. Taylor, Recent advances in the chemistry of siloxane polymers and copolymers,Chemistry of Functional Groups, John Wiley Sons, 2009 [7] W. D. Callister, Materials Science and Engineering, An Introduction,John Wiley Sons Inc., USA, 2007 [8] A. Colas and L. Aguadisch, Silicones in Pharmaceutical Applications, Chimie Nouvelle, 15 (58), 1779, 1997 [9] P.C. Hiemenz and T. P. Lodge, ÃŽÂ §ÃƒÅ½Ã‚ ·ÃƒÅ½Ã‚ ¼ÃƒÅ½Ã‚ µÃƒÅ½Ã‚ ¯ÃƒÅ½Ã‚ ± ÃŽÂ  ÃƒÅ½Ã‚ ¿ÃƒÅ½Ã‚ »Ãƒ Ã¢â‚¬ ¦ÃƒÅ½Ã‚ ¼ÃƒÅ½Ã‚ µÃƒ Ã‚ Ãƒ Ã… ½ÃƒÅ½Ã‚ ½, ÃŽÂ  ÃƒÅ½Ã‚ ±ÃƒÅ½Ã‚ ½ÃƒÅ½Ã‚ µÃƒ Ã¢â€š ¬ÃƒÅ½Ã‚ ¹Ãƒ Ã†â€™Ãƒ Ã¢â‚¬Å¾ÃƒÅ½Ã‚ ·ÃƒÅ½Ã‚ ¼ÃƒÅ½Ã‚ ¹ÃƒÅ½Ã‚ ±ÃƒÅ½Ã‚ ºÃƒÅ½Ã‚ ­Ãƒ Ã¢â‚¬Å¡ Ά¢ÃƒÅ½Ã‚ ºÃƒÅ½Ã‚ ´Ãƒ Ã…’à Ã†â€™ÃƒÅ½Ã‚ µÃƒÅ½Ã‚ ¹Ãƒ Ã¢â‚¬Å¡ ÃŽÅ ¡Ãƒ Ã‚ ÃƒÅ½Ã‚ ®Ãƒ Ã¢â‚¬Å¾ÃƒÅ½Ã‚ ·Ãƒ Ã¢â‚¬Å¡, 2014 [10] S. R. Sandler, Polymer Syntheses, Academic Press, 1997

Hiroshima and Nagasaki Essay

It was the morning of Aug 6 1945. It was a very beautiful rosy sky. You heard the birds chirping and yet it was so peaceful and calm. All of a sudden there was a thud. Then suddenly everything went quite and nothing was left of Hiroshima and Nagasaki. Then three days later the same incident was repeated again where 70,000 and 40,000 people instantly lost their lives. This was the United States first step towards technology when the first atomic bomb was dropped on the city of Hiroshima, Japan. The impact of this bomb had killed about 70,000 innocent civilians instantly. Even though the US knew the devastating effects of their weapons, they chose to drop it anyway. Three days later another bomb was dropped on the city of Nagasaki. This had demolished about two square miles of the city and had taken about forty-thousand innocent lives. This was the end of the World War II. This all had started when President Harry Truman wanted to test out the Manhattan project. The Manhattan Project was a codename for a project that that was being done in the World War II to create the first atomic bomb. The â€Å"little boy† the bomb that was dropped on Hiroshima was made with uranium-235. The bomb that was dropped on Nagasaki was made with plutonium-239 and called the â€Å"fat man†. The choice of target was recommended by the Target Committee at Los Amos and was led by J. Robert Oppenheimer. He has recommended the Kyoto, Hiroshima, Nagasaki and Kokura as the targets. There were several requirements in choosing the location to drop the fat man and little boy. The blast had to create an effective damage. The target was larger than three miles and was close to the urban area. And it was untouched from any attacks. â€Å"Hiroshima was described as â€Å"an important army depot and port of embarkation in the middle of an urban industrial area. It is a good radar target and it is such a size that a large part of the city could be extensively damaged. There are adjacent hills which are likely to produce a focusing effect which would considerably increase the blast damage. Due to rivers it is not a good incendiary target† (Wikipedia). Hiroshima also had a major army base that had headquarters to the 5th and the 2nd army headquarters. Also, Hiroshima had mountains that surrounded it so the damage could be more effective. When the planes that carried the bombs to Hiroshima they were picked up by the Japanese air raid and had send out an alarm. But when the Japanese saw that it was only three planes they had lifted the alarm thinking that they might be just the regular visitors the US was sending over. When the bomb was thrown the â€Å"Tibbets recalled: A bright light filled the plane. The first shockwave hit us. We were eleven and a half miles slant range from the atomic explosion but the whole airplane cracked and crinkled from the blast†¦. We turned back to look at Hiroshima. The city was hidden by that awful cloud†¦ mushrooming, terrible and incredibly tall† (WWII database). Many of those who had survived had it far worse than the ones that died instantly. They had been badly and severely burned that they looked like living charcoal pieces. Many of the ones that survived all of this died of radiation poisoning and some even had started to vomit their insides out and had died. Majority of the areas hospitals were in a part of Hiroshima that was destroyed and over 90 percent of the doctors were killed. People that escaped unbruised or hurt would suffered balding and nosebleeds, because days after the explosion the radiation levels were dangerously high. And by the end of 1945 the Hiroshima victims had increased from 90,000 to 150,000. Majority of the people that were killed were Koreans. Because the communication process was delayed due to the devastation president Truman said â€Å"If they do not now accept our terms, they may expect a rain of ruin from the air the likes of which has never been seen on this earth†, he said, He later gave the go-ahead to drop the second atomic weapon on Japan† (WWII database). The Second bomb was intended for the city of Kokura. But due to the bad weather that was moving in the schedule had moved up two days. The city of Nagasaki was a very important sea port in Southern Japan. The results of the Fat man was much greater than the one produced by little boy. Around 75,000 people were immediately killed. The day after the attack Japan’s emperor had over ruled the military leaders of Japan and had forced them to give into the surrender unconditionally (doe. gov). This had ended the World War II. Soon after the city was starting to be built again but the devastation area was preserved. Today both Hiroshima and Nagasaki are doing really well. They have a large automobile industry that includes brands like mazda, and Mitsubishi. There still are people who suffer the effects of the radition but very few of them are left. The population went from null to almost 1 million people in each city. In Nagasaki there are hotels on the mountainside with houses, and shops around the neighborhood. Some people had thought that because of the high radiation levels nothing would grow here for decades. But people were shocked when the plants started to grow from under the debris. People had built themselves temporary huts to avoid bad weather. But three months later aide had come from the American-Directed occupation government and the construction had began. Today the city of Nagasaki has a population of about 440,000 people. And Hiroshima today has a population of about 1. 12 million people. In todays world there major industry there is machinery, automotive which produced the Mazda car, and food processing. They have malls, and major department stores. Even though there were two big bombs dropped on the Japans two of the industrial cities, Japan had gone into a total economic and traditional decline. The Japan’s economy was devastated. America had to step in and to help the Japanese economy to get back up, so therefore most of the American values and traditions were incorporated into the Japanese culture. I think it was morally wrong for the Americans to use the atomic bombs and take so many of the innocent lives. After all as always America is the only one that wants to be in power and that was the result of that.

Am I Blue One-Act Play for Two Young Actors

There’s a lot to admire about Beth Henley’s 1972 one-act, Am I Blue. First of all, dramatic works for teenage thespians are in short supply — especially plays that aren’t too preachy. Am I Blue provides juicy roles for a young actor and actress, despite a few flaws typical of this genre. Overview Am I Blue begins in a New Orleans bar. John Polk, 17, sips a drink while he waits for midnight to arrive. At the stroke of twelve, he will officially turn 18. Yet, despite the fact that his college buddies have given him a very special gift (an appointment with a prostitute) he’s lonely and dissatisfied with his life. Ashbe, a strange 16-year-old girl, enters the bar, fresh from stealing ashtrays. She hides under John’s raincoat, fearing that the angry innkeeper from next door will come chasing after his stolen goods. At first, John wants nothing to do with this weird girl. But he discovers that she’s very street-smart. Ashbe knows that John plans to visit a brothel at midnight. As their conversation continues, each character confesses a great deal in a short amount of time: What John Reveals He is a member of a fraternity, but he doesn’t have true friends.His father expects him to become a soy farmer and attend business school.His unfulfilling future prompts him to drink excessively.He’s a virgin who wants to â€Å"face his fears† by sleeping with a prostitute. What Ashbe Reveals She sees herself as Robin Hood – doing little illegal things to help out others.She doesn’t have many friends (and practices Voodoo on her enemies).She likes to dance but dislikes school dances.Her parents are divorced; she lives with her father while her sister and mother live out of state. The dialogue in Am I Blue is fast-paced and honest. Ashbe and John Polk’s evening goes down exactly the way two awkward teenagers would conduct an evening on their own. They color paper hats, talk about drinking and whores, eat marshmallows, listen to shells, and talk about voodoo. The action strikes a real balance between the adult and childish world teenagers are stuck between. Ashbe and John Polk end the play dancing close together to Billie Holliday’s â€Å"Am I Blue.† What Works in This Play Am I Blue is set in 1968, but there’s nothing that overtly dates this play. Henley’s one-act could take place in just about any decade. (Well, maybe not during Ancient Egypt – that would be silly, and they didn’t have ashtrays back then.) This timelessness adds to the appeal of the characters and their quiet angst. John’s character is a low-key and relatively easy vehicle for a â€Å"college-age† actor. Ashbe’s character embodies creativity, voyeuristic tendencies, and a latent vitality for life that is waiting for a chance to prove itself. Teenage actresses could go in many directions with this character, switching from whimsical to dead-serious in a single beat. What Doesnt Work? The play’s main flaw is one found in most one-act dramas. The characters reveal their innermost secrets much too quickly. John begins as a tight-lipped frat boy on his way to lose his virginity in a cathouse. By the end of the play, he has morphed into a romantic, sweet-talking young-minister wannabe, all in a manner of fifteen minutes. Of course, transformation is the nature of theater, and one-acts by definition are brief. However, an excellent drama not only presents fascinating characters but also allows those characters to reveal themselves in a natural way. It should be noted that this often-anthologized one-act was the debut of Beth Henley’s playwriting career. She wrote it while attending college, marking a very promising beginning for a young writer. Seven years later she won the Pulitzer Prize for her full-length play, Crimes of the Heart.   Dramatists Play Service  holds the rights for  Am I Blue.

Conformity In Harrison Bergeron, By Kurt Vonnegut Jr.

â€Å"The year was 2081, and everybody was finally equal† (Vonnegut 22). In Kurt Vonnegut Jr.’s short story â€Å"Harrison Bergeron†, the author depicts a society set in the future where the gifted individuals are handicapped genetically in order to be equal among everyone. Not lifting up the ungifted individuals will prevent conflicts from occurring between the government and its citizens, this is exhibited by the forced conformity and revolting of characters. People are not meant to be the same; everyone has their own strengths and weaknesses. The society this short story takes place in restrains highly exceptional people, â€Å"Every twenty seconds or so, the transmitter would send out some sharp noise to keep people like George from taking unfair†¦show more content†¦To illustrate, â€Å" ‘Even as I stand here’ he bellowed, ‘crippled, hobbled, sickened - I am a greater ruler than any man who ever lived! Now watch me become what I can become!’ † (Vonnegut 26). This demonstrates what a person who has been restricted finally wants to be free of what society has set for him. Compared to â€Å"lifting up† the ungifted someone either who is naturally gifted or has been enhanced will feel as if their life is being made to strive for perfection which insinuates that in order to be equal they need to be like everyone else which sends a negative image of oneself. Even though the ungifted being li fted up may seem to have negative conflicts, equality is a positive factor. Equality is what a society wants in order to not have competition. For instance, â€Å"They were equal every which way. Nobody was smarter than anybody else. Nobody was better looking than anybody else. Nobody was stronger or quicker than anybody else† (Vonnegut 22). People not competing with one another shows how living in harmony amongst one another to avoid conflicts is what the government wants for the people. 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