Introduction Polymerization of cyclic esters has attracted a lot of interest for the synthesis of biodegradabale/ biocompatible polymeric materials, such as polylactide, polyglycolide and also other polymer compound such as linear polycarbonate. Ring opening polymerization of cyclic ester compounds is better than step polymerization for obtaining high Mw polymers in a controlled “living” fashion, while avoiding the formation of by-products. Tin octoate (tin(II) bis(2-ethyl hexanoate)), Sn(Oct)2) is one of the most used initiator in the polymerization of cyclic esters. There have been various mechanisms proposed for the initiation and propagation mechanism of cylic ester polymerization initiated by Sn(Oct)2 as these mechanisms are the least being understood. The mechanisms were summarized below (see Scheme 1 - 4): 1. Cationic polymerization Proton and cationic species were formed during the propagation process and Sn is not bound to the propagating chain (Scheme 1 ). 2. Activated monomer mechanism. Activated monomer was added to –OH group of macromolecules and ROH is strongly complexed to Sn(Oct)2, involving only the free orbitals of the catalyst 3. Formation of anhydride end group from direct reaction of Sn(Oct)2 with monomer The initiation and propagation steps proceed without co-initiator. 4. Metal alkoxide initiated-like polymerization from conversion of Sn(Oct)2 into alkoxide compound Sn(Oct)2 reacts with hydroxide groups of another compounds added or present in the reaction and formed the actual initiator, tin(II) alkoxide or hydroxide. Scheme 1. Mechanism based on cationic species formation Scheme 2. Mechanism based on activated monomer Scheme 3. Mechanism based on direct reaction of Sn(Oct)2 a... ... middle of paper ... ...n initiated with Sn(Oct)2 were studied by conducting various reactions incorporating various ratio and amount of reagents, co-initiator and trapping agents. Furthermore, reaction kinetics were monitored and intermediate /trapped compounds were isolated and identified. The results indicated that propagation did not proceed as cationic polymerization. Reaction was co-initiated by alcohol or alkoxide compound and Sn was attached to the propagating group. These findings lead to the scheme shown in Scheme 4 as the adopted mechanism of the cyclic ester polymerization by Sn(Oct)2. The polymerization proceeds on the metal (Sn(II)) alkoxide bond by insertion, like in other metal alkoxide initiators, where at least one carboxylate group in Sn(Oct)2 is replaced by alkoxide group and then polymerization proceeds by monomer insertion into the resulting tin(II)-alkoxide bond.
A group of polymer chains can be organised together in a fiber. How the polymer chains are put together is important, as it improves the properties of the material. The flexibility, strength and stiffness of Kevlar fiber, is dependent on the orientation of the polymer chains. Kevlar fiber is an arrangement of molecules, orientated parallel to each other. This orderly, untangled arrangement of molecules is described as a “Crystalline Structure”. A manufacturing process known as ‘Spinning’ is needed to achieve this Crystallinity structure. Spinning is a process that involves forcing the liquefied polymer solution through a ‘die’ (small holes).
The theoretical yield of the m-nitrobenzoate was de-termined to be 4.59 grams. The actual amount of crude product was determined to be 3.11 grams. The percent yield of the crude product was determined to be 67.75 %. The actual amount of pure product formed was found to be 4.38 grams. The percent yield of the pure product was determined to be 95.42%. Regarding the thin layer chromatography, the line from the solvent front was 8 centimeters.
The most common form of polyethylene is petroleum based or olefins based; as before mentioned polyethylene compounds have a wide commercial applicability and are made from non-renewable resources (Harding, Dennis, von Blottnitz, Harrison, & S.T.L., 2007). Its manufacturing processes are regarded as energy intensive and release significant amount of CO2 and heat into the atmosphere (Broderick, 2008). Next a little more detailed description of polyethylene’s production processes will be presented, with a focus on the way the material inputs are extracted and synthesized.
In a small reaction tube, the tetraphenylcyclopentadienone (0.110 g, 0.28 mmol) was added into the dimethyl acetylene dicarboxylate (0.1 mL) and nitrobenzene (1 mL) along with a boiling stick. The color of the mixed solution was purple. The solution was then heated to reflux until it turned into a tan color. After the color change has occurred, ethanol (3 mL) was stirred into the small reaction tube. After that, the small reaction tube was placed in an ice bath until the solid was formed at the bottom of the tube. Then, the solution with the precipitate was filtered through vacuum filtration and washed with ethanol. The precipitate then was dried and weighed. The final product was dimethyl tertraphenylpthalate (0.086 g, 0.172mmol, 61.42%).
The synthesis of polymers starts with ethylene, (or ethene). Ethylene is obtained as a by-product of petrol refining from crude oil or by dehydration of ethanol. Ethylene molecules compose of two methylene units (CH2) linked together by a double carbon
Synthesis, Mechanism and Production In free-radical co-polymerizations, the different reactivity of the growing polymer chain toward two different monomer molecules and the possibility of chain transfer reactions make calculations to predict polymer kinetics and composition extremely difficult. The first equation shows ethylene-terminated polymer radical reacting with vinyl acetate, and the second equation shows vinyl acetate terminated polymer radical reacting with ethylene. The propagation rate coefficient are used to find the reactive ratios. It is even possible to consider the effects of penultimate groups.
As part of the polymers chemistry and the environment course, we synthesized and studied many types of polymers, from biodegradable to ones used in organic photovoltaics. (more)
The product was recrystallized to purify it and the unknown filtrate and nucleophile was determined by taking the melting points and performing TLC. Nucleophilic substitution reactions have a nucleophile (electron pair donor) and an sp3 electrophile (electron pair acceptor) with an attached leaving group. This experiment was a Williamson ether synthesis usually SN2, with an alkoxide and an alkyl halide. Conditions are favored with a strong nucleophile, good leaving group, and a polar aprotic solvent.
The purpose of this experiment was to create a polymer by reacting a mixture of decanedioyl dichloride and dichloromethane with a mixture of water, 1,6-hexadiamine and sodium carbonate. Specifically, we created the polymer Nylon-6,10. Nylon-6,10 polymers are used in a vast majority of things we use in everyday life such as zippers, the bristles in brushes, and even car parts. This experiment was different from the industrial method of making nylon because that takes place at a much higher temperature. A polymer is a substance that has a structure made of similar or identical units bonded together. All polymerizations fall into two categories: step-growth and chain-growth (both of which we used to form our polymer). Step growth polymerization
David and John Free. (26 Nov 2006). MadSci Network: Chemistry. Retrieved on March 6, 2011, from http://www.madsci.org/posts/archives/2007-02/1171045656.Ch.r.html
Leja, K., Lewandowicz, G. (2010). Polymer Biodegradation and Biodegradable Polymers – a Review, Polish. J.of Environ. Stud. 19(2): 255-266.
This research brought me experience in many areas of material science: monomer preparation and purification, polymerization, polymer precipitation, and film casting. I created the monomer and worked through every step to film production and testing without needing supervision. I also had to learn and perform air-free techniques involving glove boxes and Schlenk lines. Difficulties with the different reaction conditions and ratios needed for each monomer to form correctly made every run a test of
The main problems associated with synthetic polymers are related to Environment, and these problems negatively affect the environment by pollution. The key idea of this problem is that these polymers do not breakdown therefore they harm the environment. They are also harmful for everybody’s health. Most polymers are non-biodegradable and this brings around the problem.
This chemical, Benzoin, is used in a variety of different ways. One of the main purposes for this compound is to be used as an intermediate for the synthesis of organic compound. The second major purpose for Benzoin is to be a catalyst in photo polymerization. In the photo polymerization, the chemical is used as a photo-initiator. The photo-initiators are commonly used because they can be conducted at low temperatures and easily stopped by simply removing the light source. Photo-in...
In this paper, we will explore the different biodegradable polymers and the current technologies involved in their