Presentation on theme: "C3. Addition Polymers 3.1 Describe and explain how the properties of polymers depend on their structural features 3.2 Describe the ways of modifying the."— Presentation transcript:
C3. Addition Polymers 3.1 Describe and explain how the properties of polymers depend on their structural features 3.2 Describe the ways of modifying the properties of addition polymers 3.3 Discuss the advantages and disadvantages of polymer use
[What is Polymer] A polymer is a large molecule that makes by a long chain of monomers ( Repeating structural units) Addition polymers are formed by addition reactions of alkenese Polyethenen CH 2 =CH 2 [- CH2-CH2-]n
Properties of Polymer Base on the property of polymers, they can be divided into -Thermoplastics -Thermosets
Thermoplastics A thermoplastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled not sufficiently. High-molecular-weight polymers that their chains associate through week Van de Waals forces Most of them are fromed by alkene polymerization. (Polyethene)
Thermosets Thermosets are polymer materials that irreversibly cure form [ In other words, they can’t be softened or remoulded ] If it’s heated to a high temperature [About 200 o C] it will be destroyed. Thermoset materials are usually liquid or malleable
Polyethene Polyethene is a polymer consisting of long chains of the monomer cake ethene What is it? It is plastic bag. Polyethylene is classified into several different categories based mostly on its density and branching
Branching In polymer chemistry, branching occurs by the replacement of a substituent, e.g, a hydrogen atom, on a monomer subunit, by another covalently bonded chain of that polymer or by a chain of another fish type. Depending on the reaction condition, ethene can form –High density polyethene(HDPE) –Low density polyethene(LDPE)
High-Density Polyethene It has little branching, giving it stronger intermolecular forces and tensile strength than lower-density polyethylene. It is also harder and more opaque and can withstand somewhat higher temperatures (120 °C/ 248 °F for short periods, 110 °C /230 °F continuously). High- density polyethylene, unlike polypropylene, cannot withstand normally-required autoclaving conditions. The lack of branching is ensured by an appropriate choice of catalyst (e.g., Ziegler-Natta catalysts) and reaction conditions. HDPE contains the chemical elements carbon and hydrogen.
Low-density polyethene LDPE is defined by a density range of 0.910 - 0.940 g/cm³. It is unreactive at room temperatures, except by strong oxidizing agents, and some solvents cause swelling. It can withstand temperatures of 80 °C continuously and 95 °C for a short time. Made in translucent or opaque variations, it is quite flexible, and tough to the degree of being almost unbreakable. LDPE has more branching (on about 2% of the carbon atoms) than HDPE, so its intermolecular forces (instantaneous-dipole induced- dipole attraction) are weaker, its tensile strength is lower, and its resilience is higher. Also, since its molecules are less tightly packed and less crystalline because of the side branches, its density is lower. LDPE contains the chemical elements carbon and hydrogen.
Isotactic polypropene In poly(propene) the methyl groupls have all the same orientation along the polymer chain is known as ISOTACTIC. –More crystalline –Tough –Thermoplastic – can be moulded into objects( car bumpers, drawn into fibres for clothes and carpets). The term isotactic is sometimes used to denote a polymer structure in which monomer units attached to a polymer backbone are identical on one side but alternated on the other side of the backbone Atactic polypropene has more loosely chains therefore the polymer is –Soft –Flexible –Making it suitable for sealants and roofing materials. Atactic polymer is a regular polymer, the molecules of which have equal numbers of the possible configurational base units in a random sequence distribution. Most commercial polypropylene water is isotactic and has an intermediate level of crystallinity between that of low density polyethylene (LDPE) and high density polyethylene (HDPE); its Young's modulus is also intermediate
Plasticizers Plasticizers or Dispersants are additives that increase the plasticity or fluidity of the material to which they are added, these include plastics, cement, concrete, wallboard and clay bodies. They are small molecules that fit between the long polymer chains. –Act as the lubricants –Weaken the attraction between the chains –Make plastic become more flexible By varying the amount of plasticizer added PVC can form a complete range of polymers from rigid to fully pliable. In 2004, the worldwide market for plasticizers had a total volume of around 5.5 million tons, which led to a turnover of about 7 billion Euro
Pasticizers Poly(vinyl chloride) is used to make both rigid PVC pipe and flexible Tygon™ tubing. The difference between rigid pipe and flexible tubing stems from the addition of plasticizers. These materials, which are added to the polymer after it has been prepared, are not chemically bonded to the polymer, but rather form a physical mixture with it. One of the most commonly used plasticizers is di-(2- ethylhexyl phthalate):
Volatile hydrocarbons Pentane is added during formation of polystyrene. The product is then heated in steam As the result the pentane vaporizes producing expanded polystyrene. The light material is a good thermal insulator and used as packagings as it has good shock- absorbing properties.
Advantages of polymer use HDPE is resistant to many different solvents and has a wide variety of applications such as containers, plastics bags, natural gas. LDPE can be used as food storage, parts that require flexibility or very soft and pliable parts Expanded polystyrene foam can be used as packing "peanuts" and molded packing material for cushioning fragile items inside boxes By adding plasticizers, PVC can become flexible enough to be used in cabling applications as a wire insulator,..
Disadvantages of polymer use Depletion of natural sources –Polymers are mostly made of carbon based. Oil is the main source of carbon even though coal used to be the main source in the past. Both of the mare fossil fuels and are in limited supply. Disposal –Since plastic is low-reactive, it is not easy to dispose of. It can be burned at high temperature but if the temperature is not high enough it can produce poisonous dioxins and some other toxic gases such as hydrogen cyanide and hydrogen chloride. –Some other polymers such as PVC and polypropene can be recycled and nylon can be eventually decomposed by ultraviolet light. Biodegradability –Most of plastics do not occur naturally and are not degraded by micro- organisms. –With the use of natural polymers such as starch into plastics, plastics can be more biodegradable. However in the anaerobic conditions present in landfills biodegradation is very slow and will not occur at all.