POLYMERS Group members: Nurul Athirah Binti Abd.Razak ( ) Maisarah Binti Mohamed Hanafi ( ) Nur Fasihah Binti Mohd. Ariffin ( ) Khairussyifa ‘ Binti Shukri ( )

What is Polymer? Substances containing a large number of structural units joined by the same type of linkage.

Structure of Polymer A polymer is composed of many simple molecules that are repeating structural units called monomers. Covalent bonds hold the atoms in the polymer molecules together. Secondary bonds then hold groups of polymer chains together to form the polymeric material. Copolymers are polymers composed of two or more different types of monomers.

Structure of polymers

Polymer Composition Most polymers are hydrocarbons – i.e. made up of H and C (we also recognize Si-H ‘silicones’) Saturated hydrocarbons – Each carbon bonded to four other atoms

Molecular weight, M i : Mass of a mole of chains

Configuration The two types of polymer configurations are cis and trans. These structures can not be changed by physical means (e.g. rotation). The cis configuration arises when substituent groups are on the same side of a carbon-carbon double bond. Trans refers to the substituents on opposite sides of the double bond.

Copolymer There are three important types of copolymers. A random copolymer contains a random arrangement of the multiple monomers. A block copolymer contains blocks of monomers of the same type. Finally, a graft copolymer contains a main chain polymer consisting of one type of monomer with branches made up of other monomers. The following diagram displays the different types of copolymers.

Copolymer Random Graft Block

Mechanical properties of polymers

The mechanical properties of a polymer involve its behavior under stress. How strong is the polymer? How much can you stretch it before it breaks? How stiff is it? How much does it bend when you push on it? Is it brittle? Does it break easily if you hit it hard? Is it hard or soft? Does it hold up well under repeated stress?

Tensile Strength The stress needed to break a sample. It is expressed in Pascals or psi (pounds per square inch). 1 MPa = 145 psi The tensile strength is an important property for polymers that are going to be stretched. Fibers, for instance, must have good tensile strength.

% Elongation to Break The strain on a sample when it breaks. This usually is expressed as a percent. The elongation-to-break sometimes is called the ultimate elongation. Fibers have a low elongation-to-break and elastomers have a high elongation-to-break.elastomers

Toughness The toughness of a material is the area under a stress-strain curve. The stress is proportional to the tensile force on the material and the strain is proportional to its length. The area under the curve then is proportional to the integral of the force over the distance the polymer stretches before breaking.

A material that is strong but not tough is said to be brittle. For example brittle substances are strong, but cannot deform very much is Polystyrene (PS)..

Applications of polymers

Elastomers Rubber is the most important of all elastomers. Natural rubber is a polymer whose repeating unit is isoprene. Elastomers rubbery polymers that can be stretched easily to several times their unstretched length and which rapidly return to their original dimensions when the applied stress is released. This material, obtained from the bark of the rubber tree, has been used by humans for many centuries.

Plastics The two main types of plastics are thermoplastics and thermosets. Thermoplastics soften on heating and harden on cooling. Thermosets, on heating, flow and cross-link to form rigid material which does not soften on future heating. Among the most important and versatile of the hundreds of commercial plastics is polyethylene.

Fibers Fibers represent a very important application of polymeric materials, including many examples from the categories of plastics and elastomers. Natural fibers such as cotton, wool, and silk have been used by humans for many centuries. Synthetic polymers have been developed that posess desirable characteristics, such as a -high softening point to allow for ironing, -high tensile strength, adequate stiffness -desirable fabric qualities. These polymers are then formed into fibers with various characteristics.

Agriculture and Agribusiness Polymeric materials are used in and on soil to improve aeration, provide mulch, and promote plant growth and health. Medicine Many biomaterials, especially heart valve replacements and blood vessels, are made of polymers like Dacron, Teflon and polyurethane. Consumer Science Plastic containers of all shapes and sizes are light weight and economically less expensive than the more traditional containers. Clothing, floor coverings, garbage disposal bags, and packaging are other polymer applications.I Industry Automobile parts, windshields for fighter planes, pipes, tanks, packing materials, insulation, wood substitutes, adhesives, matrix for composites, and elastomers are all polymer applications used in the industrial market. Sports Playground equipment, various balls, golf clubs, swimming pools, and protective helmets are often produced from polymers.