Transcript Slide 1
Polymer Poly (many) mer (parts) According to the amount of repeating units Monomer Oligomer It consists of one It consists of a few repeating unit repeating units It has properties which do vary significantly with the removal of one or a few of the units vinyl chloride, amino acid, glucose Sucrose Polymer It consists of a nearly unlimited number of repeating units Addition or removal of one or a few of the units has a negligible effect on the molecular properties PVC, protein, carbohydrate According to the kinds of applied monomers One kind : Homopolymer Two kinds : Copolymer Three kinds : Terpolymer Types of copolymer According to the origin of the polymer Natural polymer Starch, cellulose, rubber, enzyme, protein, etc. Synthetic polymer Fibers, elastomers, plastics, adhesives, etc. According to the structure of the polymer Linear Crosslinked Branched Network According to the structure of the molecules in solid state According to the polymer architectures (a) star polymer (c)ladder polymer (b) comb polymer (d) semi- ladder (or stepladder) polymer (f) polycatenane (e) polyrotaxane (g) dendrimer POLYMER CHEMISTRY Based on how the atoms in a molecule (large or small) are hooked together • Fiber: Fibers are linear polymers with high symmetry and high intermolecular forces that result usually from the presence of polar groups. They are characterized by high modulus, high tensile strength, and moderate extensibilities (usually less than 20%) • Elastomer: molecules with irregular structure, weak intermolecular attractive forces, and very flexible polymer chains. Chain segments of elastomers can undergo high local mobility, but the gross mobility of chains is restricted, usually by the introduction of a few cross-links into the structure. In the absence of applied (tensile) stress, molecules of elastomers usually assume coiled shapes. Consequently, elastomers exhibit high extensibility (up to 1000%) from which they recover rapidly on the removal of the imposed stress. Elastomers generally have low initial modulus in tension, but when stretched they stiffen. • Plastic: fall between the structural extremes represented by fibers and elastomers Based on thermal behavior Thermoplastics: • Upon cooling, the polymer hardens and assumes the shape of the mold (container). • Thermoplastics, when compounded with appropriate ingredients, can usually withstand several of these heating and cooling cycles without suffering any structural breakdown. This behavior is similar to that of candle wax. • Examples of thermoplastic polymers are polyethylene, polystyrene, and nylon. • Thermoplastic polymers are composed mainly of linear and branched molecules. • Linear and branched polymers consist of molecules that are not chemically tied together. It is therefore possible for individual chains to slide past one another. • At low temperatures, a thermoplastic polymer (both crystalline and amorphous) exists as a hard and rigid glass. • As the temperature is increased, it changes from a glass to a rubbery elastomer to a viscous melt that is capable of flowing — hence this phase is also known as the flow region. Thermoset: • It is a polymer that, when heated, undergoes a chemical change to produce a cross-linked, solid polymer. • Thermosets usually exist initially as liquids called prepolymers; they can be shaped into desired forms by the application of heat and pressure, but are incapable of undergoing repeated cycles of softening and hardening. • Examples of thermosetting polymers include urea– formaldehyde, phenol–formaldehyde, and epoxies. • Thermosets are made up of cross-linked systems chains will not flow freely even under the application of heat and pressure. • The modulus remains high in the rubbery region, while the flow region disappears. Depending on the distribution and degree of the chemical bonds of the polymers, elastomeric materials can have properties or characteristics similar to thermosets or thermoplastics, so elastomeric materials can be classified into: • Thermoset Elastomers - are those elastomer materials which do not melt when heated. • Thermoplastic Elastomers - are those elastomers which melt when heated. Properties of elastomer materials: • Can not melt, before melting they pass into a gaseous state • Swell in the presence of certain solvents • Are generally insoluble. • Are flexible and elastic. • Lower creep resistance than the thermoplastic materials Based on polymerization mechanism Condensation polymers are formed from a series of reactions, often of condensation type, in which any two species (monomers, dimers, trimers, etc.) can react at any time leading to a larger molecule. In condensation polymerization, the stepwise reaction occurs between the chemically reactive groups or functional groups on the reacting molecules. In the process, a small molecule, usually water or ammonia, is eliminated. Examples of condensation polymers include polyamides (e.g., nylon 6,6); polyesters (e.g., poly(ethylene terephthalate); and ureaformaldehyde and phenol–formaldehyde resins Addition polymers are produced by reactions in which monomers are added one after another to a rapidly growing chain. The growing polymer in addition polymerization proceeds via a chain mechanism. Like all chain reactions, three fundamental steps are involved: initiation, propagation, and termination. Monomers generally employed in addition polymerization are unsaturated (usually with carbon-carbon double bonds). Examples of addition polymers are polystyrene, polyethylene, polyacrylonitrile, poly(methyl methacrylate), and poly(vinyl chloride). Ring-opening polymerization polymers are derived from the cleavage and then polymerization of cyclic compounds. According to the end use of the polymer • diene polymers (rubber industry); • olefin polymer (sheet, film, and fiber industries); and • acrylics (coating and decorative materials). Molecular structure of a particle of polyethylene HDPE LDPE Molecular structure of a particle of polycarbonate (material for CD and DVD) color coding: hydrogen (white), carbon (grey), oxygen (red) Polycarbonate products Acrylic glass (PMMA), chemical structure. Main component of acrylic paint (latex) and acrylic glass. Atoms are represented as spheres with conventional color coding: hydrogen (white), carbon (grey), oxygen (red) PMMA products Polyethylene terephthalate (PET, PETE) polyester plastic, chemical structure. Mainly used in synthetic fibers and plastic bottles. Atoms are represented as spheres with conventional color coding: hydrogen (white), carbon (grey), oxygen (red) PET products 1: PET or PETE This is the thin, clear plastic used for bottled water, soda, juices, condiments, etc. This plastic can contain trace amount of the endocrine-disrupting BPA, which has been linked to breast and uterine cancer, an increased risk of miscarriage, decreased testosterone levels, birth defects, and other reproductive issues. While PET/PETE is relatively stable at normal temperatures, it will leech readily when exposed to heat such as when left in a car. It is for this reason that consumers are advised not to keep water bottles in the car. Since the plastic degrades with use, it is advised to not reuse these plastic products. VERDICT→ Moderate hazard 2: HDPE (High-Density Polyethylene) This is the thicker, more opaque plastic found in milk and water jugs, juice bottles, detergent, shampoo, and motor oil containers, and toys. Unlike #1, these are safe to refill and reuse. VERDICT→ Low hazard 3: PVC (Polyvinyl Chloride) PVC has been around the block. It’s found in everything from shower curtains to baby bibs, mattress covers, shampoo and liquid soap bottles, cling wrap, cooking oil bottles, and much more. PVC contains endocrine-disrupting phthalates, which have been linked to reproductive problems and birth defects. The cherry on top: the PVC manufacturing process releases dioxin into the environment, a potent carcinogen that bio-accumulates in our bodies, meaning it stays there for a very long time, if not forever. It also bio-accumulates in animals’ bodies, such as the ones most of us consume, which then make their way into our bodies after we eat them. It is not surprising that workers that manufacture or work with PVC have higher cancer rates. VERDICT→ High hazard 4: LDPE (Low-Density Polyethylene) This plastic is used to create flexible plastics products like grocery story bags, plastic food storage bags, bread bags, frozen food packaging bags, plastic wrap, dry cleaning bags, and garbage bags. VERDICT→ Low hazard 5: PP (Polypropylene) This plastic is used to create hard but flexible plastic products like yogurt containers, drinking straws, syrup bottles, salad bar containers, and diapers. VERDICT→ Low hazard 6: PS (Polystyrene) Found in rigid plastics such as opaque plastic spoons and forks, and in Styrofoam. These plastics can leach styrene, a known neurotoxin with other negative health effects. VERDICT→ High hazard 7: Other This symbol includes a range of plastic materials. It includes polycarbonate, which contains the endocrine-disrupting chemical BPA and is most commonly used to for baby bottles, sports water bottles, large 5-gallon water jugs, plastic cutlery, and in the lining of food and baby formula cans. VERDICT→ High hazard