for example: here is the monomer of polyethylene   Polymer a substance composed of repeating structural units, or monomers, connected by covalent chemical bonds for example: here is the monomer of polyethylene

Monomers can be chemically joined in one of two ways: Polymerization Monomers can be chemically joined in one of two ways: 1.Addition Polymerization (Acrylics, polyethylene, polystyrene) Addition Polymerization – 3 step process Initiation Propagation Termination e.g. During polymerization of ethylene “mers”, the double bonds break and bond together, propagation continues monomer bonding and when all monomers are used up Rxn terminates http://www.mpcfaculty.net/mark_bishop/addition_polymers.htm

2. Condensation Polymerization During the chemical Rxn, a small molecule is eliminated as monomers are joined together An example is the polymerization reaction involving terephthalic acid and ethylene glycol eliminating a water molecule to form an ester. The eventual result is a polyester called poly(ethylene terephthalate) or more commonly, PET http://faculty.uscupstate.edu/llever/Polymer%20Resources/Synthesis.htm

Many Addition Polymers are Thermoplastics Majority of today’s polymers are thermoplastic Easily processed, reprocessed or recycled Condensation Polymers can be Thermoplastic or Thermosetting Condensation polymers include nylons and urethanes

Thermoplastics vs. Thermosets Thermoplastic: polymers that can be repeatedly softened or melted by heating Ex. Polyethylene, acrylic, polyester, PVC   Thermoset: cross-linked polymers that do NOT soften when heated because strands are not free to move Ex. Bakelite, vulcanized rubber

What Is Thermosetting and Thermosoftening Polymers | Chemistry for All | FuseSchool

Thermoset: Polyisoprene chains ( natural rubber) + sulfur

Thermoplastics Remember the analogy to a plate of cooked spaghetti v. cold spaghetti http://farm1.static.flickr.com/203/496621094_3db122a493_o.jpg

Thermosets: http://pslc.ws/macrog/kidsmac/xlink.htm

Crosslinking polymers with organic peroxides

HDPE High-density polyethylene Uses after recycled: plastic pipes, lumber, flower pots, trash cans, or formed back into non food application bottles. Properties – stiffness, strength, resistance to chemicals & moisture, ease of forming Applications - Milk, water, detergent bottles, shampoo bottles, yogurt, retail bags

LDPE Low-density Polyethylene Properties – ease of processing, strength, toughness, flexibility, ease of sealing, resistance to acids & bases Applications - Dry cleaning, frozen food, bread bags, squeezable plastic bottles, household garbage Uses after recycled: Plastic trash bags, plastic tubing, grocery sacks, floor tile, furniture