Section 11.3—Polymers How do polymer properties vary for various applications?

Polymers & Monomers Polymer – Very large molecules built from chains or networks of smaller molecules (usually 1,000 to 50,000 smaller molecules). Monomer – The smaller molecules making up the polymer.

Polymer Structures Polymers can be made of:  Repeating patterns of monomers  One monomer over and over again  Random combinations of polymers Structure of polymer determines the properties of the polymer  Functional groups can affect properties  Sequence and type of monomers can affect properties

Thermoplastic & Thermoset Thermoplastic polymer – can be heated and molded into another shape and then cooled. This can be done over and over again. Thermoset polymer – Cannot be heated and re-molded.

Why can’t thermoset plastics be re-molded? When thermoset polymers are shaped for the first time, cross-linkages are formed.  Cross-linkages are connections between various polymer strands that hold the polymers in place next to each other Heating does not break these cross- linkages  So even when heated you can’t break these chains apart and reshape them.

Polymer Properties Strength of intermolecular forces between polymer chains depends on functional groups and side-branching of polymers More intermolecular forces between polymer chains =  Higher melting & boiling points  More rigid polymers More side-branching =  Chains less able to pack closely and form IMF’s  Lower melting & boiling points  Less rigid polymers

Polymer Properties Cross-linkages are chemical bonds (as opposed to the physical attractions of intermolecular forces)  Once formed, a chemical reaction must occur to break them (remember thermoset plastics!)  Cross-linkages can change a liquid polymer into a solid or gel-like polymer The properties of the polymer determine the recycling needs of the polymer  Triangles on the bottom of plastics with numbers in them indicate how the plastic is to be recycled

Polymers in Biology Polymers are found everywhere in nature:  Proteins  DNA  RNA The monomers that form these polymers are called amino acids  There are 20 different amino acids, that in different combinations make up the different polymers in our body.