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.