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.

Addition & Condensation reactions Addition Polymerization – each monomer is added onto the end with the use of an initiatior. Condensation Polymerization – Two monomers combine and release a small molecule, usually water.

Initiators & Radicals Initiator – Something that gets a reaction started. Often is a radical. Radical – Molecule with one free electron that is very reactive as it tries to get a full valence shell. Carbon atom with one free electron

Addition polymerization A monomer Is exposed to an initiator (Z) and forms a highly reactive structure Another monomer collides with the reactive structure And the two monomers join This is repeated over and over again to form a long chain

Addition Polymerization When the initiator reacts with a monomer, the monomer becomes very reactive and reacts with another monomer and the chain grows Only need small amount of initiator Occur rapidly Builds a chain until all the monomers are used or the reaction is quenched (stopped by the addition of another compound)

Addition Polymerization, continued Are usually exothermic Produce large polymers Can produce unwanted, uncontrolled results  Side-branching can occur, resulting in different polymers produced in the same “batch” Rubber is a polymer of isoprene.  But when allowed to react uncontrolled, rubber is not the product.  A regulator (enzyme, catalyst, etc.) is needed to insure the monomers combine in the correct order

Condensation polymerization Two monomers with functional groups react And release a small molecule And then this process repeats

Condensation Polymerization A small molecule is released when two molecules condense (combine)  Often a water molecule is released The released molecule must be removed to drive the reaction to the right  Le Chatelier’s Principle Do not need initiator Produce smaller, more controlled polymers

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.

What did you learn about polymers?

Polymers Monomers Are made of Organic compounds Which are Structure Properties vary with Bond type Which contains chains of Carbon atoms Can be Functional Group