Lecture 4 Chapter 13 - Polymers. Functional Groups Condensation Rxns Free Radical Rxns

Transcription

1 Lecture 4 Chapter 13 - Polymers Functional Groups Condensation Rxns Free Radical Rxns

2 Chemistry the whole year on one page Last semester Basic atomic theory Stoichiometry, balancing reactions Thermodynamics (intro) Light, spectroscopy Electrons, orbitals, quantum numbers Bonding, molecular shapes and orbitals Intermolecular interactions, phases This semester Solutions, colligative properties Polymers Thermodynamics (revisited), enthalpy and entropy Kinetics, reaction mechanisms Equilibria Acids, bases, and buffers Redox reactions and electrochemistry Nuclear chemistry Coordination chemistry

3 Polymers Medium to huge molecules Made by repeating many (poly) small units (mers) Enable the huge variety of life & modern materials Difficult to overestimate $$ importance of polymers Essentially all biological reactions and structures are polymers

4 Making Polymers We will deal entirely with organic polymers (C-based) Key to making polymers is controlling chemical reactions Functional groups are key sites of reactivity Basically anything that is not a C-C single bond Sites of typical reactions Used to classify organic compounds Serve as a basis for naming compounds

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6 Alcohols Alcohols are organic compounds whose functional group is the hydroxyl group (or -O) bonded to a tetrahedral carbon (i.e., four single bonds). C C O The hydroxyl functional group The chemical formula is usually written C 2 5 O

7 Thiols A thiol is just like an alcohol except the O has been replaced by S C C S The thiol functional group

8 Classification of Alcohols Classified depending on the number of carbon atoms bonded to the -C-O C 3 - C - O Primary (1 ) C 3 C 3 - C - O C 3 Tertiary (3 ) C 3 - C - O C 3 Secondary (2 ) This classification scheme is generally used for all functional groups.

9 : : : : Amines The functional group of an amine is an amino group -a nitrogen atom bonded to one, two or three carbon atoms Note that R generally means any organic thing. It could be as simple as C 3, or something really big and complicated. -N -R -N- R -N-R Ammonia not an amine R R - N - R 1, 2, and 3 amines

10 Aldehydes and Ketones Aldehydes and ketones contain a carbonyl group, C=O In an aldehyde, the carbonyl group is terminal - bonded to a hydrogen, a -CO group In a ketone, the carbonyl group is internal - bonded between two carbon atoms O O - C - C - C - - C -C -C - propanaldehyde (an aldehyde) acetone (a ketone)

11 = = = Carboxylic acid Organic acids contain a carboxyl group -COO It s a combination of a carbonyl (C=O) and a hydroxyl (-O) group carbonyl + hydroxyl = carboxyl O -C - -O O -C -O The carboxyl group always terminates a chain of carbon atoms O C 3 -C 2 -C -O propanoic acid

12 Polymerization Reactions There are four main types of polymerization reactions 1. Free Radical Polymerizations. 2. Condensation Polymerizations. 3. Cationic Polymerizations. 4. Anionic Polymerizations. We will only talk about the first two

13 Free Radical Polymerization Most free radical polymerizations involve 3-steps 1. Initiation to get things started 2. Propagation to grow the polymer 3. Termination to end the reaction A good example is the synthesis of polyethylene (polyethene) DPE and LDPE are used in beverage containers, toys, tubing, squeeze bottles, etc.

14 Initiation Formation of a free radical often by heating a peroxide. (this is slightly different than described by textbook) Propagation the free radical reacts with an ethylene, which gives a free radical to react with another ethylene, which gives Termination the process ends when two radicals collide and react.

15 Other Polyalkenes react similarly

16 Ethylene (C 2 4 ) contains a C=C double bond. ow many double bonds are in a molecule of polyethylene that is composed of 100 ethylene units? 88% % % % %

17 Condensation Reactions Reactions that generate water as a product (in general) Three main types alcohol + alcohol ether + water carboxylic acid + amine amide + water carboxylic acid + alcohol ester + water

18 Functional Group Summary Alcohol Ether Thiol Aldehyde Ketone Phosphate Carboxyl Ester Amide

19 Condensation Polymers Polymer versions of these reactions generate Polyethers Polyamides Polyesters For instance, nylon 66 is a polyamide

20 Which of the following is a polyamide? 19% 1. Nylon 86 52% 2. Kevlar 5% 3. Protein 24% 4. Silk

21 Polymer Properties Intermolecular Interactions are critical Individual molecules are weak Joining molecules together restricts motion stronger Molecules connected by Van der Waals forces (polyethylene), -bonds (silk, nylon), covalent bonds (rubber). The creation of covalent bonds between polymers is called cross-linking First big application was rubber 1839 Charles Goodyear

22 Degree of cross-linking controls properties Effect of cross-linking on rubber (Of course, properties of the monomers are at least as important.)

23 Today Finish up CAPA #2 (due tomorrow) Friday Finish reading Chapt 13 Go to seminar