Flashcards
Polymers
Cards in this deck (29)
- 1Polymer Types: (list)Thermoplastic
Thermoset
Linear or Cross-linked
Step Growth or Chain Growth - 2Polymer Classes: (List)Block
Graft
Regular
Random
Isotactic
Syndiotactic
Atactic - 3Polymer Processes: (List)Free Radical (most common half of all)
Cationic
Anionic
Metal Complex
Metal Oxide
Metallocene Catalyzed - 4Polymer Procedures: (List)Bulk
Solution
Suspension
Emulsion - 5Classification: (List)end properties and uses:
Plastics
fibers
elastomers
coating
adhesives - 6Thermoset Polymershave cross-linked 3D structures, hardened by chem reaction during the manufacturing of finished products. They decompose on heating and are in-fusible and insoluble
- 7Thermoplastic Polymers:soften or melt when heated and dissolve in suitable solvents. Can be remelted and shaped into finished product with no chemical reaction.
- 8Linear or Cross-linked Polymers:structure
- 9Step or Chain Growth Polymers:addition or condensation polymers depending on mechanism of formation
- 10Polymers: (definition)substances with repeating units and high molecular weight (MW)
- 11Polymerization: (definition)the joining of many small molecules to form very large ones with repeating units
- 12Chain Growth Polymerization (addition polymerization)- characterized b/c of ther intermediates in process (free radicals, ions, or metal complexes) are transient (last short time) and cannot be isolated.
- once initiated occurs fast
-monomer concentration decreases steadily through whole reaction
- prolonged reaction has little effect on molecular weight or yield
- no net loss of atoms in polymer
- at any point has lots of unchanged reactants and fully gown polymer but very little of growing chains (fast) - 13Step Growth Polymerization: (Condensation Polymerization)- occurs between moles with functional groups
- stopped at any time, low MW products that can be isolated (oligmers- few units not fully polymer)
- monomer concentration does not decrease steadily, disappears early, formation of oligomers.
- long reaction times, build MW
-large amount of oligomers, little reactant or full polymer
- small molecule lost (water) as two monomers combine, NOT ALWAYS - 14Radical Initiation ProcessChain Growth Polymerization:
1) Initiation: decomposition of peroxides to form free radicals (alkoxy radicals) RO*
RO* joins to double bond creating a chain free radical
2) Propagation: free radical chain joins to double bond, makes another radical on chain... continuos
3) Termination: by coupling, disproportionation or chain transfer - 15Termination: Coupling, Disproportionation, and chain transfer (picture)Radical Initiation/Chain Growth:
- 16Radical Initiation: (Description)Chain Growth:
- unsymmetrical monomers: "head to tail" addition
-chain transfer termination leads to branching (effect on polymer properties)
- chain transfer can also occur from hydrogen atom abstraction from a carbon in the same chain as the radical ( as long as 6-membered stable transition state), with C4 branch product
- 17Chain Transfer:Radical Initiation/Chain Growth:
- not desirable, only to intentionally limit MW by adding transfer agents like RSH or ArOH
- transfer of Cl limits the size of one chain and same time initiates formation of a new chain by the trichloromethyl radical, results in lower average chain length. - 18Radical Initiation Common Monomers (Picture)
- 19Radical Initiation: (diene polymers)- polymerization of dienes
- conjugated dienes (1,3-butadiene) readily polymerize free radically
- double bonds still present in polymer (critical in elastomers - rubbers) because some cross-linking with disulfide bridges can occur in finished polymer at allylic sites to give elastic properties to polymers - 20Radical Initiation: (dienes part 2)- 1,4 addition and 1,2 addition occurs, and double bonds may be E or Z (Z cis, E trans)
- only with homogenous metal complex catalysts will stereochemistry be regular
Examples of Polymerized Dienes: polychloroprene, polyisoprene - 21Ionic Initiation: (anionic)- anionic: olefins (alkene) containing electron withdrawing groups.
- anionic initiatiors: n-butyllithium, sodium amide and sodium/potassium metal in liquid ammonia or naphthalene - 22Ionic Initiation: (anionic mechanism) Picture
- 23Anionic Initiation (termination)Coupling and disproportionation not possible, two negative ions dont join.
termination is a result of proton transfer from solvent or weak acid (water)
- ionic polymerization doesnt need to terminate (living polymer. - 24"Living Polymer"ionic polymerization:
polymers in ionic polymerization need not terminate. If monomers are added, weeks or months later, there will be further MW increase as the polymer chains grow. As long as no counter ion (lithium) anionic end group is stable - 25Ionic Initiation: (Cationic)occurs with protonic acids (HF and H2SO4 or lewis acids: BF3, AlCl3 and SnCl4)
- termination proceeds loss of a proton (HSO4-) to form terminal double bond, which regenerates catalyst. - 26Metal Complex Initiation:polymerize olefins and dienes with stereoregularity
- polypropylene doesnt polymerizelymerize easily. Under Ziegler-Natta conditions: High MW and Isotactic - 27IsotacticStereoregular
- 28Atactic:Random
- 29SyndiotacticAlternate
