POLYMERISATION

POLYMERISATION

1. POLYMERS

   • THERMOSETTING
     • Rigid three dimensional network( chains maybe linear / branched)
     • Can be either liquid/solids at room temperature.
     • Examples : Polyurethanes, Epoxy, polyester
   • THERMOPLASTIC
     • Flexible linear chains (straight/ branched )
     • Processing - easy such as thermoplastics.
     • Example : polyethylene, polystyrene
   • ELASTROMER
     • Thermoplastics or lightly cross-linked thermosets, consist of spring –like molecules
     • Example : Natural rubber
     • Known as rubber

2. POLYMERISAZATION SYNTHESIS

   • Addition Polymerization @ Chain growth polymerization
     • 2) involves the linking together of molecules incorporating double or triple chemical bonds
     • 3) process involved reaction in which monomers are added one after another to a rapidly growing chains.
     • 1) unsaturated monomers (the identical molecules that make up the polymers) have extra internal bonds that are able to break and link up with other monomers to form the repeating chain.
     • 4) The growing polymer proceeds via a chain mechanism
     • 5) three fundamental steps are involved
       • a) initiation.
       • b) propagation .
       • c) termination.
         • 2_ Disproportionation
         • 1) Combination
     • 6) Chain-growth polymerization is involved in the manufacture of polymers
       • 1) polyethylene
       • 2) polypropylene
       • 3) polyvinyl chloride (PVC).
     • 7) A special case of chain-growth polymerization leads to living polymerization.
     • 8) Addition polymers can be recognized by noting that the repeating unit always has the same formula as the monomer from which the polymer is formed.
     • 9) There exists a type of addition polymerization that does not undergo a termination reaction.
     • 10) Anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of vinyl monomers with strong electronegative groups.
       • Anionic polymerizations are used in the production :
         • polydiene synthetic rubbers
         • solution styrene/butadiene rubbers (SBR)
         • styrenic thermoplastic elastomers.
   • Condensation @ Step growth polymerization
     • Condensation
       • To condense means to make something more dense, or compact.
       • Polymers formed when a small molecule condenses out during the polymerization reaction are therefore called condensation polymers.
       • Silicone, for example, is a condensation polymer formed by polymerizing (silanol) (CH3)2Si(OH)2. Each time a monomer is added to the polymer chain, a molecule of water is condensed out, as shown in the figure below.
     • Step-growth polymers = polymers formed by the stepwise reaction between functional groups of monomers.
     • Step-growth polymers increase in molecular weight at a very slow rate at lower conversions and reach moderately high molecular weights only at very high conversion (i.e. >95%).
     • Condensation polymers are formed from a series of reaction, in which two species (monomer) can react at any time leading to a larger molecule.
     • In this reaction, stepwise reaction occurs between the chemically reactive groups or functional groups on the reacting molecules.
     • In the process, a small molecule, usually water / ammonia is eliminated
       • Example: formation of polyester through reaction of glycol and dicarboxylic acid.
     • A condensation polymer is defined as a polymer that involves loss of small molecules during its synthesis, or contains functional groups as part of its backbone chain, or its repeat unit does not contain all the atoms present in the monomer to which it can be degraded.
       • Example :
         • Polyimide
         • Polyester
     • The monomers for condensation polymerization have two main characteristics:
       • Each monomer has at least two reactive sites, which usually means two functional groups.
       • Instead of double bonds, these monomers have functional groups (like alcohol, amine, or carboxylic acid groups).
     • Monomers involved in condensation polymerization have functional groups combine to form: amide and ester linkages.
       • Amide Linkages
       • Ester Linkages
     • A water molecule is removed as the ester linkage is formed. Notice the acid and the alcohol groups that are still available for bonding.
     • Differentiation between Addition Polymerization and Condesation Polymerization

3. POLYMERIISATION PROCESS

   • 1) The two carbon atoms are joined by a double covalent bond.
   • 2) Each carbon atom shares two of its electrons with the second carbon atom and two hydrogen atoms are bonded to each of carbon atom.
   • 3) Replace one of the hydrogen atoms in CH2 with CH3, benzene ring @ chlorine

4. What is needed:

   • Extremely pure ingredients.
   • Clean, very high yield reactions.
   • At least moderate reaction rates.
   • Precise balance of functional groups.

5. What Can Go Wrong

   • Impurities containing only one functional group.
   • Unwanted side reactions.
   • Decomposition of monomer.

6. Cationic polymerization

   • a type of chain growth polymerization in which a cationic initiator transfers charge to a monomer which becomes reactive.
   • This reactive monomer goes on to react similarly with other monomers to form a polymer.
   • Monomer scope for cationic polymerization is limited to two main types:
     • Olefins
     • Heterocyclic monomers

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