Polymerization Types Part-02
Steps of an-ionic polymerization:
• There are three steps of an-ionic polymerization:
In this step at first the initiator / catalyst is decomposed and produce organic +ve ion and –ve ion. Then –ve ion add to the monomer to generate an-ion or carbon ion. This is called initiation. Reaction is given bellow:
The an- ion or carbon ion obtained from initiation step combines to the next monomer with reformation carbon ion at the end of each step to produce growing polymer chain like free radical polymerization. The reaction continue until the supplied monomer is exhausted. It is called propagation.
Reaction is given bellow:
• In an-ionic polymerization termination is different type from other polymerization. Here polymer chain remain always alive. When polymer chain will be very large, then the growth of polymer chain will be stopped. It is called termination. In this case some highly -ve charged catalyst such as NH3, H-OH, alcohol etc. are used to complete termination reaction. Reaction is given bellow:
The chain polymerization in which monomer-catalyst complex is formed by the combination of monomer and catalyst is called co-ordinate polymerization. During the formation of monomer-catalyst complex a co-ordination bond is creat between metal parts of catalyst and carbon atom of monomer.In this polymerization Zieglar-Natta catalyst is used which is generally formed by a pair of compound such as
i) Halides of transition metals from group iv—group viii of the periodic table namely Ti, Zn, Sn, Ni, Mo etc.
ii) Alkyles, Aryls or Halydes of metals from group i—group iv of the periodic table namely Et3Al, Et2Zn, Et2AlCl etc. Mostly and commonly used catalyst in this polymerization is compound of Et3Al + TiCl4. The structure of this compound is
• It is a complex catalyst which is expressed as MtR.
STEPS OF CO-ORDINATE POLYMERIZATION:
In this case MtR is used as a initiator which add to the monomer and initiate the polymerization. It is called initiation.
Reation is given bellow:
Initiator added monomer obtained from initiation step add to the next monomers one after another and produce a growing polymer chain. It is called propagation.
Reaction is given bellow:
In this case termination is occurred by the following two ways:-
a) Termination is occurred with an active hydrogen compound
B. STEP POLYMERIZATION:
• The polymerization in which polymer is built up through a reaction between functional groups of the monomers in step wise manner is called step polymerization.In this case reaction take place slowlly. During polymerization some small molecules such as H2O, HCl, NH3 etc. are eleminted and bi-product is produced.
• CONDITIONS OF STEP POLYMERIZATION:-
• i)Monomer should have two reactive functional groups for polymerization.
• ii)Polymer is formed by step wise reaction between reactive functional groups.
• iii)Only one type of reaction between two functional groups is involved in polymer formation.
• iv)During polymerization small molecules such as H2O, HCl, NH3 etc. are eleminated.
• REACTIONS INVOLVED IN STEP POLYMERIZATION:-
• i)Condensation type.
• ii)Ring opening type.
• iii)Addition type.
• iv)Amidition type.
• v)Ester exchange type reaction.
i) Condensation polymerization:
Condensation polymerization is brought about by two or more functional group containing monomer and codense to each other. Step polymerization is entirely analogous to condensation in low molecular weight compounds. In polymer formation condensation reaction take pieace between poly functional monomers to produce a large poly functional compounds with possible elimination of a small molecules compound such as H2O, HCl, NH3 etc. The reaction continue until almost of all one of the reagent is used up and equillibrium is established which can be shifted at will at high temperature and controlling the reagents and products.
There are two types of condensation polymerization :-
1) A—B Type polycondensation:
When a single bi-functional monomer under goes in polymerization, then it is called A—B type polycondensation. The reaction is given bellow:
2) AA—BB Type polycondensation:
When a pair of bi-functional monomers under go in polymerization then it is called AA—BB type polycondensation . Reaction is given bellow:
n(A+B)àA-[-A.B-]-B +(2n-1) bi-product.
ii) RING OPENING TYPE POLYMERIZATION:
When monomer having ring structure can be opened and polymerised in favorable condition, then it is called ring opening type polymerization. Reaction is given bellow:
iii) ADDITION TYPE POLYMERIZATION:
This types of polymerization is brought about by the migration of hydrogen atom from one monomer molecules to another. The reaction is given bellow:
iv) AMIDATION TYPE POLYMERIZATION:
• When monomer having amide group exchange during polymerization, then it is called amidation polymerization. Reaction is given bellow:
• R-CONH-R’ + R”-NH2àR-CONH-R”+R’-NH2
V) ESTER EXCHANGE TYPE POLYMERIZAQTION:
• When monomer having ester group exchange during polymerization, then it is called ester exchange type polymerization. Reaction is given bellow:
R-COOH +R’-OH àR-COO-R’ + H2O