CLASSIFICATION OF POLYMERIZATION REACTIONS l For polymerization it

CLASSIFICATION OF POLYMERIZATION REACTIONS l For polymerization it is required that the monomer molecule is capable of being linked to two (or more) other molecules of monomer by chemical reaction (functionality). l Functionality of two or higher is needed. l Classification of polymerization are based on comparison of the molecular formed of a polymer with that of the monomer from which it was formed.

CONDENSATION POLYMERIZATION l Those which yield polymers with R. U. having less atoms than present in the monomers from which they formed (elimination of a small molecule). l Example l Polyester is a typical condensation reaction between bifunctional monomers with elimination of water. X HO-R 1 -OH + X HOCO-R 2 -COOH HO [ R 1 -OCO-R 2 -COO ]x H + (2 X-1) H 2 O

ADDITION POLYMERIZATION Those which yield polymers with repeat units having identical molecular formula to those of monomers from which the one formed. Example Polystyrene. l X CH 2 = CH ----CH 2 -CH---, etc.

The addition reaction mechanisms are result from chain reactions involving some sort of active center. l Because condensation reaction mechanisms are usually formed by the step wise intermolecular condensation of reactive groups. l And because some condensation process reacted in addition manner a new term is used to defined this process (step reaction or condensation polymer). l See table 2. 1 Billmeyer l

Step Polymerization Linear Step Polymerization Step polymerization involves successive reaction between pairs of maturely-reactive functional groups. l Functionality is a critical importance in this reaction l Example l 1)Condensation reaction of carboxylic acid groups with hydroxyl groups both acetic acid and ethyl alcohol are monofunctional compounds which yield ethyl acetate with elimination of water l CH 3 COOH +CH 3 CH 2 OH CH 3 COOCH 2 CH 3 + H 2 O From this polymer chain can not form.

l 2)If we have terephthalic acid and ethylene glycol both are difuctional COOH CH 2 -OH COOCH 2 -OH + COOH CH 2 -OH + H 2 O COOH The product is an ester which have one carboxylic acid end group and one hydroxyl end-group (i. e. it is also difunctional).

The dimers can react with molecules of acid or alcohol or dimer. formation of difuctional. Difunctional monomers linear step polymerization. Trifunctional monomers branched polymer. Example l Tetephtalic acid react with glycerol l HO CH 2 CH (OH) CH 2 OH l The product is non linear. l

POLYCONDENSATOIN Step polymerization that involve reaction in which small molecules are eliminated are termed polycondensation. l Example l (1) the formation of linear polyesters l n HOOC-R 1 - COOH + n. HO-R 2 - OH H [ OOC-R 1 -COOR 2 ]n OH + (2 n-1) H 2 O Where R 1 and R 2 general groups. It can be represented as R 1 A 2 + R 2 B 2 where: A & B are mutually reactive groups.

§Polyesters may also prepared from single monomer which contain both types of functional group. Example w-hydroxyl carboxylic acids. HOOC-R-OH This is ARB step polymerization Advantage exact stoiciometric equivalent of the two functional groups is granted.

POLYAMIDES Polyamides are prepared by polycondensation of amine groups. l Example l n. H 2 N-R 1 -NH 2 + n. HOOC-R 2 -COOH H [ NH-R 1 NHOC-R 2 -CO ]n OH + (2 n-1) H 2 O

POLYETHERS l Polyethers formed by dehydration of dioles. HO-R-OH + HO-R-OH HO [ RO ]n H + (n-1)H 2 O RA 2 step polymerization

SILOXANE l Siloxane Prepared by hydrolysis of dichloro dialkylsiloxanes e. g. dichlorodimethylsiloxene. CH 3 n. Cl-Si-Cl + (n+1) H 2 O HO [ Si-O ] H + 2 n. HCl CH 3 (poly dimethylsiloxane) (PDMS) initially hydrolysis occurs l CH 3 Cl-Si-Cl + 2 H 2 O HO-Si-OH +2 HCl CH 3 after that we can have both RA 2 + RB 2 polymerized (CH 3)2 Si. Cl 2 react with (CH 3)2 Si(OH)2 or (CH 3)2 Si(OH 2) can condense by itself (RA 2) polymer.

POLYADDITION Step polymerization in which the monomers react together without the elimination of other molecules. l Example l 1) Polyurethanes by the RA 2 + RB 2 reaction of diisocyanate with diols. l O = C = N = R 1 - N = C = O + HO - R 2 - OH O O [ C - NH-R 1 - NH-C - OR 2 -O ]n

l 2) O Polyureas O C - N - R 1 - N = C + H 2 N - R 2 -NH 2 O O [ C - NH-R 1 - NH-C-NH-R 2 -NH ]n

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