Chapter 2 Step-Growth Polymerization Part 1 An Introduction to Polycondensation.

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Slide 2 Chapter 2 Step-Growth Polymerization Part 1 An Introduction to Polycondensation Slide 3 One way is from monomer Suitable Monomer & Suitable method (polymerization) Another way is from a given polymer How to Prepare Polymer ? Slide 4 The reaction from monomer to polymer By the change of Composite and Structure between monomer and polymer Polycondensation Adduct polymerization Polymerization ? Classification 1 Slide 5 Adduct polymerization No low molecular weight material is produced. The composition of the newly produced material is the same as the monomer. There are only reactions between increasing chains and the monomers Slide 6 Polycondensation Low molecular weight material is produced. The composition of the produced chemical is different from that of the monomer Either the monomer can join in the increasing chain, or a increasing chains can connect to anther chains Slide 7 By the reaction mechanism Step-Growth Polymerization Chain Polymerization Classification 2 Slide 8 Step-Growth Polymerization the middle products can be separated out the separated middle products can react furthermore Including: Polycondensation Step adduct reaction Ring open polymerization Slide 9 Chain Polymerization A reaction in which the middle products can never be separated out. According to the active center Free Radical Polymerization Cationic Polymerization Anionic Polymerization Coordination Polymerization Slide 10 Great Industrial Value Examples Polyester Linear saturated polyester: plasticizer, Linear unsaturated polyester: glass fiber laminate, casting resin, solventless lacquer Network polyester: surface coating Why do we study the Step-Growth Polymerization ? Why do we study the Step-Growth Polymerization ? Slide 11 Most of the Polycondensation reactions are the typical Step-Growth Polymerization. Polycondensation reactions are taken as examples to illustrate the Step-Growth Polymerization. Slide 12 Condensation A reaction between two different functional groups, losing a molecule Besides main product, there is a byproduct. Whats the Polycondensation ? Slide 13 Polycondensation Polycondensation is the abbreviation of condensation polymerization. Monomers with functional group Polymer many times of repeated condensation Slide 14 functional group an atomic group in the mono- mer which participates in reac- tion in an indicated way. e.g. COOH OH NH 2 Cl NCO COOR CHO SO 3 H Key of Polycondensation Functionality Key of Polycondensation Functionality Slide 15 Functionality ( f ) the number of functional groups in the molecule which take part in the reaction. (monomer,oligomer). Slide 16 Type 1 System of f = 1 1 CH 3 COOH+HOC 2 H 5 CH 3 COOC 2 H 5 + H 2 O RCOOH + RNH 2 RCONHR +H 2 O Systems with f 1,1 1,2 1,3can condense but cannot polycondense. No macromolecule forms. No free functional group to continue the reaction How do the functionality influence the polycondensation ? Slide 17 Type 2 HOOC(CH 2 ) 4 COOH + H 2 N(CH 2 ) 6 NH 2 HOOC(CH 2 ) 4 CONH(CH 2 ) 6 NH 2 + H 2 O ( dimer) systems of f = 2 2 nHOOC(CH 2 ) 4 COOH + nH 2 N(CH 2 ) 6 NH 2 [O(CH 2 ) 4 CONH(CH 2 ) 6 NH] n + ( 2n 1)H 2 O Nylon 66 As the result, Slide 18 Systems of f = 2 2 monomer + monomer dimer dimer + monomer trimer dimer + dimer tetramer trimer + dimer pentamer tetramer + monomer pentamer tetramer + dimer hexamer tetramer + trimer heptamer tetramer + tetramer octamer etc. Slide 19 general reaction naRa + nbRb a[R R] n b + (2n 1)ab a b functional group R R construction unit ab micromolecule These reactions involve two different functional groups. One type of the functional group in each monomer. Forming linear polycondensation polymer Slide 20 Type 3 systems of f = 2 n HORCOOH [ORCO] n + (n 1)H 2 O n H 2 NRCOOH [NHRCO] n + (n 1)H 2 O general reaction naRb [R]n + (n 1)ab Systems of f = 2,3 2,4 3,3 can produce cross linking Polymers. One monomer has both types of functional groups. Type 4 systems of f = 2,3 2,4 3,3 Slide 21 1) monomers f 2 2) Changeable factors : functional groups ( OH, COOH, COOR, Cl, NH 2 ), f (linear or cross linking polycindensation) R, and R Huge sorts of polycondensation polymers 3) The polycondensation polymers are usually the heterochain polymers with N,O,S,P in the backbone and the functional groups in the end. eg. O , CONH , COO etc Summary Slide 22 Industrially, polycondensation can be divided into many types according to the group in the polymer chain. polyester, polyamide, polyether reaction Slide 23 4) The compositions and structures of the polymers are different from those of the monomer, because of the byproducts in the reaction. 5) The conversion of monomer does not increase with the reaction time in the polycondensation reactions. Slide 24 Essentially, the key of polycondensation is the reactions between the function groups. Only with the efficient reaction, the macromolecules can be prepared. Practically, polycondensation should be described by the extent of reaction. (Notes: conversion for the chain polymerization. Chapter 3) Slide 25 monomer ; structure of polymer; thermodynamics By Classifications of Polycondensation Slide 26 (1) homogeneous polycondensation, f = 2 a single monomer which two types of func- tional groups example polycondensation of amino acids n H 2 N R COOH [NH R CO]n + (n 1)H 2 O 1. By monomer Slide 27 (2) mixed polycondensation, f = 2,2 Two kinds of bifunctional monomers. Only one type of functional group in each monomer. Example: diamine / diacid, dihydric alcohol / diacid n H 2 N(CH 2 ) 6 NH 2 + HOOC(CH 2 ) 4 COOH [NH(CH 2 ) 6 NHOC(CH 2 ) 4 CO]n + (2n 1)H 2 O Slide 28 (3) co- polycondensation (two cases) Another kind of monomer with the same functional groups are added to homogeneous polycondensation (ref. (1)). The third or the fourth kind of monomers are added to mixed polycondensation (ref. (2)). Slide 29 linear polycondensation Bifunctional monomer The chain increases to two directions along the ends of the chain. 2. By Structure of polymer Slide 30 Systems of f = 2 and f = 2, 2 are linear polycondensation. The key of linear polycondensation is to control the molecular weight of the products. Slide 31 cross linking polycondensation At least one monomer has more than two functional groups (f = 2, 3 or 2,4 3,3 ) The molecule increases towards more than two directions. The crosslinking polymer forms. Example: glycerol / phthalic anhydride alkyd resin, phenol / formaldehyde phenolic-formaldehyde resin. Slide 32 The viscosity will be suddenly increased as reaction goes to the certain degree, forming the gel. --------gelation The key of cross-linking polycon densation is to forecast and crontrol the gel point This critical point is called the gel point. Slide 33 balanced polycondensation unbalanced polycondensation the rate of reverse reaction is not equal to zero K 10 3. the rate of reverse reaction is little or equal to zero. K 10 3. 3. By Thermodynamics Slide 34 The increasement of macromolecule chain is step by step. Characteristic of linear polycondensation Characteristic I. Slide 35 Any molecule with different functional group can react to each other. There are no particular active centers in the reaction. The molecular weight of the polymer gra- dually increases with the decrease of the number of the groups. Slide 36 The monomers dispear at the early stage of reaction far before forming any polymer with sufficiently high molecular weight for practical utility. High conversion of monomer is reached at early stage of reaction followed by the reaction between oligomers. As the time increases, increases instead of the conversion. Contrarily, the conversion increases with time in the chain polymerization. Slide 37 1. 2. 3. 4. 5. Figure 2.1 The polyester reaction between ethylene and diacids. Slide 38 Firstly, the diol and the diacid monomer reacts to form dimer. Then the dimer reacts with itself to form tetramer or with unreacted monomer to yield trimer. aAa: dihydric alcohol(diol); bBb: diacid Slide 39 The tetramer and trimer continues to react with themselves, with each other, and with monomer and dimer. The polymerization proceeds in the stepwise manner, resulting the continuously increases of the molecular weight of the polymer. The whole process can be expressed as Slide 40 All polycondensations are characterized by the stepwise. The mechanism of polycondensation is rather different to that of chain polymerization which will be discussed in Chapter 3. The reactivity of a functional group is independent of the size of the molecule. Slide 41 Linear polycondensation is reversible equilibrium. The equilibrium constants (K) of different linear polycondensation is different. Characteristic II. Slide 42 K 4 10, e.g kinds of polyester the existance of micromolecule will greatly affect the degree of polymerization. K 300 400, e.g kinds of polyamide the existance of micromolecule will affect the degree of polymerization to some extent. K10 3 e.g phenol ~ methanal the reaction is irreversible It is clear that the synthesize art depends on the equilibrium constant, K, will affect. Slide 43 In the closed system, the high molecular weight polymer is hardly obtained, due to the existence of byproducts and residual micromolecule. Industrially, the micromolecules can be removed by reducing pressure method in order to change the equilibrium for preparing high molecular weight polymer. e.g. The vacuum degree of the system, i.e., the quantity of residual micromolecules, control the molecular weight of terylene. Slide 44 P, the fraction of the functional groups that have reacted P = ( P1) (2 1) where, N 0 the total of the certain groups at the initial stage N the quantity of unreacted groups at time of t The extent of reaction (P) and the degree of polymerization Slide 45 the number everage of construction units in each macromolecule Slide 46 Example 1 polyester reaction nHO R COOH [ORCO] n + (n 1)H 2 O t=0 the total of the initial groups COOH N 0 t=t the quantity of unreacted groups COOH N P OH P COOH P (2 2) (2 3) Slide 47 from (2 3) (2 4) P 1 (2 5) substitutes (2 2) for (2 4) Slide 48 Example 2 HOROH + HOOCRCOOH Case 1: the same mole ratio t=0 OH: N 0 COOH N 0, the total of construction units N 0 t=t OH: N COOH N the quantity of macromolecules N P OH P COOH P Slide 49 Case 2: the different mole ratio of COOH and OH It is necessary to marking out which functional group P belongs to. Example a/b 80/100 P a 100 P b 80 (2 2) (2 5) are applied to the system in which the mole ratio is equal. increases with increase of the P Slide 50 example two kinds of the structural units in the chain unit of [CH 2 CH 2 OOC(CH 2 ) 4 CO] n M 0 : the mean molecular weight for the structural unit M 0 86 Where: Slide 51 Thus, In the polycondensation reaction increase of the degree of reaction depends on 1. prolonging the reaction time 2. increasing the reaction temperature 3. removing the micromolecule intensively 4. using high active monomer Slide 52 The equilibrium polycondensation reactions consist of a series of equilibrium reactions. As the reactivity of functional groupsare assumed to be equal to each other, all reactions can be expressed by the same K COOH OH OCO H 2 O K The equilibrium constant (K) and the degree of polymerization Slide 53 COOH OH OCO H 2 O t 0 C 0 C 0 t t C 0 (1-P) C 0 (1-P) C 0 P C 0 P Case 1 the closed system K = Slide 54 P (2 6) + 1 (2 7) Thus, has relations not only with P but also with K. Slide 55 To polyester K 4 P( equilibrium ) 2/3 3 To polyamide: K 400 P( equilibrium ) 0.95 21 K 10 4 100 Thus 1.In the closed systems especially that with small K, the high molecular weight polymer is hard to be prepared. 2. Try to remove the micromolecules is key for incre- asing the molecular weight of the polymer. Slide 56 Case 2 the unclosed system The byproducts are removed along with the reactions. In this case, the concentra-tion of the byproduct is not the same as that of polymer. K when P 1 ( P 0.99 ) So: = = (2 8) Slide 57 (2 8) is called as equilibrium equation of poly- condensation showing the relationship between and K or n w. The strategies for removing the byproducts: reducing pressure increasing the temperature adding an inert gas polyester K 4 causing 100 requiring nw410 -4 (mol/l) polyamide K 400,causing 100 requiring nw410 -2 (mol/l)