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

Suitable method (polymerization) Another way is from a given polymer How to Prepare Polymer ? One way is from monomer Suitable Monomer & Suitable method (polymerization) Another way is from a given polymer

Classification 1 Polymerization ? The reaction from monomer to polymer By the change of Composite and Structure between monomer and polymer Polycondensation Adduct polymerization

Adduct polymerization ① No low molecular weight material is produced. The composition of the newly produced material is the same as the monomer. ② There are only reactions between increasing chains and the monomers

Polycondensation ① Low molecular weight material is produced. The composition of the produced chemical is different from that of the monomer ② Either the monomer can join in the increasing chain, or a increasing chains can connect to anther chains

Classification 2 By the reaction mechanism Step-Growth Polymerization Chain Polymerization

－ the middle products can be separated out 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

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

Step-Growth Polymerization ? Why do we study the Step-Growth Polymerization ? Great Industrial Value Examples Polyester Linear saturated polyester: plasticizer, Linear unsaturated polyester: glass fiber laminate, casting resin, solventless lacquer Network polyester: surface coating

Most of the Polycondensation reactions are the typical Step-Growth Polymerization. Polycondensation reactions are taken as examples to illustrate the Step-Growth Polymerization.

Condensation What’s the Polycondensation ? A reaction between two different functional groups, losing a molecule Besides main product, there is a byproduct.

many times of repeated condensation Polycondensation Polycondensation is the abbreviation of condensation polymerization. many times of repeated condensation Monomers with functional group Polymer

Key of Polycondensation – Functionality functional group：an atomic group in the mono- mer which participates in reac- tion in an indicated way. e.g.： －COOH，－OH，－NH2，－Cl，－NCO， －COOR ， －CHO ，－SO3H

Functionality ( f ) ： the number of functional groups in the molecule which take part in the reaction. (monomer,oligomer).

How do the functionality influence the polycondensation ? Type 1：System of f = 1，1 CH3COOH+HOC2H5 CH3COOC2H5 + H2O RCOOH + R’NH2 RCONHR’ +H2O No free functional group to continue the reaction Systems with f ＝ 1,1；1,2；1,3…can condense，but cannot polycondense. No macromolecule forms.

Type 2： HOOC(CH2)4COOH + H2N(CH2)6NH2 systems of f = 2，2 Type 2： HOOC(CH2)4COOH + H2N(CH2)6NH2 HOOC(CH2)4CONH(CH2)6NH2 + H2O ( dimer) As the result, nHOOC(CH2)4COOH + nH2N(CH2)6NH2 [O(CH2)4CONH(CH2)6NH]n + ( 2n－1)H2O Nylon－66

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.

Forming linear polycondensation polymer general reaction： naRa + nbR’b a[R－R’]nb + (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

n HORCOOH [ORCO]n + (n－1)H2O n H2NRCOOH [NHRCO]n + (n－1)H2O Type 3 systems of f = 2 n HORCOOH [ORCO]n + (n－1)H2O n H2NRCOOH [NHRCO]n + (n－1)H2O One monomer has both types of functional groups. general reaction： naRb [R]n + (n－1)ab Type 4 systems of f = 2,3；2,4；3,3 Systems of f = 2,3；2,4；3,3 can produce cross linking Polymers.

Summary 1) monomer’s f ≥2； 2) Changeable factors : functional groups (－OH,－COOH,－COOR,－Cl,－NH2，……), 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

Industrially, polycondensation can be divided into many types according to the group in the polymer chain. polyester, polyamide, polyether reaction

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.

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)

Classifications of Polycondensation By monomer ; structure of polymer; thermodynamics

1. By monomer (1) homogeneous polycondensation, f = 2 tional groups a single monomer which two types of func- tional groups example： polycondensation of amino acids n H2N －R － COOH → [NH－R － CO]n + (n－1)H2O

(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 H2N(CH2)6NH2 + HOOC(CH2)4COOH → [NH(CH2)6NHOC(CH2)4CO]n + (2n－1)H2O

(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)).

① linear polycondensation 2. By Structure of polymer ① linear polycondensation Bifunctional monomer The chain increases to two directions along the ends of the chain.

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.

② 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.

The viscosity will be suddenly increased as reaction goes to the certain degree, forming the gel. --------gelation This critical point is called the gel point. The key of cross-linking polycon densation is to forecast and crontrol the gel point

3. By Thermodynamics balanced polycondensation unbalanced polycondensation the rate of reverse reaction is not equal to zero K＜103 . the rate of reverse reaction is little or equal to zero. K＞103 .

Characteristic of linear polycondensation Characteristic I. The increasement of macromolecule chain is step by step.

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.

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.

4. 体系中聚酯的总含量 3. 高分子量聚酯的含量 5. 聚酯分子量的增长（粘度法） 2. 低分子量聚酯的含量 1. 癸二酸含量 Figure 2.1 The polyester reaction between ethylene and diacids.

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

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

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.

Characteristic II. Linear polycondensation is reversible equilibrium. The equilibrium constants (K) of different linear polycondensation is different.

① K＝4～10, e.g kinds of polyester， the existance of micromolecule will greatly affect the degree of polymerization. ② K＝300～400, e.g kinds of polyamide， the existance of micromolecule will affect the degree of polymerization to some extent. ③ K≥103， e.g phenol ~ methanal the reaction is irreversible， It is clear that the synthesize art depends on the equilibrium constant, K, will affect.

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.

The extent of reaction (P) and the degree of polymerization P, the fraction of the functional groups that have reacted P = ( P≤1) (2－1) where, N0 ： the total of the certain groups at the initial stage N ： the quantity of unreacted groups at time of t

：the number everage of construction units in each macromolecule

Example 1：polyester reaction nHO－R－COOH → [ORCO]n + (n－1)H2O t=0，the total of the initial groups ： －COOH：N0 t=t，the quantity of unreacted groups ：－COOH：N P－OH＝P－COOH＝ ＝ P (2－2) ＝ (2－3)

substitutes (2－2) for (2－4)： from (2－3)： ＝ (2－4) substitutes (2－2) for (2－4)： P ＝ 1－ ＝ (2－5)

Example 2：HOROH + HOOCR’COOH Case 1: the same mole ratio t=0 －OH: N0 ，－COOH： N0, the total of construction units：N0 t=t －OH: N ， －COOH： N the quantity of macromolecules：N P－OH＝P－COOH＝ ＝ P ＝ ＝

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 Pa ＝ 100％，Pb ＝ 80 ％ (2－2) ～(2－5) are applied to the system in which the mole ratio is equal. increases with increase of the P

Where: ＝ ＝ M0: the mean molecular weight for the structural unit ＝ ＝ Where: M0: the mean molecular weight for the structural unit example：two kinds of the structural units in the chain unit of [CH2CH2OOC(CH2)4CO]n M0 ＝ 86

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

The equilibrium constant (K) and the degree of polymerization 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－～ ＋ H2O K ＝ ＝

～－COOH ＋ ～－OH ～－OCO－～ ＋ H2O t＝0 C0 C0 t＝t C0(1-P) C0(1-P) C0P C0P Case 1 the closed system K = ＝ ＝ ＝

Thus, P ＝ (2－6) ＝ + 1 (2－7) has relations not only with P，but also with K.

To polyester：K ＝ 4，P(equilibrium)＝2/3， ＝3 To polyamide: K ＝ 400，P(equilibrium)＝0.95， ＝21 K ＝ 104， ＝100 Thus： 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.

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 ＝ ＝ So: = = when P 1，( P＞0.99) (2－8) ＝

The strategies for removing the byproducts: (2－8) is called as equilibrium equation of poly-condensation，showing the relationship between and K or nw. The strategies for removing the byproducts: ① reducing pressure；② increasing the temperature； ③ adding an inert gas polyester K＝4，causing ≥100，requiring nw≤4×10-4 (mol/l) polyamide K＝400,causing ≥100，requiring nw≤4×10-2 (mol/l)