第二章 逐步聚合反应

1、12Chapter 2 Step-Growth Polymerization3Part 1 An Introduction to Polycondensation4One way is from monomer Suitable Monomer & Suitable method (polymerization)Another way is from a given polymer2.1.1How to Prepare Polymer ? 2.1 Introduction5A. Adduct polymerization No low molecular weight material

2、 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 6 By the reaction mechanismA. Step-Growth Polymerization B. Chain PolymerizationClassification 27B. Chain Polymerization A reaction in which th

3、e middle products can never be separated out.8 Great Industrial ValueExamplesPolyester Linear saturated polyester: plasticizer,可塑剂可塑剂Linear unsaturated polyester: glass fiber laminate, casting resin, solventless lacquerNetwork polyester: surface coating 2.1.3 Why do we study the Step-Growth Polymeri

4、zation ? 9 Most of the Polycondensation reactions are the typical Step-Growth Polymerization. Polycondensation reactions are taken as examples to illustrate the Step-Growth Polymerization.10B. Polycondensation Polycondensation is the abbreviation of condensation polymerization. Monomers with functio

5、nal groupPolymermany times of repeated condensation11 B. Functionality ( f ) ： the number of functional groups in the molecule which take part in the reaction. (monomer,oligomer). 12 general reaction： n aRa + n bRb aRRnb + (2n1)ab a，b functional group； R，Rconstruction unit； ab micromolecule These re

6、actions involve two different functional groups. One type of the functional group in each monomer. Forming linear polycondensation polymer 131) monomers f 2；2) Changeable factors : functional groups (OH,COOH,COOR,Cl,NH2，), f (linear or cross linking polycindensation) R, and R Huge sorts of polyconde

7、nsation polymers3) 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,COOetcSummary 14 Industrially, polycondensation can be divided into many types according to the group in the polymer chain. polyester, po

8、lyamide, polyether reaction154) 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.16 Essentially, the key of polyc

9、ondensation 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) 17 (2) mixed polycondensation, f =

10、2,2 Two kinds of bifunctional monomers. Only one type of functional group in each monomer.Example: diamine / diacid, dihydric alcohol / diacidn H2N(CH2)6NH2 + HOOC(CH2)4COOH NH(CH2)6NHOC(CH2)4COn + (2n1)H2O2.2.4 Classifications of Polycondensation 18 linear polycondensation Bifunctional monomer The

11、chain increases to two directions along the ends of the chain.2. By Structure of polymer2.2.4 Classifications of Polycondensation 19 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.2.2.4 Classifications

12、of Polycondensation 20 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 phen

13、olic-formaldehyde resin. 2.2.4 Classifications of Polycondensation 21 The viscosity will be suddenly increased as reaction goes to the certain degree, forming the gel. -gelation The key of cross-linking polycondensation is to forecast and crontrol the gel point This critical point is called the gel

14、point.2.2.4 Classifications of Polycondensation 22balanced polycondensationunbalanced polycondensation the rate of reverse reaction is not equal to zero K10103 3 . the rate of reverse reaction is little or equal to zero. K10103 3 .3. By Thermodynamics2.2.4 Classifications of Polycondensation 23 The

15、increasement of macromolecule chain is step by step.2.3 Characteristic of linear polycondensationCharacteristic I.24 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

16、with the decrease of the number of the groups.2.3 Characteristic of linear polycondensation25 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 reac

17、tion 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.nX2.3 Characteristic of linear polycondensation26HOROHHOOCRCOOHHOROCORCOOROHHOROCORCOOHHOROHHOOCRCOOH+H2OHOOCRCOOROC

18、ORCOOH trimertetramer2dimer trimer27Firstly, the diol and the diacid monomer reacts to form dimer.二醇二醇.aAa + bBb a A B b + abThen the dimer reacts with itself to form tetramer or with unreacted monomer to yield trimer.aA Bb + aAaaA B Aa + abaA Bb + bBbbB A Bb + abaA Bb + + abaA BbaA B A Bb aAa: dihy

19、dric alcohol(diol); bBb: diacid28The 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.29All polycondensations are charact

20、erized 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.30the degree of polymerization P, the fraction of the functional groups t

21、hat have reacted0001NNNNN where, N0 ： the total of the certain groups at the initial stage N ： the quantity of unreacted groups at time of t31 ：the number everage of construction units in each macromoleculenXleculesof macromonumberthesction unitof construthe total Xn P11nXnX11P=000NN1NNNP=nXnX32 Lin

22、ear polycondensation is reversible equilibrium. The equilibrium constants (K) of different linear polycondensation is different.Characteristic II.2.3 Characteristic of linear polycondensation33 K410, e.g kinds of polyester， the existance of micromolecule will greatly affect the degree of polymerizat

23、ion. K300400, e.g kinds of polyamide， the existance of micromolecule will affect the degree of polymerization to some extent. K103， e.g phenol methanal the reaction is irreversible， It is clear that the synthesize art depends on the equilibrium constant, K, will affect.34In the closed system, the hi

24、gh 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 syst

25、em, i.e., the quantity of residual micromolecules, control the molecular weight of terylene.涤纶涤纶35P, the fraction of the functional groups that have reacted0001NNNNNwhere,N0 ： the total of the certain groups at the initial stageN ： the quantity of unreacted groups at time of t2.5 The degree of polym

26、erization ：the number everage of construction units in each macromoleculenXleculesof macromonumberthesction unitof construthe total Xn 36Example 1：polyester reaction nHORCOOH ORCOn + (n1)H2O t=0，the total of the initial groups ： COOH：N0 t=t，the quantity of unreacted groups ：COOH：N POHPCOOH P (22) 00

27、01NNNNN (23)NN0leculesof macromonumberthesction unitof construthe total Xn 37from (23)： (24)nX10NN P 1nX1 (25) P11nXsubstitutes (22) for (24)： (23)leculesof macromonumberthesction unitof construthe total Xn NN0 POHPCOOH P (22) 0001NNNNN38Example 2：HOROH + HOOCRCOOHCase : the same mole ratiot=0 OH: N0 ，COOH： N0, the total of construction units：N0 t=t OH: N ， COOH： Nthe quantity of macromolecules：N POHPCOOH P 0001NNNNNnXNN0P11 39 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