25 线型缩聚物的分子量与分子量分布ppt课件

1、12Factors Influence on the Molecular WeightMolecular Weight Control in Linear PolycondensationMolecular Weight Distributions in Linear PolycondensationPart 3 Molecular Weight and MWD3Closed system： = + 1 nXKUnclossed system： = nXwPnKThe Factors Influence on the Molecular Weight of PolycondensationTh

2、e Balanced Characteristic4 Self-Catalyzed system： = 2k3 t + 12nX External Catalysis system： = k2C0t + 1nX20CThe Catalyzed System5With the same mole ratio of groups ：nX =P11The Extent of Reaction6Key: Deactivation of the functional end groups, i.e., stabilization of molecular weightMolecular Weight C

3、ontrol in Linear Polycondensation One way is slightly over weight of one reactants (non-stoichiometric). Finally another reactant completely react and all the chain ends posses the same functional group. Another way is to add a spot of monofunctional monomer. 7For the systems of a-R-a + b-R-b, not a

4、-R-b The numbers of A and B functional groups are given by Na and Nb, respectively.The stoichiometric imbalance r of the two functional groups is given by r=Na/Nb ( r1).B-B is present in excess.Case 1 Non-stoichiometric of Functional Groupsand if the reaction tends to the end,8 a-R-a b-R-b The numbe

5、r of group A is NaThe number of group B is NbThe number of a-R-a is given by Na/2 The number of b-R-b is given by Nb/2 The total of monomer molecules (namely the total of construction units) is given by（NaNb）/ 2The non-stoichiometric reactantsAt time of 0 ,9The total of macromolecules The extent of

6、reaction of group a is given by Pa Reacted a ： NaPa b : NaPa Unreacted a ：Na(1 Pa) b : Nb NaPa The total of unreacted a and b is given by: NaNb2NaPa The total of macromolecules is : (NaNb2NaPa ) /2At time of t ,Then 10Thus Substitute r=Na/NbThe moles of the two groups are equal（r=1） The group A is u

7、sed up ( Pa=1)If r =1 11 Theoretically, if the mole ratio of the two functional groups in the systems of a-R-a + b-R-b can be kept equal，the average degree of the condensation polymer will reach the maximum to the end of reaction.12The Excessive percentage q of b-R-b molecule is often used besides r

8、. The q is defined as: namelyExcessive mole-percent q13 R-b can react with group a in the polymer. By this method, the end groups are captured, giving the stabilized molecular weight. The molecular weight of polymer can be adjusted by R”-b. This method can be used for both the system a-R-a / b-R-b a

9、nd the system of a-R-b.Case 2 Adding monofunctional monomer R-b to capture the end group 14 The systems of a-R-a + b-R-b with the same mole ratioThe number of the R-b is NCThe coefficient 2 of Nc is required since quantitatively one molecule R”-b has the same effect as one excess molecule b-R-b on r

10、estricting the polymer chain growing. 15 The system of a-R-bThe number of the R-b is NC16 The high purity of monomer Precise measurement Proper temperature control Protected by inert gas, along with using catalytic agent and vacuumizing the systemSummary17The molecular weight distribution (also called Polydispersity Index) is then given by: Polydispersity IndexAs P1，D approaches to