13 Branching of High Molecular Weight Polyhydroxyethers Based on Bisphenol-A Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 23, 2017 | http://pubs.acs.org Publication Date: June 8, 1983 | doi: 10.1021/bk-1983-0221.ch013
S. A. ZAHIR Ciba-Geigy AG, Basel, Switzerland S. BANTLE Universität Freiburg, Institut für Makromolekulare Chemie, Federal Republic of Germany The kinetics of the polyaddition reaction of diglycidyl ether of Bisphenol A with Bisphenol A in solution and in the melt has been studied using tetrabutyl ammonium hydroxide and benzyl triethyl ammonium chloride as catalysts at several temperatures. The weight average molecular weight (Mw) and the number average molecular weight (Mn) can be related to the extents of reaction of the phenolic hydroxyl groups (α), the epoxide groups (β) and the branching probability p using a statisti cal method based on the cascade theory of bran ching processes. p is defined as the number of branches per secondary hydroxyl group in the chain. From p a kinetic parameter, b = k2/k1, can be determined, where k2 is the rate constant for the addition of epoxide to the secondary hydroxyl groups in the chain (the chain branching step), and k1 the rate constant for the addition of epoxide to the phenolic hydroxyl groups (the chain lengthening step). From the kinetic and mo lecular weight data, it has been possible to cal culate b. The application of the branching theory and the measurements of the kinetics of the re action are of considerable practical importance, as it enables the rational selection of catalysts, and allows the prediction of suitable reaction conditions for the synthesis of high molecular weight phenoxy resins. One of the methods for the synthesis of high molecular weight polyhydroxy ethers based on Bisphenol A is the base ca talyzed polyaddition of the diglycidyl ether of Bisphenol A (BADGE) with Bisphenol A (BPA) in the melt or in solution (Scheme 1). 0097-6156/83/0221-0245$06.00/0 © 1983 American Chemical Society
Bauer; Epoxy Resin Chemistry II ACS Symposium Series; American Chemical Society: Washington, DC, 1983.
246
EPOXY RESIN CHEMISTRY (Chain lengthening step)
Scheme 1 Ο
Ο / \ / \ CH -CH-CH 0-AR-OCH -CH-CH 2
2
2
+ HO-AR-OH
2
CH.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 23, 2017 | http://pubs.acs.org Publication Date: June 8, 1983 | doi: 10.1021/bk-1983-0221.ch013
Base
AR I
•AR-0CH CHCH HD+ o
2
[
CH.
o
(
OH
2
η
where lq = the rate constant for the addition of the epoxide group to the phenolic hydroxyl group. The final molecular weight is normally controlled by the reaction stoichiometry and the purity of the reagents. During the chain lengthening step secondary hydroxyl groups are formed. The possibility of chain branching caused by the addition of the epoxide to the secondary hydroxyl group formed during the chain lengthening step leading to chain branching cannot therefore be altogether ignored (Scheme 2). Scheme 2
(Chain branching step)
Ο / \ + CH -CHCH -0-AR-
-ARH>CH -CHCH 0-ARZ ι Ζ OH o
o
0
Ζ
0
Ζ
Base -ARHXH -CHCIU0AJR2 j 2 Ο I CH-CHCHJDARo
2,
2
OH
where l
