22 Synthesis of Copolymers Using Ionic Techniques
Anionic Polymerization Downloaded from pubs.acs.org by IOWA STATE UNIV on 01/15/19. For personal use only.
D. H . RICHARDS Propellants, Explosives, and Rocket Motor Establishment, Ministry of Defense, Waltham Abbey, Essex E N 91BP,U . K .
In recent years increasing effort has been devoted to the synthesis of novel copolymers and block copolymers in order to develop materials with predictable and controllable properties. Such materials include thermoplastic elastomers, polymers of predetermined functionality, and polymers which are v i t a l ingredients in the formulation of polymer alloys and blends. In this paper ways of synthesizing polymers and copolymers possessing ionic groups at specified points along their backbones are considered and some oftheproperties of such materials are described. Because work in this area of synthesis is continuing, this paper is necessarily a combination of well established and half-established facts interlaced with considerable speculation. It is hoped that it is made clear into which category any given topic f a l l s . The specific theme dealt with here is the development of methods of synthesizing polymers and copolymers possessing specifically sited quaternary ammonium bonds. The basic polymerization techniques employed are either anionic or cationic and these are considered separately. Anionic Techniques We have r e c e n t l y showni that l i v i n g a n i o n i c polybutadiene r e a c t s with p y r i d i n e in tetrahydrofuran (THF) t o y i e l d the 4-adduct (equation 1), and that t h i s product can be re-aromatized by r e f l u x i n g in a s u i t a b l e solvent (equation 2) t o
form polymer with a terminal p y r i d i n e .
I t has subsequently been
shown that although the 4-adduct i s the e x c l u s i v e product i n THF, a mixture of the 4- and the 2-adduct i s formed i n hydrocarbon
0097-6156/81/0166-0343$05.00/0 © 1981 American Chemical Society
ANIONIC
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POLYMERIZATION
solvents.Z More importantly from a s y n t h e t i c viewpoint it was a l s o found that, although adduct formation appeared to be q u a n t i t a t i v e , the r e - a r o m a t i z a t i o n stage was subject to some s i d e r e a c t i o n which reduced the o v e r a l l y i e l d to a maximum of about 70%. Nevertheless, the y i e l d s were high enough to demonstrate the dramatic e f f e c t s which occur when hydrocarbon polymers poss e s s i n g such t e r t i a r y amine groups are quaternized. Low molecular weight polybutadienes with t e r m i n a l p y r i d i n e groups, l i k e t h e i r hydrogen terminated counterparts, are mobile l i q u i d s . However, when quaternized in bulk with benzyl bromide (equation 3) they are transformed i n t o s o l i d m a t e r i a l s . T h i s But - ( ( N
+
