Because of the considerable interest in methods of polymer analysis by which the amount of each type of unsaturation can be determined, this paper gives a description of the method used in obtaining the data on 1,2 and trans-1,4 addition and an extension of the method that permits determination of cis-1,4 addition and combined styrene, and gives more accurate results for 1,2 and trans-1,4 addition.
MOSTof the rubberlike polymers (both natural and synthetic) are diene addition polymers or copolymers. In diene polymerization, addition may take place in several ways. With butadiene, for example, cis-1,4, trans-1,4, and 1,2 addition are all possible (Figure 1). With substituted butadienes, such as isoprene, there is the additional possibility of 3,4 addition. (Resonance considerations, 5, indicate that addition will normally be "head to tail.") Natural rubber is polyisoprene, that is all, or nearly all, in the cis-1,4 configuration. Balata is inms-1,4polyisoprene. Synthetic polyisoprene, on the other hand, is a random mixture of at least three of the possible configurations and does not have the desirable physical properties of either rubber or balata. Ordinary GR-S contains a random mixture of styrene units and the three possible types of butadiene units. Recently Hart and Meyer have shown ( 6) that, when butadiene polymers are prepared at low temperatures, the addition of the butadiene units is preponderantly trans-1,4. Low temperature butadiene polymers have also been showrn to have significantly improved (15,19) physical properties.Accordingly, there has been considerable interest in methods of polymer analysis by which the amount of each type of unsaturation can be determined. The present paper describes the method used to obtain the data for 1,2 and trans-1,4 addition, as previously reported (ß), and an extension of that method which permits the determination of cis-1,4 addition and combined Table I.