Polybutadienes modified by partial addition reactions

The main question is whether such reactions yield random or block copolymers. Random addition of a limited amount of reagent XY to the double bonds in the polymer will result in structures of the type —M1M2M1— (20), which can then be degraded by metathesis with the symmetrical olefin Q2 to give Q(M /2)(M2)-(Mi/2)Q as one of the products. For example, if XY = H2 and Q2 = oct-4-ene, this product is PrCH=CH(CH2)6CH=CHPr. 

If the addition reaction is taken to higher conversion, the products contain sequences of M2 units, and in principle the sequence distribution may be found by GC analysis of the degradation products, provided they are sufficiently volatile. This is the case for XY = H2 or CH2 products containing up to at least five M units can be detected (see Fig. 16.5). For XY = CI2, Br2, HCl, or HBr, only the first and sometimes the second member of the series (/w = 1, 2) are sufficiently volatile to be detected by GC. 

The results of this type of investigation are summarized in Table 16.1. On the heterogeneous Pd/C catalyst, there is a marked variation in hydrogenation behaviour with temperature. At 20°C no double-bond shifts are observed but at 

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Degradation of Unsaturated Polymers by Metathesis 16.3.5 Polybutadienes modified by partial addition reactions... 

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