Copolymerization of Butadiene with Ethylene or 1-Alkenes

Copolymerization of BD and ethylene is achieved by the use of the catalyst system [Me2Si(3-Me3SiC5H3)2]NdCl/BuLi/DIBAH at a molar ratio of 1/10/10. The catalyst system yields BD/ethylene copolymers with a BD-content up to 42 mol %. The copolymers are predominantly alternating and exhibit a high trans- 1,4-content of the BD moieties. This system is also active in the homopolymerization of BD [505]. Further investigations in the activation of 

By application of the dimethylsilyl-bridged bisfluorenyl neodymium chloride complex [Me2Si(Ci3H8)2]NdCl (cocatalysts Buli, DIBAH, BuMgCl, BuMgOct) a complete new class of polymers is accessible by the copolymerization of ethylene and BD [307]. By reaction of 1 eq. BD and 2 eq. of ethylene 1,2-cyclohexane units are formed along the polymer chain. More than half of the inserted BD units (53-58 mol %) are involved in the ring closure reaction. The residual non-cyclicized BD units exhibit a nearly identical ratio of trans-1,4- and 1,2-units. 

Copolymerizations of BD with 1-alkenes such as 1-octene and 1-dodecene aim at short chain branching of BR. Kaulbach et al. used the ternary catalyst system NdO/TIBA/EASC (htiba/ Nd = 25, nci/nNd = 3) for the respective copolymerizations of BD/l-octene and BD/l-dodecene [508]. These authors showed that only small amounts of 1-alkenes are incorporated and that no neighboring 1-alkene moieties are present in the copolymer. The copolymerization parameters have been determined by the method of Kelen-Tiidos rBD = 25 and ri-octene 0 rBD = 18 and r dodecene = 0.1. With increasing amounts of 1-alkene in the monomer feed catalyst activity decreases drastically. The cis- 1,4-contents of the BD units in the copolymer were around 90% and were barely affected by increases of the 1-alkene content in the monomer feed. 

Another positive aspect of Nd catalysis is the high selectivity of Nd catalysts towards the polymerization of dienes. This feature is exploited in two ways. First, homopolymerization of BD in the presence of styrene as a solvent and second, selective homopolymerization of IP in the crude C5 cracking fraction. 

In a later patent (1986) it is disclosed that phase separation of cz s-1,4-BR and BD occurs at 30 to 35 °C. Below 30 °C there is a single phase and above 35 °C there are two distinct phases of BR and BD. By the application of two polymerization steps the first of which is performed below and the second above the critical solution temperature molar mass is decreased and costs for aluminum alkyls which are used for molar mass control are reduced [511,512], Control of molar mass is further improved by the sequen- 

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