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On the 1,4‐ cis ‐Polymerization of Butadiene with the Highly Active Catalyst Systems Nd(C 3 H 5 ) 2 Cl·1.5 THF/Hexaisobutylaluminoxane (HIBAO), Nd(C 3 H 5 )Cl 2 · 2 THF/HIBAO and Nd(C 3 H 5 )Cl 2 ·2 THF/Methyl‐aluminoxane (MAO) – Degree of Polymerization, Polydispersity, Kinetics and Catalyst Formation
Author(s) -
Maiwald Steffen,
Sommer Christian,
Müller Gert,
Taube Rudolf
Publication year - 2001
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/1521-3935(20010501)202:8<1446::aid-macp1446>3.0.co;2-s
Subject(s) - chemistry , polymerization , catalysis , polymer chemistry , 1,3 butadiene , organic chemistry , polymer
The allylneodymium chloride complexes Nd(C 3 H 5 ) 2 Cl·1.5 THF and Nd(C 3 H 5 )Cl 2 ·2 THF can be activated by adding hexaisobutylaluminoxane (HIBAO) or methylaluminoxane (MAO) in a ratio of Al/Nd = 30 for the catalysis of butadiene 1,4‐ cis ‐polymerization. A turnover frequency (TOF) of about 20 000 mol butadiene/(mol Nd·h) and cis ‐selectivity of 95–97% are achieved under standard conditions ([BD] 0 = 2 m , 35°C, toluene). Molecular weight determinations indicate a low polydispersity ( M̄ w (LS)/ M̄ n (LS) = 1–1.5), the formation of only one polymer chain per neodymium and the linear increase of the degree of polymerization ( DP ) with the butadiene conversion, as observed for living polymerizations. First indications of chain‐transfer reaction occur only at the highest conversion or degree of polymerization. The rate law r P = k P [Nd][C 4 H 6 ] 1.8 is derived for the catalyst system Nd(C 3 H 5 ) 2 Cl·1.5 THF/HIBAO and for the system Nd(C 3 H 5 )Cl 2 ·2 THF/MAO the rate law r P = k P [Nd] [C 4 H 6 ] 2 with k P = 3.24 L 2 /(mol 2 ·s) (at 35°C). Taking into account the Lewis acidity of the alkylaluminoxanes and the characteristic coordination number of 8 for Nd(III) in allyl complexes the formation of an η 3 ‐butenyl‐bis(η 4 ‐butadiene)neodymium(III) complex of the composition [Nd(η 3 ‐RC 3 H 4 )(η 4 ‐C 4 H 6 ) 2 (X‐{AlOR} n ) 2 ] is assumed to be a single‐site catalyst for the chain propagation by reaction of the coordinated butadiene via the π‐allyl insertion mechanism and the anti ‐ cis and syn ‐ trans correlation to explain the experimental results.