Polymerization of Isoprene with Ni(acac)2-Methylaluminoxane Catalyst

Abstract

ABSTRACT:The polymerization of isoprene (IP) with transition metals (MtX) and methylalumoxane (MAO) catalysts was carried out. Nickcl(II) acctylacetonatc [Ni(acac)2] in combination with MAO revealed high catalytic activity. The microstructure of the polymers obtained with the Ni(acac) 2-MAO catalyst was mainly cis-1,4-units, and but no 1,2-units were observed, indicating that the polymerization of IP with the Ni(acac),-MAO catalyst proceeds through a mainly 4, I-addition mode. From the copolymerization of styrene (St) and IP with the Ni(acac)z and MAO catalyst, monomer-reactivity ratios were estimated to be rs,= 1.18 and r1r = 0.88, indicating an ideal copolymerization to proceed to give a random copolymer.The IP units in the copolymers consist of mainly cis-1,4-microstructure.KEY WORDS Polymerization / Isoprene / Nickel(II) Acetylacetonate / Methylaluminoxane / Ideal Copolymerization / Styrene / Many studies have been reported on polymerizations of olefins with group IV methallocene in combination with methylaluminoxane (MAO)_ 1-13 Group VIII metal compounds were found to be effective catalysts for the polymerization of ethylene and cx-olefins. 14 -16 On the other hand, the polymerizations of dienes with transition metals (MtX) and MAO catalysts have not been given much attention, although some works on the polymerizations of dienes have been reported. 1 7 -19 The polymerization of IP with nickel(II) acetylacetonate [Ni(acac) 2 ] in combination with MAO gives cis-1,4-poly(IP), but the detailed microstructure and kinetics of polymerization with the Ni(acac)z-MAO catalyst were not investigated. 18 Previously, we reported that the Ni(acac)z-MAO catalyst showed high catalytic activity for the polymerization of methyl methacrylate, 20 styrene (St), 21 and butadiene (BD). 22 Thus, it is interesting to know whether the Ni(acac)z-MAO catalyst is effective for the polymerization of isoprene (IP) and produces high cis-1,4 polymers as well as the polymerization of BO. 22 In this article, we investigate the polymerization of IP with MtX-MAO catalysts, especially Ni(acac)z-MAO catalyst.When copolymerizations of St and IP with anionic catalysts such as alkyllithiums were carried out, random copolymers were not produced, and IP units were incorporated predominantly into the copolymers. 23 · 24 Copolymerizations of St and IP with CpTiC13-MAO catalyst have been reported to produce fairly random copolymers, 25 • 26 but the Ni(acac)z-MAO catalyst was not examined. In a previous paper, 21 we assumed that the polymerization of St with Ni(acac)z-MAO catalyst may involves a homolytic scission of nickel-carbon bonds. Thus, it should be possible to obtain random copolymers in the copolymerization of St and IP with Ni(acac)z-MAO catalyst. To check this point, we examined the copolymerization of St and IP with the Ni(acac)z-MAO catalyst.t To whom all correspondence should be addressed. EXPERIMENT AL MaterialsIP and St were purified by distillation over calcium hydride before use. Ni(acac) 2 was used after sublimation. Other transitio...

Emprego de catalisadores à base de níquel para homo- e copolimerização de estireno

“…O acetilacetonato de níquel destaca-se pela alta atividade catalítica, pela alta incorporação de estireno e pelo controle da microestrutura do dieno inserido na cadeia polimérica [29][30][31] .…”

“…Endo e colaboradores [29][30][31] avaliaram a copolimerização do estireno com isopreno com diferentes concentrações de estireno na alimentação (Tabela 7). Como a polidispersão dos polímeros ficou em torno de dois, os autores propuseram que as copolimerizações ocorriam por meio de um sítio único, sem a formação de homopolímeros.…”

“…Dessa forma, foi proposto um mecanismo radicalar para explicar esses resultados. No entanto, um mecanismo via coordenação também deve ser considerado dado o controle estereoespecífico do catalisador 29,30 .…”

“…O produto r 1 *r 2 igual a 1,04 é indicativo de que a copolimerização ocorre de forma aleatória 29 .…”

“…Outra caracterís-tica desses catalisadores é a ocorrência de um mecanismo de re-inserção 1,ω (Figura 2), que explica a formação de poliolefinas com teor de ramificações mais baixo que o esperado, quando propileno, hexeno e outras olefinas de cadeia longa são polimerizadas [16][17][18] . Por outro lado, a homopolimerização de estireno sobre catalisadores de níquel, principalmente aqueles com acetilacetonas como ligantes, tem demonstrado uma grande versatilidade na obtenção de poliestireno e seus copolímeros [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] . A presença de triisobutilalumínio ou de trimetilalumínio residual no metilaluminoxano exerce uma grande influência sobre a atividade catalítica e a estereoespecificidade dos catalisadores de níquel na polimerização de estireno 23,26 .…”