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O objetivo deste trabalho foi estudar o efeito do tempo de envelhecimento natural do sistema catalítico versatato de neodímio/hidreto de di-isobutilalumínio/cloreto de t-butila sobre a polimerização de 2-metil, 1,3-butadieno (isopreno). Foram avaliadas a atividade catalítica e conversão, além da massa molar, distribuição de massa molar e microestrutura dos polímeros. Foi objetivo estudar também as características micro e macroestruturais do poli-1,4-cis-isopreno ao longo da polimerização. Os catalisadores envelhecidos apresentaram tempos mais curtos ao longo da polimerização e uma conversão mais alta em relação ao catalisador não envelhecido. Estes resultados em conjunto com a menor atividade catalítica nos catalisadores envelhecidos sugerem a provável desativação de alguns sítios ativos mais sensíveis. Não foi observada influência do envelhecimento do catalisador sobre a microestrutura do polímero. Houve também aumento da massa molar e estreitamento na polidispersão conforme o aumento da conversão. The goal of this work was to study the aging effects of the catalytic system neodymium versatate/diisobutylaluminium hydride/t-butyl chloride on 2-methyl, 1.3-butadiene (isoprene) polymerization. The catalytic activity, conversion and polymer characteristics (molar mass, molar mass distribution and microstructure) were evaluated. The macro and microstructural characteristics of poly-1.4-cis-isoprene along the polymerization were also studied. The aged catalysts have shorter times along the polymerization and a higher conversion than the non-aged catalyst. Together with the lower catalytic activity for aged catalysts, these results point to possible disabling of the most sensitive active sites. Aging of the catalyst did not affect the polymer microstructure. As the conversion progressed, the molar mass increased with a narrowing in the molecular weight distribution.

This article reports the results of a study comparing commercially available high-cis polybutadiene rubbers (BRs) proceeding from different production technologies and bearing distinct structural characteristics. The microstructure of these polymers was characterized by Fourier transform infrared spectroscopy; molecular weight and polydispersity values were characterized by size exclusion chromatography (SEC). The degree of branching was characterized by SEC and dynamic mechanical rheological testing (RPA 2000). Glass-transition temperature was characterized by differential scanning calorimetry, and rheological properties were characterized with an oscillating rheometer rubber process analyzer (RPA 2000). Tire tread formulations were prepared with carbon black HAF N-339 as a reinforcement filler, and we compared the mechanical properties and performance of the different elastomer compositions. The compositions were characterized by their rheological properties, tensile resistance, resistance to abrasion, resistance to tearing, permanent deformation, resilience, and fatigue properties. The tested compositions obtained from BRs with distinct structural characteristics showed different performances. Neodymium-salt-based catalysts produced BRs with higher cis-1,4 levels and higher linearities. These polymer compositions also showed higher performances in abrasion resistance, fatigue resistance, and resilience tests. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 88–99, 2006

This paper reports the study of the dependence of reaction conversion, catalyst activity, polymer microstructure, molecular weight, molecular weight distribution curves and Mooney viscosity on reaction temperature and monomer concentration in the reaction medium used in the synthesis of high cis-polybutadiene. A ternary catalyst system composed by neodymium versatate, trans-butyl chloride and diisobutylaluminum hydride was used in its synthesis. The highest molecular weights were obtained at polymerization temperatures in the range from 70 to 80 °C. The highest content of cis-1,4 repeating units (about 99%) was observed when the polymerization was carried out at the lowest initial monomer concentration (0.56 mol/l).

O objetivo deste trabalho foi estudar sistemas cataliticos ternarios constituidos por versatato de neodimio, cloreto de t-butila e hidreto de di-isobutil-aluminio para a polimerizacao de 1,4-cis de butadieno em hexano. Foram investigados os efeitos das razoes molares Cl/Nd e Al/Nd sobre a reacao de polimerizacao. Os polimeros foram caracterizados por cromatografia de exclusao por tamanho (SEC), espectroscopia na regiao do infravermelho (FT-IR) e viscosimetria no estado fundido. A atividade catalitica, massa molar, distribuicao de massa molar e viscosidade Mooney foram fortemente influenciados pela variacao da razao molar Cl/Nd. Os maiores teores de unidades cis foram observados em razoes molares Cl/Nd > 3. O valor maximo de atividade catalitica foi obtido em razoes molares Cl/Nd na faixa de 3 a 5. A microestrutura do polibutadieno foi significativamente influenciada pelo aumento da razao molar Al/Nd. Foi observado um valor maximo, 99% de unidades cis, na razao molar Al/Nd = 10. Os dados de conversao versus tempo de reacao mostraram que a velocidade de polimerizacao aumenta com a razao molar Al/Nd alcancando um valor maximo na razao molar Al/Nd=23. As curvas de distribuicao de massa molar evidenciaram um significativo processo de transferencia de cadeia para os polimeros produzidos em razoes Al/Nd mais altas.

Os catalisadores lantanídicos são muito eficientes na polimerização estereoespecífica de dienos, principalmente aqueles à base de neodímio. Neste trabalho será apresentado o estudo da polimerização do 2-metil, 1,3-butadieno com catalisadores à base de neodímio, utilizados comercialmente na polimerização do 1,3-butadieno. Foi estudado o efeito da temperatura, do tipo de alquilalumínio e da concentração de catalisador. As reações foram realizadas em reator de aço inox sob atmosfera inerte, usando como solvente o hexano e uma concentração de 2-metil, 1,3-butadieno de 12%. Foram obtidos polímeros com massas molares na faixa de 1,0 a 1,5 × 105 e teor de unidades repetitivas cis em torno de 97%. The rare earth metals catalysts are very efficient in stereospecific polymerization of dienes, especially those of neodymium. This paper reports on the polymerization of 2-methyl, 1,3-butadiene with catalysts of neodymium, used commercially in polymerization of 1,3-butadiene. Effects were studied from the temperature, type of alkylaluminum, and from the concentration of catalyst. The reactions were carried out in a stainless steel reactor under an inert atmosphere, using hexane as the solvent and a concentration of 12% of 2-methyl, 1,3-butadiene. Polymers were obtained with molecular weight from 1.0 to 1.5 × 105, with ca. 97% of cis repeating units.

The Ziegler-Natta catalyst and the polymerization thereof are systems which require careful handling and special treatment of chemicals. In spite of the use of inert atmosphere and dry chemicals, some Ziegler-Natta systems may present low activities or even may deactivate because of unsuitable handling. Some features of the TiCl3 synthesis and its characterization when related to the presence of impurities are described. Evidences of poor handling of chemicals and/or laboratory devices while in synthesis of the catalyst are emphasized. The problems arising from butadiene polymerization and some relevant details in propylene polymerization are also presented with teaching objectives.