Masato Takahashi

Lifetime of growing polymer chain in stopped-flow propene polymerization using pre-treated Ziegler catalysts

The lifetime of a growing polymer chain of monoester type and diester-type supported catalysts was investigated by the stopped-flow polymerization technique. A linear correlation of the polymerization time with both the polymer yield and the molecular weight was observed for the monoester-type supported catalyst until a certain time period (0.2 s), where the growing polymer chain is still active. The activity of the diester-type supported catalyst was found to increase gradually throughout the polymerization (0-1.2 s). The polymer yield and the molecular weight are proportional to time up to 1.2 s when the pre-treatment of the diester-type supported catalyst was conducted with triethylaluminium. The active sites on the pre-treated catalyst exert a longer lifetime (at least 1.2 s) compared with that on the monoester-type and diester-type supported catalysts without pre-treatment. Kinetic studies indicated that the pre-treatment influences not only the number of active sites, but also the ratio of isospecific active sties to aspecific ones formed on the supported catalyst.

Improvement in productivity and molecular weight of polypropene-block-poly(ethene-co-propene) obtained by a modified stopped-flow method using various external electron donors

The efficiencies of various types of external electron donors to improve the productivity and molecular weight of the block copolymer, polypropene-block-poly(ethene-co-propene), obtained by a modified stopped-flow method were investigated, directed toward commercial production. Five alkoxysilanes having different structures, and a piperidine compound were employed as external donors. In all cases, an increase in the activity and weight-average molecular weight was observed on addition of the external donor at a Si/Ti mole ratio of ca. 1.0. Diisopropyldimethoxysilane was considered to be the most suitable donor for the synthesis of the block copolymer, due to its higher initial activity and properties, giving a polymer having higher molecular weight. An improvement in the molecular weight with considerable catalyst deactivation was apparently observed by increasing the Si/Ti mole ratio and decreasing the triethylaluminum (TEA) concentration. The results in this paper are an indication that a suitable choice of the kinds of external donors, Si/Ti mole ratio, and TEA concentration are needed to obtain block copolymers with desirable performance. Die Effizienz verschiedener externer Elektronendonatoren zur Produktivitatssteigerung und Molekulargewichtserhohung bei der Herstellung von Polypropen-block-poly(ethen-co-propen) mit einer modifizierten Stopped-Flow-Methode wurde hinsichtlich der Eignung fur die kommerzielle Produktion untersucht. Funf Alkoxysilane unterschiedlicher Struktur und eine Piperidin-Verbindung wurden als externe Elektronendonatoren eingesetzt. In allen Fallen fuhrte die Zugabe dieser Substanzen bei einem Si/Ti-Molverhaltnis von etwa 1,0 zur Erhohung der Aktivitat und des gewichtsmittleren Molekulargewichts. Diisopropyldimethoxysilan wurde aufgrund seiner hoheren Anfangsaktivitat und Eigenschaften, die zu einem Polymeren mit hoherem Molekulargewicht fuhrten, als der geeignetste Elektronendonator ermittelt. Eine Molekulargewichtserhohung durch betrachtliche Katalysatordeaktivierung wurde offensichtlich durch die Erhohung des Si/Ti-Molverhaltnisses und die Verringerung der Triethylaluminium (TEA)-Konzentration verursacht. Die Untersuchungsergebnisse zeigen, das durch geeignete Wahl des externen Elektronendonators, des Si/Ti Molverhaltnisses und der TEA-Konzentration Blockcopolymere mit den gewunschten Eigenschaften erhalten werden.