ABSTRACT:The morphological and kinetic characteristics of novel Ziegler-Natta catalysts were studied. Catalysts were prepared by Borealis Polymers Oy using a new synthesis technique (emulsion technology). Video microscopy was used to study the growth of single catalyst particles during polymerization in the gas and liquid phases. The distribution of single particle activity was very narrow in the catalyst without external support and was rather broad in the the silica-supported catalyst. Video microscopy of molten polymer particles allowed observation of the process and degree of fragmentation of the catalyst particles. A correlation between the activation period during the initial stage of polymerization and catalyst fragmentation was found. Fragmentation was faster and more uniform with the catalyst without external support than with the silica-supported catalyst. Scanning electron microscopy provided information on morphology evolution and shape replication of the catalyst particles. With the catalyst without external support, good shape replication was observed, and compact and spherical particles were formed. With the silica-supported catalyst, shape replication was poor, and nonspherical porous polymer particle were formed. Modeling of the kinetics of propylene polymerization was done using a simple threestep reaction scheme neglecting mass and heat transport effects.

Summary: Analyzing polymer particles by microscopy technique at different polymerization times provided information regarding the catalyst support break‐up rate and degree of fragmentation during polymerization. Polymer samples were prepared at different polymerization times and melted under a video microscope to track the progress of fragmentation. Studies focused on effect of the catalyst support on the process and degree of catalyst fragmentation. Fragmentation behaviors of both a catalyst without an external support and a silica supported Ziegler‐Natta catalyst were compared. Fragmentation of catalyst was observed to occur in the whole catalyst matrix at the very beginning of polymerization. In the case of the catalyst without an external support, fragmentation was faster and more uniform than that of the silica supported catalyst. Results corresponded to the activity distribution of single catalyst particles as determined by video microscopy. The catalyst without an external support having particles of similar activities showed similar degrees of fragmentation. Conversely, silica supported catalyst having particles of different growth behavior produced particles having different degrees of fragmentation. The rate of increase in the number of catalyst fragments and their surface area with time during polymerization was investigated. Results correlated the catalyst activation period during the initial stage of polymerization to catalyst fragmentation.Poly(propylene) particles produced with silica supported (upper image) and non‐supported (lower image) Ziegler‐Natta catalysts.magnified imagePoly(propylene) particles produced with silica supported (upper image) and non‐supported (lower image) Ziegler‐Natta catalysts.

Summary: Self‐supported and MgCl2‐supported Ziegler‐Natta catalysts, produced by two catalyst synthesis methods are compared. Borealis Polymers OY (Finland), who supplied the catalysts, developed the catalyst synthesis methods. The first method (Method One) is based on an emulsion system and consists of an in situ single step preparation. The second method (Method Two) consists mainly of two steps: formation of the catalyst carrier particles, and their subsequent impregnation with the active material. The results showed that Method One produced catalysts of compact, spherical particles with good intra‐particle homogeneity and a narrow particle size distribution. On the other hand, Method Two produced catalyst particles whose properties depended directly on that of the catalyst carrier: they were spherical but very porous, with a broad particle size distribution. Polymer particles produced with the two catalyst systems are perfect replicas of the catalyst particles. Fines formed either during catalyst preparation or during polymerization were observed only with the catalyst prepared using Method Two. The particles of the catalysts produced using Methods One and Two had similar activities, independent of the initial particle size. Fragmentation of catalyst particles was very fast for both catalyst systems and was only observed to be 100% completed using the catalyst produced with Method One. Studies of the thermal properties showed that the catalyst prepared using Method One produced poly(propylene) of higher crystallinity and with a narrower melting peak.SEM images of polymer particles produced by (A) Method One and (B) Method Two.magnified imageSEM images of polymer particles produced by (A) Method One and (B) Method Two.

Video microscopy has been used as an effective tool for fast screening of six different metallocene/MAO supported catalyst samples. The different techniques employed for supporting the metallocene on silica gels can have an influence on the overall catalyst activity and on the activity of single catalyst particles. The kinetics of gas-phase polymerization of ethylene with supported metallocene/MAO catalysts can be modeled by using a simple reaction scheme and neglecting mass and heat transport effects.

Summary: Aqueous solutions of acrylic acid were levitated in a 40 kHz acoustic levitator. The monomer amount in the levitated droplets was monitored by Raman spectroscopy relating to an internal standard. Thus evaporation of the monomer as well as polymerization reactions initiated by a redox system were investigated by Raman spectroscopy and resultant data were compared to HPLC data. Decreases in monomer amount due to evaporation can be clearly distinguished from polymerization reactions. Additionally, temperature measurement within the droplet throughout a polymerization reaction shows the typical temperature course originating from the heat of polymerization.