Polyolefins metallocene-catalyzed

B. C. Childress, Properties of homogeneous and heterogeneous polyolefins Metallocene catalyzed versus Ziegler-Natta catalyzed resins, MetCon 94 Proceedings, USA, May 1994. 

In addition to the two-phase TPEs, two new technologies have emerged. They are the metallocene-catalyzed polyolefin plastomers (POPs, the name given to Exxon s EXACT product line) and polyolefin elastomers (POEs, DuPont Dow Elastomer s ENGAGE), and reactor-made thermoplastic polyolefin elastomers (R-TPOs). These new types of TPEs are often called metallocene elastomers-TPEs (MEs-TPEs) [87]. The new POPs and POEs are essentially very low-molecular-weight-Unear low-density PEs (VLMW-LLDPE). These new-generation TPEs exhibit mbber-like properties and can be processed on... 

We encounter homogeneous catalysts in both step-growth and chain-growth polymerization processes. We saw several examples of these types of reactions in Chapter 2. For example, the acid catalyzed polymerization of polyesters occurs via a homogeneous process as do some metallocene catalyzed polymerization of polyolefins. 

Figure 32 The dimeric organoborane chain-transfer agent, 9-BBN dimer (49), used for the in situ incorporation of B-containing group in polyolefins during the termination of a metallocene-catalyzed polymerization. (Adapted from ref. 71.)...

Orlando, FI., 7th-llth May, 2000, paper 49 EXTRUSION OF CLOSED CELL VERY LOW DENSITY FLEXIBLE SYNTACTIC FOAMS USING METALLOCENE CATALYZED POLYOLEFINS AND THERMOPLASTIC MICROBALLOONS Trainer L J Beauregard D Orroth S Schott N Massachusetts,University (SPE)... 

It was also reported that terminally borane-containing POs is available as another macroinitiator to prepare block copolymers (Fig. 4). These polymers were prepared by (1) the metallocene-catalyzed (co)polymerization of olefin(s) with organoborane compounds, for example, 9-borabicyclononane (9-BBN), as chain transfer agents [32], or by (2) the hydroboration of terminally unsaturated polyolefins with BBN [33-36]. 

Block copolymers can be produced from terminally borane-containing polyolefins. These borane-containing POs can be synthesized by the metallocene-catalyzed (co)polymerization of olefin(s) monomer with 9-BBN as a chain transfer agent or by the metallocene catalyzed copolymerization of olefins with allyl-9-BBN [55,56], as referred to above. Alternatively, borane-containing POs were prepared by hydroboration of terminally unsaturated PO, for instance, terminally vinyl PE and terminally vinylidene PP [33-35,57]. Such method could produce diblock copolymers, such as polyethylene-block-poly(methyl methacrylate) (PE-fo-PMMA), polypropylene-foZock-poly(methyl methacrylate) (PP-fc-PMMA), polypropylene-foZock-poly(butyl methacrylate) (PP-fc-PBMA), and PP-fc-PS. 

Shiomura, T. Uchikawa, N. Asanuma, T. Sugimoto, R. Fujio, I. Kimura, S. Harima, S. Akiyama, M. Kohno, M. Inoue, N. Metallocene-catalyzed Syndiotactic Polypropylene Preparation and Properties. In Metallocene-based Polyolefins Preparation, Properties and Technology, Scheirs, J., Kaminsky, W., Eds. Wiley Chichester, 2000 Vol. 1, p 467. 

Metallocene catalysis is an alternative to the traditional Ziegler-Natta vanadium-based catalysis for commercial polyolefin production, e.g. the use of metallocene-catalyzed ethylene alpha-olefin copolymers as viscosity index modifiers for lubricating oil compositions [23]. The catalyst is an activated metallocene transition metal, usually Ti, Zr or Hf, attached to one or two cyclopentadienyl rings and typically activated by methylaluminoxane. Metallocene catalysis achieves more stereo-regularity and also enables incorporation of higher alpha-olefins and/or other monomers into the polymer backbone. In addition, the low catalyst concentration does not require a cleanup step to remove ash. 

The first reactor-type thermoplastic polyolefin (R-TPO) was LLDPE/PP [Yamazaki and Eujimaki, 1970, 1972]. The three-component R-TPO s (PE with PP and EPR) soon followed [Strametz et al, 1975]. PE was also polymerized in the presence of active catalyst and an olefinic copolymer [Morita and Kashiwa, 1981]. Blending amorphous co-polyolefins with crystalline PO s (HDPE, LLDPE, PP), and a filler resulted in moldable blends, characterized by excellent sets of properties [Davis and Valaitis, 1993, 1994]. Blends of polycycloolefin (PCO) with a block copolymer (both polymerized in metallocene catalyzed process) and PE, were reported to show outstanding properties, viz. strength, modulus, heat resistance and toughness [Epple and Brekner, 1994]. 

That is, in terms of reaction rates, the molecular weight of polyolefins is given by the ratio between the overall rate of propagation (Rp) and the sum of all rates of chain release (Rr) reactions this means that the molecular weight is dependent on the type of catalyst and the kinetics of the process, that is, the polymerization conditions (polymerization temperature, monomer concentration, catalyst/cocatalyst ratio). Hence, understanding the details of the mechanisms of chain release reactions is the key to molecular weight control in metallocene-catalyzed olefin polymerization. Here, chain release reactions (usually referred to as termination or transfer reactions) are all those steps that cause release of the polymer chain from the active catalyst, with the formation of a new initiating species (see section... 

Recent research and development (R D) work used metallocene-catalyzed PP to make submicron diameter MB fibers [16]. The polyolefin used in this work had a narrow molecular weight distribution and an MFR greater than 1000 g/10 min, a typical range for MB non woven polymers. 

Zheng, L., Farris, R.J. and Coughlin, E.B. (2001). Novel Polyolefin Nanocomposites Synthesis and Characterizations of Metallocene-Catalyzed Polyolefin Polyhedral Oligomeric Silsesquioxane Copolymers, Macromol, 34(23) 8034-8039. 

Fas Fasce, L. A., Frontini, P. M., Wong, S.-C., Mai, Y.-W. Polypropylene modified with elastomeric metallocene-catalyzed polyolefin blends Fracture behavior and development of damage mechanisms. J. Polym. Sci. Part B - Polym. Phys. 42 (2004) 1075-1089. 

Zheng, L., Farris, R. J., and Goughlin, E. B. 2001. Novel polyolefin nanocomposites Synthesis and characterizations of metallocene-catalyzed polyolefin polyhedral oligomeric silsesquiox-ane copolymers. Macromolecules 34 8034-8039. 

As much as 30% of all polyolefin products involve blends (Robeson 2007). It has been found, for example, that blending metallocene-catalyzed linear low-density polyethylenes (mLDPEs) with HDPE improves the Izod impact strength and some tensile properties of HDPE. Adding mLLDPE to LDPE increases the ductility of LDPE (Cran and Bigger 2009). In general, PE blends can be divided into three categories (1) PE lots blended to meet standard specifications for density and melt flow, (2) PE modified with <15 wt% of other polymer(s), and (3) PE bends with other thermoplastics or thermoplastic elastomers. 

The MBS market is decreasing partially due to PVC bottles being replaced by PET. This trend is more evident in Europe due to widespread use of water bottles. In contrast, the film and sheet market remain strong. Overall, MBS sales are heavily dependent on the future of PVC, particularly flexible PVC. Flexible PVC, comprising 15% of the total PVC market, is vulnerable to penetration by metallocene catalyzed polyolefins (for example, super soft polypropylene ). 

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