Compatibilised polyolefin compositions

Compatibilised polyolefin compositions combining the positive properties of their respective components by using an olefinic di- or triblock copolymer as compatibiliser to generate a finely dispersed phase structure in the molten state and to improve adhesion between the blend components in the solid state, while not compromising processability of the polyolefin composition

Accelerating the Research Approach to Ziegler–Natta Catalysts

Despite 60 years of history and a stunning success, Ti-based Ziegler–Natta catalysts for the production of isotactic polypropylene remain black-box systems, and progress still relies on trial and error. This represents a limitation in a moment when the most widely used industrial systems, containing phthalates as selective modifiers, need to be replaced because of a recent REACH ban. In view of the great complexity of the chemical and physical variables and the heavy nonlinearity of their effects, a high-/medium-throughput approach to this catalysis is highly desirable; herein we introduce an integrated medium-throughput workflow spanning from propene polymerization to polypropylene microstructural characterization and combining a 10²-fold throughput intensification with quality standards equal or higher than conventional methods

Molecular Kinetic Study of “Chain Shuttling” Olefin Copolymerization

Statistical olefin block copolymers (OBCs) with “hard” and “soft” linear low-density polyethylene (LLDPE) blocks can be synthesized by tandem catalysis under “coordinative chain transfer polymerization” (CCTP) conditions. This process, disclosed in 2006 and commonly referred to as “chain shuttling copolymerization” (CSCP), is now exploited commercially by Dow Chemical, to produce thermoplastic elastomers with the Infuse trade name. Whereas the general kinetic principles of CSCP as well as the fundamental physical properties of the products are rather well-understood, the details are still poorly defined, to the point that even average block numbers and lengths of commercial Infuse grades are not available in the public domain. In this paper, we report the results of a molecular kinetic investigation in which high throughput experimentation tools and methods were employed to unravel the microstructure and architecture of these materials. The problem was factored in two parts. First, each of the two catalysts in the original Dow Chemical formulation was studied individually in ethene/1-hexene CCTP. Next, the two catalysts together were used in CSCP experiments under otherwise identical reaction conditions. The robust database thus obtained enabled us to disambiguate the interpretation of the results, and sort out system behavior as a function of the relevant variables. Plausibly, the process turned out to be governed by the relative probabilities of “self-shuttling” versus “cross-shuttling” (that is, of exchanging blocks of the same or different type). In particular, the synthesis of OBCs with long hard blocks and an excess of soft blocks, which are those featuring the most desirable application properties, requires a moderate chain shuttling rate and an excess of the catalyst with the higher comonomer incorporation ability; as a result, at practical average molecular weight values, these products are characterized by a pronounced interchain disuniformity, with an abundant fraction of chains undergoing exclusively “self-shuttling” at the aforementioned catalyst, and therefore consisting of just one soft block

Structure/Properties Relationship for Bis(phenoxyamine)Zr(IV)-Based Olefin Polymerization Catalysts: A Simple DFT Model To Predict Catalytic Activity

The productivity of a number of bis­(phenoxyamine)­Zr­(IV)-based catalysts (bis­(phenoxyamine) = <i>N,N</i>′-bis­(3-R₁-5-R₂-2-O-C₆H₂CH₂)-<i>N,N</i>′-(R₃)₂-(NCH₂CH₂N)) in ethene and propene polymerization was evaluated for different R₁/R₂/R₃ combinations. In previous studies on this class we demonstrated that the cations that form upon precatalyst activation (e.g., by methylalumoxane) adopt a “dormant” <i>mer-mer</i> geometry, and an endothermic isomerization to the active <i>fac-fac</i> geometry is the necessary first step of the catalytic cycle. Herewith we report a clear correlation between catalyst activity and the DFT-calculated energy difference Δ<i>E</i>_<i>i</i> between the active and dormant state. The correlation only holds when the calculations are run on ion pairs, which is less obvious than it may appear because the anion in these systems is not at the catalyst front. This finding provides a comparatively simple and fast method to predict the activity of new catalysts of the same class

Chain Transfer to Solvent in Propene Polymerization with Ti Cp-phosphinimide Catalysts: Evidence for Chain Termination via Ti–C Bond Homolysis

Propene polymerization using Ti Cp-phosphinimide catalysts in toluene and related aromatic solvents leads to the formation of benzyl-terminated polymer chains. End-group analysis suggests that these are formed after a 2,1-insertion event; density functional theory (DFT) studies support a mechanism involving homolysis of a Ti-<i>sec</i>-alkyl bond. This reaction could enable the catalytic formation of chain-end functionalized polyolefins. More importantly, it demonstrates that Ti–C homolysis might limit activity but does not necessarily constitute an irreversible deactivation mechanism

Structure/Properties Relationship for Bis(phenoxyamine)Zr(IV)-Based Olefin Polymerization Catalysts: A Simple DFT Model To Predict Catalytic Activity

The productivity of a number of bis­(phenoxyamine)­Zr­(IV)-based catalysts (bis­(phenoxyamine) = <i>N,N</i>′-bis­(3-R₁-5-R₂-2-O-C₆H₂CH₂)-<i>N,N</i>′-(R₃)₂-(NCH₂CH₂N)) in ethene and propene polymerization was evaluated for different R₁/R₂/R₃ combinations. In previous studies on this class we demonstrated that the cations that form upon precatalyst activation (e.g., by methylalumoxane) adopt a “dormant” <i>mer-mer</i> geometry, and an endothermic isomerization to the active <i>fac-fac</i> geometry is the necessary first step of the catalytic cycle. Herewith we report a clear correlation between catalyst activity and the DFT-calculated energy difference Δ<i>E</i>_<i>i</i> between the active and dormant state. The correlation only holds when the calculations are run on ion pairs, which is less obvious than it may appear because the anion in these systems is not at the catalyst front. This finding provides a comparatively simple and fast method to predict the activity of new catalysts of the same class

The Interplay of Backbone Stiffening and Active Pocket Design in Bis(phenolate-ether) Zr/Hf Propene Polymerization Catalysts

For [OOOO]-type catalysts, the introduction of two methyl substituents behind the active site, at the backbone C3 linker, can substantially impact performance in propene polymerization catalysis depending also on the nature of the R1 substituent neighboring the active pocket. Catalyst molar mass capability and productivity can increase by 2–3 orders of magnitude; also, regioselectivity and stereoselectivity increase (2–3 fold). The results highlight (a) the importance of stiffening catalyst backbones of post-metallocene catalysts for high-temperature applications and (b) the complex interplay between backbone and active pocket design in post-metallocene olefin polymerization catalysis