Temporal Control over Two- and Three-State Living Coordinative Chain Transfer Polymerization for Modulating the Molecular Weight Distribution Profile of Polyolefins

The Highly Controlled and Efficient Polymerization of Ethylene

The highly controlled and efficient polymerization of ethylene is a very attractive but challenging target. Herein we report on a Coordinative Chain Transfer Polymerization catalyst, which combines a high degree of control and very high activity in ethylene oligo- or polymerization with extremely high chain transfer agent (triethylaluminum) to catalyst ratios (catalyst economy). Our Zr catalyst is long living and temperature stable. The chain length of the polyethylene products increases over time under constant ethylene feed or until a certain volume of ethylene is completely consumed to reach the expected molecular weight. Very high activities are observed if the catalyst elongates 60 000 or more alkyl chains and the polydispersity of the strictly linear polyethylene materials obtained are very low. The key for the combination of high control and efficiency seems to be a catalyst stabilized by only one strongly bound monoanionic N-ligand.

Tailoring Glass Transition Temperature in a Series of Poly(methylene-1,3-cyclopentane-stat-cyclohexane) Statistical Copolymers

A systematic investigation of the synthesis and characterization of a new class of amorphous atactic cis, trans poly(methylene-1,3-cyclopentane-stat-cyclohexane) statistical copolymers (I) is reported. Production of different grades of I that vary with respect to the ratio of 5- and 6-membered cycloalkane repeat units was achieved through the living coordinative chain transfer cyclopolymerization of different initial feed ratios of 1,5-hexadiene and 1,6-heptadiene comonomers. It was determined that the glass transition temperature, T_g, of I can be systematically increased from -16 to 100 °C as a function of increasing 6-membered ring content, although not in a strictly linear fashion. It was further determined that a small level of 6-membered ring content is sufficient to disrupt the crystallinity of the limiting atactic cis, trans poly(methylene-1,3-cyclopentane) (PMCP) homopolymer that possesses a melting temperature, T_m, of 98 °C. These results establish a foundation for future potential technological applications of this unique class of polyolefin copolymers.

Highly Versatile Strategy for the Production of Telechelic Polyolefins

A general and versatile synthetic strategy for producing practical quantities of a wide range of phenyl-group-terminated hetero- and homotelechelic semicrystalline polyethenes and amorphous atactic and semicrystalline isotactic poly(α-olefins) is reported. The phenyl groups serve as synthons for functionalities of additional classes of telechelic polyolefins that can be "unmasked" through simple high yielding postpolymerization reactions. A demonstration of the value of these materials as building blocks for structural classes of polyolefin-based synthetic polymers was provided by syntheses of well-defined polyolefin-polyester di- and triblock copolymers that were shown to adopt microphase-segregated nanostructured mesophases in the condensed phase.

Tuning Ligand Concentration in Cu(0)-RDRP: A Simple Approach to Control Polymer Dispersity

Cu(0)-reversible deactivation radical polymerization (RDRP) is a versatile polymerization tool, providing rapid access to well-defined polymers while utilizing mild reaction conditions and low catalyst loadings. However, thus far, this method has not been applied to tailor dispersity, a key parameter that determines the physical properties and applications of polymeric materials. Here, we report a simple to perform method, whereby Cu(0)-RDRP can systematically control polymer dispersity (Đ = 1.07-1.72), while maintaining monomodal molecular weight distributions. By varying the ligand concentration, we could effectively regulate the rates of initiation and deactivation, resulting in polymers of various dispersities. Importantly, both low and high dispersity PMA possess high end-group fidelity, as evidenced by MALDI-ToF-MS, allowing for a range of block copolymers to be prepared with different dispersity configurations. The scope of our method can also be extended to include inexpensive ligands (i.e., PMDETA), which also facilitated the polymerization of lower propagation rate constant monomers (i.e., styrene) and the in situ synthesis of block copolymers. This work significantly expands the toolbox of RDRP methods for tailoring dispersity in polymeric materials.

Tailoring polymer dispersity by mixing ATRP initiators

Herein we present a simple batch method to control polymer dispersity using a mixture of two ATRP initiators with different reactivities.