Polyolefin Block Copolymers Research Articles

Threading-the-Needle: Compatibilization of HDPE/iPP blends with butadiene-derived polyolefin block copolymers

Management of the plastic industry is a momentous challenge, one that pits enormous societal benefits against an accumulating reservoir of nearly indestructible waste. A promising strategy for recycling polyethylene (PE) and isotactic polypropylene (iPP), constituting roughly half the plastic produced annually worldwide, is melt blending for reformulation into useful products. Unfortunately, such blends are generally brittle and useless due to phase separation and mechanically weak domain interfaces. Recent studies have shown that addition of small amounts of semicrystalline PE-iPP block copolymers (ca. 1 wt%) to mixtures of these polyolefins results in ductility comparable to the pure materials. However, current methods for producing such additives rely on expensive reagents, prohibitively impacting the cost of recycling these inexpensive commodity plastics. Here, we describe an alternative strategy that exploits anionic polymerization of butadiene into block copolymers, with subsequent catalytic hydrogenation, yielding E and X blocks that are individually melt miscible with PE and iPP, where E and X are poly(ethylene-ran-ethylethylene) random copolymers with 6 wt% and 90 wt% ethylethylene repeat units, respectively. Cooling melt blended mixtures of PE and iPP containing 1 wt% of the triblock copolymer EXE of appropriate molecular weight, results in mechanical properties competitive with the component plastics. Blend toughness is obtained through interfacial topological entanglements of the amorphous X polymer and semicrystalline iPP, along with anchoring of the E blocks through cocrystallization with the PE homopolymer. Significantly, EXE can be inexpensively produced using currently practiced industrial scale polymerization methods, offering a practical approach to recycling the world's top two plastics.

Catalytic synthesis of functionalized (polar and non-polar) polyolefin block copolymers.

Herein, we report a methodology for the synthesis of polyolefin containing block-copolymers using a catalytic postpolymerization modification strategy. The most common polyolefin grades are converted into macroinitiators using a cross-metathesis reaction. These functionalized polyolefins are then used to initiate living: coordinative ring opening polymerization of lactide, anionic ring opening polymerization of epoxide, and radical polymerization of styrene to yield the corresponding block copolymers. The high activity of the catalysts employed in the different steps offers improved practicality for scalable synthesis.

De Novo Design of a New Class of "Hard-Soft" Amorphous, Microphase-Separated, Polyolefin Block Copolymer Thermoplastic Elastomers.

Sequential cyclic/linear/cyclic living coordination polymerization of 1,6-heptadiene (HPD), propene, and HPD, respectively, employing the well-defined and soluble group 4 transition-metal initiator, {(η5-C5Me5)Hf(Me)[N(Et)C(Me)N(Et)]}[B(C6F5)4], provides the stereoirregular, amorphous poly(1,3-methylenecyclohexane)-b-atactic polypropene-b-poly(1,3-methylenecyclohexane) (PMCH-b-aPP-b-PMCH) polyolefin triblock copolymer (I) in excellent yield. By varying the weight fraction of the end group, minor component "hard" PMCH block domains, fPMCH, relative to that of the midblock "soft" aPP domain, three different compositional grades of these polyolefin block copolymers, Ia-c, were prepared and shown by AFM and TEM to adopt microphase-separated morphologies in the solid state, with spherical and cylindrical morphologies being observed for fPMCH = 0.09 (Ia) and 0.23 (Ic), respectively, and a third more complex morphology being observed for Ib (fPMCH = 0.17). Tensile testing of Ia-c served to establish these materials as a new structural class of polyolefin thermoplastic elastomers, with Ia being associated with superior elastic recovery (94 ± 1%) after each of several stress-strain cycles.

Mechanical Consequences of Molecular Composition on Failure in Polyolefin Composites Containing Glassy, Elastomeric, and Semicrystalline Components

In order to gain insights into the mechanisms of deformation and ultimate failure in a homologous series of lamellae-forming polyolefin block copolymers comprised of glassy poly(cyclohexylethylene)...

Control of Mechanical Behavior in Polyolefin Composites: Integration of Glassy, Rubbery, and Semicrystalline Components

The mechanical properties of a homologous series of polyolefin block copolymers comprised of glassy poly(cyclohexylethylene) (C), elastomeric poly(ethylene-alt-propylene) (P), and semicrystalline poly(ethylene) (E) are documented. Monodisperse CPEPC, CPE, and CEPEC with mass fractions wC ∼ 0.39−0.44 and 0 ≤ ξ ≤ 1, where ξ = wE /(wE + wP), were synthesized by sequential anionic polymerization of styrene, isoprene, and butadiene followed by catalytic hydrogenation. These materials hierarchically microphase separate into lamellae, within which templated crystallization-induced segregation occurs. As ξ increases, the unoriented, polydomain CPEPC materials exhibit monotonically increasing elastic moduli and yield stresses, comparable ultimate tensile strengths, and decreasing failure strains. Cold drawing the CPEPC polymers yields high-strength materials, the structures of which are examined by small- and wide-angle X-ray scattering. Drawn CPEPC-70 (ξ = 0.70) exhibits improved toughness with an ultimate tensile strength σfail = 75 ± 10 MPa and elongation at break of εfail = 1.22 ± 0.22, as compared to σfail = 92 ± 21 MPa and εfail = 0.86 ± 0.18 for drawn CEC (ξ = 1.00). Elasticity measurements on the drawn samples demonstrate that materials with ξ > 0 exhibit low degrees of stress softening, while smaller permanent sets and higher failure strains are observed as ξ decreases.

Optically Transparent and High Molecular Weight Polyolefin Block Copolymers toward Self-Assembled Photonic Band Gap Materials

Block copolymers based on readily available olefins have been synthesized to construct self-assembled one-dimensional (1-D) photonic crystals. Using living olefin polymerization via a bis(phenoxyimine)titanium dichloride/MAO catalyst system, optically transparent and high molecular weight polyolefin block copolymers have been prepared with a narrow molecular weight distribution. The resulting copolymers exhibited a partial 1-D photonic band gap with an excellent optical transparency. Random copolymerization of olefin monomers provided a route to tune the refractive index of each block as well as to suppress the crystallinity for optical transparency. Ternary blending of diblock copolymer with homopolymers further afforded a pathway to control the wavelength of the peak reflectivity of the polyolefin-based photonic structures.

FI Catalysts: A New Family of High Performance Catalysts for Olefin Polymerization

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FI Catalysts: A New Family of High Performance Catalysts for Olefin Polymerization

This paper reviews a new family of olefin polymerization catalysts. The catalysts, named FI catalysts, are based on non-symmetrical phenoxyimine chelate ligands combined with group 4 transition metals and were developed using “ligand-oriented catalyst design”. FI catalysts display very high ethylene polymerization activities under mild conditions. The highest activity exhibited by a zirconium FI catalyst reached an astonishing catalyst turnover frequency (TOF) of 64,900 s –1 atm –1, which is two orders of magnitude greater than that seen with Cp2ZrCl2 under the same conditions. In addition, titanium FI catalysts with fluorinated ligands promote exceptionally high-speed, living ethylene polymerization and can produce monodisperse high molecular weight polyethylenes (Mw/Mn<1.2, max. Mn>400,000) at 50 °C. The maximum TOF, 24,500 min –1 atm –1, is three orders of magnitude greater than those for known living ethylene polymerization catalysts. Moreover, the fluorinated FI catalysts promote stereospecific room-temperature living polymerization of propylene to provide highly syndiotactic monodisperse polypropylene (max. [rr] 98%). The versatility of the FI catalysts allows for the creation of new polymers which are difficult or impossible to prepare using group 4 metallocene catalysts. For example, it is possible to prepare low molecular weight (Mv∼103) polyethylene or poly(ethylene-co-propylene) with olefinic end groups, ultra-high molecular weight polyethylene or poly(ethylene-co-propylene), high molecular weight poly(1-hexene) with atactic structures including frequent regioerrors, monodisperse poly(ethylene-co-propylene) with various propylene contents, and a number of polyolefin block copolymers [e.g., polyethylene-b-poly(ethylene-co-propylene), syndiotactic polypropylene-b-poly(ethylene-co-propylene), polyethylene-b-poly(ethylene-co-propylene)-b-syndiotactic polypropylene]. These unique polymers are anticipated to possess novel material properties and uses.

Living Ziegler−Natta Cyclopolymerization of Nonconjugated Dienes: New Classes of Microphase-Separated Polyolefin Block Copolymers via a Tandem Polymerization/Cyclopolymerization Strategy

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTLiving Ziegler−Natta Cyclopolymerization of Nonconjugated Dienes: New Classes of Microphase-Separated Polyolefin Block Copolymers via a Tandem Polymerization/Cyclopolymerization StrategyKumudini C. Jayaratne, Richard J. Keaton, David A. Henningsen, and Lawrence R. SitaView Author Information Department of Chemistry and Biochemistry University of Maryland College Park, Maryland 20742 Cite this: J. Am. Chem. Soc. 2000, 122, 42, 10490–10491Publication Date (Web):October 6, 2000Publication History Received13 July 2000Published online6 October 2000Published inissue 1 October 2000https://doi.org/10.1021/ja002558cCopyright © 2000 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1345Altmetric-Citations146LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (115 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information SUBJECTS:Catalysts,Copolymers,Crystal structure,Cyclopolymerization,Materials Get e-Alerts

Interfacial Thermodynamics of Polyolefin Blends and Copolymers

Some universal aspects of interfacial thermodynamics in nearly athermal blends and block copolymers are discussed. While the primary application of the theoretical analysis is to interfaces between polyolefins, the analysis also applies to interfaces between chemically identical but architecturally asymmetric components, such as linear and comb polystyrenes. Specific cases treated are interfaces between linear and short-branched polyolefins and interfaces between linear and comb polymers. For both situations, we derive expressions for the interfacial tension and profile and provide numerical results where appropriate. The implications for the phase diagrams of polyolefin block copolymers are also briefly discussed