Grubbs polyethylene

Synthetic methods targeting amino acid incorporation into functional materials vary widely. Free-radical polymerization of various amino acid substituted acrylates has produced many hydrocarbon-amino acid materials [161, 162]. In separate efforts, MorceUet and Endo have synthesized and meticulously characterized a library of polymers using this chain addition chemistry [163- 166]. Grubbs has shown ROMP to be successful in this motif, polymerizing amino add substituted norbornenes [167-168]. To remain within the scope of this review, the next section wiU focus only on ADMET polymerization as a method of amino add and peptide incorporation into polyethylene-based polymers. 

The Ni complex incorporating mixed-donor P/O-ligands find industrial application in the Shell Higher Olefin Process (SHOP) to yield a-alkenes, while the complex (71) has been shown to be active in the polymerization of olefins and will also tolerate functionalized monomers such as methyl methacrylate. Grubbs and coworkers have adapted the standard SHOP catalyst to yield a highly active family of catalysts (eg. 72) for the polymerization of low-branched polyethylene. This is in contrast to the diimine catalysts (Section 5.2) which lead to a more highly branched polyethylene. 

In 1998, Grubbs and co-workers [83, 84] reported on a new type of neutral Ni(II) complexes with salicylaldimin ligands (32). With these catalysts low-branched polyethylenes were obtained with a narrow molecular weight distribution. The copolymerization of ethylene and norbomene is possible. Fe and Co catalysts were used for the linear polymerization of ethylene by Gibson [85] and Brookhart [86] independently (33). Activities of 10 TONs were reported. The polyethylenes obtained are highly crystalline with a broad molecular weight distribution. 

The Chow equations [5] and the Halpin-Tsai equations [8,9] are also useful in modeling the effects of the crystalline fraction and of the lamellar shape (see Bicerano [23] for an example) on the moduli of semicrystalline polymers. Grubb [24] has provided a broad overview of the elastic properties of semicrystalline polymers, including both their experimental determination and their modeling. Janzen s work in modeling the Young s modulus [25-27] and yielding [27] of polyethylene is also quite instructive. 

Grubb et al. [43] studied this question on single crystal mats of polyethylene. The samples, previously crystallized at 80 °C, were annealed in a flow of hot helium at different temperatures above 120 °C. WAXS was observed during recrystallization by means of a vidicon detector, the time resolution being 0.3 sec. A strong decrease of the intensity of the (110) crystal reflection and therefore of the crystallinity is observed during the first few seconds of the experiment. Simultaneously a rapid in-... 

Tentagel, described above, is in wide use today in solid phase syntheses. Polyethylene glycol has also been attached to various other polymers to form support resins. For instance, Frechet and coworkers [37] used cross-linked methacrylate esters of ethylene glycol oligomers in a suspension polymerization to synthesize hydroxyl group functionalized beads. These beads swell well in a variety of polar solvents. Another example is that of Grubbs attaching a ruthenium metathesis catalyst to polyethylene [38] ... 

The neutral salicylaldimine nickel complexes described hy Grubbs and coworkers (195,196) show unprecedented fimctional group tolerance and are capable of incorporating substituted norbornenes, carbon monoxide, and a-co fimctional olefins into polyolefins with well-defined compositional distributions (eq. 7) (196). Furthermore, ethylene can be homopoljnnerized with these catalysts in the presence of various functional additives including acetone, water, ethyl alcohol, and triethyl amine. In the presence of 1500 equivalents of H2O, polyethylene was produced at a rate of 5.4 x 10 g PE/mol Ni/h. 

The Grubbs second-generation catalyst will efficiently ring open cyclooctene to make a linear polymer as shown below. The resulting polyoctenamer can be hydrogenated to make polyethylene. 

In 1998, Grubbs [171,172] reported on a new type of neutral nickelll-complexes with salicylaldimin ligands (structure (31)). With these catalysts low branched polyethylenes were obtained with a narrow molecular weight distribution. The copolymerization of ethene and norbornene is possible. 

K Prasad, DT Grubb. Direct observation of taut tie molecules in high-strength polyethylene fibers by Raman spectroscopy. J Polym Sci B Poly Phys 27 381-403, 1989. 

Simple nonfunctional hydrocarbon polymers such as polyethylene (PE), polypropylene, poly-a-olefins and their copolymers are synthesized by uncontrolled high-pressure-high-temperature radical, metathesis or transition-metal-catalyzed coordination polymerization (Natta, 1956 Ziegler et al, 1955 Wu and Grubbs, 1994 Chanda and Roy, 1993). Although catalysts of exceptional efficiency that produce polymers on a huge scale are in common use, control that approaches a hving polymerization for these methods has not been realized. 

There are now a number of alternative approaches for synthesizing linear polyethylene (Arthur and Charles, 1959 O Gara et al., 1993 Sita, 2009 Wagener et al., 1991 Wu and Grubbs, 1994 Wu et al., 1992 Zhang et al., 2008 Morita et al, 2000). Although at present these reactions are not competitive with existing commercial processes for bulk polymer production, they can provide quantities of specialized materials for study. 

Wu, Z. and Grubbs, R.H. (1994) Synthesis of narrow dispersed linear polyethylene and block copolymers from polycyclobutene. Macromolecules, 27,67(X)-6703. 

Grubb DT, Prasad K. High-modulus polyethylene fiber structure as shown by X-ray diffraction. Macromolecules 1992 25 4575 582. 

Figure 3.54 TEM of a microtomed and stained section of polyethylene that had been crystallized in bulk at 125°C for 3 hours. Light portions are lamellar crystals viewed edge-on, while dark traces are the amorphous intercrystalline layers. Outlined are examples of branches (B), lamellar ends (E), nucleation sites (N), and a zigzag region (ZZ). After Grubb and Keller [75] with permission from John Wiley and Sons, Inc.

The structure of high modulus polyethylene fibres obtained by optimized drawing of linear polyethylene is viewed as crystalline lamellae linked by intercrystalline bridges.Accordingly, the component B is then viewed as crystalline, and its content (1 — >1) corresponds to the volume fraction of the material incorporated in the crystalline bridges. A more complex model consisting of four components has been proposed for these fibres by Grubb. 

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