Ethylene-propylene copolymer methyl branches

Figure 3.7 Effect of short-chain branches on polyethylene density and crystaUiiiity. (o) Methyl branch from ethylene/propylene copolymers ( ) Ethyl branch from ethylene/1-...

Ethylene/propylene copolymers made with these nickel catalysts contain up to 6 mol % propylene. When the nickel catalysts were combined with supported chromium catalysts, branched polyethylene (5.0 methyl-ended branches per 1000 carbon atoms) was produced by the chromium copolymerizing ethylene with the a-olefins that were produced in situ by the nickel catalyst. Like the catalysts above, nickel catalysts with anionic ligands may themselves be supported on inorganic supports and polymeric supports. " ... 

It can be seen that major differences occur in the products of thermal degradation that are obtained for these three similar polymers. PE produces major amounts of normal to Cg alkanes and minor amounts of 2-methyl and 3-methyl compounds such as isopentane and 3-methylpentane, indicative of short-chain branching on the polymer backbone. For PP, branched alkanes predominate, these peaks occurring in regular patterns, e.g., 2-methyl, 3-ethyl, and 2,4-dimethylpentane and 2,4-dimethylheptane, which are almost absent in the PE pyrolysate. Minor components obtained from PP are normal paraffins present in decreasing amounts up to -hexane. This is to be contrasted with the pyrogram of PE, where n-alkanes predominate. The ethylene-propylene copolymer, as might be expected, produces both normal and branched alkanes. The concentrations of 2,4-dimethylpentane and 2,4-dimethylheptane are lower than those that occur in PP. 

Figure 4. 15) M. Brookhart s new late transition metal systems using Pd and Ni. 16) Ethylene/Propylene copolymers from the work of Wunderlich. 10) J. E. O Gara and K. B. Wagener PE produced by ADMET polycondensation. 13, 14) Kaminsky, Cecchin, and Zucchini s work reviews on metallocene PE catalysis. 11, 12) J. D. Hoffman s equilibrium values derived for an infinitely long PE chain. 9) Work in this study-PE model polymers made by ADMET with precise placement of methyl branches along the backbone.

Sworen, J.C., Smith, J.A., Wagener, K.B., Baugh, L.S., Rucker, S.P., Modeling random methyl branching in ethylene/propylene copolymers using metathesis chemistry synthesis and thermal behavior, J. Am. Chem. Soc. 2003, 125 2228-2240. 

Lieser, G., Wegner, G., Smith, JA., Wagener, K.B., Morphology and packing behavior of model ethylene/propylene copolymers with precise methyl branch placement. Colloid Polym. Sci. 2004,282 773-781. 

Randall [56] has developed a C-NMR quantitative method for measnring ethylene-propylene mole fractions and methylene number-average sequence lengths in ethylene-propylene copolymers. He views the polymers as a snccession of methylene and methyl branched methine carbons, as opposed to a succession of ethylene and propylene units. 

Perez and Vanderhart [60] investigated the morphological partitioning of chain ends and methyl branches in ethylene copolymers by C-NMR in the solid state. The PE samples, which were crystallised from the melt, varied in molecular weight, polydispersity, crystallisation rate, and comonomer content. For the limited set of samples considered, the ratio of crystal to overall end concentration is independent of those variables. This ratio takes the values of 0.75 and 0.60 for the methyl and vinyl ends, respectively. When the crystalline fraction of these samples is taken into account, 50-75% of the total saturated ends and 42-63% of the total vinyls reside in the crystal. For an ethylene/propylene copolymer, 21-27% of the methyl branches were determined to be in the crystal. This level of incorporation puts methyl branches in a position intermediate between chain ends and ethyl branches. 

These materials can be considered linear copolymers of ethylene and propylene or precisely methyl-branched polyethylene. In addition, copolymerizations of the methyl-containing monomers with 1,9-decadierie yield polymers with lower propylene content [50]. These materials are of great interest to the polyolefin community, especially in the physical understanding of the effects of branching on physical properties. Polyethylenes with a variety of main chain functionality have also been synthesized and analyzed [51-54]. 

Linear low-density polyethylene (LLDPE)440-442 is a copolymer of ethylene and a terminal alkene with improved physical properties as compared to LDPE. The practically most important copolymer is made with propylene, but 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene are also employed.440 LLDPE is characterized by linear chains without long-chain branches. Short-chain branches result from the terminal alkene comonomer. Copolymer content and distribution as well as branch length introduced permit to control the properties of the copolymer formed. Improvement of certain physical properties (toughness, tensile strength, melt index, elongation characteristics) directly connected to the type of terminal alkene used can be achieved with copolymerization.442... 

Alexandridis et al. have studied a number of block copolymers of ethylene oxide (EO), propylene oxide (-OCH2CHCH3-, PO) and butylene oxide (-OCH2CH(CH2CH3)-, BO) in water and in ternary systems with p-xylene. The polypropylene oxide and butylene oxide blocks are the hydrophilic portions. Obviously, the short methyl and ethyl branches will need to be included in any packing constraints considerations. 

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