Ethylene-propylene, conformations

Mean-square unperturbed dimensions a and their temperature coefficient, d tin 0) I d T, are calculated for ethylene-propylene copolymers by means of the RIS theory. Conformational energies required in the analysis are shown to be readily obtained from previous analyses of PE and PP, without additional approximations. Results thus calculated are reported as a function of chemical composition, chemical sequence distribution, and stereochemical composition of the PP sequences. Calculations of 0 / nP- are earned out using ( ) r r2 = 0.01, 1.0, 10.0, and 100.0, (ii) p, = 0.95, 0.50, and 0.05, liii) bond length of 153 pm and bond angles of 112°for all skeletal bonds, iv) = 0 and 10°, and (v) statistical weight factors appropriate for temperatures of 248, 298, and 348 K. Matrices used are ... 

RIS theory is used to predict values of the optical-configuration parameter Aa for ethylene - propylene copolymers as a function of chemical composition, chemical sequence distribution, and stereochemical structure of the propylene sequences. The calculations are based on information available for ethylene and propylene homopolymers, and on the model used to interpret the unperturbed dimensions of these copolymers. Values of Aa are generally found to decrease significantly with increase in the fraction of propene units, but to be relatively insensitive to chemical sequence distribution and stereochemical structure. Geometries and conformational energies are the same as those used for the interpretation of the unperturbed dimensions of these chains. The conformational energies used are E(q) = 0, EM 2.09, and E a>) = 0.37 kJ mol-1. 

Opschoor, A., and W. Prins Thermoelasticity and conformational behaviour of polyethylene and ethylene-propylene copolymers. J. Polymer Sci., Pt. C16, 1095 (1967). 

NOESY has also been used to elucidate the chain conformation of poly(styrene-a/ -MMA).220,221 2D INADEQUATE has been applied to studies of monomer sequence distribution in ethylene-propylene copolymer.223 Additivity rules for the 13C chemical shifts of ethylene-propylene copolymer were devised for configurational sequences as well as substituent effects.226... 

Experimentally, Thomas and coworkers found that hydrocarbon-coated gold nanoparticles, with a diameter of 3.5 nm, segregated to the interface between the microdomains of poly(styrene-btock-ethylene propylene) (PS-fe-PEP) copolymer, whereas larger hydrocarbon-coated silica nanoparticles (21.5nm in diameter) were located at the center of the PEP domains [79], In the absence of specific enthalpic interactions between the two types of nanoparticles and the polymer matrix, the result suggests a profound influence of entropic contributions to the self-organization process. For large particles, the decrease in conformational entropy of the respective polymer subchains after particle sequestration is dominant, whereas for smaller particles, the decrease in entropy is outweighed by the particle translational entropy. 

The DSC technique was used by Li et al [42] to investigate a series of segmented PUs with different HS flexibilities, based on the aliphatic diisocyanate HDI or aromatic MDI, as the HS showed a folded-chain conformation. The chain extenders were the diol BDO or 4,4 -diaminodiphenyl ether (DDE) the SS macrodiols were PTMO or poly(ethylene/propylene adipate) (PES) with a molar mass 2 000 g/mol. The materials were prepared by a solution polymerization. 

Norbomene can be copolymerized with olefins such as ethylene, propylene, 1-butene, and longer-chain a-olefins using early and late transition metal catalysts. The resultant copolymer properties depend on different parameters, such as comonomer content and distribution throughout the polymer chain, as well as the conformational orientation of the comonomer units. The microstmcture of the copolymer can be controlled by the appropriate choice of reaction conditions and catalyst stmcture. The most powerful method to determine copolymer microstmcture is NMR spectroscopy. In the past years, much progress has been achieved in making peak assignments for olefin-norbornene copolymers. - ... 

Conformations and Transitions of Perfluorinated Ethylene-Propylene Copolymers (FEP)... 

The chain dimensions of virtually alternating ethylene-propylene model polymers PEP have been studied experimentally [36,38,145,147] and theoretically [160]. PEP is intermediate in structure between PE and PP with substituents on roughly every fourth backbone carbon. The Ca, value of 6.8 for this polymer is also intermediate between those for PP and PE. It reflects the fact that, relative to PP, a lower level of gauche conformers is adequate to relieve steric effects caused by substituents. Similar to PEP, PEB represents copolymers... 

Figure 3.7 Hole formation via a packing arrangement of four participating polymer chains [37]. (a) Natural rubber, (b) ethylene-propylene-diene rubber. The holes are just large enough to allow diffusion of another polymer molecule of the same chemical species. However, the distance between the participating chains forming the hole needs to increase by 15% for natural rubber but by 27% for ethylene-propylene-diene rubber, compared to their respective close-packed chain conformations.

Low-temperature crystallisation of ethylene-propylene copolymers was followed by DSC and solid-state NMR. The trans conformation fraction identifying the aggregates was detected for all temperatures independent of thermal history. 41 refs. 

Monocyclopentadienyl complexes of titaninm (Cp TtXs) perform poorly as catalysts for ethylene or propylene polymerization, bnt in the presence of MAO, they polymerize styrene to stereo- and regioregnlar syndiotactic polystyrene, a crystalline material with very high melting point (273 °C) and glass transition temperature (100°C). In this case, the active polymerizing species is a Ti complex (Figure 8). Each styrene monomer inserts in a secondary manner and the stereoregularity is maintained by the conformation of the last inserted unit (chain-end control). 

The sum of these AF , S AF , taken over all the nonpolar residues found in typical protein molecules, can attain very large negative values. If the native conformation of a protein molecule in aqueous solution is indeed in considerable part stabilized by lyophobic interactions, it follows that this stabiUzation should be substantially if not completely lost on transferring the protein molecule to almost any pure nonaqueous solvent. This destabilization might be expected to be less extensive in those few weakly protic nonaqueous solvents with which hydrocarbons are only partially miscible, such as glycerol, ethylene and propylene glycols, and formamide, than in the other solvents with which hydrocarbons are completely miscible. Furthermore the latter solvents should be very little differentiated under these circumstances, since AFt is so similar for most of them. As is demonstrated subsequently, these expectations are closely realized in fact. 

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