Effect of Molecular Composition

Ree van Reenen, A. J., Shebani, A. N. The effect of molecular composition and heterogeneity on the environmental stress cracking resistance (ESCR) of propylene impact copolymers. Polym. Degr. Stab. 94 (2009) 1558-1563. 

Studied effect of molecular composition leading to changes in the mesophase state on flexural modulus. Revealed thickness and test-direction dependence of mechanical properties. 

The authors also investigated the effect of solvent composition on the retention of a series of solutes including a dispersion of silica smoke (mean particle diameter 0.002 pm). The silica smoke was used to simulate a solute of very large molecular size... 

In comparing observed reactivity ratios between various polymerization systems, it is important to take into account the possible effect of molecular weight on copolymer composition.3475 19 In conventional radical eopolymeri/.ation, the specificity shown in the initiation and termination steps can have a significant effect on the composition of low molecular weight copolymers (usually <10 units). These effects are discussed in Section 7.4.5. In a living polymerization molecular weights are low at low conversion and increase with conversion. In these... 

Fig. 22. The effect of solvent composition on the molecular weight ( ), conversion (O), and molecular weight dispersity ( ) of PaMeSt prepared using the HSi(CH3)2CH2CH2

Since the chemical composition of a polymer defines its flow behavior, we will now explore the effects of molecular architecture, such as chain length, the presence of branching, and polarity on these properties. 

Working with less dilute solutions of elastomers one cannot fail to notice the influence (the stiffer the greater the effect) of molecular structure on the onset and course of non-Newtonion flow, on gelation and swelling, and the influence of the solvent as expressing itself by virial coefficients, molecular dimensions in solution, spinnability, and film forming. The sensitivity with which the tack of adhesives, demonstrated by pressure sensitive tapes which at that time reached the market, depends on the structure and composition of the elastomer was similarly striking and raised the question, which molecular structure or state was best suited to exhibit tacky adhesion, or adhesion per se. 

The prime object of the present study was to determine the compositional polydlspersity of commercial cellulose triacetate and to examine the effect of molecular weight and molecular weight distribution on the mechanical properties of the fibres. 

Lipid membranes are quite deformable, allowing water and head groups into their interiors when perturbed. A "water defect" is shown in Figure 1C, where water and lipid head groups enter the hydrophobic interior of only one of the bilayer leaflets. Figure ID shows a "water pore," where both leaflets are perturbed. At the molecular level, pore and defect formation are directly related to specific lipid-lipid interactions. It is important to understand the free energy required for pore formation in membranes and the effect of lipid composition on the process. In Section 3 of this chapter, we review recent MD studies of the thermodynamics of pore formation. 

The effect of solvent composition on the retention of a series of solutes, commonly used to measure column dead volumes, was also investigated by these authors. They employed mixtures of methanol and water as the mobile phase and measured the retention volume of the same salts together with a silica gel dispersion (containing particles 0.002 micron in diameter). They also measured the retention volume of the components of the mobile phase methanol, and water. The silica dispersion was chosen to simulate a solute of very large molecular size. The results they obtained are shown in figure (2). 

Borgstrom, J., Egermayer, M., Sparrman, T., Quist, P.O., Piculell, L. (1998). Liquid crystallinity versus gelation of K-carrageenan in mixed salts effects of molecular weight, salt composition and ionic strength. Langmuir, 14, 4935 1938. 

Effect of the composition of the starting mixture on the molecular weight of the products... 

In Section IV, the kinetics and mechanisms of catalytic HDM reactions are presented. Reaction pathways and the interplay of kinetic rate processes and molecular diffusion processes are discussed and compared for demetallation of nickel and vanadium species. Model compound HDM studies are reviewed first to provide fundamental insight into the complex processes occurring with petroleum residua. The effects of feed composition, competitive reactions, and reaction conditions are discussed. Since development of an understanding of the kinetics of metal removal is important from the standpoint of catalyst lifetime, the effect of catalyst properties on reaction kinetics and on the resulting metal deposition profiles in hydroprocessing catalysts are discussed. 

Effect of Molecular Configuration of Elastomer. The extent of the impact and strength improvements of ERL-4221 depends on the chemical structure and composition of the elastomer modifier. The data shown in Table I indicate that the carboxyl terminated 80-20 butadiene-acrylonitrile copolymer (CTBN) is the most effective toughening and reinforcing agent. The mercaptan terminated copolymer (MTBN) is considerably less effective as far as tensile strength and heat distortion temperature are concerned. The mercaptan groups are considerably less reactive with epoxides than carboxyls (4), and this difference in the rate of reaction may influence the extent of the epoxy-elastomer copolymerization and therefore the precipitation of the rubber as distinct particles. 

JorzikU, Wolf BA (1997) Reduction of the interfacial tension between poly(di-methylsiloxane) and polyethylene oxide) by block copolymers Effects of molecular architecture and chemical composition. Macromolecules 30(16) 4713-4718... 

In an effort to define more clearly the effects of molecular weight and composition on polymer compatibility, a study was undertaken on the effect of PS molecular weight on compatibility and physical properties of blends of PS with PMMA and PS with styrene(S)/methyl methacrylate (MM A) copolymers. The range in M investigated for PS was 600-110,000, and the S/MMA ratio was varied from 0 to 4.0. The results of this study are reported below. 

Impact and shock sensitivities depend upon a variety of factors chemical, structural and physical. We shall limit our discussion to the effects of molecular structure (i.e. chemical composition and molecular geometry). 

Table 13.3 Effect of molecular weight and composition on selected properties of SAN copolymers"...

Effect of Oil Composition. Experimental data on the gas solubility in numerous crude oils indicate that the solubility increases as the specific gravity of the oil decreases. A low liquid gravity indicates the presence of appreciable concentrations of low molecular weight liquid hydrocarbons. Consequently there is a greater chemical similarity between the gas and the oil and a greater gas solubility is to be expected. 

Examples of the relationship da/dN versus /4Kj are given in Fig. 4.3 for PMMA and PVC In addition to the chemical composition of the polymer, the configuration of the macromolecules plays an important role as can be seen from the effect of molecular weight on the fatigue crack resistance Copolymerisation and... 

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