Polymers factors affecting

THE CHEMICAL DEGRADATION OF BIODEGRADABLE POLYMERS Factors Affecting the Velocity of Passive Hydrolysis The Type of Chemical Bond... 

In addition to graft copolymer attached to the mbber particle surface, the formation of styrene—acrylonitrile copolymer occluded within the mbber particle may occur. The mechanism and extent of occluded polymer formation depends on the manufacturing process. The factors affecting occlusion formation in bulk (77) and emulsion processes (78) have been described. The use of block copolymers of styrene and butadiene in bulk systems can control particle size and give rise to unusual particle morphologies (eg, coil, rod, capsule, cellular) (77). 

Factors affecting RO membrane separations and water flux include feed variables such as solute concentration, temperature, pH, and pretreatment requirements membrane variables such as polymer type, module geometry, and module arrangement and process variables such as feed flow rate, operating time and pressure, and water recovery. 

Another important factor affecting the electronic properties is the steric barrier to planarity along the polymer chain. Since polyheterocycles and polyarylenes must adopt a planar geometry in the ionized state to form quinoid-like segments, steric factors that limit the ability of the polymer to adopt geometries which are planar with respect to adjacent rings have a detrimental effect on the electronic properties (181). 

If a polymer molecule has a sufficiently regular structure it may be capable of some degree of crystallisation. The factors affecting regularity will be discussed in the next chapter but it may be said that crystallisation is limited to certain linear or slightly branched polymers with a high structural regularity. Well-known examples of crystalline polymers are polyethylene, acetal resins and polytetrafluoroethylene. 

The properties of a given polymer will very much depend on the way in which crystallisation has taken place. A polymer mass with relatively few large spherulitic structures will be very different in its properties to a polymer with far more, but smaller, spherulites. It is thus useful to consider the factors affecting the formation of the initial nuclei for crystallisation (nucleation) and on those which affect growth. 

Moderate insulators with lower resistivity and higher dielectric constant and power factor affected further by the conditions of the test. These materials are often referred to as polar polymers. 

One of the most important conclusions from this is that since both the viscous and the high elastic components of deformation depend on both time and temperature, the total deformation will depend on time and temperature. Since this fact has been shown to be an important factor affecting many polymer properties it is proposed to consider the background to this in greater detail in the following section. 

Factors affecting laboratory polymerisation of the monomer have been discussed" and these indicate that a Ziegler-Natta catalyst system of violet TiCl3 and diethyl aluminium chloride should be used to react the monomer in a hydrocarbon diluent at atmospheric pressure and at 30-60°C. One of the aims is to get a relatively coarse slurry from which may be washed foreign material such as catalyst residues, using for example methyl alcohol. For commercial materials these washed polymers are then dried and compounded with an antioxidant and if required other additives such as pigments. 

The formation mechanism of structure of the crosslinked copolymer in the presence of solvents described on the basis of the Flory-Huggins theory of polymer solutions has been considered by Dusek [1,2]. In accordance with the proposed thermodynamic model [3], the main factors affecting phase separation in the course of heterophase crosslinking polymerization are the thermodynamic quality of the solvent determined by Huggins constant x for the polymer-solvent system and the quantity of the crosslinking agent introduced (polyvinyl comonomers). The theory makes it possible to determine the critical degree of copolymerization at which phase separation takes place. The study of this phenomenon is complex also because the comonomers act as diluents. 

T. Moussa and C. Tiu. Factors affecting polymer degradation in turbulent pipe flow. Chem Eng Sci, 49(10) 1681-1692, May 1994. 

Table 2.1 Factors affecting polymer/additive analysis...

Factors Affecting SFE from Polymer Additive Matrices... 

Several authors [92,292,317] have discussed a number of factors affecting SFE from polymers. All classic and new extraction techniques require pre-extraction procedures to ensure that appropriate solvent contact is maximised for solid and semisolid matrices. The preextraction strategies for SFE are given in Table 3.17. 

Diffusion of small molecular penetrants in polymers often assumes Fickian characteristics at temperatures above Tg of the system. As such, classical diffusion theory is sufficient for describing the mass transport, and a mutual diffusion coefficient can be determined unambiguously by sorption and permeation methods. For a penetrant molecule of a size comparable to that of the monomeric unit of a polymer, diffusion requires cooperative movement of several monomeric units. The mobility of the polymer chains thus controls the rate of diffusion, and factors affecting the chain mobility will also influence the diffusion coefficient. The key factors here are temperature and concentration. Increasing temperature enhances the Brownian motion of the polymer segments the effect is to weaken the interaction between chains and thus increase the interchain distance. A similar effect can be expected upon the addition of a small molecular penetrant. 

Name three factors that affect a polymer s random walk configuration. How does each factor affect molecular volume ... 

Chemical structure factors affect the melting point and glass transition temperature in much the same manner. A good empirical rale for many polymers is (142-144)... 

---