Properties of the Bulk Polymer

The term molecule has been purposely avoided in the above discourse for the reason that it cannot be applied appropriately to a most important class of polymers, namely, those composed of indefinitely large network structures. Even In the case of linear polymers, which are composed of finite (although in many cases exceedingly large) molecules, the continuity of structure may deserve greater emphasis than the individuality of the molecules. This is particularly true insofar as properties of the bulk polymers are concerned. 

Table 3.3. Molecular weight My, polydispersity My,/Mn and mechanical properties of the bulk polymers investigated.

The properties of dense films are often equated with the Intrinsic properties of the bulk polymer. However, this comparison must be made with caution because chain packing, and thus transport properties, may be dependent upon thermal history or solution history during film preparation and upon the attainment of equilibrium prior to characterization. Dense films can be prepared by melt extrusion, compression molding or solution casting,... 

The mechanical properties of the bulk polymer remain almost unchanged, since the observed reactions occur on the surface. The elongation and strength of polyethylene samples, for example, are only slightly reduced after reaction with atomic oxygen. The addition of an antioxidant in amounts up to 10% does not influence the reaction course at all. Further investigations of the mechanism and kinetics of reactions between polymers and atomic oxygen are still necessary to fully elucidate all the problems involved. 

The crystal orbital approach (see ref. 94 for a review of the recent computational developments in this field) has dominated the electronic structure calculations on polymers for several years. However, the recently published reports on the finite-cluster calculations reveal that the latter methodology has several definite advantages over the traditional approach. Let P(N) be an extensive property of a finite cluster X-(-A-)j -Y, where N is the number of repeating units denoted by A, while X and Y stand for terminal groups. The corresponding intensive properties, p(N) = P(N)/N, are known only for integer values of N. However, provided the polymer in question is not metallic, P(v) can be approximated by a smooth function p(v) of v = 1/N, which in turn can be extrapolated to v = 0 yielding the property of the bulk polymer. 

In our work presented below, free and bonded films of variable thicknesses were investigated using triblock copolymers. We were interested in this because other workers have cited data to indicate that adhesive joints often do not perform as predicted from properties of the bulk polymer adhesive. However, some researchers (17) have reported good correlation between situ and bulk properties. In our present investigation, the observations... 

Properties of the Bulk Polymer.—Solution Properties and Molecular Weight Studies. The interaction of 2GT with binary mixtures of chlorinated hydrocarbons has been described and inverse gas-chromatography has been used to study the interaction of organic liquids with 2GT. ... 

These monomers are known as reactive flame retardants, and yield a polymer that has an inherent flame retardant characteristic - much more controllable than additives that are placed randomly within the polymer. However, this approach is not widely used due to its relatively high production cost. Further, the inclusion of functionalized monomeric units within the polymer chains may alter the physical properties of the bulk polymer. 

In general, the properties of surfaces and interfaces differ from those of the bulk. In particular, this phenomenon is important for polymer blends, as they consist of at least two constituents with different surface energies. To obtain materials which combine good mechanical properties of the bulk polymer with specific surface properties, such as hydrophobicity, wettability, adhesion, or biocompatibility, is a challenging issue. 

It was pointed out in the previous chapter that the geometric arrangement of the atoms in polymer chains can exert a significant influence on the properties of the bulk polymer. To appreciate why this is so, the subject of polymer morphology, the structural arrangement of the chains in the polymer, is introduced here. 

Step growth polymers, such as polyesters, are often manufactured via bulk polymerization. The reactive species are mixed together in a stirred reactor designed to promote intimate contact between the reactants. Variables such as temperature and pressure are used to control the molecular properties of the final polymer. 

Most of published results deal with very high graft yield and consequently the bulk properties of the base polymer are altered by grafting. In principle, graft polymerization is an attractive method to impart a variety of surface properties on the condition... 

The resistance to fluid flow is a measure of the physical structure of the foam. In order to control the flow through a foam, ceU size, degree of reticulation, density, and other physical factors must be controlled. The control of these physical factors, however, is achieved through the chemistry and the process by which the foam is made. The strength of the bulk polymer is measured by the tensile test described above, but it is clear that the tensile strengths of the individual bars and struts that form the boundaries of an individual cell determine, in part, the qualities of the cells that develop. A highly branched or cross-linked polymer molecule will possess certain tensile and elongation properties that define the cells. The process is also a critical part of the fluid flow formula, mostly due to kinetic factors. As discussed above, the addition of a polyol and/or water to a prepolymer initiates reactions that produce CO2 and cause a mass to polymerize. The juxtaposition of these two reactions defines the quality of the foam produced. Temperature is the primary factor that controls these reactions. Another factor is the emulsification of the prepolymer or isocyanate phase with the polyol or water. 

The review also highlights, how and to what extent metal ion incorporation can modify the essential bulk properties of the base polymer - such as thermal stability, dielectric, conductivity and other physicochemical characteristics. 

In the case of the bulk polymer, the requirement of self-consistency of the theory states that the relaxation time r can be interpreted as a characteristic of the whole system. Properties of the system will be calculated in Sections 6.3.2 and 6.4.3, which allows one to estimate relaxation time r and quantity y. It will be demonstrated that, for weakly entangled systems (2Me < M < 10Me), the quantity x has the self-consistent value... 

Effect on the Bulk Property of the Adhesive. Moisture can alter the properties of the bulk material by changing its glass transition temperature, inducing cracks, or chemically reacting with the polymer—a process called hydrolysis. But before these mechanisms occur, the moisture must first find its way into the bulk polymer. 

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