Three-dimensional polymeric networks structural characteristics

Gelation and the attendent insolubility mentioned above are encountered in all of the nonlinear polymerizations listed in Table I and in many others likewise. Naturally these characteristics have been attributed to the restraining effects of three-dimensional, or space, network structures of infinite size within the polymer. This is the feature which distinguishes most nonlinear from linear polymers. 

These are long chain molecules consisting of multiples of repeat units (monomers). These are linked by covalent bonds in a three-dimensional network which is characteristic of a polymer. The magnitude of the length of a polymeric molecule can extend up to several hundred nanometres. The dimensions of individual polymer molecules and their arrangement define the structure of polymers and their properties. Many catalytic processes are aimed at producing polymers as we describe in the following chapters. (Polymers can also be used as catalyst supports.)... 

Rubbers and gels are three-dimensional networks composed of mutually cross-linked polymers. They behave like solids, but they still have high internal degrees of freedom that are free from constraints of external force the random coils connecting the cross-links are free in thermal Brownian motion. The characteristic elasticity of polymeric materials appears from the conformational entropy of these random coils. In this chapter, we study the structures and mechanical properties of rubbers on the basis of the statistical-mechanical models of polymer networks. 

The nature of the co-continuous phases in the polypropylene S-EB-S blends leads to a generalization of the specific function of the block copolymer in systems like this. The now-classical model of this characteristic phase structure is that of the chemical IPNs where each network is actually a phase which is constrained or condensed by a mechanism which has infinite relaxation time and where three dimensional spatial continuity of each phase is achieved. This is topologically identical to those IPNs which are achieved by sequential polymerization and crosslinking within a pre-existing network structure or the... 

The efficient utilization of any polymeric material requires a detailed molecular understanding of its unique properties. In its most useful form, such information consists of quantitative relationships between the physical properties of interest and the structural characteristics of the material that determines them. In the case of elastomeric materials, the molecular feature of surpassing importance is the interlinking or cross-linking of the polymer chains into a macroscopic, three-dimensional network structure ". Such networks can not be molecularly dispersed in a solvent, and the usual solution characterization techniques can not be applied to obtain the required structural information. For this reason, it has been exceedingly difficult to obtain reliable structure-property relationships for elastomeric materials ... 

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