Diluent chain conformation

It was also found that the diluents added after the end-linking were more easily removed, possibly because they were less entangled with the network structure, and this could correspond to differences in diluent chain conformations. Such comparisons can thus provide valuable information on the arrangements and transport of chains as constrained within complex network structures [20]. 

The ordered structures of some polymers are governed by the influence of specific diluents. This involves a specific type of polymorphism, the more general aspects of which will be discussed in the chapter concerning thermodynamic quantities. Syndiotactic poly(styrene) is a polymer that is rich in compound formation with solvent mediated polymorphic behavior.( 126-130) The polymer can crystallize in four major crystalline modifications that involve two different chain conformations. In the a and p modifications the chains adopt an all trans planar zigzag conformation. These two modifications are formed by crystallization from the melt and, under special conditions, from solution. In contrast the y and 5 modifications are characterized by a helical conformation. The 5 polymorph can only be prepared in the presence of solvent. Its exact crystal structure depends on the nature of the solvent. Compound formation between the 5 form of the polymer and the solvent has been demonstrated. Complete elimination of the solvent results in the pure, helical y form. 

The interfacial properties of chain-like molecules in many polymeric and colloidal systems are dependent on the conformation of the chains adsorbed at the interface (.1). Chains adsorbed at the solid-liquid interface may be produced by anchoring diblock copolymers to particles in a polymer dispersion. Such dispersions are conveniently prepared by polymerizing in the presence of a preformed AB diblock copolymer a monomer dissolved in a diluent which is a precipitant for the polymer. The A block which is... 

Macrosyneresis, in which the network polymer is contained only in one phase is not the only possibility for phase equilibria in networks. Under favorable conditions two polymer phases can coexist in a network with a diluent phase (50). The two polymer phases in equilibrium differ in the conformations of the network chains. The transition resembles the condensation of a real gas or, in macromolecules, an intramolecular transition due to long-range net attraction between segments in a poor solvent (coil-globule type transition [139)). 

Because the monomers themselves act as diluents in the crosslinking (co)polym-erization process and the monomers and (co)polymer concentration depend on the duration of polymerization, the question of how to find the critical conversion at which phase separation takes place (described as function phase equilibrium versus conversion) becomes very important. Apart from the effect of phase separation, the diluent produces other effects such as lowering the glass transition temperature and the reaction rate, promoting the cyclization reaction, and changing the conformation of chains when it is removed from the network. 

Various reasons for supramolecular ordering in polymer systems, short of crystalline three-dimensional periodicity may be envisaged ( ). Polymer chains in solution may form aggregates, a phenomenon often preceded by conformational transitions in the separate chains and followed by a sol gel transition Such a gelation process is usually sensitive to the temperature and the nature of the diluent including... 

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