Extended polymer segments

Conditions that cause the extended polymer segments to become insoluble in the medium will also, in general, give rise to flocculation and even coalescence of the emulsion. Flory (3) defined theta conditions as conditions of temperature and solvent composition under which the free energy of interaction between polymer segments equals the free energy of polymer-solvent interaction. Under theta conditions, the soluble segments of a steric stabilizer would collapse, the repulsion between droplets would diminish, and flocculation of the system would be expected to ensue. This prediction has been demonstrated experimentally (20, 21). 

Earlier work on chain extended HPLs has shown that these derivatives produce uniform (i.e., single phase) polymers with Tg varying in accordance with the Gordon-Taylor relationship (12). Polyurethanes from chain-extended HPLs were found to be rubber-like at room temperature with modulus declining as lignin content is reduced (8). Star-like structure determines functionality, Tg, viscosity, and several other properties that influence utility as polymer segment. 

However, as Ringard-Lefebvre et al. [58] have noted, such comparisons are only valid if the assumption that polymer molecules which in bulk solution form tightly bound three-dimensional coils could, during the spreading process from organic solvents onto aqueous subphase, extend to cover the available area with every polymer segment on surface layer. 

For the investigation of the molecular dynamics in polymers, deuteron solid-state nuclear magnetic resonance (2D-NMR) spectroscopy has been shown to be a powerful method [1]. In the field of viscoelastic polymers, segmental dynamics of poly(urethanes) has been studied intensively by 2D-NMR [78, 79]. In addition to ID NMR spectroscopy, 2D NMR exchange spectroscopy was used to extend the time scale of molecular dynamics up to the order of milliseconds or even seconds. In combination with line-shape simulation, this technique allows one to obtain correlation times and correlation-time distributions of the molecular mobility as well as detailed information about the geometry of the motional process [1]. 

It is usually assumed that the micellar corona is a continuous phase extending from the micellar core to the micellar radius Rm. The internal structure of the micelle can be described by a density profile as shown in Fig. 8. The micellar core is a homogeneous melt or glass of insoluble polymer blocks. For hydrophobic blocks in aqueous solutions, the polymer volume fraction in the micellar core is 0C 1. The micellar shell is swollen with water or aqueous salt solution and has a polymer segment density that is expected to decrease in the radial direction as 0(r) r-a as typical for star polymers or... 

Sanchez and Lacombe (1976) developed an equation of state for pure fluids that was later extended to mixtures (Lacombe and Sanchez, 1976). The Sanchez-Lacombe equation of state is based on hole theory and uses a random mixing expression for the attractive energy term. Random mixing means that the composition everywhere in the solution is equal to the overall composition, i.e., there are no local composition effects. Hole theory differs from the lattice model used in the Flory-Huggins theory because here the density of the mixture is allowed to vary by increasing the fraction of holes in the lattice. In the Flory-Huggins treatment every site is occupied by a solvent molecule or polymer segment. The Sanchez-Lacombe equation of state takes the form... 

This major morphological difference between 1,4-BDO extended polymers (crystalline hard segment) and those extended with any of the diols containing pendant groups (non-crystalline hard segment) also yields significant differences in the shear moduli and loss factors of these polymer systems. 

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