Polymer with interphase regions

Internal surfactants, i.e., surfactants that are incorporated into the backbone of the polymer, are commonly used in PUD s. These surfactants can be augmented by external surfactants, especially anionic and nonionic surfactants, which are commonly used in emulsion polymerization. Great attention should be paid to the amount and type of surfactant used to stabilize urethane dispersions. Internal or external surfactants for one-component PUD s are usually added at the minimum levels needed to get good stability of the dispersion. Additional amounts beyond this minimum can cause problems with the end use of the PUD adhesive. At best, additional surfactant can cause moisture sensitivity problems with the PUD adhesive, due to the hydrophilic nature of the surfactant. Problems can be caused by excess (or the wrong type of) surfactants in the interphase region of the adhesive, affecting the ability to bond. 

Restrained layers—coupling agents develop a highly crosslinked interphase region with a modulus intermediate between that of the substrate and the polymer. 

Several analytical techniques have been used to characterize the polymer/ silane coupling agent interphase. Culler et aL [2] used Fourier transform infrared (FT-IR) spectroscopy to characterize the chemical reactions at the matrix/silane interphase of composite materials. They correlated the extent of reaction of the resin with the coupling agent (as determined by FT-IR) with the extent of interpenetration. Culler et al. [2] have also used observations of improved resistance of the interphase region to solvent attack as indirect evidence to support the interpenetrating network theory. 

A temperature dependence of k suggests that it increases with a rise in temperature for all the penetrants except j -xylene and bromobenzene. Furthermore, k appears to depend on structural characteristics of the penetrant molecules i.e., it decreases successively from benzene to mesitylene this decrease in k parallels the decrease in the values of sorption equilibrium. Similarly, for chlorobenzene to nitrobenzene via o-dichlorobenzene k decreases successively. Thus, it appears that k not only depends on the structural characteristics of the polymer and penetrant molecules, but also on solvent interactions with the polyurethane chains. At any rate, the greater tendency for non-Fickian coefficients in Equation (1) seen for 60°C, may reflect some aspect of swelling of interphase regions between the hard and soft domains. 

Lipatov (22) investigated the effects of interphase thickness on the calorimetric response of particulate-filled polymer composites. Based on experimental evidence, his analysis led to the conclusion that the interphase region surrounding filler particles had sufficient thickness to give rise to measurable calorimetric response. The proposed existence of a thick interphase region correlates with limitations of molecular mobihty for supermolecular structures extending beyond the two-dimensional filler boundary surface. 

Lipatov (22) analyzed specific heat data for an array of filled polymer composites. He characterized the interactions due to the existence of the interphase region surrounding filler particles as a function of filler content. Because the magnitude of the specific heat jump at the glass transition temperature decreases with increase in filler content, this is indicative of exclusion of a certain portion of macromolecules in the polymer matrix to participating in the cooperative process of glass transition. 

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