Properties of Thermoplastic Apparent IPNs

Presently, some hybrid polyblends, such as the thermoplastic apparent interpenetrating polymer networks (AIPNs), call for a broader view, hi contrast to traditional IPNs, in thermoplastic AIPNs the components are cross-linked by means of physical, instead of chemical, bonds. These physical bonds are glassy domains of block copolymers, ionic clusters in ionomers, or crystalline domains in semicrystalline polymers. The components of thermoplastic AIPNs are capable of forming physical networks and are characterized by mutual penetration of phases. Thermoplastic AIPNs are intermediate between mixtures of linear polymers and true IPNs because they behave like chemically cross-Unked polymers at relatively low temperatures, but as thermoplastics at elevated temperature [208]. The blends based on combinations of physically cross-Unked polymer and Unear polymer, or physicaUy cross-Unked polymer and chemically cross-Unked (thermoset) polymer, where the physically cross-Unked polymer network constitutes the continuous phase and the other component disperses into domains, will also exhibit the properties of thermoplastic compositions. 

Thermoplastic AIPNs of several compositions prepared by mechanical blending in a roll mill of crystallizable polyurethane (CPU) and styrene-acrylic acid random copolymer (S-co-AA) have been investigated using different techniques by VataUs et al. [212,213]. The CPU was based on TDI (mixture of 2,4- and 2,6-isomers, molar ratio 65 35) and oligomeric buty- 

The method of mechanical blending of two (or more) polymers in the melt is one of the main methods of producing thermoplastic IPNs [208]. Thermoplastic AIPNs based on the same CPU and S-co-AA by mechanical blending of components in a common solvent were investigated by DMTA, DSC, WAXS, SAXS, TSDC, and other techniques by Sergeeva, Kyritsis et al. [218-222]. DMTA measurements have shown that thermoplastic AIPNs can be considered as multiphase systems having at least two amorphous and one crystalline 

Dielectric TSDC measurements [225] of the blends have shown four relaxation mechanisms. The subglass secondary y relaxation (at 120 K) is associated with local motions of parts of the molecular chain. The fi relaxation (at 160 K) is attributed to the motions of the polar carbonyl groups of the polymer chain. A systematic change of the magnitude (maximiun of the current) and position (temperature of the maximum current) of these two re- 

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