Interpenetrating polymer networks (IPN’s) are a unique type of polyblend, synthesized by swelling a crosslinked polymer (I) with a second monomer (II), together with crosslinking and activating agents, and polymerizing monomer II in situ (Sperling, 1974–1975 ; Sperling and Friedman, 1969). The term IPN was adopted because, in the limiting case of high compatibility between crosslinked polymers I and II, both networks could be visualized as being interpenetrating and continuous throughout the entire macroscopic sample.* As with other types of polyblends, if components I and II consist of chemically distinct polymers, incompatibility and some degree of phase separation usually result (Sperling, 1974–1975; Sperling and Friedman, 1969; Sperling et al., 1970a,b,c; 1971). Even under these conditions, the two components remain intimately mixed, the phase domain dimensions being on the order of hundreds of angstroms. If one polymer is elastomeric and one polymer is plastic at the use temperature, the combination tends to behave synergistically, and either reinforced rubber or impact-resistant plastics result, depending upon which phase predominates (Curtius et al., 1972; Sperling and Mihalakis, 1973; Sperling et al., 1971; Huelck et al., 1972). Among the other kinds of polymer blends discussed in this monograph, the graft-type copolymers are the ones most closely related to the IPN’s.

Interpenetrating Polymer Networks

Publisher Summary This chapter provides an overview of polymer-polymer compatibility. The term "polymer compatibility" refers to the total miscibility, on a molecular scale, of homo-polymers and of random copolymers with each other in various combinations. In the chapter, no distinction is made between polymers in the rubbery or glassy state. The chapter discusses the crystallizable polymers in which the polymer remains at least partially amorphous and in which the miscibility with other polymers are investigated in the amorphous state. The chapter briefly reviews methods for predicting compatibility and presents a method for predicting compatibility along with its limitations. It explains the prediction schemes for polymer-polymer compatibility. The experimental methods for determining solubility parameters of polymers involve studies of the polymers in solution or swollen by solvent, that is, the thermodynamics of the situation involves the entropy contribution to the polymer-solvent interaction parameter and it complicates the theoretical treatment. It often turns out that experimental solubility parameters for the same polymer vary a great deal, depending both on the method used and on the experimenter. The two methods used are (1) swelling of a cross-linked polymer, where it is assumed that the solubility parameter of the polymer is equal to that of the solvent which swells it most highly and (2) intrinsic viscosity of a soluble polymer sample, where the solubility parameter of the polymer is equal to that of the solvent in which its intrinsic viscosity is greatest. For the same polymer, these methods often give different results depending on the nature of the solvents, which may be non-polar, polar, or hydrogen bonding.

Polymer–Polymer Compatibility

Studies on the thermal stability of natural rubber/polystyrene interpenetrating polymer networks: thermogravimetric analysis

Several models have been proposed in the literature over the last two decades in order to simulate free-radical homopolymerizations. However, most of these models deal with one specific monomer system, usually under restricted polymerization conditions.

A Comprehensive Simulator/Database Package for Reviewing Free-Radical Homopolymerizations

We review the synthesis, morphology, and physical and mechanical properties of IFNs as well as the related pseudo-IPNs, in which only one of the polymers is crossliriked. Recent studies have shown that the degree of phase separation achieved in these materials is strongly dependent on the compatibility of blends of the linear polymer constituents of the IPN components as well as the kinetics of chain extension and the presence of grafting between component polymers. We illustrate this by a series of IPNs consisting of a polyurethane and an acrylic copolymer. The acrylic is a typical automotive enamel. An enhancement in properties results, which is dependent on the amount of grafting and the kinetics of polymerization. Also discussed are IPNs of a polyurethane and an epoxy, which exhibit a synergism in adhesive properties, and IPNs of a RIM polyurethane with several epoxies and unsaturated polyesters. In addition, also reported are the preliminary studies on the first successful preparation of a three-component IPN, consisting of a polyurethane, an epoxy, and an acrylic.

Recent advances in interpenetrating polymer networks

A series of interpenetrating polymer networks were prepared containing PMMA and PEA as their two components. Corresponding telomer mixtures and random copolymers were also prepared for comparison purposes. The glass-rubber transition studies were made via shear modulus and dilatometric measurements. The results indicate one very broad transition for the IPN's rather than two transitions expected for incompatible polymer pairs. An interpretation based on the compatibility or near-compatibility of the PEA/PMMA pair is offered.

D. R. Bardman

Papers

Glass-rubber transition behavior and compatibility of polymer pairs: Poly(ethyl acrylate) and poly(methyl methacrylate)