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

Pervaporation separation of water + isopropanol mixtures using novel nanocomposite membranes of poly(vinyl alcohol) and polyaniline

Structural effects of chain extender on phase mixing and coating properties of polyether-based moisture-cured polyurethane ureas (MCPUs) were determined with a polytetramethylene glycol (PTMG-1000), trimethylol propane (TMP), and isophorone diisocyanate (IPDI)-based system. The reaction of PTMG/TMP/IPDI was carried out using a NCO/OH ratio of 1.6:1. The excess isocyanate of the prepolymer was chain extended in the ratio of 2:1 (NCO/OH) with different aliphatic diols and 4:1 with different aromatic diamines just before the coating application. The viscoelastic properties of the cross-linked films were evaluated with a dynamic mechanical and thermal analyzer (DMTA). The mechanical film properties such as tensile strength, adhesion strength, and hardness were measured and related to chemical composition and cohesion of the hard segment. Surface properties were evaluated through angle resolved X-ray photoelectron spectroscopy (AR-XPS). The degree of phase mixing was found to be dependent on the chain extender...

Effect of Chain Extender on Phase Mixing and Coating Properties of Polyurethane Ureas

The key physicochemical problems of the formation and properties of interpenetrating polymer networks (IPNs) are considered. The main feature that determines the structure and properties of IPNs consists of the thermodynamic incompatibility of two constituents that arises in the course of the chemical reactions leading to the formation of IPNs. The peculiarities of the chemical reactions of IPN formation are the dependence of the reaction rate of the formation of each network on the presence of another. The chemical reactions are accompanied by the processes of phase separation. The conditions of the phase separation (its rate and degree) are dependent on the chemical kinetics. The heterogeneous structure (two evolved phases and the interfacial region between them) and the thermophysical, viscoelastic, and other physical properties of phase-separated IPNs are governed by the degree of segregation of the system into two phases. The formation of IPNs proceeds under conditions of superposition of the chemical kinetics of two reactions and the physical kinetics of phase separation, both proceeding in nonequilibrium conditions. The result is incomplete phase separation and a lack of interpenetration over the entire volume of the system.

Phase-Separated Interpenetrating Polymer Networks

Polysiloxanes in macromolecular architecture

Theoretical prediction of domain sizes in IPN's and related materials

A series of interpenetrating polymer networks, IPN's, and semi-1 IPN's of poly(n-butyl acrylate) and polystyrene were prepared. The glass transition behavior via dynamic mechanical spectroscopy (DMS) and the morphology via transmission electron microscopy (TEM) were studied as a function of composition ratio and crosslink density. Transition-broadening was observed at low crosslink concentrations, while a single broad glass transition peak at an intermediate position was attained at high crosslink density levels. A cellular domain structure was the morphological characteristic of those IPN's and semi-1 IPN's possessing a low cross-link density and mid-range composition ratio. At higher levels of crosslink density, irregular shapes of the domain morphology prevailed. Phase connectivity was also observed at high polymer II compositions. Theoretical phase domain sizes of polymer II were calculated using both the theories developed by the present authors and that published earlier by Donatelli, et al., and were found to agree with the experimental domain sizes. While the theory was developed for uniform spheres, some of the domain structures observed experimentally for high polymer II contents had connectivity and/or a cylindrical shape.

Poly(n-butyl acrylate)/polystyrene interpenetrating polymer networks and related materials I. Dynamic mechanical spectroscopy and morphology

The glass transition, rubbery modulus, and tensile behavior of poly(n-butyl acrylate)/polystyrene interpenetrating polymer networks (IPN's), semi-1 IPN's, and their corresponding random copolymer networks were studied as a function of both composition ratio and crosslink density. Two temperatures were selected for analysis: 25°C, halfway between the two transition temperatures, and at 160°C., in the rubbery plateau region. The modulus data at 25°C were compared with wellknown composite models. The moduli of the IPN's and semi-1 IPN's lie close to the Davies model in the polymer II rich region but follow the Budiansky model in the polymer I rich region. In one interpretation of the Coran-Patel model, a phase inversion takes place around ϕ2 = 0.8, which is higher than the composition at which the phase connectivity of polymer II begins to appear, ϕ = 0.5, via electron microscopy studies. The rubbery modulus behavior of the full and semi-1 IPN's follow the equation of Siegfried, et al. reasonably well, which considers the deformation effect of polymer I in terms of the rubber elasticity front factor.



The stress-strain behavior of both the full and semi-1 IPN's was similar to that of toughened plastics at polymer II rich compositions, and to that of reinforced elastomers at polymer I rich compositions.

Poly(n-butyl acrylate) polystyrene interpenetrating polymer networks and related materials. ii: aspects of molecular mixing via modulus-temperature studies

A series of poly(n-butyl acrylate)/polystyrene IPNs and semi-1 IPNs with deliberately controlled graft levels were synthesized via a urethane chemical coupling method. Also prepared were a series of semi-2 IPNs with the molecular weight of polymer II as the variable. The more highly grafted IPNs displayed poorly defined morphologies in which the domain structures were irregular and phase domain boundaries were characterized by fibrillar and interphase regions. A single glass transition peak was another feature of the more highly grafted IPNs. Polymer network II formed in the presence of linear polymer I results in morphologies dependent on the molecular weight of linear polymers. In the semi-2 IPNs, polymer I molecular weights below Mv = 20,000 caused polymer I to behave like a plasticizer or a diluent. The domain sizes of semi-2 IPNs agree with theoretical predictions developed by the present authors.

Poly(n-butyl acrylate)/polystyrene interpenetrating polymer networks and related materials. III. Effect of grafting level and molecular weight in semi-2 IPNs

The rubber elasticity characteristics of poly(n-butyl acrylate) networks crosslinked with tetrafunctional (EGDM and TEGDM), hexafunctional (TMPTM), and octafunctional (PETMA) vinyl crosslinkers were investigated. Both gel—sol analyses and crosslinking efficiency theories were used to evaluate the chemical crosslink contribution vc and the entanglement contribution vp to the elastically effective network chains ve, and the effect of the crosslink junction functionality f on the front factor g. The front factors obtained were in the range of 0.50–0.92, depending upon the network system and the counting method for vc. The relationship of g = [(f − 2)/f]/〈r2〉/〈r2〉o seems reasonable in the case of the tetrafunctional and hexafunctional networks, but deviates in the case of the octafunctional network. It is also evident that the functionality scheme for the front factor could only be valid under the postulate of a high vp, which increases with increasing vc, especially in the high vc region near the Gaussian limit. The average energetic contribution to the retractive force of the present systems, expressed as Fe/F, is −0.30 ± 0.1.

J. K. Yeo

Papers

Theoretical prediction of domain sizes in IPN's and related materials

Poly(n-butyl acrylate)/polystyrene interpenetrating polymer networks and related materials I. Dynamic mechanical spectroscopy and morphology

Poly(n-butyl acrylate) polystyrene interpenetrating polymer networks and related materials. ii: aspects of molecular mixing via modulus-temperature studies

Poly(n-butyl acrylate)/polystyrene interpenetrating polymer networks and related materials. III. Effect of grafting level and molecular weight in semi-2 IPNs

Rubber elasticity of poly(n‐butyl acrylate) networks formed with multifunctional crosslinkers