Interpenetrating polymer networks (IPNs) are unique alloys of crosslinked polymers. This article reviews the studies on kinetic effects involved in IPN formation. Several investigators have studied the effect of kinetics of curing reactions on the morphology and properties of IPNs. It was found, in general, that the faster the rates of the respective chain extension and crosslinking reactions are and the closer they are to simultaneity, the more homogeneous are the IPNs. Other investigations revealed that the individual components sometimes can polymerize more rapidly in the IPN than alone, due to a “solvent effect” of the IPN. Effects of changing reaction variables, such as NCO/OH ratio, composition activators and temperature were used to study reaction kinetics as well as phase morphology by the Fourier transform infrared technique. Thermochemical techniques have been utilized to study the kinetics of IPN formation which influence phase separation. Small‐angle X‐ray scattering and small‐angle neutron scattering techniques were used to estimate the extent of microheterogeneity of the phase domains in a study of the kinetics of phase separation in the IPNs.

SynopsisCastor oil-a renewable resource-is abundantly grown in tropical countries. It is a triglyceride of glycerol and ricinoleic acid containing hydroxyl functionality. These hydroxyls were reacted with 4,4'-diphenyl methane diisocyanate to form prepolyurethanes with different NCO/OH ratios.The prepolyurethane was swollen in ethyl methacrylate monomer containing 1% ethylene glycol dimethacrylate as crosslinker by radical polymerization initiated with benzoyl peroxide. The polyurethane/poly (ethyl methacrylate) interpenetrating polymer networks (IPNs) PU/PEMA were obtained as tough films by casting into glass molds. These IPNs were characterized by their resistance to chemical reagents, optical properties ( % transmittance), thermogravimetric analysis and mechanical properties, dynamic storage modulus ( c') , loss modulus ( c"), and loss tangent (tan 6 ) by dynamic mechanothermal analysis, morphology by scanning electron microscopy, and dielectric properties ( u , c', c", and tan 6 ) a t different temperatures.

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ABSTRACT:Crosslinked polyurethanes were obtained when trifunctional -OH group containing castor oil was reacted with difunctional toluene-2,4-diisocyanate under different stoichiometric conditions varying NCO/OH ratio. These polyurethanes swelled in n-butyl acrylate monomer and subsequently polymerized by radical polymerization initiated with benzoyl peroxide in presence of crosslinking agent ethylene glycol dimethacrylate. A series of interpenetrating networks, PU/PnBA IPNs, were obtained as tough films by transfer moulding. All these IPNs films were characterized by resistance to chemical reagents, thermal behavior (DSC, TG), and mechanical studies such as tensile strength, Young's modulus, elongation at break (%) and hardness shore A. The mechanothermal (DMA) and morphological (SEM) behavior were studied. Dielectric properties such as electrical conductivity, dielectric constant (e'), dielectric loss (e"), and dielectric loss tangent (tan b) were estimated.

SYNOPSISThree series of interpenetrating polymer networks ( IPNs.) based on a polyurethane (castor oil + toluene diisocyanate ) with polystyrene, poly (methyl methacrylate), and poly ( nbutyl methacrylate) were synthesized and characterized. Dielectric relaxation studies of these IPNs were carried out from -150 to 100°C in the 100 Hz to 100 kHz range. The effects of structural variables such as composition, type of vinyl monomer, as well as the effect of interaction of the phases on the dielectric properties were studied. A certain degree of phase mixing was observed to exist in all series as detected by the variation of the glasstransition temperatures of the IPNs. Maxwell-Wagner-Sillars polarization at the interface of the two phases was observed.