Simultaneous interpenetrating network method

Figure 6.1. Two synthetic methods for preparing interpenetrating polymer networks. A, sequential IPNs, and B, simultaneous interpenetrating networks, SlNs.

For simultaneous interpenetrating networks (SINs), two independent, non-interfering reactions are required. Thus, a chain and a step polymerization have been the method of choice for many such polymerizations. Typical examples have involved PS and polyurethanes [Hourston and Schafer, 1996 Mishra et ai, 1995], and PMMA. A key factor in the kinetics of such polymerizations is to keep the system above the glass transition temperature of both components. If the glass transition of either the polymer network I or polymer network II rich phase vitrifies, the polymerization in that phase may slow dramatically. 

This paper reports what we believe to be the first true IPN, i.e., no grafting between polymers and a single phase morphology (i.e., complete chain entanglement). In order to achieve this, pol3nners of known compatibility were used. Thus, IPN s, pseudo-IPN s (PDIPN s - only one polymer crosslinked), and linear blends of polystyrene (PS), and poly(2,6-dimethyl-l,4-phenylene oxide) (PPO) (whose compatibility has been reviewed elsewhere (14)) were prepared by the simultaneous interpenetrating network (SIN) technique. The polystyrene was crosslinked by incorporating divinylbenzene. Several methods have been reported to synthesize... 

Fig. 2. Two basic synthetic methods of preparing IPNs, sequentially and simultaneously, (a) Sequential IPNs (b) simultaneous interpenetrating network (SIN).

Over the years, people have discovered many different ways of synthesizing IFN s. Figure 2 Illustrates the sequential IPN synthesis, top, and the simultaneous Interpenetrating network, SIN, synthesis, bottom. In the sequential synthesis, polymer network I Is swollen with monomer II plus crosslinker and activator, and polymerized In situ. The SIN synthesis begins with a mutual solution of both monomers or prepolymers and their respective crosslinkers, which are then polymerized simultaneously by noninterfering modes, such as stepwise and chain polymerizations. These methods have been used In the bulk, suspension, and latex states. Each will yield a distinguishable composition, even for the same polymer pair. 

There are several techniques for producing polymer mixtures for further processing into articles by the reactive (chemical) molding methods simultaneous formation of two polymeric systems with mutual entanglement of their chains and the appearance of so-called interpenetrating networks synthesis of the second polymer within an expanded network of the initial polymer incorporation of oligomers into a polymer matrix as a temporary plasticizer followed by polymerization. 

There are two general methods of synthesizing IPN s, see Figure 1. For sequential IPN s, polymer network I is synthesized, and monomer II plus crosslinker and activator is swelled in and polymerized. For simultaneous interpenetrating polymer networks, SIN s, both monomers and their respective crosslinkers and activators are mixed together and polymerized, usually by separate and non-interfering kinetic methods such as stepwise and chain polymerizations. Of course, there are many... 

J.A. Pojman, et al., Binary frontal polymerization a new method to produce simultaneous interpenetrating polymer networks (SINs). J. Polym. Sci. A Polym. Chem. 1997, 35(2), 227-230. 

A series of castor oil polyurethane/poly(methyl methacrylate) interpenetrating polymer networks (IPNs) and gradient IPNs, cured at room temperature, were prepared by a simultaneous IPN method, and nanocomposites with BaTiOs superfine fibre were reported for the systems. A dose-dependent improvement in thermoelectric and mechanical properties was observed in the nanocomposites compared to the pristine systems. 

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