Interpenetrating networks SIN

The first type, termed sequential IPN s, involves the preparation of a crosslinked polymer I, a subsequent swelling of monomer II components and polymerization of the monomer II in situ. The second type of synthesis yields materials known as simultaneous interpenetrating networks (SIN s), involves the mixing of all components in an early stage, followed by the formation of both networks via independent reactions proceeding in the same container (10,11). One network can be formed by a chain growth mechanism and the other by a step growth mechanism. 

Simultaneous Interpenetrating Networks. An interpenetrating polymer network, IPN, can be defined as a combination of two polymers in network form, at least one of which was polymerized or synthesized in the presence of the other (23). These networks are synthesized sequentially in time. A simultaneous interpenetrating network, SIN, is an IPN in which both networks are synthesized simultaneously in time, or both monomers or prepolymers mixed prior to gelation. The two polymerizations are independent and non-interfering in an SIN, so that grafting or internetwork crosslinking is minimized (23-26). 

In the simultaneous interpenetrating networks (SIN), the two reactions are run simultaneously. This reaction will be emphasized in the present paper. One reaction, for example, can be a polyesterification or a polyurethane stepwise reaction, while the other is an addition reaction using styrene to make polystyrene via free radical chemistry. 

Figure 1. The synthesis of sequential IPN above and simultaneous interpenetrating networks, SIN, below. For the synthesis of SIN, two different reactions operate simultaneously such as condensation polymerization and addition polymerization. Reproduced with permission from Ref. 23. Copyright 1981, Plenum Publishing.

Interpenetrating polymer networks are defined in their broadest sense as an intimate mixture of two or more pol)Mners in network form [1,2]. Ideally, they can be synthesized by either swelling the first crosslinked polymer with the second monomer and crosslinker, followed by in-situ polymerization of the second component (sequential IPN s) or by reacting a pair of monomers and crosslinkers at the same time through different, non-interfering reaction mechanisms, simultaneous interpenetrating networks, SIN s. In fact, many variations of these ideas exist in both the scientific and the patent literature. In any case, at least one of the two components must have a network structure, as an IPN prerequisite. ... 

Simultaneous interpenetrating networks (SIN s) are produced by running two essentially independent and noninterfering, crosslinking... 

IPN s and related materials) in fact) have a long history. For example) IPN s were first synthesized to produce smooth sheets of bulk polymerized homopolymers (11), IPN s were next used as solution polymerized ion exchange resins. (12) 13) Further development of IPN s included the syntheses oT interpenetrating elastomer networks (lEN s) and simultaneous interpenetrating networks (SIN s) (14). lEN s consist of a mixture of different emulsion polymerized elastomers which are both crosslinked after coagulation. SIN s are formed by the simultaneous polymerization of mixed monomers by two noninterfering reactions (3 ) 16). 

Studies of preparation and properties of the so-called Simultaneous Interpenetrating Networks (SIN) occupy a special position among these works. SIN is a complex system of two or more three-dimensional network polymers which are chemically not bonded but are inseparable due to mechanical entanglement of chains. A detailed description of the preparation and properties of SIN is given by Lipatov and Ser-geeva . ... 

Although interpenetrating polymer networks (IPNs) are now beginning to be commercially exploited, little is known about many types of engineering behavior, such as fatigue. In this paper, energyabsorbing simultaneous interpenetrating networks (SINs) based on polyether-type polyurethanes (PU) and poly(methyl methacrylate)... 

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. 

Polymer networks synthesized by mixing monomers or linear polymers (prepolymers) of the monomers together with their respective cross-linking agents and catalysts in melt, solution, or dispersion, followed, usually immediately, by simultaneous polymerization by noninterfering modes, are called simultaneous interpenetrating networks (SIN). In the latter process, the individual monomers are polymerized by chain or stepwise polymerization, while reaction between the polymers is usually prevented due to different modes of polymerization. 

This novel class of polymers, together with simultaneous interpenetrating networks (SIN s) and interpenetrating elastomeric networks (lEN s)... 

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... 

Simultaneous Interpenetrating Network, SIN. The monomers and/or prepolymers plus cross-linkers and activators of both components are mixed, followed by simultaneous polymerization via noninterfering reactions see Fig. 6.1b. Typical syntheses involve chain and step polymerization kinetics. While both polymerizations proceed simultaneously, the rates of the reaction are rarely identical. 

Fig. 6.1 Two synthetic methods for preparing interpenetrating polymer networks, (a), sequential IPNs and, (b), simultaneous interpenetrating networks, SINs...

A simultaneous interpenetrating network, SIN, as the name suggests, starts with a mix of both monomers and both polymers. These are polymerized simultaneously, but by different routes, such as chain and step polymerization. Thus, while reacting, the two polymers do not interfere with each other, but merely dilute... 

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. 

As part of an investigation of the use of renewable feedstocks to synthesize polymers, a series of simultaneous interpenetrating networks (SINs) were prepared in which an elastomer network based on epoxidized botantical oils was combined with a glassy polymer network of crosslinked polystyrene (PSN). Thus SINs were successfully prepared containing from 5% to 40% elastomer based on epoxidized linseed, crambe, lunaria, and lesquerella oils. 

Vernonia Oil Sebacic Acid/Polystyrene (VOSAN/PSN) Simultaneous Interpenetrating Networks (SIN S)... 

These soft elastomers can be swelled by other monomers such as styrene, which together with crosslinkers such as divinylbenzene, can be polymerized in situ to form a sequential interpenetrating polymer network, IPN. Alternately, and in some cases preferably, the two polymerizations can be carried out simultaneously, since the esterification of the oil and the vinyl polymerization do not significantly interfere with one another. These latter products are called simultaneous interpenetrating networks, SINs. 

Figure 1. Simultaneous interpenetrating network (SIN) synthesis based on botanical oils. ...

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