Interpenetrating homopolymer network

Interpenetrating elastomeric network Intumescent flame retardant Interpenetrating homopolymer network Elastomerie eopolymer from isobutene and isoprene (ANSI/ASTM, lUPAC) see also Butyl, GR-I, PlBl Poly(isobutylene) see also PIB Intermediate molecular weight Isophthalic acid... 

This is a theoretical study on the entanglement architecture and mechanical properties of an ideal two-component interpenetrating polymer network (IPN) composed of flexible chains (Fig. la). In this system molecular interaction between different polymer species is accomplished by the simultaneous or sequential polymerization of the polymeric precursors [1 ]. Chains which are thermodynamically incompatible are permanently interlocked in a composite network due to the presence of chemical crosslinks. The network structure is thus reinforced by chain entanglements trapped between permanent junctions [2,3]. It is evident that, entanglements between identical chains lie further apart in an IPN than in a one-component network (Fig. lb) and entanglements associating heterogeneous polymers are formed in between homopolymer junctions. In the present study the density of the various interchain associations in the composite network is evaluated as a function of the properties of the pure network components. This information is used to estimate the equilibrium rubber elasticity modulus of the IPN. 

An interpenetrating polymer network (IPN) consisting of an epoxy and an elastomer has been developed by Isayama.29 This is a two-component adhesive-sealant where the components are simultaneously polymerized. It consists of the MS polymer, developed in Japan by Kanegafuchi and commonly used in sealant formulations, with the homopolymerization of DGEBA using a phenol catalyst and a small amount of silane as a graft site to connect the MS polymer and epoxy homopolymer networks. 

A random co-polymer or a blend of compatible polymers will have a single glass transition temperature intermediate between those of the two homopolymers. An example is shown in Figure 14 for nitrile-butadiene-rubber (22). The specific weight percents shown are those of commercial interest for NBR. In contrast, most polymer blends, graft and block copolymers, and interpenetrating polymer networks (IPN s) are phase separated (5) and exhibit two separate glass transitions from the two separate phases. Phase separated systems will not be considered here. 

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). 

The use of labile crosslinks allows a different approach to the study of interpenetrating polymer networks. With acrylic acid anhydride as the crosslinker, hydrolysis leads to a linear polymer easy to extract and characterize, and to a pure homopolymer network whose characteristics can be compared with an identical network prepared by classical methods. 

Figure 1 An illustration of three main types of hydrogels. Homopolymers (left) are composed of a single polymer type multipolymers (middle) are composed of two or more polymers cross-linked together (or arranged on individual chains) and interpenetrating polymer networks (IPNs) (right) comprise two different polymers that are separately cross-linked.

Figure 8.24. Temperature dependences of the dynamic storage modulus E and the loss modulus E" of the interpenetrating elastomeric networks. Filled circles observed values. Solid lines calculated for Takayanagi s model 2. Dashed lines component homopolymers. (Klempner et al., 1970.)...

Fig. 1. Hybrid organic-inorganic polymer systems can be devised for all structural paradigms of polymer chemistry including (a) homopolymer, (b) block copolymer, (c) copolymer, (d) graft copolymer, and (e) interpenetrating polymer networks, including, shown as geometrical abstractions, (f) true and (g) semi-interpenetrating versions, where crosslinks are depicted as junctions of horizontal and vertical lines.

Most recently, two other groups have undertaken the study of castor oil-based IPN s. Tan and Xie investigated the conditions for formation of castor oil polyurethanes with homopolymers or copolymers of styrene, methyl methacrylate and acrylonitrile. Simultaneous interpenetrating polymer networks were made which had high strength, good resilience and high resistance to abrasion and hydrolysis. 

The highest sonic damping is obtained in transition zones. The glass transition can be used for this purpose if cross-linked polymers are applied, with a rubbery solid state until far above Tg. Very interesting work in this field was done by Sperling and his coworkers (1987,1988) who studied the damping behaviour of homopolymers, statistical copolymers and interpenetrating networks (IPNs) of polyacrylics, polyvinyls and polystyrenes. 

---