Polymer network definition

IPNs are found in many applications though this is not always recognised. For example conventional crosslinked polyester resins, where the polyester is unsaturated and crosslinks are formed by copolymerisation with styrene, is a material which falls within the definition of an interpenetrating polymer network. Experimental polymers for use as surface coatings have also been prepared from IPNs, such as epoxy-urethane-acrylic networks, and have been found to have promising properties. 

Silicone co-polymer networks and IPNs have recently been reviewed.321 The development of IPNs is briefly described, and the definitions of the main (non-exclusive) classes of the IPNs are cited. Examples of latex IPNs, simultaneous and sequential IPNs, semi-IPNs, and thermoplastic IPNs are provided. The use of silicone-silicone IPNs in studies of model silicone networks is also illustrated. Networks in which siloxane and non-siloxane components are connected via chemical bonds are considered co-polymer networks, although some other names have been applied to such networks. Today, some of the examples in this category should, perhaps, be discussed as organic-inorganic hybrids, or nanocomposites. Silicone IPNs are discussed in almost all of the major references dealing with IPNs.322-324 Silicone IPNs are also briefly discussed in some other, previously cited, reviews.291,306... 

A substantial number of definitions in the terminology section are either of physical quantities or are expressed mathematically. In such cases, there are recommended symbols for the quantities and, when appropriate, corresponding SI units. Other terms have eommon abbreviations. The following format is used to indicate these essential eharaeteristics name of term (abbreviation), symbol, SI unit unit. Typical examples are tensile stress, interpenetrating polymer network (IPN). If there are any, alternative names or synonyms follow on the next line, and the definition on the sueeeeding lines. 

When characterizing polymer networks, the following definitions are typically applied [150] and are illustrated in Fig. 7. When a radical on a polymer chain propagates through a pendant double (i.e. a double bond from a monomer with one double bond already reacted), a crosslink, secondary cycle, or primary cycle can be formed. A crosslink forms when the radical reacts with a pendant... 

It has long been a mystery why diffusion coefficients of polymer-diluent systems, especially when the diluent is a good solvent for a given polymer, exhibit so pronounced a concentration dependence that it looks extraordinary. Several proposals have been made for the interpretation of this dependence. Thus Park (1950) attempted to explain it in terms of the thermodynamic non-ideality of polymer-diluent mixtures, but it was found that such an effect was too small to account for the actual data. Fujita (1953) suggested immobilization of penetrant molecules in the polymer network, which, however, was not accepted by subsequent workers. Recently, Barrer and Fergusson (1958) reported that their diffusion coefficient data for benzene in rubber could be analyzed in terms of the zone theory of diffusion due to Barrer (1957). Examination shows, however, that their conclusion is never definitive, since it resorted to a less plausible choice of the value for a certain basic parameter. 

Abstract This article summarizes a large amount of work carried out in our laboratory on polysiloxane based Interpenetrating Polymer Networks (IPNs). First, a polydimethylsiloxane (PDMS) network has been combined with a cellulose acetate butyrate (CAB) network in order to improve its mechanical properties. Second, a PDMS network was combined with a fluorinated polymer network. Thanks to a perfect control of the respective rates of formation of each network it has been possible to avoid polymer phase separation during the IPN synthesis. Physicochemical analyses of these materials led to classify them as true IPNs according to Sperling s definition. In addition, synergy of the mechanical properties, on the one hand, and of the surface properties, on the other hand, was displayed. 

One should also consider the glycocalyx, a carbohydrate-containing polymer network between the microvilli and the mucus gel coat. It probably consists mainly of oligosaccharide chains that are covalently linked to the lipids and proteins of the brush border membrane. The definite structure of the glycocalyx is not yet available, and nothing can be said about its possible importance as an absorption barrier. 

Definition and Structure of Polymer Networks A polymer network can be defined as a highly crosslinked macromolecule in which essentially all units are connected to each other in some way, either via chemical bonds or physical associations. 

During emulsion polymoization proccesses crosslinking can occur due to the presence of radicals and unsaturation in the polymer chain. Chain transfer agents are often used to decrease the level of crosslinking during polymerization. The gel content of a crosslinkable polymo is d ned as the fraction of material of infinite MM experimental criteria are usually more aibitraiy, and strongly depend on the experimental procedure. The same holds for the gel point, Le. the conversion at which the first insoluble polymer network makes its appearance. For example, in ABS gel content can be based on the toluene extraction of the soluble fraction of the polybutadioie. Hie insoluble residue is the gel fraction by definition. 

Fig. 7.8 The dependence of (engineering) stress

Polymerization of monomer II in the presence of polymer I definitely leads to increases in molecular weight, increased viscosity, and often true gel formation. This latter is actually a form of joined IPN or AB crosslinked copolymer. Using the cellular model of phase separation, we may predict that gelation, if it occurs, will be most extensive near the cell wall. In Section 3.1.1.3, we concluded that polymer II was unable to pass easily through polymer I even in the highly swollen state, because of polymer incompatibility. Obviously, this transport difficulty is augmented by a surrounding gel network. 

One method to obtain solvent activities in swollen polymer networks in equilibrium is to apply vapor pressure measurements. This is discussed in detail above in the Subchapter 4.4.3.1.1 and most methods can be used also for network systems, especially all sorption methods, and need no further explanation. The VPO-technique can be applied for this purpose, e.g., Amdt. IGC-measurements are possible, too, if one realizes a definitely erosslinked polymer in the column, e.g., Refs. " " ... 

Incorporation of multifunctional POSS into polymer systems has been investigated with different polymers [6,62-66]. In these cases, single-phase polymer networks with POSS molecularly dispersed are often formed. POSS acts as a polyhedral cross-link. But no definite effect of POSS on network properties has been established. Both a decrease [64,65] and no change in Tg [6] were reported. The rubbery modulus increases due to a high crosslink density, and thermal stability increases with POSS content. 

In its broadest definition, an interpenetrating polymer network, IPN, is any material containing two polymers, each in network form/" A practical restriction requires that the two polymers have been synthesized and/or crosslinked in the immediate presence of each other. Two types of IPNs are illustrated in Figure The sequential IPN begins with the... 

The above represents the classical definition of an IPN. The term interpenetrating polymer network was coined before the extent or conseqnences of phase separation were fully realized. This article covers sequential and simultaneous types of IPNs made in bulk and also includes such materials as IPNs based on latexes and suspension-sized particles thermoplastic IPNs, which contain physical cross-links in one or both polymers, and hence may be (partly) soluble and a number of other closely related materials. 

Multicomponent polymeric materials consist of polymer blends, composites, or combinations of both. A polymer blend has two definitions The broad definition includes any finely divided combination of two or more polymers. The narrow definition specifies that there be no chemical bonding between the various polymers making up the blend. Table 2.5 and Section 2.7 summarize the basic types of polymer blends based on the broad definition primarily these are the block, graft, star, starblock, and AB-cross-linked copolymers (conterminously grafted copolymers), interpenetrating polymer networks, as well as the narrow definition of polymer blends. More complex arrangements of polymer chains in space can be shown to be combinations of these several topologies. 

AB crosslinked polymers, ABCP s, and interpenetrating polymer networks, IPN s, more precise definitions of crosslinks became required. While AB crosslinked polymers are listed in Table I, graft and block copolymer bonds per se are not included because these materials remain soluble (uncrossiinked) in the simple case. 

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