Covalent semi-IPNs

IPNs A type of polymer blend prepared to modify the properties of NR. They are composed of two or more polymers with at least one being poly-merized/crosslinked in their networks both without and/or with covalent bonds between the chains of the same or different polymer types. They can be categorized into two types non-covalent IPNs and covalent semi-IPNs (Figure 7.1). For the covalent semi-IPNs, the crosslinked covalent bonds occur between the different polymer chains. In addition, non-covalent IPNs can be further categorized into full IPNs and semi-IPNs. Full IPNs are defined as a combination of NR and other polymers in a network in which each is synthesized by polymerization with a crosslinking agent. In semi-IPNs, in contrast, only one type of polymeric component is crosslinked. However, there are no covalent bonds between the chains of the different polymer types, but the chains of the polymer become inserted into the framework of the other polymers. Moreover, pseudo-IPNs are defined as a type of IPN in which one of the... 

Interpenetrating polymer networks (IPNs) are a combination of two or more polymers in networks where a partial interlacing on the molecular scale is present in the matrix. There is no covalent bonding and therefore the polymers cannot be separated unless the chemical bonds are broken (Fig. 1.5). Thus the mixtures of two prepared polymers, networked without any interlacing, are not generally considered to be IPNs, although many researchers have treated them as such. IPNs are of different types, viz. sequential, simultaneous and semi IPNs. As their names suggest, sequential... 

Figure 1.3. Simple two-polymer combinations, (a) illustrates a polymer blend, without covalent linkages, (b) is a graft copolymer, (c) is a block copolymer, (d) illustrates a semi-IPN, (e) a full IPN, and (f) designates an AB-crosslinked polymer. Structure (f) requires two polymers to make one network, while (e) has two independent networks. ...

Fu et al. [124] prepared a series of novel covalent organic-inorganic hybrid proton-conductive membranes, each with a semi-interpenetrating polymer network (semi-IPN), for DMFC applications through polymer reactions and sol-gel method. A sulfonation reaction was produced as last step. The developed copolymer chains interpenetrated into the PVC matrix to form the semi-IPN structure, and the inorganic silica was covalently bound to the copolymers. 

Another kind of mixed network comes about when two linear polymers that are incompatible at room temperature are simultaneously cross-linked at a high temperature at which they are compatible. Phase separation on cooling may be inhibited by the covalent bonds, which limit the movement of polymer chains. The term semi-IPN can refer to a linear polymer trapped in a network of another polymer. 

Figure 2.10 Six basic modes of linking two or more polymers are identified (20). (a) A polymer blend, constituted by a mixture or mutual solution of two or more polymers, not chemically bonded together, (b) A graft copolymer, constituted by a backbone of polymer I with covalently bonded side chains of polymer II. (c) A block copolymer, constituted by linking two polymers end on end by covalent bonds, (d) A semi-interpenetrating polymer network constituted by an entangled combination of two polymers, one of which is cross-linked, that are not bonded to each other, (e) An interpenetrating polymer network, abbreviated IPN, is an entangled combination of two cross-linked polymers that are not bonded to each other, (f) AS-cross-linked copolymer, constituted by having the polymer II species linked, at both ends, onto polymer I. The ends may be grafted to different chains or the same chain. The total product is a network composed of two different polymers.

From a topological point of view, the IPN s are closely related to polymer blends, block and graft copolymers, AB-crosslinked copolymers " and ionomeric blends. Some interesting hybrids exist between the IPN s and other polymer materials. The thermoplastic IPN s contain physical crosslinks rather than chemical (covalent) crosslinks. Physical crosslinks can be formed from block copolymers, ionomers or semi-crystalline polymers. When the temperature is raised above the softening point of the respective components, the material flows like a thermoplastic. At service temperatures, it behaves like an IPN, with thermoset behavior. Table 1 summarizes some of the terminology used to describe IPN structure and morphology. 

The thermoplastic IPN s are heavily represented in Table 4. Both the polypropylene-mt r-poly(ethylene-stat-propylene) types and the block copolymer/semi-crystalline polymer types are represented. In fact, both sequential and simultaneous methods of covalent bonding are also represented. 

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