Covalently bonded polymer chains

The expansion of a covalently bonded polymer chain will be restricted by the valence angles between each chain atom. In grareral, this angle is 0 for a homoatomic chain, and Equation 10.4 can be modified to allow for these short-range interactions. 

In a filled rubber, agglomeration of the particles produces a filler network, in addition to the network of covalently-bonded polymer chains. In fact, Reichert et al. [30] modeled the deformation of single network of filled rubber as a double network, adopting an approach similar to that used to analyze unfilled double networks [35-37]. This implies that double-network mbber reinforced with filler can be viewed as a composite of three distinct networks. 

There are many different polymers which are long chains of molecules linked by covalent bonds. The chains can be either intertwined in a loose assembly, or they can be cross-linked by covalent bonds to form a very strong lattice. Chromophoric molecules can be included in polymers in two different ways they can be dispersed at random, rather like in a glassy matrix, or they can be part of the polymer chains themselves. 

Crosslinking - Reaction or formation of covalent bonds between chain-like polymer molecules or between polymer molecules and low-molecular compounds such as carbon black fillers. As a result of crosslinking, polymers such as thermosetting resins may become hard and infusible. Crosslinking is induced by heat, UV or electron-beam radiation, oxidation, etc. Crosslinking can be achieved either between polymer molecules alone as in unsaturated polyesters or with the help of multifunctional crosslinking agents such... 

Some plastics, called thermoplastics, are able to repeatedly undergo this shape-changing treatment. Others, known as thermoset, can be shaped only once because they form irreversible covalent bonds between chains during the setting process and consequently will no longer melt and flow. Vulcanized rubber is an example of a thermoset polymer. Thermoset polymers tend to have relatively high chemical resistance and excellent mechanical properties. However, the vast majority of plastics used in packaging are thermoplastics. 

One-dimensional chains may be formed by inorganic materials either as stacks of individual molecules or as covalently bonded polymers. Emphasis is given to the former approach as these complexes are presently better characterized. It may also be possible to generate systems with one-dimensional properties through plastic deformation of normally three-dimensional materials (135,444). This class of materials is not yet widely characterized and is not discussed further. 

There is considerable interest in organizing polymer domains on the nanometer length scale. Block copolymers comprising covalently bonded immiscible chains offer one avenue for creating such structures. These molecules are amphiphilic and thus organize into microphases that are similar to those found in systems containing surfactants. The main purpose of this paper is to provide a listing of the properties that enable the determination of the phase... 

Two examples from the second approach are presented here. Both add covalently bonded polymeric chains to ultra-fine cellulose fiber surfaces. One tethers enzyme from the surface by amphiphilic linear PEG spacers that carry reactive end groups to form covalent bonds with enzyme proteins. The other adds polyelectrolyte PAA grafts that are sufficiently polar to attract enzymes via secondary forces. Both surface polymer chains are compatible with aqueous and organic media. 

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.

The permanent gels consist of solvent-logged covalently bonded polymer networks. One family of such networks is formed by cross-finking preexisting polymer chains, such as by vulcanization. Another family makes use of simultaneous polymerization and cross-linking. Some of the more important types of gels are delineated in Table 9.3 some specific examples include Jello (com-... 

We now turn our attention to hairy rods consisting of a conjugated polymer backbone, in which case the hairy-rod concept offers possibilities to achieve processible, i.e., soluble or fusible, electroactive materials. It allows one to control the chain conformation in solution [154] and to obtain improved charge transport in the self-organized bulk phase [155]. Here the discussion will still be limited to covalently bonded side chains. In the next section, the extension to supramolecular hairy rods will be considered. 

Polymers are made up of monomer molecules covalently bonded into chains or networks. 

Free radicals are particularly reactive species and there are several ways in which the growing chains can react to form inert covalently bonded polymer molecules. The most important mechanisms of termination are when two growing chains interact with each other and become mutually terminated by one of two specific reactions. One of these reactions is combination where the two growing chains join together to form a single polymer molecule... 

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