Monomer bifunctional

The and e values of the aHyl group in DAP have been estimated as 0.029 and 0.04, respectively, suggesting that DAP acts as a fairly typical unconjugated, bifunctional monomer (42). Cyclization affects copolymerization, since cyclized radicals are less reactive in chain propagation. Thus DAP is less reactive in copolymerization than DAIP or DATP where cyclization is stericaHy hindered. Particular comonomers affect cyclization, chain transfer, and residual unsaturation in the copolymer products. DiaHyl tetrachloro- and tetrabromophthalates are low in reactivity. 

As with addition polymers, molecules with a range of molecular weights are produced. In the condensation of bifunctional monomers... 

Later, Kricheldorf and coworkers [93,94] extensively demonstrated the use of 0-silylated bifunctional monomers, such as diphenols, for synthesis of a wide variety of polycondensation polymers. The silylated oxygen of difunctional phenols may be condensed with activated... 

The synthetic strategy towards the copolymers is shown in Figure 16-3. The use of bifunctional monomers in a Heck reaction allows the synthesis of polymers, and the great potential of this approach has been demonstrated previously [53-55]. The syntheses have been described in detail by Hilberer el al. [16],... 

The use of furan bifunctional monomers for the preparation of linear polyesters and polyamides has been reported by several authors in the last two decades and two... 

On the other hand, nylon 6 is prepared from caprolactam, which behaves as a bifunctional monomer bearing two different functional groups, and hence the polymer is made up of just one type of unit along the backbone it is therefore a homopolymer. 

THE NETWORK POLYMER-BIFUNCTIONAL MONOMER REVERSIBLE SYSTEM Endo T Suzuki T Sanda F Takata T Tokyo,Institute of Technology... 

Details are given of the successful construction of a novel reversible system of network polymers between bifunctional monomers by utilising the equilibrium polymerisation system of a spiro orthoester. Molecular structures were determined by NMR and IR spectroscopy. 9 refs. 

Most pol3TTiers in production today are made from two different monomers because this s mthetic route offers advantages over the use of bifunctional monomers. First, monomers with two identical functional groups are easier and less expensive to produce than monomers with two different groups. Second, the properties of the pol3Tner can be varied easily by changing the structure of one of the monomers. 

The process proceeds through the reaction of pairs of functional groups which combine to yield the urethane interunit linkage. From the standpoint of both the mechanism and the structure type produced, inclusion of this example with the condensation class clearly is desirable. Later in this chapter other examples will be cited of polymers formed by processes which must be regarded as addition polymerizations, but which possess within the polymer chain recurrent functional groups susceptible to hydrolysis. This situation arises most frequently where a cyclic compound consisting of one or more structural units may be converted to a polymer which is nominally identical with one obtained by intermolecular condensation of a bifunctional monomer e.g., lactide may be converted to a linear polymer... 

In Section 3 of this chapter it was mentioned that polymers obtained by intermolecular condensation of bifunctional monomers may often be prepared alternatively by an addition polymerization of a cyclic compound having the same composition as the structural unit. Typical examples are shown in Table III. The processes indicated are appropriately regarded as addition polymerizations. Each of these polymers may also be prepared through the condensation of suitable bifunctional monomers. The dimethylsiloxane polymer, for example, may be prepared, as indicated in Table I (p. 45), through the condensation of dimethyl dihydroxysilane formed by hydrolysis of the di-chlorosilane... 

The chemical and physical properties of the polymers obtained by these alternate methods are identical, except insofar as they are affected by differences in molecular weight. In order to avoid the confusion which would result if classification of the products were to be based on the method of synthesis actually employed in each case, it has been proposed that the substance be referred to as a condensation polymer in such instances, irrespective of whether a condensation or an addition polymerization process was used in its preparation. The cyclic compound is after all a condensation product of one or more bifunctional compounds, and in this sense the linear polymer obtained from the cyclic intermediate can be regarded as the polymeric derivative of the bifunctional monomer(s). Furthermore, each of the polymers listed in Table III may be degraded to bifunctional monomers differing in composition from the structural unit, although such degradation of polyethylene oxide and the polythioether may be difficult. Apart from the demands of any particular definition, it is clearly desirable to include all of these substances among the condensation... 

In a linear polyesterification involving bifunctional monomers exclusively, the hydroxyl and carboxyl groups being present in equal numbers, the number of unreacted carboxyl groups must equal the number of molecules present in the system, provided that no side reactions occur the number of molecules in moles per unit volume is equal, therefore, to co(l—p). If each residue from a glycol and from a di-... 

The condensation of amino acids likewise may produce cyclic and/or linear products the same is true of virtually all polyfunctional condensation reactions. The conversion of cyclic monomers and dimers (or other cyclic low polymers) to chain polymers was discussed in the preceding chapter the reverse reaction may often occur as well. Thus the alternative ring and chain products which may be produced by condensation of a bifunctional monomer usually are interconvertible, but with varying degrees of facility. 

Bifunctional monomers capable of forming six- or seven-membered rings condense variably, depending upon the particular monomer. The products normally obtained in the absence of diluent in various representative bifunctional condensations are listed in Table IX for unit lengths of six and seven members. The term interconvertibility refers to the reversible transformation between the ring and the linear polymer. Several of the six-membered units (Table IX) prefer the ring form exclusively, but most of them yield both products, or at any rate the ring and chain products are readily interconvertible. Seven-membered units either yield linear polymers exclusively, or, if the cyclic monomer is formed under ordinary conditions, it is convertible to the linear polymer. 

X represents the combined number of both types of units in the polymer chain. Eq. (3) applies also to polymers stabilized (see Chap. Ill) with small amounts of monofunctional units, although here it becomes necessary to replace the extent of reaction p with another quantity, namely, the probability that a given functional group has reacted with a bifunctional monomer. Type ii polymers stabilized with an excess of one or the other ingredient will be discussed later. 

Derivation of the Molecular Distribution for the Random Condensation of Bifunctional with Pol3ffunctional Monomers. —Let a bifunctional monomer A----- A condense with a polyfunctional monomer... 

Step polymerizations of linear chains can involve either two different bifunctional monomers in which each monomer possesses only one type of functional group (commonly represented by X-X or Y-Y), or a single monomer containing both types of functional groups (common representation X-Y). However, whatever the monomer type, a linear polymer molecule contains, on average, one functional group of each species per chain (molecule). 

Crosslinked macromolecules can be formed from bifunctional monomers by first polymerising them, then by performing coupling reactions onto existing chains. The latter mechanism is often called vulcanisation.11 Several chemical routes can be followed to accomplish vulcanisation, depending on the functions available on polymer chains. 

Chemical Crosslinking. Only linear polymers are produced from bifunctional monomers. The reaction system must include a polyfunctional monomer, i.e., a monomer containing 3 or more functional groups per molecule, in order to produce a crosslinked polymer. However, the polyfunctional reactant and/or reaction conditions must be chosen such that crosslinking does not occur during polymerization but is delayed until the fabrication step. This objective is met differently depending on whether the synthesis involves a chain or step polymerization. In the typical... 

In the early days of polymer science, when polystyrene became a commercial product, insolubility was sometimes observed which was not expected from the functionality of this monomer. Staudinger and Heuer [2] could show that this insolubility was due to small amounts of tetrafunctional divinylbenzene present in styrene as an impurity from its synthesis. As little as 0.02 mass % is sufficient to make polystyrene of a molecular mass of 2001000 insoluble [3]. This knowledge and the limitations of the technical processing of insoluble and non-fusible polymers as compared with linear or branched polymers explains why, over many years, research on the polymerization of crosslinking monomers alone or the copolymerization of bifunctional monomers with large fractions of crosslinking monomers was scarcely studied. 

Probably most network structures obtained by copolymerization of bifunctional monomers and larger fractions of monomers with a higher functionality... 

For the formation of microgels the presence of a crosslinking monomer is not always necessary. Thus, microgels have also been detected in polymers prepared with bifunctional monomers, e.g. poly(acrylonitrile-co-vinylacetate) [39], polyethylene [40],poly(vinylchloride) [41] andpoly(vinylidenefluoride) [42].Obviously, the reason for the intramolecular crosslinking with the formation of microgels are side reactions. 

In linear EP of bifunctional monomers, such as S, with water soluble initiators, the monomer droplets do not compete with micelles in capturing radicals from the aqueous phase because the total surface area of the droplets is much smaller than that of micelles and growing particles. Nevertheless, if some radicals enter monomer droplets, rapid termination takes place. Therefore, polymerization in monomer droplets is negligible [88]. However, if in the crosslinking EP of 1,4-DVB a few radicals are captured by monomer droplets, they can polymerize completely because the recombination of radicals is suppressed by the gel effect. Moreover, in thermal initiation or in initiation by hydrophobic initiators, such as AIBN, radicals are formed predominantly in the hydrophobic phase, i.e. in monomer droplets and in micelles, and crosslinking EP is initiated in the organic phase. 

By emulsion copolymerization (ECP) of self-emulsifying unsaturated polyesters (EUP) and bifunctional monomers, such as styrene (S), microgels may be prepared which have a rather uniform diameter [109]. This uniformity of size is due to a special mechanism of particle formation involved in using EUP as comonomers. 

Reactive microgels may be incorporated into plastics by covalent bonds. It could be demonstrated that substantial amounts of polymer chains from bifunctional monomers can be attached at microgel surfaces and thus become insoluble [313, 377-380]. 

Figure 5.2 Formation of branched molecules from tetrafunctional and bifunctional monomers...

Hirshfeld and Schmidt (168) proposed that this problem might not arise in the polymerization of long bifunctional monomers in crystals of suitable structure, as in 97 — 98. They predicted that reaction in such systems would occur via a tilt of each molecule about its center of mass, so that little or no net displacement of the molecules would be involved. In fact, two successful realizations of this approach were subsequently reported, for the diacetylenes, which will be discussed in a later section, and for distyrylpyrazines and related compounds. Here we discuss the latter series. 

In most cases no special care is taken in chemistry to achieve regularity /-func-tional and bifunctional monomer units are mostly just mixed together and left for reaction without any constraints. 

Polymers result from polymerization—the chemical combination of a large number of molecules of a certain type, called monomers. Monomers can be bifunctional (capable of joining up with two other monomers) and tri- or polyfunctional (each may join up with three or more monomers). When bifunctional monomers react with each other, you get linear thermoplastic... 

Copolymers. Mixtures of two or more different bifunctional monomers can undergo additional polymerization to form copolymers. Why copolymerize Well, polymers have different properties that depend on their composition, molecular weight, branching, crystallinity, etc. Many copolymers have been developed to combine the best features of each monomer. For example, polystyrene is low cost and clear, but it is also brittle with no toughness. It needs internal plasticization. By copolymerizing styrene with a small amount of acrylonitrile or butadiene, the impact and toughness properties are dramatically improved. 

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