Tetrafunctional

Comonomers can be used to create a variety of polymer stmctures that can impart desirable properties. For example, even higher molecular weight PPS polymers can be produced by the copolymerization of a tri- or tetrafunctional comonomer (18). The resultant polymer molecules can have long-chain branching, which can be used to tailor the rheological response of the polymer to the appHcation. 

This compound is soluble in most organic solvents and may be easily copolymerized with other vinyl monomers to introduce reactive side groups on the polymer chain (18). Such reactive polymer chains may then be used to modify other polymers including other amino resins. It may be desirable to produce the cross-links first. Thus, A/-methylolacrylamide can react with more acrylamide to produce methylenebisacrylamide, a tetrafunctional vinyl monomer. 

Polymetallocarbosilanes. PolymetaHocarbosilanes having a number-average molecular weight of 700—100,000 can be prepared by reaction of polycarbosilane, /2 2 fx where R is H, or lower alkyl, with a tetraalkyl titanate, to give a mono-, di-, tri-, or tetrafunctional polymer... 

Fig. 2. Polytitanosiloxane polymers, where M is Ti/Zr and X is Cl. (a) Monofunctional, (b) dihinctional, (c) trifunctional, and (d) tetrafunctional polymers.

In the 1960s, CIBA Products Co. marketed and manufactured glycidylated o-cresol novolak resins, which had been developed by Koppers Co. as high temperature-resistant polymers. Dow offered glycidylated phenol novolak resins, SheU introduced polyglycidyl ethers of tetrafunctional phenols, and Union Carbide developed a triglycidyl p- am in oph en o1 resin. 

As with the flexible foams there has been a shift to the use of polyethers. These are largely adducts based either on trifunctional hydroxy compounds, on tetrafunctional materials such as pentaerythritol or a hexafunctional material such as sorbitol. Ethylene diamine and, it is understood, domestic sugar are also employed. Where trifunctional materials are used these are of lower molecular weight (-500) than with the polyethers for flexible foams in order to reduce the distance between hydroxyl groups and hence increase the degree of cross-linking. 

Figure 9.12. GPC distributions obtained during bulk thermal polymerization of S at 110 °C (a) with tetrafunctional RAFT agent 339 (0.0074M) at 6 h, 25%...

Weidisch R., Gido S.P., Uhrig D., latrou H., Mays J., and Hadjichristidis N. Tetrafunctional multigraft copolymer as novel thermoplastic elastomer, Macromolecules, 34, 6333, 2001. 

Kinetic gelation simulations seek to follow the reaction kinetics of monomers and growing chains in space and time using lattice models [43]. In one example, Bowen and Peppas [155] considered homopolymerization of tetrafunctional monomers, decay of initiator molecules, and motion of monomers in the lattice network. Extensive kinetic simulations such as this can provide information on how the structure of the gel and the conversion of monomer change during the course of gelation. Application of this type of model to polyacrylamide gels and comparison to experimental data has not been reported. 

After secretion from the cell, certain lysyl residues of tropoelastin are oxidatively deaminated to aldehydes by lysyl oxidase, the same enzyme involved in this process in collagen. However, the major cross-links formed in elastin are the desmosines, which result from the condensation of three of these lysine-derived aldehydes with an unmodified lysine to form a tetrafunctional cross-hnk unique to elastin. Once cross-linked in its mature, extracellular form, elastin is highly insoluble and extremely stable and has a very low turnover rate. Elastin exhibits a variety of random coil conformations that permit the protein to stretch and subsequently recoil during the performance of its physiologic functions. 

Figure 21. Atom transfer radical polymerization (ATRP) synthetic route to tetrafunctional initiators of a star polymer with adamantyl (adamantane core). Taken from Ref. [91] with permission.

A pair of cross-linked chain units may be regarded as a single tetra-functional unit according to the scheme applied to polyfunctional condensation. In order to demonstrate the correspondence between the two treatments, consider the condensation of tetrafunctional units A... 

If we regard it as a cross-linked polymer, we require ywj the weight average degree of polymerization if all cross-linkages were severed. This operation would amount to replacing each tetrafunctional unit, or pair of cross-linked units, with two bifunctional units. The extent of reaction p would not be affected. Hence, according to Eq. (VIII-8)... 

The other case which we consider is that of a most probable primary distribution. The molecular size distribution after random cross-linking must correspond exactly to that which would be obtained by random condensation of a mixture of bifunctional and tetrafunctional units. This follows as an extension of the correspondence between these two cases considered in the discussion of the critical condition given in the preceding section. The equations developed there are applicable to this case. 

Occurrence of either step causes the polymer molecule I to be incorporated in the growing chain. The unit of the polymer to which the radical adds becomes a tetrafunctional unit, which is equivalent to a pair of cross-linked units, i.e., to a cross-linkage. 

The treatment given here, like that of rubber elasticity in Chapter XI, is developed for a network in which the ends of the chains are united tetrafunctionally,... 

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