Initiators, difunctional/trifunctional

Initiation sites, in VDC polymer degradation, 25 714-715 Initiator bonds, breaking, 14 278 Initiators. See also Anionic initiators Cationic initiators Free-radical initiators alkoxide, 14 259 copolymerization, 14 252 difunctional and trifunctional, 14 252— 254... 

Polyfunctional OH Components (Crosslinkers). For crosslinking, trifunctional alcohols are used mainly. Some are of the same type as the difunctional prepolymers—e.g., polyethers derived from trifunctional initiators (glycerol, trimethylolpropane, 1,2,6-hexanetriol) and propylene or butylene oxide—and are preferred. Low molecular weight alcohols are used also. Examples are the ones listed above and glycerol monoricinole-ate, glycerol triricinoleate and amino alcohols like triethanolamine. 

The value of Fn was determined by 1H NMR spectroscopy and found to be close to unity. By essentially the same method, bifunctional and trifunctional cyanoacrylate functional PIBs have also been prepared. Anionic polymerization of CA-PIB with N,N-dimethyl-p-toluidine as initiator in solution resulted in high MW product (Mn 35,000 gmol ) [107]. Anionic copolymerization of difunctional and trifunctional PIB yielded clear flexible films with low sol fraction. The... 

Other ABC triblock copolymers were prepared using mono-, di-, and trifunctional initiators to produce ABC, ABCBA, and [ABC]3 linear and 3-arm star block copolymers. For example, a difunctional pSt macroinitiator (Mn=1100, Mw/Mn=1.17) was chain extended with tBA (Mn=l 1,200, Mw/Mn=1.16) which was subsequently chain extended with MA (Mn=27,250, Mw/Mn=l. 14), as shown in Fig. 21. 

Cyclic dialkylboranes are prepared by hydroboration of dienes with 1 1 HjB THF. Trifunctional boranes give with difunctional dienes polymeric organo-boranes. Fortunately, these products can be transformed into monomers or dimers by further reaction. Thus, the hydroboration product obtained from 1,3-butadiene is polymeric " . The initial products, which are dumbbell-shaped organoboranes, are cleaved by the remaining borane to give the polymer. 

In addition, dihlock copolymers, triblock copolymers, star homopolymers, and block copolymers can be obtained via anionic polymerization methods using difunctional and trifunctional initiators. Suitable initiators include sulfonyldiphenol bisphenol A, and phloroglucinol. 

Figure 12.4 shows that the a,oo-difunctional silicone acrylate is more reactive than the mono- and trifunctional acrylate. The heat of reaction evolved in each case permits the calculation of the conversion of the acrylate groups by means of the standard heat of acrylate polymerisation. A comparison with the initial acrylate contents determined by titration clearly demonstrates that the acrylate functions of the trifunctional siloxane react incompletely. 

The hydrolysis of di- and trifunctional organosilanes produces mixtures of polysiloxanes the composition and structures of these vary widely, depending on the initial reactants and the hydrolysis conditions. Difunctional organosilanes usually... 

Difunctional and Trifunctional Organolithium Initiators Based on 1,1-Diphenylethylene... 

Studies of the polymerization and gelation process of difunctional monomers forming a network with trifunctional branchpoints consisting of 2,4,6- or 1,3,5-substituted 1,3,5-triazines indicate that the approach to the gel point is inconsistent with the mean field approach to percolation initiated by Flory [39] and Stockmayer [10] and later elaborated by Gordon [557], This approach calls for a 50% monomer conversion at the gel point, substantially below the 60... 

The product of their reaction is an ester which possesses one carboxylic acid end-group and one hydroxyl end-group (i.e. it also is difunctional). This dimer, therefore, can react with other molecules of terephthalic acid, ethlyene glycol or dimer leading to the formation of difunctional trimers or difunctional tetramer. Growth of linear polymer chains then proceeds via further condensation reactions in the manner indicated for step polymerization in Table 2.1. Hence linear step polymerizations involve reactions of difunctional monomers. If a trifunctional monomer were included, reaction at each of the three functional groups would lead initially to the formation of a branched polymer but ultimately to the formation of a network. For example, if terephthalic acid were reacted... 

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