Butadiene telechelics synthesis

Ebdon and coworkers22 "232 have reported telechelic synthesis by a process that involves copolymerizing butadiene or acetylene derivatives to form polymers with internal unsaturation. Ozonolysis of these polymers yields di-end functional polymers. The a,o>dicarboxy1ic acid telechelic was prepared from poly(S-s tot-B) (Scheme 7.19). Precautions were necessary to stop degradation of the PS chains during ozonolysis. 28 The presence of pendant carboxylic acid groups, formed by ozonolysis of 1,2-diene units, was not reported. 

ADMET depolymerizations with substituted alkenes have been done as well, thereby generating perfectly difunctional telechelic molecules. As an example, 1,4-polybutadiene has been depolymerized in an inert atmosphere with a 10-fold molar excess (based on the repeat unit) of either allyltrimethylsilane or allylchlorodimethylsilane (equation 23). In these examples, the chemistry can be driven to complete depolymerization to yield structures with either one, two, three, or four repeat units of 1,4-butadiene. The synthesis of perfectly difunctional oligomers by this chemistry offers significant opportunity, particularly for functional groups such as alcohols, esters, carboxylic acids, and amines. 

This strategy is used for the synthesis of three different exact-mass telechelic oligomers. GPC, NMR, and GC/MS evidence indicates that clean depolymerization chemistry occurs for all three samples. Poly( 1,4-butadiene) (38) is broken down into oligomeric units with two, three, and four repeat units using catalyst 23. Catalyst 14 is more efficient and produces even lower molecular weight oligomers, primarily one and two repeat units. When allylchlorodimethylsilane is used instead of ethylene with 14, telechelic dimers are the only product. 

They are prepared from the addition of CS2 to the corresponding alcohols in basic medium. They are known to exhibit high transfer constants (Cr = 1-20) [21]. Constanza et al. [210], Otsu and Yoshida [49], Uraneck [121] and Fokina et al. [229] intensively studied the polymerization of styrene, MMA and butadiene with these compounds in order to obtain telechelics with functional xanthogens. Furthermore, chemical change (e.g., hydrolysis) was also performed to achieve the synthesis of corresponding a,co-dithiols [229] such as from 49 ... 

Telechelics. Nitrogen was used as an inert atmos-phere. The synthesis is either run in a flow reactor if the reaction time is short (e.g. styrene) or a glass pressure vessel is used as a discontinuous reactor (for butadiene at lower temperatures) or a steel autoclave (with ethylene as the monomer). 

Another variant for the synthesis of hydroxy telechelic polybutadiene is based on the anionic living polymerisation of butadiene, using sodium naphthalene as catalyst [16]. Sodium naphthalene generates, by reaction with butadiene, a radical anion (9.8). If two of these radicals are coupled together, they generate a dianion (9.9), which is an ideal bifunctional initiator for the synthesis of perfectly bifunctional polybutadiene by anionic polymerisation. 

The synthesis of low molecular weight difunctional carboxyl-terminated butadiene-based polymers via either free radical or anionic polymerization is well established. Teyssie and co-workers have converted such carboxyl-terminated polymers to salt forms, which they refer to as halato-telechelic polymers, by neutralization with metal alkoxides in appropriate solvents. The quantitative removal of low molecular weight reaction products is necessary to drive the reaction to completion and fully realize the ionomeric properties of these materials. 

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