Oligomerization of styrene

ZSM-5 Oligomerization of styrene Higher activity Higher selectivity [72]... 

It is noted that Mo/DM is the best performing catalyst with the highest steady state activity and lowest deactivation rate. The deactivation rate is the lowest even under the influence of intense acid-catalyzed side reactions known to produce coke, i.e. oligomerization of styrene and cracking of ethylbenzene. Obviously, the high surface area and high connectivity of the support have played a determining role in the catalytic reaction. The effects they exert can be looked at in two ways ... 

Nafion-H has also been used as a catalyst for the oligomerization of styrene. The reaction was studied by Higashimura and co-workers.933,934 Hydroxy-terminated poly (alkylene)oxides were prepared by condensation-polymerization of 1,8-octanediol and 1,10-decanediol in the presence of Nafion-H.935 It showed higher activity than sulfuric acid consequently, polymerization could be carried out at lower temperature. 

The coupling of the unsubstituted carbon atom of the mono-olefin with the Cs chain, which was observed in the co-oligomerization of styrene with butadiene, and of acrylic esters with butadiene, is not, however, a general phenomenon. For example, the co-oligomerization of 1-decene with butadiene using nickel-tricyclohexylphosphine as catalyst leads (after... 

Catalysts of this type have been studied extensively for the polymerization of butadiene [32], the oligomerization of styrene [33], and the dimerization of acrylates [34]. Indeed it was my becoming aware of this work that led to all of our subsequent discoveries. 

The formation of cyclic dimer (2-10 % yield) in the cationic polymerization of styrene oxide was reported by different authors 25 27). More recently, Yamashita studied the catonic oligomerization of styrene oxide in the presence of various Lewis and protic acids as initiators (SnCl4, BF3 0(C2H5)2, HOS02CF,) and found a 100 o conversion to cyclic oligomers with n = 2-5 28). 

Oligomerization. NAFION has been used In the cationic oligomerization of styrene. Oligomers range from dimer to hexamers... 

Saito, J., Kara, J., Toda, S., and Tanaka, S., Analysis of radical oligomerization of styrene by field desorption mass spectrometry, Chem. Lett. (Japan), 1982, 311. 

The problem of determining the exact nature of the initiating species in cationic polymerizations of alkenes conducted in the presence of metal perchlorates led to the use of a sterically hindered proton scavenger, 4-methyl-2,6-di-t-butyl pyridine. Since initiation occurred in solutions containing this compound it was concluded that protons derived from impurities were not responsible for the reaction and direct initiation by the metal perchlorates was postulated. However, results from experiments with the BClj/HjO system suggest that hindered pyridines act as proton transfer agents. Differences in mechanism between protonic acid — and metal halide - initiated oligomerizations of styrene " and DPE - have been defined. 

Several studies deal with the cationic polymerization and oligomerization of epoxides. "" Particularly interesting is the oligomerization of styrene oxide," which is characterized by hydride shift and back-biting reactions to form cyclic oligomers. 

The cationic oligomerization of styrene by a perfluorinated resin sulfonic acid proceeds at 303 — 343 K in a liquid phase. Complete conversion of the monomer was... 

The properties of styrenic block copolymers are dependent on many factors besides the polymerization process. The styrene end block is typically atactic. Atactic polystyrene has a molecular weight between entanglements (Me) of about 18,000 g/mol. The typical end block molecular weight of styrenic block copolymers is less than Mg. Thus the softening point of these polymers is less than that of pure polystyrene. In fact many of the raw materials in hot melts are in the oligomeric region, where properties still depend on molecular weight (see Fig. 1). 

In the biphasic batch reaction the best reaction conditions were found for the system [EMIM][(CF3S02)2N]/compressed CO2. It was found that increasing the partial pressure of ethylene and decreasing the temperature helped to suppress the concurrent side reactions (isomerization and oligomerization), 58 % conversion of styrene (styrene/Ni = 1000/1) being achieved after 1 h under 40 bar of ethylene at 0 °C with 3-phenyl-1-butene being detected as the only product and with a 71 % ee of the R isomer. 

The above evidence strongly suggests that the pseudocationic reactions involve the ester 1-phenylethyl perchlorate and its oligomeric homologues as catalyst. It also shows that the ester is only stable when an excess of styrene is present in the reaction mixture. Spectroscopic and conductimetric studies on the present system confirmed this interpretation and indicated that at least four molecules of styrene are required for the stabilisation of one molecule of ester. Details of the experiments carried out to investigate the stoicheiometry of ester stabilisation will be given in a later paper. The mode of this stabilisation is not clear at present and we do not known the location of the four styrene molecules with respect to the ester. 

Molybdenum complexes A (Figure 3.46) react efficiently with terminal and internal alkenes in toluene (e.g. 500 eq. Z-2-pentene are metathesized in 2 min at 25 °C 20 eq. of styrene in 2 h at 25 °C). These catalysts also oligomerize 2,4-hexadiene [808] and 1,5-hexadiene [809] and promote RCM of enol ethers. Isomerization of alkenes by catalysts A is a potential catalytic side-reaction [810-812]. 

NMR study shows that the block copolymer of styrene-methyl methacrylate is present in the product of esterification. It confirms that the original copolymer consists of blocks of styrene units and the ladder type blocks. Analysis of a few fractions of the copolymer obtained from oligomeric multimonomer and styrene confirmed this type of structure. Data recalculated from publications are presented in Table 5.1. 

Template copolymerization seems to be applied to the synthesis of copolymers with unconventional sequences of units. As it was shown, by copolymerization of styrene with oligomers prepared from p-cresyl-formaldehyde resin esterified by methacrylic or acrylic acid - short ladder-type blocks can be introduced to the macromolecule. After hydrolysis, copolymer with blocks of acrylic or methacrylic acid groups can be obtained. Number of groups in the block corresponds to the number of units in oligomeric multimonomer. Such copolymers cannot be obtained by the conventional copolymerization. 

Based on the formal analogy between the intermolecular hydrovinylation and the intramolecular cycloisomerization process, we have chosen catalysts with proven potential for the first reaction type [48, 51] as the starting point of our study. The results are summarized in Table 2.1.5.7 [64]. Despite its excellent performance in the hydrovinylation of styrene [51], the [ Ni(allyl) Br 2]/(Ra, Sc, Sc)-26/NaBARF system led to disappointingly low conversions and selectivities in the cycloisomerization of 27a (entry 1). Similarly, the [ Ni(allyl)Cl 2]/(Ra,Rc)-4cel/Na-BARF system is not effective for the cycloisomerization of 27a (entry 2) even though it is able to promote the hydrovinylation. The other diastereomer, (R ,Sc)-4cel, however, which forms an active nickel catalyst for styrene oligomerization... 

Analogously, the use of m-divinylbenzene [108-57-6] has been reported (76). However, oligomerization occurs on treatment of divinylbenzene with butyllithium resulting in initiators with functionalities greater than two (68). From a commercial perspective this oligomerization and lack of precise functionality control is not necessarily a problem and useful multifunctional initiators have been prepared from the reaction of butylithium with varying amounts of divinylbenzene (commercial divinylbenzene contains 22% meta, 11%para, and 66% o-, / -, and%ethylvinylbenzene) (77) often in the presence of styrene or diene monomer to provide solubility (seeding technique). 

---