Oligomeric styrene

BMA, AMPS/ EDMA Thermal, AIBN 1-Propanol, 1,4-butanediol/water 100 and 150pm I.D., CEC of small molecules (alkylbenzenes) and styrene oligomeres [146-148]... 

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... 

The interaction of HC1 with an alkene in a non-polar medium results in a simple addition of the hydrogen halide. The centre generated from the proton and monomer is immediately deactivated by the strongly basic and mobile Cl-. In a solvating medium, e.g. nitromethane, styrene oligomerizes in the presence of HC1 [91 ]. Thus the combination of the solvated ions is relatively slow so that propagation can compete with it. 

However, ionization of the adducts should be more pronounced in more polar solvents and at lower temperatures if ionization is exothermic. Most vinyl ethers polymerize under these conditions [114]. Nevertheless, traces of iodine may catalyze polymerization, because Lewis acids act as coiniti ators. Moreover, even styrene oligomerizes in the presence of high concentrations of dry HC1 in polar solvents at -78° C [115]. 

A better agreement between the theoretical and experimental data was obtained in79 where styrene oligomerization in carbon tetrachloride was studied. Five different variants of the functions interpolating the dependence of the chain propagation constant on chain length were computed, with kp regarded as a constant. Therefore, the relations were only empirical. 

Telechelics have also been synthesized from azo compounds similar to AIBN, but in which either the methyl (34) or the nitrile (35) group has been modified. Methyl-2,2-azobisisobutyrate (35 R = Me) (MAIB) has been used to initiate the polymerization of styrene to yield a,cu-bis(2-methoxycarbonyl-methylethyl)oligostyrene with a functionality of /=2. Using 3,3-azo-bis(3-cyanovaleric acid) (34 R = C02H) or 4,4-azobis(cyanopentanol) (34 R=CH20H) as initiator for styrene oligomerization respectively. - ... 

Other high molecular weight hydrocarbon polymers are not biodegradable, but oligomers of <7j -l,4-isoprene (83), butadiene (84), and styrene (85), are degradable. And there has been further confirmation of biodegradation of oligomeric ethylene (86). 

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. 

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

Monomers, such as styrene or methyl methacrylate, are oxidized to oligomeric peroxides also [107] ... 

With an effective catalytic resolution of allylic styrene ethers in hand, we focused our attention on the Ru-catalyzed reaction of disubstituted styrenyl ethers (e.g., 49). When we treated (S)-49 with 10 mol% la under an atmosphere of Ar (Scheme 12), we found chromene formation to be sluggish 25-30% of dimer (S,S)-50 was isolated after 48 h at 45°C, together with substantial amounts of oligomeric materials. 

The protonation of substituted styrenes generally leads to sequential oligomerization and polymerization reactions (3). Only when carefully... 

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. 

Our interpretation of these phenomena is as follows the ester styryl perchlorate is not stable alone in solution, but this ester and its oligomeric homologues do exist in the presence of excess styrene, consequently the styrene must stabilise the ester. Presumably it does this by being co-ordinated (probably to the oxygen atoms) and thus reduces the polarity of the ester carbon-oxygen bond. It is not known yet whether any other compounds can exert the same effect. 

A procedure used in the self-branching polymerization reaction for the preparation of dendritic polystyrenes is outlined in Scheme 7. Oligomeric polystyryl-lithium chains are reacted with a coupling agent such as 4-(chlorodimethyl-silyl)styrene (CDMSS), which contains both a polymerizable double bond as well... 

Beyond dimerization and oligomerization, [2 + 2]- and [4+ 2]-cycloadditions with conjugated dienes and styrenes and the addition of nucleophiles are typical reactions of strained cyclic allenes. These transformations have been studied most thoroughly with 1,2-cyclohexadiene (6) and its derivatives [1, 2]. Concerning the cycloadditions, a theoretical study had the surprising result that even the [4+ 2]-cycloadditions should proceed in two steps via a diradical intermediate [9]. In the case of nucleophiles, the sites of attack at several 1,2-cyclohexadiene derivatives having an... 

For example, XI will copolymerize with styrene to give a copolymer containing carbonate groups in the main polymer chain (20). Ifydrolysis gives the oligomeric polystyrene capped with reactive hydroxyl groups (2). 

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]. 

The hydrovinylation reaction, the codimerization of ethene and styrene (Scheme 2), provides easy access to chiral building blocks from inexpensive hydrocarbon feedstocks, which can be used further for the preparation of fine chemicals. Key problems in this reaction include the selectivity of the reaction and the stability of the catalyst. The main side reactions are oligomerization and isomerization of the product to internal achiral alkenes. The latter reaction can be suppressed by... 

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