Styrene and Homologues

The triad distribution in the copolymer was found to be bernoullian and is accounted for by a one-parameter model therefore, chain end control of the stereochemistry was assumed [80]. For the systems based on bipyridine, no influence of the counter-ion on the stereochemistry of the produced copolymers was found however, the catalytic activity was highest with the weakest coordinating anion [81]. Bis-chelated complexes of 2,2 -bipyridine or 1,10-phenanthroline [ Pd(N-N)2 X2 ] were efficient catalyst precursors, particularly when used in 2,2,2-tri-fluoroethanol as the solvent [82] under these conditions stabilization of the catalytic system by an oxidant is unnecessary, and very high molecular weights were obtained [83]. 

A better selectivity than with 1,10-phenanthroline (90% MM-triads) was obtained with 5-nitro-l,10-phenanthroline [84] and, more recently, with 1,4-di isopropyl-1,4-diaza-l,3-butadiene 53 [85]. Model studies with the latter catalytic systems have 

For the first experiments aiming to achieve isotactic copolymerization, optically active 2-pyridinecarboxaldehyde(l-phenylethyl)imine was used as the ligand (58) nevertheless, a prevailingly syndiotactic copolymer (ww H-triads 56 20 20 4) 

The intermediate M -complex (this relative absolute configuration refers to the ligand and to the center of asymmetry of the growing chain closest to the metal), which forms as a consequence of olefin insertion, is less stable than and transforms rapidly into the l -complex. The latter complex is more reactive towards ole- 

As mentioned above and as demonstrated by model studies using various acetyl complexes, the insertion of styrene usually takes place with secondary regiochemistry [8]. However, styrene was found to insert with both primary and secondary regiochemistry into the metal-acetyl bond of a complex obtained by carbonylation of 66. It is very remarkable that primary regiochemistry only was observed for the insertion in a homologous complex, in which a polyketone chain (CH ),CO CH(CH ),)CH2C()[ i--,) was substituted for the acetyl ligand. Thus, it was proposed that, for this catalytic system, primary insertion of styrene is responsible 

Nikolayev and collaborators have restudied the polymerisation of styrene by trifluoroacetic acid and H(CF2)6COOH. Limiting yields were often obtained, coinciding with the total consumption of the acid, and polymerisation could be reinitiated at this point by addition of further acid. It seems obvious from the ensemble of their results that although the ester is inactive in the absence of free acid, the active species are probably ester molecules solvated by the add, and not carbenium ions. The dielectric constant in these reactions was in fact low and it is difficult to envisage that the 1-phenylethylium cation could survive in these media. 

Recently, Sawamoto et al. have restudied this system in 1,2-dichloroethane, nitrobenzene and mixtures of 1,2-dichloroethane and benzene, at 50 °C. They noticed again that esterification of styrene accompanied the polymerisation, but limiting yields were not detected. In fact, even in the media of lower polarity the polymerisation proceeded slowly but steadily over periods of days. The authors argued in favour of ionic chain carriers because the monomeric trifluoroacetate failed to promote the polymerisation of styrene. They also used alternative kinetic treatments to prove that only 

The problem of the nature of the active species in the polymerisation of styrene and p-methoxystyrene by trifluoroacetic add is still unsettled and although we favour the pseudocationic mechanism (except in pure acid), more work is needed to reach a clear answer. Stq)-flow studies would undoubtedly help in this context. 

Some puzzling experiments were recently reported by Nikolayev and cowork- 

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This absorption is in fact due to the ions derived from l-methyl-3-phenylindane (the cyclic dimer of styrene) and its higher homologues (oligostyrenes with indanyl end groups). There can be no doubt that the ions formed at the end of the polymerisation of styrene belong to the same families of compounds (indanyl and various phenyl alkyl carbonium ions [7]). Our evidence showed that the 1-phenylethyl cation is absent from the ions formed from styrene by excess of acid its dimeric homologue, the l,3-diphenyl- -butyl cation, is a minor component of the ion mixture. We refer to this mixture of ions formed rapidly from styrene by excess acid, or at the end of a styrene polymerisation, as SD (styrene-derived) ions. 

Other furan monomers which polymerize cationically include 2-furfuryl vinyl ether, 2-vinyl furoate (albeit through a polyalkylation mechanism giving a polyester incorporating the ring into the pol5mer backbone), F and MF as co-monomers in conjunction with substituted styrenes and vinyl ethers, as well as 2-furfurylidene methyl ketone (obtained by the base-catalyzed condensation of F with acetone) and its homologues [4d]. 

The synthesis of poty-2,S-bis[(4-medio benzoyl)oxy]styrene and its homologues has been described (9-10). Table I shows some of the characterization results for these polymers. 

The aspect of stereocontrol in achiral systems is particularly evident in the case of the regiospecific copolymerization of styrene (and of homologues thereofi ) with [(L L)Pd(S2)](X2) or [(L L)Pd(CH3)(S)](X) catalyst precursors (L L is 1,10-phenanthro-line or 2,2 -bipyridine) to poly(l-oxo-2-phenyl-l,3-propanediyl) with the prevailing ( 90%) formation of M-diads, independent of the anionic tigand. According to... 

Insertion of aromatic olefins (styrene and/or homologues thereof) was studied not only with the aforementioned N N-modified catalytic systems (N N is 2,2 -bipyildine or 1,10-phenanthroline) but also with [ (5)-Bz-DBHOSOX Pd(COCH3)(Solvent)](OTf), where (,5)-Bz-DBPHOSOX is (5)-2-[2-(5 /-benzo[fc]phosphinindol-5-yl)phenyl]-4-benzyl-4,5-dihydrooxazole (Scheme The insertion was regiospecific, both with... 

PRs have been known since 1925. During World War II, Germany made liquid polybutadiene (LPB) under the trade name Plastikator 32, used as a curable and adhesive plastificant for synthetic rubber. A similar product was obtained in United States in 1950, with the aid of a semi-industrial plant at Borger, Texas, under the trade name Butarez [3]. At the same time, petroleum resins based on indene and styrene and their homologues were produced. Their industrial production started in 1950 [2]. 

A variety of trichloroethylene copolymers have been reported, none with apparent commercial significance. The alternating copolymer with vinyl acetate has been patented as an adhesive (11) and as a flame retardant (12,13). Copolymerization with 1,3-butadiene and its homologues has been reported (14—16). Other comonomers include acrylonitrile (17), isobutyl vinyl ether (18), maleic anhydride (19), and styrene (20). 

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. 

Merrett, F. M. The interaction of polymerizing systems with rubber and its homologues. Part 2. Interaction of rubber in the polymerization of methyl methacrylate and of styrene. Trans. Faraday Soc. 50, 759 (1954). 

Studies on local viscosity effects can be carried out using a free probe molecule, such as naphthacene, in polymer solution. Thus poly(styrene) in benzene solution has been studied with this probe at a concentration of 10 mole S,. Two stepwise increases In local viscosity at polymer concentrations of 20 to 30% and 60 to 70% were taken as indications of internal structure in the polymer solution at these concentrations (4). Similar studies were carried out on melts of n-paraffin homologues and poly(ethylene) at 150°C. The local viscosity increased with increasing molecular weight in the low molecular-weight range, but reached a plateau at around MW 2000. 

Organosikali Initiators. In general, the simple organoalkah metal derivatives other than lithium are not soluble in hydrocarbon media. However, higher homologues of branched hydrocarbons are soluble in hydrocarbon media. The reaction of 2-ethylhexyl chloride and sodiiun metal in heptane produces soluble 2-ethylhexylsodium (37). This initiator copolymerizes mixtin-es of stsn-ene and butadiene to form styrene— butadiene copolymers with high (55-60%) vinyl microstructure (38,39). 

For the purposes of this chapter, acrylic polymers are defined as polymers based on acrylic acid and its homologues and their derivatives. The principal commercial polymers in this class are based on acrylic acid itself (I) and methacrylic acid (II) esters of acrylic acid (III) and of methacrylic acid (IV) acrylonitrile (V) acrylamide (VI) and copolymers of these compounds. Copolymers of methacrylic acid and ethylene are described in Chapter 2. The important styrene-acrylonitrile and acrylonitrile-butadiene-styrene copolymers are discussed in Chapter 3 whilst acrylonitrile-butadiene copolymers are dealt with in Chapter 18. 

The development of petrochemistry after World War II and especially the building up of some large pyrolysis plants as a source of ethene and propene led to the emergence of large amounts of secondary fractions with an increased content of unsaturated compounds. We refer to fractions 4,05 (piperylenes), and Q—Cio containing styrene, vinyl toluene, indene, and their homologues. 

The decomposition of benzene and naphthalene and its homologues by microorganisms has already been discussed earlier. The metabolizing mechanisms of naphthalenes in fish have been well studied [47, 49]. Decomposition products of chlorobenzene in daphnia, mosquitos, snails and fishes are the polar compounds chlorophenol and chloro-o-dihydroxybenzene amongst other compounds, those of nitrobenzene aniline, acetanilide, aminophenols and nitrophenols and those of hexachlorobenzene pentachlorophenol and unknown compounds [71]. Bromoben-zene is deactivated to the toxic bromophenol [217]. In the case of man and land mammals, studies have concentrated on the metabolism of benzene, toluene, xylenes and styrene, which are also significant in occupational medicine [12, 13, 136, 195, 196, 215-217], A comparison of the metabolism of benzene into phenol in various animal species with the aid of microsomal preparations of the lungs or liver yielded vast differences. However, it is possible for benzene, in part, to inhibit or prevent its own metabolism [218]. 

Figure 1.2. Dependence of density pa on a molecular weight of tetramethyleneoxide (1) and ethyleneoxide (2) homologues at 75°C and styrene (3) at 25 C.

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