Styrene-diphenylethylene polymers

Recent work on the dimerisation of 1,1-diphenylethylene by aluminium chloride produced conclusive evidence that direct initiation does not lead to the total ctmsump-tion of the catalyst. This excellent piece of research diowed that about 2.5 aluminium atoms are needed to give rise to one carbenium ion. Similar indications were reported by Kennedy and Squires for the low temperature polymerisation of isobutene by aluminium chloride. They underlined the peculiar feature of limited yields obtained in flash polymerisations with small amounts of catalyst. The low conversions could be increased by further or continuous additions of the Lewis acid. Equal catalyst increments produced equal yield increments It was also shown that introductions of small amounts of moisture or hydrogen chloride in the quiescent system did not reactivate the polymerisation. This work was carried out in pentane and different purification procedures for this solvent resulted in the same proportionality between polymer yield and catalyst concentration. Experiments were also performed in which other monomers (styrene, a-methylstyrene, cyclopentadiene) were added to the quiescent isobutene mixture. The polymerisation of these olefins was initiated but limited yields were again obtained. Althou the full implications of these observations must await more precise data, we agree with the authors interpretation that allylic cations formed in the isobutene polymerisation, while incapable of activating that monomer, are initiators for the polymerisation of the more basic monomers added to the quiescent mixture. The low temperature polymerisation of isobutene by aluminium chloride was also studied... 

Copolymerization studies involving the Cs salts of living polymers of p-substituted styrenes and 1,1-diphenylethylene in THF have enabled the reactivities of the corresponding free ions and ion pairs to be assessed. The method used for the calculation of rate constants appears to be satisfactory, and the values obtained in the case of poly-(p-methylstyryl) caesium and poly-(/ -methoxystyryl) caesium correlate well with the accepted values for the unsubstituted styrene system. For example, kp —) values in THF at 0 °C are 95 000, 220 000, and 1 000 000 M" s for the series styrene, p-methylstyrene,... 

In combination with Cu(II) and Cu(I) salts, the polymer-anchored, enantio-merically pure bisoxazoHnes showed only poor enantioselectivity in the Diels-Alder cycloaddition between N-acryloyloxazolidinone and cyclopentadiene (up to 45% ee). Better stereocontrol was found in the cyclopropanations of styrene and 1,1-diphenylethylene with ethyl diazoacetate (up to 93% ee) and in the ene reactions between ethyl glyoxalate and a-methylstyrene or methylenecyclohexane (up to 95% ee), which was comparable to the structurally related, unsupported ligands. Only a slight decrease in activity and in stereocontrol was observed upon recovery and recycling of the catalyst. The catalytic transformations were as efEdent as if performed with the corresponding catalysts supported on insoluble polymers. 

Box 74a and 74b have also been immobilized onto the soluble polymer MeOPEG (a monomethylether of polyethylene glycol, Mn > 2000 Da) and employed as ligand in the Cu-catalyzed cyclopropanation of styrene and 1,1-diphenylethylene with EDA with up to 93% ee. 

Yamagishi, A. Szwarc, M. Kinetics of styrene addition in benzene solution to living lithimn polymers terminated by 1,1-diphenylethylene units. The effect of mixed dimerization of monomeric polymers. Macrvmolecules 1978,11, 504—506. 

Boileau, Kaempf, Schue and coworkers have studied the cryptate mediated anionic addition polymerization of several systems including ethylene oxide [38], propylene sulfide [39-40], isobutylene sulfide [40], isoprene [38], methyl methacrylate [38], hexamethyl trisiloxane [40], e-caprolactone [41], styrene [38, 40, 41], ct-methylstyrene [41], 1,1-diphenylethylene [41] and /3-propiolactone [42]. The polymerization of the latter compound induced by dibenzo-18-crown-6 complexed sodium acetate has also been reported [43]. In general, it was found that the polymer-... 

Many interesting and important synthetic applications of 1,1-diphenylethylene and its derivatives in polymer chemistry are based on the addition reactions of polymeric organolithium compounds with 1,1-diphenylethylenes. Therefore, it is important to understand the scope and limitations of this chemistry. In contrast to the factors discussed with respect to the ability of 1,1-dipheny-lalkylcarbanions to initiate polymerization of styrenes and dienes, the additions of poly(styryl)lithium and poly(dienyl)lithium to 1,1-diphenylethylene should be very favorable reactions since it can be estimated that the corresponding 1,1-diphenylalkyllithium is approximately 64.5kJ/mol more stable than allylic and benzylic carbanions as discussed in Sect. 2.2 (see Table 2). Furthermore, the exothermicity of this addition reaction is also enhanced by the conversion of a tt-bond to a more stable a-bond [51]. However, the rate of an addition reaction cannot be deduced from thermodynamic (equilibrium) data an accessible kinetic pathway must also exist [3]. In the following sections, the importance of these kinetic considerations will be apparent. 

A further limitation with respect to the coupling reaction is the requirement that the living carbanionic polymers utilized must be sufficiently reactive to undergo facile addition reactions to 1,1-diphenylethylene units. In practice, this means that the first arms are limited primarily to styrene- and diene-type monomers. 

The living anionic polymers of protected functional methacrylate monomers herein introduced are very similar in reactivity and stability to those of MMA. Accordingly, these living polymers can initiate the polymerization of MMA, tBMA, and other protected functional methacrylate monomers, resulting in block copolymers with tailored chain structures. Complete aossover block copolymerizations among these methacrylate monomers are possible. Furthermore, living anionic polymers of styrene, a-methylstyrene, isoprene, and 1,3-butadiene initiate the polymerization of protected functional methacrylate monomers to afford well-defined AB diblock copolymers. In order to avoid ester carbonyl attack by the chain-end anions, the living anionic polymers should be end-capped with 1,1-diphenylethylene... 

It is also worth remembering that, in contrast to the cyclic monomers, the large majority of unsaturated compounds polymerize, leaving a relatively low monomer concentration at the point of equiUbrium. Indeed, when considering the nonsolvent, bulk polymerization of monomers such as ethylene, methyl acrylate or styrene, then at 25 °C the situation is that [Mjeq = 10 , 10or 10 moll", respectively. When unsaturated monomers providing steric hindrance in the polymer units are considered, then homopolymerization may be hampered here, 1,1-diphenylethylene is the best example, as the joining of two consecutive units is prohibited. The introduction of a second (even small) substituent causes a considerable increase in [Mjeq. For example, in the case of methyl methacrylate or a-methylstyrene, [Mjeq = 10 or 2.2 molT at 25 °C, respectively, have been determined [50, 51]. 

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