Indanyl end group

Oligostyrene with +HA Allylic indanyl end-groups lons... 

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. 

If the reaction mixture was left under vacuum for several hours after the end of the ionogenic reaction described in Section 3, the polymer no longer contained double-bonds (UV spectrum), indicating that the formation of indanyl end-groups went to completion. At the same time D424 fell to zero and the conductivity decreased to the background level due to impurities. 

When the conductivity and optical density had attained their maximum values, the spectra showed that double bonds were still present. The acid released by the decomposition of the ester catalyses the subsequent slow cyclisation whereby these terminal double bonds form indanyl end groups [23]. 

The species IA, IB, IC represent the chain-propagating ester molecules, stabilised by styrene, and they are equivalent from the point of view of the polymerisation. At the end of the polymerisation, the now unstabilised ester II reacts with its own kind to give the indanyl ion III and a saturated linear polymer IV. It is also in equilibrium with unsaturated polymer V, and it reacts with acid and/or V to give the polymer with indanyl end groups VI. This is equivalent to the transfer reaction with monomer which gives the indanyl end groups [23]. The oligostyryl ion VII can only be present in very small concentration, as it is much less stable than the other SD ions which co-exist with ion III [7] these other SD ions have been omitted from the scheme so as not to complicate it unnecessarily. 

A similar procedure was also used for the synthesis of methacrylate functional poly(a-MeS) [80]. Thus, 31 was used in conjunction with SnBr4 in CH2C12 at -78 °C, to obtain the macromonomer with Mns substantially (-50%) higher than the theoretical value. This was probably due to the formation of terminated low MW oligomers with indanyl end group structure. The eliminated proton was as-... 

Electrophilic aromatic substitution also occurs intramolecularly to generate polymers with indanyl end groups [Eq, (93)] entropy strongly favors this unimolecular reaction. 

In many cases, transfer must occur before this termination take place. As outlined below, the requisite transfer reactions include proton transfer reactions and formation of polymer chains with unsaturated or indanyl end groups. The resulting chains then undergo further reactions to generate stable and unreactive carbenium ions, such as indanyl ions, sterically protected tertiary carbenium ions, and highly delocalized protonated polyenes. 

The formation of stable carbenium ions can be observed visually and/ or spectroscopically. For example, styrene and a-methylstyrene polymerizations are generally colorless because the growing carbenium ions absorb at approximately 340 nm (cf., Sections II.B and IV.B.l). However, these systems may turn brown or dark red at longer reaction times due to formation of indanyl carbenium ions (A 440 nm) [14,26,325] and other delocalized carbocations similar to those in Eq. (121). The stable cyclic diaryl carbenium ions are generated by hydride transfer from the initially formed indanyl end groups [Eq. (124)] in styrene polymerizations, and by methide transfer in a-methylstyrene polymerizations. The prerequisite for this termination is therefore intramolecular transfer by Friedel-Crafts alkylation protons liberated in the first stage can then reinitiate polymerization. 

In the polystyrenes produced by cationic initiators most of the chain-ends are terminal indanyl groups, and olefinic groups are rare. As this terminal indanyl group cannot be aluminated like a double bond, the amount of tritium incorporated comes only from the initial AlBr2CH2CHPh-groups and the few residual terminal double bonds and it, therefore, represents (approximately) the total number of initiated chains. 

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