Initiators, cationic, from

Injected 6.5 ml (5.90 g or 0.00566 mol) of styrene monomer to the tube containing 30 ml methylene chloride. After this tube has cooled for about 10 min in the ice bath to 0°C, inject with 4 ml of the cool stannic chloride solution (cationic initiator) from the other test tube. Recorded the time it is injected (start of polymerization). 

Figure 16-2. Change in the polymer fraction with polymerization on temperature for the bulk polymerization of tetrahydrofuran with various cationic initiators (from date of three research groups). Solid line gives the curve progress calculated according to Equation (16-32) with Xmp = 0.5, AHl = -12.4 kJ moF and ASl = -40.8 J K moF. ...

Weight gain of the epoxy matrix cured with a catalyst, SarCat CD1012 (CD1012) cationic initiator from Sartomer was examined to compare with the hydrophilic cured matrix of GMAEVC and epoxy resin. The active molecule of the catalyst is the diaryl iodonium hexafluoroantimonate that decomposes imder thermal curing (140°C) [31]. 

An analogous mechanism should also produce polymers on irradiation of epoxies. Crivello s recent mechanistic suggestions [29] are consistent with the mechanisms given above. One can conclude that radiation-induced polymerization of epoxies can proceed via several mechanisms. However, further work is needed to determine the relative contributions of the different mechanisms, which might vary from one epoxy to another. As part of the Interfacial Properties of Electron Beam Cured Composites CRADA [37], an in-depth study of the curing mechanism for the cationic-initiated epoxy polymerization is being undertaken. 

The initial step is the coordination of the alkyl halide 2 to the Lewis acid to give a complex 4. The polar complex 4 can react as electrophilic agent. In cases where the group R can form a stable carbenium ion, e.g. a tert-buiyX cation, this may then act as the electrophile instead. The extent of polarization or even cleavage of the R-X bond depends on the structure of R as well as the Lewis acid used. The addition of carbenium ion species to the aromatic reactant, e.g. benzene 1, leads to formation of a cr-complex, e.g. the cyclohexadienyl cation 6, from which the aromatic system is reconstituted by loss of a proton ... 

ESR experiments employing in situ photolytic decomposition of the peroxydisulfate anion (S20g ) have been carried out to study the reaction of S04 with aliphatic sulfoxides. In the case of dimethyl sulfoxide three radicals are detected ( CHj, CH3 S02, CH2 S(0)CH3), the proportion being pH-dependent. The reaction is assumed to proceed via an initially formed radical cation (not detected) which would be rapidly hydrated to give an intermediate identical with that generated by OH addition on the sulfoxide. Such a process parallels the rapid hydration of radical cations formed from thiophene in their reactions with SO/ and... 

The work by Hill et al. also noted differences for ASTA compared with the other carotenoids studied. Its radical cation was not formed initially from CC1302 but was formed solely through the proposed addition radical. Unfortunately, LYC could not be studied due to its insolubility in TX 100 micelles. However, since LYC appears, from its quenching of 02 and its protection against N02 to be the most efficient natural carotenoid antioxidant, we repeated this work using 4% TX 405 TX 100 (4 1) mixed micelles for both 0-CAR and LYC (unpublished) and have observed LYC behaving in a different manner to the other carotenoids as there appears to be no conversion of the adduct to the radical cation. 

Another differential reaction is copolymerization. An equi-molar mixture of styrene and methyl methacrylate gives copolymers of different composition depending on the initiator. The radical chains started by benzoyl peroxide are 51 % polystyrene, the cationic chains from stannic chloride or boron trifluoride etherate are 100% polystyrene, and the anionic chains from sodium or potassium are more than 99 % polymethyl methacrylate.444 The radicals attack either monomer indiscriminately, the carbanions prefer methyl methacrylate and the carbonium ions prefer styrene. As can be seen from the data of Table XIV, the reactivity of a radical varies considerably with its structure, and it is worth considering whether this variability would be enough to make a radical derived from sodium or potassium give 99 % polymethyl methacrylate.446 If so, the alkali metal intitiated polymerization would not need to be a carbanionic chain reaction. However, the polymer initiated by triphenylmethyl sodium is also about 99% polymethyl methacrylate, whereas tert-butyl peroxide and >-chlorobenzoyl peroxide give 49 to 51 % styrene in the initial polymer.445... 

The idea that a metal-centred cation, arising from a BIE, can cationate an alkene and thus be an initiator could have been propounded by this author when he discovered the BIE of titanium tetrachloride [30] ... 

It now remains for us to discuss our Supposition 2 (see, note added in proof). At this stage it is useful to distinguish two separate features of this supposition. The first is that the true initiating species are cations derived from the initiator, which may be formed by selfionisation, reaction with the solvent or impurities, or by a combination of these ways. 

R+ is an organic or metal-organic cation originating from side reactions in the initiator solution.)... 

If the reactivity of the cations (II) and (III) towards the monomer is sufficiently great, these reactions represent initiation without formation of an Al-C bond, but if these ions are too stable to add to monomer, their formation represents a wastage of the cations originating from the initiator. 

The cation 1 then starts the polymerisation. Cations derived from some impurities may also act as initiators. The ensuing polymerizations are terminated fairly rapidly. Since the concentration of cations of all kinds in the initiator solutions is much smaller than that of aluminium halide, the notoriously low efficiency (mol polymer/mol A1X3) can be explained on this basis. 

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. 

Around 1962, this author recognised that the polymerisation of styrene by many cationic initiators differed in several respects from that of isobutene, and he had begun to assemble the experimental facts from the Literature with a view to devising an explanation. Also, in an attempt to clarify this difference experimentally, he had undertaken a comparative study of the polymerisations of isobutene and of styrene by TiCl4 [4, 7, 12, 15-17, 38, 40, 54, 59]. 

Reaction kinetics. The time-development of sorption processes often has been studied in connection with models of adsorption despite the well-known injunction that kinetics data, like thermodynamic data, cannot be used to infer molecular mechanisms (19). Experience with both cationic and anionic adsorptives has shown that sorption reactions typically are rapid initially, operating on time scales of minutes or hours, then diminish in rate gradually, on time scales of days or weeks (16,20-25). This decline in rate usually is not interpreted to be homogeneous The rapid stage of sorption kinetics is described by one rate law (e.g., the Elovich equation), whereas the slow stage is described by another (e.g., an expression of first order in the adsorptive concentration). There is, however, no profound significance to be attached to this observation, since a consensus does not exist as to which rate laws should be used to model either fast or slow sorption processes (16,21,22,24). If a sorption process is initiated from a state of supersaturation with respect to one or more possible solid phases involving an adsorptive, or if the... 

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