Polymer Journal, Vol. 12, No. 9, pp 65i-659 (1980)

Recent Evidence for the Association of Initiator with Counter Ion in Cationic Polymerization

Pierre SIGWALT and Georges SAUVET

Universite Pierre et Marie Curie, Laboratoire de Chimie Macromoleculaire, 4, Place Jussieu, 75230 Paris, Cedex 05, France.

(Received April 15, 1980)

ABSTRACT: Spectroscopic studies (by UVand NMR) of the reaction of 1,1-diphenylethylene with trifiuoromethanesulfonic acid have been made in dichloromethane, at temperatures (- 30°C to - 90°C) at which the carbocations are stable. A 33% average yield in carbocations with respect to CF3 S03 H was found in a large concentration range and interpreted as a complexation of the CF3S03 - anion by 2 inactive acid molecules. For 3-phenylindene, the yield was 50%. Further model

studies have shown that various trifiic salts (of Ph3 C +, Bu4 N +, Ag +) are strongly solvated by trifiic acid, and the results are in agreement with the formation of complex counter ions of structures A -(HA); A -(HA)2 and A -(HAh. The implications of these results for cationic polymerizations are discussed and particularly the interpretation of various observations made in the literature about the effect of common salt addition and of a variation of the dielectric constant of the medium. KEY WORDS Cationic Initiation I Trifiic Acid I Salt Effects I Anion Solvation 11, 1-Diphenylethylene I Trifiuoromethanesulfonic Acid I Cationic Polymerization I

The central problem of cationic polymerization of added water on the polymerization rate. But water ethylenic monomers is still that of the nature and may inhibit the polymerization when it is premixed concentration of the active species, and is linked (in equimolar ratio) to the perchloric acid. Several with the mechanism of initiation. It has not been kinetic data about monomer consumption are in really solved in the case of protonic acid initiation agreement with a solvation of the active perchlorate generally still written as a simple electrophilic ester by 4 styrene molecules, the propagation being proton addition on the double bond as in the written2 : pioneer work of Pepper with the styrene-sulphuric 4M + M -----> acid system. 1 I Ph The system styrene-perchloric acid in various 4M chlorinated solvents has been one of the most I I studied, but the kinetics are quite different at Ph Ph various temperatures. Near room temperature (in Initiation by acetyl perchlorate at ooc also gave a CH2Cl2 or CH2 ClCH2 Cl solution), polymerization reaction without visible species and without kinetic is slow and without kinetic termination, but there is no visible species during the propagation step in the termination, but a bimodal molecular weight (MW) distribution was obtained for the polymer3 and 300--450 nm range. In their pseudocationic theory, attributed to the independent growth of two types of Gandini and Plesch2 proposed that the active active species, a non-dissociated one, giving the low­ invisible species are esters, but this has been molecular-weight peak, and another dissociated challenged by other authors who suggested an one, giving the high molecular weights. The latter equilibrium reaction giving a very low concen­ tration of ionic species, the ester being inactive. could be suppressed by addition of tetraalkylam­ monium perchlorate or by using solvents of lower However, the best argument for the pseudocationic theory remains that there is a very limited effect of dielectric constants.

651 P. SIGWALT and G. SAUVET

Bimodal distributions were also observed with of Bu4 N+, S03CF3- to the system. But this effect perchloric acid at ooc, with a reduction of the high­ did also occur in benzene, showing that a simple molecular-weight peak by salt addition.4 "salt effect', cpuld not explain all the results. For At low temperatures (-70°C to - 98°C in dielectric constants of about 6-8, bimodal distri­

CH2Cl2), the kinetics are completely different, butions were obtained for the polymer, and attri­ polymerization being very rapid and completed in a buted to the presence of two types of independent few seconds, with limited yields.4 •5 Stopped-flow active species, dissociated and non-dissociated. methods permitted the detection of ionic species Unimodal distributions were obtained for low absorbing at 340 nm, supposed to be carbocations, (benzene) and high (nitrobenzene) dielectric but with maximum concentrations of about I% of constants. the initiator only. The presence of perchlorate end The use of stopped-flow experiments permitted groups (unreactive with styrene at low temperature) the observation of transient cationic species in the is likely since block copolymers could be prepared system styrene-CF3S03H-CH2 Cl/1 by recording with high yields with N-substituted aziridines ini­ of rapid-scan spectra. A peak at 340 nm was attribut­ tiated at low temperature.6 However, it should be ed to the polystyryl cation, and had very short life­ noted that such type of end groups could not be times of 200-300 ms at 30°C. The maximum con­ detected by the NMR technique for polymerizations centration [P+lmax observed was about 1% of realized in CC14 at room temperature. 7 CF3S03H. From the visible active species con­ Several other features of these polymerizations by centrations kP values could be obtained (2 x 105- perchloric acid are not completely explained, such 4 x 105 M -l s -l at 30°C). But contrarily to what as the increase of the apparent kP with an was found by Higashimura et a!. for the same increase of [M]0 and with an in salt system, bimodal distribution was not observed in concentration for the low-temperature reaction.4 this case. More recent studies have used the strongest Very recently, Kunitake et a!Y published the protonic acid available, trifluoromethanesulfonic results of their investigations between - I oc and (triflic) acid, that gives high polymerization rates 30°C, giving a positive activation energy for the even at high temperatures. Three main series of propagation of 7 kcal mol-1. The effect of [P+lmax studies have been made, by Chmelir et a!., concentration on kP was studied, and assuming an Higashimura et at., and Kunitake et al. ion-pair-free ions equilibrium, kP values of0.5 x 105 Styrene polymerization by triflic acid ([C] 10-4 to 1 x 105 were obtained at ooc. The effect on kP of moll-1) in dichloromethane solution at -l5°C8 •9 an addition of a common ion salt (Bu4 N+, was rapid and completed in a few minutes when the CF3S03 -) was also studied, and assuming a initiator concentration was high enough. S-shaped straightforward concentration effect of Bu4 N+, curves were observed for low [C]. There was also a CF3S03- kp ( +) (about 3 X 105 at ooq and ko of strong negative effect of monomer concentration on the ionic species ( X 10-6 at 0°C) COUld be the rate8 that was attributed to an inactivation of the calculated (with an estimated dissociation constant initiator through complexation with the monomer K,=5 x 10-5 for the ammonium salt). However, a ([M] varying between 0.05 and 0.5 mol1-1). very strange result was obtained for the activation In order to explain the kinetic results and energy on free ions: EP(±)= 14 kcal mol-1 (whereas conductimetry experiments, initiation was supposed the activation energy on ion-pairs was to occur through ionization of acid aggregates, such EP( ±) = 5 kcal mol-1). The first value looks quite as unlikely if one compares those obtained for cationic polymerizations under radiation. It should be observed that in most studies10 - 13 Similar results were observed by Higashimura et the initiator was used without further purification, a!., 10 who, however, found a strong positive effect of and that in one case10 the water concentration was an increase of the dielectric constant of the medium estimated to be ca. 3 x I 0-4 moll-1 which was of on the rate constant kP and attributed the monomer the same order as that of the initiator. concentration effect to this phenomenon. These Another recent study is that of p-methoxystyrene authors also found a decrease of kP on the addition polymerization by stopped-flow methods.13 The

652 Polymer J., Vol. 12, No. 9, 1980 Association of Initiator with Counter Ion

active centers for this monomer were known to be received in graduated tubes equipped with break much more stable than for styrene14 near room seals, that were sealed. It remained prefectly temperature and the maximum [P+lmax was observ­ colourless even after several months. ed at 30°C for longer times and with much higher Tetrabutylammonium triflate was purified ac­ concentrations. This permitted the measurement of cording to Higashimura et a/. 10 kP on these visible species (about 105 M -l s -l ). The Triphenylmethyl triflate samples could not be catalyst efficiency ([P+lmax/[CF3 S03 H]) varied from isolated in the pure state and were studied in situ by 36 to 42% in CH2 Cl2 . Two observations were, UV and NMR. Ph3C+, CF3 S03 - was prepared by however, made: the maximum concentration of p+ reacting Ph3 CC1 with AgCF3 S03 in CH2Cl2 , and decreased considerably with the dielectric constant Ph3C+, (CF3S03 -, CF3 S03H) was obtained by D of the solvent, while the corresponding kP reacting Ph3C-OH with triflic anhydride. increased when D became lower. This was explained by assuming the formation, in solvents of low Spectrophotometry polarity, of active "invisible species." A similar Measurements were performed under vacuum in effect was observed on the addition of a common sealed vessels, using Cary 15 and Cary 118C ion electrolyte, which led to a decrease of [P+lmax spectrophotometers. intensity and to an increase of kv. The initiation reaction was followed using an From this discussion, it may be seen that the apparatus for relatively fast spectrophotometric nature, the relative proportions and the reactivities measurements, 19 the acid phial being broken inside of ionic and non-ionic species involved in protonic the monomer solution. acid-initiated polymerizations are still far from The experiments measuring the initiation yield being completely understood. The very low ini­ were realized using a spectrodilatometer15 per­ tiation efficiency observed in some cases is par­ mitting to determine both the cations concentration ticuarly intriguing. and the dimerization rate. A bulb containing an acid We have thought that model studies of initiation solution in CH2 Cl2 was broken into the DPE of carbocation formation by reaction of triflic acid solution. In another series of experiments, the acid with 1,1-diphenylethylene (DPE), similar to those solution was broken above the cooled monomer we have already carried out for Friedel-Crafts solution, but some acid was apparently lost by a catalysts initiation/4 - 16 could give more precise reaction with DPE on the walls and the yields were informations about the structure of the active lower (mean value of about 20% instead of 29%). species, since the derived carbocations are stable in a wide temperature range. The results we shall NMR Spectroscopy describe show that even in this case, the efficiency of 1 H NMR spectra were obtained from a JEOL triflic acid is lower than 100%, which may be C60HL and 19F NMR spectra from a JEOL PS 100 explained by the inclusion of at least one unreactive FT spectrophotometer. The tubes were filled in acid molecule in the counter ion. The implications vacuum, the acid being distilled first and frozen in on cationic polymerizations of these results and of liquid nitrogen. Pure solvent was added and was the studies of the interaction of triflic acid with separated from the acid by a void space. The various triflates shall also be discussed. monomer solution was then condensed on the top and the tube was sealed. The two layers of reactants EXPERIMENTAL could be thus melted quickly and mixed at the temperature chosen. Materials 1,1-Diphenylethylene and CH2 Cl2 have been Reactions of Alcohols with Triflic Anhydride· purified and stored in evacuated sealed vessels as Reactions were carried out in CD2 Cl2 directly in previously described. 17 the NMR tubes, alcohol being introduced by 3-Phenylindene was a sample prepared by fractions under argon atmosphere. Hung. 18 Triflic acid was distilled under vacuum, and a middle fraction (bp 8loC under 4 torr) was directly

Polymer J., Vol. 12, No. 9, 1980 653 P. SIGWALT and G. SAUVET

REACTION OF 1,1-DIPHENYLETHYLENE Table I. Initiation of DPE by CF3S03 H at - 30°C WITH TRIFLIC ACID, (Spectrophotometric Experiments) IN DICHLOROMETHANE [M]0 X 103 [HAlo X !if [C +lmax X 10'' Yield SOLUTION ---- moll- 1 moll- 1 moll- 1 This reaction was studied by two different % techniques in a wide concentration range. 170 1.49 0.362 24.3 112 6.03 1.53 25.4 Spectrophotometric Study 34.2 6.35 2.25 35.4 Spectrophotometric experiments were made be­ 167 10.60 3.08 29.1 tween - 30°C and - 76°C with DPE concentrations from 3 X 10-3 to 10-1 M and CF3S03H con­ centrations from 1.5 X w-4 to 12 X w-4 M. In a few experiments, the initiation reaction was dilatometer (introduction of the acid in the liquid followed using the apparatus for fast spectropho­ phase) are given in Table I (temp, - 30°C). The tometric measurements, 19 but it could not follow the yields in carbocations with respect to the acid rate of initiation. This is in agreement with the value introduced have a mean value of 29%, whatever the of k; = (j-4) x 103 M - 1 s - 1 found by Kunitake at concentrations of monomer and acid (monomer 30°C by a stopped-flow method. A maximum being always in excess). An experiment made at constant yield in carbocations was obtained in a few - 76°C gave a similar value. seconds, and did not vary during the polymerization ofDPE. Proton Magnetic Resonance Studies The results of experiments made with the spectro- They were made between - 95°C and - 30°C

Ph CH3 ---1.5 (s) + + <;:H C,PhzC!i= ?Hz= 3 o:;CHz .•. 3.25 (q) 5.55ts) 7.45(s) 3.75(s) 8.05(m) 1.4(s) 7:6 and 8.2(s) tf5(s) Ph Ph ( E.o.) ( I.D.)

I I = 52 hours I

I I= 5 min

TMS

I 4

Figure 1. 1 H NMR spectra of the different species formed by reaction ofDPE with CF3 S03H in CD2 CI2 at -70°C; reaction time, 5 min and 52 hours; [DPE]0 , 0.5 M; [CF3 S03 H]0 , 0.5 M. The region of aromatic protons (6.5 to 8.5 ppm) is not shown on the same scale. ·The singlet Sat 5.4ppm comes from residual

CH2Cl2 •

654 Polymer J., Vol. 12, No. 9, 1980 Association of Initiator with Counter Ion

with the much higher concentrations of 0.2 to 1.4 M reminiscent of what was described by Gandini and for DPE and 8 x 10-2 to 1M for CF3S03H. Plesch for perchloric acid: a rapid consumption of The different species that could be identified the last styrene molecules, supposed to solvate the during the reaction are the monomer (M), the active centres, with a change in their nature. monomeric cation (M+), the dimeric cation (D+), The yield of initiation Y was calculated according the ethylenic dimer (ED), and the indanic dimer to the equation (ID), as shown in Figure 1. [M+]+[D+] xlOO, The variation of the concentrations of the various y species with time is discussed elsewhere.20 [M+] + [D+] + [HA]. Carbocations are formed very rapidly at the [M+], [D+], and residual [HA] being obtained by beginning of the reaction and then remain perfectly NMR. The values are given in Table II. The mean stable, but dimeric cations are formed from the value of Y for 8 experiments was 33%, and was very beginning. Their concentration then decreases little dependent on temperature, with however whereas the concentration of monomeric cations higher values at the lowest temperatures. increases with time, the sum remaining constant Similar studies using the ethylenic dimer of DPE (see Figure 2). have given the same yield of initiation. The concentration of unreacted acid is de­ The spectrophotometric and NMR experiments termined from the absorption at 17.3 ppm (at thus gave similar values for the yield of initiation - 80°C) and remains also constant. A rapid change though the range of concentrations for NMR of this chemical shift to 14.4 ppm should be noted at experiments was 1.000 times higher. The global the end of the monomer consumption. This value is equation for the formation of carbocations may be consistent with that observed for mixtures of an written ionic triflate with triflic acid in 1 : 2 proportion, and + 3 CF3 S03H+CH2 =CPh2----+ CH3 CPh2 , is quite different from the 11.0 ppm value for the acid alone in the same solvent. This behaviour is CF3S03 - (HOS02 CF3h (1)

c 0.3 0.15 \ 0 . \ . \ \ \ c \ \ -Cll . u . '\ o+ ... c + ••• 0 . u 0.2 0.10 .·· .··

0.1 ...... _ 0.05 ' ..... _..... _

0 10 20 30 0 50 100 150 time (min) time (hours)

Figure 2. Evolution of the reaction of DPE with CF3 SQ3H at -70°C: M, monomer; M +, monomeric

cation; D +, dimeric cation; ED, ethylenic dimer; ID, indanic dimer; [DPE]0 , 0.5 M; [CF3 S03 H]0 , 0.5 M.

Polymer J., Vol. 12, No. 9, 1980 655 P. SIGWALT and G. SAUVET

Table II. Initiation of DPE by CF3S03H at low temperature. (PMR experiments)

Dimeric Monomeric Unreacted IDPEI 0 LHAJo T carbocation," [D+] carbocation," [M +] acid," [HA], Yieldb

moll- 1 moll-1 oc moll- 1 moll- 1 mol r 1 %

1.385 0.60 -95 0.156 0.216 42.0 0.879 0.514 -80 0.150 0.296 33.6 0.50 0.50 -70 0.164 0.328 33.5 1.61 0.361 -50 0.086 O.o35 0.294 29.0 1.43 0.58 -36 0.080 0.094 0.389 31.0 0.224 0.448 -30 0.1155 0.248 31.8

• Concentrations determined by integration on the first spectrum obtained a few minutes after initiation. b "Internal" yield of initiation, Y={([M+]+[D+]/[M+]+[D+]+[HA],)} x 100.

One experiment has been made with 3-phenylin­ According to eq I and 2, the fraction of acid not dene at - 60°C. The initiation was very fast. The consumed becomes inactive and is trapped in an concentration of monomeric carbocation and that adduct with the CF3 S03 - moiety. A direct exam­ of the unconsumed acid remained constant with ination of this type of complexation is made in a time while the monomer was slowly consumed. The following section. acid proton chemical shift varied from 17.7 to 15.9 ppm (linearly with monomer concentration) (see REACTIONS OF VARIOUS ALCOHOLS Figure 3) In this experiment, the yield of initiation WITH TRIFLIC ANHYDRIDE was 49%, which corresponded to the equation: The 19F NMR spectra of esters are quite different from those of the corresponding ionic species, and it is then possible to identify their presence or absence. The non-formation of esters during the reaction of (2) DPE with trifiic acid at low temperatures (and even after warming the solution) was concluded from the presence of a single peak for the anion (at -78.1

ppm from CC13F at - 85°C) and no peak in the region of triflic esters (-74 to -77 ppm). 18 r------... •. 5 Attempts to synthesize various esters by the reaction of alcohols with trifiic anhydride11 were not N 2: u successful in the case of all tertiary alcohols .i. ..• investigated, but gave an ester in the case of 1- ... phenylethanol. Triphenylmethanol + Triflic Anhydride 0 Triphenylmethyl trifiate presented a double max­ 15 0 imum at 410-435 nm characteristic of the Ph3 C + cation, with an e435 = 39 000 1 mol- 1 em -I. 1 H and 19 3.5 F MR confirm that no free acid is present in the 0.1 0.2 0.3 0.4 0.5 solution. The single peak at -78.3 ppm (at room monomer cone. (M) temperature) is assigned to a trifiate anion solvated Figure 3. Reaction of 3-phenylindene with CF3S03H. Influence of monomer concentration on the chemical with a molecule of trifiic acid. shift of unreacted-acid proton and of the IX -CH2 of monomeric cation. Temp, - 60°C.

656 Polymer J., Vol. 12, No. 9, 1980 Association of Initiator with Counter Ion

Ph3COH + (CF3 S02) 20 _____, addition of salt. The same curve was obtained whatever was the cation (see Figure 4) and could be Ph C+, H (OS0 CF ) - 3 2 3 2 analysed in three linear parts with angular points at 1,1-Diphenylethanol + Triflic Anhydride ratios [anion]/[acid] equal to 0.5 and I. The first The reaction at room temperature give DPE and linear part corresponds to the formation of the an­ neither ester nor carbocation, with a single peak at ion CF3S03H, CF3 S03 - the second one to 19 -79.7ppm in the F spectrum. This corresponds [(CF3S03Hh, CF3 S03 -]. After a ratio of 1, the to the hydronium trifl.ate (H30) +, CF3 S03 -. chemical shift remained approximatively constant. The balance of the reaction is: The cations from diphenylethylene and from 3- phenylindene behaved in a similar fashion. 3 Ph2 (CH3)COH+(CF3 S02h0 _____,

3 CH3 =CPh2 +2 H30+, CF3S03 - 19F NMR Studies The 19F NMR experiments were made at 20°C, 1-Phenylethanol + Triflic Anhydride and the variation of the chemical shift was observed The reaction carried out at - 20°C gave an ester as a function of the ratio [salt]/[ acid+ salt] since the (b=-74.5ppm) and an ionized compound salt as well as the acid brings CF groups. In all (b= -78.7 ppm) in equal amount. 3 cases, only one singlet is observed between -76.3 The reaction is probably and -78.6 ppmjCCl3 F corresponding to a rapid 2 Ph(CH3)CHOH+(CF3 S02h0 -----> exchange between the different species. There is again a strong change in the chemical shift as long as Ph(CH )CHOS0 CF + 3 2 3 the 1 : 1 stoechiometry is not attained and it then + Ph(CH3)CHOH 2 , CF3S03 - remains constant for higher ratios (Figure 5). Angular points may be detected at molar fractions On warming the solution, the species at -74.5 of 0.25, 0.33, and 0.50. They are in agreement with ppm (ester) remained stable. This is quite interesting the possible formation of counter-ions of structures since the ester is a model of polystyryl trifl.ate. A-, (HA)3; A -(HA)2 , and A-, HA. On Figure 5, Similar results were obtained with benzyl alcohol the results for silver trifl.ate are also plotted, but at -20°C.

COMPLEXATION OF VARIOUS TRIFLATES BY TRIFLIC ACID21 + 0 + 0 u In order to confirm the formation of species in which the acid molecules are trapped in an adduct of the CF3S03 - moiety, we studied the 1H and 19F NMR spectra of mixtures ofCF3S03H with several ionic trifl.ates: Bu4 N+, CF3 S03 -; Ag+, CF3 S03 - and Ph3C+, CF3S03 - for increasing proportions of added salt. Ph3 C+, CF3 S03 - free from solvating acid was prepared by reacting silver trifl.ate with Ph3CC1 (and studied "in situ"). 0.5 1.0 1.5 2.0 Proton NMR Studies lsaltl/lacidl These experiments were generally not made under Figure 4. 1H NMR: variation of the chemical shift of vacuum except the experiment shown on Figure 4. the acid proton for mixtures of tritlic acid with various In deuterated dichloromethane at various tem­ tritlates in CD2Cl2 . +, Ph3 +ccF3 S03 - (temp, 20°C); peratures ( -95°C to 20oC) according to the cation, EE>, Ph3 +cCF3 S03 - in sealed tube (anhydrous con­ the chemical shift of the acid (9.5 to 16.2 ppm) was ditions, temp, 20°C); Q, Bu4 +NCF3S03 - (temp, 20°C}; .a., cation from 1,1-dipheny1ethylene (temp, -30 to strongly shifted downfield with the progressive -95°C); ., cation from 3-phenylindene (temp, - 60°C).

Polymer J., Vol. 12, No. 9, 1980 657 P. SIGWALT and G. SAUVET

which leads to low initiation rates, permitting the Ph c+ establishment of a quasi-stationary state in the + -----"----1' presence of enough water. When [CF3S03 H]/[H20]

lo&-11":1 -78 is higher than 1, the faster initiation leads then to a u ? : 1 u ' ' rapid non-stationary polymerization. e But this does not explain the low initiation yields ' ' (l to 3% relative to acid) observed by Kunitake et al. E I li _; Ag+ ; v-: for styrene. The major formation of unreactive or "' .., -77 little reactive esters would be a tentative expla­ + : : i ' ' ' nation. We have found that the corresponding ester f ' ' ' ' ' ' ' ' : ' could be stable enough in some conditions, but more data on polymerizing and polymerized so­ lutions would be necessary before coming to a 0.25 0,33 0.5 conclusion. lsaltlj{lsaltl + lacidl) With p-methoxystyrene13 the initiation yields are Figure 5. 19F NMR: variation of the chemical shift of much higher than for styrene (36 to 42%) and the the CF3 groups for mixtures of trifiic acid with various initiation is very rapid (giving a polymerization triflates in CD2 CI2 . Temp, 20oC; +, Ph3 +ccF3S03 -; without stationary state), which shows that the 63, PH3+ccF 3S03- in sealed tube (anhydrous con­ hydrate is probably a much better initiator for this ditions); 0, Bu4 N+ CF3S03-; t:,., Ag+ CF3S03-. very nucleophilic monomer. The catalyst con­

since silver triflate is soluble in CH2 Cl2 only in the centration does not influence significantly presence of an excess of triflic acid (3 : I ratio), the [P+lmax/C0 which would be the case if water (at a spectra obtained at ratios higher than 0.25 are constant concentration) was an inhibitor of the fast meaningless since precipitation occurs. initiation. The initiator efficiency is much better explained by a complexation of acid in an unactive INFLUENCE OF COUNTER-ION form, as in the case of DPE or PI, since the values COMPLEXATION ON CATIONIC found are intermediate between these two cases. POLYMERICA TION Our demonstration of the existence of these stable counter-ions in the case of monomers very reactive We shall examine now, in the light of the results in the initiation step put a new light on the various described here, the various problems rised by the results about the negative effect of salt addition on published results relative to cationic initiation by the initiator efficiency and its positive effect on the triflic acid. The case of perchloric acid shall not be rate constants, and with similar observations made discussed in detail, since we did not make similar when the dielectric constant of the medium experiments in this case, but it will be obvious that decreased. the same kind of interpretation is often possible. In dichloromethane, the addition of a common­ A problem that has not been mentioned so far is ion electrolyte such as y+, CF3 S03 - leads to the that a large discrepancy exists between the rates formation ofY+ CF3S03 -, (HOS02CF3). (n= 1 or observed by Higashimura et al. and Chmelir et al. 2) and the trapped acid is not available for on one hand and by Kunitake et al. on the other initiation, which lowers the initiator efficiency and hand (the rate constants kPapp. differing by a also the overall rate. The higher kP observed for the factor of several hundred). This is probably the "visible species" may tentatively be explained by a consequence of the much higher initiator con­ similar association of the propagating species with centrations used by Kunitake et al. that exceeded the ammonium salt, giving a more bulky counter­ largely the assumed water concentration in the ion and more reactive species. The formation of 10 medium,11•12 while Higashimura (and probably such aggreagates in the case of perchloric acid has also Chmelir) had water concentrations of the same been shown by Coutagne23 and the possible effect of order of magnitude as that of the initiator. It is very such a complexation on styrene polymerization has likely that triflic acid hydrate (CF S H 0+) is a 3 -o3 3 already been mentioned.24 More recently, interest­ much less efficient electrophile than CF3S03H, ing data have been available about the auto-

658 Polymer J., Vol. 12, No. 9, 1980 Association of Initiator with Counter Ion association of quaternary phosphonium salts, that is 5. J. P. Lorimer and D. C. Pepper, Proc. R. Soc. higher in cyclohexane than in chlorobenzene.25 We London, Ser. A, 351, 551 (1976). have found that on the progressive addition of 6. P. K. Bossaer, E. J. Goethals, P. J. Hackett, and D. dimethyldodecylamine to a triflic acid solution in C. Pepper, Eur. Polym. J., 13, 389 (1977). 7. S.D. Hamann, A. J. Murphy, D. H. Solomon, and CH Cl , there is first a large increase of the 2 2 R. I. Willing, J. Macromol. Sci., Chern., A6, 771 conductivity (assigned to the formation of bulky (1972). ions of high K0 ) followed by a decrease at higher 8. M. Chmelir, Makromol. Chern., 176, 2099 (1975). ammonium salts concentrations, showing the lower 9. M. Chmelir, N. Cardona, and G. V. Schulz, conductivity of the equimolar salt Makromol. Chern., 178, 169 (1977). 10. T. Masuda, M. Sawamoto, and T. Higashimura, [HN(CH3 h(C12H25)] +, CF3 S03 -. With a lowering of the dielectric constant of the Makromol. Chern., 177, 2891 (1976); ibid., 177, 2995 (1976). medium, one may expect an increase of the number 11. T. Kunitake and K. Takarabe, Polym. J., 10, 105 of acid molecules solvating the anion, giving lower (1978). initiation yields, more bulky counter-ions and more 12. T. Kunitake and K. Takarabe, Macromolecules, 12, reactive ionic species. However, we think that the 1067 ( 1979). situation is probably more complicated, if the active 13. M. Sawamoto and T. Higashimura, Macromolecules, species reactivities are also modified by monomer 11, 328 (1978). solvation. This is suggested by the variation of the 14. G. Sauvet, J. P. Vairon, and P. Sigwalt, J. Polym. Sci., Polym. Symp., No. 52, 173 (1975). proton chemical shift in the presence of monomer, 15. G. Sauvet, J. P. Vairon, and P. Sigwalt, J. Polym. observed in the case of DPE and PI. A competition Sci., Polym. Chern. Ed., 16, 3047 (1978). for the complexation of the various ionic species 16. M. Masure, G. Sauvet, and P. Sigwalt, J. Poym. Sci., may exist between unconsumed acid and monomer. Polym. Chern. Ed., 16, 3065 (1978). It is possible that such a competition might occur 17. G. Sauvet, J. P. Vairon, and P. Sigwalt, Bull. Soc. Chim. Fr., 4031 (1970). also in solvents of medium polarity such as CH2 Cl2 , that may also be involved into the equilibria. 18. Nguyen Anh Hung, These Doctorat d'Etat, Paris, 1976. 19. J. C. Favier, P. Sigwalt, and M. Fontanille, Eur. REFERENCES Polym. J., 10, 717 (1974). 1. R. E. Burton and D. C. Pepper, Proc. R. Soc., 20. A. Leborgne, D. Souverain, G. Sauvet, and P. London, Ser. A, 263, 58 (1961); M. J. Hayes and D. C. Sigwalt, Eur. Polym. J., in press (1980). Pepper, ibid., Ser. A, 263, 63 (1961); D. C. Pepper and 21. D. Souverain, A. Leborgne, G. Sauvet, and P. P. J. Reilly, ibid., Ser. A, 291, 41 (1966). Sigwalt, Eur. Polym. J., in press (1980). 2. A. Gandini and P. H. Plesch, Proc. Chern. Soc., 240 22. M. Sawamoto, T. Masuda, and T. Higashimura, (1964); A. Gandini and P. H. Plesch, J. Chern. Soc., Makromol. Chern., 177, 2995 (1976). 4826 ( 1965). 23. D. M. Coutagne, J. Am. Chern. Soc., 93, 1518 (1971). 3. T. Masuda and T. Higashimura, J. Polym. Sci., B, 9, 24. P. Sigwalt, Makromol. Chern., 175, 1017 (1974). 783 (1971). 25. A. Landini, A. Maia, and F. Montanari, Nouv. 4. D. C. Pepper, Makromol. Chern., 175, 1077 (1974). J. Chern., 3, 575 (1979).

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