British Polymer Journal 23 (1990) 55-62

Synthesis and Viscoelastic Properties of a,m-Diquaternary Ammonium

Polybutadiene Ionomers

Caroline Roberts, W. Edward Lindsell* & Ian Soutart

Department of Chemistry, Heriot-Watt University, Riccarton, Edinburgh EH 144AS, UK

(Received 1 December 1989; accepted 8 December 1989)

Abstract: Telechelic ionomeric elastomers with quaternary ammonium groups (Me,RN') attached terminally to polybutadiene (Mn - 2.7 x lo3; M,,,/Mn = 1.27; containing 62% 1,4-linkages) have been synthesised by an anionic technique using a functionalised initiator and terminator, followed by quaternisation of the resulting z,o-bis(dimethy1amino)polybutadiene. By using differing alkyl halides for quaternisation and by ion exchange chromatography, a series of dialkylated telechelic cationomers has been produced containing alkyl groups, R = Me, Et, n-Pr, n-Bu or n-C,H,, with counter anions X = I - , Br-, PF, or SO:-. The glass transition temperatures, T,, of these cationomers are c. 6°C higher than for the precursor, non-quaternised polymer but are essentially unchanged with variations in groups R or anions X. Dynamic mechanical thermal analyses of the cationomers have been carried out and a secondary transition, T,, associated with relaxation of ionic cross-linking interactions, observed. Values of T, decrease as the size of R increases from C , to C,, and as the anion X is changed from Br- to I - to PF, or SO:- to PF,.

Activation energies can be derived from the frequency dependence of Ti values or from the temperature dependence of shift parameters, obtained from the master curves of the dependence on frequency of the shear storage(G') and loss (C) moduli; these activation energies are dependent on the nature of the counter anion, being greatest for the polymer containing the dinegative SO:-, but are essentially unchanged by the variations in alkyl group, R, implemented in this study. Other results of the dynamic mechanical analyses on the cationomeric elastomers are discussed in relation to their ionic cross-linking.

Key words: telechelic, cationomer, polybutadiene, anionic polymerisation, quaternary ammonium.

INTRODUCTION by copolymerisation of non-polar and polar mono- mers or by functionalisation of the preformed

In recent years there has been considerable interest non-polar polymer. The ionic groups in these in the synthesis and properties of ionomers, i.e. materials interact by coulombic associations to form polymers containing c 10-15 mol% ionic groups networks which may dramatically modify the attached to a non-polar chain.' - Much of the properties of the parent polymer. Specifically, in the research in this area of polymer chemistry has case of elastomeric materials, these ionic interac- involved randomly functionalised materials, formed tions may introduce thermoplastic behaviour giving

such elastomeric ionomers potentially important * To whom correspondence should be addressed. commercial properties. Early developments with $ Present address: Chemistry Department, Lancaster Univers- neutralised acidic elastomers derived from ity, Lancaster, LA1 4AY, UK. butadiene-styrene-acrylic acid terpolymer4 led to

55 British Polymer Journal 0007-1641/90/$03.50 0 1990 SCI. Printed in Great Britain

56 Caroline Roberts, W. Edward Lindsell, Ian Soutar

many related studies of carboxylated elastomer^.^ Elastomeric ionomers containing sulphonate groups were subsequently produced by sulphonation of EPDM terpolymers6 and these materials were found to have stronger ionic associations and better mechanical properties. Other elastomeric ionomers to have received attention include7 polypentenamers with various ionic functions (including carboxylate, thioglycolate, sulphonate and phosphonate groups) grafted-on at double bonds' and segmented polyurethanes incorporating anionic, cationic or zwitterionic function^.^^'^ Although all these materials possess distinctive and useful properties they contain randomly distributed functions and are not so readily amenable to systematic investigations of structure-property relationships.

Telechelic ionomeric elastomers containing a,o- ionic functionalities are well defined polymeric systems. These ionomers possess no free chain ends which could impair the properties in the rubbery region and are good model systems. Since there are precisely two ions per chain, the mol% of ionic groups is dependent only on the molar mass of the polymer and this can be controlled by the method of polymerisation. The first telechelic elastomeric ionomers to be subjected to physical studies were dicarboxylated polybutadienes." More recently extensive physical studies have been made on telechelic dicarboxylato polybutadiene' 2 , 1 and polyisoprenes' 3,14 with a variety of neutralising counter metal ions under a range of conditions. The use of an anionic technique to form these polyiso- prenes provided a range of ionomers with varying molar mass and low p01ydispersity.l~

Telechelic anionomeric polyisobutylenes have been synthesised by terminal sulphonation of polymer, propagated cationically via an inifer process, and detailed investigations of the physical behaviour of these sulphonates have also been r e p ~ r t e d . ' ~ ' ~ The formation of terminally sul- phonated polybutadiene has also been mentioned in the context of related work on non-elastomeric telechelic polystyrene ionomers,' and telechelic polybutadiene with terminal, anionic triphenyl- borate groups has been r e p ~ r t e d . ' ~ The phase morphologies and the ionic microstructures of both carboxylated and sulphonated telechelic elastomers have been probed by the techniques of SAXS and

To date, cationomeric telechelic elastomers have received little attention. Polybutadiene with a,o- quaternary ammonium groups has been synthesised, although the telechelic material was made using a difunctional anionic initiator in tetrahydrofuran solvent, giving polymer with a predominance of 1,2-linkages.lg The synthesis and characterisation of mixed telechelic polybutadienes with a-quater-

EXAFS.7.120,14a,l8

nary ammonium and o-quaternary phosphonium groups has also been reported.20 The coupling of tertiary-amine terminated polyisoprenes by silyl reagents has also produced telechelic polymers which were converted into zwitterionic materials by reaction with 1,3-propanesultone; some physical properties of these zwitterionic polymers have been reported.21

In this paper we present synthetic and physical studies on cationomers obtained from a telechelic polybutadiene of fixed molar mass, with a relatively high content of 1,4-links, and containing a range of a,w-quaternary ammonium groups and correspond- ing counter anions.

EXPERIMENTAL

All reactions were carried out under dry argon in clean, dry glassware. Reagents were handled and transferred under argon or nitrogen, using Schlenk- type techniques, or in a vacuum system. Also, solvents were purified and dried as in previous work20,22 and were freshly distilled before use. 1,3- Butadiene ( > 99*5%, Union Carbide) was passed over molecular sieves, collected over CaH, and distilled from a graduated tube into the reaction vessel. Dry 3-dimethylaminopropyl chloride was preparedig from the hydrochloride (Aldrich) and converted into 3-dimethylaminopropyl lithium23 by reaction with lithium slurry in hexane, using a method similar to that recently reported.24 Alkyl halides were obtained commercially (Aldrich) and distilled before use.

NMR spectra, 'H, 13C and ,lP, were obtained with a Bruker WP 200 SY instrument using CDCl, as solvent and shifts are quoted with reference to SiMe, ('H and 13C) or 85% H,PO, ("P). Elemental analyses were obtained at UMIST, Manchester, UK. Gel permeation chromatography (GPC) was carried out at RAPRA, Shawbury, UK, on a Waters GPC system equipped with four polystyrene gel columns of porosities 105-102 A; molecular weights were determined from a universal polystyrene calibration and corrected for polybutadiene by using reported Mark-Houwink coefficients (i.e. for 62% 1,4- polybutadiene; a = 0.693, k = 4.43 x lo-,; inter- polated from the data of Ref. 25; although data based on end-group analysis of the polymer supported molecular weights some 20-300/0 higher).

Polymerisation

1,3-Butadiene (50 ml; 0.68 mol) was distilled under argon into hexane (200ml) at -78°C in a three- necked polymerisation flask fitted with a septum, an argon inlet/outlet and an efficient stirrer. The

BRITISH POLYMER JOURNAL VOL. 23, NOS 1 & 2,1990

qw- Diqua fernury u ~ ~ m ~ ~ ~ i ~ m po Iyhutadime ionomers 57

solution was warmed to c. -30°C and 3-dimethyl- aminopropyl lithium in benzene (0.248 mol litre- '; 40 ml) was introduced by syringe in order to initiate polymerisation. The reaction temperature was maintained at c. - 30°C for > 4 h and then the flask slowly warmed to ambient temperature over a total of 18 h; during this time propagation of polymerisa- tion occurred but some of the butadiene was lost by evaporation. At this point 20 ml of the solution was removed and terminated by addition to methanol to provide a sample of protonated polymer for comparative studies. Freshly distilled 3-dimethyl- aminopropyl chloride (1.5 ml; 0.012 mol) was added to the remaining, well stirred 'living' polymer solution and the reaction mixture left for 24h at room temperature to complete the termination reaction (in other reactions tetrahydrofuran (20 ml) was added to the hexane solution before the introduction of chloroamine to increase the rate of this reaction). The terminated polymer was pre- cipitated by addition to methanol (500 ml), repre- cipitated twice from 60-80 petroleum ether into methanol, collected and dried under vacuum. The liquid polymer had M J M , = 1.26, fin = 2700 (from GPC, using calibration parameters given above, although elemental analysis and NMR spectroscopy supported a slightly higher fin, c. 3500); chain stereochemistry 1,2 = 38%, 1,4 = 62% with cis/traiZs = 0.72 (from NMR); absence of any proton terminated material (from NMR); characteristic 3C NMR resonances at 6 = 59.5 (CHzN), 45.5 (CH3N) PPm.

0 ua tern isa tion

In a typical experiment, a small molar excess (<20%) of pure alkyl halide (RX; R = Me, Et, n-Pr, n-Bu, n-Am; X = I or Br) was added to a solution of 1-5 g of a,w-bis(dimethy1amino)polybutadiene in dichloromethane (20-50 ml). The reaction was left for 24 h under argon in the dark. The solvent and remaining volatiles were removed under vacuum and the resulting rubbery-solid polymer was dried under vacuum (< lO-'mmHg) at 100°C for 18 h. (Since these polymers were hygroscopic they were always carefully dried in this manner before being subjected to critical physical studies.) The product was stored under nitrogen at 4°C. Quantitative quaternisation was indicated by analysis of the I3C NMR spectrum; characteristic I3C NMR resonances: 6 = 66.0 (CHzN+), 53-0 (CH,N+) ppm.

ion exchange

Anion exchange was carried out using a column of Amberlyst 27 macroreticular resin (Aldrich) in the appropriate anionic form.

(i) Hexafluorophosphate: the column was gener- ated by passage of aqueous KPF, solution and then the water was displaced with tetrahydrofuran and finally dichloromethane. a,u-Bis(trimethy1- ammonium)polybutadiene diiodide (1 g) in CH,Cl, was passed through the column and eluted with CHzClz until most of the iodide had been ex- changed. The polymer was recovered by evaporation of solvent and dried under vacuum. Analysis: found C 81.7; H 10.9; P 1.3; N 0.75; 10.4%; calcd (for M,, c. 3800; 90% exchanged) C 81.5; H 10.2; P 1.47; N 0.74; I 0.67%; 31P NMR: 6 = - 143.5 ppm.

(ii) Sulphate: in a manner similar to the above, the column was converted to the sulphate form by using aqueous Na,SO,, the solvent was changed to CHzClz and the iodide ions of a,u- bis(trimethy1ammonium)polybutadiene diiodide (0-5g) were exchanged for sulphate. Analysis of polymer: found C 82.8; H 11.3; S 0.6; N 0.7; I 1.4%; calcd (for M , c. 3660; 80% exchanged) C 85.1; H 10.6; S 0.70; N 0.77; I 1.39%.

Thermal analyses of polymers

Differential scanning calorimetry (DSC) was carried out on dry polymer in the temperature range - 110 to +2O"C using a Perkin Elmer DSC-7 Series Analysis System purged with dry nitrogen; measure- ments in the range -40 to + 150°C were made using a Perkin Elmer DSC-4 instrument; in both cases a heating rate of 10°C min- was employed.

Dynamic mechanical thermal analysis (DMTA) was carried out using a Polymer Laboratories Dynamic Mechanical Analyser over the range - 100 to + 150°C at heating rates of 10°C min-' and/or 1°C min- l. (Note: although data collected at the same heating rate were reproducible and self- consistent, differences were noted for data at the different rates, especially for tan 6.) A nitrogen atmosphere was used in some experiments but comparable results were obtained under normal atmospheric conditions. The well-dried ionomers were examined using a shear mode assembly at frequencies in the range 10~' '5-10z Hz. (Viscous liquid non-ionic polymers could only be impreg- nated on to a glass braid and examined in the cantilever mode of operation.)

RESULTS AND DISCUSSION

Synthesis of cationomers

1,3-Butadiene was polymerised to a DP of c. 50-60 by an anionic techniquez6 using the functionalised organolithium initiator, Me,NCH,CH,CH,Li, in hexane :benzene (5 : 1). These experimental con- ditions produced living polybutadienyllithium of

BRITISH POLYMER JOURNAL VOL. 23, NOS 1 & 2,1990

58 Caroline Roberts, W. Edward Lindsell, Ian Soutar

low polydispersity (specifically, from GPC: quaternary ammonium functions has been varied by mw/Mn = 1.26, = 2.7 x lo3 (although analytical introducing different primary-alkyl groups, C,H,+ 1, data supported 8, - 3.5 x lo3)) with a terminal with n = 1-5, and the ionic interactions have also dimethylamino functional group (eqn (1)). been altered by the presence of differing counter - . _

hexane/benzene anions, i.e. I - , Br-, PF; and SO:-. n + Me,NCH2CH,CH2Li -

Me,N(CH2),(C4H,),Li (1) Dsc studies (high 1,4)

The hydrocarbon medium promotes high 1,4-regio- selectivity in the propagation of polymerisation, in spite of the presence of the polar, terminal amino groups, and the isolated polymer contained 62% 1,4- linkages with a cis/trans ratio of 0.72 (cf. Ref. 24).

The living polybutadienyllithium reacted with 3- dimethylaminopropyl chloride, giving a high yield of the C-C coupled product (cf. Ref. 19) and forming the liquid telechelic a,w-bis(dimethylaminopropy1)- polybutadiene (eqn (2)).

Me2N(CH2),(C,H,),Li + Me,N(CH,),Cl -+

A high degree of terminal functionalisation was indicated by I3C and 'H NMR spectra in which the expected resonances of CH,N and CH,N groupings are identifiable, with approximately the correct intensities relative to the polybutadiene chain, and no resonance assignable to simple proton termi- nated polymer was observed. Quaternisation of the liquid telechelic amino-polymer with alkyl halides, RX (R = primary-C,H,+ (n = 1-5), X = Br; R = C,H, + , (n = 1,2), X = I), occurred quantitatively in dichloromethane over 24h, as indicated by 13C NMR spectroscopy (eqn (3)).

Me,N(CH,)3(C4H6),(CH2),NMe, + 2RX -

Me2N(CH2)3(C4H6)n(CH2)3NMe2 (2)

R R I I

X - X - Me2N+(CH2)3(C4H,),(CH2)3N+Me2 (3)

The cationomeric polymers were isolated as rubbery-solid materials.

Anion exchange, using a macroreticular resin, was carried out on one cationomeric system to produce polymers with alternative counter anions. Exchange of iodide by hexafluorophosphate, PF;, and by sulphate, SO; - (SO-90%), gave products suitable for study, but exchange by ortha-phosphate, PO:-, occurred only to a relatively low extent.

By using the techniques described above, a range of telechelic cationomeric polybutadienes incor- porating the same hydrocarbon backbone with 62% 1,4-~tereochemistry was produced. The loading of terminal quaternary ammonium ionic groups corre- sponded to 3-4mol% with respect to monomer units in the polymer. The steric bulk of the

Investigations of the telechelic ionomers by DSC clearly revealed the glass transition temperature, T,, and, within experimental error, this was invariant at -73 2°C for all systems. This T, value was not affected by the presence of significant amounts of absorbed water. The non-quaternised a,w-bis- (dimethy1amino)polybutadiene precursor showed a T, at -79°C so that a small increase of c. 6°C in T, occurs on ionisation. It may be noted that the introduction of a terminal, non-ionised tertiary amine into a proton-terminated polybutadiene of comparable molar mass may also cause a small increase (c. 3-4°C) in T,.

Therefore, it appears that cation formation at the terminal nitrogen functionalities of telechelic poly- butadiene causes a minor increase in T,. This is contrary to observations on a,w-di(carboxy1ato)- polybutadiene (Mn = 4.6 x lo3), for which no change in T, was found on conversion of the acid precursor into a range of neutralised salt^.'^',^^ However, in random ionomers of polybutadiene, an enhancement of T, over that of non-ionic forms, dependent on the concentration of ions, is a well documented p h e n ~ m e n o n ~ " , ~ ~ and is attributable to limitations on backbone mobility. Thus, in the cationomers studied here, the ionic end groups must cause a minor perturbation on such segmental mobility via ionic interactions but these effects are essentially independent of both the size of cation or anion and the type or charge of the anion. The difference between the telechelic quaternary am- monium and the carboxylate systems may arise from the presence of hydrogen bonding in the non-ionised acids, which is not possible between the tertiary amine precursors of the former systems, although the behaviour of the carboxylate systems has been attributed to the opposing effects of restricted chain- end mobility and reduced crowding at the ionically linked branch points.27 The important point of relevance to the cationic polybutadienes reported here, of relatively high 1,4-content, is that 7'' remains low so that elastomeric behaviour can occur over a wide temperature range.

DSC studies on the majority of the telechelic cationomers revealed no transitions, other than T,, up to 15OoC, in spite of the fact that all the rubbery- solid materials were visually observed to flow within this temperature range (mainly < l 0 O O C ) . However, well-dried samples containing trimethylammonium

BRITISH POLYMER JOURNAL VOL. 23, NOS 1 %I 2,1990

a,o- Diquaternary ammonium polyhutadiene ionomers 59

terminal groups and counter anions I- or PF; did display small reproducible endotherms at 76 or 11 5"C, respectively. These higher temperature transitions may be associated with a relaxation process involving the ionic groups and related to q, observed by DMTA for all the cationomeric telechelic systems. It is not entirely clear why this should be observed by DSC for only two of the polymers, but it may be noted that these specific samples contain the smallest cationic end group and the largest mononegative counter anions employed in this study.

DMTA studies

A series of investigations of the telechelic cat- ionomers by dynamic mechanical analysis in the shear mode has been carried out at frequencies within the range 10-1'5-102 Hz and at temperatures between - 100 and + 150°C. The variation of loss tangent (tan S = G"/G') and storage (G') and loss (G") moduli with temperature and frequency have been monitored. At lower temperatures, the glass tran- sition is observed at a temperature which is dependent on the test frequency (see Fig. 1).

A second transition is apparent, mainly above ambient temperature, which can be attributed to a relaxation of the ionic interactions in the cat-

4 i 2 I 'i i :9

A+ +-

o + * + 0

+

+ t

+

t a n 6 +

+

0 -9 -7 -5 -3 - 1 1 3 5 7 9 1 1

x10 T ( O C )

Fig. 1. Variation of complex dynamic shear modulus (Pa) and of loss tangent (tan 6 = G"/G) at 10 Hz with temperature a t a heating rate of 10°C min- for a,w-bis(trimethy1ammonium)-

polybutadiene diiodide (R = Me; X = 1).

10

O/ 8

7

6

cg

c 5 e .J

4

3

T t'C) x10

Fig. 2. Variation of loss tangent with temperature, at 10 Hz, for ?,a-bis(alkyldimethylammonium)polybutadiene dibromide,

containing alkyl (R) = Me, Et, n-Pr, n-Bu and n-Am.

ionomers and may be designated T (see Figs 1 and 2). This transition is also frequency dependent but, at any given frequency of observation, it may be noted that decreases as the size of the quaternising alkyl group R increases from C, to C, (cf. Fig. 2). Also, Ti decreases progressively in a cationomeric system as the mononegative counter anion Br- is replaced by the larger anions I - and PF; (e.g. at 10 Hz, values are 120, 93 and 80°C for Br-, I - and PF,, respectively). Moreover, q is lower for PF; as a counter anion than for the sterically comparable, dinegative SO:- (e.g. at lOHz, q = 80 and 102"C, respectively). Ionic radii of Br- and I - are 1.96 and 2.20& respectively, whereas S-0 and P-F bonds in SO: - and PF; are 1.49 and 1.56 A, respectively, and an effective thermochemical ionic radius for the SO: - anion has been estimated as 2.3081. The trends in T values can be simply explained in terms of the strength of the electrostatic interaction between the ionic groups, which is inversely proportional to the separation between opposite charges and propor- tional to the product of the charges. However, it should also be noted that the ease of polarisation (degree of softness) of the anions varies in the order I - > Br - > PF; and SO: - > PF;, and such polari- sation will also affect the strength of 'ionic' cross- linking interactions.

BRITISH POLYMER JOURNAL VOL. 23, NOS 1 & 2,1990

60 Caroline Roberts, W. Edward Lindsell, Ian Soutar

- 3 L. . , , , , , , , , , , . _ _ ~ 24 26 2- 32 r 3 6

xi 0-4 Fig. 3. Plots of log,(frequency, Hz) versus T - ' { (K) = secondary ionic transition temperature} for some r,w-bis(alky1- dimethylammonium)polybutadicne dihalides {alkyl (R) = Me,

Et, n-Am; halide (X) = Br or I}.

The Ti values display an Arrhenius-type relation- ship to the frequency and reasonable linear log,(fre- quency)/T- dependencies are obtained (see Fig. 3) from which activation energies, E,, can be derived (Table 1). Values of E, vary within the range 60- 160 kJ mol- according to the counter anion in the

TABLE 1. Activation energies of ionic relaxation and equilibrium shear storage moduli for cationomeric a m - bis( alkyldimethylammonium)polybutadiene (M, - 3 x lo3) with alkyl group R and counter anion X

Anion Alkyl Activation Modulus Geb X group energya (Pa x

R (kJ mol-')

Br- Br Br ~

Br ~

Br 1 - I - P F; so: -

Me Et

n-Pr n-Bu n-Am

Me Et Me Me

84 " 82" 74d 0.93 79 " 91 " 84 69" 95d 0.98 71 "

108" 118d >2 151"

a Estimated error 5 + I 0 kJ rno1-l.

" From log, (frequency)/T-' plot. 303K.

From log, a,/T-' plot.

order SO:- > PF; > Br- 2 I-. Activation energies can also be derived from the logarithmic dependence of shift parameters uT (obtained from the construc- tion of master curves for dynamic shear moduli, see below) versus temperature; these values of E, are comparable, within experimental error, with the values derived from Ti variations (see Table 1). It may be noted that the highest value of E, occurs for the sulphate counter anion, in line with the expected greater electrostatic interactions for the dinegative charge. On the other hand, the order of decreasing E, values for the mononegative counter anions does not simply reflect the increasing size of the anion since the value for PF; is higher than for Br- or I-; this is contrary to the order of Ti values but could arise if the ionic aggregates incorporating the former, larger, non-polarisable complex anion were structurally different from those containing the halide anions. There is little variation in E, values of cationomers containing different alkyl groups, R = Me to n-Am, and it could be concluded that the steric effects of a single alkyl group at the quaternary ammonium centres have a small influence on the strength of the ionic interaction, in spite of variations in Ti noted above.

A closer analysis of the Arrhenius-type relation- ship of the frequency/T data does show that, at the lowest frequencies and temperatures, some devi- ation from a simple linear dependence occurs for the iodide containing cationomers; this may be indica- tive of a secondary ionic relaxation mechanism (cf. Ref. 29) in these iodide systems, although further analysis is not possible with the limited data available.

Both dynamic storage (G') and loss (G") moduli of the cationomers measured at eight temperatures in the range 303-353 K display good time-temperature equivalence, as shown by the partial master curves at 303K of Figs 4-6 for polymers with Br-, I - and PF; counter anions, respectively. The experimental shift factors uT used in constructing these curves are characterised by an Arrhenius-type dependence on temperature, giving the activation energies of Table 1. Within the range of frequencies studied it is apparent, being most clearly evident for the iodide containing system (Fig. 5), that the master curves comprise a rubber-like plateau and a region of viscous flow; the maximum in G" is attributable to the secondary ionic relaxation. From the plateau (or incipient plateau) of the storage modulus it is possible to derive a value for the equilibrium storage modulus G, (see Table 1). Values of G, for I - and Br- containing polymers are almost the same (- 1 x lo6 Pa) whereas G, for the polymer with PF; anions is higher ( > 2 x lo6 Pa). For an ideal rubber with tetrafunctional cross-links the equilibrium shear modulus may be related to the number average

BRITISH POLYMER JOURNAL VOL. 23, NOS 1 & 2,1990

a,o-Diquaternary ammonium polyhutadiene ionomers

G ' + + +

+ + + +

( 3 .

d '

(3

[r 0 '

61

X X X

xx x * : R X X

G" XX +

x x + xx

x +

cd xx ++

xx +

x x x +

-J 0 4 1 XX x +

+ + 1 x x +

31 x: ++++++ +

2 -3 -2 - 1 0 1 2

Log( a+=) Fig. 4. Master curves of dynamic shear storage (C') and loss (C") moduli (Pa) versus reduced frequency (Hz) for a,w- bis(ethyldimethylammonium)polybutadiene dibromide (R = Et; X = Br); temperature range 303-353 K; reference temperature

303 K.

I 6 G'

+ + ++++ + uc L++++" ++ +

0 '1 + ; + O 6:

I

2 1 1 2 -5 - 4 -3 -2 - 1 0

Log( a+) Fig. 5. Master curves of dynamic shear storage (G') and loss (C") moduli (Pa) versus reduced frequency (Hz) for M,O-

bis(trimethylammonium)polybutadiene diiodide (R = Me; X = I); temperature range 303-353 K; reference temperature

303 K.

G'

+ + $ +

++ +

8 0 GI'

00

0

I

-6 - 4 -2 0 2 4

Log (a$)

Fig. 6. Master curves of dynamic shear storage (C') and loss (C") moduli (Pa) versus reduced frequency (Hz) for a,w- bis(trimethylammonium)polybutadiene bis(hexafluorophosphate) (R = Me; X = PF,); temperature range 303-353 K; reference

temperature 303 K.

molecular weight between cross-links, Mnc, as follows:3o

Ge = gpRTIli-i,c Assuming that g = 1 and that the density is 0-9 g

ml- (cf. Ref. 12) a value of Mnc N 2400 is calculated for the iodide and bromide containing systems. This cross-linking chain length is close to, but a little lower than, A?,,.of the basic telechelic polymer so that a model involving tetrafunctional ionic cross-linking with ionic interactions between multiplets of approximately four ion-pairs may be appropriate for these systems. However, for the hexafluoro- phosphate containing cationomer the calculated value of Mnc is < 1100, and a model involving ionic clusters comprising greater aggregates of ion-pairs must be considered.

CONCLUSIONS

Well defined a,u-diquaternary ammonium poly- butadiene ionomers can be prepared by an anionic technique, using an initiator and a terminator incorporating a tertiary amine function, followed by quaternisation of the telechelic diamino-polymer. Polymer with a relatively high 1,4-content (> 60%) and low polydispersity (BW,/Mn c 1-3) is obtained by

BRITISH POLYMER JOURNAL VOL. 23, NOS 1 81 2,1990

62 Caroline Roberts, W. Edward Lindsell, Ian Soutar

using a hydrocarbon solvent. The resulting cat- ionomer possesses a low T, (I -70°C) which is slightly higher than the of the non-ionised precursor.

Terminal interactions between the telechelic cationomers produce elastomeric systems and give rise to secondary relaxation transitions observable by dynamic mechanical analysis. Relaxation of the ionic interactions in the telechelic cationomers is characterised by an activation energy with a value which, in systems of the same molecular weight (i.e. 3 4 mol% ions), is mainly dependent on the nature of the counter anion. Cationomer with the di- negative sulphate anion exhibits a higher activation energy than with mononegative anions, although the hexafluorophosphate counter anion forms material of higher dynamic storage modulus and this may arise from a higher degree of aggregation between the ion-pairs of the latter material.

ACKNOWLEDGEMENTS

We thank Heriot-Watt University for the award of a studentship (to C.R.) and SERC/MoD for support. We also thank Dr M.J. Stewart, MOD RARDE, Waltham Abbey, UK, for helpful discussions and Dr S. Holding, RAPRA, Shawbury, UK, for GPC analyses.

REFERENCES 1 (u) Eisenberg, A. & King, M., Ion-Conlaining Polymers. Academic

Press, New York, 1977; (h) Eisenberg, A. (Ed.), Ions in Polymers, Adv. Chem. Ser., Vol. 187. American Chemical Society, Washington DC, 1980;(c) Eisenberg, A. & Bailey, F. E. (Eds), Coulombic Interactions in Macromoleculur Systems, ACS Symp. Ser. 302. American Chemical Society, Washington DC, 1986.

2 ((I) Holliday, L. (Ed.), Ionic Polymers. Applied Science Publishers, London, 1975; (b) Wilson, A. D. & Prosser, H. J. (Eds), Deoelopments in Ionic Polymers. Applied Science Publishers, London, 1983; (c) McKnight, W. J. & Earnest, T. R., J. Polym. Sci., Mucromol. Rev., 16 (1981) 41.

3 (u) Tant, M. R. & Wilkes, G. L., J. Macromol. Sci., Rev. Marromol. Chem. Phys., C28 (1988) I; (b) Mauritz, K. A,, ibid., p. 65; (c) Fitzgerald, J. J. & Weiss, R. A., ibid., p. 99.

4 Brown, H. P., Rubber Chem. Technol., 30 (1957) 1347; 36 (1963) 931. 5 Jenkins, D. K. & Duck, E. W., in Ref. 2a; see also Sato, K., Rubber

6 Agarwal, P. K., Garner, R. T. & Lundberg, R. D., Macromolecules, 17 C'hrm. Technol., 56 (1 983) 942.

(1984) 2794, and earlier refs.

7 Bagrodia, S., Tant, M. R., Wilkes, G. L. & Kennedy, J. P., Polymer, 28

8 Rahrig, D. & McKnight, W. J., in Ref. Ib, Chapter6. 9 Dieterich, D., Keberle, W. & Witt, H., Angew. Chem., In/. Ed, En,& 9

(1970) 40. 10 (a) Hwang, K. K. S., Speckhard, T. A. & Cooper, S . L., J. Mucromol.

Sci.-Phvs.. B23 (1984) 153: (b) Speckhard, T. A,, Hwdng, K. K. S.,

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11

12

13 14

15

16

17

18

19

, . . . Yang, C.'Z., Laupan, W. R. & Cooper, S. L., ibid., p. 1.757 (a) Otocka, E. P., Hellman, M. Y. & Blyler, L. L., J. Appl. Phys., 40 (1969) 4221; (b) Pineri, M., Meyer, C., Levelut, A. M. & Lambert, M., J. Polym. Sci., Polym. Phys. Ed., 12 (1974) 115. (a) Horrion, J., Jerome, R., Teyssie, Ph., Marco, C. & Williams, C. E., Polymer, 29 (1988) 1203; (b) Broze, G., Jerome, R. & Teyssie, Ph., J. Polym. Sci., Polym. Phys. Ed., 21 (1983) 2205. Jerome, R. & Broze, G., Rubber Chem. Technnl., 58 (1985) 223. (u) Register, R. A,, Foucart, M., Jerome, R., Ding, Y. S. & Cooper, S. L., Macromolecules, 21 (1988) 1009; (b) Tant, M. R., Song, J . H., Wilkes, G. L., Horrion, J. & Jerome, R., Polymer, 27 (1986) 18 15; (c) Broze, G., Jerome, R., Teyssie, Ph. & Marco, C., Mrccron~olrculrs, 16 (1983) 1771. (a) Tant, M. R., Song, J. H., Wilkes, G. L. & Kennedy, J. P., Polym. Prep., Am. Chem. Soc., Div. Polym. Chem., 27 (1986) 351; (b) Bagrodia, S., Wilkes, G. L. & Kennedy, J. P., Polym. Eng. Sci., 26 (1986) 662; (c) Mohajer, Y., Tyagi, D., Wilkes, G. L., Storey, R. F. & Kennedy, J. P., Polym. Bull., 8 (1982) 47. Omeis, J., Muhleisen, E. & Moller, M., Polym. Prrpr., Am. Chem. Soc., Diu. Polym. Chem., 27 (1986) 21 3; see also Moller, M., Omeis, J. & Muhleisen, E., Reversible Polymeric Gels and Related Systems, ACS Symp. Ser. 350. American Chemical Society, Washington DC, 1987, p. 87. Morrell, R. K., Service, D. M., Stewart, M. J., Viguier, M. & Richards, D. H., Brit. Polym. J., 19 (1987) 241. ((I) Vlaic, G., Williams, C. E., Jerome, R., Tant, M. R. & Wilkes, G. L., Polymer, 29( 1988) 173; (h) Williams, C. E., Russell, T. P., Jerome, R. & Horrion, J., Macromolecules, 19 (1986) 2877. Richards, D. H., Service, D. M. & Stewart, M. J., Brit. Polym. J., 16 (1984) 117.

20 Lindsell, W. E., Radha, K., Soutar, I. & Stewart, M. J., Polymer, in press.

21 (u) Davidson, N. S., Fetters, L. J., Funk, W. G., Graessley, W. W. & Hadjichristidis, N., Mucromolecules, 21 (1988) 112; (h) Fetters, L. J., Graessley, W. W., Hadjichristidis, N., Kiss, A. D., Pearson, D. S . & Younghouse, L. B., ibid., p. 1644.

22 Lindsell, W. E., Service, D. M., Soutar, I . & Richards, D. H., Brit. Polym. J., 19 (1987) 255.

23 Eisenbach, C. D., Schnecko, H. & Kern, W., Euv. Polym. J., 11 (1975) 699.

24 Stewart, M. J., Shepherd, N. & Service, D. M., Brit. Polym. J., 22 (1990) 319.

25 Kraus, G. & Stacy, C. J., J. Polym. Sci., A-2, 10 (1972) 657. 26 Young, R. N., Quirk, R. P. & Fetters, L. J., Ad[) . Poljm. Sci., 56

27 Jerome, R., Horrion, J. & Teyssie, Ph., Macromolecules, 17 (1984)

28 Otocka, E. P. & Eirich, F. R., J. Polym. Sci., A-2, 6 (1968) 921. 29 Eisenberg, A,, Matsuura, H. & Tsutsui, T., J. Polym. Sci., Polym.

30 For example, see Ferry, J. D., Viscoelastic Properties of' Polymers,

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BRITISH POLYMER JOURNAL VOL. 23, NOS 1 81 2,1990