AD-A260 058 DTIC1S ELECTE

CINFLUENCE OF CURE SYSTEMS ON DIELECTRIC KN1) VISCOELASTIC RELAXATIONS IN

CROSSLINKED CHLOROBUTYL RUBBER

Rodger N. Capps and Christopher S. Coughiin -

Naval Research LaboratoryUnderwater Sound Reference DetachmentP.O. Box 568337Orlando, FL 32856

and

Linda L. Beumel ............. .......

TRI/TESSCO ._ Dioun azu,=" - 17-WOrlando, FL 32806

INTRODUCTION

Dielectric spectroscopy has been used as a probe of molecularbehavior in organic molecules for a number of years. ' In conjunctionwith dynamic mechanical spectroscopy, it has been used to correlate thedynamic mechanical and dielectric relaxation behavior of a number ofpolymer systems, as well as providing insight into the molecularstructural factors responsible for multiple relaxation mechanisms inpolymers.

In many instances where simultaneous measurements of dynamicmechanical and dielectric behavior were performed,s- the polymersinvolved were comparatively simple systems. Although synthetic rubbershave been extensively characterized by dynamic mechanical measgroments,fewer dielectric studies have been performed on these systems. - In arecent work, we showed that the dielectric behavior of filledchlorobutyl and butyl rubber was significantly influenced by carbon blackparticle size, type, and loading. Results obtained on unfilled systemsindicated that the principal dielectric relaxation was a cooperativeprocess involving molecular motion of chain segments coupled withthermally activated rotation of polar crosslinking molecules. It wasalso shown that the dielectric behavior followed the Kolrausch-Williams-Watts (KWW) "stretched exponential" function, which has recently receivedgreat interest as a sort of 'universal relaxation' function, withapplicability to a large number of physical systems. 1-13 In the presentwork, we have extended our study to compare the dielectric andviscoelastic behavior of chlorobutyl rubber (CIIR) cured only with zincoxide, and with increasingly complex cure systems, as well as varyingplasticizer loadings. For comparison purposes, we have also included thestructurally related butyl rubber (IIR), which does not possess moleculardipoles due to chlorine atoms. The similarity between the observed

Symhesis. Chracterizatw. and Theory of Polymeric Networks and GelsEdied by S.M. Aharoi. Plenum Press, New York. 1992 269

is I oR

3 I: P,

viscoelastic behavior* and dielectric behavior is discussed in terms ofmolecular motions.

EXPERIMENTAL

The polymer systems studied are summarized in Table 1. Compoundedrubber samples were obtained from the Burke Rubber Company of San Jose,CA. Proper cure conditions were determined with a Monsanto oscillatingdisc rheometer as per ASTM D2084.

Experimental samples were compression molded at 155 degrees C.Dynamic mechanical and dielectric measurements were performed aspreviously described. Tensile measurements were performed as per ASTMD412.

Table 1. Formulations for IIR and CIIR Rubbers

System IIR CIIR

Component (Parts per Hundred of Rubber (P.H.R.))Exxon Butyl 268 100.0Chlorobutyl HT1066 100.0Zinc Oxide 5.0 5.0Schenectady SP1055" 12.0 0-8.0MBTS** 0-2.0Stearic Acid 1.0 1.0Diphenyl guanidine 0-0.5Sunpar 120** 0-10.0 0-10.0

* Brominated methylol phenol resin•* 2, 2'-Benzothiazyl disulfide•** Paraffinic oil

RESULTS

Dynamic Mechanical Behavior.

Fig. 1 shows the isochronal, temperature-dependent storage Young'smodulus and loss tangent, obtained with a Polymer Laboratories DynamicMechanical Thermal Analyzer (DMTA), for three different cure systems inthe chlorobutyl rubber. One primary transition is clearly evident in theloss ttfgent, with a secondary shoulder that has been classified byothers in the analogous bromobutyl as a P transition due to therotation of pendant methyl groups. Similar behavior was observed for thebutyl rubber. It can be seen that the increased crosslinking in thechlorobutyl rubber causes an increase in the storage modulus, a slightdecrease in the peak magnitude of tan 6, and a shift upward in thetemperature at which the maximum of tan 6 occurs.

These trends are mirrored in the extended master frequency curvesconstructed by time-temperature superposition using measurements from thetransfer function technique. Fig. 2 shows master frequency curves fortwo different cure systems. All of the materials tested behaved asthermorheologically simple materials, and could be shifted equally wellby either an Arrhenius shift function, or standard WLF form. Note that,although the tan 6 scale is a linear one, the apparent superposition isgood. The shoulder seen in the DUTA scans appears to manifest itself asa shoulder on the high frequency side of the tan 6 curve in the masterfrequency curves, at approximately 100 kHs. This is interpreted as a

270

10 21OHz

E'

9 1.6

8 -1.2

"-J 7 ,.8

6-. ton 6

5-100 -50 0 50

TEMPERATURE (-C)

Fig. 1. Plot of storage Young's modulus and loss tangent for chlorobutylrubber as a function of temperature at 10 Hz: solid lines,5 phr of ZnO; dashed lines, 5 phr ZnO and 6 phr SP1055; doubledashed lines, 5 phr ZnO, 6 phr SP1055, 2 phr MBTS, 0.5 phr DPG.

--To,,273K0 • . n

01.0

10010 9 Ton 61

.8ZnO + SP1055 + MBTS + DPG

to 10 .6 Q4108 "ZnO + SP1055 + M + OP.

.4

107 E#

" ZnO .2

100 101 102 103 104 105 106

RDUCED FREQUENCY (Hz)

Fig. 2. Plot of storage Young's modulus and loss tangent as a functionof reduced frequency for chlorobutyl rubber with two differentcure systems at a reference temperature of 273.15 K: clearsquares and circles, 5 phr of ZnO; solid squares and circles,5 phr ZnO, 6 phr SP1055, 2 phr MBTS, 0.5 phr DPG.

271

coupling of the a and P processes in the primary glass-to-rubberviscoelastic relaxation.

Addition of nonpolar plasticizer at a constant level of crosslinkinghad the expected effects in both the butyl and chlorobutyl rubbers. Theincreased free volume led to a decrease in the storage modulus, alowering of the temperature of maximum tan 6, and increase in the maximumof tan 5. This is shown for the butyl rubber in Fig. 3. The chlorobutylrubber showed similar effects.

10 210 Hz

S• _".- O 10 ph r

9 1.6X'x'• \ .ao5 phr

8 1.2

0.8

6 -. 4

tand 6 '

5-100 -50 0 50

TEMPERATURE (-C)

Fig. 3. Plot of storage Young's modulus and loss tangent for plasticizedbutyl rubber as a function of temperature at 10 Hz: solidlines, 0 phr of Sunpar 120; double dashed lines, 5 phr Sunpar120; dashed lines, 10 phr Sunpar 120.

The KWW function has been used as a fitting function for botmechanical relaxations and dielectric spectra. Roland and Ngai

recently applied the KWW function to the glass transition dispersion ofthe dynamic mechanical spectrum of polybutadiene-polyisopreniblends.Muzea, Perez, and Johari recently described its application to theshear modulus and loss spectrum of the P-relaxation of poly(methylmethacrylate). This was the approach used to fit the dynamic mechanicalspectra of the chlorobutyl rubber samples to the KWW function.

Two different methods were used to examine the glass transitiondispersion region for purkoses of fitting to the KWW function. The firstused the step-isotherm mode of a Polymer Laboratories DVTA to measure theYoung's loss modulus at ten different frequencies from 0.1 to 30 Hz, attemperatures near the glass transition. This resulted in a relativelynarrow isothermal frequency spectrum, and considerable scatter in KWWfits. The second approach used the transfer function technique and timetemperature superposition to construct extended master frequency curvesat a reference temperature of 243.15 K, so that the dispersion curve inthe loss modulus covered approximately the same frequency range as the

272

dielectric loss. These were then :onsidered to renresent isothermal

frequency curves at the reference temperature. An exampie of such a

curve is shown in Fig. 4. A third crier polynomial was used to find the

maximum in the loss modulus and f:recuency of maximum >os before fittingthese to the KWW function.

10 10 _ _ 1 l_ 1 Hil ill f _ 1_lll_ _ __ 1 1 1__ll _11 1 1 1_1_1 1 1_11111_110 !0

01

10~10

-. , 0

10 7 10 7

0 1, .1- -1

1 0 11 0 1 102 01 I 04 I I 105

REDUCED FREQUENCY (Hz)

Fig. 4. Reduced frequency curve of Young's storage and loss moduli forchlorobutyl rubber-u w,-• . 5 nhr ZO., :; -hr -P1055, `,MTS, an-DPG. T, 0 243.15 K.

Figs. 5 L.nd 6 show the ncrmai:izeo+ u','niamic mechanical snectra for onematerial, and the resultant fit zo ihe K'AW function using an exponent of0.475. This is the chlorobutyl ro'bber w.•ith the most c',r ux cure system.using ZnO, SP1055, .BTS, and DPG. In contrast, chlorobutvy; rubbers curedwith ZnO alone, and ZnO combined with SP1055, were fitted to the KWWfunction with an exponential factor of 0.375. This indicates a broaderdistribution of relaxation times in the dynamic mechanical behavior ofthe rubbers with the simpler cure systems.

Dielectric Behavior

The dielectric behavior of the chiorobutyl rubber was significantlyaffected by the crosslinking system used. Relative permitivitties werelow for the systems, on the order of 2.7, and showed little frequencydependence. Fig. 7 shows the dielectric loss for four iifferent curesystems, plotted as a function of frequency at 295.15 degrees K. In allcases, a secondary maximum is seen at approximately 22-25 kHz. The exactnature of this peak is nut clear. It was also observed in the butylrubbers, but not in other polymers with higher losses, such as peroxidecured acrylonitrile rubber, and sulfur cured natural rubber. It did notshow any frequency shift as a function of temperature, indicating that itis probably an instrumental artifact, and not a separate transition.

273

1.0

0.8

0.6/xaE

> 0W 0.4-

0.2-00

-1. -1 -0.5 0 0.5 1 1.5

LOG (f/fma,)

Fig. 5. Plot of normalized Young's storage modulus versus normalizedfrequency for chlorobutyl rubber at T. = 243.15 K. Linerepresents fit from KWW function with P 0.475.

1.2

1.0 o 3

( 0

x 0 001aZE ox.8

W q

0.6

0.4-/

0,2-1.5 -1 -0.5 0 0.5 1 1.5

LOG (flfmc)

Fig. 6. Plot of normalized Young's loss modulus versus normalizedfrequency for chlorobutyl rubber at T. = 243.15 K. Linerepresents fit from KWW function with f 0.475.

274

.05 I I I I IIIII

295K

.04

. Zr'0 ±' 6 phr SP1055 +OPG + M6TS

.03 - -Ooi0

# 00',,4 ZnO + 8 phr SP1055 0000

.02 0 * o

ZnO + 6 phr SP1%05ý5 g* 0

.01 -- Ill • ::ii 0 2,.,~o Zon0ooo C) 0

0 =%R9M1--bO[] 0 0 El Rb 0

102 103 104 105FREQUENCY (Hz)

Fig. 7. Plot of dielectric loss as a function of frequency at 295.15 Kfor chlorobutyl rubber: clear squares, cured with 5 phr ZnO;solid squares, 5 phr ZnO and 6 phr SPl055; solid circles, 5 phrZnO and 8 phr SP1055; clear circles, 5 phr ZnO, 6 phr SP1055,2 phr MBTS, 0.5 phr DPG.

The effects of different cure systems upon dielectric relaxationbehavior can be more clearly seen in Fig. 8, where the dielectric loss isplotted as a function of temperature at a reference frequency of 1000 Hz.The systems that use the brominated methylol phenol resin, SP1055, showrelatively strong maxima in the range of room temperature, although someweaker frequency dependent dispersion is still present at lowertemperatures. This is consistent with the primary mechanism of chargeconduction in these materials being due to polar materials used in thecrosslinking system.

Plots of log f versus 1/T were linear for the systems usingbrominated methylolzphenol resin cures, indicative of a thermallyactivated process. An example of this is shown in Fig. 9, which depictsrelaxation maps for a butyl and two different chlorobutyl rubbercompounds. The range of log f versus 1/T values that could be plottedwas limited by the fact that W peak of the dielectric loss tended todrop below the lowest frequency at which reliable measurements could beachieved as the temperature was lowered. It was found that thedielectric spectra taken at different temperatures could be superimposedreasonably well in a master curve of e /' versus log (f/fl ), whenthe portion of the transition considered tm"be alpha in character wasconsidered (Fig. 10).

"275

.051000 Hz

.04

_.0 ZnO + SP1055 +

o° 0 o MBTS + DPG

0 0wo000

0 0ee0 ee00 ZnO + 8 phr.02 0 SP1055

0 0 ZnO + 6 phro • a 0 IOO SP 1055

e 0.01 o° • 0

0 a 0 0 ZnO

200 225 250 275 300 325 350

TAPERATURE ('K)

Fig. 8. Plot of dielectric loss as a function of temperature at 1000 Hzfor chlorobutyl rubber: solid squares, cured with 5 phr ZnO;clear squares, 5 phr ZnO and 6 phr SP1055; solid circles, 5 phrZnO and 8 phr SP1055; clear circles, 5 phr ZnO, 6 phr SP1055,2 phr MBTS, 0.5 phr DPG.

5

3

Ot+ ZI O + ....0

is 3.1 3.3 3.5

I/t EI000 ('K')

Fig. 9. Relaxation maps for butyl rubber and chlorobutyl rubber with twodifferent cure systems.

276

Aj~

.75 3C-2C7K

X O~ 293K=E

S .5K'-C

.2 5 o0

0

313K

CI o

-2 -1

LOG (f " )

Fig. 10. Master curve of normalized dielectric loss versus f/f for

chlorobutyl rubber cured with 5 phr ZnO and 6 phr SP105rsin:

open circle, 313K; open square, 307K; open triangle, 293K; and

solid circle, 287K.

Addition of plasticizer showed an effect upon the dielectricrelaxation, in both the butyl and chlorobutyl systems, that was analogousto the dynamic mechanical relaxation when plotted as a function oftemperature at a fixed frequency. The maximum in the dielectric lossincreased, and showed slight temperature shifts, as shown in Fig. 11.

The dielectric behavior of the systems could be fitted reasonablywell using the KWW function. This was done using both the tables ofMoynihan, Boesch, and Laberge' 5 , and a slight modification of the methodof Weiss, Bendler, and Dishon (WBD) 1. These authors define thedielectric loss function as

E'" = A z QP(z) (1)

where z= wr, P is the exponential factor (called a by WBD), r is therelaxation time in the KWW function 0(t) = exp -(t/r) , w=2rf, with

Q•(z) = eP cos(zu) du, (2)

0

and

A = E0 - , (3)

277

The peak of the loss data was first fitted with a third orderpolynomial to locate the peak position and height. The values of r and Awere then determined by using the approximations found in Ref. 16. Thisinformation was used, along with approximations for Q given in Ref. 17,to calculate the loss values for a given combi;fation of beta andfrequency. Brent's method'i was employed to determine the value of betaiteratively by minimizing the value of the difference function

max

D(P) = (e'' ()calc - '(W)data 32 (4).

W=W mimmn

The two methods gave good agreement. An example of the type of fitobtained is shown in Fig. 12. The fit was found to be better for certainmaterials and at certain temperatures than for others. All of thematerials showed values of the fit factor, P, in the neighborhood of 0.4,as has been observed for many other types of polymers. The value of Palso tended to vary somewhat with temperature. In comparing differentchlorobutyl rubbers, those with the more complex crosslinking systems hada greater temperature dependence of P (Fig. 13). The KWW fits were notdone at all temperatures for these materials, due to the fact that theloss tended to decrease in magnitude and shift to lower frequencies asthe temperature was lowered. The entire transition region was thereforenot covered at lower temperatures. The low temperature dielectricspectra of the zinc oxide cured rubber could be fitted to the KWWfunction, with a PO value of 0.375.

.051000 Hz

.04-

.03

.02 10 phr Plaacizer 0 0 %Soo 5 phr PloavclIer

00O00 03

0.01- 0 00

0~~ 00 o 0-o

0200 225% 0 phr Plasticizer

20 225 250 275 300 325 350TEMPERATURE (- K)

Fig. 11. Plot of dielectric loss as a function of temperature forchlorobutyl rubber with varying plasticizer loadings.

278

7 -

.75 \//

, -"W 00-w "/ " "•

/ .50 /

01 1

W "\0

50 9

-2 -1.5 -1 -. 5 0 5 1 1.5 2

LOG (f/fmaxi

Fig. 12. Normalized diejectric spectrum for chiorobutyl rubber at294.15 K. System cured with 5 phr ZnO, 6 phr SPI055, 2 phr

MBTS, 0.5 phr DPG. Lines r-oresent solines through points

calculated from KYX function with f 0.35.

0.5

EU

znO+

0.45 -A SP1055

0.45

A

A A

0.35 ZnO + SP1055 +

MM + DPG

A0.3

0.25 1 A280 290 300 310 320

TEMPERATURE (" K)

Fig. 13. Effect of temperature on value of exponential factor in KWW

function for chlorobutyl rubber with two different cure

systems.

279

DISCUSSION

The primary molecular mechanism involved in both the dielectric andviscoelastic relaxations in these materials is largely an alpha one, withsome merging of beta character. Phenomenologically, the polymer networkscan be viewed as long-chain molecules that are tied together at certainpoints by other smaller mclecules, perpendicular to the main chains, thathave rotatable, permanent dipole moments. These can be perturbed bythermally induced interactions with near neighbors in such a way as toproduce a set of oscillators with a distribution of frequencies. Theoverall effect is one of cooperative relaxation, i.e., thermally inducedrotation coupled with main chain segmental motion.

The fit parameter, P, in the KWW function can be viewed as a measureof the variance of the underlying distribution of relaxation times 1 9 . Inthe present case, the fact that the more complex cure systems havesmaller values of p for the dielectric curves can be rationalized on aphenomenological basis by noting that they contain additional types ofcrosslinks that differ in the rotational energy required, and thepolarity of molecules that are contributing to the oscillator strength.In all three cases, stearic acid is also used as a processing aid whenthe rubber compounds are milled. It is not clear what role, if any, thisplays in the dielectric behavior. Some small residual dipolar activitywill also be present from butyl zimate and calcium stearate that are usedas stabilizers in the butyl and chlorobutyl gums, respectively. Thebrominated methylol phenol resin-zinc oxide system will form carbon-carbon bonds, and bonds which incorporate the resin between polymerchains. The systems incorporating MBTS and DPG use these as cureaccelerators. It is not clear from published literature whether theywill also form sulfidic crosslinks, and possibly crosslinks incorporatingthe amine structure, or accelerator decomposition products that areattached in some manner to the rubber chains. In contrast, the behaviorof the zinc oxide-cured system appears to lend support to the formationof carbon-carbon crosslinks in this cure system, rather than carbon-oxygen-carbon crosslinks2 2 ' 23 . These would be expected to show behavior

8analogous to sulfur cured systems

It was desired to determine whether the dynamic mechanical data couldbe related on a molecular level to the observed dielectric behavior, ashas been done for other polymers. DeMarzio and Bishop24 have derivedrelationships between dielectric and mechanical susceptibilities foramorphous polymers. Diaz-Calleja derived simple relationships fromthese for calculating the viscoelastic tan 6 from dielectric data, andcompared experimental data for a number of polymer systems.

The question to be considered here is whether the KWW function issimply an empirical fitting function of such generality that it will fita large variety of physical phenomena, or if the differences between thefit parameters for the dynamic mechanical and dielectric data for themore complex cure systems can be explained in terms of basic molecularstructures and crosslink densities. The crosslink densities, and averagevalues of M between crosslinks, were evaluated from the tensile moduliat 100% elongation. As was also evidenced earlier by the Young's modulishown in Figs. 1 and 2, the crosslink density increases in going from theZiJ cure system to the ZnO, SP1055, MBTS, and DPG cure. The numberaverage molecular weight of segments between crosslinks decreases fromapproximately 22,00 to 14,000.

The dielectric relaxations are clearly cooperative ones. The dynamicmechanical relaxations are also cooperative, but appear to be influencedmore by segmental motions of the u-.in chains. The fit parameter for the

280

dielectric and dynamic mechanical data are the same for the ZnO curedmaterial, indicating a similar distribution of relaxation times andinvolvement of similar molecular motions for both processes. The basepolymer itself is a random copolymer of polyisobutylene and trans-isoprene, with approximately 2 mole % unsaturation. In the case of thechlorobutyl, it also contains 1.1-1.3 weight % chlorine, existing in theform of approximately 20% tertiary allylic chlorides, and a mixture ofisomeric secondary allylic chlorides in approximately equal"concentrations20 . These will differ in their reactivity, with thetertiary allylic chlorides being most reactive. These are the probablecrosslinking sites for the ZnO cure. This system will have the mostrandom distribution of crosslinking sites and largest average molecularweight of polymer between crosslink sites.

Increasing the complexity of the cure system increases both thecrosslink density and the types of crosslinks formed. The average"molecular weight of polymer between crosslinks will decrease, and therelaxation times for the polymer segments will become more uniform.Thus, the 2xponent in the KWW function will increase, indicating a moreuniform distribution of relaxation times as the rubber becomes morehighly crosslinked.

If this is a correct phenomenological explanation of the differencein the KWW fits to the dynamic mechanical behavior of chlorobutylcrosslinked with different curatives, then it is still not clear why thevalue of the exponent for the system cured with ZnO and SPIOS does notdiffer from that of the ZnO cured system. Part of the reason for thismay be a temperature dependence of the KWW distribution for the rubberscured with the three different cure systems. This can not bedefinitively established by the method used here, since shifting themaster curves to another reference temperature will simply transpose themalong the frequency axis, and have no effect on the KWW fit. All threecure systems were shifted to the same reference temperature, but thetemperature dependeaice of their dynamic mechanical relaxations isdifferent, as shown earlier in the Young's modulus and loss tangentcurves of Figs. 1 and 2.

SUMMARY

The temperature and frequency-dependent Young's modulus and losstangent have been examined as functions of cure systems and plasticizerloading in chemically crosslinked butyl and chlorobutyl rubbers. Thecrosslinked materials exhibited thermorheologically simple behavior.Dielectric permittivity and loss were measured as functions of frequencyand temperature. The viscoelastic and dielectric behaviors weresignificantly influenced by the type of crosslinking system and byplasticizer loading. The Kolrausch-Williams-Watts "stretchedexponential" function was found to be a reasonable fit to both thedielectric and dynamic mechanical spectra. The effects of molecularmotions and cooperative behavior upon the two types of relaxations havebeen discussed.

ACKNOWLEDGEMENTS

This work was supported by the Office of Naval Research.

REFERENCES

1. P. Hedvig, Dielectric Spectroscopy of Polymers, Ch. 5 and referenceslisted therein, Halsted Press, New York (1977).

281

2. N. G. McCrum, B. E. Read, and G. Williams, Anelastic and DielectricEffects in Polymeric Solids, Ch. 10 and references listed therein,John Wiley & Sons, New York (1967).

3. B. E. Read, Polymer 30, 1439-1445 (1989).4. P. Colomer-Vilanova, M. Montserrat-Ribas, M. A. Ribes-Greus, J. M.

Meseguer-Duenas, J. L. Gomez-Ribelles, and R. Diaz-Calleja, Polym.-Plast. Technol. Eng. 28, 635-647 (1989).

5. E. R. Fitzgerald, Polymer Bull. 3, 129-134 (1980).6. R. N. Capps and J. Burns, J. Non-Crystalline Solids 131, 877-882

(1991). See also Refs. 7-9 in this paper.7. S. P. Kabin and G. P. Mikhailov, J. Tech. Phys. (USSR) 26, 493-497

(1956).8. R. Bakule and A. Havranek, J. Polym. Sci. C53, 347-356 (1975).9. D. Boese and F. Kremer, Macromolecules 23 829-835 (1990).

10. Relaxations in Complex Systems, K. L. Ngai and G. B. Wright, Eds.,Naval Research Laboratory, Washington, D. C. , Oct. 1984.

11. J. Non-Crystalline Solids, Vols. 131-133.12. C. M. Roland and K. L. Ngai, Macromolecules 24, 5315-5319 (1991).13. E. Mazeau, J. Perez, and G. P. Johari, Macromolecules 24, 4713-4723

(1991).14. N. K. Dutta and D. K. Tripathy, Polym. Degr. and Stability 30, 231-

256 (1990).15. C. T. Moynihan, L. P. Boesch, and N. L. Laberge, Phys. Chem. Glasses

14, 122-125 (1973).16. G. H. Weiss, J. T. Bendler, and M. Dishon, J. Chem. Phys. 83, 1424-

1427 (1985).17. M. Dishon, G. H. Weiss, and J. T. Bendler, J. Res. Nat. Bur. Stand.

90, 27-39 (1985).18. W. H. Press, B. P. Flannery, S. A. Teukolsky, W. T. Vetterling,

Numerical Recipes: The Art of Scientific Computing, CambridgeUniversity Press, NY, 1986, pp. 283ff.

19. C. P. Lindsey and G. D. Patterson, J. Chem. Phys. 73, 3348-3357(1980).

20. R. L. Zapp and P. Hous, "Butyl and Chlorobutyl Rubber", in RubberTechnology, 2nd. Edition, Maurice Morton, Ed., Van NostrandReinhold, New York, 1973.

21. L. Bateman, C. G. Moore, M. Porter, and B. Savile, "Chemistry ofVulcanization", in The Chemistry and Physics of Rubber-likeSubstances, L. Bateman, Ed., John Wiley & Sons, New York, 1963.

22. S. W. Schmitt, in Vanderbilt Rubber Handbook, R. 0. Babbit, Ed.,Norwalk, CT., 1978, p. 1 4 4 .

23. I. Juntz, R. L. Zapp, and R. J. Pancirov, Rubber Chem. Technol. 57,813-825 (1984).

24. E. A. DiMarzio and M. Bishop, J. Chem. Phys. 60, 3802-3811 (1974).25. R. Diaz-Calleja, Polymer 19. 235-236 (1978).

AC :om 3 &an For j/jDTIC QUALITY INSPECTE D 5 M13 1 (

Justif Lati-

AveilabilltT CoftdSail sad/or

Dist I Special

282

REPORT DOCUMENTATION PAGE Form Approved

I 0MB No. 0704 -0188

Public reDorting burden for this collection of information is estimated to average i hour oer respor'se. Fnctuding the time for reviewing instructions, sear(hing eistng data sources.

gathering and maintaining the data needed, and Completing and reý ewing the collection of information Send comments regarding this burden estimate or ano other aspect of this

collection of information. including suggestions for reducing this burden to Washington Headquarters Services. Directorate for information Operatoons and Reports, 12 15 jefferson

Davis Highway. Suite 1204. Arhngton. VA 22202-4302, and to the Office of Management and Budget. Paperwork Reduction Prclect (0704.0188). Washington. DC 20503

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED1 19921

4. TITLE AND SUBTITLE S. FUNDING NUMBERS

Influence of Cure Systems on Dielectric and Viscoelastic PE - 61153NRelaxations in Crosslinked Chlorobutyl Rubber TA - RRO11-08-42

WU - DN280-2426. AUTHOR(S)

Rodger N. Capps, Christopher S. Coughlin and*Linda L. Beumel

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

NAVAL RESEARCH LABORATORY REPORT NUMBER

UNDERWATER SOUND REFERENCE DETACHMENTPO BOX 568337ORLANDO FL 32856-8337

9. SPONSORING/ MONITORING AGENCY NAME(S) AND ADDRESS(EA) 10. SPONSORING/ MONITORING

OFFICE OF NAVAL RESEARCH AGENCY REPORT NUMBER

800 N QUINCY STREETARLINGTON VA 22217-5000

11. SUPPLEMENTARY NOTES*TEXAS RESEARCH INSTITUTE, INC., 415 CRYSTAL CREEK DRIVE, AUSTIN, TX 78746-4725

12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Approved for public release; distribution unlimited.

13. ABSTRACT (Maximum 200 words)

The temperature and frequency-dependent Young's modulus and loss tangent have beenexamined as functions of cure systems and plasticizer loading in chemically cross-linked butyl and chlorobutyl rubbers. The crosslinked materials exhibitedthermorheologically simple behavior. Dielectric permittivity and loss were mea-sured as functions of frequency and temperature. The viscoelastic and dielectricbehaviors were significantly influenced by the type of crosslinking system and byplasticizer loading. The Kolrausch-Williams-Watts "stretched exponential"function was found to be a reasonable fit to both the dielectric and dynamicmechanical spectra. The effects of molecular motions and cooperative behaviorupon the two types of relaxations have been discussed.

14. SUBJECT TERMS 15. NUMBER OF PAGES

Dielectric spectroscopy Young's modulus 14Kolrausch-Williams-Watts function Cure systems 16. PRICE CODE

Chlorobutyl rubber Copperative relaxations17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT

OF REPORT OF THIS PAGE OF ABSTRACT

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED ULNSN 7540-01-280-5500 Standard Form 298 (Rev 2-89)

Pre.(cribd by AN%1 tld 139-18298 102