Properties of Polyorganosiloxane Surfaces on Glass t o l W 1 3 . These high i F.iRIETY of organoM . J . H U N T E R AND M . S. GORDON silicon films h a l e been resisti7ities were mainDOW CORNING CORPORATION. M I D L A N D . M I C H . applied to glass surtained until the confaces. Contact angle tact angle to water A. J . B A R R Y with water, surface redropped below 60°. The histi\ ity, and dry lubricthermal stability of T H E DOW C H E M I C A L COMPANY, M I D L A N D . M I C H niethy lsiloxanes was i t ) of t h e treated surfaces T+ ere intariably higher t h a n t h a t of J. F. HYDE found to be ronsideraother aliphatic groups hl? increaaed oier the CORNING GLASS WORKS, CORNING, N. Y . inFestigated. Phenyl Talues for untreated groups appear to haFe R. D. HEIDENREICH glass. Contact angles thermal stabilitv i n t h e same range as methyl. of 90-110' were readily BELL TELEPHONE LABORATORIES, M U R R A Y HILL, N . obtained from a wide A study was made of selection of organothe f i l m spreading of several organosilicon derivatives on w-ater. RIonolayers silicon structures )t ith no marked systematic variations between species. The coefficient of friction for glass surof organosiloxanes transferred from water to glass surfaces treated with a series of alk>-ltrichlorosilanesdecreased faces by the Langmuir technique behave similarly- to films progressively as t h e length of the alkyl chain increased. All prepared b y dipping in solvent solutions. Development types of organosilicon films studied were capable of raising of these surface propertie; are attributable to t h e forniation of a chemical bond between surface film and glass. the surface resistivitv of glass from 10Wgor l W 9up to
,,
I
S EARLY laboratory research on organosilicon synthesis it was observed t h a t the surface of glass apparatus used in this work quickly changed from the normal behavior of the watxr]vetting type t o one of extreme water-repellent character. -%t the same time the feel of the glass became much smoother: this iiitlicated that the coefficient of friction also had been considerably affected. The tenacity v i t h which these filnis adhered t o t lie glass surfaces suggested the pospihliity of iniportant applicnticins in glass and ceramic industries. Furthermore, it was found ( 6 . 10, that the large loss in surface resistivity coninion to glass hodies under high humidity conditions could hr coniin:itetl by trc~atnirntwith a variety of organosilicon r ( ii n pounds. The present pitper deals with the results of a further stud. of t l i i i i l f f of ~ ~a ~varicAty of organoeilicon compounds on cleaned p1:t.s surf:rccs. The) treating method was varied iii accordance, tvirii the rcquiremvnts of 3pecific experimc,nts :ind the type of r~t~g:iiiosilicon compound involved. 1Icasurcmcntr of the contact a i i g l i s Irith \vatt.r, c~oc~ftiric~nt of friction, and el(~ctriealr t k t i v i t y iv('i't' u c c d :is iii(~:iiis o f cwduation. In this nxrnner thi, cffect of b t I uvturi, or (~Iiaraeter of the organosilicoii compound, d k y l chain lt'iipt 11, and t h e effect of tciniperaturp on such trcatcd surface;
PREPARATORY PROCEDURES
G L . I ~ . Cenco niicroscope hlidc>soi soda-iiiiic glarh. irhere indicated, n-ere cleaned n-ith chromic acidhult'uric ar,i(l cleaning solution, repeatedly ~ a ? l i e t irith l distilled n-at er, : t t i ( I tlried first with a blast of tr-arm air and thcn over an open gas fl:inic,. Slides clcaned in this nianncr showed a 0" contact angli. \\.it h n-ater. 111t h e crperirnents \rliere . borosilicate glass was used, t h e pinto and the rider n-ere 111 eally cleaned by polishing v-ith i'ouge a n d water, rinsed, and d.ried as n-ere t h e slides. The Slides I'REPARIh-G SPECIMEh-S FOR RESISTII-IT?STTDIEd. ivity were handed n i t h uw.1 for measurcnient of surface r( ( 'LE.\SlSG
iiscd
d v e r by painting with Du Pont Company silver paint S o . 4503 and baking 5 minutes at 450" C. Two bands 0.5 cm. wide, 2.0 cni. loiig, and 1.5 cni. apart ivere applied t o each slide. For the tests performed on soda-lime SL-RF-ICE TREATAIESTS. glass, the microscope slides w r e immersed for 30 minutes in solutions containing 0.02'3 of Trarious organosilicon compounds in rcdist il1f.d benzene. The slides w r e then rrmovcd and air-dried. In some instances monolayers cast on n-ater by the Langmuir tcchnique Irere transferred to glass surfaces for comparison n-it,h films obtained by t h e solut,ion treatments just described. I n ord(,r t o deterniirie the effect of heat on the surface films so obc in a small muffle furnace for 15 minutes tsinrd, slidcs ~ e r placed wc.h at loo3 intervals up t o 600" C.. using individual slides for c,tich cxvnlua tion. I n thc study of trcatnipnts on borosilicate. glass the test surfaces consisted of 2-inch plane-squsre p1att.s. After rouge-polisliiiig, the!- n-ere immersed for 1 minute iii 0.1 III solution of the organoailicon derivative in toluene, tlrziiiled, dried in war111 air, i,inurvl iritli distillid \\-:iti,r, anti a,gaiii tlricd TEST IIETHODS
The angle of n-ottiiig 11-ith n a t r r vas iiimsC'os,r.tci. .ISGLE. ured in the nianiier of Adam and Jessop ( 1 ) coninionly 1cnon.n as the pIittc method. Static frici ion measurements were C'OEFFICIIXT O F FRICTIOS. conduc.ttd on treated microscope slitles hi- the tilting plate method of Imipiiiuir (8). The cocficient \vas evaluated :ts t,he tangent of t h angle t h a t t,hc plate !\-as tipped ai\-ay from the horizontal ixforr nioveinent of t h e glass rider occui~ivd. The rider used in tlic nieasurenients on thc slides of soda-lime glass \vas a borosilicate tripod n-eigliiiig 1.4 grams, the fcct of which were three spherical beads of about l.'s-inch radius stit about 0.5 inch apart. The rider in these tests n'as untreated; it n-as polished with clean crocus cloth before ench evaluation. Thrv tests werr nisde in an atniosphcxrc, of 50C; rplative humidity. 1389
INDUSTRIAL AND ENGINEERING CHEMISTRY
1390
W
W
z a I-
O
a *z 0 0
eo IoL-0
.
-
~
.
-___--
100
_L
+L -4
t,?
t---
3=---I
400
zoo
TEMPERATURE OF TREATMENT
('C)
Figure 1. Coefficient of Friction and Contact ingle Rleasured on Soft Glass Treated by Dipping in 0 . 0 2 q ~ Benzene Solutions of Alkjldichlorosilane*
I n ebaiuating the treatments on borosiliatc glass plt~tes,thc rider consisted of a hollow spherical segment of borosilicate glass of 3/4-inch radius weighing 8.6 grams; it was cleaned and treated in each test in a manner identical with the treatment of the plates. These tests were carried out under a bell jar in a n atmosphere of dry nitrogen. SURFACE RESISTIVITY.The surface resistances of the treated &des w r e measured a t 50% relative humidity betwren t n o dvered bands 1.5 cm. apart a t a potential of 500 voltq. DISCUSSION OF RESULTS
Experimental work reported here covers data obtaincd from a wide selection of organosilicon structures. These data are compiled in Table I. The observations on related compounds are discussed together under the appropriate group headings a? follow. ~~OSOALKYLDICHLORObIL4SES.The data, r e h t ing to contact angle and coefficient of friction measured on surfacw of sodalime glass treated with this class of compounds, are plotted in Figure 1, correlated with the temperature of the heat treatment of the slide after application of the layer. The contact angle initially observed with no heating, or on the slide heated t o 100' C., shows a n increase with the length of the alkyl group in the dichlorosilane used. Similarly, the coefficient of friction is reduced in a n orderly manner with increasing size of the alkyl group, just as found by Hardy and Bircumshaw (3) for homologous series of alkanols and fatty acids. These properties do not persist at elevated temperature, apparently because of oxidative attack of the alkyl group. In this regard the long lauryl group is quite vulnerable, and serious loss of hydrophobicity and dry lubricity are already apparent at 200' C. The contact angle for the ethyl and propyl compounds is quite low a t 300" C., whereas the relatively stahlc, methvl derivntivc s h o u i it, sharpest drop beyond
Vol. 39, No. 1:
300" C. For the surfaces treated with the lower alkyldichlor(tsilanes the change in coefficient of friction is not so striking, an11 even after 15 minutes a t 400" C., the surface treated ivit,h t,h(mct'hyl derivative is still at, it,s original level. The coefficient 0 friction for the glass used in these experiments was found to 11. 1.46. The absence of st'rict parallelism between the contact anglc a11i friction coeficicnt where the burning off of the methJ-1 group 1: concerned can probably be explained by the fact, that only b, random or patchwork defect in the surface layer is created. Contact angle measurements are a function of adsorptioIi, a molcr.. ular phenomenon which is not critical where the adsorp'tioii areas are in t,hc order of t,he size of n-ater molecules or aggregates O ' water molecules, whereas frict,ionmeasurement, probahly conccrns a niacro effect distributed over the whole area of contact betwr~cr t.he surfaces involved. The fisat,ion of the surface layers responsible for t lit, propertirJ> just given is believed to be attributable t o a reaction. n-ith thc vlimination of hydrogen chloride bot.wcen thc organosilicori halidc and the surface hydroxyls (both Si- -OH of thc glass snrfnce ant; ihv rvater adsorbed thereon). ALKYLHYDROPOLY~ILOXASES, (ItHSiO),. These coniposit,iuiic are derived from the above alkylhalosilanes by hytlrolysis ir , ether solution a t 0-10' C. 'Benzene solutions thereof, appliec t o soda-lime glass, show coefficients of friction and contact anglet which correspond quite closely to the values for the nionoalkyltliclilorosilant~s. These data are plotted in Figure 2 . .\gain the vontsct, angle is highest for the Lorol d e r i v a t i h (derivcd from DIJ l'ont Lorol chloride, a technical grade of lauryl chloridc) ; t h e values for nicthyl and ethyl derivatives are sonicvhrt lower Thc results without heat treatmcnt irere slightly e r r a r k . T h e 1ut)ricating character resulting from these treatments is clit,cctl> tlrpendent on the size of the R group in the compound eiiiploycd T h c Lorol derivative s h o w the loaest coefficient of friction hui ,uffcrs thc most, serious destruction on hcating around 200" c'. 07 ahovc. .~LKYLTRICHLOROSILASES, RSiClS. The Lorol aiid stcary. inembers of this class of compounds irere applied to soda-lime and the glass in thr samc manner as the rrlk~-ltiichlorosilani~~.
2
P I-
o
LL
iL LL
0
c
,
w
I
2
-
0 LL
LL
W
0 0
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A (3
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U
b 2 z 0
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TEMPERATURE OF TREATMENT (T.)
Figure 2.
Soft Glass Treated in 0.02% Beezene Solutions of hlonoalkylsiloxanes
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1947
PROPER TIE^ TABLE I. SL-RFACE Cornrround MeHSiCln EtHSiCln PrHSiCIz LoHSiCI? [.\IeHBiOII [EtHSiOIr [PrHSiO], [BuH8iOjr rLoHSiOIz [Ph€IFiOil LOPIC13 StSiClr [StSOl.sIn StBi(0Et)s [StXeSiO I StMeRiCltt LoMeSi(OEtj2 L o h l e Si f 0 E t j n Lo.\leSi(OEtj? ' 500-cs. dimethylsiloxane
OF
SODA-LIXE GLASPTREATED T? ITII Y.~RIOL-S ORG.ISOSII,ICOZDERKATIVES
C o n t a c t Angle after 1 5 Min. a t the Following T e m p . ( " C.) 25 i u o 1.x x i 0 2 x 1 YOU 400 87 IJ V1 B :i
Coefficient of Friction after 15 A h . a t t h e ~ l ~ ~ ripsistanc:t ~ i Folloa-ing Temp. f o C.) ___ at 50% Relative 100 1% 200 250 300 400 IIuniidit>-,Ohms , . . . . .' 0 60 o.tin 0 . ~ 5 I!. (in 0 62 .... . . , 0.55 0.53 0.78 . ,.. 0.51 0.42 0 . 5 9 0.81 0 3 x l(!l, 0.31 I ) . .i5 0 . 5 9 0 50 . .., 0 . 5 4 0.59 0.40 0 . (52 . . . . . , , . . . . 0.44 0.02 @:is 0.33 U.4.5 0 . 5 8 ... ,. 0.40 11.44 0 . 4 4 . .... 9 . 0 Y 1012 n 36 o.~.~$Ii ! , 4 i (1.ci0 O i T , 070 1.0x 101, 0.36 i . 0 X 101: , , 3 . L i X 10'2 ..
83
8n 9 il
T0 107 95 2! i
e
. . ( 0 a t 350',
Stearic acid Stearic acid i, a C e n t o rnicruscol>c qlides: :iirst~,lcr angle b R-l:iyprs transferred from water 2 B-layers transferred f r o m 0.01 . Y HCI.
(0 a t 350") ii (0 a t 4AOC! 103 (85 a t ?$I,
0 a t LO , 63 (44 a t 4 7 5 0 0 a t 500:1 51 81 (GO a t 460 , 0 a t 473:' nii 3 4 (33 a t 3.50 , 0 a t 425'! 7-1 , , ($9 a t 350". 0 a t 375') 'I 1 83 lsiloxane IIeptamer (1,lY-Diethoxytetradecaheptasiloxane)
--.
-.-,
on 0.01 V hydrochloric acid on distilled water
November 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
1393
\\.here a,: is taken as the extrapolate area at zero p
TABLE111. FORCE-.~RE.I REL.\TIOSY FOR DIUETHTLSILOXISE change in area \vith P, the chiingc in force. HEPTAJIER FILMox 0.01 .V HYUROCHLORIC Icm The limiting area au io e expansion curve in F i p e 7 is (Weight of polymer spread, 2.28 X 10-0 grams; number of niolecules i n film, 1.095 x l O 1 ; ; number of lIe28i0 units represented, 7.665 X IO") Calculations Observations Torsion Pressure on Harrier position o n a angle 8, I;ilpl area, film = 0.299, 14-cm trough, e m . degrees sq. X./Si unit dynesjen~.
Iluring Colnpresaion
0 00
20
0 58 3 48 7 25 13 6 18 3 22 3 27 6 30 7 30 7 30 7
18
16 11 12 11 10
9
s 6 Iluring Expansion
8 Y
10 11 12 13 14 16
106 68
11.8 16 4
41
IS 0
27 16 8 2 0
21.6 23 4 26.2 28.8
19.6
30 7 19 7 11.9 7 83 4 35 2 32 0 58 0 00
gram of the derivative was placed on the freshly s w p t water surface of a Cenco hydrophil balance. After evaporation of the solvent, the area of the remaining H-laver was compressed and expanded by nieans of a movable barrier while the surface pressure was simultaneously determined by nieans of a float connected to a torsion head. The data relating t o the h:ptamer appear in Table 111. The area, computed in square Angstroms for one (.\Ie2SiO)unit, was plotted against the observed pressure of dynw per mi.; the fbrce-area curve so obtained is illustrated in Figure 6. On pure distilled water the film behavior was as sketched i n Figure 6 by the broken line. I t s large area a t lon pressures intlicated a highly unoriented film which showed a high degree 01' compression at 12-15 dynes per cm., apparently attributable t . ) poor orientation. This erratic character \vas overronie when the layers were cast on 0.01 S hydrochloric acid. Here the molecules were probably oriented with respect t o the aqueous surface by a n ion-dipole interaction hetn-een thc hydrochloric acid and the Si-0 bonds, enhanced by a strong dipole-dipole interaction between the water and t'he terminal hydroxyls generated by hydrolysis of the ethoxy groups in the presence of hydrochloric acid as a catalyst. The better orientation of the molecules n-ith respect t o the aqueous surface apparently permitted easier orientation with respect t o each other on the application of slight pressure (to about 14 dyne? per cni. on the compression curve). Above this point the niolecular orientation appears t o be nearly complete, and the curve straightens out and shows a normal compressibility behavior. The film collapsed a t a pressure of about 31 dynes per cm. X h e n pressure was slo\vly released, t,he expansion curve showed hysteresis; it \vas roughly linear down t o about 6 dynes per cm., beloiv n-hich pressure the expansion Lvas enhanced by disorientation or reversion of the film t o a state represented by that of the compression curve. The behavior of t.he heptainer was typical of the series of pol)-mers from pentamer through undecanier. D a t a taken from the curves for each polymer are compiled in Table IT'. The average values representative of t'he series were used t,o construct Figure 7 . The linear portions of t'he compression and expansion curves are nearly parallel and indicate essentially the same compressibilities in the order of 0.016-0.019 per dyne per em. calculated from the formula:
-1 , Aa _ (I"
AF
011 curve ahout 25 square Angstroni about 22, and for the comp units, From the limiting density of 0.075 for dimethylsilosane polymers the xolumc of one flIrs2SiO) unit, may be computed to be 125 cubic Angstriinis. Dividing the limiting area: into thie volume gives a film thickness in the range of 5.0-5.7 A. This is compatible n-ith measurcments made on Fisher-Hirschfelder 'models of the polymers in their most extended form. I1 is concluded from these ohscrvations that the films w r c monomol(vular layers. The trimer and tetramer depart from the other members i n the, above series (Table IT). The thickness of the layer generated on expansion of the compressed film, particularly in the case of the t,rimer, suggests that the niolecules have been up-ended and lifted from the surface, and that a random network of strong dipole interactions (hydroxyl end groups) maintains the film in a disoriented state. The behavior of the high polymer coniniercial (DC 200) fluids was inconsistent, with observations on t h e group typified by Figure 7. The force-area curves for a 7 k e n t i s t o k e and a 200centistoke commercial fluid are sketched in the figure by dotted lines; these shon- collapse of t,he films at, rather low pressui'cs (about 10 d)-nes per em.). Sonpolar end groups (.\le3SiO-~l and possibly a small amount of chain branching in these conipounds may be responsible for easier lifting of the films. That solution treatment of glass with t,hese fluids gave better contact angles than the more easily orientable ethoxynnd-blocked dccamer (Figure 5 ) is at,tributable to loss of the latter, since this lon. polymer is more easily volatilized. This was overcome, and the tiilcanier showed much improved contact angles when it was trarisferred as a B-layer from 0.01 S hydrochloric acid, where hydrolysis of the ethoxy groups generated strongly polar hydroxyl group?, which fixed the chains to the glass surface (Table I ) . CO?JP.%RISOS O F B-LAYERS A S D S-LAYERS.K h e n nionohyers of a number of organosilicon compounds were prepared on an ttqueous surface and transfrrred t o glass slides by the technique of Langniuir, a number of interesting observations were made. First, the slide did not pick up a layer when passcd d o x n through the surface film on water; when PvithdraTvn, a monolayer was picked up. This signifies that polar centers vere absent on the top face of the layer hut were concentrated on the film-nater
___
I -
COLLAPSE
-
I
30
I
I
I
AREA
PER DIMETHYL SILOXANE
3")
G :[ o
IN
Az
Figure 7. Force-Area Curves Showing .li+erage Values for t h e Ethoxyl-End-Blocked Dimcthylsiloxanes, EtO(JIe,SiO),Et, from t h e Pentamer through Hendecamer on 0.1 S Hydrochloric Acid
P 394
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 39, No. 11
interface. The amount of material transferred to the glass slide in e:tcil case could be read directly from t,ht, hydrophil balance. and it checked the, apparent area of tht, slide \vithin a fer< per cent. Further, the slitic \vas n-et when \tithdia\vir from thr n.atei,; thi.: TEMPERATURE OF TREATMENT PC3 indicated that t h c Figure 8. (.oitiparison of S o l ~ m t - . ~ p p l i e tFilmc l v ith silosaiie i Icri vat iw Films of (:ompressed IIoriolaj ers Transferred t o (;lass was aepar:ttcd froiii from i q i i e o i i 6 Surface the gla.ss surface t)) a film of xater. -11 tcuipt'i'ature+. 'r1~1, high c o n t a ~ ariglcs i rhus are atttributablc buth this poini tlic 1ayc.i t o a layer ol h y h p h o b i c alkyl group!: oriented outward in a n u ~ i could e:isily t x ible film and t80a paucity 01'polar centers ( t h Si-- 0 -Si washed i i ~ u m thc iOII groups of the original glass surface) where the natcr glass st1rf:iw: :+tmight i.>tablishIiyclrogm bridges as a prerequisite to nc.tting. tempts t o mc':%sur(That the solvunt, layers n-ere ne>xlyidentical in character t o thi. cont:ict :ingl~onth(, trniisi'errcd monolayers (E-layers) was demonstrated by contact f r e s h f i l n i oitc,rl P on mivroxopr slicles for several compound: a ~ i g mc~aaurenient l~ ahon-cd ricarly 0" valurs. Ihi ~ i i ~ i i ~ l - laid i1on.n in tmtti nianriers. -1 few examples are plotted i n Figuw 8, where tlic contact ang1t.s were determined on the heatiiig at rooni terntrcaatcct slides; the d-layer:, (those from solvents) arc indicated pc'rilture until the by the solid lirics and the E-layers by the broken lines. I n the water film \ i - : i ~dricd loiwr ret of curvcs, st,ea,ricw i d shall-ed practical identity of hoff, t l w contact havior Cor the two nictliods of application. The same may br angles \vera found said for I,olIedi[OEt)r a 3 justified hy the middle eet of CUI Tiit, uppc'r set of i-urves comp:tres the application of (StlIeS valucs recorded i l l or StlIeSi(OI-I)pfrom solution with the B-layer from 8tlleSiCIz, the t:ihlcx: they im\thicli v a s hydrolyzed at, the aquenus surface from which the proved oiily hlightly bscquently transferred. The close agreement of E011 aging 12 hours. siiggwt. that the latter wprosent essentially monoThe layers wore layer depusitions in common firmly adht.rcbiit t o The corit,act angles for the the glass, probably wlative1~-lon- compared wit,h the oqganosilicon film5 which arc by dipole aasociahigh by virtue of fixation, t o some w t e n t a t least, by chemical tion or hydrogen react,ion (silanol c:ondcnsatiiin) as already described. Further bonding o f the silyindicatiori of t,his vimvpoirit is manifest in the tenacity of t h r anol hydrosyls t o stearyl niethyl silicone film on washing tlic slide with solveiits the Si--O---Si or under conditions ~vherebystearir acid films 1yei-e removed. The SiOH of tlic pies., rase for the LolTeSi(0Et)p is probably intermediate by rcason of and vice vers:-siloxane,dimethylsilosane, diethylsilosane, and nieth~lplienylsilosanepolymers $iio\vetl surface resistances in the order of 10'2 t o 10'3 ohms against n value of 108 t o 109 for tlic untreated glass slide. On testing the treated slides after 15 minutes of heating a t various tivities persisted up t o 375temperatures, the high surface r 400' C., hut the films burned off above this temperature range. Although stearic acid films shorved resistivities of the same order of magrlituric. the effect \vas lost sharply above 300" C.
1395
I n general the data show that, when the contact angle of a treated surface drops below 50-60", the electrical resistivity diops by a factor of the order of lo4. There does not seem t o be any direct correlation between resistivity and contact angle for angles above 60". The resistivlties are pretty much the same ithether the contact angle is 70" or 110'. From Livingston (9) a contact angle of 50-60" would correspond t o about 75q0 of a complete layer adsorbed. On this basis three fourths of a complete layer is sufficient coverage such t h a t the film conductivity becomes quite small. -1possible conclusion, then, is t h a t for contact angles greater than 60°, the conductivity is due chiefly to the subsurface moisture which passes from t h e atmosphere through the layer of organic molecules and into the surface la\-ers of t h r glass. Thus, Ivhile the contact angle, determined by the characteristics of the top of the organic layer, is high, the resistivity reaches a limiting value, since the conductivity is deti~rminedby the moieture content just beloiv the organic layer. LITERATURE CITED
K., "Physics and Chemistry of Surfaces," 3rd ed., p, 182, London, Oxford Univ. Press, 1911. Adam, N. K., and Jessop, G., Proc. R o y . SOC.,110, 423 (1926). Hardy, IT.,and Biicumshaw, I., Ihid., A108, 2 (1925). Hunter, 11.J., and Fletcher, H. J. (to The Dow Chemical Co.), G. S. Patent 2,415,389 (Feb. 4 , 1947). Hunter, hl. J., Hyde, J. F., Warrick, E. L., and Fletcher, €1. J., J . Am. Chem. Soc., 68, 667 (1946); Hunter, SI. J., Tarrick, E. L., Hyde, J. F., and Currie, C. C., Ibid., 68, 2284 (1946). Johansson, 0 . K., and Torok, J. J., I'roc. Inst. R a d i o Eng., 34, 296 (1946). Langmuir, I . , J . Am. Chem. SOC.,39, 1848 (1917). Langmuir, I . , Trans. Faradag Soc., 15, 62 (1920). Liringston, H. K . , J . Phgs. Chem., 48, 120 (1944). Korton, F.J., Gen. Elec. Rev., 1 (Aug. 1944). Yorton, F. J. (to General Electric Co.), U. S.Patent 2,386,259 (Oct. 6, 1945). Sauer, R . O . , Scheiber, W. J., and Brewer, S. D., J . Am. Chem. Soc., 68, 962 (1946).
(1) Adam, N.
(2)
(3) (4) (5) (6)
(7) (8) (9) (10) (11) (12)
RECEIVED M a y 28, 1947.
POLYMETHYLSILOXANES..
..
Thermal and Oxidation Stabilities D. C. ATKINSI, C. M.
M U R P H Y ,A N D C. E. SAUNDERS
NAVAL R E S E A R C H L A B O R A T O R Y . W A S H I N G T O N . D . C.
. i R L 1 in the war the polvorganosiloxanes (19), or silicone fluids, were brought to the attention of the S a v y although they Tv-ere still in the development stage. Because of their small rates of decrease of viscosity with temperature, their lo^ vapoi pressures and low freezing points, and the vide range of viscosity grades available, these fluids were investigated as possible lubricants and poTver transmission fluids for unusual applications. -4s the polymethylsiloxanes have very low temperature coefficients of viscosity and adequately low freezing points and vapor pressures, this type of silicone polymer has been the most carefullvstudied t o date. The synthesis and many of the physical and chemical properties of the methyl-substituted polyorganosiloxanes have already been described ( 5 , 4 , 6 , 7 ,11, 12, 17, 18, 19, 81, 2 3 ) . Silicone polvmers may be prepared having linear, cyclic, branched, and cross-linked structures ( 4 , 11, 17, 18)) depending .on the methylchlorosilanes hpdrolvzed. The commercial polymethylsiloxanes ( 4 , 17, 18, 19, 21) are mixtures of essentiallv 1
Present address, The Cniversity of California at Loa Angeles, Calif
linear homologs with a more or less wide range of molecular weights, depending on the viscosity. The polymethylsiloxanes may be used as lubricants under certain conditions ( 5 ) and as hydraulic fluids in systems employing gear and piston type pumps (9). Other applications to lubrication have been discussed (6, 14, 15, 18, 19, 21,bd). These fluids were also found t o be much less flammable than commercial lubricants and hydraulic fluids (20). The polymethylsiloxanes have been reported to be very resistant to heat and thermal oxidation, but no information is available concerning the safe temperature range of operation, the nature and objectionability of the decomposition products, and possible catalytic effects of metals. This article is a summary of our work on the oxidative and thermal breakdown of polymethylsiloxanes and related catalytic effects. Table I lists the polymethylsiloxanes discussed and some of their viscometric properties. The viscosity-temperature coefficient (24, $5) is defined by the relation,
