TitleThe reaction of high polymers in solution : the alkalinesaponification of polyvinyl acetate : I. On the method ofmeasurement of reaction velocity

Author(s)

Citation 物理化學の進歩 (1941), 15(3): 78-85

Issue Date 1941-05

URL http://hdl.handle.net/2433/46267

Right

Type Departmental Bulletin Paper

Textversion publisher

Kyoto University

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THE REACTION OF HIGH POLYMERS 1N SOLUTION:

THE ALKALINE SAPONIFICATION OF

POLYVINYL ACETATE.

I. On the Method of Measurement of Reaction Velocity.

By A•rsuvnsu Iiox~uc~ii.

Introduction.

In the preliminary report it has been made clear that the formula;

(CH, : CH • COOCIi,)n+ nNaOH=(CHo : CHO H)„+nCHsCOONa

which was proposed to explain the saponification reaction of polyvinyl acetate with NaOH in metlv~tnol solution, is invalid in the case when NaOH is used in a less

amount than the equivalent quantity ; and, accordingly, it has been concluded that

it is irrationa] to measure the reaction velocity only from the concentration of

a~IaOIi in the said reaction.

In the present experiments, the reaction was carried oub in the water-methano]

system as in the case of Lee-Sakunda's experiment so that the reaction product may not be separated, in other words the system may be considered as homo-

geneous. It was exlxrimcntally examined whether the Cvatcr-insoluble part of thr sample collected at intervals from the reaction system was pure polyvinyl acetate and the part soluhle in water was proved to be almost pure polyvinyl alcohol.

tlnd by the determination of the forn~er the progress of the reaction was considered.

The Method of Measuring the Reaction Velocity.

S. Lee measured the reaction velocity only by the titration of NaOH from

the system, but the author pointed out in the previous report that it was not appropriate. The author also found that the polyvinyl alcohol which is insoluble

'in acetone is very -hygroscopic and apt to adsorb foreign substances so that the change of its weight does not follow any regular and dependable. course.

On the contrary, the weighing of the polyvinyl acetate separated by throwing the sample into water was found to be a very easy matter and the weight also

varied very regularly. Therefore, this method of weighing was adopted. Besides, the change of viscosity of the reaction systeiu was observed:

at a time • and poured mto 50o c.c. of distrlled water ; some precipitate was then obtained. The polyvinyl acetate thus formed-was filtered, washed, dried at [o5°C,

for 5 hours, and weighed. Thus the progress'of saponification reaction was observed

from moment to moment. , Front the pw'pose of the rapid coagulation of. the precipitate, g c.c. of saturated

ammonium bicarbonste solution was added. The order of mining solutions A and B was determined so as to avoid a temporary hirbidity produced immediately-after

mixing. Ry means of Ostn•ald's viscosimcter placed in the thermosLlt, viscosity was also measured, using g c.c. of the sample which was taken out 5 minutes after

mixing. In this case the change of specific gravity could not be measured.

(b) Identification of the Substance Weighed se Polyvinyl Acetate.

Ay the above stated method, commercial polyvinyl acetate, whose Imlymerisa-

tion degree was Got, ryas saponified.. The precipitate insoluble in water was t

collected from moment to moment during the reaction and dissolved in methanol till the amount reached a given vohime (25o~c.c.). 5oc.c. of it was poured into water, and from the precipitate obtained its concentration tvas.estimated, NaOfI methanol solution of known concentration was added to the rest of the solution and, from

Na01I consumed, the acetyl values as CFI,COOH were Calculated, tvhiCh arc shown

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N°. 3 TI[E ALKAt.INA SAPONIPICA770N OP POLYVINYL. ACETATE 79

Experimental Method and Examinations. ,~ (a) Experimental Method. -

flbout I5 g. of Itolyvinyl acetate manufactured by the Nippon Cbisso Company

was. dissolved in Sao c.c. of methanol at 20°C:; which is here called solution f1.

toc.c. of solution R was poured into distilled water. The precipitate obtained was

filtered, dried, and weighed to know the amount of the polyvinyl acetate used.

On the other hand, about log, of sodium hydroxide t<<-rs dissolved in 4ao c.c. of

ntcthanol, which is here called solution 6. "Phe concentrations of both solutions

tvcre properly regulated according to the object of the experiment. 8o c.c. of sol~-

tion B was put in a reaction vessel a•itha stirrer and held in a themtostat kept

at of I~[o°C. Iyoc.c. of water and ISoc.c, of methanol being added to it, the mixture teas stirred nt o°C. ~ Then, 2ooc,c, of solution fI kept at o°C, was added x;~ to it The volume change bytbe mixing being neglected, the ratio of the volumes ~̀ '~' of water and methanol ryas formd to be 43oi Iyo=2.5: t. ~'!

From the reactimt'system 20 c.c. of the material for analysis was taken out.~

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in Table I. '

If is not strange that the observed values are fairly discrepant from the theo-

retical value, G9.8/o, because tpe determination of the acetyl value is really hard

to make according to the theory. Judging from the (act that thc ,acetyl values arc not much different from one another in spite of the progress of the reaction,

the substance weighed may be regarded as pure polyvinyl acetate, and not a

partially snponified product.

Table I. Aaty] value of the weighed sample.

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q. 63.zfi 6o.z[ ~-53 6[.59 60.35 bq.3z

+• 5~ 6t.fiz 63A3 6[.59 60.53 . 64.v W.ob

(c) Identification ofthe high polymer in the filtrnte a polyvinyl alcohol.

It is important to ascertain whether the high polymer dissolved in water con-sists of polyvinyl alcohol only, or it contains any partially saponified product.

Experiments I and z were made for this object.

Experiment r.

The sanm materials were used as above (b) : sodium hydroxide of 3.33 g/I-initial concentration and polyvinyl acetate of ro.3o g/L initial concentration. The

reaction was made to take place at o°C. 20, 30, 40, and 5o minutes after the start

of the reaction, 500, 300, 200, and too c.c. of the solution were collected res-

pectively and poured into distilled- water and coagulated quickly with NhI,I-ICO„ and then the precipitate (polyvinyl acetate) «.~s separated by filtration. Froni [he

mixhire of the filtrate and washings, polyvinyl alcohol was easily coagulated, by adding pure Na~50., of 3o g. per rooc.c. of the mixture. The coagulated sub-sta~ice was filtered and the precipitate was washed with a saturated sohition of

sodium sulphate, until it no longer coloured pink with phenolphthalein.

The substance obtained was dissolved. in water and made up to 25o c.c. ; 50 c.c. of it was poured into acetone and the precipitate (polyvinyl alcohol) was

separated and weighed. As this. precipitate was very hygroscopic, the weighing

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was carried out with the greatest possible care to keep the air out. \M1'ith the .

rest of the solution, CH,COOH nas determined by the said n)ethod. The analytical

values obtained arc shoum in Table IL T'rom the table, it is clear that the poly-

vinyl alcohol which is soluble in water has :dtnost perfectly lost the acetyl radical, '

and that a little amount of Ci-I,000f{ remains adhering owing to impeticct purr ~~ fication or other cause. The analytical values show a tendency of a little decrease

as time goes on.

Ey)erin)cnt a.

The filtrate was evaporated under vacuum. and from the solution thus concent-

rated polyvinyl alcohol teas separated with acetone, not by the coagulation method 1'

with Na.SO,. The analytical method was the same as Ix fore. The result obtained

is shown in Tab1c~I, _ 'T'able II. ~~

Acetyl vnlue ns CHnCOOH of the pdyvinyl nlcohul. ,~ Atinules go qo go

F:xp. [. z.[4% [.z7% o.8q% r.

Exp, z. z.o3p(, [.3z% 0.69% •}

It is clear from this table that the acetyl value of the part of the saponified , }

product, which is soluble in water and coagulated and separated tvith Na.SQ. or ~, acetone, G not greater than ago, and that if may Ue regarded as almost pure

- polyvinyl alcohol in `comparison with &j.8/, the theoretical value of polyvinyl

acetate. 9

A very small number of acetyl radicals e'hidt decreases according to the lapse

of time is considered to depend upon the adsorption of methyl acetate due fo the

poorness of the metho(I of purification of such a high polyn)er.

(dl The Quantitative Correspondence between Polyvinyl Acetate

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Commercial polyvinyl acetate, (mean polymerisztion degree=535) was used

ryithout fractionation. ' Saponification xeaction was brought about a[ o°C. with

polyvinyl acetate of Ii.3oog/I. and sodium hydroxide whose initial concentration was 3.053 g/L. 3ooc.c. of the material was collected in aliquots to, zo, 30, and

4o minutes after the start of the reaction and poured into yaoc.c. of water to d•hich 5 c.c. of the saturate[l solution of ammonium bicarbonate was added. Over

a night iC was filtered anct washed. The precipitate obtained (polyvinyl acetate)

was weighed by the same method' as already mentioned. 1'he filtrate was concent-

rated to about [oo c.c. and poured into 30o c.e. acetone The following day the

precipitate thus obL•rined was filtered and washed .vith acetone and Neighed accord- ing to the method under (c). The quantitative relations of the both are shown in

Table III. - The ground molecular weight of polyvinyl alcohol is qq, a»d that of polyvinyl

acetate 8G. Though there is sudl a great difference in the ratio of nearly L: z

behveen them, the sum of their mots almost agrees with the values obtained irres-

pective of the lapse of time, It is, therefore, inferred that there is no room for eXistence of any other ;substance beside the above two and that the decrease of

polyvinyl acetate mot is equal to the increase of polyvinyl alcohol mot.

Tahle Iii.

Affnules 0 Io zo 30 qo

Nater iowluLle Subs. g/I. Ix.3ooo 8.7696 6.94z6 5•SSz6 o.o36a

Afol. as polyvinyl acetale. (alwve valoe-i-86J o.i3iq o.ro±a o.oSo7 a.o646 o.oaoq

\Valer soluble, aeetone insoluhie Sabstance C14 a r.~6q z.zi 3z z.y8;s 5.953z

~- bfol. ns pnlyvinyl alcohol (above value-4 qq) 0 ao3o6 0.503 o.a678 o.c353

Snm of the holh val. mol. o.t3[4 o.i3z6 oS3ia ai3zq o•I357

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The Preliminary Examination of the Reaction Velocity.

The above method mentioned under (a) was carsidend as one of the. direct

methods of m~suring the generated polyvinyl alcohol, and its applicability was

proved by the experiments render (b), (c) & (d). The follo~ring are preliiviniSry experiments of the saponification of the mmmcrcial sample at o°C. The conditions

of .the reaction are, summarized in Table IV. The progress of the reaction is

,graphically shown in the following figures, which arc very different Gom those in the ordinary case. I[ has rivo remarkable breaks. The concentration of alkali

greatly affects the reaction velocity. Tire polymerisation degree also affects the reaction velocity; the larger the holymerisation degree, the faster the reactio~i,

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The. viscosity change of the reaction system was measured ; chimgerof the trend of the curve agrees with the said breaks obtained from the above mentioned method

of weighing polyvinyl acetate in the reaction system.

The nature of the reaction will be examined in detail in the- next report. 'Cable IV.

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degreeInitial NnOH

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~ Summary.

The saponification of polyvinyl acetate has been made to take place with alkali

in water-methanol solution so as to be treated as a homogeneous reaction in solu- tion. The method of measuring the progress of the saponification by weighing

polyvinyl' acetate yet unreaeted has been adopted. 1'he preliminary c.periments were made at o°C. on commercial polyvinyl acetate, 1'he results obtained are. as

follows

(t) Wlten the cogcentration of polyvinyl acetate yet unreacted is measured during the saponification reaction, the number of the needy fomred mots of poly-

vinyl alcohol is readily given, and there is no room for esis[ence of any partially saponified product. 1t is, therefore, possible to measure the reaction velocity by

-this n~thod.

(z) From the preliminary experiments on connnercial polyvinyl acetate carried out Uy the method mentioned in the present report, it has been found that the

progress of the reaction is not smooth, but has two remarkable breaks. (3) 1'he concentratiml of alkali greatly affects the reaction velocity.

(4) The so-called holymcrisation degree affects the. reaction velocity ; the larger the polymerisation d~ree, the (aster the reaction.

(5) The relation •behveen the progress of the reaction and the viscosity change has been investigated. The viscosity change is also represented by a curve with

breaks correslwnding to the curve obtained by the R•elghiny method.

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No. 3 TIIE ALKALINE SAPONIh7CA'I'ION OF POLS'VINYL ACETA'1'b; ~ 85 ~'.

Lt closing, the author wishes to express his sincere thanks to Mr. S. Tachi- >r

kata, Managing Director of the Asahi I3emberg Silk Co. who gave him permission / - I

to publish the present report, to Professor S. Iloriba of the Kyoto Imperial'

University for his encouragement, to D-Tr. R. Goto of the Chemical Research Labo-

story of the same university for ]tis guidance, and to NIr. RT. Tanutra for his

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LaLoratory at Otmt, ~ ~ ~

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