Pyrolytic mass spectrometry as a means of investigating liquid epoxy resins

1302

I. M. LUKASHENKO et al.

3. V. Ye. GUL', N. M. DVORETSKAYA, G. A. IVANENKO, V. A. MARKINA and R. A. YERO~HINA, Mekhanika polimerov, 1134, 1974 4. V. Ye. GUL', L. N. TSARSKII and S. A. VIL'NITS, Kolloidn. zh. 20: 318, 1958 5. G.L. ANDREYEVSKAYA, Yu. A. GORBATKINA, A. V. ZAMOTOVA, R. L. KISELEVA, T. V. ODNOLETKOVA and R. Ya. SVILIVITSKH, Mekhanika polimerov, No. 1, 93, 1965 6. Yu. S. LIPATOV, Fiziko-khimiya napolnenykh polimerov (Physico:chemistry of Filled Polymers). Izd. " N a u k o v a d u m k a " , 1967 7. Yu. M. MALINSKII, Uspel~hi khimii 39: 8, 1970 8. V. Ye. GUL', N. M. DVORETSAYA, G. G. POPOVA and V. G. RAYEVSKII, Dokl. A N SSSR 172: 637, 1967 9. N. M. DVORETSKAYA, L. P. MAKAROVA, L. A. VAKHORUSHINA and V. Ye. GUL', Mekhanika polimerov, 256, 1974 10. N. M. DVORETSKAYA, R. N. DIMITROV, O. N. MIKHAILENKO and V. Ye. GUL', Vysokomol. soyed. A14: 299, 1972 (Translated in Polymer Sei. U.S.S.R. 14: 2, 333, 1972)

PYROLYTIC MASS SPECTROMETRY AS A MEANS OF INVESTIGATING LIQUID EPOXY RESINS * I . 1~/[. LUKASHENKO, R . A . KHMEL'NITSKII, YE. S. BRODSKII, G. A . KALINKEVICH,

N. M. KOVALEVA and V. P. BATIZAT K. A. Timiryazeva Agricultural Academy, Moscow

(Received 29 September 1975) A m e t h o d is proposed for use in identification and quantitative analysis of the composition of volatile products of pyrolysis of high molecular compounds b y means of pyrolytic mass spectrometry. The method involves repeated recording of mass spectra during processes of pyrolysis. The composition of volatile products formed during the pyrolysis of ED-20 epoxy resin is investigated, using the method in question. Commercial ED-20 resin contains 47'2~o low molecular products of which 32~o are accounted for b y phenylglyeidyl ether. Tile composition of the components of ED-20 resin is determined on the assumption t h a t polymer distribution according to the degree of condensation of diphenylolpropane and epichlorohydrin follows Poisson distribution. I t is shown t h a t most of the high molecular fraction of the resin is made up of components with MW 340, 624 and 908.

PYROLYTIC mass spectrometry is one of the principle methods used in structural analysis of complex high molecular substances such as polymers, resins, rubbers and many natural compounds. Through the use of this method one can identify and ascertain the composition of degradation products collected during pyroly* Vysokomol. soyed. A18: :No. 5, 1133-1140, 1976.

Investigating liquid epoxy resins

1303

sis and then introduced into the mass spectrometer [1]. In addition kinetic characteristics of the degradation process can be determined [2, 3]. The yield of information is largest when the pyrolysis is performed directly in the mass spectrometer ion source or in a cell attached to it with programmed temperature changes and non-stop recording of the total ion current and t h e

z,%

~q

BO

/40

Z8

57

a.

5I

'°I

g7111

77

lJ ,m, .............. l . . . . .

,

I

,

IU9

z1357

= I t6~

I

b

gq

NI lit

135

21J

20

157

,,

253 Z69

LJnL,,hIJl.,,,, ,~,,,,b,,..,,,°,,.,,..Lhhh.,,,.,lIJ.,,,

h

,J,....

,., .,,

700 !

li

60

z/~ 3g

60 /.5

3Z5 I/g 135 IZI9

, ,h,~,,,I,,I,IL,,ttl,,,,,,,,h,,,,I,,,,,,,,,

Igl ,,,I, h,l ZIJ

zsg

,,1,,,~=, ,,, i, '7~, ,,, I, 3~o ], I

9z/ d

zg zT~

56

I/551

,,,I

//g/3u

ZO I ,,lhl,,,l,,°

100

32o3oo

z/z/

fO0

2g

1

,,l,,l

,~II,,~,,,

.,

,

,,

,

~

,

i

///4

MS.~zlg

325

I1579111g

213

e,

6O 20

! 6g~7

lL/g

Zql

3qO

Jl I

I 50

log

lSg

290

ZSII

300

lr 35g m/e

FIG. 1. Mass spectra of volatile products of pyrolysis obtained at the following temperatures: a - - 4 0 , b - 120, c--290, d--370, e--500 °.

1304

I.M. LUKASHE17KOet

al.

.entire mass spectrum. The latter method was practicable with the aid of a time of flight mass spectrometer [2-4] whereby rapid recording of the mass spectrum is feasible. However, the scope of the method as regards investigations of low molecular compounds is limited b y the relatively poor resolving power of this mass -spectrometer. The instrument used b y us was the MX-1303 magnetic mass spectrometer which provides for recording of the mass spectra of degradation products under the conditions normally adopted for the analysis of organic compounds. The pyrolysis system and experimental procedure were described in some .,detail in [5]. In this w a y a study was made of the thermal degradation of commercial liquid ED-20 epoxy resin of average MW 450, containing 21.0-21.07% epoxy .groups, total chlorine 1% and 1% volatiles. The mass spectra of the volatile products obtained at different pyrolysis temperatures are seen in Fig. 1. A feature .of the spectrum recorded at 40 ° is the presence of intense peaks for ions in the range of mass numbers up to 150. At 120 ° relatively intense peaks appear for ions with higher mass numbers, all the w a y to 340. The intensity of peaks for these ions in the mass spectrum increases at 290 °, and simultaneous reductions ~appear in the intensities of the peaks for ions with mass numbers up to 150. I f the temperature is further increased, marked changes appear in the mass-spectra of the volatile products. The intensities of peaks for ions with large masses a r e reduced at 370 ° accompanied b y a marked rise in the intensity of peaks for ions o f masses 66, 94, 134, etc. At a still higher temperature (500 °) the intensity of peaks for ions with high mass numbers is once again increased, and these peaks predominate in the mass spectrum. Considerable difficulties arise in connection with identification of the degrad a t i o n products as the masses of molecular and fragment ions of various substances may be identical. One has therefore to begin b y picking out probable peaks for molecular ions. It appears from the results of elemental analysis that the substance being investigated does not contain nitrogen, and so molecular ions will necessarily have even mass numbers. Starting with ions with the largest masses all the ions with even masses were checked for probable classification under molecular ions on the following basis: 1) the relative intensity of peaks for the latter ions increases when the energy of the ionizing electrons is reduced, 2) the latter are non-isotopic, 3) the intensity of their peaks exceed that observed for the respective fragment ions of like masses in the mass spectra of compounds already identified. Final classification of the latter ions under molecular ions is possible when one is able to identify one or more structures corresponding to each .of them and to find fragment ions bearing out their disintegration under electron impact in accordance with known spectrum-structural correlations. In cases where the degradation products contain several components the mass spectra of which cannot be completely superposed on one another, these m a y be identified in the usual w a y from the masses of characteristic ions. Given

Investigating liquid epoxy resins

1305

mutual superposition of the mass spectra of the degradation products, molecular ions and fragment ions corresponding to disintegration of the latter under electron impact can be identified b y comparing mass spectra recorded at different moments of time and at different temperatures. All the ions belonging to one and the same degradation product are interrelated b y the constant intensity ratios of their peaks. Given a change in the rate of formation of a given product the intensity ratios of the peaks for all the latter ions remain constant if these correspond to to the mass spectrum of one and the same product. Next, we analysed mass differences for the latter ions, the relative intensities of their peaks, and the isotopic ratios, etc. Thus, repeated recording of the mass spectra during pyrolysis is conducive not only to identification of the kinetic characteristics of degradation, b u t also makes it possible to identify the degradation products present in a complex mixture. I 7.0

!

g.6 g.Z J

log

3gg

500 7;,°C

~FIG. 2. Temperature dependence of the intensities (arb. units) of some peaks for ions in the mass spectra of the products of pyrolysis of ED-20 resin: 1--149, 2--150, 3--94 role.

This is exemplified b y Fig. 2 showing the temperature dependence of the intensities of peaks for ions with masses of 150, 149 and 94 in the mass spectra of the pyrolysis products of ED-20 epoxy resin. I t can be seen that for the ions of masses 150 and 149 the shape of the curves is practically identical over the entire range of pyrolysis temperatures. In the temperature interval 40-120 ° tim change in the intensity of the peak for the ion of mass 94 is similar to the change in the intensities of the peaks for ions of masses 150 and 149; in the interval above 120 ° a different type of change is observed in the intensity of the peak for the ion of mass 94, pointing to the existence of competing processes of formation of the ion in question. The ion of mass 150 is the "heaviest" in the mass spectrum of degradation products in the interval 40-120 °, and is apparently a molecular ion, which is corroborated b y the increase in its intensity accompanying a reduction in the energy of the ionizing electrons. The degradation product in question ( M = 150) was identified aS phenylglycidyl ether in view of the presence of characteristic fragment ions [(I~I--H) + of masa 149, (IVI--C2H3)+ of mass 107 and (M--C3H40)+ of mass 94, etc.], together with

I. M. L u ~ s ~ N x o

1306

et al.

the intensity ratios of the peaks for these ions, and the isotropic ion of mass 151. The mass spectrum of a model compound prepared under similar conditions closely resembles that of the degradation products of the epoxy resin within the temperature interval. The products identified in the interval 100-250 ° include diphenylolpropane ( M ~ 2 2 8 ) , glyeidyl ether of diphenylolpropane (M----284) and diglycidyl ether of diphenylolpropane (M=340). A number of relatively low molecular components were identihed from the mass spectra of the ED-20 degradation products obtained in the interval 250-400 °, including CO ( M = 2 8 ) , C02 and ethylene oxide (M----44), acrolein ( M = 5 6 ) , acetone and propionic aldehyde (M----58), benzene (M~--87), toluene ( M = 9 2 ) , phenol ( M = 9 4 ) , etc. More high molecular components with M----228, 284 and 340 were identified among the products of pyrolysis at higher temperatures as diphenylolpropane, and glycidyl and diglycidyl ethers of diphenylolpropane on the basis of the masses of the molecular ions and characteristic fragment ions. I;%

1ooF

/~l

a

4, npb.units 1.0

0"6 ~0

25 [;, ',,'o

,

g5

I

25

i /

75 I ~

O'2

e

i~

I

25 lO0 FIG. 3

300

500 T,°C

L~O0 500

600 T,°O

FIG. 4

Fie. 3. Integral curve of gas evolution during the pyrolysis of ED-20 epoxy resin. FIG. 4. Rate of formation of some degradation products versus pyrolysis temperature (% on maximum yield): a: 1--phenylglycidyl ether, 2--isopropylphenylglyeidyl ether, 3-- diphenylolpropane, 4-- diglycidyl ether of diphenylolpropane; b: 1 -- ethylene oxide -t-CO2, 2--CO, 3--acrolein, 4--acetone +propionie aldehyde; c: /--phenol, 2--ethylphenol, 3--isopropenylphenol; d: /--toluene, 2--isopropylphenol, 3--cresol, 4--benzer~e; e: 1--diphenylolpropane, 2--diglycidyl ether of diphenylolpropane, 3--monoglycidyl ether of diphcnylolpropane. The formation of relatively " h e a v y " degradation products in the early stages of the pyrolysis is apparently the result of evaporation of the low molecular fraction of the epoxy resin. The presence of the latter products in the commercial resin is probably due to incomplete conversion of the initial compounds as well as to relatively low molecular side products formed during the synthesis of the epoxy resin. The integral curve of gas evolution has a characteristic flex point at ~ 250~

1307

Investigating liquid epoxy resins

(Fig. 3). The first temperature interval appears to relate to evaporation of the lowmolecular fraction from the epoxy resin, and the second interval to degradation of the resin. Figure 4 shows the rate of formation of some of the degradation products relative to the temperature of pyrolysis. The degradation of components making up the composition of the resin starts at 220-250 °. The process begins with the separation of endgroups on the aliphatic ether bond with formation of acetone, propionic aldehyde and acrolein (Fig. 4b): R--0--CH2--CH--CH.z ~ R--O" -l- "CII~--CH--CH,~ \ / \. ,/ o o "CHe--CH--CHe -~ CH3CCH2" ( t ~ CltaCCHa '\ / ; i! 0 0 0 1~ CH~=:C[t--CIIO -t- H"

I

(H') 1-~ •CH2CIt~CH0 - - - , Ctt3CHo.CHO R--O" + H ~ h o e At 300-400 ° more deep seated degradation of the main chain takes place and is accompanied b y the evolution of phenol, ethylphenol and isoprophenylphenol, and, at higher temperatures, cresol, toluene and benzene (Fig. 4c, d) CH3 I

CH3 1

CH3

CHa

+. FS

_o,

.

CH3 .:---,

I

CHa

I

(H')

CH~ ~

(E')

]

1

CHz

CH~

"l

!!C3 At temperatures above 450 ° larger fragments, such as diphenylolpropane, glycidylether, etc., appear in the pyrolysis products of ED-20. The activation energies for the formation of these components were calculated for the main products of pyrolysis, using the method described in [6]. The average activation energy for the evolution of phenol was 21.5 kcal/mole, and for diphenylolpropane and glycidyl ether of diphenylolpropane 36.5 and 42.5 kcal/mole respectively. To determine the quantitative composition of the degradation products one has to determine the contribution that each component is making to the

1308

I . M . LUKASHENKO et a~.

total ion current, zf the mass spectra of the volatile products of pyrolysis contain peaks free from superposition on the part of other components, the fraction of the total ion current pertaining to a given compound can be defined as

j=Ij/Kj.S, where I~ is the intensity of the j t h peak in the mass spectrum of the products, E is the total ion current, Kj is the intensity of the j t h peak in the mass spectrum of a given component relative to the total ion current, and ~1 is the volume fraction of a given component of a mixture. According to [I] the amount of a liquid sample is proportional to the total ion current. In cases where peaks being used for the calculation are subject to superposition on the part of the mass spectra of other components, one has first of all to take this into account, and the true intensities oi the peaks for characteristic ions must be determined. The intensity of a given peak in the mass spectrum of a mixture is made up of the corresponding values for the intensity of the peak in question in the mass spectra of the components:

Ij I>

(I) k

(2) where I¢ is the intensity of a given peak in the mass spectrum of the degradation products, Ij~ is the intensity of a given peak in the mass spectrum of the kth component; % is the contribution made b y the kth component to the total ion current. The inequality in relation (1) is realized in cases where any of the components in a mixture of degradation products have not been taken into account. The ~ values m a y be determined from the condition for a functional minimum

F, k.Ij ) J

(3)

k

under conditions (1) and (2). Methods of linear programming were thus used to find the content of individual components at each moment of time. The total amount of each component in the pyrolysis products was determined b y integrating total currents contributed b y the individual components with time. This method of calculation was used to determine the content of the main volatile components in the products being investigated. Table 1 gives the results of analysis of the composition of products liberated from ED-20 in the temperature interval 40-250 °. As can be seen from the tabulated results, phenylglycidyl ether is the main component of volatile products in this temperature interval. Table 2 gives the composition of the volatile products in the interval 250-550 ° . In the latter interval the main components are phenol, toluene and ethylene oxide; there are also appreciable amounts of acrolein, acetone and more high molecular products such as ethylphenol, isopropylphenol,

Investigating liquid epoxy resins diphenylolpropane and tified p r o d u c t s we find of e p o x y resins [8], as some unidentified high TABLE

I. C O M P O S I T I O N

1309

glyeidyl ether o f d i p h e n y l o l p r o p a n e . A m o n g t h e u n i d e n p r i m a r i l y w a t e r - - o n e o f the m a i n d e g r a d a t i o n p r o d u c t s well as m e t h a n e a n d o t h e r light h y d r o c a r b o n gases, a n d molecular c o m p o n e n t s .

OF

PRODUCTS

RELEASED

FRO~I ED-20

RESIN

ON

HEATING

IN THE

INTERVAL 40--250° 31

Mole fractioI] of volatile products, o/0,

Phenylglyeidyl ether Isopropylphenylglyeidyl ether

150

32-0

192

12.0

Diphenylolpropane

228

1"2

Compound

Compound Glycidyl ether of diphenylolpropane I Diglycidyl ether of I diphenylolpropane Unidentified

~I/

Mole fraction of volatile products, %*

284

1.1

340

2.1 1.2 Total 49"6%

* Released a¢ 40-250° and formed during pyrolysis in the interval 250-550° (Table 2). TABLE 2. COMPOSITIONOF VOLATILEPRODUCTSFROMEDDURINGTHE PYROLYSIS OF ED-2G RESIN I N THE TEMPERATUREI N T E R V A L 250--550° Compound CO2 Ethylene oxide Aerolein Acetone Propionic aldehyde Benzene Toluene Phenol Cresol Et,hylphenol

M

Mole fraction of volatile products, 0/0

44

3.3

56

1.2

58 78 92 94 108 122

1.3 1.0 2.9 5.8 1-0 1.6

Compound Isopropenylphenol Isopropylphenol Diphenylolpropane Glycidyl ether of diphenylolpropane Diglyeidyl ether of diphenylolpropane Unidentified

M

Mole fraction of volatile products, 0/0

134 136 228

1.0 1.6 2-0

284

1.4

340

3.1 23.2 Total 50-4%.

Qualitative analysis revealed the presence of insignificant a m o u n t s of epic h l o r o h y d r i n a n d o t h e r chlorine containing c o m p o u n d s in ED-20, i.e. c o m p o u n d s f o r m e d during the synthesis o f the resin. I t follows f r o m these findings t h a t commercial E D - 2 0 contains an appreciable a m o u n t of relatively l o w - m o l e c u l a r c o m p o u n d s , these being u n r e a c t e d s t o c k or s e c o n d a r y p r o d u c t s of condensation, along with oligomers including one or more d i p h e n o l p r o p a n e molecules. Given the average molecular weight of the e p o x y resin, as well as the composition a n d a m o u n t of low molecular p r o d u c t s it contains, one can determine t h e average value of the degree of p o l y c o n d e n s a t i o n , n. I n some cases the MWD~

I. M. LUKASn~XO et al.

1310 TABLE

3. C O M P O S I T I O N OF

ED-20 ErOXY R E S I N (AVERAGE M O L E C U L A R MASS 450)

Compound

CoD.telxt, mole %

M

Phenylgyeidyl ether Isopropylphenylglycidyl ether Diphenylolpropane Glyeidyl ether of diphenylolpropane E p o x y polymers CH~CHCH2[OArOCH~CH(OH)CH~]n--

150 192 228 284

32"0 12"0 1"2 1"1

340 624 908 1192 1476 1760

15.2 18.9 11.9 5.4 1.1 0-3

O --OArOCH2CHCI-I*

\/

O with following n-values n=0 n----1 n=2 n=3 n=4 n~5 CHs [

!

CHs

,of polymers prepared by polycondensation follows Poisson distribution [9] n

/ ) ( n ) = ~ e -~ l&'.

P(n) being the distribution function, and ~ the parameter. For

ED-20 the average molecular weight calculated from the data in Tables 1 and 2 is 700, the average value of n = 1.28, and the distribution according to the number o f units is as follows: 2tl n P (n), %

340 0 28.0

624 1 35.0

908 2 22-0

1192 3 10.0

1476 4 3.3

1760 5 0.6

Table 3 gives the general composition of ED-20 epoxy resin. The major part of the resin, apart from the phenylglycidyl ether, is made up of components with M----340, 624 and 908. Translated by R. J. A. H E N D R Y REFERENCES 1. S. MADORSKII, Termieheskoye razlozheniye orgauicheskikh polimerov (Thermal Dogradation of Organic Polymers). Izd. " M i r " , 1967 2. H. L. FRIEDMAN, J. Macromolec. Sei. A I : 5779, 1967 3. C. P. SHULMAN, J. Macromolee. Sei. A I : 107, 1967

Kinetics of emulsion polymerization of ethyl acrylate

1311

4. O. P. KOROBEINICHEV and G. I. ANISIFOROV, Izv. SO AN SSSR. seriya ki~imieh., No. 9, 38, 1974 5. Ye. S. BRODSKII, I. M. LUKASHENKO, V. G. LEBEDEVSKAYA, V. Ye. ZOLOTUKHIN and Yu. A. VOLKOV, Zh. fiz. khimii, 49: 792, 1975 6. R. A. KH3IEL'NITSKII, I. M. LUKASHENKO, G. A. KALINKEVICH, V. A. KONCHITS and Ye. S. BRODSKII, Izv. TSKhA, No. 6, 170, 1975 7. J. F. KINDOR, Developm. Appl. Spectr. 9: 111, 1971 8. H. LEE and K. NEVILLE, Epoxy YCesin Handbook, 1973 9. V. V. KORSHAK, Obshchiye metody sinteza vysokomolekulyarnykh soyedineniyi (General Methods of Synthesis for High Molecular Compounds). AN SSSR, 1963

KINETICS OF EMULSION POLYMERIZATION OF ETHYL ACRYLATE* V. I. YELISEYEVA, A. MAMADALIEV a n d A. V. ZUIKOV Ir,stitute of Physical Chcmislry, U.S.S.I~. Academy of Sciences (Received 1 October 1975)

A study was made of emulsion polymerization of ethyl acrylate. I t was shown that the rate of polymerization in the eor~stant seetiotl is described by the equation ~U -x 0.5 --]CCemC i n , where x varies between 0-2 and 0.4 for various ernulsif~drtg agents. Th(~ constant velocity section continues after the disappearance ef the monomer phase and is characterized by a variable Immber of particles. Deviati(ms h'om "classical" kinetics are due to the complex structure of p.'~rticlcs and the redistribution of t,ht monomer between "live," artd "dead" primary globules after the disappearane,,~ of the monomer phase. IT WAS p r e v i o u s l y i n d i c a t e d t h a t u n l i k e r e l a t i o n s w h i c h g o v e r n e m u l s i o n p o l y m e r i z a t i o n e s t a b l i s h e d for s t y r e n e , t h e r a t e of p o l y m e r i z a t i o n of e t h y l a c r v l a t e (EA) a n d t h e n u m b e r of p a r t i c l e s sb.ow n o c o r r e l a t i o n [1[. T h e causes of t h i s d i s c r e p a n c y h a v e b e e n e x p l a i n e d i n t h i s p a p e r a n d a s t u d y m a d e of t h e r e l a t i o n b e t w e e n t h e r a t e o f p o l y m e r i z a t i o n of t h e s a m e m o n o m e r a n d t h e c o n c e n t r a t i o n of t h e i n i t i a t o r a n d emulsifier~; of d i f f e r e n t t y p e s . K i n e t i c s o f p o l y m e r i z a t i o n w e r e c o m p a r e d w i t h t h e e q u i l i b r i u m e o n c e n t r a t d o n of t h e m o n o m e r i n p a r t i c l e s d e t e r m i n e d b y m e a s u r i n g m o n o m e r v a p o u r p r e s s u r e [2 I. E x p e r i m e n t s were c a r r i e d o u t t o s t u d y t h e k i n e t i c s of t h e v a r i a t i o n of t h e overMl s u r f a c e b y a d s o r p t i o n t i t r a t i o n [3]. R e s u l t s led to ~t n e w h y p o t h e s i s a b o u t t h e m e c h a n i s m a n d k i n e t i c s of e m u l s i o n p o l y m e r i z a t i o n of p o l a r m o n o m e r s . EA was twice distilled in vacumn, a fraction taken of b. p. 42.5°/100 torr. Chemically pure a m m o n i u m persulphate (AP) was reerystallized t,wie,~ from a dilute solution. Three types of emulsifie,r were used: sodium lauryl sulphate produced by "Serva" (GPt~), which * Vysokomol. soyed. A18: No. 5, 1141-1145, 1976.