Investigation of chloroparaffin structure by IR spectroscopy

INVESTIGATION OF CHLOROPARAFFIN STRUCTURE BY IR SPECTROSCOPY* M. N. GUSEV, Y u . V. KISSIlV, ~¢L M. VOROI~OVITSKII a n d A. A. BERLI~

Institute of Chemical Physics, U.S.S.R. Academy of Sciences (Received 14 September 1967) OnE of the new trends in the synthesis of polymerizable oligomers is the chemical modification of non-polymerizing oligomers, i.e. by the addition of functional groups capable of polymerization or polycondensation. Among oligomers of this type chloroparaffins are of special interest owing to highly reactive available C1 atoms and because they are obtainable and inexpensive. Investigations are being carried out to convert chloroparaffins to oligomers which can be polymerized by dehydrochlorination, followed by epoxidation, carboxylation, etc. [1] and by methacrylation and acrylation [2]. The structures of the oligomers obtained cannot be elucidated without knowing the structure of the initial chloroparaffins and the related reactivity of separate chlorine atoms. Investigation of similar viscous liquid, or solid systems is hindered by the very high boiling points and low thermal resistance so that they cannot be separated by rectification or gas-liquid chromatography. There are several papers in the literature on the IR spectroscopic study of chlorinated polyethylene. According to data from former studies [3-5] on the qualitative examination of spectra at the initial stages, chlorination takes place of the series --CH2CH 2 - to form -- CH2CHC1-- units. After the chlorine content in polyvinylchloride reached 56.7%--CHC1CHCl--units are formed. --CH2CC12- units were not detected even at high degrees of chlorination (up to 68%). A study by Oswald and Kubu [6] is unique since it provides quantitative data on the contents of --CH2CH2CH2--; --CH2CH2CHC1-- and --CHC1CH2CHC1-- groups and seeks to consider chlorinated polyethylene as a ternary copolymer of ethylene, vinylchloride and 1,2-dichlorethylene. According to this paper a certain number of -- CHC1CHC1-- units are formed at early stages of chlorination and, starting from a degree of chlorination of about 65 % (about 0.7 C1/1C), -- CH2CC1~ - units are formed. Dzhagatspanyan, Sokolov, Khromenkov and Korolev by an X-ray study of the variation in the degree of crystallinity of radiation-chlorinated polyethylene came to the conclusion that polyvinylehloride is apparently the end product of chlorination * l~eftekhimiya 8, No. 3, 435-441, 1968. 138

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139

and a mixture of polyethylene and polyvinylchloride units is formed in the early stages and subsequent chlorination is considered as the transition of part of polyethylene to polyvinylchloride [7]. Thus, there is no uniform view in the literature regarding the structure of products of chlorination of polyethylene. Hardly any information is available on the structure of products of chlorination of long-chain paraffins. This paper reports an investigation by I R spectra of the products of chlorination of C~0-C25 paraffin wax (C2~ average) of an approximate melting point of 52 °, purified by the carbamide method. Bands typical of branches, rings a n d aromatic structures are practically absent from the spectra of the initial paraffin.

/.,x j/!

e

1500 I#00 !300 800 700 600 500

cm-I

FzG. 1. IR spectra of C2o-C~5 chlorinated par82fins. C1 content (wt.%): a--0; b--26; c--34; d--44; e--73. Chloroparaffin samples with a chlorine content of up to 50% were obtained by chlorination in melt heated to temperatures of 80-110 °. Samples with a chlorine content of more than 50% were obtained in a C014 solution at 70 °. in the presence of 0.5% azobisisobutyronitrfle. The spectra were obtained in a UR-10 device at 20 °. The samples were prepared as thin chloroparaffirL films applied on the surface of a KBr window, the spectra being qualitatively studied and as solutions in CC14 and cyclohexane with quantitative measurements. Figure 1 illustrates I R spectra of films in the ranges of 800-500 a n d 1500-1300 cm -1 for samples with a chlorine content of 0, 26, 34, 44 and 73%.

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GUSEV et al.

The initial paraffin and chloroparaffin with a chlorine content of 73°/) were crystalline, while the other samples were amorphous. As the degree of chlorination increases the band intensity of stretching and deformation vibrations of CH~ groups in the spectrum of paraffins decreases (2930, 2850 and 1470 cm-1). At the same time relative band intensity at 1380 cm -1 due to symmetrical deformation vibrations of the CH 3 groups varies comparatively slightly. This proves that chlorination, at least in the early stages, mainly involves the CH 2 group. I t is very difficult to observe the variation of intensity oi~other bands characterizing methyl groups (2960 and 2870 cm-l--antisymmetrical and symmetrical bond-stretching vibrations of C - H in CH 3 groups a n d 1450 em-l--antisymmetrical deformation vibrations of CH 3 groups), since these bands are overlappe d by closely situated and more intensive bands of corresponding vibrations of CH,~ groups. However, at high degrees of chlorination (50-70%) the intensity of bands characterizing the CH2 group markedly decreases and bands typical of CH 3 groups exceed timm in intensity. A combination of data obtained, mainly in respect of the band at 1380 cm -1, lead us to the conclusion that chlorination mainly takes place in the CH 2 groups and not in the CH 3 groups. Qualitative views on chloroparaffin structure may be formed from the analysis of I R spdetra in the range of deformation vibrations of CH 2 groups and bond-stretching vibrations of C--C bonds. An intense doublet is present in the spectrum of unchlorinated paraffin at 720 .... 729 cm -~, typical of rocking vibrations of long sequences of CH~ groups which are in a flat zig-zag configuration and form part of crystalline units [8]. Even with low degrees of chlori~lation the doublet component disappears at 729 cm -1 and band intensity at 72(I cm --~ considerably decreases and shoulders appear on its contour in the short-wave range. The disappearance of the compoimnt at 729 em -~ is the result of the sample changing from the crystalline to amorphous state during chlorination [9]. It is well known that the band at 720 c m is typical of polymethylene units which consist of not less than five CH 2 groups, one after the other [10]. A reduction in the intensity of this band confirms on the one hand t h a t the sample becomes amorphous during chlorination and on the other, t h a t chlorine atoms at random entering the paraffin molecule reduce the proportion of CH 2 groups in long units [9]. With degrees of chlorination of 33-34~o (Fig. lc) the maximum of the band widens and is displaced to 727-731 cm -~ and an intense shoulder is formed at about 750 c m ' (the band typical of three CH 2 groups), which proves that there is a reduction in t~he average length of the polymethylene unit. With degrees of chlorination of 44% the maximum below 750 cm -1 is displaced (Fig. ld) and completely disappears from spectra of samples of higher chlorine content (Fig. le). At the ~ m e time as these variations in the range of 700-750 cm -1 changes take place in the range of deformation vibrations of CH 2 groups (1470-1400 cm-~). Literature data indicate that the position of the band iu this range in tile spectra of chlorinated hydrocarbons is seusitive to the structure of units

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141

surrounding the CH, group: a band at 1460-1470 cm -1 [4, 11] corresponds to the group - - C H , - - C H , - - C H , . Group

Band, cm -1 1434-1428112, I~,

-- CHCICH~CHCI --CHCICH2CCI --CCI2CH2CCI

2 2

1423[12], 1407-1404112, 14].

The band at 1440 cm -1 m a y apparently be attributed to vibrations of --CH~CH2CHC1-- groups (e.g. [4]). I n the spectra of chloroparaffms studied bands occur at 1464, 1445, at about 1435 (shoulder, Fig. ld) and 1428 cm -1 (Fig. l e ) a n d the maximum absorption in this range is shifted in the direction of the long-wave range, in proportion to the increase in the degree of chlorination. The band in the 1430 cm-1 range can also be attributed partly to antisymmetrical and deformation vibrations of CH 8 groups. It follows from these data that, during chlorination, structures are formed in which the chlorine atoms are mainly linked to carbon atoms, separated by at least one CH~ group (i.e. --CH~CH~CHC1-- and CHC1CH~CHC1-- structures are formed). I n the range of stretching vibrations of C-- C1 two bands at 608 and 659 cm -1 are present in the spectra of samples of low chlorine contents, these bands being typical of isolated--CHCl--groups and, according to former studies [15, 16], attributed to stretching vibrations of C--C1 in SHH conformations (chain configuration being plane zig-zag, two H atoms being arranged in the trans-positions in relation to the C1 atom) and in SCH conformations (convolute chain structure, C and H atoms being arranged in the trans-position to the C1 atom). I n proportion to the increase of the degree of chlorination (Fig. le), the band at 670-680 cm -1 becomes the dominant band in the spectrum in this range and this may be attributed to vibrations of SCH type in the presence of closely situated C1 atoms (Table 2 in another paper [16]), or to vibrations of --CHC1CHC1-- units of trans-eonfiguration [17]. Bands corresponding to CC12 groups were not observed in the I R spectra of samples investigated. In general, an analysis of I R spectra of chlorinated paraffins indicates that chlorination mainly involves CH~ groups and takes place statistically. The inductive effect of the substituent (C1 atom) practically excludes the formation of CC12 groups and to some extent prevents chlorination of CH 2 groups situated close to the CHC1 group. These data also confirm that the structures of chlorinated low-molecular weight paraffins and polyethylene are qualitatively the same. Quantitative evaluation of chloropara~n structure. For the quantitative evaluation of chloroparaffin structure two idealized models were examined of a chain structure for C22 paraffins. It was assumed in every case that the

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m e t h y l e n d groups were n o t chlorinated (i.e. the chains consist of 20 units) a n d t h a t the chain only consisted of two t y p e s of u n i t s - - C H 2 a n d CHC1. Model 1. Chlorination takes place a t r a n d o m , C H 2 a n d CHC1 units can be in a n y sequence. Model 2. Chlorination takes place a t r a n d o m , however, the CHC1 groups are separated b y a t least one CH 2 group. T h e possibility of selection of these models is based on the fact t h a t , ~s indicated, the relative b a n d i n t e n s i t y a t 720 cm -1 is d e t e r m i n e d b y t h e proportion of CH 2 groups in p o l y m e t h y l e n e sequences of a length not less t h a n five groups (in relation to all CH 2 groups in ehloroparaffin). E x p e r i m e n t a l l y this value was d e t e r m i n e d b y measuring b a n d i n t e n s i t y a t 720 cm -~ in spectra of solutions of various chloroparaffins in cyclohexane (Table). D I S T R I B U T I O I ~ OF M E T H Y L E N E G R O U P S I N

CHLORINATED PARAFFIN

Vessel thickness /=0.5 mm C1 content, wt. °o

Number of C1 atoms per molecule, q

Cxn concentration in C6H12, mol./1.

0 l0 22"5 26 34.5 44.5

0 0'96 2"5 3"1 4"5 7'2

0.293 0.262 0'233 0.214 0.200 0.177

D7~o*

0"632 0"572 0-311 0"259 ~0'143 $ 0'00

Proportion of CH2 groups in blocks of more than 4 units?, mole % 100 98 71 66 ~43 0

* Result of two or three nleasurclnents. t Calculated from the formula where K720 is calculated from spectra of paraffin and is 2"15 1.[mole.cm. $ Results are exaggerated because of the marked overlapping of bands at 720 and 730 em - I .

[D720[K72o.l]/(20-q).Ccp.lO0~,

Q u a n t i t a t i v e d a t a [6] of p o l y e t h y l e n e chlorination only refer to short sequences w i t h o u t considering m u t u a l a r r a n g e m e n t a n d do n o t enable conclusions to be d r a w n in principle on t h e d i s t r i b u t i o n of chlorine in the molecule as a whole, p a r t i c u l a r l y in initial stages of chlorination. The results shown in the last column of the Table indicate t h a t , e v e n with an insignificant chlorine content, the p r o p o r t i o n of CH~ groups in long sequences markedly decreases, i.e. chlorination is statistical. F r o m a statistical point of view the p r o p o r t i o n of C H 2 groups m e a s u r e d e x p e r i m e n t a l l y in blocks of a t least five units length corresponds to the formula 20--q

20--q

z = E Pk/E kPk, k=5

1

Investigation of chloroparaifm structure

143

where q is the number of CHC1 units per chloroparaffin molecule and P , is the number of parts containing k units of CH2 one after the other (if in the chain segments from k groups of CH 2 occur f times one after the other, this p a r t occurs f times). Expressions for P, corresponding to two different models are given below.

Exl~ressions for Pk, number of distribution~ containing k units one after the other. Model 1. Assume we have a chain of an overall length of N units, from which m units are of t y p e B and N and m units of type A. Let us examine, inside the chain, a segment of k units of type B, on the side of which two elements of t y p e A are situated. To the right from the segment in question let there be x units, of which y units are of type B. Then, N--k--x--2 units are situated to the left, of which m--k--y units are of type B. The number of parts, in which the segment in question can be found of k units of type B, values of x and y being fixed, is N--k--x--2" ~x"

Considering that there are parts in which the segment studied is at the end of the chain, we obtain:

Addition is made of y from 0 to m-k and for x from y to N ~ y - - m - - 2 ff x ~ y and N--k--x--2 ~m--k--y. Model 2. As with model 1, we consider a chain of N units in length, conraining m units of t y p e B and N, m units of type A, where units A cannot continue one after the other. Let us examine inside the chain the segment consisting of k units of type B, along the edges of which unit A and then unit B occur singly. To the right from the segment in question let there be x units, of which y units are of type B. Then, to the left are N--k--x--4 units, of which m--k--y--2 units are of type B. Considering that there are parts in which this segment is at the end of the chain, we obtain t ) k = ~ ~'~~m--b--y--2 . Dy~_ ppm--k--l_l_ O~m--k--3

Addition is made for y ,from 0 to m--k--2 and for x from max ( N - - l ~ k --2y--2m, y) to rain (2y-I-l, N--M--2~-y) if x ~ y and N - - k - - x - - 4 ~ m - - k - - y - - 2 . In the above expression R~ is the number of distributions of y units of type B and x--y of units of type A in the segment consisting of x units i f two elements A cannot exist side b y side. Let there be 51 elements in this segment of one unit B, 52 elements of two units B, etc. down to $v elements of y Y

units of type B and ~ 5ii=y. Since between each of the elements examined i~l

144

M.N. GusEv et al. Y

there is a unit of type A, ~ 5i--~n (three cases are possible: n = x - - y +

i,

i=1

n=x--y

and n - ~ x - - y - - 1 ) . n!

l

u

n Z~i=n (~1!52 ! ' ' ' 5 y ! ZiS~ =y

The value of Q~nis calculated using the generating function ~o=(z+z~-+-...-Fz~) n and is equal QU__dU~ -dz i j ' where

~z u-

CuC"

t ! n . . . ( n ~ - y - - t - - 1 ) (--1) U

This sum allows for items for which ( t - - n ) / y is an integer, starting from t----n to t~--min [y, ( y + 1)n]. The value of L as a function of chlorine content in the chloroparaffin molecule was calculated for the above models b y computer M-20.

(:6

[

2

#

5

8

lO 12

_

lq

Number'of C! atoms~molecule FIG. 2. Dependence of the proportion of--CH2--units arranged in blocks of ~ 5 units

one after the other on the degree of chlorination. Curves: /--model 1; //--model 2. Points indicate experimental data, sign ~ indicates a point of which the coordinates are exaggerated because of overlapping bands (Table). Figure 2 diagrammatically illustrates the dependences calculated for models 1 and 2 and shows experimental data. It follows from this Figure that the experimental points are situated on a curve which lies between the curves representing models 1 and 2, closer to model 2, i.e. during chlorination in the above stages, in the chlorol~raffin formed between the--CHCl--groups there is at least one--CH2--group in most parts, although at the very early stages of chlorination comparatively few--CHC1--CHCl--groups can form. This conclusion agrees with that previously drawn from a qualitative analysis of chloroparaffin spectra. I t should be noted that, even in the case of idealized model 2, ehloroparaffins have a different stl-acture to polyvinylchloride since with

Investigation of chloroparaffm structure

145

a sufficient degree of chlorination, in a d d i t i o n to--CHC1CH~CHCl--groups, - - CHC1CH~CH~CHCI-- groups occur fairly o f t e n a n d i n t e r r u p t t h e c h e m i c a l r e g u l a r i t y of t h e chain. SUMMARY 1. C20-C25 c loroparaffin s a m p l e s containing 0 to 73 wt.~/o C1 were studied: by IR spectroscopy. 2. I n t h e e a r l y stages of c h l o r i n a t i o n - - C H C l - - g r o u p s are f o r m e d , b e t w e e n which t h e r e is n o r m a l l y a t least one group, - - C H , - - , a n d a small n u m b e r of - - C H C 1 C H C l - - g r o u p s c a n be formed. D u r i n g f u r t h e r chlorination - - CHC1CHC1-u n i t s are formed. H o w e v e r , e v e n w i t h high degrees of c h l o r i n a t i o n (up t o 7 3 % ) - - C C 1 2 - g r o u p s w e r e n o t detected. 3. A q u a n t i t a t i v e s t u d y of chloroparaffin s t r u c t u r e carried o u t using a r e l a t i v e b a n d i n t e n s i t y of 720 cm -1 (swinging v i b r a t i o n s of --(CH2) n groups, w h e r e n>~5) s h o w e d t h a t t h e s t r u c t u r e of chloroparaffins w i t h a C1 c o n t e n t of a b o u t 45 w e i g h t °/o can be satisfactorily described s t a t i s t i c a l l y for a l i m i t e d n u m b e r of chains, in w h i c h a t least one C H 2 g r o u p lies b e t w e e n t h e - - C H C 1 - groups. Translated by E. S~MERE REFERENCES 1. A. A. BERLIN and S. I. BASS, Plasticheskie massy, No. 1, 3, 1965 2. A. A. BERLIN, L. Ye. OSTROUMOVA, M. N. GUSEV and Ye. L. MARTSENITSENA~ Auth. Cert. 179919, 1966; Izobreteniya, prom. obraztsy i toy. znaki :No. 6, 74, 1966 3. H. W. TOMPSON and P. TORKINGTON, Trans. Faraday Soc. 41, :No. 279, 1945 4. K. NAMBU, J. Appl. Polymer Sei. 4, :No. 10, 69, 1960 5. S. A. ADYLOV, I. F. LESHCHEVA, D. Ye. IL'INA, M. V. SHISHKINA and B. A. KRENTSEL', :Neftekhimiya 8, :No. 1, 82, 1963 6. H. OSWALD and E. KUBU, SPE Trans. 3, :No. 3, 168, 1963 7. R. V. DZHAGATSPANYAN, V. A. SOKOLOV, L. G. KHROMENKOV and B. M. KOROLEV, Vysokomol. soyedineniya 8, :No. 2, 193, 1966 8. R. SHEIN, J. Chem. Phys. 23, 734, 1955 9. I. Ye. LEIFMAN, Issledovanie tverdykh neftyanykh parafinov metodami refraktometrii i infrakrasnykh spektrov pogloshcheniya (Study of Paraffin Wax by Methods of Refractometry and I R Absorption Spectra. Dissertation, Moscow Institute of Petrochemical and Gas Industry). 1967 10. N. L. McMURRY and V. TORNTON, Analyt. Chem. 24, :No. 2, 318, 1952 11. S. KRIMM, Y. ZIANG and G. SUTHERLAND, J. Chem. Phys. 25, 549, 1956 12. H. GERMAR, Makromol. Chem. 86, 89, 1965 13. S. NARITA, S. ICHINOE and S. ENOMOTO, J. Polymer Sci. 37, 281, 1959 14. S. NARITA, S. ICHINOE and S. ENOMOTO, J. Polymer Sci. 37, 251, 1959 15. S. KRIMM, J. Polymer Sci. C7, 3, 1964 16. J. SHIPMAN, V. FOLT and S. KRIMM, Spectrochim. acta 18, :No.12, 1603, 1962 17. R. L. I~WLLER, J. Polymer Sci. 46, 303, 1960