the polymerization characteristics of lactones in the presence of trityl salts

Polymerization characteristics of lactones 1209

REFERENCES

1. R. HELLWEGE, H. KNAPPE and P. LEHMAN, Kolloid-Z. und Z. fOr Polymere 18@: 110, 1962

2. P. HEYDEMANN and H. D. GUICK1NG, Kolloid-Z. f'0r und Z. Polymere 193: 16, 1963 3. S. A. ARZHAKOV, G. L. SLONIMSKII, B. P. SHTARKMAN and V. A. KARGIN, Vysoko-

reel. soyed. 5" 1854, 1963 (Translated in Polymer Sci. U.S.S.R. 5: 6, 986, 1964) 4. R. W. WARFILD, Polymer Engng. Sci. 6: 176, 1966 5. N. WALDMAN, G. H. BEYER and R. G. GRISKEY, J. Appl.Polymer Sci. 14: 1507, 1970 6. R. F. BOYER and R. SIMHA, J. Polymer SoL, Polymer Letters Ed. 11: 33, 1973 7. A. A. ASKADSKII, G. L. SLONIMSKII and A. I. KITAIGORODSKII, Vysokomol. soyed.

AI6: 424, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 2, 495, 1974) 8. Yu. S. SEREDA, B. P. SHTARKMAN and S. A. ARZHAKOV, Dokl. Akad. Nauk SSSR

214: 1358, 1974 9. G. L. SLONIMSKII, A. A. ASKADSKll and A. I. KITAGORODSKII~ Vysokomol. soyod.

AI2: 494, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 3, 556, 1970)

THE POLYMERIZATION CHARACTERISTICS OF LACTONES IN THE PRESENCE OF TRITYL SALTS*

A. K. KHOMYAKOV, YE. B. LYUDVIO, A. T. GORELIKOV and N. N, SHAPET'KO

L. Ya. Karpov Research Institute of Physical Chemistry

(Received 11 July 1975)

PMR, UV and IR spectral studies were used to show that the initiation of #- propiolactono polymerization is the result of a hydride transfer reaction proceeding at a rate which depends on the counter ion present. The reaction in which relatively small monomer concentrations are used will progress at some residual trityl io 1 concentration which depends on the original monomer concentration. This residual concentration will be due to the existence of an acylium ion reaction with triphenylmethane; this has been confirmed kinetically and spectrally.

TrrE cationic polymer iza t ion o f lactonos, when rapidly ini t iated wi thou t a n y chain t e rmina t ion [1], is character ized b y two main reactions, i.e. a chain pro- paga t ion and reversible binding of the acyl ions b y the carbonyl groups o f the monomer and polymer . There is a t the same t ime little to be found in the liter- a ture abou t the ini t iat ion mechanism of the cationic polymer iza t ion of lactones in the presence of any type of initiators.

The aim of this invest igat ion is to clarify the mechanism of the ini t ia t ion s tage in the cationic polymer iza t ion of lactones over t r i ty l salts b y spectral

* Vysokomol. soyed. A18: No. 5, 1053-1060, 1976.

1210 A . K . K~co~rAXOV et aL

methods. The relative ease by which these salts are synthesized with various anions, their stability, and the possibility of studying the initiation by spectra ! methods, has drawn the attention of many investigators to these initiator types in r e c e n t yea r s .

The reaction of the triphenylmethane cation with oxygen containing compounds can proceed in two ways according to the literature. (The initiation of the vinyl polymerization can proceed only by the monomer adding on to the double bond [2-6J), namely by adding to the oxygen and the possibility of further initiation which leads to the formation of an ether end group,

P h , C + + O ( ~ P h , ~ ) ( - * Ph ,COCH,~ ,

as well as by a hydride transfer reaction and the formation of triphenylmethane,

+ Ph3C+~-- -O--CHs- - -* PhsCH~- -- O----CH--

The first route assumes that the tri tyl ion reacts with the epoxide [71, while the second was proved by NMR spectroscopy as taking place during initiation of the polymerizations of T H F [81, 1,3-dioxolane [gJ and trioxane [10].

T A B L E l . COMPABISON OF THE EQUILIBRIU~I CONSTANTS ~t~ I N REACTION (4) W I T H ~ ' n ~ AP.

VALUES FOR A NUMBER OF COMPOUNDS

K, L/mole Av, Compound K, 1./mole Av, Compound (25 °, CHzCI~) cm -1 (25 °, CH~Cla) em -z

Water T H F Diethyl ether 2-Methyl 1,3-dioxo-

lane

12.0 1.6

0.23 0.24

9O

73 61

1 , 3 - D i o x o l a n e 2-Phenyl-l,3-dioxo-

lane PL

0.063 0.044

~ 1 0 - 3 .

58 56

34

* Estimated from the linear K - d r function.

The PhsC + reaction with B-propiolactone (PL) having two differing oxygen atoms musl~ take into accolmt the following three reaction possibilities:

PhsC W O = C - - O

0 + --[

PhsO + ~ - - C = O -~ PhsCOCH,CH,~ +

O

PhsC+~M -* Ph3CH-~M+ +~ ~~+

The probability of reaction (I) was assessed as follows. literature [I 11 for the equilibrium reaction

(i)

(2)

(3)

The constants contained in the

K + Ph.C++ Ph.O--O( ( .


which are listed in Table 1, are compared with the frequency shifts of the deuterized metha- nol Av in the presence of the respective oxygen containing substance [12]. According to the tabulated values, K for PL ought to be small, so that eqn. (1) can be neglected when exam- ining the trityl ion reaction with PL. Reactions (2) and (3) are obviously the two likely routes of initiation of the PL polymerization with trityl ions.

The main inves t igat ion m e t h o d of the po lymer iza t ion ini t ia t ion of lactones was PI~II~ spec t roscopy and the spectra were in t e rp re t ed b y a pre l iminary de- t e rmina t ion of the chemical shifts of the t r i ty l salt p ro ton signals, also those o f the lactones and polylactones , t r i p h e n y l m e t h a n e and e t h y l t r i p h e n y l m e t h y l e ther . I t was also used to iden t i fy the laetone reac t ion produc ts wi th the t r i t y l

I D I

g 8 7 if, rnag.div.

17IO, 1. The PI~IR spectra of PhsC+A - in A--methylene chloride, B--nitromethane. A-=__.SbCl[, SbF;, AsF[, BF~.

salts. The chemicM shifts of the e n u m e r a t e d compounds l isted in Table 2 were those ob ta ined in solvents of differing polarit ies. Typica l spect ra for the t r i t y l salts in me thy lene chloride and n i t r ome thane as solvents are reproduced in :Fig. 1. One can see t h a t t h e y have Well resolved signals for the t r i ty l cation, i.e. a doublet , t r ip le t for the o-, m- and p -p ro tons respect ively . The change f rom one coun te r ion to the o the r has a lsmot no effect on the chemical shift of these signals. Change

TA

BL

E 2

. T

HE

C

HE

MIC

AL

SH

IFT

S I

N T

HE

PM

R S

PE

CT

RA

OF

CO

MP

OU

ND

S I

N V

AR

IOU

S S

OL

VE

NT

S

So

lven

t

~H2C

12

~HC

ls

~H

,NO

I

Phs

C+

A-(

A-:

SbC

l~, S

bF~

, P

hsC

H

Ph3

CO

CH

~C

H 8

P

L

Po

ly-P

L

CL

P

oly

-CL

A

sF~

, B

F~

) .~

a b

I c

d i

e I

f g

] h

i I

k l

] m

I

n o

I p

1 r

.~

o-

J, m

- J

p-

P.C

J C

H

P.C

IO

CH. I

CH

. O

CH

,IC

H~

CO

CO

H,

iCH

aCO

OC

Ha[

CH

,CO

(C

H~)

, O

CH

~[C

HaC

O

I(C

H,h

7-65

7.

85

(D)

(T)

7.72

7.

87

(D)

(T)

! 7.7

0"

7.89

* (D

) (T

)

8-23

7.

25

(T)

(M)

8"25

7.

27

(T)

(M)

8.30

* 7.

30t

(T)

(S)

5.60

7.

25

3.05

(S

) (M

) (K

) 5.

60

--

--

(s)

5.70

t 7.

30t

3.08

t (S

) (M

) (T

)

1"2'

) 4"

28

3"55

(T

I (T

) (T

) --

--

3.

50

(T)

4.30

(r

)

4.33

5 (T

)

2.60

4-

25

(T)

(M)

2.60

(T

) 2.

605

(T)

2.61

(M

) I

~ 1.

7 4.

08

(M)

(r)

2"30

{T

) ~1

"5

(M)

O

O

* Ph

tC+A

- so

lutio

n in

(C

HIC

lh [3

]. t

Ph~C

H an

d Ph

tC0(

CH

i)sC

Hs-

-sol

utio

ns in

CCI

~ [8]

. {

Poly

-PL

sol

utio

n in

CH

2Cls [

13].

(The

mul

tiple

t typ

e in

show

n in

the

brac

kets

as

sym

bols

: D-

doub

lets

, M -

mul

tiple

t, S -

sin

glet

, T-

trip

let,

k-

quad

rupl

et).

Polymerization characteristics of lactones 121~.

in solvent polarity however produced a noticeable change (Table 2). The lack of signals around ~ 7 . 2 5 mag.div, indicates tha t the salt does not contain any admixtures of PhsCC1 or Ph3COH. One gathers from the Table 2 data tha t the initiation by the addition reaction (2) can be established from the triplet having B~3.08 mag.div., while a hydride transfer by reaction (3) would have a singlet with ~--~5.6 mag.div, as typical. Aromatic proton signals produced by products of initiation by reactions (2) and (3) will be practically the same (multiplets around 7.25 mag.div.).

a b

~ 3

_1-

J II h

_ I I !

~', mag.dN

F~G. 2. The PMR spectra during the bulk polymerization of PL over PhsC+SbCI~ at 0°C after a reaction time (rain) of: 1--2; 2--5; 3--25; 4--180 (the small letters of the alphabet used here and iu Figs. 3-5, namely a-r, coincide with those given for the compounds

in Table 2).

Examination of the PL spectrum after polymerization in bulk (without solvent) over Ph3C+SbCI~ (Fig. 2) indicated that the PhaC + reaction with PL was by a hydride transfer. The signal for PhaC + (a) becomes smaller during the reaction and those for PhaCH appear (b, c). Almost all of the trityl salt is con- verted into tr iphenylmethane in this reaction. The PL polymerization is evident in the spectrum as a decrease and subsequent complete disappearance of the signal given by the CHaCo group of the monomer (h) while that for the same group present in the polymer appears and becomes larger (k). The two signals (h, i) practically coincide for the OCH~ group present in the monomer and polymer.

The fact that reaction (2) does not take place in the system was confirmed by the comparative analysis of the IR spectra of the oligo-lactones produced over tr i tyl and oxonium salts as initiators. The samples were found to be spectrally identical; no tr iphenylmethyl groups were detected. Reprecipitation o f

:]214 A . K . K~O~YAKOV et al.

I I t

b

I

, I 1 I 8 6

k

13 6

I I I I

q 2 , maff. d[v.

FI6 . 3. The PM__R spectra of system PL-PhsO+BF~-CHsNOs a t 25°0 a t the: I - - s t a r t ; I I - - a n d of polymerization. [M]=3-82 mole/L, c----7× 10 -2 mole/L, e - - t r i t y l sal t concentration

used here and in Figs. 4-9.

J

a b

I . I I

1 I I

8 7 5

t3 G

i

F ,f

I , l I

q g 2 ~ m~.d~.

~Hz~1,z

I

,9' h

f

q i I

3 2 ~, mzzg. ~':;v.

FIG. 4. The PMR spectra of system PL-PhsC+SbC16---CH,C1, po]ymerized a t 25°C; [i~@ 23.82, c = 9 . 2 5 × 10 -3 mole/1. Durat ion of process (min): 1--3; 2--10; 3--35; 4--90.


the P L oligomers from chloroform solution with ether yielded triphenylmethane

in the filtrate. The s tudy of the solution polymerization of PL in methylene chloride or

nitromethane at relatively low monomer concentrations (Figs. 3 and 4) showed tha t the hydride transfer was incomplete. Some residual PhsC + content, depending on experimental conditions, was detected in both the solvents after the polymerization (depending on solvent, monomer, initiator concentrations, etc.). The presence of the PhaC + ions in the system after the polymerization was also indicated by the presence of PhsCH and Ph3COH in the solution after the polymer had been precipitated with wet ether (PMR spectra). A similar incomplete conversion of the trityl salt in the solution was found in the s tudy of the polymerization of e-caprolactam (CL), which shows this phenomenon to be general for the polymerization of cyclic esters (the CL polymerization is initiated by a hydride transfer reaction). (See Fig. 5 and Table 2).

L

OHz[;tz , . I ~ I i f I

8 7 5 5 i/ 3 Z ! o p /7,,P

2 GH~t3 [ I I

~ LlzCtz

T I I ] I I I I1 6 7 # 5 q 3 2

8~ mag.d[v.

FIG. 5. The PMR spectra of CL polymerized over PhaC+SbCI~ in methylene chloride at 25°C; 1--at the start; 2--at the end of the process. [M]0= 1.0 mole/L, c--1.55 × 10 -1 mole/1.

The above results are evidence of the incomplete consumption of the tri tyl salt not being associated with a slow initiation.

The results reproduced in Figs. 6 and 7 show that the type of counter ion does not significantly affect the rate of the tri tyl salt reaction with PL. The substantial drop in the reaction rate on changing from SbCl~- to SbF~ or AsF~- appears to be connected with the effect of the anions on the chain propagation stage.

The UV and I R spectral data permit the following conclusions to be drawn: 1) Initiation of lactone polymerization takes place over trityl salts as a result of hydride transfer reaction (3). 2) The hydride transfer reaction is incomplete

1216 A. K. ~[_.tIOMYAKOV e~ al.

an d this is p robab ly due to a t r i pheny lme thane par t ic ipa t ion in a react ion wi th the reac t ive centres. I t could be t h a t the t r i ty l ions form in the sys tem b y react ion:

~ C O + + P h 3 C H ~ ~ CHO + P h s C + (5)

t0 9 [M]o l-g - [M]

A 0"8

0"6 ~

0.0

O.Z

0 30 Time, m/n

D 1"6

I'Z

0"8

O.q

1.6 D

1"2

0"8

I I I 2 68

Time, rain

Fxo. 6 FIG. 7

120

Fxo. 6. The optical density D and the polymerization kinetics for system PL-PhaC+SbCI[- CH,C12 at 25°C; [M]0= 3.82 mole/]., c= 4.6 × l0 -3 mole/1.

Fie. 7. The optical density D for system PL-Ph3C+A--CH,C12 at 25°C. [M]o=3.82 mole/]., c= 4.6 × 10 -3 mole/]. A- : 1 - - SbF~; 2--AsF~. The polymerization did not take place in the

selected conditions.

The exis tence of this reac t ion in the presence of the monomer and po lymer ought to resul t in the es tab l i shment of the following equilibrium:

\ 0

, , ~ + + PhaCH

0 0 I1 ÷ I I II 4- I

,~'C--O=C--O -~" C--O----C--O--

M

0 .~_' II

-~C--H + PhaC +

+ [ - q ÷ I Ph3C--O----C--O Ph3C---O=C--O--

in which M is the monomer ; P, polymer; KI~K~>>Ks~K 4 in the case of P L . Addi t ion of t r i pheny lme thane ought to shift the equil ibr ium to the r ight according to this scheme and reduce the aeyl ion concent ra t ion as well as the react ion rate , while a ldehyde addi t ion would shift i t to the left and increase the rate . Increase in the initial m onomer concent ra t ion ought to reduce the residual t r i ty l ion concent ra t ion . The exper imenta l findings of the effects of ace ta ldehyde and tri- p h e n y l m e t h a n e on the process are shown in Fig. 8, while Fig. 9 shows the effect of the initial monomer concent ra t ion on the conversion of the t r i ty l salt b y the hydr ide t ransfer react ion. These diagrams make i t clear t h a t the expec ted in-


fluence of the component concentrations on the reaction parameters actually takes place.

The occurrence of reaction (5) was also confirmed experimentally. Addition of acetylhexachloro-antimonate to a tr iphenylmethane solution in methylene chloride immediately produced an intense colour which had absorption peaks corresponding to those given by the trityl ions. Their formation was also estab- fished by PMR spectroscopy. The same result was also found in the reaction of tr iphenylmethane with the poly-acyl ion ~OCH2CH2CO + (the lactone was pre- polymerizcd over CH3CO+SbCI~). As the equilibrium of reaction (5) is strongly

[H]0 t°9EM] I'0- 3 I

0"8 2 /

0.6

0.~

O.2

0 60 18g 300 7-[me , rain

Drnin/DO x I00, ~

Igo

\ 80 o SbC[s

\ • AoFo

5O °o~ + ~bF6

I I \ I 0 2 # B

HO , mole/[.

FIG. 8 Fro. 9

FIG. 8. The kinetic curves of the PL polymerizotion in methylene chloride over Ph3C+SbCI~ at 20°(3; l--no additions; 2--2-13 × i0 -~ mole/L, triphenylmethane; 3--2.20× 10 -2 mole/L

acetaldehyde. [M]0=3.82 rnole/l., c~6.15 × l0 -a mole/l.

FIO. 9. The reduced residual optical density Dmln/D o at ~=430 nm as a function of the initial monomer concentratior~ at 25°C. c~4.6 × 10 -8 mole/l.

displaced to the right as a result of a large difference in stability between the participating ions, any reversal of the reaction will be observable only after the acyl ion concentration was reduced, which will give rise to an additional reaction. The PMI~ spectral s tudy of the acetaldehyde reaction with the trityl salt showed that there was substantial consumption of CHaCHO and formation of triphenylmethane only in the presence of the monomer, which reduces the acyl ion concentration due to reaction with carbonyl groups [1].

The fact that the trityl salts are not fully utilized due to a reversal of reaction

1218 A. K. K~o~rAxov et al.

(5) has been observed here for the first time. I t had no t been detec ted dur ing the t r i ty l salt react ions wi th o ther oxygen containing hetero-rings, such as T H F

or 1,3-dioxolane.

EXPERIMENTAL

The P L and CL were purified as described elsewhere ([14] and [15] respectively]). The solvents were t r ea ted as described by K h o m y a k o v [16]. The t r i ty l salts were synthesized b y the L y u d v i g and Belenkaya me thod [15]. The components were

added under vacuum. The P M R spectra were recorded on a " J E O L " JNM-PS-100 ins t rumen t

working a t 100 MHz. The chemical shifts were de termined relat ive to the solvent

present , or to te t ramethyls f lane as reference s tandards . The I R spectra were taken , af ter t ab le t t ing the samples wi th KBr , on a UR-20 ins t rument . The UV

spect ra were p roduced in an a u t o m a t e d "Perk in -E lmer" -450 spectrometer .

Translated by K. A. ALLE~

REFERENCES

1. A. K. KHOMYAKOV and Ye. B. LYUDVIG, Dokl. Akad. Nauk SSSR 201: 877, 1971 2. T. HIGASHIMURA, T. FUKASHIMA and S. OKAMURA, J. MacromoL Sci. AI: 683,

1967 3. T. KUNIT2,KE, Y. MATSUGUMA and C. ASO, Polymer J. 2: 345, 353, 1971 4. H. S. SAMBI, Macromoleeu]es 3: 351, 1970 5. C. E. H. BAWN, C. FITZSIMMONS, A. LEDWITH, J. PENFOLD, D. C. SHERRINGTON

and J. A. WEIGHMAN, Polymer 12: 119, 1971 6. G. SAUVET, J. P. VAIRON and P. SIGVALT, J. Polymer Sci. 7, A-l : 983, 1969 7. J. KUNTZ and M. H. MELOHIOR, J. Polymer Sei. 7, A-l : 1959, 1969 8. J. KUNTZ, J. Polymer Sei. 5, A-l : 193, 1967 9. St. SLOMKOWSKI and St. PENCZEK, Chem. Cornmun., No. 20, 1347, 1970

10. Yu. N. SMIRNOV, V. P. VOLKOV, E. F. OLEINIK, B. A. KOMAROV, B. A. ROZENBERG, and N. S. YENIKOLOPYAN, Vysokomol. soyed A16: 735, 1974 (Translated in Polymer Sci. U.S.S.R. 16: 4, 846, 1974)

11. St. PENCZEK, Makromol. Chemic 175: 1217, 1974 12. T. KAGIYA, Y. SUMI~A and T. INOUE, Bull. Chem. Soc., Japan 41: 767, 1968 13. T. SAEGUSA, S. KOBAYASHI and Y. KIMURA, Macromolecules 7: 256, 1974 14. A. K. KHOMYAKOV, G. S. SANINA and E. B. LUDWIG, J. Polymer Sci. C42: 289,

1973 15. E. B. LUDWIG and B. G. BELENKAYA, J. Macromol. Sci. A8: 819, 1974 16. A. K. KHOMYAKOV, Dissertation, 1973

the polymerization characteristics of lactones in the presence of trityl salts

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