Tetrafunctional acid ester condensations with di- and tetrafunctional organosilicon alcohols

TETRAFUNCTIONAL ACID ESTER CONDENSATIONS W I T H DI- AND TETRAFUNCTIONAL ORGANOSILICON ALCOHOLS* K. A. A~DR~_XOV and V. l~. YE~EL'YA_WOV Institute of Organometallic Compounds, U.S.S.R. Academy of Sciences

(Received 21 April 1965) THE condensation study of tetrafuactional acid esters of the general formula C[CH20C(O) (Ctt2) . C00H]4, in which n = 2 , 4, 8, with glycols [1] and with trihydric organosilicon alcohols of general formula RSi [0Si (CH3)~CHz0CH~CH~0H]3 [2] showed the presence of some characteristics cormected with the structure of the branching units. This paper is a report of the study of tetrafnnctional acid ester condensations with dihydric [3] and tetrahydric organosilicon alcohols which can be generally described b y formula: C[CH~OC(CH~)nC00H]4 ( n = 2, 4, 8) II O 2[HOCH2CH~OCH~Si(CH3)~]O

Si[OSi(CH3)~CH~0CH~CH~0H]4 CH3

--C~--CH~OC(CH2)nCOCH~CH~OCH~Si0--Si--

CHaC:Ha

I ¢ I J I --C--CH,,OC( CI-I~,)nCOCI-IaC~I,,OCH2SiOSiC~I~OCH~CI-I2OC(CI-I~)nCOCH~--C-I-IaCI:[a

O

O

I n the condensation of tctrafunctional esters with dihydric organosilicon alcohols the central atoms forming the polymeric network are only the carbon atoms, while these and Si atoms are involved in the case of tetrafu_actional organosilicon alcohols. The rate of growth of the specific viscosity diminished in the case of bis(hydroxyethoxymethyl)tetramethyldisiloxane condensation with increasing degree of braching of the acid ester (Fig. 1: compare curve 3 with 1 and 2). The condensation of the same acid esters with tetrahydric alcohols gave a much more rapid viscosity increase but the same principle was valid, i.e. an increase of n in the acid ester reduced the rate of viscosity increase (compare curve 6 with 4 and 5). * Vysokomol. soyed. 8: ~o. 4, 668-673, 1966. 733

K. A. ANDI~IAI~OVand V. A. YENIEL'YAlVOV

734

Figure 2 shows the changes of the acid numbers of the reaction products. A more intense condensation takes place at the start of gelling while the distance between the atoms at the centre of the newtwork is still large. For example, a 21~o condensation efficiency was obtained w h e n a difunctional organosilicon alcohol was condensed with pentaerythritol tetrasuccinate at the gel point, 40% in the case of pentaerythritol tetra-adipate and 46~/o with pentaerythritol tetrasebaceate.

•Sp.

O.lG 6

2

3

4 0¢0

0.04 i

i

60

i

l

T

120

I

NO Tz'me , rain

Fro. 1. Specific viscosity changes during the condensation of bis-(hydroxyethoxymethyl)tetramcthyldisiloxane with the tetrasuccinate (1), tetra-adipate (2) or tetrasebaceate (3) of pentaerythritol, or of the tetrakis-(hydroxyetohoxymethyldimethylsiloxy)silane with the same 3 compounds of pentaerythritol (4), (5), (6).

The s t u d y of the bis-(hydroxyethoxymethyl)tetramethyldisiloxane and tetrakis-(hydroxyethoxymethyldimethylsiloxy)silane condensations with the tetraadipate, tetrasebaceate and tetrasuceinate of pentaerythritol showed these processes to follow a second-order reaction (Fig. 3). The polycondensation rate constants calculated from the changes of acid numbers, using the equation for a himolecular irreversible reaction, i.e. k----p/(ta (l--p)), in which k is the rate constant, p the extent of reaction at time t, a the original concentration of carboxyl groups, are listed in Table 1. In accordance with the statistical calculations of Flory [4] the condensation of tetrafunctional branched units with difunctional compounds, using equivalent amounts of reagents, should produce structuration (gelling) at a critical branching coefficient a c r ~ l / ( f - - 1 ) = 0 . 3 3 and a critical reaction efficiency pcr=v/~----57.5~o. A comparsion of the reaction efficiency results obtained before structuration showed even the best (46~o), the pentaerythritol tetrasebaceate

T e t r a f u n c t i o n a l acid ester condensations

735

condensation with bis-(hydroxyethoxymethyl)tetramethyldisiloxane to be lower than the calculated. Similar results were also established in the case of tetrafunctional acid esters with tetrafunctional organosilicon alcohols. Flory gave ~cr=0"33 for such systems and per=acre33 %. The maximum efficiency for this type of condensation was actually found to be only 22%. Zg9

"--~ 150 %

110 ]

0

90 Time, rain

30

~Z)

I20

FzG. 2. Changes of the acid n u m b e r s of the c o n d e n s a t i o n p r o d u c t s of c o m p o n e n t s as n a m e d in Fig. 1 (1) to (6) respectively.

The study of polymer structuration beyond the gel point from the yield of gel fractions showed here also typical changes which depended on the nature of the acid esters used at the start and the organosilicon acids. 5

~y

4

3 1

0

20

40 T/kne , rn/n

I

60

FIG. 3. Inverse eonoentration o£ the carboxyl groups in the mixture as a £tmetion o£ t ~ e d ~ m g the tetrak~s-(hyc1~oxyethox-L~ethy1~ethyIBiloxy)sil~o condensation w i t h the t e t r a s u c c i n a t e (1), t e t r a - a d i p a t e (2) or t e t r a s e b a c e a t e of p e n t a e r y -

t h r i t o l (3).

736

K. A. AlgDRIANOVand V. N, YEMEL'YANOV

As Fig. 4 shows, t h e 9 0 % gel f r a c t i o n yield was o b t a i n e d quickest w i t h acid esters h a v i n g short branches a n d w i t h a n alcohol f u n c t i o n a l i t y of 4 (curve 1), while t h e slowest yield was o b t a i n e d w i t h long-chain acid esters a n d a n alcohol f u n c t i o n a l i t y o f 2 (curve 5). T A B L E I . I ~ A T E C O N S T A N T S OF T H E t'OLYCONDEI~'SATIOI~" OF ORGANOSILICOI~ ALCOHOLS W I T H O L I G O ~ E R I C A C I D E S T E R S TO T H E G E L P O I N T

Components

k, min -1 (equiv./g) -1

Bis- (hydroxyethoxymethyl)tetramethylsiloxane+ pentaerythritol tetrasuccinate Bis- (hydroxyethoxymethyl)tetramethylsiloxane+ pentaerythritol tetra-adipate Bis -(hydroxyethoxymethyl)tetramethylsiloxane-~pentaerythritol tetrasebaeeate Tetralds- (hydroxyethoxymethyldimethylsiloxy)silane-p pentaerythritel tetrasuccinate Tetrakis -(hydroxyethoxymethyldimethylsiloxy)silane+ pentaerythritel tetra-adipate Tetrakis- (hydroxyethoxymethyldimethylsiloxy)silane+ pentaerythritel tetrasebaceate

1.65 1.59 1.50 3.49 2.58 1.69

The s t u d y o f the soluble p a r t of t h e polymer, before reaching t h e 90% gel fraction, showed it to h a v e a c o n s t a n t acid n u m b e r which was identical w i t h t h a t o f t h e s y s t e m a f t e r r e a c h i n g t h e gel point. This was observed to be valid for all the systems studied.

oI00~ ~

0

I 3

I G

] 9

I I2

T/me , hp

FIG. 4. Gel fraction content produced when eondensmg tetraMs-(hyc~oxyethoxy-

methyldimethylsiloxy)sflane with the tetra-adipate (1), tetrasebaeeate (2), or bis(hydroxyethoxymethyl)tetramethylsiloxane with the tetrasuceinate (3), tetra-adipate (4) or tetrasebaceate (5) of pentaerythritol.

Tetrafunctional acid ester condensations

737

The calculation of the polymer structuration rate based on the formation of the gel fraction showed this process to be a second-order reaction. The calculated reaction rate constants of gel fraction formation are given in Table 2. T A B L E 0. I ~ A T E C O N S T A N T S OF GELATIOIW I N T E E COI~'DE1WSATIONS OF O R G A N O S I L I C O I ~ ALCOH O L S W I T H OLIGOI%IERIC A C I D E S T E R S

Components Bis- (hydroxyethoxymethyl)tetramethylsiloxane+ pentaerythritol tetr asuccinate Bis- (hydroxyethoxymethyl)tetramethylsiloxane+ pentaerythritol tetra-adipate Bis(hydroxyethoxymethyl)tetramethylsiloxane+ pentaerythritol tetr asebaeeate Tetrakis-(hydroxyethoxymethyldimethylsiloxy)silane + pentaerythritol tetra-adipate Tetrakis- (hydroxyethoxymethyldimethylsiloxy)silane+ pentaerythrito1 tetrasebaceate

]cx l0 s, rain -1 (rel. cone.)-*

1-3 0-7 0.6 5.4 1-5

According to the results given in the Tables and in Fig. 4, one can see t h a t an increase of the distance between the caxboxyl group and the central atom in the acid ester, and a decreasing functionality of the alcohol reduced the rate of condensation prior to the gel point, but also the rate of polymer strueturation. The s t u d y of the thermomechanical properties of the polymer showed typical changes with respect to acid ester condensations with di- as well as tetrafunctional organosilicon alcohols. The condensation products obtained prior to reaching the gel point axe characterized by curves 1 and 2 in Fig. 5a, or by curve 1 in Fig. 5b; these do not show a n y region corresponding to a highly elastic state but a course typical for liquids. Substantial changes of the thermomechanic~fl properties took place with the development of structuration. Where its degree was low (40% gel-fraction content of polymer), one could observe a highly elastic state in the temperature range from --30 to +300°C at a high deformation stress ( e - 65%). The increase of the gel fraction content of the polymer to 75% caused e to drop to 35%; the range of elastic state temperature remained the same. dropped to 20% at 90% gel fraction content. These changes characterize the subsequent development of the cross-linking structure. EXPERIMENTAL

The following compounds were used in this work: pentaerythritol tetrasuccinate (I), acid number 430, ester number 430; pentaerythritol tetra-adipate (II), acid number 345, ester number 346; pentaerythritol tetrasebaceate (III), acid number 255, ester number 254. The acid esters were produced by an earlier described method [1]. The bis-(hydroxyethoxymethyl)tetramethyldisiloxane (IV) [3], b.p. 133/2 ram, n~ 1.4425. Tetrakis-(hydroxyethoxymethylsiloxy)silane(V) [5] had a 10.65% OH content; n~ 1.4500.

K. i . kNDaU~OV a n d V. ~ . YEMEL'YANOV

738

Compound I I I (10.56 g) was condensed with I V (6.48 g) at 160°C in a dry nitrogen stream in a flask fitted with a thermometer, stirrer a n d condenser. The reaction was regulated on the basis of the acid numbers b y titration with a 0.05 normal alcoholic solution of K O H or

C~ EL

f00 Z

/

o

Tempepature , °0

~, %

/ 2

/62

J

320 Tern,oeratz~pe ~ °0

Fza. 5. Thermomechanical curves of the condensation product of: (a) bis-(hydroxyethoxymethyl)tetramethylsiloxane with pentaerythritol tetra-adipate; (b) tetrakis(hydroxyethoxymethyldimethylsiloxy)silane with the tetra-adipate at different stages; a: 1 -- starting mixture; 2 -- polymers at 40 % conversion (on CO OH ); 3 -- polymers with 40% gel fraction content; 4 - - 7 5 % gel fraction; 5--90~o gel fraction. b : / - - p o l y m e r s after 20% conversion (on COOH); 2--polymer with 20% gel fraction content; 3-- 75~o gel fraction; 4-- 90% gel fraction.

HC1, and on the basis of viscosity increase (the spec. viscosity of 1 ~o solutions in a 1 : 1 ethanol/toluene mixture). The results are reproduced in Figs. 1 and 2. The gel point was the point at which the polymer was insoluble in the boiling solvents. Mixing was stopped at the start of gelation and the subsequent progress of condensation was followed from the increase of gel fraction content. Periodically, samples were extracted with absolute alcohol in a Soxhlet of 30 ml working capacity. The gel fraction was dried to constant weight at 1-2 tara v a c u u m and 50-60°C, also determining the acid n u m b e r of the extracted fraction. The gel fraction contents are given in Fig. 3. The acid numbers of the soluble fraction during condensation a n d after reaching gel point was (rag KOH/g): 78 (30 rain), 85 (4 hr), 92 (7 hr). The acid number of the eondensates prior to gelation was 82.

Tetrafunctional acid ester condensations

739

Compound I I (14.48 g) was condensed with IV (12.61 g) and followed in the same manner; the results are shown in Figs. 1, 2 and Tables 1, 2. The thermomechanical curves of the products axe given in Fig. 5a. The acid numbers of the soluble fraction after reaching the gel point were: 92 (30 min), 91 (1 hr 20 min), 88 (4 hr 30 rain). Compound I (6"92 g) was condensed with IV (7.29 g) under the same conditions. The acid numbers of the soluble fraction were: 149 (45 min), 153 (2 hr), 151 (4 hr 30 min), 157 (5 hr 10 rain). Compound I I I (7.67 g) was condensed with V (5-50 g) in a similar manner. The acid numbers of the soluble fraction were: 119 (30 rain), 114 (1 hr), 123 (3 hr 30 min). Compound I I (7.82 g) was condensed with V (7-50 g) by the same method. The acid numbers of the soluble fraction were: 133 (12 min), 128 (30 min), 133 (1 hr), 137 (1 hr 30 min). Compound I (3.27 g) was condensed with V (3.82 g) by the same method. The acid number of the soluble fraction was about 140 mg KOI-I/g. CONCLUSIONS

(1) Some of the kinetic principles o f t h e c o n d e n s a t i o n o f acid esters o f general f o r m u l a C [CH~OC (O) (Ctt2)nCOOH]4, in w h i c h n : 2,4,8, w i t h b i s - ( h y d r o x y e t h o x y m e t h y l ) t e t r a m e t h y l s i l o x a n e a n d t e t r a k i s - ( h y d r o x y e t h o x y m e t h y l s i l o x y ) s i l a n e were studied. T h e r a t e c o n s t a n t s of t h e polyesterification a n d f o r m a t i o n of t h e gel f r a c t i o n were calculated. (2) I t was established t h a t t h e r a t e o f c o n d e n s a t i o n prior to gelation, b u t also a f t e r t h e s t a r t of gel f o r m a t i o n was inversely p r o p o r t i o n a l to t h e l e n g t h of b r a n c h ing in t h e acid esters a n d d i r e c t l y p r o p o r t i o n a l to t h e f u n c t i o n a l i t y of t h e o r g a n o silicon alcohol. (3) I t was f o u n d t h a t t h e c o n d e n s a t i o n efficiency u p to gelation increased w i t h increasing l e n g t h o f b r a n c h e s in t h e acid esters. (4) T h e soluble f r a c t i o n was f o u n d t o h a v e a c o n s t a n t acid n u m b e r after t h e gel p o i n t was r e a c h e d a n d was t h a t of t h e s y s t e m prior to gelation. Translated by K. A. ALLEN REFERENCES 1. K. A. A_N])RULNO¥ and ¥. N. Y E M E L ' Y A ~ I ) ¥ , Ptast. massy, No. 2, 22, 1965

2. 3. 4. 5.

K. K. P. K.

A. ANDRIANOV and V. N. YEIVIEL'YAN(}V,Vysokomol. soyed. 7: 534, 1965 A. ANDRIANOV and L. I. ~ O V A , Dokl. Akad. Nauk SSSR 127: 1213, 1959 FLORY, J. Am. Chem. Soc. 63: 3083, 1941 A. ANDRIANOV and L. I. MAIKAROVA, Dokl. Akad. Nauk SSSR 161: 5, 1965