Investigation of the molecular weight distribution of organosilicon oligomers and its effect on the MWD of foam stabilizers

Polymer Bcleace U.S.S.R. Vol. 22, 1~o. 12, pp. 2877-2881, 1 9 8 0 Printed in Poland

0032-3950/80/122877-05507.50[0 ~) 1981 Pergamon Press Ltd.

INVESTIGATION OF THE MOLECULAR WEIGHT DISTRIBUTION OF ORGANOSILICON OLIGOMERS AND ITS EFFECT ON THE MWD OF FOAM STABILIZERS* A. P. ANDREYEV,I. A. VAKHTINA and O. G. TARAKANOV All-Union Scientific Research Institute for Synthetic Resins (Received 3 November 1978)

Organosilicon foam stabilizers have been obtained by the grafting of polyethcr molecules on to polydimethylsiloxane. The way in which the molecular weight distribution and the number distribution of the polyether blocks in these compounds depend on the MWD of the organosilicon oligomer and the distribution of reactive hydrogen atoms along the oligomer chain has been determined. THE use of polydimethylsiloxane oligomers in the industrial production of organosilicon foam stabilizers for polyurethan compositions has posed a number of questions concerning the investigation of their composition, molecular-weight properties as well as the distribution of reactive hydrogen atoms (at which the addition of the polyether blocks occurs) along the oligomer chain. Clarification of these questions will enable the reproducibility of the synthesis and the high quality of the foam stabilizers to be ensured. The investigations were made on batches of organosilicorz oligomers produced in the U.S.S.R. and G.D.R. used for the production of t y p e K E P - 2 and K E P - 3 foam stabilizers. A foam stabilizer is a graft copolymer obtained b y the copolymerization of an organosilicon oligomer with an oligomeric ether. The general formula of the organosilicon oligomer has the following form: (CH~)

r

1 r 1,

.s~ o - 7 / - s , - o _ J o t , " s , - o - J:/si .

I f a random copolymer of ethylene oxide and propylene oxide (1 : 1)* with M~=1500-3000 is grafted on to this oligomer at the S i - - H bond, K E P - 2 is obtained; K E P - 3 is the graft copolymer formed with ethylene oxide having M n = 5 0 0 . We have previously shown [1] that type K E P - 3 foam stabilizers have a broad molecular weight distribution and there is, related to this, a distribution in the number of polyether blocks in the molecule, which has an effect on the foam stabilizing capacity of the compounds. * Vysokomol. soyed. A22: No. 12, 2627-2631, 1980. ¢ Molar ratio.

2877

2878

A.P. ~REYEV

et al.

The aim of the present investigation has been to determine the way in which the MWD and the distribution of the number of polyether blocks in KEP depend on the MWD of the organosilicon oligomer and on the distribution of reactive hydrogen atoms along the chain. The oligomers investigated have the following properties: Specimen

A

Mol.wt, specified during synthesis Hr* 9o Stoichiometry t

B

2900 0"152 M~D HD40

C

3900 0"157 M,D12HQ84

D

3000 0"204 M2D6HD~3.~

3000 0"198 M2DsHD3~.4

The properties of the two batches of type KEP-2 foam stabilizer synthesized from the organosilicon oligomer A and the polyether with M----1600 are shown below. The MWD and the distribution with respect to the blocks were determined for these batches of KEP-2. Molecular weight Uncombined polyether, ~/o H r (residual), ~o Kinematic viscosity at 20 °, cSt Si, %

6000 18'8 0.013 1350.52 11.0

6200 16.4 0.015 1539.65 13.0

The fractionation of the initial organosilieon oligomers and the type K E P foam stabilizers synthesized from them was carried out by glc with a standard waters chromatograph with a system of 3000, 1000, 1000 and 500 • styrogcl columns (solvent, ethyl acetate; working temperature, 30 ° C; rate of flow of the solvent, 1.2 ml/min). I n the analytical fractionation, 10 ml of the organosilicon oligomer and 6 ml of K E P were introduced into the column, working at a sensitivity of 4x. I n the case of preparative fractionation, 100 ml portions of the product to be investigated were introduced into the column. The necessary n u m b e r of narrow fractions were made in parallel experiments. I f there were any high or low molecular "tails", these were removed b y recycling the fractions. The number-average molecular weights were determined by ebulliometry (with a R a y type ebulliometer with 24 thermocouples). The concentration of reactive hydrogen atoms in the fractions was determined b y oxidizing the bromine in N-bromosuccinimide to bromide and the amperometrie titration of the excess N-bromosuceinimide with an 0.1 ~r solution of as'orbie acid. ~ This enabled the concentration of active hydrogen to be determined with an accuracy of up to 5= 2 rel. %.

Figure 1 shows the records of gel-chromatography for the uafractionated organosilicon oligomers. It may be seen that they all have a broad bimodal MWD. * Hr represents a reactive hydrogen atom. CH3 t M-- (CHs)sSi-- O-- 0.5;

I

CHs

I

DH----Si--O--;

D-- --Si--O--.

I

f

Hr CHa The method was kindly placed at our disposal b y colleagues from Forschungsstelle Rabedeul des VEB Chemiewerk Nunehritz (G.D.R.).

Investigation of MWD of organosilicon oligomers

2879

T h e specimens A a n d D were s e p a r a t e d into fractions, t h e fractions being selected i n t h e zones as shown in Fig. 1. T h e fractions were dried a t r o o m t e m p e r a t u r e a n d t h e p e r c e n t a g e c o n t e n t was d e t e r m i n e d b y weight. The M W D was calculated for each f r a c t i o n a n d the molecular weight a n d active h y d r o g e n c o n t e n t were determined. The results are shown in t h e Table.

llI

19

23

27

31

V3 , coun~

Fie. 1. Gel-chromatographic records of organosilicon oligomers showing the zones where. the fractions were selected. The numbering of the zones corresponds to the fractions in Table 1. I--specimen A; I I - - B ; I I I - - C and IV--D. A glc calibration curve was p l o t t e d f r o m t h e fractions of specimen A (Fig. 2) a n d t h e coefficients of polydispersity s h o w n in the Table were calculated for all t h e u n f r a c t i o n a t e d specimens a n d the molecular weight fractions. I t m a y be seen f r o m Fig. 2 t h a t f r a c t i o n 5 o f specimen A does n o t lie on t h e calibration line 1, R~.SULTS OF ANALYSISOF THE ORGANOSILICONOLIGOMERSAND THE FRACTIONSOF SPECIMENS A AND D VE

Specimen A

Fraction, No. Unfractionated 1

2 3 4 5 B

Unfractionated 1 2 3 4 5

in peak, ml I

113.75 123.75 134.75 146.50 161.00 m

112.50 118.00 130.00 143.75 150.50

Content, wt. %~

Hr, ~o

100.00 17.64 34-17 26.85 13.71 7-63

2100 9600 5000 2100 1000 1000

2'04

100.00 7.00 34.38 41.72 14.50 2-40

2550 10,230 7080 3130 1120 800

2"19 1 '05

1"10

0-19g 0.195 0-196: 0.197 0.194 0.190,

1"29 1'24 1"23 1"27 1"24

1"23 1"26 1"28

0.152 0.155 0.149 0.149' 0.15I 0-15(b

C

Unfractionated

100.00

2760

2"24

0-157

D

Unfractionated

100.00

2070

2"80

0-204

A. P. AZ~D~V.VEVe~ al.

2880

having the same molecular weight as fraction 4 b u t a greater elution volume. Since it differs in hydrodynamic volume b u t has the same molecular weight, this fraction may represent ring compounds formed in the first stage of the synthesis of the polydimethylsiloxanes. The presence in this fraction of components crystallizing at room temperature is evidence in favour of their being ring compounds [ogM 4

3 -

"-~,2 20

28

2q

32 'v3" ~coun~

FIG. 2. Calibration curves for/--linear and 2--ring oligomers. (the rings Ds and Ds are crystalline substances). B y taking gel-chromatography records of the ring products Ds and D~,* the values of their elution volumes were plotted on the graph (Fig. 2). It may be seen that the point corresponding to the fifth fraction lies in the elution region for the ring compounds. It m a y be suggested

1"0

~U

0"6

/

o2

4 '

0"2

/ I

~

2

I

I

4

r

I

I

6' PI. I 0 - *

FIG. 3. Integral MWI) curves for KEP-2 specimens calculated theoretically from the MWD of the organosilicon oligomer: 1 and 2 are points obtained by the preparative fraetionation of two batches of foam-stabilizer specimens based on oligomer A and a polyether with M=1600. 1--1~z~v.p_~6000 and 2--Mxsp_==6200. in this case that the later fractions of the oligomers investigated contain cyclic oligosiloxanes with M = 7 0 0 - 8 0 0 (Dg-Dll). Low-molecular ring compounds (just like the low-molecular linear fractions) increase, if they are present, the volume of the fractions of the organosilicon oligomer containing one active hydrogen * The authors wish to thank A. B. Zachernyuk for the ring oligosiloxanes made available.

Investigation of MWI) of organosilioon oligomers

2881

a t o m . This, in its turn, leads in the s u b s e q u e n t s y n t h e s i s t o a n increase in t h e yield of copolymer with a low content of grafted polyether blocks, whereas the basic product should contain 4 to 5 polyether blocks. The investigations showed that the active hydrogen contents in the initial samples and in the fractions were practically the same, that is, there is a single active hydrogen atom to a siloxane chain length with M ~ 6 6 0 in specimen A and with M----510 in specimen B, both in the low- and also in the high-molecular fractions. The grafted polyether blocks are also positioned in the same way in the foam stabilizer. It is known from analysis of the data t h a t approximately 1 0 ~ of the active hydrogen (see above) does not participate in the reaction. I t has been assumed, in connection with this, that the remaining hydrogen is uniformly distributed over all the fractions and the appropriate corrections have been introduced. The theoretical MWD of two batches of KEP-2 have been calculated from the MWD of the organosilicon oligomer an d the MWD of the polyether with M----1600, which was used in the synthesis. (It has been shown previously that polyethers of the type used have a narrow MWD [3]). Figure 3 shows their integral MWD curves. The points for the fractions obtained by actual fraetionation are shown on the same figure (preparative fraetiouation with a gel-chromatograph, as described above). The experimental data agree well with the calculations. Chemical analysis of the silicon content of the KEP-2 fractions shows that, in fact, a siloxane chain section containing 10 silicon atoms is associated with a polyether molecule for all the fractions, independently of their molecular weights. CH3

I

There is thus the same number of - - O - - S i - - links on average to each grafted

I

CH3 polyether block in the foam-stabilizer, independently of the molecular weight of the foam-stabilizer fraction. Organosilicon oligomers used for the synthesis of foam-stabilizers contain up to 10% of low-molecular (most probably ring) fractions. The broad MWD of the final products is dictated by the broad MWD of the organosilicon oligomers. Translated by G. F. ]~/~ODLEN REFERENCE5

1. I. A. BAKHTINA, A. P. ANDREYEV, A. V. GURYLYOV and O. G. TARAKANOV,

Vysokomol. soyed. B20: 416, 1978 (Not translated in Polymer Sci. U.S.S.R.) 2. ~I. C. MOORE, J. Polymer Sci. A2: 835, 1964 3. I. A. BAKHTINA, Candidate's Dissertation, Chernogolovka, Branch of the Institute of Chemical Physics, Academy of Sciences U.S.S.R., 1973