Silicones and Silicone-Modified Materials - ACS Publications

Chapter 30

Block Copolymers Containing Silicone and Vinyl Polymer Segments by Free Radical Polymerization 1

1

2

2

2

D. Graiver , B. Nguyen , F . J. Hamilton , Y . Kim , and H . J. Harwood 1

Dow Corning Corporation, Midland, MI 48686-0994 Maurice Morton Institute of Polymer Science, The University of Akron, Akron, OH 44325-3909

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Polysiloxanes with terminal hexenyl groups were converted by ozonolysis into polysiloxanes with terminal aldehyde functionality. These were used in combination with copper octanoate, triethylamine, pyridine and triphenylphosphine to initiate the polymerization of styrene, methyl methacrylate and styrene/methyl methacrylate mixtures at 70°C. The polymerizations yielded block copolymers containing polysiloxane and vinyl (co)polymer segments. Depending on how the polymerizations terminated, the block copolymers had triblock or multiblock architec tures.

The reactions of the enolates of aldehydes and ketones with copper (II) salts have been known for many years to yield α-acylcarbon-centered radicals which couple to form 1,4-dicarbonyl compounds in nearly quantitative yields (7-5).We have found that the radicals that are intermediates in these reactions are useful for initiating polymeriza tion reactions and have shown that these reactions are very valuable for the synthesis of polymers with useful end-group functionality, block copolymers and graft copoly mers (4-8). In this paper we report the application of this chemistry to novel polysiloxanes with terminal aldehyde functionality. These materials have recently been synthesized in Dow Corning laboratories via the reaction of ozone with polysiloxanes having ter minal olefmic unsaturation (8,9). Since unsaturated polysiloxanes can be prepared in considerable variety using conventional polysiloxane technology, and since the ozonolysis process is simple (9,10), these new polysiloxanes are also potentially available in considerable variety. When these materials are used, in conjunction with copper salts, to initiate vinyl monomer polymerizations, a large variety of multi-segment block copolymers containing polysiloxane segments can be synthesized. In this paper we discuss the preparation of multi-block copolymers containing poly(dimethylsiloxane) and polystyrene and/or poly(methyl methacrylate) segments. Block copolymers containing polysiloxane segments are of interest because the polysiloxane blocks can

© 2000 American Chemical Society

Clarson et al.; Silicones and Silicone-Modified Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

445

446

impart impact resistance, toughness, water resistance and valuable surface properties to products containing the block copolymers and because the copolymers can be valuable as thermoplastic elastomers, compatibilizing agents, wetting agents and emulsifiers, etc. Burger and Kreuzer (II) have recently reviewed other ways of making such copolymers.


Experimental Aldehyde-Functional Polysiloxane Synthesis. Poly (dimethylsiloxanes) containing 1-hexenyl-dimethylsiloxane end groups, D C 7691 (n = 200), D C 7692 (n = 100) and D C 7697 (n = 30), were dissolved in hexane or methylene chloride (1 g/ml) and the solutions were cooled to -20°C. Ozone was then bubbled through the solutions and then into a Nal solution to decompose any excess that had not been reacted and prevent its release to the atmosphere. Treatment of the reaction mixtures with ozone was stopped after the Nal solution developed a blue color indicating that all the unsaturation had been consumed. The reaction mixtures were then allowed to warm to room temperature and heated for one hour at 40°C with Zn powder/acetic acid (1:1 molar ratio) to convert the ozonized groups on the polymers to aldehyde groups. The reaction mixtures were then filtered to remove zinc oxide, washed with water to remove excess acetic acid and then dried. Removal of the solvent by distillation then yielded the aldehyde-functional polysiloxanes. Listed below are the polymers prepared for use in this study. The polymers exhibited characteristic aldehyde absorption a t - 1733 cm" . 1

CH CH

O

II

I

I

3

3

3

CH

I

O

II

3

H C ( C H ) Si (O Si) O Si ( C H ) C H 2

4

n

CH

3

CH

2

3

£H

4

3

Table I. Aldehyde-Functional Poly(dimethylsiloxanes) Employed in This Study Mw/Mn Polysiloxane Mn n Parent Polysiloxane GPC** Calc* 1.88 4800 2522 I 30 D C 7697 II

100

DC 7692

III 200 DC 7691 * Calculated from n. **Polystyrene calibration.

7702

10000

1.81

15102

20400

1.69

Polymerization Procedure. All polymerizations were conducted in one ounce bottles under an argon atmosphere either in bulk or using benzene as a solvent to minimize chain transfer reactions. A typical reaction mixture contained 10 ml benzene that had been distilled from CaH , copper octanoate (0.1 g, 2.86 x 10' mole), pyridine (0.5g), triphenylphosphine (0.3g, 1.14 x 10" mole), triethylamine (O.lg, 1 x 10~ mole), monomer (~ 5 ml) and aldehyde-functional polydimethylsiloxane (0.4 - 2.34 g, 3.1 x 10" mole of aldehyde groups). After being heated at 70°C for 21 hr., the reaction mixtures were cooled to room temperature, diluted with benzene, and added to methanol to pre4

2

3

3

4


447

cipitate the polymers. The products were washed with fresh methanol and dried to a constant weight under vacuum at room temperature. They were then analyzed by H N M R and G P C . In some cases, the products were extracted with hexane and reana lyzed by * H - N M R . Control experiments i n which aldehyde-functional polysiloxane was omitted from the formulation or replaced by silicone o i l either failed to yield polymer or yielded only small amounts o f very high molecular weight homopolymer ( M n ~ 300K). When styrene was polymerized using butyraldehyde as the coinitiator instead o f aldehyde-functional polysiloxane but in which silicone o i l was present in an amount equivalent to the aldehyde-functional polysiloxane only polystyrene formed. This result is consist with the report that chain transfer constants for polysiloxanes i n styrene and M M A polymerizations are very low (12). Downloaded by IOWA STATE UNIV on March 2, 2017 | http://pubs.acs.org Publication Date: May 4, 2000 | doi: 10.1021/bk-2000-0729.ch030

1

Decomposition of Polysiloxane Segments in Polydimethylsiloxane-Polystyrene Block Copolymers. T o characterize the polystyrene segments i n polydimethylsiloxane-polystyrene multi-block copolymers, the copolymers were degraded by a strong acid. This was achieved by dissolving 0.5 g samples o f the copolymers i n toluene (40 m L ) and adding p-toluenesulfonic acid monohydrate (0.3 g). The solutions were refluxed for four hours at 120°C, concentrated to about one-half their volume and poured into methanol to precipitate the hydrolyzed polymers. These were then washed with water and dried. The N M R spectra o f the products were equivalent to the spectra o f conventional polystyrene samples and contained only very weak signals i n the 0 ppm region, where residual polydimethylsiloxane segments would be detected. The polymers were then characterized by G P C . In other experiments, samples o f the co polymers (0.5 g) i n benzene (40 m L ) containing a few drops o f concentrated H S 0 were refluxed overnight before the degraded products were isolated. Control experi ments indicated that polystyrene segments were also degraded somewhat when H S 0 was used but not when p-toluenesulfonic acid monohydrate was used. 2

4

2

4

N M R Spectra. ' H - N M R spectra o f the copolymers (~ 20 mg) i n C D C 1 (~ 0.7 m L ) solution containing a small amount o f M e S i internal standard were recorded at 200 M H z using a Varian Gemini 200 N M R spectrometer, a pulse angle o f 90°, an acquisi tion time o f 3.74 sec and a 5 sec delay between pulses. C - N M R spectra were re corded at 100 M H z using C D C 1 as the solvent and M e S i as the internal reference. A 90° pulse, a pulse delay o f 4 sec and an acquisition time o f 1.6 sec were employed. 3

4

I 3

3

4

Results and Discussion General Chemistry. Although polysiloxanes that bear aldehyde functionality have not been described previously, they can be prepared quite easily by ozonolysis o f pre cursors that bear terminal olefmic groups. Hydrosilation can be used to prepare such materials from readily available precursors. The following series o f reactions was thus used to prepare polysiloxanes with terminal aldehyde functionality.


448

CH

CH

3

i

CH

3

i

3

i

H S i - (0 Si^- 0 S i - H

+ excess C H = C H - ( C H ) - C H = C H

2

CH

CH

3

CH

3

2

CH

3

1 2

n

4


CH 2

1

= C H - ( C H ) S i - (0 Si) - 0 S i - ( C H ) C H = C H 2

CH

3

4

0 — 0

CH

2

2

CH

3

n : 2

CH

3

4

3

OSi-(CH ) CH 2

CH

3

2

3

CH, CH

3

CH-(CH ) Si-(0-Si) 2

2

CH3

3

1

CH

CH

2

3

CH CH

2

CH

4

2

0—0

3

Zn, H O A c

f O

CH

II

I

CH

I

I

3

CH

3

O

II

3

H C - ( C H ) S i - (O - S i ) : O - S i - ( C H ) C H 2

4

n

CH

CH

3

2

2

CH

3

4

3

Except for ozonides obtained from vinylsiloxanes, the ozonides that result from these reactions are surprisingly stable. Figure 1 shows the C - N M R spectrum o f an ozonide that was prepared from D C 7697 (n = 30). It contains resonances at 1, 18, 23, 29, 41, 94 and 104 ppm. Chemical shifts calculated for the carbon atoms in this compound (1.5(3,4),15.7(1),24(2),26.3(6),30.4(7),97.3(5) and 99.3(6) ppm) correspond reasonably well with those observed. Polysiloxanes containing the ozonide functional ity can, i n fact, be used as macroinitiators for block copolymer synthesis (13). 1 3

(3) H s

? (6)/°\(5) O Si - C H C H C H C H - C H CH 2

fk (l) (4) 3

2

(2)

2

(8)

2

(7)

2

\J Q

Reaction o f ozonized polysiloxanes with zinc and acetic acid at 40° converts the ozonide groups to aldehyde groups. Table I provides information about the alde hyde-functional polysiloxanes that were employed i n this investigation. When solutions o f aldehyde-functional polysiloxanes, copper octanoate, triethylamine, pyridine, triphenylphosphine and monomer i n inert solvents such as benzene are heated, radicals can be generated at the polysiloxane ends and these can initiate polymerization. This is shown below, where M is a monomer unit.



449

CUCU

CH C1 2

2

r

j .

HI

L

I 100

90

80

70

60

50

40

30

20

10

6 ppm

Figure 1.

13

C - N M R Spectrum of Ozonide Obtained from D C 7697.


450

O

CH

CH

3

CH

3

O

3

H C - ( C H ) ii - (O - Si) _ O - Si - ( C H ) ! : H 2

4

n

CH

2

CH

3

3

2

CH

4

3

CgOCOR): ^Pyridine, (|) P 3

O

CH

CH

3

3

H C - ( C H ) si - (o - k) . Downloaded by IOWA STATE UNIV on March 2, 2017 | http://pubs.acs.org Publication Date: May 4, 2000 | doi: 10.1021/bk-2000-0729.ch030

2

4

2

CH

3

O

3

o - si - ( C H ) C H ! : H

n 2

CH

CH

3

CH

3

3

nM O

CH

3

H C - ( C H ) k - (O 2

4

CH

3

CH

3

ii) _

2

CH

3

n

CH

O

3

O - Si - (CH 2 ) 4 I:H - M n . CH

CHO

3

Depending on the mode of termination of the propagating polymer radicals, and the efficiency of the initiation process, the block copolymers that result can have diblock, triblock or multiblock structures. When methacrylate esters are polymerized, diblock ( A B ) or triblock ( A B A , where A = polyM and B = polysiloxane) copolymers are expected because termination occurs by disproportionation. When acrylates or styrenes are polymerized, multiblock ( A B ) should be obtained. Information about the size of the individual blocks in some types of block copolymers can be obtained by degrading the polysiloxane segments with acid and then examining the A segments that remain. For example, when block copolymers containing polystyrene and polysiloxane segments are degraded with toluenesulfonic acid monohydrate, the polysiloxane segments are destroyed and the polystyrene segments can be isolated. [-(polysiloxane) - (polystyrene)-] IRSO3H x polystyrene

x

Polysiloxane-Polystyrene Block Copolymers. Figure 2 shows G P C curves measured from polymer I (A), a polysiloxane-polystyrene block prepared from it before (B) and after (C) hexane extraction and the hexane extract (D). Very little, if any, of material eluting above 22.0 mL is evident in the B and C chromatograms and it appears that most of the product that is soluble in hexane has a higher molecular weight than polymer I. This result, the low amount of the hexane extract (13 wt%) and the fact that its N M R spectrum indicates it to contain about 30 weight percent polystyrene, suggest that block copolymer formation occurred efficiently. Figure 3 shows the 'H-NMR spectrum of a polysiloxane-polystyrene copolymer in CDC1 solution that was prepared from polymer I and then exhaustively extracted with hexane. It contains resonances characteristic of polystyrene [8 = 1.0-1.6 (2H, CH ), 1.6-2.0 (1H, C H ) , 6.2-6.8 3

2



451

Figure 2. G P C Curves Observed for Parent Polysiloxane ( A ) , a PolysiloxanePolystyrene B l o c k Copolymer Derived From it Before (B) and After (C) Hexane Extraction and the Hexane Extract (D).



452

l

Figure 3. 200 M H z H - N M R Spectrum of a Polysiloxane-Polystyrene Block Copolymer.


453

(2H, o-phenyl-H) and 6.8-7.3 (3H, m + p-phenyl-H) ppm] and polydimethylsiloxane (8 = 0). The relative areas o f the polystyrene ( A ) and polysiloxane ( A ) resonances and the degree o f polymerization (n) o f the parent polysiloxane can be used to calcu late the average number o f styrene units in the polystyrene segments (N) as follows: st

si

A /(6n)


si

This equation is based on the assumption that there are as many polystyrene segments in the copolymer as polysiloxane segments which, i n turn, is based on the assumptions that each aldehyde group in the parent polysiloxane yields a radical and that termination occurs exclusively by radical combination. Figure 4 shows the ^ - N M R spectrum o f the polystyrene that was obtained after the block copolymer was degraded by heating at 120°C with a solution o f p-toluenesulfonic acid i n toluene for four hr. The spectrum is almost devoid o f polysilox ane resonances at 0 ppm. Control experiments with polystyrene demonstrated that polystyrene was not degraded by this treatment. Figure 5 compares the G P C curves observed for the parent polysiloxane, the polysiloxane-polystyrene block copolymer, and the polystyrene that was obtained after the polysiloxane segments had been destroyed by treatment with acid. The molecular weight and molecular weight distribution results obtained from such G P C data provide a considerable amount o f information about the structures o f the copolymer. Table II provides information about styrene polymerizations that were initiated by polymers I, II, and III in combination with copper octanoate, 0 P , E t N and pyri3

3

Table II. Synthesis and Properties of Block Copolymers Containing Polysiloxane and Polystyrene Segments Ill Starting Polysiloxane II / / Wt. Polysiloxane (g)

0.4

0.4

1.2

2.3

Wt. Polystyrene (g)

5.0

5.0

5.0

5.0

Y i e l d o f Copolymer (g)

3.0

2.45

2.26

5.75

% Styrene Polymerized

52

41

21

69

M n o f Copolymer ( G P C )

98K

83K

32K

156K

M w / M n o f Copolymer

5.7

6.8

2.2

3.8

M n o f Copolymer ( H - N M R )

23K

31K

20K

36K

M n o f Copolymer (Calc)

20K

23K

14K

37K

M n o f Recovered PS

14K

36K

M w / M n o f Recovered PS

3.7

——

!

3.3



454

—r-r-» 10

' ' 1 t 9

"i r r . t- r -i -i i -i | • , i i ! i t i I T 1 • ' •-T'"' • '"1 8 7 6 5 4 3 2 1

"'') ' • • ' 1 -' " ' '"'1 0 ppm

Figure 4. 200 M H z 'H-NMR Spectrum of a Polystyrene Recovered After Degrading a Polysiloxane-Polystyrene Block Copolymer with p-Toluenesulfonic Acid Hydrate.

Figure 5. GPC Curves Observed for Parent Polysiloxane (A), a PolysiloxanePolystyrene Block Copolymer Derived from it (B), and the Polystyrene Obtained After Degrading the Copolymer with Sulfuric Acid (C).


455

Included in the table are M n and M w / M n values measured for the copolymers by along with values that were obtained for the polystyrenes that were recovered the copolymers after the polysiloxane segments had been degraded by treatment H S0 . In most cases, the molecular weights o f the polymers are approximately four times the calculated sums o f the molecular weights o f the parent polysiloxanes and the polystyrenes recovered from the degraded copolymers. They are also approximately four times the molecular weights that can be calculated from the styrene unit/siloxane unit ratios (determined by N M R or from the styrene conversions and molecular weights o f the parent polysiloxanes) o f the copolymers, assuming one polystyrene segment per polysiloxane segment. A l l this information is consistent with the copoly mers having structures that can be represented as shown above. Downloaded by IOWA STATE UNIV on March 2, 2017 | http://pubs.acs.org Publication Date: May 4, 2000 | doi: 10.1021/bk-2000-0729.ch030

dine. GPC from with

2

4

O

CH

CH

3

CH

3

CH

3

3

CH

O

3

H (:!((CCHH 2) 4) S ^H i-O ( 0--kS-i^- )O0 S ^ i - ( C H ) 2l cCHH--PPoollyyssttyyrreennee--C CH H--( C H ) S i - ( 0 SSii)) (( C H ) - J : H 2

T

CH

CH

3

2

CH

3

22

CHO

3

CHO

3

nn

CH

3

CH

2

33

3

Such structures are believed to result from termination o f growing polystyrene segment radicals by combination. Each such termination reaction yields a polysiloxane-polystyrene block copolymer (or a multiblock copolymer) with terminal polysil oxane segments that can also bear aldehyde ends. These, in turn, can initiate the poly merization o f other polystyrene segments and ultimately larger multiple segment block copolymers can be formed. This view o f the polymerization process is supported by the fact that the co polymers have multimodal molecular weight distribution curves and M w / M n values that increase with styrene conversion, becoming as large as 6.8. In addition, the mol ecular weights o f the polystyrene segments that were obtained by degrading the co polymers with H S 0 followed by G P C analyses were consistent with those expected based on N M R analyses o f the block copolymers and the reactant quantities and con versions used to prepare them. A s should be expected, the M w / M n values o f the poly styrene segments were less than those o f the parent block copolymers. 2

4

Block Copolymers Containing Polysiloxane and P o l y M M A Segments. Figure 6 shows the H - N M R spectrum o f a polysiloxane-polyMMA block copolymer prepared from polymer I. It contains resonances typical o f p o l y M M A [8 = 0.7-1.3(3H,CH ), 1.3 - 2 . 2 ( 2 H , C H ) , 3.5-3.7(3H,OCH ) ppm] and polydimethylsiloxane ( 8 - 0 ppm) seg ments. Assuming one polysiloxane segment per molecule, the number average molec ular weight o f the copolymer can be calculated from the relative areas o f the reso nances due to p o l y M M A ( A ) and polysiloxane ( A ) segments as shown below where n is the D P o f the parent polysiloxane. ]

3

2

3

M M A

1

Mn=

si

MM A

AAl

\

~

14A ^ 6n ;

A f 7 5 ( n - 2 ) + 30Q 6

s i

s i

6n


Clarson et al.; Silicones and Silicone-Modified Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2000. I

'

'

'

'

I

9

1

' 1

1

8

1

'

1

1

I

7

'

'

'

'

6

1 '

1

'

1

5

I

1

'

1

1

4

i

1

'

'

1

3

I

1

'

2

1

1

I

'

1

' •

1

—I—

Figure 6. 200 M H z 'H-NMR Spectrum of a Polysiloxane-PolyMMA Block Copolymer.

'


Oppm

457

The weight percentage o f M M A units i n the copolymers can also be calculated from the A and A values, as follows: M M A

s i

14 A

s

6n

100

xlOO

wt%MMA =14 A

100

s


6n

7 5 ( n - 2 ) + 300

Since poly(methyl methacrylate) radicals terminate by disproportionation, the p o l y s i l o x a n e - p o l y M M A block copolymers may not have the multiblock structures the polysiloxane-polystyrene block copolymers have. Instead they might be expected to have B A B triblock or A B diblock structures. In accord with this expectation, the poly s i l o x a n e - p o l y M M A blocks prepared (Table III) have narrow molecular weight distri butions, M w / M n ~ 2, and monomodal G P C curves. Table III lists M n values determined for the copolymers by G P C along with values calculated as described above, assuming one polysiloxane segment per copoly mer molecule. For copolymers prepared from I (n = 30), the M n values measured by G P C are nearly twice those calculated from A and A values. This indicates that the copolymers contain, on an average, 1 . 7 - 1 . 9 polysiloxane segments per molecule. However, for copolymers prepared from II or III, the M n values determined by G P C and from A and A values are rather similar. They very likely have the A B A or A B structures expected. It appears that some process which is dependent on conver sion and end group concentration can cause the copolymers to contain more than one polysiloxane segment. This could indicate involvement o f radicals derived from the aldehydes in ter mination reactions. W e have observed that the parent aldehyde-functional polysiloxM M A

M M A

s j

s i

Table III. Synthesis and Properties of Block Copolymers Containing Polysiloxane and P o l y M M A Segments /

/

/

/

Wt. Polysiloxane (g)

0.4

0.4

0.4

Wt. M M A (g)

5.0

5.0

Y i e l d o f Copolymer (g)

4.9

% M M A Polymerized

II

III

0.4

1.2

2.3

5.0

5.0

5.0

5.0

5.0

4.2

4.6

4.3

6.8

89

92

76

84

62

90

M n o f Copolymer ( G P C )

81K

78K

82K

74K

128K

99K

M n o f Copolymer ( N M R )

43K

46K

48K

40K

124K

79K

M n o f Copolymer (Calc)

30K

31K

30K

29K

27K

44K

1.9

2.1

1.9

2.1

2.3

1.9

Starting

Mw/Mn

Polysiloxane


458

anes couple to form higher molecular weight polymers upon being exposed to the polymerization conditions in the absence of monomer. This will be the subject of a subsequent publication Block Copolymers Containing Polysiloxane and Poly(styrene-co-MMA) Segments. Table IV provides results obtained when polymer I was used to initiate polymerizations of styrene, M M A and styrene-MMA mixtures. The H - N M R spectra of the products corresponded well with those of conventional polymers and copolymers having the same composition except for the presence of a signal at ~ 0 ppm due to the polysiloxane segments. Exhaustive extraction of the products with hexane failed to remove this component, providing evidence that block copolymers had indeed been formed. The GPC curves of the products were, with the exception of the polysiloxanepolyMMA block copolymer, all multimodal, and their Mn values, measured by GPC, were approximately 4x those calculated by N M R analysis, assuming one polysiloxane segment per molecule. This indicates that the copolymers containing statistical styrene-MMA copolymer segments had multiblock structures similar to those of copolymers with polystyrene segments. The Mw/Mn values observed for the copolymers tend to increase with styrene content. This may reflect the fact that termination by disproportionation of propagating methacrylate radicals may be significant when the M M A content of the copolymerization mixture is high but that termination by combination of propagating styrene radicals with other propagating styrene radicals or with propagating M M A radicals will become of increasing importance as the styrene content of the polymerization mixtures increases.


!

Table IV. Results of Copolymerizations Conducted Using Polymer I 4 Experiment 3 1 2

5

0.4

0.4

0.4

0.4

0.4

0

2.0

2.5

3.0

5.0

5.0

5.0

2.5

2.0

0

4.76

4.62

2.84

3.12

2.66

Mn (GPC)

56.7K

158K

93.3K

102K

83.4K

Mn (NMR)

28.4K

41.8K

20.9K

19.8K

20.8K

1.8

2.6

4.0

7.5

6.8

1(g) Styrene (ml) M M A (ml) Polymer Yield (g)

Mw/Mn

100 59 49 Mole% Styrene in Monomer 0 28 Feed 100 58 Mole% Styrene in 50 0 33 Copolymer Segment (Calc)* 100 62 Mole% Styrene in 47 0 31 Copolymer Segment (NMR) *Calculated from monomer feed composition, conversion and reactivity ratios of 0.52 and 0.46 for styrene and M M A , respectively.


459


Conclusions Hexenyl groups i n polysiloxanes react readily with ozone to form rather stable ozonides that can be converted to aldehydes by treatment with zinc and H O A c . This flexible ozonolysis process yields aldehyde-containing siloxanes, cyclic polysiloxanes and polysiloxanes. Polydimethylsiloxanes containing terminal aldehyde functionality that are prepared by this process can be used i n conjunction with copper octanoate and organic bases to initiate polymerizations o f styrene, M M A , and other monomers and thereby obtain copolymers with polysiloxane and organic polymer segments. The re actions described herein provide the basis for an extremely versatile and diverse route to multiblock copolymers containing polysiloxane segments. Depending on the struc ture o f the starting polysiloxane, block copolymers, graft copolymers, and polymers with star structures can be prepared. In one sense, polysiloxanes with terminal alde hyde functionality can be regarded as multifunctional components o f redox initiation systems, but i n a perhaps more significant sense, they can be regarded as starting ma terials for the synthesis o f a multitude o f multiblock copolymers containing organic polymer and polysiloxane segments. In future publications we w i l l provide more in formation about the scope o f this chemistry and about the properties o f the materials that are obtainable with it.

Literature Cited 1. 2. 3. 4.

5.

6. 7.

8. 9. 10. 11. 12. 13.

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Silicones and Silicone-Modified Materials - ACS Publications

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