Block and Graft Copolymers Containing Poly ... - ACS Publications

Chapter 25

Downloaded by UNIV OF TEXAS AT DALLAS on July 14, 2016 | http://pubs.acs.org Publication Date: March 10, 2003 | doi: 10.1021/bk-2003-0838.ch025

Block and Graft Copolymers Containing Poly(dimethylsiloxane) and Poly(4-vinyl-pyridine) Segments by Free Radical Polymerization 1

2

2

Yongsin Kim , Daniel Graiver , Gary T . Decker , Fernando J. Hamilton , and H. James Harwood 1

1

1,*

Maurice Morton Institute of Polymer Science, The University of Akron, Akron, O H 44325-3909 Dow Corning Corporation, 2200 West Salzburg Road, Midland, MI 48686-0994 2

Polysiloxanes with terminal or pendent aldehyde functionality can be used as components of copper salt-based redox initiation systems to prepare block, graft and crosslinked copolymers containing poly(4-vinylpyridine) and polysiloxane segments. The block and graft copolymers form very viscous solutions in dilute HCl and have useful anti-foam activity.

Introduction Block and graft copolymers containing polysiloxane backbones and tenninal or pendent hydrophilic polymer segments can be expected to have useful properties, particularly as antifoaming or defoaming agents, surfactants, wetting agents and hydrogels. This paper concerns polysiloxanes containing tenninal or pendent poly(4-vinylpyridine) segments.

296

© 2003 American Chemical Society

Clarson et al.; Synthesis and Properties of Silicones and Silicone-Modified Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2003.


297

Previously, block copolymers containing polysiloxanes and poly(2-vinylpyridine) or poly(4-vinylpyridine) segments have been prepared using anionic polymerization techniques (i-5). Synthesis via controlled radical polymerizations of 2-vinylpyridine or 4-vinylpyridine initiated by poly(dimethylsiloxane) macroinitiators containing bis(silyl pinacolate) groups has also been reported (6). We have previously reported that polysiloxanes with tenriinal or pendent aldehyde functionality can be prepared by ozonolysis of polysiloxanes containing tenninal or pendent hexenyl groups and then used as macromolecular reducing agents for the synthesis of block and graft copolymers (7, 8). In this paper, we report the synthesis of both block and graft copolymers containing poly(dimethylsiloxane) and poly(4-vinylpyridine) segments by polymerizations in which polysiloxanes with terminal or pendent aldehyde groups serve as macroreductants for redox-initiated reactions.

Experimental

Polysiloxanes with Aldehyde Functionality The preparation of aldehyde-functional polysiloxanes by ozonolysis of polysiloxanes containing hexenyl groups was described in previous patents, publications and abstracts (7^10). Table I provides information about the materials employed in this investigation. Polymers I-III contain terminal aldehyde groups and can be used to prepare block copolymers. Polymer IV contains two mole percent pendent aldehyde functionality and can be used to prepare graft or crosslinked copolymers.

4-Vinylpyridine Polymerization Procedure All polymerizations were conducted in 1 ounce bottles under an argon atmosphere using benzene as a solvent to rninirnize chain transfer reactions. A typical reaction mixture contained 10 ml benzene that had been distilled from CaH , copper octanoate, triphenylphosphine, triethylamine, pyridine, 4-vinylpyridine and aldehyde-functional poly(dimethylsiloxane). The amounts of aldehyde-functional poly(dimethylsiloxane) and copper(II) salts were varied to increase the amount of polysiloxanes in the copolymers. Tables II-IH provide recipes for the polymerization mixtures. 2



298

After being heated at 70°C for 21 hours, the reaction mixtures were cooled to room temperature and added to hexane or ether. The emulsions that formed were placed in a hood until the solvents had evaporated. The products were then dried for several days under vacuum at 55°C and ground to fine powders. They were then extracted with THF to remove catalyst components and residual polysiloxanes and were analyzed by ^ - N M R . THF extractions were performed by mixing 0.5 g samples with 10 ml THF and by shaking constantly overnight. Then the supernatent THF layers were removed and the polymer precipitates were washed with additional THF three times. A control experiment in which aldehyde-functional polysiloxane was omitted from the formulation failed to yield polymer (#14-2). Homopolymers of 4-vinylpyridine were also prepared by initiation using AJBN (#14-1) or butyraldehyde (#14-4).

Table I. Aldehyde-Functional Poly(dimethylsiloxanes) Employed in This Study Polysiloxanes Containing Aldehyde-Functional Groups at Chain Ends (I, Π and III) Ο

CH CH CH Ο II I I I I I HC(CH )4Si(OSi) OSi(CH )4CH 3

3

2

3

n

2

CH CH3 C H 3

3

Polysiloxanes Containing Aldehyde-Functional Groups at Branch Sites (IV) CH C H I I 3

3

(CH )3Si(OSi) (OSi) OSi(CH )3 3

n

CH

Polymer I II III

rv

η 30 100 200 50

3

m

3

(CH ) CH Ο 2

4

Mn Calculatedfromη 2,522 7,702 15,102 3,306

Mn GPC 4,800 10,000 20,400 3,800

Mw/Mn 1.88 1.81 1.69 2.12



10

5.00 4.76 I 0.40 1.59 10

5.00 4.76 I 0.40 1.59 10

5.00 4.76 I 0.40 1.59 10

5.00 4.76 butyraldehyde 0.03 3.61 10

5.00 4.76 none

5.00 4.76 AIBN

0.01 0.48

(g) (mole,xl0" ) Initiator

(g) (mole.xlO )

Benzene (ml)

4

2

10

0.80 3.17

0.50 6.32

0.25 3.16

0.63 7.90

0.63 7.90

0.63 7.90

0

3

(g) (mole,xlO" ) 4-Vinylpyridine

10

5.00 4.76 I

0.10 0.99

0.05 0.49

0.13 1.24

0.13 1.24 0.50 6.32

0.10 0.99

0.30 1.14

0.13 1.24

0.30 1.14

0.15 0.57

0.38 1.43

0.38 1.43

0.10 2.86

0

3

(g) (mole,xlO~ ) Pyridine

3

(g) (mole,xl0 ) Triethylamine

-4

(g) (mole.xlO ) Triphenylphosphine

0.38 1.43

0.10 2.86

0.05 1.43

0.13 3.58

0.13 3.58

4.00 2.65 10

2.00 2.60 10

1.60 6.34 10

5.00 4.76 III

0.50 6.32

0.10 0.99

0.30 1.14

0.10 2.86

5.00 4.76 II

0.50 6.32

0.10 0.99

0.30 1.14

0.10 2.86

5.00 4.76 I

0.50 6.32

0.10 0.99

0.30 1.14

0.10 2.86

vinylpyridine) block copolymers Polysiloxane -poly(419-4 19-2 19-3 83-3 19-1 17-3

14-3

14-4

0

Controls 14-2

0.13 3.58

14-1

0

Experiments Sample # Cu(II)Octanoate

Table Π. Polymerization Recipes for Controls and Block Copolymers



IV 0.32 0.84 5

IV 0.66 1.74

10

4

(g) (mole.xlO' )

Benzene (ml)

Initiator

1.25 1.19

5.00 4.76

(g) (mole,xl0 )

2

0.25 3.16

0.50 6.32

3

3

(g) (mole,xl0" ) 4-Vinylpyridine

Pyridine

0.05 0.49

0.10 0.99

(g) (mole,xl0 )

5

IV 0.64 1.68

1.25 1.19

0.50 6.32

0.10 0.99

0.30 1.14

5

IV 0.97 2.55

1.25 1.19

0.75 9.49

0.15 1.48

0.45 1.72

5

IV 1.28 3.37

1.25 1.19

1.00 12.7

0.20 1.98

0.60 2.29

5

IV 2.56 6.74

1.25 1.19

2.00 25.3

0.40 3.95

1.20 4.58

0.40 11.4

0.15 0.57

0.20 5.71

0.30 1.14

3

0.15 4.29

(g) (mole,xl0 ) Triethylamine

0.10 2.86

0.05 1.43

0.10 2.86

(g) (ΓηοΙβ,χΙΟ ) Triphenylphosphine

-4

Polysiloxane-poly(4-vinylpyridine) graft copolymers 27-2 27-3 27-4 27-5 27-6

27-1

Experiments Sample # Cu(II) Octanoate

Table III. Polymerization Recipes for Graft Copolymers


5

IV 5.09 1.34

1.25 1.19

3.00 38.0

0.80 7.91

2.40 9.15

0.80 22.9

27-7

301

Solution Properties


To study solution properties of polysiloxane-poly(4-vinylpyridine) block or graft copolymers, the copolymers (0.1 g) were mixed in distilled water (5 ml) and 5% HC1 was gradually added to the mixtures until gels formed. The addition of 5% H Q was continued until the polymer gels dissolved. The amounts of H Q added at the points of hydrogel formation and polymer dissolution were noted. Once polymer dissolution occurred, the reversion of their solutions to hydrogels was tested by adding NaOH solution.

Anti-foaming Experiments To evaluate the potential use of polysiïoxane-poly(4-vinylpyridine) block or graft copolymers as anti-foaming agents, the ability of the copolymers to break soap emulsions was tested. This was performed by nrôung 0.5 ml - 1 ml of polymer solutions in 5% HC1, obtained as above, with 5 ml soap water (0.5 g Dial hand soap containing mostly sodium laurel sulfate dissolved in 500 ml distilled water) in test tubes and shaking them vigorously. The heights of foam formed were measured after five minutes and compared to those formed by soap water alone, by soap water containing poly(4-vinylpyridine) solution in 5% H Q and by soap water containing only 5% H Q .

Results and Discussion

Polysiloxane-Poly(4-vinylpyridine) Block Copolymers Table IV provides information about 4-vinylpyridine polymerizations that were initiated by Polymers I, II and III in combination with copper octanoate, triphenylphosphine, triethylarnine and pyridine. Included in the table are yield, % conversion, the molecular weights that can be calculated from the 4-vinylpyridine unit/siloxane unit ratios detennined by NMR (Mn) along with wt. % of polysiloxane in the copolymers and the percent polysiloxane incorporated in the copolymer. In efforts to isolate the copolymers by pouring the polymerization mixtures into hexane or ether, emulsions formed that had to be concentrated to dryness to obtain the polymers. These were then purified by extraction with THF. Figure 1 shows the *H-NMR spectrum of polymer 19-3 after purification. Typically, the polysnoxane-poly(4-vinylpyridine) block copolymers contained 2-10 wt. % polysiloxane segments and the peak molecular weights of the polymers obtained


302


Table IV. Block Copolymers Containing Polysiloxane and Poly(4-vinylpyridine) Segments Sample #

14-3

17-3

83-3

19-1

19-2

19-3

19-4

Starting polysiloxane

I

I

I

I

I

II

III

Polysiloxane (g)

0.4

0.4

0.4

0.8

1.6

2.0

4.0

4-Vinylpyridine (g)

5.0

5.0

5.0

5.0

5.0

5.0

5.0

Copolymer yield (g)

4.2

4.3

4.4

4.4

5.0

4.3

5.4

VP conversion (%)

77.8

79.6

81.5

75.9

75.8

61.4

59.6

98K

115K

115K

85K

70K

107K

148K

2.6

2.2

2.2

3.0

3.6

7.2

10.2

26.9

23.5

24.2

16.3

11.3

15.5

13.8

...

383K

429K

526K

402K

—

—

Mn copolymer (*H-NMR) Wt. % polysiloxane in copolymer Polysiloxane incorporation (%) M copolymer (GPC) p

by GPC, using DMF as the solvent, M , were approximately 4xMn. This suggests that the copolymers have multiblock structures similar to the polysiloxanepolystyrene block copolymers previously obtained with the same initiating system. Such structures are believed to result from termination of growing poly(4vinylpyridine) segment radicals by combination. p

Polysiloxane-Poly(4-vinylpyridine) Graft Copolymers Table V lists the results of 4-vinylpyridine grafting onto Polymer IV. The products obtained were only partially soluble in chloroform and were mostly swollen gels. The gel contents of the copolymers increased as the amount of polysiloxane used in the polymerizations increased (27-1 < 27-5 « 27-6 « 277). The strong tendency of propagating poly(4-vinylpyridine) radicals to terminate by combination is believed to be responsible for the crosslinking reaction that occurs during these polymerizations. NMR analysis of swollen polymer gels allowed us to calculate the Mn's of the PVP segmentsfromthe 4-vinylpyridine unit/siloxane unit ratios. The polysiloxane contents of the copolymers were in the range of 2-12 wt. % and increased with the amount of Polymer IV employed.



303

J

Figure L H-NMR Spectrum of Purified Polysiloxane-Poly(4-vinylpyridine) Block Copolymer (19-3) in CDCl . 3

Solution Properties Polysiloxane-poly(4-vinylpyridine) block copolymers (#19-2, 19-3 and 194) were tested for solubility in dilute HC1 solution. Solutions of copolymers (2 wt %) in 0.1% HC1 were very viscous and gel-like but became milky solutions of very low viscosity in 5% HC1. When base was added to one polymer solution (#19-3), the polymer reprecipitated. The NMR spectrum of the recovered polymer was the same as that of the original polymer. Anti-foaming Properties Table VI compares the relative heights of the foams present five minutes after soap solutions containing small amounts of the polymer solutions in 5% HC1 were vigorously shaken. The results indicate that the block and graft copolymers have useful anti- or de-foaming properties and that their effectiveness depends on both the sizes of the poly(4-vinylpyridine) and polysiloxane segments and on whether they have block or graft architectures. Clarson et al.; Synthesis and Properties of Silicones and Silicone-Modified Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

304


Table V. Graft Copolymers Containing Polysiloxane and Poly(4-vinylpyridine) Segments Sample #

27-1

27-2

27-3

27-4

27-5

27-6

27-7

Starting polysiloxane

IV

IV

IV

IV

IV

IV

IV

Polysiloxane (g)

0.66

0.33

0.64

0.97

1.28

2.56

5.09

4-Vinylpyridine (g)

5.0

1.25

1.25

1.25

1.25

1.25

1.25

Copolymer yield (g)

5.3

1.3

1.4

1.3

1.8

1.6

2.0

VP conversion (%) Mn of Ρ VP segment

93.6

80.6

72.5

56.8

72.3

42.5

31.5

187K

99K

51.7K

36.6K

45.2K

33.2K

28.4K

2.0

3.7

6.9

9.4

7.8

10.3

11.8

16.0

14.6

15.0

12.6

10.9

6.4

4.6

(Ή-NMR) Wt. % polysiloxane in copolymer Polysiloxane incorporation (%)

Conclusions Polysiloxanes with pendent aldehyde functional groups can be used to syn thesize block and graft copolymers bearing poly(4-vinylpyridine) segments. The copolymers appear to have useful anti-foam activity.

Table VI. Relative Foam Heights After Vigorous Shaking Copolymer None 14-1 19-2 19-3 19-4 27-4

Polysiloxane Segment Type None I II III IV

Relative Foam Height (%L 50* 12 6 12 0 0

*100x Foam Height/Combined Height of Foam and Solution

References 1. 2. 3. 4.

Dean, J.W. U.S. Patent 3,673,272, 1972. Dean, J.W. U.S. Patent 3,875,254, 1975. Lee, J.A.; Hogen-Esch, T.E. Polymer Preprints 1993, 34(1), 556. Lee, J.A.; Hogen-Esch, T.E. Polymer Preprints 1996, 37(1), 591.



305

5. Nugay, N.; Kucukyavuz, Z.; Kucukyavuz, S. Polym.Internat.1993, 32, 93. 6. Crivello, J.V.; Lee, J.L.; Corlon, D.A. J. Polym.Sci.Part A Polym. Chem. 1986, 24, 1251. 7. Graiver, D.; Nguyen, B.; Hamilton, F.J.; Kim, Y.; Harwood, H.J. In Silicones and Silicon-Modified Materials; Clarson, S.J.; Fitzgerald, J.J.; Owen, M.J.; Smith, S.D., Eds.; ACS Symp. Series 2000; American Chemical Society, 2000; Vol. 729, Chapter 30. 8. Graiver, D.; Decker, G.T.; Tselepsis, A.J.; Hamilton, F.J.; Harwood, H.J. Polymer Preprints 1999, 40(2), 146. 9. Graiver, D.; Khieu, A.Q.; Nguyen, B.T. U.S. Patent 5,739,246, 1998. 10. Graiver, D.; Khieu, A.Q.; Nguyen, B.T. U.S. Patent 5,789,516, 1998.


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