Flammability Improvement of Polyurethanes by Incorporation of a

Chapter 14

Flammability Improvement of Polyurethanes by Incorporation of a Silicone Moiety into the Structure of Block Copolymers

Downloaded by MONASH UNIV on November 27, 2015 | http://pubs.acs.org Publication Date: July 21, 1995 | doi: 10.1021/bk-1995-0599.ch014

Ramazan Benrashid and Gordon L. Nelson College of Science and Liberal Arts, Florida Institute of Technology, Melbourne, FL 32901-6988

In recent years there is significant demand for flame retardant polymers which do not contain halogen or other additives. New polyurethane block copolymers containing silicone as the soft segment have been synthesized. This class of block copolymers microphase separates allowing formation of a siliconated surface. ESCA and X-ray analyses confirm enhanced siliconated surfaces for these block copolymers. Thermal analysis (TGA)shows these materials are thermally more stable than polytetrahydrofuran polyurethane and polyethyleneglycol polyurethane block copolymers (reference materials). Thermal stability of these siliconated block copolymers depends upon the content of the silicone soft segment. Oxygen index, a convenient technique for evaluation of theflameretardancy of polymers, shows siliconated polyurethanes have higher oxygen index values compared to reference materials. Siliconated block copolymers with higher polydimethylsiloxane content have higher oxygen index values. The oxygen index values also depend upon the diisocyanate used. For example, block copolymers made of hydroxy-terminated polydimethyl -siloxane, H M D I and 1,6-hexanediol show higher oxygen index values compared to block copolymers made of hydroxy terminated polydimethyl -siloxane, TDI and 1,6-hexanediol. This difference is related to the extent of soft block segregation. 1 2

Polymers used in engineering applications should withstand a variety of external stresses, e.g., heat, fire, moisture, ozone, corona, etc. Indeed materials which can be specially tailored by chemistry and by processing are required for many applications. Many materials to be used successfully require significant fire retardant properties. It is increasing recognized that such materials should be halogen free, given the potential for severe damage by even a small fire in electrical and other systems when HX or other corrosive gases are released . In one approach this can be done either by introducing silicone or phosphorus, which have inherent flame retardancy in the backbone of a 1

0097-6156/95/0599-0217$12.00/0 © 1995 American Chemical Society In Fire and Polymers II; Nelson, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


218

FIRE AND POLYMERS II

polymer (block copolymer) or by blending a silicone polymer with other polymers. This method has an advantage over heavily loading a base resin withfillersand additives to reach a desired level of flame retardancy. In the additive approach physical and mechanical properties of the base polymers are affected, and generally not for the better. Furthermore, systems heavily loaded with halogen containing materials or metal compounds are coming under scrutiny in many industries for other safety and environmental reasons. Silicone polymers have a different backbone versus more common polymers, a backbone consisting of alternating silicon and oxygen atoms rather than carbon atoms. The side groups are similar to those found in natural rubber and many other organic polymers. The resistance of silicone rubber to high temperature, ozone, corona, weathering and other environmental factors that tend to deteriorate insulation, is attributed to the silicone-oxygen linkage. Previous work has shown that incorporation of a siloxane moiety into the polymer back-bone provides enhanced thermal stability, hydrolytic properties and low energy surface properties, gas permeability, chain flexibility, oxygen plasma resistance and blood compatibility " 1. Silicones contribute to flame retardancy of other polymers in two ways: l)as a silicone flame retardant additive for thermoplastics with major application in polyolefins " , or 2) by incorporation as a part of the backbone, e.g., a silicone polyimide copolymer which is a non-halogen inherently flame retardant thermoplastic. Fire resistant materials have been synthesized by insertion of siliconated materials into the structure of a variety of polymers " . The formation of intumescent char is a highly effective flame retardant mechanism. Ideally, the substrate under burn conditions is protected from catastrophic destruction by a cellular char that is formed from at least partial involvement of the polymer substrate itself. The greater the substrate contribution to the char matrix the greater the effectiveness of the char. Benefits include lower additive loading and better overall mechanical performance. Kambour and co-workers > studied the effect of the siloxane moiety on the flame retardancy of polymers. They reported that the silicone moiety has a positive effect on the oxygen index values of polymers, causes a rise in pyrolytic char, and improvement in char oxidation resistance. The improvement may stem principally from enhanced oxidation resistance arising from the silicon retained in the char and converted to a continuous protective silica layer. In this paper we discuss the synthesis of flame retardant, thermally stable silicone urethanes block copolymers made as shown in Figure (1) and the evaluation of their thermal stability, flame retardancy and the effect of segregation on the flammability behaviour of the block copolymers. 2

12

1

15

16

19

20

21

Experimental Materials. Dihydroxy-terminated polydimethylsiloxanes (OHPDMS), poly-dimethyl siloxane-aminopropyl terminated (NH2PDMS) (different molecular weight), 1,3bis(hydroxypropyl)tetramethyldisiloxane (OHTMS), 1.3-bis(3-amino-propyl) 1,1,3,3-

In Fire and Polymers II; Nelson, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1995.


J

CH

0

=

C

=

N

_

R

N

3

i

3

C

2

6

XTTT

3

Ό

Λβ

>Block Copolymer

>. Block Copolymer

v s t

Cataly

TT

Hydroxy terminated Siloxane ^ Catalyst . . . or + HN - ( H ) - NH ^ B l o c k Copolymer 3 - Aminopropyl terminated S iloxanej | CH CH T

a t a

3-AmirK)propyltenTiinated Siloxane

o r

r

O ^ C I ^ N r ^ + HO-R'-OH

Block Copolymer

Figure 1. Synthesis Scheme for Silicone Urethane Block Copolyurethanes.

— =C=0 +

Oligomeric Diisocyanate +

2

CH Hydroxy terminated Siloxane

2

3

+

0)n-H HO-R'-OH

0=ON—R —N=C=0 4H N(CH )—(-^

3

3

CH

0=C=N—R —N=C=0+ HO—(-^i

CH



220


tetramethyldisiloxane (NH2TMS), and 1,4-bis(dihydroxy-dimethylsilyl)-benzene (OHDMSB) were purchased from Huls America. The oligomeric materials were degassed in a vacuum oven at 30 °C for 48 hr. Dicyclohexylmethane-4,4' diisocyanate (H12MDI), diphenyl-methane 4,4'diisocyanate (MDI), toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI) were supplied by Miles Corporation. 1,6Hexanediol (HDO), 1,4-benzenedimethanol (BDM), 2,2-bis'(4hydroxyphenyl)hexafluoropropane (FBPA), and hydroxy terminated poly(l-4butoxy)ether, were supplied by Aldrich Chemical Co. Dibromoneopentyl glycol (Saytex FR-1138) and the diol of tetra - bromophthalic diol, Saytex (RB-79), were supplied by Ethyl Corporation. Phosphorated diol FRD was supplied by FMC. Phosphorated polyol (Vircol) (M.Wt. 545) was supplied by Albright & Wilson. Polyamine 1000 (Eq. Wt. 555-625) , Polyamine 650 (Eq. 355-475) and Ultracast™ PE 35 (Eq. Wt 1150-1250) and Ultracast^PE 60 (Eq. Wt. 650-750) were supplied by Air Products Company. Dimethylacetamide (DMAC) was stirred over MgO for one week, then distilled under vacuum and kept over molecular sieves 4Â, and under a nitrogen atmosphere. Methylene chloride was refluxed over CaH2 and distilled immediately before use. Tetrahydrofuran (THF) and 1,4-dioxane were distilled from benzophenone ketyl immediately before use. Synthesis of Block Copolymers (Group A or B). Block copolymers were prepared by a technique called "a one shot technique" , from a diol terminated polysiloxane and corresponding diisocyanate and a chain extender, mixed at room temperature under a 23 dry atmosphere (N2). Synthesis details are published elsewhere To a specific amount of oligomer (dihydroxy terminated poly-dimethylsiloxane, or aminopropyl terminated polydimethylsiloxane) in 100 mL CH2CI2 were added HDO dissolved in 15 mL DMAC, and bis(4,4'-diisocyanatocyclohexyl)methane (H12MDI) or toluene diisocyanate (TDI) in 100 mL CH2CI2. Several drops of catalyst solution (dibutyltin dilaurate) were added and the solution was mechanically stirred under nitrogen at room temperature for specific period of time. Completion of the reaction was monitored by disappearance of the isocyanate IR absorption at 2270 cm" . The solvent was evaporated in vacuo leaving a viscous oil. The polymer was dissolved in 50 mL 1:1 CH2CI2/DMAC, THF or 1,4-dioxane, and the solution was cast into films on glass plates. Thefilmswere removed from the glass after drying and stored for at least 4 weeks before test. For reference, the side of the film which faces the glass was considered the backside of the film. All Group A and Β polymers and films were made using the same general procedure. The variations in reaction parameters are reported in Tables (1 and 2). GPC on one set of copolymers (Group B) showed Mw of 118000-150000 and Mn 37000-103000. 22

1

Synthesis of Diisocyanate Terminated Oligomers (C-51> 2,2-Bis(4hydroxyphenyl)hexafluoropropane 20 g, ( 0.059 mol) was dissolved in 80 mL dried


14.

Flammability Improvement of Polyurethanes

BENRASHID & NELSON

Table 1. Synthesis of Block Copolyurethanes: Group A Polymer

Oligomer weight

Wt

CH2C12

Wt(g)

Wt

Cosolvent

Soft block

g

mL

Diisocyanate

(g)Diol

DMAC

%

Film Flexibility


mL

-

20

250

13.8 H

15

50

20

250

13.8H MDI

6.3 H D I O L

15

50

36000 H O P D M S

10

180

12.8 H , M D I

20.7 H D I O L

20

35

36000 O H D M S O

7.5

150

20.5 H

MDI

9.3 H D I O L

20

20

A-20

36000 O H P D M S

4

200

24.8 H i M D I

11.2HDIOL

20

10

+

A-21

18000 O H P D M S

10

180

19.6 H i M D I

10.4 H D I O L

20

25

-

A-22

18000 O H P D M S

4

180

24.8 H , M D I

11.2 H D I O L

20

10

+

A-25

18000 O H P D M S

3

200

25.5 H , M D I

11.5 H D I O L

15

7.5

+

A-26

18000 O H P D M S

1.5

200

19.6 H

8.9 H D I O L

20

5

+

A-27

18000 O H P D M S

1

200

26.9H1 MDI

12.1 H D I O L

15

2.5

+

A-30

36000 O H P D M S

1

180

13.1 H I J M D I

15.9 H D I O L

15

5

+

A-34

36000 O H P D M S

1

180

26.9 H M D I

12.1 H D I O L

15

2.5

+

A-35

36000 O H P D M S

2

200

17 H P . M D I

7.6 H D I O L

15

7.5

+

A-39

36000 O H P D M S

4

200

20.2

15.9 F R D

20

10

-

A-42

36000 O H P D M S

3

180

16.1 T D I

10.9 H D O L

20

10

+

A-43

18000 O H P D M S

3

200

16.1 T D I

10.9 H D O L

20

10

+

A-44

18000 O H P D M S

7.5

200

18.8 T D I

12.3 H D O L

20

20

+

A-45

4200 O H P D M S

6

200

14.3 T D I

9.7 H D O L

20

20

+

A-46

18000 O H P D M S

8

200

11.1 T D I

7.6 H D O L

20

30

+

A-47

4200 O H P D M S

8

200

11.1 T D I

7.7 H D O L

20

30

+

A-48

18000 O H P D M S

12

200

10.7 T D I

7.3 H D I O L

15

40

+

A-49

4200 O H P D M S

12

200

10.7 T D I

7.3 H D I O L

15

40

+

A-50

18000 O H P D M S

15

200

8.9 T D I

6.1 H D I O L

15

50

+

A-51

4200 O H P D M S

15

200

8.10 T D I

6.1 H D I O L

15

50

+

A-52

18000 O H P D M S

10

200

24.8 I I , M D I

2 OHTMS

10

10

-

A-55

18000 O H P D M S

3

200

13.9 H i M D I

13.1 A P T M S

15

10

+

A-59

36000 O H P D M S

8

200

20.2 T D I

12.9 H D I O L

20

120

-

A-60

36000 O H P D M S

12

200

16.7TDI

11.3 H D I O L

20

30

+

A-61

36000 O H P D M S

15

200

13.4 T D I

9.1 H D I O L

20

40

+

A-62

36000 O H P D M S

15

200

11.2 T D I

8.8 H D I O L

A-64

18000 O H P D M S

3.6

200

16.2 H , M D I

15.8 D B N P D O

A-65

1200-2000 O H P D M S

4

200

21.5 T D I

A-66

1200-2000 O H P D M S

8

200

19.1 T D I

A-ll

36000 O H P D M S

A-12

2000 O H P E

A-17 A-18

1

4

MDI

1 2

1 2

2

L 2

2

2

2

2

MDI

1 2

2

1 2

5

2

2

2

2

6.3 H D I O L

3

6

7

20

50

+

20

20

+

14.6 H D I O L

20

10

+

12.9 H D I O L

20

20

+

8

A-67

1200-2000 O H P D M S

12

200

16.7TD1

11.3 H D I O L

20

30

+

A-68

1200-2000 O H P D M S

16

200

14.3 T D I

9.7 H D I O L

20

40

+

A-69

1200-2000 O H P D M S

20

200

11.9 T D I

8.1 H D I O L

20

50

+

A-70

36000 O H P D M S

20

200

11.9 T D I

8.1 H D I O L

20

A-71

36000 O H P D M S

5

200

12.5 T D I

32.5 T B P D O

20

10

-

A-72

990

8

200

19.1 T D I

11.3 H D I O L

20

20

+

A-73

990

12

200

16.7 T D I

11.3 H D I O L

20

30

+

9.7 H D I O L

20

40

+

19.5 D B N P D O

15

10

-

21.7 0 H T M D S

15

20

1 0

A-74

990

16

200

14.3 T D I

A-79

36000OHPDMS

4

200

16.5 I P D I

A-80

36000 O H P D M S

4

200

11.6 H M D I L 2

1 1

9

+

-

1) Hydoxy terminated polydiinethylsiloxane, 2.) Dicyclohwxylmethane-4,4'-diisocyanate, 3.) 1,6-Hexanediol, 4 ) Hydroxy terminated polyethylene ether, 5 ) Toluene Diisocyanate, 6)Hydroxy terminated tetramethydisiloxane, 7.) 3-aminopropylterminated tetramethyldisiloxane, 8 ) Dibromoneopentyldiol, 9)Tetrabromophthalic diol, 10) Poly(niethyl-phenylsiloxane), 1 l)Isophrone diisocyanate


221

222

FIRE AND P O L Y M E R S II

THF. To this solution was added 17.60 g (0.10 mol) IPDI under nitrogen over a period of 45 minutes. The solution was heated for 4 hrs at 120 °C (oil bath) under a nitrogen atmosphere. The reaction mixture was cooled to room temperature. The solvent was evaporated in vacuo leaving 37.8 g of product. The molecular weight by end group analysis was 850. The above procedure was used to make all the diisocyanate terminated oligomers. The experimental variations are presented in Table (3). 24

Synthesis of Block Copolymers Group C, (C-53). To 11.9 g of oligomer (C-51) in 80 mL CH C1 were added 17.24 g of hydroxy terminated poly-dimethylsiloxane (M.Wt 1500) in 80 mL THF at room temperature under a nitrogen atmosphere over a period of 45 minutes. Stirring was continued at room temperature for 2 hrs. The reaction mixture was stirred at 55-60 °C for 93 hrs. Completeness of the reaction mixture was monitored by disappearance of the isocyanate IR absorption at 2267 cm" . The viscous solution was cast as a film on a glass plate using a 10 mil film applicator. After standing 24 hrs, the films were removed from the glass. The experimental variations are presented in Table (4). All samples intended for surface analysis were exposed to an additional 4 days in a vacuum oven at 25-30 °C. The samples used for TGA and DSC were dried in a vacuum oven at 65-70 PC for 14 days. The polydimethylsiloxane is the soft block and the polyurethane is the hard block.


2

2

1

Synthesis of Block Copolymers Group D. The procedure was as described for Group A and B, except NjN'dimethylhexamethylenediamine was used as the chain extender. Table (5). Measurements Thermogravimetric analysis was performed on a DuPont model 951 TGA attached to a DuPont model 9900 analyzer. Version 2.2 analysis software was utilized to calculate the percent residue. The samples were analyzed in a tared aluminum pan placed in a platinum basket. The purge rate was set at 50-60 rnL/min for N2 or air and the heating rate was set for a 20°C/min increase from ambient temperature to 630°C. Differential scanning calorimetry (DSC) experiments were performed on a DuPont model 910 DSC attached to a DuPont model 9900 analyzer using version 2.2 DSC software to analyze some of the transitions. Samples were analyzed in a crimped aluminum pan with lid. An empty aluminum pan with lid served as a reference. The purge rate was 34 rnL/min N2and the heating rate was 10 °C/minfrom-75 to 150°C. SEM and EDS analyses were performed on a model S-2700 Hitachi scanning electron microscope with an attached Kevex light element detector. Electron beam energies were 20 Kev. Data were collected from a scanned region of approximately 100 X 100 square micrometers. The X-ray detector was operated in the thin window mode at less than 20 percent dead time. A Denton Desk II Sputter coater with a Pd/Au target was employed for coating SEM samples to reduce surface charging effects.


14.


BENRASHID & NELSON

223

Table 2. Synthesis of Block Copolyurethanes: Group Β Polymer

Oligome rMWt*

Wt g

CH C1 mL 2

2

H12MDI Diisocyanate

Chain Extender g

Cosolvent mL

Soft Film Bloc Flexibility


g B-63

18000

4

120

24.8

B-64 B-65 B-66 B-67 B-68 B-69 B-72

18000 36000 18000 18000 18000 18000 18000

9 9 13.5 18 22.5 27 23

150 150 180 180 180 200 100

24.8 24.8 21.7 18.6 15.5 12.4 29.5

11.2 HDIOL 11.2 HDIOL 11.2 HDIOL 9.8 HDIOL 8.4 HDIOL 7.0 HDIOL 5.6 HDIOL 13.3 HDIOL

1

DMAC 15

k % 10

15:50 DMACTHF 80 THF THF 100 THF 100 15:10 DMAC:THF 15:90 DMAC:THF 120 THF

20 20 30 40 50 60 5

1) 1,6-Hexanediol

Table 3. Synthesis of Oligomers for Group C Block Copolyurethanes Oligomer

Diisocyanate*

Diamine

Diol

g

C-26

g Des-W 25,3

g 1,4-Bis(dihydoxydimetliylsilyl)benzene 12.5

C-27

Dew-W31.3

C-28

Isophrone 26.6 Isophrone 13.2 Des w 26.5 Isophrone 17.6 Isophrone 7.8

Bis(Ethylamino> dimethyl Silane 10 Bis(Ethylamino> dimethyl Silane 10

C-29 C-30 C-51 C-55

M.wt 1216 1700 1700

1,4-Bis(dihydoxydimethylsilyl)benzene 7.7 Phosphorated diol 30 2,2-Bis(4-hydroxyphenyl)hexafluoropropane 20

4,4-diaminophenylhexa-fluoropropane 10 Mole ratio of diisocyanate/diol or diisocyanate/diamine=l .6-1.7.

2700 1140 850 2067


+ + + + +

-

+ +

224


Table 4. Synthesis of Block Copolyurethanes: Group C


Polymer

diisocyanate terminated Oligomers

Wt

THF' mL

Oligomer

g

Oligomer M.Wt

wt g

Stirring period (hrs)

Film Flexibility

+

-

CMO C-42

2500 1140 (C-30)

20 17.3

50 100

OHPBE N H PDMS

2900 2500

23.2 38

96 14

C-43 C-44 C-45

2700 (C-29) 1140 (C-30) 1700 (C-27)

6.9 17.3 11.5

80 80 60

OHPBE OHPBE N H PDMS

2900 2900 2500

7.25 16.9 16.9

24 24 24

+

C-48

1700 (C-28)

11.5

90

Polyamine^

1238

8.4

40

C-49

1700 (C-27)

11.5

60

Polyamine^

950

6.4

149

C-50

1700 (C-27)

11.5

90

8.4

155

850 (C-51) 850 (C-51) 2067 (C-55)

11.9 11.9 8.5

80 80 80

Polyamine-* OH PDMS OHPBE

1238

C-53 C-54 C-57

1500 2000 545

22.4 28 2.3

93 93 95

-

2

2

2

Phosphorated diol^

+

+ •

1) Co-solvent was CH C1 (80-150 mL) 2) Hydroxy terminated polydimethyl siloxane. 3) 3-Aminopropyltenninated polydimethylsiloxane. 4) Ultracast PE 60. 5) Vircol (Albricht & Wilson). 2

2

Table 5. Synthesis of Block Copolyurethanes: Group D Polymer

D-77 D-78 D-79 D-80 D-81

Oligomer weight

OHPDMS (M.Wt. 2500) = = =

wt

Soft block %

TDI, 24.6

Wt(g) N,N'-Dimethylhexamethylene diamine 20.4

TDI.21.9 TDI, 19.2 TDI, 16.4 TDI, 13.7

18.1 15.8 13.6 11.3

20 30 40 50

g

THF mL

Wt(g) Diisocyanate

5

180

10 15 20 25

180 180 180 180

10


14.

BENRASHID & NELSON


225

Electron Spectroscopy for Chemical Analysis (ESCA) or X-ray Photoelectron Spectroscopy (XPS) data were obtained with a Phi model 15-255G Cylindrical Mirror Analyzer (CMA) attached to a Phi model 590 Scanning Auger Microprobe. The spectra were generated with Mg K-alpha X-rays at a power of 400 watts. The analysis area covered about 1 mm . Oxygen indices were performed on an original GE oxygen index tester. Oxygen index measures the ease of extinction of materials, the minimum percent of oxygen in a oxygen / nitrogen atmosphere that will just sustain combustion of a top ignited vertical test specimen. Oxygen index is one measure of flame retardancy and can be conveniently made on small quantities of sample. Oxygen index was performed on 2


25

samples in powder or flake form . A small porcelain cup was used which was installed on the clamp, the cup was loaded with sample, and the sample first was melted and then ignited for test. Results and Discussion Thermogravimetric Analysis. Introducing a silicone moiety into the structure of block copolymers increases the thermal stability of block copolymers in nitrogen and air compared a non-siliconated polyurethanes, Table (6). Char formation in air is characteristic of silicone polymers, because reaction of silicone with oxygen at high temperature leads to formation of inorganic silicon dioxide. The amount of weight residue increases with increasing the amount of silicone in the structure of block copolymer, Figure (2). EDS spectra of char resulting from air pyrolysis of polymer samples show only Si and oxygen peaks. Block copolymers containing higher silicone content show higher thermal stability, Figure (3). DSC. The results are shown in Table (7). The DSC measurements show two thermal transitions; the one at low temperature (-45 °C) is the m.p. for the siloxane moiety of the block copolymer and the one above room temperature is related to the glass transition of the urethane hard segment. Two Tg's at -120 and -150 °C and a low m.p —45 °C were reported by Inoue, et.al., for siloxane PPMA block copolymers. A melting point of -50 °C was reported for a polyurethane-polysiloxane graft copolymer by Kazama, et.al. 26

27

Oxygen Index. The oxygen index test of theflameretardancy of polymers is based on measuring the ease of extinction for materials in an oxygen / nitrogen mixture. The oxygen index can be measured for bar samples as well as flake, powder or liquid samples» ^» ^. The latter is useful for small amounts of sample. While oxygen index is only one fire parameter, materials with high oxygen index values are generally more flame retardant. The oxygen index value for non-siliconated ether-urethane block copolymers is in the range of 18 as shown in Table (8). We found that as the amount of siloxane in the structure of the block copolymers increases oxygen index values increase. For example oxygen indices for polymers with 2.5 to 50 percent siloxane 2

2


226


Table 6. Thermal Analysis of Block Copolyurethanes in Nitrogen and (Air)


Polymer

Τ (°C at 10% Weight Loss)

A-12 A-ll A-17 A-18 A-27 A-26 A-25 A-22 A-21 B-63 B-64 B-68 B-72 C-45 D-79

316 (325) 319(310) 300 (311) 325 (323) 261 (252) 267 (273) 297 (298) 314(316) 335 (335) 308 (313) 309 (318) 313 (327) 308 (313) 290 (310) 322 (319)

Τ (°C at 50% Weight Loss)

1.0(0.9) 0.4(22) 1.2(4.1) 1.1(8.0) 0.4 (0.4) 0.2 (2.0) 1.6 (3.4) 1.0 (3.2) 0.0 (4.2) 0.8 (2.1) 1.5(4.1) 1.3 (5.0) 1.6 (5.8) 1.8 (3.5) 5.7(6.1)

389 (370) 374(367) 383 (402) 381 (379) 353 (359) 353 (365) 356 (370) 374 (370) 389 (386) 357 (357) 357 (357) 443 (435) 356 (357) 446 (454) 389 (403)

Table 7. DSC Data of Block Copolyurethanes. Polymer A-27 A-26 A-25 A-22 A-21 B-63 B-64 B-68 C-56 C-45

Soft block m.D°C

-

-45 -47 -47 -47 -41.6 -42.5 -43.7 -44.1

-

Residue (%)

Tg°C

Tm°C

53 31 51 47 54 68.6 82.0 83.1 60.2 93.7

93

-

120 93 119 126.3 114.6

-



14.


BENRASHID & NELSON

10

15

Silicone Content (%) Figure 2. Effect of Silicone Content of Block Copolyurethanes on Weight Residue from Thermal Analysis in Air (A-27, A-26, A-25, A-22 and A-21).

U ο

03 lm

ε Η

5 7.5 Siloxane Content (%)

10

Figure 3. Effect of Silicone Content of Block Copolyurethanes on Thermal Stability of Polymers (A-27, A-26, A-25, and A-22): Temperatures Related to 10 % Weight Loss in N (I), and in Air (II), and Temperatures Related to 50 % Weight Loss in N (III), and in Air (IV). 2

2


227

228

FIRE AND P O L Y M E R S II

Table 8. Oxygen Index Values of Example Block Copolyurethanes


Polymer

Silicone Content (%)

Oxygen Index

1-(Reference)* 2-(Reference)** 3-(Reference)*** Polydimethylsiloxane A-34 A-30 A-35 A-20 A-18 A-17 A-ll

0 0 0 2.5 5 7.5 10 20 35 50

18.2 18.6 PolyTHF(M.Wt 2500)+Hi MDI+HDIOL 17.6 Oligomeric polydimethylsiloxane 29.8 OHPDMS(M.Wt. 36000)+Hi MDI+HDIOL18.6 = 19.1 = 19.6 = 21.0 = 21.8 26.0 = 29.8 =

A-27 A-26 A-25 A-22 A-21

2.5 5 7.5 10 20

OHPDMS(M.Wt. 18000)+Hi MDI+HDIOLl 8.9 19.6 = 20.8 = = 21.5 22.2 =

A-45 A-47 A-49 A-51

20 30 40 50

OHPDMS(M.Wt. 4200)+TDI+HDIOL

A-43 A-44 A-46 A-48 A-50

10 20 30 40 50

A-42 A-59 A-60 A-61 A-62

10 20 30 40 50

A-65 A-66 A-67 A-68 A-69

10 20 30 40 50

Polyether(M.Wt 2900)+H MDI+HDIOL 12

=

2

2

******* 2

******** = = = *********

OHPDMS(M.Wt. 18000)+TDI+HDIOL = = = = *********

OHPDMS(M.Wt. 36000)+TDI+HDIOL = = *********

22.0 22.5 22.5 24.2 18.6 19.6 21.8 22.5 24.3 18.6 19.6 23.4 22.3 24.0

OHPDMS(M.Wt.l200-2000)Hi NTOH-l,6-HDIOL 19.5 = 22.8 21.3 = 22.8 24.3 = 2


14.


BENRASHID & NELSON

229

Table 8. continued


Polymer

Oxygen Index

Silicone Content (%)

A-72 A-73 A-74 A-64 A-79 A-80 A-39'

20 30 40

B-63 B-64 B-65 B-66 B-67 B-68 B-69 B-72

10 20 10 30 40 50 60 5

C-40 C-42 C-43 C-44 C-45 C-48 C-49 C-50 C-53 C-54 C-57

-

D-77

10

D-78 D-79 D-80 D-81

20 30 40 50

22.2 OHDMDPS(M.Wt. 990)+TDI+l .6-HDIOL = 22.2 23.2 = 25.7 OHPDMS(M.Wt.l8000)+Hi MDI +DBNPDO OHPDMS+IPDI+DBNPDO 25.8 29.8 OHPDMS+H12MDI +OHTMDS 21.0 OHPDMS+H12MDI+FRD ********** NH (CH )3PDMS(M.Wt.l8000)+Hi MDI+l,6HDIOL19.8 NH (CH )3PDMS(M.Wt.36000)+H, MDRl,6HDIOL20.7 NIl (CII )3PDMS(M.Wt.36000)+H MDI+l,6HDIOL19.8 = 24.3 = 25.9 27.4 = 27.9 = = 18.9 ********** 20.1 Ultracast PE 60 + PBE 20.7 C-30 + NH PDMS 19.8 C-29 + HOPBE 21.2 C-30 + HOPBE 20.5 C-27 + NH PDMS 24.0 C-28 + OHPDMS 23.9 C-27 + Polyamine 22.1 C-27 + Polyamine' 27.9 C-51 + OHPDMS 20.5 C-51 + PBE 20.1 C-55 + Phosphorated diol ********* 25.2 OHPDMS(M.Wt2500)+TDI + N.N'Dimethylhexanediamine = 27.4 28.7 = = 30.2 30.2 = 2

2

2

2

2

2

2

2

2

12

a

b

2

c

2

d

r

*10% Soft Segment, ** 20% Soft Segment, *** 10% Soft Segment a) Air Product Ultracast PE 60, b) 3-Aminopropyl terminated polydimethylsiloxane, c) Hydroxy terminated polydimethylsiloxane, d) Air Product Polyamine 650, e) Air Product polyamine 1000, 0 Vircol (Albricht & Wilson)


230

FIRE A N D POLYMERS II

content, (A34 through A l 1) oxygen index valuesrisefrom18.6 to 29.8, which is close to the oxygen index value for neat polydimethyl-siloxane oligomers. The effects of siloxane content on O.I. values for four sets of block copolymers containing 10 to 60 percent siloxane soft segment are presented in Figure (4). Different systems have different O.I. values. Phase segregation in these block copolymers leads to domination of siloxane on the polymer surface. Siloxanes have solid phase activity rather than vapor phase activity and reduceflammabilitythrough increased formation of pyrolytic char and also increased resistance to char oxidation ^" 1. Char acts as an insulator betweenfireand bulk, and prevents fire spread. Figure (5) shows a photograph of two samples before and after oxygen index testing. The surface of the tested sample was covered with silicon dioxide. Oxygen index data for a variety of block copolymers are presented in Table (8). There is a clear difference in oxygen index resulting from Hi MDI as the isocyanate versus TDI. Very short OHPDMS ( A l l versus A69) segments result in lower O.I. values due to lower expected segregation. Block polyurethanes with Ν,Ν-dimethylhexamethylenediamine as chain extender have higher oxygen index values compared to block polyurethanes with 1,6-hexanediol as chain extender, these results correlate with the thermogravimetric results.


2

2

2

SEM and EDS. While detailed surface studies of these materials have been published elsewhere **, not only is the microphase segregation phenomenon evident in block copolymers containing siloxane moiety, but the solvent from which a film is cast can have an effect on the extent of segregation and the amount of siloxane on the surface. For materials cast as films on glass plates, surfaces facing the glass showed lower silicone compared to the surface facing air, which is probably due to a hydrogen bonding interaction between the glass surface and the hard segment of the block copolymers. Figure (6) illustrates EDS spectra for polymer and its char. Comparison of these two spectra show that the carbon peak in the char spectrum has vanished, and that only peaks related to Ο and Si remain on fire exposure. Organic silicones convert to inorganic silicon dioxide. 3

ESCA ESCA studies for films resulting from casting of block copolymers with different siloxane content reveal that films cast from block copolymers with high silicone content show higher silicon concentration on the surface, Figure(7). A-51 with 50% silicone moiety shows higher silicon on the surface compared tofilmswith 40, 30 and 20 percent silicone content in which the silicon content on the surface was found to be 23.6, 10.7, 8.3 % compared to 29.2 %for A-51. The high degree of segregation of the soft block is due to a large difference between the solubility parameter of the two blocks " It is expected that the top surface of graft and block copolymers is significantly dominated by the siloxane segment component, even if the bulk siloxane is as small as 5 Wt percent . The thickness of the siloxane layer ranges from 100 to 20 Â depending on the soft segment length and siloxane content ^. It is also reported that the hard segment domains of 60-70 A long are found embedded in the soft segment matrix 5. 31

32

33

3

3


BENRASHID & N E L S O N



31

-•— IV —o— m —Δ— I Π

18

10

20

40

30

50

Silicone Content (%) Figure 4. Effect of Silicone Content of Block Copolyurethanes on Oxygen Index: (I) A-20, A-18, A-17, A-l 1; (II) A-43, A-44, A-46, A-48; and A-50, (ΠΙ) B-65, B-64, B-66, B-67, B-68, and (IV) D-77, D-78, D-79, D-80, D-81.

Figure 5. Photograph of Silicone Urethane Block Copolymer Samples (A) Before and (B) After Oxygen Index testing. The Surfaces of Samples After Test Were Covered with Si0 . 2


231


Si


Au

Pd

β Char

Kev Figure 6. EDS Spectra of Block Copolyiirelhane A-l 1, (A) Neat Film, (B) Pyrolytic Char; Carbon is Absent in the Latter.

1

1000

1

900

1

1

1

700

1

500

1

1

300

1

100

Binding Energy EV Figure 7. ESCA Spectra for Block Copolymer Films [A)A-45(20%), B)A-47 (30%), C) A-49 (40%) and D)A-51 (50%)]. Film Cast from DMAC/CH Cl . (Hard Segment Contains TDI). 2

2


14.

BENRASHID & NELSON


It is noted that block copolymers resulting from hydroxy terminated polydimethylsiloxane, H12MDI, and 1,6-hexandiol have better segregation compared to block copolymers obtained from hydroxyterminated polydimethylsiloxane, TDI and 1,6hexanediol, Figure 8 versus Figure 7. The compounds shown in Figure (8) show a minimal Nls peak despite low overall silicone content. This can explain why block copolymers from Hi MDI have higher oxygen index values compared to block copolymers obtained from TDI. In the case of first one, better segregation leads to a surface with higher silicone. Fire is a surface phenomenon, therefore having higher inherent flame retardant siloxane on the surface reduces theflammabilityof the block copolymers.


2

Binding Energy EV Figure 8. ESCA Spectra for Block Copolymer Films [A) A-27(2.5%), B)A-26 (5%), C)(A-25 (7.5%) and D) A-22(10%)]. Film Cast from DMAC/CH C1 . (Hard Segment Contains H12MDI). 2

2

Conclusions Segregated block copolymers of dimethylsiloxane urethane block copolymers can be made from hydroxy or amine terminated siloxanes a diisocyanate and a chain extender, or from diisocyanate terminated oligomers and hydroxy or amine terminated siloxane oligomers. A large number of new polymers have been synthesized.


233


234


These materials are microphase segregated and surface studies show an enhanced siliconated surface. Surfaces of the films show higher silicon compared to back or bulk of the films. These novel materials show most (>95 % ) of their siloxane content at the surface offilmscast from solution. Soft-hard block segregation makes these materials interesting for different applications. These materials show a low m.p. for the soft segment and a Tg above room temperature for the hard segment. By increasing the content of the siloxane moiety a more distinctive sharp peak is obtained in DSC. These materials are thermally stable, with stability increasing with increasing siloxane in the structure. Polymers with high silicone content show high oxygen index. Block copolyurethanes prepared from OHPDMS, H12MDI and 1,6-hexanediol have higher oxygen index values compared to block copolymers prepared from OHPDMS, TDI, and 1,6-hexanediol, which is due to better phase separation for the former block copolyurethanes. Block copolymers made of OHPDMS, TDI and N,N'dimethylhexamethylenediamine also show higher oxygen index values. While oxygen index is only one parameter for materials to be considered as flame retardant, polymers with a higher oxygen index and silicone content have higher weight residue. The enhanced flame retardancy of these materials is due to formation of S1O2 on the surface which insulates and protects the bulkfromfire. Silicone polyurethanes have three degrees of design freedom to achieve the desired silicone surface: chemistry (siloxane, isocyanate, chain extender), block size, and solvent or processing conditions. Clearly one can achieve significant fire retardancy (OI >28) at 50% or less silicone in the copolymer. References: 1. 2. 3. 4. 5.

6. 7. 8. 9. 10.

Hilado, C. J.; Casey, C. J.; Chistenson, D. F. and Lipowitz, J., J. Combustion Toxicology, 1978, vol. 5, 130. Hoshino, Y. K.; Katano, H. H.; and Oskubo, S. Japan Kokai Tokkyo Hoho, Jpn. Pat. 60,258,220. Dec 20, 1985; Chem. Abstr. 105:98559y. Toga, T. Y.;and Ikeda, N. Ger. Offen, D.E., March 21, 1985, 3.432.509. Mitsui Nisso Corp. Japan Kokai, Tokkyo, Koho, Jpn. Dec. 17, 1983, Pat. 58,217,515. Kotomkin, V. Y.; Baburina V. Α.; Lebedov E. P.; Bylev V. A.; Yasmikova T. E.; and Reikhsfeld V. O. Khimya i Parki Primonenie, Kremnii i Fosforogan, Soedin L, 23, 1980, Chem. Abstr. 95:43841d. Kotomkin, V. Y.; Baburina,V. Α.; Lebedev V. P.; and Kercha Y. Y. Sint Poliuretanov, 1981, 86-90. Kotomkin, V. Y.; Baburina, V. Α.; Lebedev, V. P. and Kercha, Y. Y.Plastic Massy, 27, 1981, Chem. Abstr. 95:43841d. Tsybul'ko, N. N.; Martinovich, F. S.; Satsura, V. M. and Mandrikova, A I.,USSR, Sept. 15, 1982, SU 958,432. Sodova, V. L.; Shepuev, E. L. ; Sergeev, L. V.; Sidorkova, T. V. and L. I. Makorova, Opt. Mekh. Prom-St, 1976, vol.43(5) 481/24/92. Ho Tai and Wynne, K. J. Preprints, American Chemical Society, Polymeric Materials Science and Engineering Division ( Washington DC), 1992, vol. 67,445.


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11. 12. 13. 14. 15. 16. 17. Downloaded by MONASH UNIV on November 27, 2015 | http://pubs.acs.org Publication Date: July 21, 1995 | doi: 10.1021/bk-1995-0599.ch014

18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

30. 31. 32. 33. 34. 35.

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Connell, J. W.; Smith Jr., J. W. and P. M. Hergenrother, P. M., J. of Fire Sciences, 1993, 11, 137. Bopp, R. C. and Miller S. US Patent, 22 May, 1979, 4,155,898. Mamoru Kondo, Jpn Kokai, Tokkyo Koho JP, 29 July, 1988, vol. 63,183,960. Frye, R. B., US Patent, August 20, 1985, 4,536,529. Winfried, P.; Jyergen, Κ. H.; Wolfgang S.; Christian, L.; Dieter, N.; and Werner, N., Offen DE, 14 March, 1985, 3,347,071. Factor, A.; Sannes, Κ. N.; and Colley, A. M., Fire and Flammability Series, part 3, edited by C. J. Hilado, Technomic Publishing Co., 1985, vol. 20,156-162. Collyer, Α. Α.; Clegg, D. W.; Morris, D. C.; Parker, G. W.; Wheatley G. W. and Arfield, G. C., J. Polym Sci., Part A. Polym. Chem. 1991, vol. 29, 193-200. Jadhav A. S.; Maldar, Ν. N.; Shide, Β. M. and Vernkar S. P., J. Polym Sci., Part A. Polym Chem., 1991, vol. 29, 193-200. Lavin, K. D. And Williams D. Α., International Wire and Cable Symposium Proceedings, 1986, 286-292. Kambour, R.P.; H.J. Klopfer, H. P.; and Smith, S. Α., J. Appl. Polym Sci. 1981, vol. 26(3), 847-859. Kambour, R.P., J.Appl. Polym. Sci., 1981, vol. 26(3), 861-877. Zdrahala, R. J.; Gerkin, R. M.; Hager, S. L. and F. E. Critchfield, J. Appl. Polym. Sci., 1979, vol. 24, 2041. Benrashid, R.; Nelson, G. L., J. of Polym. Sci., Polym. Chem., 1994, vol. 32, 1847-1865. ASTM Procedure D-1638-74, using bromophenol blue as indicator, American Society for Testing and Materials, Philadelphia, PA. Nelson, G. L.; and Webb L. L., J. Fire and Flammability, 1973, vol. 4, 325. Inoue, H.; Ueda, Α.; and Nagai, S. J., Appl. Polym. Sci., 1988, vol. 35, 20392051. Kazama, H.; Ono, T.; Tezuka, Y. and Imai, K. Polymer, 1989, vol. 30, 553-557. Benrashid, R.; and Nelson, G. L. Proceedings of the Fire Safety and Thermal Insulation, St. Petersburg, FL, November 4-7,1991, 189-201. Benrashid, R. and Nelson, G. L. Proceedings of Second Annual BCC Conference on Flame Retardancy, Crown Plaza Hotel, Stamford, Connecticut, May 19-21, 1992, 47-54. Benrashid, R.; Nelson, G. L.; Linn, J. H.; Hanely K. H.and Wade, W. R. J. Appl. Polym. Sci., 1993, vol. 49, 523-537. Shibayama, M. Inoue, M; Yamamoto, T. and Normura, S., Polymer, 1990, vol. 31, 749-757. Pascault, J. P. and Camberlin, J. P., Polym. Commun., 1986, vol. 27(8) 230 Tezuka, Y.; Kazama, H.; and Imai, K. J. Chem. Soc., Faraday Trans, 1991, vol. 87(1),147-152. Tezuka, Y.; Ono, T.; and Imai, K. J. of Colloid Interface Sci., 1990, vol. 16(2), 408-414. Shibayama, M.; Suetsugu, M.; Sakurai, S.; Yamamoto, T.and Nomara, S., Macromolecules, 1991, vol. 24, 6254-6262.

RECEIVED January 4,

1995


Flammability Improvement of Polyurethanes by Incorporation of a

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