Compatibility of iron-containing polymeric additives with a cable-grade plasticized poly(vinyl chloride)

Eur. Po!vm. J. Vol. 20, No. 11, pp. 1107-1111, 1984 Printed in Great Bri(ain. All rights reserved

0014-3057/84 $3.00+0.00 Copyright t" 1984 Pergamon Press Ltd

COMPATIBILITY OF IRON-CONTAINING POLYMERIC ADDITIVES WITH A CABLE-GRADE PLASTICIZED POLY(VINYL CHLORIDE) E. W. NEUSE*, N. SONNENBERG* and H. D. CHANDLERt *Department of Chemistry and tDepartment of Mechanical Engineering, University of the Witwatersrand, Johannesburg 2000, Republic of South Africa

(Received 22 February 1984) Abstract--Several linear polymeric ferrocene compounds with ~/, in the range 1200-3000 have been compounded with a cable-grade, DIOP-plasticized PVC at concentrations of 1-5~0; two non-polymeric ketoferrocenes and a heteroferrocene have been included for comparison. Moulded sheets, prepared from the compounded materials, have been evaluated for compatibility by visual inspection, from analyses prior to and after a heat aging treatment, and from stress strain data. Best performance with respect to all three compatibility criteria has been observed for a a poly(ferrocenylenemethylene) with ~/n = 2400, which shows excellent compatibility up to a loading of 90,/o. Good performance has also been demonstrated for a number of related polymers substituted at the bridging carbon atom. These findings suggest promising applications for selected polymeric ferrocenes as multifunctional additives for PVC-based engineering and biomedical materials.

INTRODUCTION The catalytic properties of ferrocene and some of its derivatives in hydrocarbon and solid propellant combustion have been amply explored and utilized over the past three decades. Intimately connected with this combustion-catalytic function are the more recently observed characteristics of flame retardance and smoke suppression shown by ferrocene additives in burning poly(vinyl chloride) (PVC) materials and other plastics compositions [1]. While these technologically important properties suggest challenging applications for such additives in the field of polymeric industrial and construction materials, the high vapour pressures of ferrocene and its simple alkyl derivatives present an obstacle to the general use of such compounds as smoke suppressants. As a result of high volatility, the additive, once migrated to the surface of the material, will suffer depletion by volatilization during (i) thermal processing of the compounded stock, (ii) extended storage or use under room temperature operational conditions, and (iii) forced heating to incipient pyrolysis levels preceding the flame front in material exposed to an actual fire situation. As part of a project to develop ferrocenecontaining smoke suppressants possessing structures incapable of migration and volatilization under these conditions, we have prepared a number of polymeric ferrocenes in a molecular mass range low enough to suggest an acceptable compatibility with the plastics base stock, yet again large enough to prevent loss of the additive during the aforementioned stages of the material's lifetime. PVC represents one of the most outstanding macromolecular engineering materials. We have, therefore, focused our prime interest on this class of polymers, although we are aware of many other thermoplasts and elastomers of the carbochain type that should equally invite research on improvement of their flame resistance and smoke sup-

pressant behaviour. The present communication is concerned with a determination of the compatibility of the prepared ferrocene polymers (and, for comparison, of three non-polymeric ferrocene derivatives) with plasticized PVC. The smoke evolution behaviour of promising test materials, to be singled out from the collection of materials prepared in this work, will be evaluated in a subsequent effort. EXPERIMENTAL

Analytical and instrumental methods Iron contents were determined by atomic absorption spectroscopy against ferrous ammonium sulphate standards. To this end, the samples (1-3 mg for additives 1-12; 20-25 mg for PVC sheet samples) were dissolved in a boiling acid mixture (10 20 ml) containing analytical grade H N O 3 (55~o), HCIO 4 (70°Jo), and H2SO 4 (98°/0) in a volume ratio of 136:44:18 [3]. Determinations were in triplicate on ferrocene derivatives 1-12. Iron analyses of additive-modified PVC material were performed on at least 6 samples randomly cut from each moulded sheet, and the results were averaged. Number-average molecular masses, ~/n, of the polymeric additives were determined with a Knauer Vapour Pressure Osmometer in benzene, chloroform, or pyridine solutions. Synthesis qf Jerrocene-type additives The non-polymeric and polymeric additives 1 11 were prepared by literature procedures [2] as cited in Table 1. and their purities were checked by i.r. spectroscopy (KBr matrix) and iron analysis. The polyphosphine 9 was synthesized per quoted publication [2f], except that the oxidation step with hydrogen peroxide was omitted. 3,3',4,4'-Tetramethyldiphosphaferrocene was prepared and supplied by Dr F. Mathey. Compounding t?f poly(vinyl chloride) A plasticized cable-grade PVC compound (3.26 kg) was prepared by mixing and gelling, o.ver a 6-min period in a Banbury mixer, the following ingredients (parts by weight): a suspension-polymerized PVC resin (Corrie S 6617; 100), plasticizer (DIOP, di-2-ethylhexyl phthalate; 26), ohio-

1107

E. W. NEUSE et al.

1108

Table 1. Monomeric and polymeric ferrocene-containing additives %Fe

Additive

Synthesis

no.

ref.

&/,

Calculatedt

Found:~

l

~Fc

CHJ--,

Structure*

2a

2400

Tan-brown

Colour

28.3

28. l

2

~Fc

CH2~ .

2a

1200

Dark orange-brown

28.5

28.1

3

~Fc--CHJ--, I

2b

2700

Light tan-brown

19.1

18.6

o-C6Ha--OCH 3 4

--[Fc--CH2]-- . I p-C6H4--COOH

2c

2100

Dark brown

18.6

18.1

5

--[Fc--CH2~. I p -C6H4--CN

2c

2200

Light brown

19.6

18.8

6

~Fc

2d

2000

Brown

19.7

18.9

2c

2600

Brown

18.5

14.9

2e

2200

Dark red-brown

26.1

24.8

CHJ--. I CH=CH--C6H 5 C~H4--CO

7§

I i/o/ --[Fc C~,,

8

~1,1'

9

~[Fc--P]--,, I C6H5

2f

2300

Light orange-brown

20.2

16.1

10

HFc-COCH 3

2g

22811

Brick-red

24.5

24.3

II

I,I'-Fc(COCH:CH

2h

446AI

Dark-red

12.5

13.2

20.1

20.0

Fc

P

CO~.

~

CH3

Fe 12

CH3

_ _ ~

CH3

C6H5)2

2i

27811

Dark-red

P

CEI3 *Fc = ferrocenediyl; see text for substituent dispositions, tCalculated for 1-9 on the basis of a structure terminated at both ends by a ferrocenyl group. ~:+ 0.3%. §Additionally contains some ferrocenylene-o-carboxybenzal units; see original literature. IlMolecular mass, calculated. rinated paraffin extender (Plasticlor 52L; 26), tribasic lead sulphate stabilizer (Almstab CM6; 4), and calcium carbonate filler (Omya BCH; 7). The pregelled base stock was further homogenized on heated rollers at 150-160 ° and, after cooling, shredded into small pellets.

Modification o f base stock with additive A given quantity of additive, in grammes, was made up to 100 g with pelletized PVC base stock so as to afford the compositions listed in Table 2. The mixture was recompounded and gelled in the Banbury mixer and on the hot rollers as described for the base stock. The cooled material was moulded at 150 ° between preheated platens into fiat sheets, 210 x 210mm, of nominal 1.3mm thickness. The specimens were allowed to cool to 50 ° in the press prior to removal. Strips, 30 x 10 mm, of selected samples were subjected to heat aging in an air convection oven for 7 days at 100 ° and the relative weight loss (average 8 _ 2%) determined gravimetrically. Tensile testing The instrument used was an Instron TT-M tensile testing machine. Five micro-dumbbell tensile specimens, with 30mm gauge lengths and nominal 15.5 mm 2 cross-sectional

area, were cut from each sheet and were drawn to fracture at a cross head speed of 100 mm min-~. The tensile strength at break and percentage elongation determined from the stress-strain curve are reported as averages of the 5 runs in Table 2. RESULTS

T h e p o l y m e r i c f e r r o c e n e c o m p o u n d s selected for the p r e s e n t study, a n d p r e p a r e d b y literature m e t h o d s [2], are listed in T a b l e 1 t o g e t h e r with p e r t i n e n t analytical a n d molecular-mass data. Included in the t a b u l a t i o n are t h r e e n o n - p o l y m e r i c f e r r o c e n e derivatives, viz., t h e simple, p o l a r acetylferrocene (10), t h e m u c h bulkier a n d very rigid 1 , 1 ' - d i c i n n a m o y l f e r r o c e n e (11), a n d the h e t e r o ferrocene derivative, 3,Y,4,4'-tetramethyldiphosp h a f e r r o c e n e (12); the l a s t - n a m e d c o m p l e x w a s c h o sen f o r its p h o s p h o r u s c o n t e n t a n d t h e r e s u l t a n t possibility o f i n t r a m o l e c u l a r P - F e s y n e r g i s m . F o r the s a m e p u r p o s e , a p h o s p h o r u s - b r i d g e d p o l y m e r (9) has b e e n included. T h e u n s u b s t i t u t e d f e r r o c e n e p a r e n t c o m p l e x has been o m i t t e d f r o m this t a b u l a t i o n after

Compatibility of iron-containing polymeric additives

1109

several preliminary compounding runs had given of the sheet material for 7 days at 100 ~in convecting inconsistent evaluation results as a consequence of air and redetermining the iron content, allowance massive loss of the additive during the processing being made for weight loss (8 _+ 2°Jo) through plasoperations at elevated temperature (cf. Introduction). ticizer and extender volatilization during this heating The symbol Fc used in the Table stands for the period. The analytical results are contained in the disubstituted ferrocene (ferrocenediyl or ferro- same Table. Stress-strain data were obtained in the cenylene) complex. The positional prefix l,l', when- tensile mode on test specimens cut from the sheets ever associated with this abbreviation, denotes the and were compared with those of the standard matedisubstitution to be heteroannular (one substituent rial; the data are presented in Table 2 as tensile link attached to each cyclopentadienyl ring). In all strength at break and percentage elongation. other cases not so designated, the disubstitution pattern compromises all three possible dispositions DISCUSSION (i.e. 1,2-, 1,3-, and 1,1'-), and the original literature Visual in,spection should be consulted for detailed comments. The polymers listed have in common a system of single Whereas the blank sheet is seen (Table 2) to be bonds connecting the ferrocenylene units via carbon light-cream coloured, a yellow-brown to red or clark or phosphorus bridges. The existence of C - - C or brown colouration is indicated for all sheet samples C - - P single bonds interconnecting the metallocene containing the inherently coloured ferrocene comcomplex and the bridging atom assures free rotation pounds. The colouration of the sheet samples is and, hence, chain flexibility, considered to be a considerably deeper than would be expected from the prerequisite for compatibility. additive quantities incorporated, suggesting that the The PVC base stock was a di(2-ethylhexyl) metallocene has been partially oxidized during prophthalate-plasticized and chloroparaffin-extended cessing to the (bluish-black) ferricenium cation. [A cable sheathing formulation selected here as a repre- preliminary investigation of a sample of 7-5 by X-ray sentative engineering material exposed to the typical photoelectron spectroscopy (re 2p 3..2 core electron hazards of accidental fires in industrial or residential level) has indeed revealed the presence of a ferenvironments. The compounded, pregelled and pel- ricenium iron peak (Ebb--709.6eV), although this letized stock was homogenized with the ferrocene- peak's intensity relative to that of the ferrocene signal type additives and moulded into flat sheets by con- could not be determined for lack of resolution.] Good ventional techniques. Additive quantities were to excellent homogeneity is apparent from Table 2 for generally in the range of 1 3~0 by weight of total the samples containing the two non-polymeric ferromodified stock. Given a sufficient supply of additive, cene additives 10 and 12, as well as for those modified as in the cases of 1, 3-5, 7, 9, and 10, several mixtures with the polymeric ferrocenes possessing the simple varying in additive concentration from 1 to 5°/'o were methylene (1 and 2), carbonyl (8) or phenylphosphine prepared, and for the amply available methylene- (9) bridges between the metallocene units. Good bridged polymer 1 further mixtures containing 7 and homogeneity is observed also for the material 9'!~ were made up. modified with the methoxybenzal-bridged additive An additional mixture containing the exceptionally (3). On the other hand, polymers characterized by the high proportion of 33~; of this polymer additive was presence of a bridging group of the carboxybenzal prepared with great compounding difficulties and was (4), cyanobenzal (5), styrylmethinyl (6), or phthalide therefore not deemed suitable for comparative exam- (7) type are seen to give more or less inhomogeneous ination and inclusion in the tabulation. The moulded material as evidenced by the appearance of dark sheet did, however, give a respectable 15.7MPa brown spots of agglomerated additive left unbreaking strength and 182°o elongation. dispersed in the PVC matrix. Blank sheets were moulded from the same PVC The least satisfactory behaviour is indicated for the base stock in the absence of additive for use as non-polymeric, yet bulky and stiffdiketone 11: immestandards. As a check on completeness of additive diately following preparation of the sheets, a thin film incorporation and uniform distribution, the iron of whitish, semi-solid exudate appeared on the surcontents of the additive-containingsheets (sampled at face, and after several months at room temperature random from various sites on the sheet specimens) the coating, now reddish in colour because of an were determined microanalytically and compared appreciable inclusion of the ferrocene derivative, had with those calculated on the basis of the respective developed into a thick oily layer containing some of additive concentrations employed (Table 2). the extender and plasticizer as well. This beha~iour Additive compatibility with the base stock was suggests the ferrocene additive not only to be poorly evaluated (i) by visual inspection of the sheet samples, compatible p e r se with the base stock, but also to (ii) by comparison of iron contents prior to and after induce exudation of other solid and liquid ingredia heat-aging treatment of selected samples, and (iii) ents. The two sheet samples containing additive 11 from stress-strain data. The visual inspection, per- were, therefore, excluded from further testing. formed immediately after sheet moulding and, again, after 8-month storage at ambient temperature, in- Iron contents cluded checking for homogeneous distribution of It can be seen from Table 2 that the Fe coments additive (absence of macroscopic aggregates) and analytically determined on both the freshly prepared surface cleanliness, i.e. lack of additive-induced ex- sheet samples and those subjected to the 100 aging udation (migration of liquid or solid components to test are in reasonably good to excellent agreement the surface). The results are summarized in Table 2. with those calculated on the basis of the introduced The heat-aging tests were performed by heating strips additive quantities. Specifically, in no instance has

1 1 1 ! 1

2

3 3 3

4 4 4

5 5 5

6 6 6

7 7

8 8

9 9

10 10

11 11

12 12

Standard 1-1 1-3 1-5 1-7 1-9"*

2-3

3-1 3-3 3-5

4-1 4-3 4-5

5-1 5-3 5-5

6-1 6-2 6-4

7-3 7-5

8-2 8-3

9-3 9-5

10-2 10-5

11-1 11-3

t2-1 12-3

1 3

1 3

2 5

3 5

2 3

3 5

1 2 4

1 3 5

1 3 5

1 3 5

3

1 3 5 7 9

Additive concentration in PVC compound/~t

As above.

Homogeneous; glossy, n o exudation.

Very mildly inhomogeneous; glossy, no exudation.

Inhomogeneous, numerous fine, J black spots; glossy, n o exudation.

"~

t

t Slightly inhomogeneous, fine black spots; glossy, no exudation.

t As above.

As above.

t Homogeneous; no exudation.

Light tan Tan

Light red Red

Light brown Dark brown As above.

"),Homogeneous; glossy J n o exudation.

"~Fairly homogeneous; fine whitish J s o l i d filmtt.

~

Dark brown Blackish brown >Homogeneous; glossy, no exudation.

Brown Dark brown

Brown Dark brown

Light brown Brown Dark brown

Light Brown Brown Dark brown

Tan-brown Brown Dark brown

Tan-brown Light brown Brown

Brown

Colour Off-white Light tan Tan Tan-brown Light brown Brown

Surface appearance S

0.20 0.60

0.13 0.38

0.49 1.22

0.48 0.81

0.50 0.75

0.45 0.75

0.19 0.38 0.76

0.19 0.56 0.94

0.23 0.57

0.41 1.01

0.43 0.78

0.53 0.69

0.44 0.73

0.20 0.38 0.68

0.20 0.57 0.91

0.19 0.49 0.82

0.15 0.48 0.80

0.19 0.56 0.93 0.18 0.54 0.91

0.82

0.84

Calculated 0.00 0.03 0.28 0.29 0.84 0.79 1.40 1.35 1.96 1.90 2.52 2.46

Fe

0.30 0.65

0.42 0.99

0.44 0.75

0.58 0.79

0.45 0.72

0.22 0.33 0.75

0.23 0.65 1.01

0.20 0.52 0.95

0.20 0.50 0.86

0.90

Found§ 0.05 0.33 0.81 1.38 1.92 2.53

20.2 21.3

19.0 20.3

20.2 18.6

19.2 18.1

20.4 19.9

20.1 19.7

21.0 21.7 19.8

18.2 18.6 19.3

17.8 18.7 19.2

18.4 20.8 18.5

19.5

a/MPall 19.1 18.5 21.3 19.9 21.9 19.1

266 285

290 305~:~

390 295

320 305

342 330

290 332

220 275 195

232 290 266

255 283 267

298 354 311

350

E/%¶ 308 270 387 332 385 317

*From Table 1. tBased on total compound (PVC base stock + additive). :~As inspected immediately upon moulding of specimens. No change observable after 8 months at ambient temperature except in 11-1 and 11-3 (see footnote it). §_+0.01~ for standard, _+0.04~o for all other samples. Left column: on freshly moulded specimens; right column: on specimens after heat treatment (7 days at 100°). I1+0.3~o for standard; + 1.5~o for 1-3, 1-5, 3-5, 8-2 and 9-3; + 1.0~ for all other samples. Data obtained on freshly moulded sheet; similar results after 8 months except in 11-1 and 11-3 (see footnote$$). ¶ _+40~o. **See text for mechanical performance data at 33~o loading, ttAfter 3 months, exudate forms greasy, reddish film incorporating additive 11. :~:~Elongation reduced by 20~ after 8 months.

Additive no.*

Sample designation

Table 2. Surface appearance and iron contents of plasticized PVC modified with ferrocene-containing additives

2

Z

Compatibility of iron-containing polymeric additives there been a loss of polymeric additive either during the processing or in the heat aging treatment. The same resistance to migration and volatilization is displayed, quite unexpectedly in light of its small molecular size relative to the polymeric additives, by the non-polymeric diphosphaferrocene 12. This compound clearly warrants further tests at higher ( > 5)o) loadings. Contrasting with 12, the acetylferrocene (10) did suffer some weight loss in the PVC processing step as well as in the heat aging test, although the figures in Table 2 show this loss to be remarkably small. [In a preliminary aging test involving, inter alia, ethylferrocene and 1,1'-dimethylferrocene in addition to 10, the last-named compound exhibited superior retention in the PVC sample, which may hence be associated with the polar nature of the substituent.] Mechanical properties

The tensile strength and elongation data reported in Table 2 demonstrate a remarkable lack of strength reduction and embrittlement in the additivecontaining samples relative to the blank material used as the standard. In fact, for the majority of samples, the strength and elongation values are at least comparable to, and in many instances exceed, those of the standard, suggesting that, within certain concentration limits, the additives function not merely as inactive fillers but tend to exert a modest collaborative effect with the plasticizer. This even holds for sample 11-3 containing the otherwise poorly performing biscinnamoylferrocene. It is only with 4, 5 and 6, the additives found earlier by visual inspection (vide supra) to resist complete homogenization, that mildly substandard mechanical properties of the derived PVC samples are evident from the Table. Data obtained on material modified at the 1~ additive concentration level should be treated with reservation. As illustrated by the stress strain data of 1-1 and 3-1 to 6-1, rather mediocre mechanical performance is indicated for polymer additives at this level, which appears to be below the critical additive concentration effective in contributing to the material's strength. Comparing the remaining polymeric additives at the significant 3~o loading level, one finds the methylene-bridged 1 to be outstanding, closely to be followed by the lower-molecular homologue 2 and the polymer types 3, 7, 8 and 9. As the additive concentration is increased to 5~0, 3 and 9 give slightly reduced mechanical property values, suggesting that their optimal loading level is below 5~o. On the other hand, both ! and '7 are seen to give samples retaining their strength and elongation performance. The former gives excellent values even at 7~o, and it is only at the 9% level that both strength and elongation reduce to the values of the standard. Acetylferrocene (10), the only non-polymeric additive tested at the 5')/o level, affords a sample with poorer performance than achieved at 3~o, which, again, indicates the optimal concentration to be below 5~. CONCLUSIONS Using the criteria of good homogenization with, and retention in, the PVC base stock, coupled with strength and resistance to embrittlement of the EPJ

20'11

F

1111

modified stock, one finds the poly(ferrocenylenemethylene) type 1 (K4o= 2400) to be outstanding among the non-polymeric and polymeric additives tested. Properties comparable, or superior to, those of the additive-free standard are observed on samples with a concentration of 1 as high as 9~0, and even higher additive loading might well be tolerated by the base stock without detriment to surface appearance, homogeneity, and stress-strain data. At concentrations not exceeding 5~0, the poly(ferrocenylene-omethoxybenzylidene) type (3), the phthalidebridged 7, poly(ferrocenylenecarbonyl) (8), and poly(ferrocenylene(phenyl)phosphine) (9) also show remarkably good compatibility. The diphosphaferrocene 12, up to Y'/o concentration (higher levels not tested), possesses a compatibility superior to that of the equally non-polymeric acetylferrocene (10), whereas the non-polymer 11, 1,1'-biscinnamoylferrocene, is poorly compatible with the base stock and additionally induces exudation of co-additives. Future work should focus on the evaluation of ! and other non-polar (e.g. ethylidene- or benzylidenebridged) ferrocene polymers in molecular mass ranges of 2000-3000 and higher. The non-polymeric diphosphaferrocene 12 should also be investigated at loading levels higher than 3~o. For subsequent smoke suppression studies, the methylene-bridged 1 represents itself as the most promising candidate, followed by the types 3, "7and 8, as well as the non-polymer 12. Acknowledgements The authors gratefully acknowledge the financial support given by Chemical Services (Pty) Ltd, and the assistance rendered by Mrs S. Heiss and Mr B. S. Mojapelo with the iron determinations and the preparation of some of the ferrocene compounds. Special thanks are also due to Dr G. Meats, AEC! Limited, for his friendly co-operation in the compounding and moulding of the PVC stock and permission to use AECI facilities for these operations. Dr F. Mathey, SNPE, Thiais, France, kindly provided a generous sample of the diphosphaferrocene. REFERENCES

1. S. K. Brauman, J. Fire Retard. Chem. 7, 161 (1980); C. F. Cullis, Metal compounds as flame retardanls for organic polymers. In Developments in Polymer Degradation-3 (Edited by N. Grassie), Applied Sciences, London (1981), and references cited therein. 2. (a) E. W. Neuse and E. Quo, Bull. chem. Soc. ,lap. 39, 1508 (1966). (b) E. W. Neuse and K. Koda, J. Or ganometal. Chem. 4, 475 (1965). (c) E. W. Neuse and K. Koda, J. Polym. Sei. A-I 4, 2145 (1966). (d) E. W. Neuse and H. Rosenberg, Metallocene Polymers, Marcel Dekker, New York (1970). See also: E. W. Neuse, K. Koda, E. Quo and R. K. Crossland, Tech. Rep. AFML-TR-65-158, Part I, AD 473 383 (1965). (e) E. W. Neuse and R. M. Trahe, J. Macromol. ('hem. 1, 611 (1966). (f) E. W. Neuse and G. J. Chris, J. Macromol. Sci., Chem. AI, 371 (1967). (g) F. S. Arimoto and A. C. Haven, J. Am. chem Soc. 77, 6295 (1955); C. Galli, Synthesis 1979, 303 (1979). (h) T. A. Marshburn Jr, C. E. Cain and C. R. Hauser, J. org. Chem. 25, 1982 (1960). (i) G. De Lauzon, B. Deschamps, J. Fischer, F. Mathey and A. Mitschler, J. Am. chem. Soc. 102, 994 (1980). 3. A. M. Elgala and A. Amberger, J. Plt Nutr. 5, 841 (1982).