Addition of dialkyl phosphites to difurfurylidene acetone

Lur. Polym. J. Vol. 19, No. 9, pp, 827 829. 1983

0014-3057 S3S300+0.00 Copyright © 1983 Pergamon Press Lad

Printed in Great Britain. All rights reserved

A D D I T I O N O F D I A L K Y L P H O S P H I T E S TO DIFURFURYLIDENE ACETONE G. BORISOV, I. KRAICHEVA and S. VARBANOV Central Laboratory on Polymers, Bulgarian Academy of Sciences, Sofia 1000, Bulgaria

(Received 5 November 19821 Abstract Phosphorus- and difuryl-containing reactive monomers have been synthesized by adding dimethyl or diethyl phosphite to difurfurylidene acetone. The monomers have been homo and copolymerized with difurfurylidene acetone affording polymers and copolymers with improved resistance to combustion.

INTRODUCTION

ether from chloroform solution. Drying to constant weight was performed in argon and vacuum (yield 19.3 g). Diethyl phosphite was added to difurfurylidcnc acetone similarly using a saturated ethanolic solution of NaOC2H 5 as catalyst. Dimethyl phosphite was added to difurfurylidene acetone in the presence of triethylamine as catalyst. The reaction mixture was stirred at 60 for 2.5 hr after adding catalyst. The characteristics of the monomers are listed in Table 1.

Furan m o n o m e r s are often used for preparing thermoresistant polymers, inert to aggressive media. Introduction of phosphorus into the molecules improves their resistance to combustion. The synthesis of phosphorus- and furyl-group containing m o n o m e r s by adding dialkyl phosphites to furfurylidene acetone [1] and furyl acrolein [2] has been described; these reactions proceed with good yields in the presence of basic catalysts. Dialkyl phosphites with groups from Ca to C4 have been added to furfural [3]. The ~-hydroxy-c~-furylphosphonic acid esters arising from the interaction of furfural with higher (C6 to Cto) and some heterocyclic dialkyl phosphites, as well as with diphenyl phosphite, have also been reported [4]. The aim of the present investigation was the synthesis of reactive phosphorus-containing c o m p o u n d s from difurfurylidene acetone and dialkyl phosphites, suitable for preparing polymers and copolymers with improved resistance to combustion.

Polymerization and eopol)'merization o[ phosl~horus- and dijuryl-containin,q compounds The phosphorus- and difuryl-containing products were polymerized with p-toluenesulphonic acid 14 weight 7,0 as catalyst. The samples were heated in glass ampoules at 80 for 2hr and at 180 for 5hr. The characteristics of the polymers are given in Table 2. Copolymerizations of difurfurylidene acetone and the addition product of dimethyl phosphite and difurfurylidene acetone were performed for various compositions. The characteristics of the copolymers are listed in Table 3.

Characterization ql" the phosphorus- and d(li~r)l-eontaimn~! products obtained and of the polymers based ( m them

EXPERIMENTAL

Starting compounds: difurfurylidene acetone was prepared as previously described [5] and purified by two recrystallizations from petrol ether, m.p. 5 6 ; dimethyl phosphite (Fluka, purum), was distilled under vacuum, b.p. 56/3 mmHg n2° = 1.4039; diethyl phosphite (Fluka, purum), distilled under vacuum, b.p. 72' mmHg, n~° = 1.4086; triethylamine (purum) distilled b.p. 89~: p-toluenesulphonic acid, m.p. 92 .

Adding] dimethyl phosphite to difiofurylidene acetone Difurfurylidene acetone (0.056 mol, 12 g) and dimethyl phosphite (0.179mol, 19.74g) were placed in a flask provided with a stirrer, reflux condensor, thermometer, dropping funnel and an argon inlet. A saturated NaOCH3 methanolic solution was added dropwise with stirring until exothermicity ceased. Stirring was continued for 2 hr at 35; the reaction mixture was dissolved in benzene; NaOCH3 was removed and the desired product was precipitated with petrol ether. The dark-brown viscous product was purified by two precipitations in petroleum

--CH=CH--C--CH=CH--~'~O"

The molecular masses were determined b3 the \apour pressure technique using a Knauer instrument ~ith chloroform as solvent, i.r. Spectra were recorded on a UR-20 spectrometer using films (monomers) and in KBr (pol 3mers). ~H-NMR spectra were determined on a JEOL-PS (100 MHz) apparatus at room temperature using CDCI3 as solvent and hexamethyldisiloxane as standard. Thermograms were taken on a Paulik Erdey instrument at a heating rate of 10/min in air. The oxygen index was determined according to ASTM-D-2863 on a Module FTA (Stanton Redcrofi, England) apparatus. Samples with dimensions of 100/10 mm were prepared by soaking glass wool with an acetone solution of the phosphorus- and difuryl-containing products. Polymerizations were carried out under the described conditions after removal of solvent. DISCUSSION The interaction of dimethyl and diethyl phosphitc with difurfurylidene acetone resulted in phosphorusand difuryl-containing reactive products according to the scheme : o

+ (ROI2PH ~,-

--i

._%_?,C-X-%o'J V-ql

0~--- P(OR )2 827

828

G. BORISOVet al.

Table 1. Addition products of difurfurylidene acetone with dimethyl or diethyl phosphite

CH -- CH,p-- C - X - - ~ , , 0 ,,,~

I

O=PIOR)

No.

Molecular m a s s

z

R

X

1.

CH 3

CH2--CH

2.

C2 H~

CH2--CH

3.

CH3

Phosphorus content

Yield (%)

Found

Calculated

Found

Calculated

79.3

455

434

13.61

14.2

66.4

611

490

12.4

12.65

50

374

324

10.2

9.6

O=~(OCH 3)2

O=~(OC2H5 )2

where R ~ C H 3 or

C2H5

CH=CH

and

higher than the theoretical values. A fraction (13% of the theoretical yield) was separated as a result of the O=I~(OR)2 interaction between diethyl phosphite and difurfurylior - - C H = C H - dene acetone; this fraction had the same phosphorus As catalysts in the addition of dialkyl phosphites to content as the main fraction (No. 2, Table 1) but a difurfurylidene acetone, saturated alkoxide solutions molecular mass of 1065. It was established that the in the corresponding alcohol and triethylamine were molecular masses of the products increased on standused. The latter compound is a weaker catalyst than ing probably as a result of condensation between the the alkali metal alkoxides and therefore is needed in carbonyl and the methylene groups, similar to the greater amounts. The addition of dialkyl phosphites resinification of furfurylidene acetone [5]. The monowas conducted with an excess of the phosphorus-con- addition product can also react with the double bond. taining component. The structures of the products were confirmed by i.r. The presence of the alkoxides led to addition and 'H-NMR spectroscopy. products of the dialkyl phosphites along the The following characteristic absorption bands are two double bonds in difurfurylidene acetone i.e. 1,5- observed in i.r. spectra of the addition products di(2-furyl)-3-oxo-l,5-bis(dimethoxyphosphone)pentane between dialkyl phosphite and difurfurylidene ace(No. 1)and 1,5-di(2-furyl)-3-oxo-l,5-bis(diethoxyphos- tone: carbonyl absorption for compounds Nos 1, 2 phone)pentane (No. 2) (see Table 1). The use of tri- and 3, respectively, 1715, 1720 and 1685 cm- 1 [6] ; for ethylamine as a catalyst resulted in the formation an aliphatic C = C bond in compound No. 3 at of 1,5-di(2-furyl)- 3-oxo- 1-dimethoxyphosphone-pent- 1640cm-1; for t r a n s --CH~--~-CH-- bonds in com4-ene (No. 3 of Table 1) with a phosphorus content pound No. 3 at 980 cm- 1. Absorption bands due to a and molecular mass corresponding to the addition of furan ring system are observed at 1500, 1555 and one molecule of diakyl phosphite (Table 1). The for1630 cm-X arising from the unsaturated moiety and mation in this case of the mono-addition product at 1030 and 1040cm -1 ascribed to the C - - O ~ C is probably due to the effect of the weak catalyst tri- groups; absorption due to the P = O function at ethylamine (in comparison with the alkoxides) also to 1250cm -1, the P-OCH 3 at l l 9 0 c m -1 and P-OCzHs the steric hindrance caused by the bulky phosphorus- groups at l l 6 0 c m -1. containing substituent to the addition across the The 1H-NMR spectra corroborate the assumed second double bond. structures of the compounds. Thus the spectrum of Table 1 shows that the molecular masses of two of compound No. 3 reveals absorption at 7.31 and the synthesized products (Nos 2 and 3) are slightly 6.52ppm due to the protons O = C - - C H = and = C H - - C 4 H 3 0 . The methoxyl group protons in comTable 2. Oxygen index of the polymers pounds Nos 1 and 3 resonate as doublets (JP-oCH3 = 10.5 Hz) centered at 3.66ppm for comPhosphorus Oxygen pound No. 1 and 3.81ppm for compound No. 3. Polymer obtained content index The protons of the --OC2H5 group (compound from (%) (% 02) Table 3. Oxygen index of copolymers Dimethyl phosphite and 13.61 56.3 difurfurylidene acetone Phosphorus Oxygen di-addition product Additive content index (%) (%) (% o2) Diethyl phosphite and 12.4 33.3 difurfurylidene acetone 0 0 23 di-addition product 10 1.36 28.8 Dimethyl phosphite and 10.2 40.7 2O 2.72 35.1 difurfurylidene acetone 3O 4.08 41.6 mono-addition product 5O 6.80 48.5 Difurfurylidene acetone 0 23 100 13.61 56.3 X=CH2--CH--

829

Addition of dialkyl phosphites to difurfurylidene acetone No. 2) resonate as a complex quartet at 4.06 ppm 6 Hz: J O C H 2 ~ C H 3 = 7.3 Hz). The CHa--CH20-protons appear as a triplet at 1.26 ppm. The protons from the P - C H - - C H 2 moiety in products Nos 1 and 3 appear as unresolved multiples overlapping with the signals of the C k I a O - group protons. The protons from the P - C H - - C H 2 group in compound 2 absorb as a multiplet in the 2.14 3.18 ppm region. The proton of the P-CH moiety in the same fragment of the same compound overlaps with the multiplet due to the protons in P-OCEI 2 group. The signals due to the alpha-protons in the furan ring appear at 7.22, 7.26 and 7.30ppm, for compounds Nos 1, 2 and 3, respectively, while the betaprotons absorb at 6.20, 6.25 and 6.32 ppm, respectively. The phosphorus- and difuryl-containing products are viscous dark-brown to red-brown liquids, soluble in benzene, chloroform, dichloroethane and acetone. The products of addition of dialkyl phosphites to difurfurylidene acetone contain two reactive furan rings and, like difurfurylidene acetone, when used alone are suitable for preparing highly dense polymers [7]. Polymerization in the presence of p-toluenesulphonic acid results in the formation of solid, nonmelting and insoluble phosphorus-containing furan polymers dark-brown to black in colour and containing up to 99!}~, of a gel fraction. The i.r. spectra of the crosslinked polymers reveal the presence of furan diene absorption bands with considerably reduced intensity. This indicates that the crosslinking proceeds via the furan double bonds; in the mono-addition product, the ethylene double bond also polymerizes. An attempt was made to copolymerize the di-addition product between dimethyl phosphite and difurfurylidene acetone with styrene. A crosslinked copolymer was obtained containing phosphorus and aromatic nuclei. The thermograms of the polymers obtained from the di-addition products of dimethyl and diethyl phosphite and difurfurylidene acetone (Fig. 1, curves 2 and 3) indicate an insignificant decrease in thermal stability in comparison to the polymer from difurfurylidene acetone that does not contain phosphorus (Fig. 1, curve 1). Above 700 ~' there is a gradual decrease in the destruction rate of the phosphoruscontaining furan polymers. Beyond 800 ° this rate approaches zero (Fig. 1, curves 2 and 3), while the decomposition rate for the polymer based on difurfurylidene acetone remains basically unaltered between 450 and 1000 (Fig. 1. curve 1). The differences observed in the destruction rates with the synthesized phosphorus-containing furan polymers and the analogous polymer based on difurfurylidene acetone (not containing phosphorus) is due to the presence of phosphorus which favours coke formation [8, 9]. The oxygen index of the phosphorus-containing polymers indicates that they possess increased resistance to combustion (Table 2) due to the higher degree of crosslinking (the initial monomers contain two polymerizable furan rings), to the presence of rings and carbonyt groups. The effect of these factors on the

(Jla.ocn2 ~

o~ 90 f 80

'~

60I 50

40 3O 2O 0

3 ]

I 200

I

I 400

I

I 600

1

L 800

I

I iooo

T(°C)

Fig. 1. Thermogravimetric curves of the polymers: curve l--difurfurylidene acetone (phosphorus-free): curve 2 diaddition product of difurfurylidene acetone and dimethyl phosphite; curve 3 di-addition product of difurfurylidene acetone and diethyl phosphite.

resistance to combustion has also been established for other phosphorus-containing polymers [10]. The efficiency of the di-addition product between dimethyl phosphite and difurfurylidene acetone (product No. 1, Table 1) as a flame retardant additive to difurfurylidene acetone was also studied. Copolymers between difurfurylidene acetone and the phosphorus-containing component were prepared in various weight ratios: oxygen index was determined also (Table 3). The results in Table 3 reveal the existence of a linear increase of the oxygen index with higher antipyren concentration within the limits of 0.5 ~ 2.5 mass ",, of phosphorus, an observation in agreement with data reported for other phosphoruscontaining polymers I l l ] . The computed efficiency coefficient (a) of the flame retardant additive is quite high riz. a = 4.5. The investigations indicated that the use of the suggested products as antipyrens is efficient for improving the resistance to combustion of the difurfurylidene acetone polymers. REFERENCES

1. A. N. Pudovik, Zh. Obshch Khim. 22, 462 (1952). 2. A. N. Pudovik and Yu. P. Kitaev, Zh. Obshch Khim. 22, 467 (1952). 3. V. S. Abramov and A. S. Kapustina. Zh. Ohshch Khim. 27, 173 (1957). 4. 1. K. Rubtzow~ and V. I. Kirilovich. Plast. Massy 4, 59 (1965). 5. I. V. Kamenskii and N. V. Ungurean. Pla.st. Massy 8, 17 (1960). 6. R. Silverstein, G. Bassler and T. Morril, Spektrometricheskaya htentifikatsya Organicheskykh Soedinenii. pp. 173, 177. Myr. Moskva (1977). 7. N. A. Lapina, V. S. Ostrovskii and I. V. Kamenskii, [/ivsokomolek. Soedin. At 1, 9, 2073 (1969). 8. C. J. Hilado, Flammability Handhookjbr Plastics, p. 82. Technomic, Stamford (1969). 9. C. J. Hilado. J. cell. Plast. 4, 339 (1968). 10. V. I. Kodolov, L. A. Sapogova and S. S. Spasskii, Plast. Mass), 10, 40 (1969). 11. R. M. Aseeva and G. E. Zaikov, Gorenie Polimernykh Materialor. p. 247. Nauka, Moskva (1981~