Synthesis and characterization of some Para-nonylphenol formaldehyde resins

Eur. Polym. J. Vol. 30, No. 3, pp. 329-333, 1994 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0014-3057/94 $6.00 + 0.00

Pergamon

SYNTHESIS A N D CHARACTERIZATION OF SOME PARA-NONYLPHENOL F O R M A L D E H Y D E RESINS C. N. CA~CAVAL, D. Ro~u and F. MUSTA']]'.~ "P. Poni" Institute of Macromolecular Chemistry, Aleea Gr. Ghica Vodfi, 41A, 6600 Jassay, Romania

(Received 26 January 1993; accepted 28 May 1993) Abstract--Para-nonylphenol formaldehyde resins with molecular weights ranging within 490 and 1400 were synthesized in acidic catalysis. The resins were characterized by spectral methods (i.r. and ~H-NMR spectroscopy) and as rbeological behavior. The i.r. spectra put in evidence the bands characteristic to ---OH phenolic group, respective to ~ C H 2 and ---CH3 groups placed in the nonyl radical, and the bands for substituents in positions of the aromatic ring as follows: 1.2, 1.4 and 1.2.4, respectively. With the aid of ~H-NMR spectroscopy there have been calculated some structural parameters, such as: formaldehyde/ para-nonylphenol molar ratio and the number of aromatic protons per phenolic units. The variation of the apparent shear viscosity vs the shear rate showed that para-nonylphenol formaldehyde resins have a non-Newtonian rhelogical behaviour of pseudoplastic type.

INTRODUCTION

Phenolic resins are the condensation products obtained by reaction of phenol with aldehydes. The most known phenolic resins are those obtained by reaction of phenol with formaldehyde. The resins synthesized in acidic catalysis contain only methylene bridges in ortho and para positions of the phenolic ring and are rending in a phenolic unit. The resins synthesized in basic catalysis are usually mixtures of a n u m b e r of methylol phenols, with small amounts of higher condensation products involving methylene and benzilic ether linkages. Phenolic resins synthesized on the basis of paraaikylphenol do not have the reactive positions, which can participate to the branched systems. These resins have the linear molecules, are soluble in various organic solvents and many of them can be used as tackifiers in adhesives synthesis [1, 2]. With a view to detect the vibrational absorbtion characteristics of certain functional groups, as well as the position of various substituents in the phenolic ring, the i.r. spectroscopy has been applied to the analysis of formaldehyde containing resins [3~]. The structural parameters, such as, methyiol content, formaldehyde/phenol molar ratio, polymerization average degree and the number of aromatic protons, remaining unsubstituted in the phenolic ring, can be semiquantitatively evaluated by integrat-

ing of ~3C-NMR [7] or t H - N M R [8-11] signals of various structural units. The para-substituted phenolic resins, with special reference to para-nonylphenol formaldehyde resins type, were less analysed by both i.r. and N M R spectroscopy or other experimental methods. The present paper reports on the synthesis of some para-nonylphenol formaldehyde resins and their characterization by i.r. and I H - N M R spectroscopy. The rheoligical behaviour of the resins having different molecular weights are also emphasized. EXPERIMENTAL PROCEDURES

Synthesis of para-nonylphenol forrnaldehyde resins The starting materials were para-nonylphenol and paraformaldehyde, the last being a concentrated source of formaldehyde [12,13]. Para-nonylphenol, a commercial product with d] 5 0.955 and n~ 1.511, and paraformaldehyde (Fluka, Switzerland) were used as received. The synthesis of the resins was carried out in acidic catalysis (H2504, 96% with d~° 1.83), using a reaction mixture with a formaldehyde (F)/para-nonylphenol (p-NF) molar ratio ranging within 0.32 and 1.00, in cyclohexane (fresh distilled). The reaction was performed in a flask fitted with a stirrer, water condenser, heating system and a device used with a view to move off the water formed during the process. Solutions of 540 g para-nonylphenol (2.45 mol) in cyclohexane and 5.4 g H:SO4 were heated at 80°, under vigorous

Table 1. Some characteristics of para-nonylphenol formaldehyde resins Sample No.

F/p-NF molar ratio used at synthesis

Number-average molecular weight (h4,)

Apparent shear viscosity* r/~e(P)

1 2 3 4

0.32 0.50 0.67 1.00

490 580 630 1400

136 18138 20657 solid

*Measured at 25", [br a shear rate of 0.333sec t. 329

330

C.N. 0

CA~CAVALet al.

m

0.1 0.2 "~ 0.3 ,.~ 0.4 < 0.5 1.0

I 4000

I 3500

I 3000

I 2500

I 2000

I 1800

I I I 1600 1400 1200

I 1000

I 800

I 600

I 400

I

200

Wavenumber (cm -1) Fig. 1. Infrared spectrum of para-nonylphenol formaldehyde resin.

stirring and over a period of I hr. After this time,

paraformaldehyde was gradually added to the solutions for the purpose of obtaining resins with different molecular weights. The reaction mixture was kept at 80° for additional 2 hr, with stirring, after which the samples were extracted several times with cyclohexane, then the solutions were filtrated and concentrated. The crude product obtained was dried in vacuo at 100°.

Resins characterization The resins were primarily characterized by measuring of the apparent shear viscosity, respective of the numberaverage molecular weight, which was determined in hexane by cryoscopic method [14]. The data obtained by the two methods used are listed in Table 1. The i.r. spectra ofpara-nonylphenol formaldehyde resins were recorded by means of a Perkin-Elmer spectrophotometer type 577, using KBr pellets. The ~H-NMR spectra of the resins solutions in CDCI3 as solvent and tetramethylsilane as internal standard were obtained with the aid of a JEOL-JNMC 60-HL equipment at 55 °. With the object of separation and evaluation of the protons, which show superposition in ~H-NMR, the original samples were acetylated, as a preliminary. Acetylation was carried out with acetic anhydride in pyridine solution [15]. The rheological parameters were measured on a coaxial cylinder viscometer of type RV 2 (Germany), at temperatures ranging within 20 and 90 ° and the shear rates varying between 1 and 1310sec -~. The rheoligical experimental data were obtained on a wide range of the shear stresses (104500 Pa).

RESULTS A N D DISCUSSION

Infrared analysis The i.r. spectra recorded for the resins listed in Table 1 (from which, as a n exemplification, Fig. 1 shows the spectrum of the sample 2) present b r o a d a n d intense b a n d s specific to ---OH g r o u p stretching vibrations, which are intramoleculare associated by hydrogen bonds. The characteristic a b s o r b t i o n b a n d s for the para-nonylphenol formaldehyde resins analysed are specified in Table 2. As can be seen in Table 2, in addition to the valence vibrations of - - O H group and the presence of the hydrogen bonds, the i.r. spectra of para-nonylphenol formaldehyde resins are characterized and by the valence vibrations, which are specific to the aromatic ring, symmetric and asymmetric vibrations and deformative vibrations of b o t h ---CH2 and - - C H 3 groups, respectively. A t the same time, Table 1 puts in evidence and the presence of the vibrations, which are characteristic to the substituents in the positions of the aromatic ring as follows: 1.2, 1.4 and 1.2.4, respectively.

IH - N M R analysis The I H - N M R spectra recorded for b o t h paran o n y l p h e n o i formaldehyde resin unmodified (sample 2 - - T a b l e 1) a n d t h a t one acetylated are shown in Figs 2 a n d 3, respectively.

Table 2. Infrared absorption bands, which are characteristic to para-nonylphenol formaldehyde resins Band, cm-t Assigning 3100-3500 #(OH); broad band; valence vibrations of OH groups. 3200-3400 ~(OH); intense bands; hydrogen bonds. 2860-2950 symmetric and asymmetric vibration bands of--CH 2 and ~ H 3 groups. 1510-1610 p(C-.----C);valence vibrations specific to the aromatic ring. 1450 ~(CH2); deformative vibrations of--CH 2 groups. 1370 6(CH3); deformative vibrations of--CH3 groups. 1220-1250 /~(C--~OH); valence vibrations of C OH bond. 1170 6(C--H); deformative vibrations of C--H bond. 810 aromatic substitution in 1.4 and 1.2.4 position. 750 Aromatic substitution in 1.2 position.

Synthesis and characterization of some para-nonylphenol formaldehyde resins

331

R

t - -

__/

M Ar

8

7

6

5

--''U

I

3

2

4

ppm Fig. 2. JH-NMR spectrum of para-nonylphenol formaldehyde resin. As revealed by Fig. 2, the LH-NMR spectrum of the original sample shows the signals situated in the interval 0.4-2 ppm, which are specific to the protons placed in nonyl radical (R), the interval 3.7~1 ppm for methylenic protons, which are characteristic to the diphenyl methane structures (M), and 6.5-7.3 ppm interval for aromatic protons (Ar). The tH-NMR spectrum obtained for acetylated resin shows the possibility of----OH phenolic protons separation by shifting the signals from 6.5-7.3 ppm (superposition with aromatic protons) to 2-2.4 ppm

(Ac). The integration of the peak area of resonances in tH-NMR spectrum of acetylated samples provides a means of monitoring the F / p - N F molar ratio, respective the number of aromatic protons per phenolic units, on the basis of relationships (1) and (2) as follows: F molar r a t i o p-NF

total methylene bridge units 3M total phenolic units - 2A c

(1)

number of aromatic protons per phenolic units =

total aromatic protons total phenolic units

Ar Ac/3

(2)

The data obtained for parameters calculated with the aid of the relations (1) and (2) vary between 0.32 and 0.95, respective 3.2 and 2.5, showing that the number of aromatic protons per phenolic units decreases together with increase of the F / p - N F molar ratio. Both the constant decrease of the number of aromatic protons and the fact that this number has values higher than 2 show that the reactive positions in the aromatic ring are still available for reaction with formaldehyde, in succession.

Rheological behaviour The apparent shear viscosity ( q a p ) , evaluated for all the resins synthesized, was plotted logarithmically vs

Table 3. Influence of temperature upon some rheological parameters of the resins analysed Temperature ( C ) 30

40

60

Sample

k

No.

(Pa)

n

aT

k (Pa)

n

ar

I 2 3 4

288 1546

0.86 0.98

38 58

93 34

0.86 0.98

12 12

80

90

k (Pa)

n

aT

k (Pa)

n

ar

9 31 434

0.96 0.96 0.90

1 I 1

1 6 53

0.96 0.96 0.95

0.15 0.18 0.11

k (Pa)

n

at

I 5 44 244

0.96 0.90 0.95 1.00

0.11 0.20 0.12 0.11

332

C . N . CA~CAVALet al. ¢

-

-

Ac

At M

I

I

f

I

I

I

I

J

8

7

6

5

4

3

2

1

ppm

Fig. 3. ~H-NMR spectrum of acetylated

the shear rate (i) in the temperature range within 20 and 90 °. The plots recorded in Figs 4-7 show a decrease of rhp with increase of i. The decrease of ~/ap is more pronounced at lower temperatures. This

para-nonylphenol formaldehyde

resin.

behaviour indicates the fact that para-nonylphenol formaldehyde resins, with molecular weights ranging within 490 and 1400, have a non-Newtonian rheological behaviour of pseudoplastic type.

3 3

-

X~X'x-X~x.X_x. 2

-

X~xx-x~x~x

2

- -

m--m--mmmn--m--m-,m-m.m

_o

I

o

-

1

+---F'F--++~+--+,+ 0

oo----0(3....o0.-..o

-1 0

I

I

f

1

2

3

log y(sec -1)

Fig. 4. Variation of rhp vs ~ in the case of the resin with M, = 490. Temperatures (°C): 30, A ; 40, x ; 50, m; 60, O; 70, D; 80, + ; and 90 O.

0

I

I

)

1

2

3

log y(sec -1)

Fig. 5. Variation of ~/ap vs y in the case of the resin with Mn = 580. Temperatures (°C): 40, ( x ); 50, I ; 60, 0 ; 70, + ; 80, D; and 90, C).

Synthesis and characterization of some para-nonylphenol formaldehyde resins -

3

333

10 4

•

•

•

00

/3

2

1

10 3

¢

2 -o/) o

- n ...,.,.

,an..,..,,

~.,

10 2

×o~'

-i1,,,._ I

.~

101 0

1

2

log ~(sec -1) Fig. 6. Variation of q~p vs )~ in the case of the resin with M~ = 630. Temperatures CC): 60, O; 70, [~; 80, i ; and 90, O.

100 lO-1

1

I

I

I

l0 0

101

10 2

10 3

aT.~(sec-l)l

04

rheological data consists in estimate of the experimental values on a large domain of temperatures and

Fig. 8. Generalized master curves. The curves I, 2 and 3 (corresponding to the samples I, 2 and 3--Table 1) were shifted at 60° (To), while the curve 4 (sample 4) was obtained at 90 °. Temperatures (°C): 30, ~ ; 40, I ; 50, +; 60, Q; 70, I--1; 80, ×; and 90, O.

the obtaining of the generalized flow master curve [16, 17]. Taking into consideration the rheological behaviour of rt,p and making use of the rheological model type:

q,p = A e E/gr (5) E being the flow activation energy a n d R is the gas

The usual procedure used in the analysis of the

z = k?"

(3)

where ~ is the shear stress, k is the consistency index (Pa) and n is the flow indice. We have obtained the master curves for the para-nonylphenol formaldehyde resins, which were analysed (Fig. 8). The values of k, which were evaluated both at a certain temperature T (kv) and at the standard temperature To/(kTo = 60 ~) by extrapolation to zero ~, were used to calculate the shift factor aT through the means of: ar

\k+,,]

"

(4)

The values of k, aT a n d n, which were measured at various temperatures, are summarized in Table 3. It can be seen in Table 3 that b o t h k and aT values decrease together with increase of the temperature, while n has sub-unit values. These things confirm once more the n o n - N e w t o n i a n rheological b e h a v i o u r of the resins analysed. In the case of p a r a - n o n y l p h e n o l formaldehyde resins the variation of qap VS temperature obeys the A r r h e n i u s law:

3

-

o

1

2

log ~(sec -1 ) Fig. 7. Variation of r/,p vs ? in the case of the resin with M, = 1400 temperature of 90'.

constant. The flow activation energies were evaluated in the temperature range within 20-90 °, using the straight lines from plots log qap vs 1/T. The E values vary between 10 and 16 kJ/mol for ~ values placed in the range of 10-400 Pa, respectively.

REFERENCES

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