Identification of Polyester Resins by Nuclear Magnetic Resonance

Identification of Polyester Resins by Nuclear Magnetic Resonance D. F. PERCIVAL and

M. P.

STEVENS

California Research Corp., Richmond, Calif.

b A method for the identification and semiquantitative determination of various constituents in unsaturated polyester resins has been worked out using nuclear magnetic resonance. Samples can b e run directly in monomer solution or in acetone or benzene. The latter solvents are particularly useful when monomer peaks overlap those of resin constituents. The spectra are used much like infrared to identify and measure the acids and glycols present.

I

'

CONTINUATION of our work on polyester resins (1) we have obtained a number of nuclear magnetic resonance (KMR) spectra on resins of varying composition and can now make qualitative and semiquantitative identification of various commonly used acids and glycols. This method is very fast since no degradation or prior treatment of the resin is necessary before obtaining the spectra. Various constituents give rise to definite peaks, and the peak areas give an estimate of the moles of each constituent.

f l l 'c=c' H'

(8

'c q -

N

EXPERIMENTAL

Apparatus and Materials.

NMR.

A Varian Model A-60 proton magnetic resonance spectrometer equipped with a variable temperature probe was used in all of our studies. POLYESTERS. Gnsaturated polyesters were prepared by normal fusion technique from commercially available raw materials. Procedure. Monomer need not be removed from the resin. Well-defined spectra are obtained from styrene solutions of the resin simply by adding more styrene to decrease t h e viscosity and also by increasing the temperature. A typical spectrum of a resin in 50y0 styrene is shown in Figure 1. This spectrum was obtained a t 125" C . using a 500-cycle sweep width and 10-second sweep time. To prevent gelation a t this temperature, 500 p.p.m. of diphenyl quinone was used as inhibitor. For samples of unsaturated polyester that are monomer free, one can use benzene or acetone as solvent. I n all cases, the spectrometer was externally zeroed with 5y0 tetramethyl silane (TMS) in CCla. The peak positions are reported against this reference point without bulk susceptibility corrections. The solvents used also provide excellent reference

1574

ANALYTICAL CHEMISTRY

points for establishing peak position. More accurate measurements of peak position are not needed for this work. RESULTS A N D DISCUSSION

Eighteen different resins have been studied by NMR. Table I shows the various formulations used while Table I1 gives the chemical shift(s) for the various constituents in parts per million downfield from tetramethyl silane measured as described above. This table clearly shows that constituents are easily distinguished from each other. Table I. Unsaturated Polyester Formulations Studied

Constituents" Mole ratio IP/MA/PG IP/MA/PG IP/MA /PG IPIMA~PG 1/2/3 PA/MA/PG 2/1/3 IP/FA/DEG 1/1/2 IP/MA/HD 1/1/2 FA/MBA 1/1 IP/FA/PEG 3/1/4 IP/MA/Ad/DEG 1/1/1/3 PA/MA/Ad/DEG 1/I /1 /3 IP/MA/Ad/DPG 1/1/1/3 DA/MA/PG 1/1/2 IP/FA/DEG/PEG 3/1/2 7/1 3 IP/FA/DEG/EG 3/4/5 6/1 4 IP/MA/Ad/HD/EG 1/1/2/3 6/0 4 MA/Ad/HD/DEG 1/3 5/3 6/0 9 PA/MA/DEG 1/1/2 a See Table I1 for abbreviations.

Even long methylene chain compounds, such as adipic acid and 1,6-hexanediol, can be distinguished. Adipic acid, as expected, gives rise to two strong absorption areas a t approximately 1.2 (CHZCH~-CH~)p.p.m. and 1.8 (CHzCOZ-) p.p.m., whereas, 1,6-hexanediol absorbs strongly in two areas-one at 0.8 (CHzCH2CHz)p.p.m. and the other at

0

I1

3.6 (-CH20C-) p.p.m. Polyethylene glycol of 200 molecular weight gives rise to very strong absorptions a t about 3.0 (-0CH2--) p.p.m. and a much 0

1:

weaker absorption a t 4.0 (-CH20C-) p.p.m. This easily distinguishes long chain polyethylene glycols from the simpler types, such as diethylene glycol, which also absorb in these same areas but much more weakly at 3 p.p.m. As one would expect, propylene glyeol give? rise to twostrongabsorptions; whereas, ethylene glycol shows only one strong absorption area. Three distinct areas of absorption are apparent for isophthalic acid, and one prominent area for o-phthalic acid. Esters of maleic acid absorb (CH==CH) in a lower range (higher field) than esters of fumaric acid, and the two constituents can be easily distinguished from each other when acetone is used as solvent. Line positions may not always agree with literature data on lines due to

Table II.

1

PPM

A

I SOPHTMAL I C

IP

0-PHTMAL 1 C

PA

MALE IC

MA

FUMAR I C

FA

ADIPIC

AD

DIMER ACID ( EMPOL 101 4 )

DA

P.p.rn. ranges' for Polyester Constituents

A. In acetone solvent 2 3 4 I

I

I

GLYCOLS PROPYLENE

PG

DIETHYLENE

DEG

0 1 PROPYLENE

DPG

POLYETHYLENE ( 2 0 0 MOL. W T . )

PEG

6

7

I

a

I

I

I

-R (cn,o-c)

EG

ETHYLENE

5

I

0-

0 (CHOEand -CH,O!J

1,Q-MEXANEDIQL M O O l F l E D BISPHENOL A

MBA~

B

PPM

1 I

B. In benzene sulvent 2 3 4 I

I

I

5

6

7

I

I

I

ISOPHTMALIC

8

-

I

(RiwB H

T

(Ad)

0-PMTHAL I c

ki'l

MALEIC

(ZH1

FUWR I C ADIPIC

D l L K R A C I D (EMPOL 1 0 1 4 )

GLYCOLS E T H Y L EWE

(en,)

PROPYL E NE DIETMYLENE

DI PROPYLENE POLYETMYLENE ( 2 0 0 MOL.

WT.)

1 ,@-MEXANEDIOL

M O D I F I E D BISPHENOL

A*

-0

0

(CHd and -CH,d- ) (Continued)

various kinds of protons, but this is because the method of referencing combined with solvent effects is unique to this misture of components. Ranges of line positions shown in Tables IIA, IIB, and I I C are due to line splitting and variations as a function of resin composition, concentration, and temperature.

Semiquantitative results are obtained from the areas of the various peaks. Table I11 shows a comparison of the determined mole ratios of constituents with the actual mole ratios. These values were obtained on 50Oj, styrene solutions of the unsaturated polyester by relating the peak areas to moles of reactants. For instance, the mole ratio

of isophthalic acid to fumaric acid is obtained by comparing the area of the peaks at 7.7 and 7.8 p.p.m. with the area of the peak at 6.4 p.12.m. Since the peaks at 7.7 and 7.8 p.p.m. arise from two protons and the peak a t 6.4 p.p.m. also arises from two protons, the areas are directly proportional to the mole ratio. The area of the peak a t 8.3 VOL. 36, NO. 8, JULY 1964

1575

Table It.

(Continued)

In styrene solvent 2 3

C. C

PPM

1 I

I

I

4 I

5 I

6 I

7 I

a I

ACIDS I SOPHTHAL I C 0-PHTHALIC MALEIC FUMARIC

-- 4 --(cn2cn2cn2) -P

ADIPIC

(CH2CHICH2)

DIMER A C I D (EMPOL 1 0 1 4 )

(CHIC-0)

(-cH~c-o)

(cH?)

GLYCOLS E THY LENE PROPYLENE D I ETHYL €NE DIPROPYLENE POLYETHYLENE ( 2 0 0 MOL.

WT.)

1 ,@-HEXANE0 I O L

M O D I F I E D BISPHENOL A

M)WMERS' STYRENE METHYLMETHACRYLATE -0

V I N Y L ACETATE

(CH>CfO

' P E A K S I N (-) WERE O B S C U R E D B Y SOLVENT P E A K S .

2D0W-565 JNO

S O L V E N T USED.

Table It.

P.p.m. ranges' for polyester constituents A. 6. C.

Table 111.

Constituents" IP/MA/PG IP/MA/PG IP/MA/PG

In acetone solvent In benzene solvent In styrene solvent

Determination of Mole Ratio of Polyester Constituents

Mole ratio 1/1/2 2 ~ 3 3/1/4 1/1/1/3 1/1

PA/MA/Ad/DEG F A / h l BA a See Table I1 for abbreviations.

Mole ratio

by NMR 1/1/2 1 2 / 1 4/3 3 3/1/4 1 0 8/1/1/3 1/1

Peaks integrated, approx. p.p.m. 8 3,6 4,3 7 i,6 4,3 8 3, 6 4, 0 i2,64,1 6 4, 1 05

6

7 75 1,37

version of maleic to fumaric in polyester processing, and these data will be published a t a later date. Most of the maleic is converted to fumaric d:uing esterification, but the areas attributed to both should be totaled for quantitative estimations of the amount of unsaturated dibasic acid in a polyester formulation. ACKNOWLEDGMENT

p.p.m. arising from one proton on isophthalate ester should be half the area of the peaks a t 7.7 and 7.8 p.p.m. This kind of determination is accurate to about 20 mole per cent of the individual components. In cases where there is some question of peak assignment or area caused by mononier overlap, the resin can be freed of monomer by a technique described earlier ( 1 ) and the resin dissolved in acetone or benzene. Acetone 1576

ANALYTICAL CHEMISTRY

is an excellent solvent for studying aromatic and unsaturated dibasic acids, and benzene is excellent for studying saturated dibasic acids and glycols. As shown in Table 11, monomers other than styrene can be identified by NhlR. Methyl methacrylate and vinyl acetate are easily distinguished from resin constituents. Table I1 also demonstrates that little shifting occurs on going from one solvent to another. At present, we are studying the con-

We acknowledge the assistance of P. H. Leon in preparing the polyester samples, of V. L. Torjesen in obtaining the spectra, and of R. S. Porter and S. W. Sicksic for their helpful comments and discussion. LITERATURE CITED

(1) Percival, D. F., AXAL. CHEM.35, 236 (1963).

RECEIVED for review Xovember 13, 1963. Accepted April 9, 1964.