High-Performance Gel Permeation Chromatography Characterization

11

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High-Performance Gel Permeation Chromatography Characterization of Oligomers Used in Coatings Systems C H E N G - Y I H K U O and T H E O D O R E P R O V D E R Glidden Coatings and Resins, Division of S C M Corporation, 16651 Sprague Road, Strongsville, OH 44136

Over the last five years the Coatings industry has had to develop new technologies to meet the challenges of governmental regulations in the areas of energy, ecology and consumerism. The greatest changes have occurred in the industrial or chemical coatings areas with the development of environmentally acceptable coatings systems such as High Solids, Powder, Water-borne and radiation curable coatings. These new coating technologies require the use of tailor-made low molecular weight polymers, oligomers and reactive additives which when further reacted produce higher molecular weight and crosslinked polymers concomitant with the minimization of the evolution of volatile products. In these types of coatings systems the control of the oligomer/polymer composition and molecular weight distribution (MWD) is critically important. Conventional GPC does not provide the required resolution in the low molecular weight region for the control of MWD in these oligomer/polymer systems. With the advent of high efficiency columns, the resolution in the lower molecular weight region (molecular weights in the range of 200 to 10,000) has been greatly improved and the speed of analysis increased. These f e a t u r e s make h i g h performance GPC (HPGPC) an i n d i s p e n s a b l e c h a r a c t e r i z a t i o n t o o l f o r the a n a l y s i s o f oligomers/polymers i n environmentally acceptable coatings systems. In t h i s paper, we w i l l d e s c r i b e the q u a l i t a t i v e and q u a n t i t a t i v e HPGPC methodolog i e s we have developed f o r the a n a l y s i s o f oligomers and p o l y mers. S p e c i f i c a p p l i c a t i o n s i n c l u d e a) q u a l i t y c o n t r o l of s u p p l i e r raw m a t e r i a l s , b) g u i d i n g r e s i n s y n t h e s i s and p r o c e s s i n g c) modifying r e s i n s y n t h e s i s t o improve end-use p r o p e r t i e s and d) c o r r e l a t i n g oligomer and polymer MWD w i t h end-use p r o p e r t i e s . Experimental The instrument used i n t h i s study was an in-house c o n s t r u c t ed HPGPC composed o f a Waters A s s o c i a t e s M-6000 s o l v e n t d e l i v e r y system, Waters A s s o c i a t e s U6K i n j e c t o r , V a r i a n Instruments f i x e d 0-8412-05 86-8/ 80/47-13 8-207$05.00/0 © 1980 American Chemical Society Provder; Size Exclusion Chromatography (GPC) ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

SIZE E X C L U S I O N C H R O M A T O G R A P H Y

208

(GPC)

wavelength (254 nm) UV d e t e c t o r , V a r i a n Instruments d i f f e r e n t i a l r e f r a c t o m e t e r (DRI) and Waters A s s o c i a t e s l i q u i d volume counter. The instrument was operated a t room temperature w i t h Burdick and Jackson d i s t i l l e d i n g l a s s THF as the e l u t i n g s o l v e n t . The sample column bank c o n s i s t e d of s i x μ-Styragel columns w i t h t h e f o l l o w i n g p o r o s i t y d e s i g n a t i o n s : 10*, 1 0 , 500» 500, 100, 100A. The f l o w r a t e was adjusted to 0.6 ml/min. A 2.2- m i l l i l i t e r syphon was used to monitor r e t e n t i o n volume. The column p l a t e count was determined from the e x p r e s s i o n 3

o

P l a t e Count - 16 (V /Wb)

2

(1)

R

where V R i s the r e t e n t i o n volume and Wf> i s the b a s e l i n e w i d t h of the p l a t e count standard. Using o-dichlorobenzene as the p l a t e count standard y i e l d e d 24,000 p l a t e s f o r 180 cm. of column. The r e s o l u t i o n of the column set was determined from the e x p r e s s i o n d e r i v e d by B l y [1] 2 S

C V

V

V

+ W

R

)

I

log

b2

1 ( )

(M!/M )

V

}

2

where VR« and V R ^ are r e t e n t i o n volumes, W^ and W^ are base l i n e widths and, and M are peak molecular weights f o r p o l y mer standards 1 and 2, r e s p e c t i v e l y . For t h i s set of columns, a p o l y s t y r e n e standards of molecular weights 37,000 and 2,000, obtained from Pressure Chemical Co., P i t t s b u r g h , Pa., were used f o r standards 1 and 2, r e s p e c t i v e l y . The v a l u e obtained f o r R was 2.2 a t a f l o w r a t e of 0.6 ml/min. This v a l u e of R compares to a value of 1.14 a t a 2 ml/min. f l o w r a t e r e p o r t e d i n the l i t e r a t u r e [ 2 ] . At t h i s f l o w r a t e the column s e t gave the o p t i mum r e s o l u t i o n per u n i t time. T h i s r e l a t i v e l y low f l o w r a t e a l s o i s r e q u i r e d to preserve the column r e s o l u t i o n over an extended p e r i o r of time. This f l o w r a t e c o n d i t i o n corresponds to the minimum i n a Van Deemter p l o t of h e i g h t e q u i v a l e n t t h e o r e t i c a l p l a t e s U 6 . l i n e a r v e l o c i t y and i s i n agreement w i t h other pub l i s h e d data on μ-Styragel ® columns [_3,4J . The column s e t was c a l i b r a t e d w i t h Pressure Chemical p o l y styrene standards over the molecular weight range of i n t e r e s t . The c a l i b r a t i o n curve f o r t h i s column set i s shown i n F i g u r e 1. The p o l y s t y r e n e molecular weight s c a l e was used to p r o v i d e quan t i t a t i v e estimates of MWD parameters such as number- and weightaverage molecular weight (M , M ) f o r r e l a t i v e comparison pur poses i n c o n j u n c t i o n w i t h the a n a l y s i s of the MWD of oligomers and low molecular weight polymers used i n c o a t i n g s systems. 2

s

s

n

w

Data A c q u i s i t i o n and A n a l y s i s The HPGPC has been i n t e r f a c e d to a Data General NOVA Model

Provder; Size Exclusion Chromatography (GPC) ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

11.

κυο AND PROVDER

30

HPGPC

35

of

40

RETENTION F i g u r e

1.

Polystyrene

209

O l i g o m e r s

4S VOLUME

m o l e c u l a r

weight

50

Û

ώ

(ml) calibration

c u r v e


210


(GPC)

1230 minicomputer f o r r e a l - t i m e data a c q u i s i t i o n and a n a l y s i s . The minicomputer system has been d e s c r i b e d p r e v i o u s l y [ 5 ] . The subsequent_datja r e d u c t i o n and a n a l y s i s provides molecular weight averages (M , M , M , M +i) or the e q u i v a l e n t extended c h a i n l e n g t h averages as w e l l as v a r i o u s p o l y d i s p e r s i t y i n d i c e s . In a d d i t i o n , s t a t i s t i c a l shape parameters such as v a r i a n c e , skewness and k u r t o s i s f o r the number-, weight- and z - d i s t r i b u t i o n s are provided. A t y p i c a l computer generated a n a l y s i s r e p o r t i s shown i n F i g u r e 2. The data a n a l y s i s program provides p l o t s of base l i n e - a d j u s t e d height U6. r e t e n t i o n volume as shown i n F i g u r e 3, as w e l l as p l o t s of the w e i g h t - d i f f e r e n t i a l and cumulative d i s t r i b u t i o n s of molecular weight w i t h the l o c a t i o n s of the respec t i v e molecular weight averages (Mn, M , M , Μ +χ, M +2> marked on the d i f f e r e n t i a l curve as shown i n F i g u r e 4. The computation of MWD s t a t i s t i c s and p l o t s are based on the method g i v e n by P i c k e t t , Cantow and Johnson [ 6 ] . For o l i g o m e r i c samples w i t h w e l l d e f i n e d peaks as shown i n F i g u r e 5, the r e l a t i v e percentage f o r each component can be ob t a i n e d by i n t e g r a t i n g the area under each peak v i a a gas chroma tography data r e d u c t i o n package a l s o r e s i d e n t on the NOVA m i n i computer [5] . n

w

z

z

w

z

ζ

z

R e s u l t s and D i s c u s s i o n The r e s o l u t i o n c a p a b i l i t y of the y - S t y r a g e l ® column s e t i s shown i n F i g u r e 6. A mixture of p o l y s t y r e n e s w i t h molecular weights ranging from 97,000 to 600 were separated according to t h e i r molecular weights. The unique f e a t u r e of m i c r o p a r t i c u l a t e h i g h e f f i c i e n c y columns, which i n c l u d e μ-Styragel ® , i s the high r e s o l u t i o n i n the low molecular weight r e g i o n [_3,4^,7^,8^,9^, 10]· For the 600 molecular weight p o l y s t y r e n e standard, conven t i o n a l GPC columns would g i v e . o n l y a broad peak. However, the μ-Styragel ® columns separated t h i s sample i n t o a t l e a s t s i x w e l l - d e f i n e d peaks as shown i n F i g u r e 6 corresponding to monomer, dimer, t r i m e r and other h i g h e r molecular weight oligomers. Even s m a l l molecules such as ortho-dichlorobenzene and benzene are r e a d i l y separated. The h i g h r e s o l u t i o n i n the low molecular weight regions i s p a r t i c u l a r l y s u i t e d f o r f i n g e r p r i n t i n g the oligomers used i n chemical c o a t i n g s systems. I n F i g u r e 6, both UV and DRI t r a c e s are shown. For c l a r i t y i n comparisons, o n l y UV t r a c e s w i l l be shown f o r examples i n subsequent d i s c u s s i o n unless where s p e c i f i e d otherwise*. Powder Coatings. One of the new c o a t i n g s t e c h n o l o g i e s which has developed as an i n n o v a t i v e response to governmental r e g u l a t i o n i s powder c o a t i n g s . These c o a t i n g s systems are designed to be 100% s o l i d s . The development of c o a t i n g s p r o p e r t i e s are a r e s u l t of r e a c t i n g the low molecular weight polymer w i t h an oligomer c r o s s l i n k i n g agent to produce c r o s s l i n k e d polymer. The


11.

HPGPC

κυο AND PROVDER

GPC:10

211

O l i g o m e r s

1/14/80

JOB 30289

OPR:AFK

REV 6.4

OPERATOR SELECTED BASELINE

RERUN OF JOB 30211 SAMPLE ID RUN NO.

of

5299

DETECTOR:

ULTRAVIOLET

MOLECULAR WEIGHT DISTRIBUTION

MEAN VARIANCE SKEWNESS KURTOSIS

NUMBER .723E 03 .3/ΟΕ 06 .292E 01 .154E 02

WEIGHT .124E 04 .102E 07 .238E 01 .105E 02

MEAN WT/MEAN NMBR MEAN Z/MEAN WT MEAN Z+1/MEAN Ζ MEAN Z+2/MEAN Z+l MEAN Ζ * MEAN Z+1/MEAN WT ,144E 03 RANGE

Z+l 2206E .232E .212E .765E

04 07 01 01

Z+2 .465E 04

. 318E 04

1.708 1.667 1.546 1.461 .531E 04 TO .132E 05

RAW CHROMATOGRAM STATISTICS .217E .689E .143E .239E .180E

MEAN VARIANCE SKEWNESS KURTOSIS AREA

02 00 00 01 04

MAX PEAK MAX PEAK MOMENT 3 MOMENT 4

COUNT! HEIGHT ABOUT MEAN ABOUT MEAN

21.56 835.81 .938E-01 .263E 01

COLUMN AND BASELINE PARAMETERS COLUMN SET SOLVENT VOID VOLUME TOTAL VOLUME CALIBRATION CURVE CALIBRATION POLYMER

7 STARTING BASELINE COUNT THF ENDING BASELINE COUNT 8.00 BASELINE SLOPE 28.00 FIRST DATA POINT COUNT 21 LAST DATA POINT COUNT POLYSTYRENE 1/80

#1 count unit * 1 syphon dump of 2.2 milliliters. Figure 2.

Typical computer-generated data analysis report


18.00 28.00 -.0160 19.00 24.80


212

JOB

30289C3021O

—

r

10.

Figure 3.

(GPC)

UV

I 20. 15. R E T E N T I O N VOLUME

V 25. IN COUNTS

30.

~35.

Typical computer-generated plot of baseline-adjusted height vs. retention volume


11.

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HPGPC

of

JOB 30289C30211)

Oligomers UV

ο

LOG MOLECULAR WEIGHT

Figure 4.

Typical computer-generated plot of weight differential and cumulative distributions of molecular weight

INTERMEDIATE

RETENTION V O L U M E (ml) Figure 5.

HPGPC chromatogram of a model compound of epoxy-ester


213

214


(GPC)

R E T E N T I O N VOUJME(mi)

Figure 6. HPGPC traces ( U V and DR!) of a polystyrene standard mixture (operating conditions: columns—(xStyragel 1 0 \ J O , (2) 5 0 0 , (2) 1 0 0 A; solvent— 3

THF;

flow—0.6

X-03

X-38

X-.36

X-02 .°

3

mL/min)

.

,°

4

.

y

R E T E N T I O N V O L U M E (ml)

Figure 7.

HPGPC chromatograms of four isocyanate cross-linkers


11.

κυο AND PROVDER

H P G P C

of

215

O l i g o m e r s

powder c o a t i n g u s u a l l y contains a s m a l l amount of an o l i g o m e r i c flow agent to a i d f l o w and l e v e l i n g d u r i n g the baking process. The MWD of the low molecular weight polymer, o l i g o m e r i c c r o s s l i n k i n g agent, and o l i g o m e r i c flow agent must produce a c o a t i n g s system such t h a t a) the powder p a r t i c l e s w i l l not "block (co a l e s c e ) upon shipment or storage, b) the r e s i n system w i l l melt and f l o w w i t h a p p r o p r i a t e l e v e l i n g c h a r a c t e r i s t i c s optimum f o r appearance p r o p e r t i e s p r i o r to the c r o s s l i n k i n g r e a c t i o n w i t h i n s p e c i f i c time c o n s t r a i n t s at a given temperature, and c) the c r o s s l i n k i n g r e a c t i o n must occur at the a p p r o p r i a t e p o i n t i n time a f t e r the r e s i n has melted c o n s i s t e n t w i t h the development of both good appearance p r o p e r t i e s and good mechanical p r o p e r t i e s . Thus, the MWD of the polymer, c r o s s l i n k i n g agent and f l o w modi f i e r must be c a r e f u l l y designed and c o n t r o l l e d to produce a powder c o a t i n g s system which meets d e f i n e d r h e o l o g i c a l , r e a c t i v i t y and mechanical property c o n s t r a i n t s . Figure 7 i l l u s t r a t e s the use of HPGPC to a i d a r e s i n chemist i n developing an in-house isocyanate c r o s s l i n k e r f o r a powder c o a t i n g system. Isocyanate c r o s s l i n k e r X-02 gave d e s i r e d pro p e r t i e s and i s considered the standard. At the e a r l y stage of the development, r e s i n X-03 was i n i t i a l l y made. By changing the types of r e a c t a n t s , molar r a t i o of r e a c t a n t s and r e a c t i o n c o n d i t i o n s , r e s i n X-36 was the next i t e r a t i o n i n the r e s i n s y n t h e s i s process. F i n a l l y , X-36 was f i n e - t u n e d to produce X-38 which matched X-02 i n both i t s chemical r e a c t i o n p r o p e r t i e s and i t s MWD. HPGPC a l s o was used f o r q u a l i t y c o n t r o l of incoming raw m a t e r i a l s . F i g u r e 8 shows the chromatograms of two d i f f e r e n t batches of blocked isocyanate c r o s s l i n k e r s . One was acceptable and the other was too r e a c t i v e . As can be seen from the HPGPC t r a c e s , the l e v e l of the component e l u t e d at r e t e n t i o n volume 40 i s much higher f o r CX-46 than f o r CX-48. This component was a s s o c i a t e d w i t h f r e e isocyanate f u n c t i o n a l i t y which i n excess would make CX-46 too r e a c t i v e . With t h i s i n f o r m a t i o n , e i t h e r the necessary adjustment f o r the presence of e x c e s s i v e f r e e i s o cyanate f u n c t i o n a l i t y c o u l d be made or t h i s p a r t i c u l a r batch from the s u p p l i e r c o u l d be r e j e c t e d . Another example i n v o l v e d a batch of isocyanate c r o s s l i n k e r which was too tacky. Upon comparing the HPGPC t r a c e of t h i s sample w i t h that of a c o n t r o l as shown i n Figure 9, i t i s seen that the major d i f f e r e n c e between these two samples was the l e v e l of f r e e caprolactam. The high content of f r e e caprolactam i n sample CX-006 depressed the g l a s s t r a n s i t i o n temperature (Tg) of the sample to such an extent that CX-006 became too tacky. T h i s method of a n a l y s i s has proved t o be a r e l i a b l e and u s e f u l t e c h nique f o r d e t e c t i n g low l e v e l s of f r e e caprolactam i n t h i s type of o l i g o m e r i c c r o s s l i n k e r . F i g u r e 10 shows the HPGPC t r a c e s of two d i f f e r e n t batches of in-house a c r y l i c r e s i n s f o r powder c o a t i n g s . I t i s seen t h a t due to the presence of high l e v e l s of low molecular weight components 11


216

SIZE E X C L U S I O N

2 0

L.

AO

3 0 1

ι

1

1

.

1

RETENTION Figure 8.

H P G P C

c h r o m a t o g r a m s

S O

. ι

1

of

CHROMATOGRAPHY (GPC)

- * ι

6

-L.

0

:

V O L U M E (ml)

two

isocyanate

cross-linkers

f r o m

different

batches

20

1

30

40

I

I

50

60

I

1

R E T E N T I O N V O L U M E (ml) F i g u r e

9,

H P G P C


of

two

isocyanate

cross-linkers

f r o m

batches


different

11.

κυο

A N D PROVDER

HPGPC

of

217

Oligomers

and r e s i d u a l monomer and s o l v e n t i n sample TG-37, the Tg i s 20°C lower than t h a t of sample TG-57. Reducing the amount of low molecular weight components and r e s i d u a l monomer and s o l v e n t by vacuum s t r i p p i n g gave an i n c r e a s e i n the Tg from 37°C to 48°C f o r sample TG-37. This brought the sample w i t h i n the m i n i mum acceptable Tg l e v e l c o n s i s t e n t w i t h n o n - " b l o c k i n g of the sample. M

High S o l i d s . Another technology which has evolved as a r e sponse t o governmental r e g u l a t i o n s i s h i g h s o l i d s c o a t i n g s . High s o l i d s c o a t i n g s are those which are u s u a l l y 62.5% n o n - v o l a t i l e or g r e a t e r on a volume b a s i s . These c o a t i n g s systems c o n t a i n oligomers which are g e n e r a l l y low i n molecular weight, on the order of 500. As i n powder c o a t i n g s , these systems develop mech a n i c a l p r o p e r t i e s upon r e a c t i o n w i t h a c r o s s l i n k i n g agent t o p r o duce a c r o s s l i n k e d polymer. The key design parameters i n h i g h s o l i d s c o a t i n g s are low v i s c o s i t y , low v o l a t i l i t y and c o n t r o l l e d r e a c t i v i t y [11,12]. Low c o a t i n g s v i s c o s i t y (100-500 cps) i s r e q u i r e d i n order to be able to apply the c o a t i n g w i t h convention a l spray a p p l i c a t i o n equipment. However, v o l a t i l i t y of the r e s i n system at the c u r i n g temperature must be minimal. These c o n s t r a i n t s n e c e s s i t a t e the design of a c a r e f u l l y t a i l o r e d mole c u l a r weight d i s t r i b u t i o n to minimize the presence of v o l a t i l e components c o n s i s t e n t w i t h molecular weights h i g h enough to a i d mechanical p r o p e r t y development upon c u r i n g , but not too h i g h to have a d e l e t e r i o u s e f f e c t upon a p p l i c a t i o n p r o p e r t i e s and the u l t i m a t e appearance p r o p e r t i e s of the c o a t i n g . The c u r i n g mech anism should be c o n t r o l l a b l e under v a r y i n g r e a c t i o n c o n d i t i o n s to produce c r o s s l i n k e d c o a t i n g s a t temperatures low enough to minimize v o l a t i l e e v o l u t i o n and a t the same time minimize energy usage d u r i n g the cure process. I n order to compensate f o r the decrease i n molecular weight of a polymer designed f o r h i g h s o l i d s c o a t i n g s , there i s an i n c r e a s i n g dependence on the c r o s s l i n k i n g agent f o r the development of mechanical p r o p e r t i e s . I t becomes important to c a r e f u l l y match the c r o s s l i n k i n g agent w i t h the polymer both i n terms of r e a c t i v e f u n c t i o n a l i t y and MWD. For h i g h s o l i d s c o a t i n g s HPGPC i s very u s e f u l f o r s c r e e n i n g v a r i o u s r e s i n s f o r the o p t i m i z a t i o n of c o a t i n g s v i s c o s i t y and cured f i l m p r o p e r t i e s . Among the f i v e p o l y e s t e r r e s i n s shown i n Figure 11, E-17 was f i n a l l y chosen to be scaled-up due to the unique combination of good f i l m p r o p e r t i e s (hardness and s a l t spray r e s i s t a n c e ) and lowest v i s c o s i t y . The three r e s i n s on the r i g h t hand s i d e of F i g u r e 11 (E-44, E-38 & E-42) were not accept able because t h e i r v i s c o s i t i e s were too h i g h as a r e s u l t of h i g h molecular weight components. While r e s i n E-13 met the r e q u i r e ment of low v i s c o s i t y f o r h i g h s o l i d s , the f i l m p r o p e r t i e s were not as good as those of E-17 due to the presence of a h i g h l e v e l of unreacted monomer. F i g u r e 12 shows the HPGPC DRI t r a c e s of f o u r h i g h s o l i d s a c r y l i c oligomers. The r e s u l t s of p a i n t performance e v a l u a t i o n


218

SIZE EXCLUSION C H R O M A T O G R A P H Y ( G P C )

R E T E N T I O N V O L U M E (ml) F i g u r e

20 i

-ι

30 ι

ι

10.

H P G P C

40 ι

»

*


50

20

J

'

RETENTION F i g u r e

11.

H P G P C

of

acrylic

resins

30 »

'

40 *

»

5,0 «

V O L U M E (ml)


of

high

solids

polyesters


I

11.

κυο A N D PROVDER

HPGPC

of

Oligomers

219

on these a c r y l i c s showed that a c r y l i c A-8 possessed s i m i l a r p a i n t v i s c o s i t y , p e n c i l hardness, impact, MEK r e s i s t a n c e and adhesion p r o p e r t i e s to the commercial high s o l i d s a c r y l i c R-42 due to the s i m i l a r molecular weight range. A c r y l i c s A-15 and A-16 possessed two to three u n i t s higher i n hardness than a c r y l i c A-8 due to the presence of l a r g e amounts of h i g h molecular weight components. However, the c o a t i n g s v i s c o s i t y of coatings systems made with A-15 and A-16 was unacceptably too high. HPGPC a l s o was used to analyze the MWD of v a r i o u s amino c r o s s l i n k e r s , which are the most f r e q u e n t l y used c u r i n g agent f o r i n d u s t r i a l c o a t i n g s . I t i s seen from Figure 13 that HPGPC r e solved each c r o s s l i n k e r i n t o s e v e r a l components d e s p i t e the f a c t that the v e n d o r s l i t e r a t u r e s t a t e d that M-03 and M-56 are monomeric. The e f f e c t of these amino c r o s s l i n k e r s i n the p r o p e r t i e s of a c r y l i c high s o l i d s coatings has been s t u d i e d . Using the same set of a c r y l i c r e s i n s , i t has been shown that c o a t i n g s prepared with the M-70 c r o s s l i n k i n g agent had b e t t e r 500 hours s a l t spray r e s i s t a n c e but lower impact r e s i s t a n c e than c o a t i n g s prepared with the M-03 c r o s s l i n k i n g agent. These p r o p e r t i e s are b e l i e v e d to be a s s o c i a t e d w i t h the higher molecular weight of M-70. 1

Water-Borne Coatings. Water-borne c o a t i n g s are r e p l a c i n g solvent-based c o a t i n g s i n such markets as metal d e c o r a t i n g (bev erage can l i n e r s ) , c o i l c o a t i n g s and wood c o a t i n g s as a response to meeting government r e g u l a t i o n s with r e s p e c t to allowable amounts of v o l a t i l e s o l v e n t emission during the baking process. These c o a t i n g s u s u a l l y are i n the 5,000-30,000 molecular weight range and are prepared i n water-miscible organic s o l v e n t s up to 70 to 80% s o l i d s by volume. Chemically, these r e s i n s can be p o l y e s t e r s , a l k y d s , a c r y l i c s and epoxy e s t e r s . G e n e r a l l y , these r e s i n s can s e l f - e m u l s i f y i n t o water when t h e i r s o l u t i o n i n organ i c s o l v e n t s i s introduced i n t o water c o n t a i n i n g some amine [13]. In the p r o d u c t i o n of epoxy e s t e r water-borne c o a t i n g s , i t becomes important to monitor changes i n the molecular s t r u c t u r e of low molecular weight epoxy r e s i n s during storage. I t i s w e l l known that c a t a l y z e d l i q u i d epoxy r e s i n s w i l l undergo f u r t h e r r e a c t i o n upon aging. HPGPC has been used to monitor r e t a i n s of i n coming shipments from the r e s i n s u p p l i e r and monitor p e r i o d i c samples from storage tanks of p r o d u c t i o n p l a n t s . F i g u r e 14 shows that at the time of sampling the samples that came from the p l a n t storage tank was e s s e n t i a l l y s i m i l a r to the r e t a i n e d samples from the s u p p l i e r . Also shown i n the f i g u r e i s an epoxy sample which has been aged f o r a year. I t i s seen that the low molecular weight components had undergone f u r t h e r r e a c t i o n to form a much higher molecular weight compound. Observation of any changes i n oligomer d i s t r i b u t i o n such as t h i s , at any time, w i l l a l e r t the r e s p e c t i v e p r o d u c t i o n p l a n t to take proper a c t i o n . UV Curable Coatings. T y p i c a l l y , UV c u r a b l e c o a t i n g s c o n s i s t of very low molecular weight m u l t i - f u n c t i o n a l oligomers d i l u t e d


220

SIZE EXCLUSION CHROMATOGRAPHY


(GPC)

11.

κυο AND PROVDER

HPGPC

of

Oligomers

RETENTION V O L U M E (mi) Figure 14.

HPGPC chromatograms of epoxy resins


221

222

SIZE E X C L U S I O N C H R O M A T O G R A P H Y ( G P C )

A

Β

20

30

40

50

RETENTION V O L U M E (ml) F i g u r e

15.

HPGPC


(DRI

traces)

of

polyester

methane


11.

κυο

AND PROVDER

HPGPC

of

Oligomers

223

with r e a c t i v e monomers and c o n t a i n a p h o t o s e n s i t i z e r to promote the c r o s s l i n k i n g r e a c t i o n . The almost instantaneous r a t e of r e a c t i o n permits very f a s t l i n e speeds. T h i s type of technology i s i d e a l l y s u i t e d f o r f l a t stock such as f l o o r t i l e and i n t e r i o r wood p a n e l i n g . Often such coatings are a p p l i e d by r o l l c o a t i n g a p p l i c a t i o n methods. In order to have acceptable appearance pro p e r t i e s a f t e r cure, the MWD of the oligomer system i s one v a r i able along with t o t a l coatings v i s c o s i t y which must be c o n t r o l l e d to have the a p p r o p r i a t e r h e o l o g i c a l p r o p e r t i e s w i t h respect to r o l l t r a n s f e r , flow and l e v e l i n g . The MWD of the oligomer must be maximized c o n s i s t e n t with acceptable r h e o l o g i c a l p r o p e r t i e s i n order to generate acceptable mechanical p r o p e r t i e s i n the cured film. HPGPC i s very u s e f u l f o r g u i d i n g r e s i n s y n t h e s i s and process development. Figure 15 shows the HPGPC t r a c e s of two p o l y e s t e r based urethane oligomers produced by v a r y i n g the order of monomer a d d i t i o n to the r e a c t o r . The d i f f e r e n c e i n the oligomer d i s t r i bution i s c l e a r l y seen i n the 38-45 ml r e t e n t i o n volume r e g i o n . Due to the presence of the high l e v e l of very low molecular weight components, the r e s i n produced from process A d i d not have acceptable mechanical p r o p e r t i e s compared to the r e s i n produced from process B. The coatings system c o n t a i n i n g r e s i n A produced a c l e a r p r o t e c t i v e surface c o a t i n g which when subjected to cure v i a UV r a d i a t i o n d i d not meet hardness s p e c i f i c a t i o n s . Conclusions The emergence of new c o a t i n g s technologies such as high s o l i d s , powder, water-borne and r a d i a t i o n curable coatings as a response to governmental r e g u l a t i o n s has l e d to the development of r e s i n systems where the measurement of the oligomer and low molecular polymer MWD i s c r i t i c a l l y important i n order to c o n t r o l the p r o p e r t i e s of these c o a t i n g s systems. I t has been shown that the HPGPC technique using high e f f i c i e n c y columns provides the necessary r e s o l u t i o n i n the low molecular weight regions of i n t e r e s t f o r these coatings systems. This technique can be extended by use of other d e t e c t o r s . Chromatix [14] have shown that an o n - l i n e l i g h t s c a t t e r i n g de t e c t o r , under a p p r o p r i a t e c o n d i t i o n s can provide absolute mole c u l a r weight i n f o r m a t i o n i n the low molecular weight r e g i o n . In a d d i t i o n , i t should be p o s s i b l e to unravel the s u b t l e and im portant compositional dependence of the molecular weight d i s t r i b u t i o n f o r these systems i n the low molecular weight r e g i o n by use of u l t r a - v i o l e t and i n f r a r e d d e t e c t o r s [15].


SIZE EXCLUSION CHROMATOGRAPHY (GPC)

224 Literature Cited 1.

Bly, D. D.; J. Polym. Sci., Part C, 21, 13 (1968).

2. Yau, W. W., Kirkland, J. J., and Bly, D. D.; "Modern Size -Exclusion Liquid Chromatography", Wiley-Interscience, New York, 1979, p. 111. 3.

Vivilecchia, R. V., Colter, R. L . , Limpert, R. J., Thimof, Ν. Ζ., and Little, J . N.; J. Chromatogr., 99, 407 (1974).

4.

Dark, W. Α., Limpert, R. J., and Carter, J . D.; Polym. Eng. and Sci., 15 (12), 831 (1975).

5. Niemann, T. F., Provder, T., Metzger, V., and Kearney, R. J.; ACS Organic Coatings and Plastics Chemistry Preprints, 38, 133 (March, 1978). 6. Pickett, H. E . , Cantow, M. J . R., and Johnson, J . F.; J . Appl Polym. Sci., 10, 917 (1966). 7. Kirkland, J. J.; and Antle, P. E.; J. Chromatogr. Sci., 15, 137 (1977). 8. Krishen, Α.; J. Chromatogr. Sci., 15, 434 (1977). 9.

Krishen, Α., and Tucker, R. G.; Anal. Chem., 49, 898 (1977).

10.

Majors, R. Ε., and Johnson, E. L.; J. Chromatogr. Sci., 167, 17 (1978).

11.

Antonelli, J. Α.; Am. Paint J., 44 (March 31, 1975).

12.

Koleske, J. V., Smith, O. W., and Kucsona, J . G.; Modern Paint and Coatings, 39 (Dec, 1977).

13.

Myers, R. R., Gardon, J. L . , Lauren, S.; Ed; Proceedings Science of Organic Coatings Workshop, Kent State University, Kent, Ohio; "Gaps in the Current Physical Chemical Chemistry State-of-the-Art Related to New Coatings Systems", J . L. Gardon, 65 (June, 1978).

14.

Chromatix KMX-6 Application Note, LS10, "Molecular Weight Distribution of Low Molecular Weight Polymers".

15.

Provder, T., and Kuo, C.; ACS Organic Coatings and Plastics Chemistry Preprints, 36 (2), 7 (1976).

RECEIVED May 20, 1980.


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