Identification of Products from Polyolefin Oxidation by Derivatization

Chapter 27

Identification of Products from Polyolefin Oxidation by Derivatization Reactions 1

D. J. Carlsson, R. Brousseau, Can Zhang , and D. M. Wiles

Downloaded by CORNELL UNIV on August 25, 2016 | http://pubs.acs.org Publication Date: December 22, 1988 | doi: 10.1021/bk-1988-0364.ch027

Division of Chemistry, National Research Council of Canada, Ottawa K1A 0R9, Canada A series of reactions with gases have been selected for the rapid quantification of many of the major products from the oxidation of polyolefins. Infrared spectroscopy is used to measure absorptions after gas treatments. The gases used and the groups quantified include phosgene to convert alcohols and hydroperoxides to chloroformates, diazomethane to convert acids and peracids to their respective methyl esters, sulfur tetrafluoride to convert acids to acid fluorides and nitric oxide to convert alcohols and hydroperoxides to nitrites and nitrates respectively. In some cases it is possible to differentiate between the various alkyl substituents. Primary, secondary and tertiary nitrates and nitrites all show clearly diffe rent infrared absorptions. The spectra of acid fluo rides can be used to differentiate chain-end groups from pendant acid groups. Furthermore, the loss of all -OH species upon sulfur tetrafluoride exposure allows the reliable estimation of ketones, esters and lactones without the complication of hydrogen-bon ding induced shifts in the spectra. Preliminary re sults from the use of these reactions to characterize γ-ray oxidized polyethylene and polypropylene are used to illustrate the scope of the methods. H y d r o c a r b o n s o x i d i z e to g i v e a complex m i x t u r e of p r o d u c t s w h i c h i n clude h y d r o p e r o x i d e s , alcohols, ketones, acids, esters, etc. (1). P o l y o l e f i n s s i m i l a r l y c a n be o x i d i z e d b y h e a t , r a d i a t i o n o r m e c h a n o initiated processes. T h e p r e c i s e i d e n t i f i c a t i o n a n d q u a n t i f i c a t i o n of t h e s e o x i d a t i o n p r o d u c t s a r e e s s e n t i a l f o r t h e complete u n d e r s t a n d i n g a n d c o n t r o l of t h e s e d e s t r u c t i v e reactions. Conventional m e t h o d s f o r t h e i d e n t i f i c a t i o n of o x i d a t i o n p r o d u c t s i n c l u d e i o d o m e N O T E : This chapter was issued as N R C C No. 27914. 1

Guest research scientist from Academia Sinica, Institute of Chemistry, Beijing, China 0097-6156/88/0364-0376506.00/0 Published 1988 American Chemical Society

Benham and Kinstle; Chemical Reactions on Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

27.

CARLSSON ET AL.

377

Products from Polyoiefin Oxidation


try a n d i n f r a r e d (IR) s p e c t r o s c o p y (2-4). Iodometry sums a l l h y d r o p e r o x i d e s a n d p e r a c i d s , b u t also may i n c l u d e some d i a l k y l p e r oxides. IR c a n n o t d i f f e r e n t i a t e b e t w e e n h y d r o g e n - b o n d e d a l c o h o l and h y d r o p e r o x i d e - O H groups and is only paritally successful i n t h e r e s o l u t i o n of t h e mix of c a r b o n y l s p e c i e s f o r m e d . In c o n t r a s t , l i q u i d p h a s e , n u c l e a r m a g n e t i c r e s o n a n c e ( n . m . r . ) has t h e r e s o l u t i o n to p o t e n t i a l l y d i f f e r e n t i a t e a l l of t h e s e p r o d u c t s ( 5 , 6 ) . This m e t h o d i s limited i n t h r e e a r e a s ; low s e n s i t i v i t y (as c o m p a r e d to IR f o r e x a m p l e ) , l o n g d a t a a c q u i s i t i o n times a n d t h e n e e d to d i s s o l v e the samples. T h e n e c e s s i t y for p r o l o n g e d h i g h t e m p e r a t u r e s to a c h i e v e s o l u t i o n makes q u e s t i o n a b l e t h e f i n a l a n a l y s e s b e c a u s e of t h e t h e r m a l i n s t a b i l i t y of s e v e r a l o f t h e k e y p o l y m e r o x i d a t i o n p r o d u c t s . Derivitization reactions have previously been employed to e x t e n d the s e n s i t i v i t y a n d r e s o l u t i o n of I R , u l t r a v i o l e t a n d X - r a y photo-electron spectroscopy (7-13). Y e t no p r o p o s e d method has t h e r a n g e to accommodate the major o x i d a t i o n p r o d u c t s from p o l y o l e fins. A s p a r t of an o n g o i n g s t u d y of p o l y m e r o x i d a t i o n a n d s t a b i l i z a t i o n , we d i s c u s s h e r e a s e r i e s of r e a c t i o n s with s m a l l , r e a c t i v e gas molecules. T h e p r o d u c t s from t h e s e r e a c t i o n s c a n b e r a p i d l y i d e n t i fied and quantified b y I R . Some of t h e s e r e a c t i o n s a r e n e w , o t h e r s have already been d e s c r i b e d i n the l i t e r a t u r e , although t h e i r p r o d u c t s h a v e not a l w a y s b e e n f u l l y i d e n t i f i e d . Experimental A d d i t i v e - f r e e film samples of i s o t a c t i c p o l y p r o p y l e n e ( i P P , 30pm Himont P r o f ax r e s i n ) a n d p o l y e t h y l e n e s ( L L D P E , 120pm, l i n e a r low d e n s i t y D u P o n t S c l a i r r e s i n , a n d U H M W - P E , 120pm, u l t r a h i g h m o l e c u l a r w e i g h t , h i g h d e n s i t y Himont L S R 5641-1B r e s i n ) were o x i d i z e d by exposure i n a i r to γ - r a d i a t i o n ( A E C L Gamma C e l l 220, 1.0 Mrad/h). Films were s t o r e d at - 2 0 ° u n t i l a n a l y s i s c o u l d be c a r r i e d out. O x i d i z e d films a n d d e r i v a t i z e d , o x i d i z e d films were c h a r a c t e r i z e d b y i o d o m e t r y ( r e f l u x with N a l i n i s o p r o p a n o l / a c e t i c a c i d ) a n d b y t r a n s m i s s i o n F o u r i e r T r a n s f o r m ( F T ) IR ( P e r k i n E l m e r 1500), u s i n g t h e s p e c t r a l s u b t r a c t i o n t e c h n i q u e ( 3 , 14). F r e e r a d i c a l s were m e a s u r e d b y the e l e c t r o n s p i n r e s o n a n c e t e c h n i q u e ( e . s . r . , V a r i a n E4 s p e c t r o m e t e r ) . Films were e x p o s e d to e a c h r e a c t i v e gas at room t e m p e r a t u r e i n a simple flow s y s t e m w h i c h c o u l d be sealed o f f b y v a l v e s to allow r e a c t i o n to p r o c e e d . A f t e r r e a c t i o n , t h e v a r i o u s g a s e s were s w e p t out with N b e f o r e film a n a l y s i s . T h e g a s e s u s e d i n c l u d e d SF^ , S 0 , COCl a n d N O ( M a t h e s o n , u s e d as s u p p l i e d ) . T h e e x c e p t i o n was CH N w h i c h was g e n e r a t e d as r e q u i r e d i n s m a l l amounts a d j a c e n t to t h e films b y t h e r e a c t i o n of e t h a n o l i c K O H o n D i a z a l d ( A l d r i c h ) i n t h e r e a c t o r d e s c r i b e d b y F a l e s et al (15). The C H N r e a c t i o n s were p e r f o r m e d with films at 2 2 ° C a n d also at - 7 8 ° C , b u t t h e the C H N r e a g e n t s at ~ 2 0 ° C i n b o t h c a s e s . To prevent N 0 f o r m a t i o n from NO-0 r e a c t i o n , films were s w e p t with N f o r a b o u t 5 m i n u t e s p r i o r to N O i n t r o d u c t i o n . Because SF attacks g l a s s , these reactions were c a r r i e d out i n an a l l - p o l y e t h y l e n e flow s y s t e m with Monel v a l v e s . F r o m t h e F T I R c h a n g e s , a l l gas r e a c t i o n s were v i r t u a l l y complete i n ~ 15 h f o r t h e t h i n i P P films a n d ~ 24 h f o r t h e L L D P E . 2

2

2

2

2

2

2

2

2

2

2

l+


2

CHEMICAL REACTIONS ON POLYMERS

378

F o r c o m p a r i s o n p u r p o s e s , some m o d e l c o m p o u n d s a n d m o d e l p o l y m e r s were r e a c t e d with the g a s e s . L i q u i d models were u s e d as d i l u t e s o l u t i o n s i n h e x a n e o r h e x a d e c a n e ; m o d e l p o l y m e r s were u s e d as s o l i d f i l m s . n - P e r o c t a n o i c a c i d was sunthesised from n - o c t a n o i c acid

w i t h 30% h y d r o g e n p e r o x i d e

(-C^

I R a b s o r p t i o n s at 1755

cm" in hexane solution)(16). Tert.-buty?Siydroperoxide (99%) was p u r i f i e d b y the a z e o t r o p i c d i s t i l l a t i o n of t h e c o m m e r c i a l 70% hydroperoxide/water mixture ( A l d r i c h ) . n-Octanoic acid, 2-ethylhexanoic acid, stearic a c i d , γ - d e c a l a c t o n e , 1,1,3,3-tetramethylbutane 1-hydrop e r o x i d e ( L u c i d o l ) were u s e d as s u p p l i e d . P o l y m e r s u s e d to i d e n t i f y gas r e a c t i o n s i n c l u d e d p o l y ( m e t h y l m e t h a c r y l a t e ) , a p r o p y l e n e / a c r y l i c acid c o p o l y m e r , poly ( v i n y l alcohol) ( Poly sciences ), P h e n o x y ( U n i o n C a r b i d e , p o l y m e r of t h e 2 - h y d r o x y p r o p y l e t h e r of b i s p h e n o l A ) a n d an e t h y l e n e / c a r b o n m o n o x i d e c o p o l y m e r .


1

Results and Discussion T h e γ - i n i t i a t e d o x i d a t i o n of p o l y o l e f i n s p r o d u c e s a p r o d u c t mix w h i c h i s l e s s complex t h a n t h a t r e s u l t i n g from p h o t o - o r t h e r m a l l y i n i t i a t e d degradation. T h i s r e s u l t s from the mild c o n d i t i o n s i n the γ - c e l l , w h e r e the major i n i t i a l o x i d a t i o n p r o d u c t , t h e - O O H g r o u p , i s s t a b l e . A l t h o u g h the d e r i v a t i z a t i o n methods a r e a p p l i c a b l e to a l l t y p e s of o x i d a t i o n , f o r s i m p l i c i t y o n l y the γ - i r r a d i a t e d s y s t e m s will b e c o n sidered here. T h e γ - i n i t i a t e d o x i d a t i o n of i P P a n d L L D P E p r o d u c e s IR s p e c t r a l c h a n g e s i n the ~ 3400 c m " , ~ 1715 cm" a n d ~ 1170 cm" r e g i o n s ( F i g s . 1 and 2). T h e s e r e g i o n s a r e b r o a d l y a t t r i b u t e d to h y d r o g e n b o n d e d alcohol a n d / o r h y d r o p e r o x i d e , c a r b o n y l and - C - 0 - ? a b s o r p tions, respectively. 1

1

1

I n i t i a l l y , v a r i o u s l i q u i d p h a s e r e a g e n t s were e x p l o r e d f o r t h e i d e n t i f i c a t i o n of t h e d i f f e r i n g - O H s p e c i e s a n d c a r b o n y l s p e c i e s i n the solid films. T h e s e r e a g e n t s i n c l u d e d e t h a n o l i c sodium h y d r o x i d e [to generate IR-detectable c a r b o x y l a t e g r o u p s from a c i d s (10)], a n d benzidine [ f o r the c o l o r i m e t r i c d e t e r m i n a t i o n of p e r a c i d s (17 ) ] . H o w e v e r , r e s u l t s were d i s a p p o i n t i n g with little r e a c t i o n o b s e r v e d . T h i s may h a v e r e s u l t e d e i t h e r from l a c k of p e n e t r a t i o n of t h e r e a g e n t s i n t o the p o l y o l e f i n s o r f a i l u r e of t h e l i q u i d r e a g e n t s to s w e l l the p o l y m e r s . Similar p r o b l e m s h a v e b e e n r e p o r t e d p r e v i o u s l y (10, 12). O n the o t h e r h a n d , s u c c e s s f u l complete r e a c t i o n s h a v e b e e n r e p o r t e d b e t w e e n g a s e s o r v a p o u r s a n d o x i d a t i o n p r o d u c t s (7, 8, 12, 13, 18). A p p a r e n t l y , s m a l l gas molecules c a n p e n e t r a t e the p o l y mer s t r u c t u r e a n d r e a c h most s i t e s p r e v i o u s l y a c c e s s a b l e to 0 . In t h e f o l l o w i n g s e c t i o n s , some of t h e p r e v i o u s l y p r o p o s e d g a s - p o l y m e r r e a c t i o n s are r e - e x a m i n e d a n d c o m p a r e d with some newly d e v e l o p e d methods. 2

SQ Reactions. E x p o s u r e to S 0 has b e e n p r o p o s e d to lead to a q u a n t i t a t i v e r e a c t i o n with - O O H g r o u p s to g i v e a p r o d u c t with a m a r k e d i n c r e a s e i n IR a b s o r p t i o n o v e r t h a t of the o r i g i n a l - O O H g r o u p s (7, 18). H o w e v e r , we h a v e f o u n d the r e a c t i o n s with o x i d i z e d 9

2


CARLSSON ET AL.

Products from Polyolefin Oxidation


LLDPE + 2 0 Mrad

WAVENUMBER Figure 1

IR s p e c t r a of p r o d u c t s from gas r e a c t i o n s pre-oxidized LLDPE

with

Film o x i d i z e d i n a i r b y γ - i r r a d i a t i o n (20 M r a d . ) . F T I R s p e c t r a r e s u l t from the s u b t r a c t i o n of t h e s p e c t r u m of n o n - o x i d i z e d L L D P E .


380


^ i P P + 10 Mrad


1

t: 4000

,

au 3000

ι

1800

.

ι

1400

.

L _

1000

WAVENUMBER Figure 2

IR s p e c t r a of p r o d u c t s from gas r e a c t i o n s pre-oxidized iPP

with

Film o x i d i z e d i n a i r b y γ - i r r a d i a t i o n (10 M r a d . ) . F T I R s p e c t r a r e s u l t from t h e s u b t r a c t i o n of the s p e c t r u m of n o n - o x i d i z e d i P P .


27.

C A R L S S O N ET A L .

381

Products from Polyolefin Oxidation

i P P a n d L L D P E to be c o m p l e x , n o n - q u a n t i t a t i v e a n d to g i v e o n l y m a r g i n a l e n h a n c e m e n t i n the IR a b s o r p t i o n o v e r the b a s i c 3400 cm"" absorption. O u r r e s u l t s of s t u d i e s of S 0 r e a c t i o n s on o x i d i z e d p o l y m e r s a n d m o d e l c o m p o u n d s h a v e b e e n r e p o r t e d p r e v i o u s l y (19). The S0 method seems to b e d i s t i n c t l y i n f e r i o r to o t h e r m e t h o d s ( e s p e c i a l l y N O t r e a t m e n t d i s c u s s e d below) a n d w i l l n o t b e c o n s i d e r e d further. 1

2

2

SF Reactions. In c o n t r a s t to S 0 r e a c t i o n s , the SF^ r e a c t i o n as p r o p o s e d o v e r 20 y e a r s ago b y H e a c o c k i s a c l e a n , q u a n t i t a t i v e r e a c t i o n a l t h o u g h with p o t e n t i a l b e y o n d t h a t o r i g i n a l l y p r o p o s e d ( 8 J . From F i g u r e s 1 a n d 2, SF^ e x p o s u r e c a u s e s complete l o s s of a l l - O H a b s o r p t i o n s with the g e n e r a t i o n of - C ( = 0 ) F a b s o r p t i o n s at 1842-1848 cm"" a n d p o s s i b l y weak - C - F a b s o r p t i o n s at ~ 1000 c m " . Oxidized L L D P E a n d i P P give r i s e to d i s t i n c t l y d i f f e r e n t - C ( = 0 ) F a b s o r b a n ces. T h e a b s o r b a n c e i n L L D P E l i e s at 1848 cm" w h e r e a s t h a t from i P P i s at 1842 cm" , with a w e a k e r s h o u l d e r at ~ 1848 c m " . C o m p a r i s o n s t u d i e s on e x t r e m e l y l i n e a r p o l y e t h y l e n e ( U H M W - P E ) also g a v e the 1848 cm" a b s o r p t i o n a f t e r o x i d a t i o n a n d SF exposure. This b a n d c a n r e a s o n a b l y be a t t r i b u t e d to c h a i n - e n d a c i d f l u o r i d e s ( r e a c t i o n 1). In i P P , c a r b o x y l i c a c i d g r o u p s c a n b e e x p e c t e d from t h e f r e e - r a d i c a l o x i d a t i o n of t h e m e t h y l s i d e g r o u p s , a n d to a l e s s e r k

2


1

1

1

1

1

1

k

Ο - CH 2 — CH 2 - C

-

CH

CH

0

2

- C

1)

OH e x t e n t from the 3 - s c i s s i o n of a l k o x y l r a d i c a l s ( I ) , r e a c t i o n s e q u e n c e 2. I

/

3

~~ c

CH.

CH CH,

I

• ο

I

p o s s i b l y v i a the

CHo

Q

- CHU

- Ο Ι Η

I

-

C~ I Η

Ύ

I I

I R0 2

O

c HD

/

-t \

Η

C RH

/ HDD

I ο-

Ι

Η

CHo

Ο

I

RQ>*

c - c~

ROH

"EH

/ Η

I Η

2)

(R0 take II).

e 2

r e p r e s e n t s a n y p e r o x y l r a d i c a l f o r m e d from i P P , w h i c h will p a r t i n a t e r m i n a t i o n r e a c t i o n with the p r i m a r y p e r o x y l r a d i c a l From a c o m p a r i s o n with a c i d f l u o r i d e s p r e p a r e d from m o d e l


382


acids

(TableII)

V

~CH2

-

the d o m i n a n t 1842 cm"

F

C -

C H

~

2

group

1

a b s o r p t i o n i n P P is from

w h e r e a s t h e 1848 c m

- 1

the

shoulder probably

H comes from the c h a i n - e n d a c i d p r o d u c e d v i a r e a c t i o n 2. In tions,

a d d i t i o n to the c l e a r g e n e r a t i o n of t h e a c i d f l u o r i d e a b s o r p

the

SF^ f l u o r i n a t i o n

advantages.

1

which absorb tions),


In

or

at ~ 1710 cm"*

as

free,

addition,

complexes

may

(the

of

- O H groups

exist

as

very

normally accepted

non-hydrogen-bonded

carboxylic from

extraneous

acids

take

acids

part

other

dimers,

a c i d IR a b s o r p

at 1755

in

has

stable

cm"

1

hydrogen

(20). bonded

1755

through

absorptions

are

to

~

1

1710

eliminated

by

cm" .

All

SF^ t r e a t m e n t ,

of

these

as

shown

t h e n a r r o w i n g of t h e c a r b o n y l maximum a n d l o s s of f e a t u r e s

1714

and

~

1

1750

absorption of

cm" .

cause

spectra

This

shifts

from

SF

model

that

?

in

dized

polyolefins

complimentary reactions

can

to

at

the

1784

of t h e

b o t h the only

with

ducts).

both

lactone

with

SF

4

(CH N ) 2

1

reactions,

CH N 2

on

level

of

the

prior

attempted,

are

to

now

with

peracid

(

Identification of Products from Polyolefin Oxidation by Derivatization

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