Thermal and Thermoxidative Degradation of PS in the Presence of Br Containing FRs

7/30/2019 Thermal and Thermoxidative Degradation of PS in the Presence of Br Containing FRs

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Journal o f Thermal Analysis, VoL 33 H988) 12 13 -12 19T H E R M A L A N D T H E R M O - O X I D A T IV E D E G R A D A T I O N O F P O LY -S T Y R E N E IN T H E P R E S E N C E O F B R O M I N E -C O N T A IN I N G F L A M ER E T A R D A N T S

S . A . D a u e n g a u e r 1, O. G . U t k i n a 2 a n d Y u . N . S a z a n o v aI L E N I N G R A D B R A N C H , M A C H I N E S C I E N C E I N S T I T U T E , A C A D E M Y O F S C I EN C E S O F T H E

U.S.S .R .2 " P L A S T P O L Y M E R " S C I E N T I F I C I N D U S T R I A L A S S O C I A T I O N , L E N I N G R A D , U . S .S .R .3 I N S T I T U T E O F M A C R O M O L E C U L A R C O M P O U N D S , A C A D E M Y O F S C IE N C E S O F I I t E U . S .S . R. ,L E NINGR AD, U . S . S . R .

T h e k i n e t i c o f t h e r m a l a n d t h e r m o - o x i d a t i v e d e g r a d a t i o n o ! p o l y s t y r e n e i n t h e p r e s e n c e o fbromine-containing f l a m e r e t a r da n t s w a s i nve s t i ga t e d . I t w a s shown that t h e k i ne t i c s is l i m i t e dby di f fus ion in a ir and by t h e p r oc e s s e s oc c u r r i ng a t t h e i n t e r f a c e i n he l i um .T h e f l a m e r e t a r d a n t s a f f e c t the degradation o f p o l y s t y r e n e b o t h c h e m i c a l l y and physically,an d c h a n g e t h e m e c h a n i s m o f t h e l i m i t i n g s ta g e t o s o m e e x t e n t .

T h e t h e r m a l d e g r a d a t i o n o f p o l y s t y r e n e ( P S ) h a s b e e n s t u d i e d i n g r e a td e t ai l. T h u s , i t m a y b e c o n s i d e r e d a s e s ta b l is h e d t h a t i n t h e t h e r m a l d e g-r a d a t i o n o f P S t h e m a i n p ro c e s s is i ts d e p o l y m e r i z a t i o n , w i t h t h e p r e -d o m i n a n t i s o l a t io n o f t h e m o n o m e r , s t y r e n e [ 1, 2 ]. T h e r e a c t i o n p r o c e e d sb y a f r ee - ra d i ca l m e c h a n i s m [ 2, 3 ]. T h e p r o c e s s o f t h e r m a l d e g r a d a t i o n o fP S is e n d o t h e r m i c [ 4] . A d e t a i l e d r e v i ew o f t h e d a t a o f th e r m o g r a v i m e t r i ca n a ly s is [ 5 ] h as l e d t o t h e c o n c l u s i o n t h a t t h e t h e r m a l d e g r a d a t i o n o f P Sp r o c e e d s a s a f i r s t - o r d e r r e a c t i o n w i t h a n a c t i v a t i o n e n e r g y o f 2 5 0 + 2 0 k Jm o 1 -1 . I n t h e t h e r m a l o x i d a t i o n o f PS , a p a r t f r o m s t y r e n e , w h i c h re m a i n st h e m a i n d e g r a d a ti o n p r o d u c t , b e n z a l d e h y d e , b e n z en e , t o l u e n e a n d , i n t h el a t e r d e g r a d a t i o n s t a g e s, c a r b o n o x i d e s a r e a l s o i s o l a t e d [ 6 ].T h e a im o f t h p r e s e n t p a p e r w a s t o e l u c i d a t e t h e e f f e c t s o f a n u m b e r o fb r o m i n e - c o n t a i n i n g f la m e r e t a r d a n t s o n th e p r o c e ss e s o f t h e r m a l a n d t h e r m o -- o x id a t iv e d e g r a d a t i o n o f P S , a n d t o e s t a b li s h t h e c o r r e l a t i o n b e t w e e n t h ise f f e c t a n d t h e m e c h a n i s m o f a c t i o n o f t h e f l a m e r e t a r d a n t .

E x p e r i m e n t a lT h e p o l y s t y r e n e ( P S- S ) w a s o b t a i n e d b y s u s p e n s i o n p o l y m e r i z a t i o n a n d

p u r i f i e d b y r e p r e c i p i t a t i o n w i t h m e t h a n o l f r o m C C1 4 s o l u t i o n .T h e b r o m i n e - c o n ta i n in g f la m e re t a rd a n t s d e c a b r o m o d i p h e n y l o x i d e

John Wiley & Sons, Limited, ChichesterAkaddmiat Ktadd, Budapest


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1 2 14 D A U E N G A U E R E T A L .: T H E R M A L D E G R A D A T I O N

(DBDPO), hexab romodi phenyl , (HBDP) and hexabromocyc lododec ane(HBCD) were prepared and purified at the Iodine-Bromine ResearchInstitute.Thermal' analysis was carried out with a Q-derivatograph (MOM, Hungary)at a heating ra te of 10 deg min -1 in an atmosphere of air or in a heliumstream (flow rate 25 1 h- I ). The sample mass was 50 mg. The sample holderswere ceramic or platinum crucibles without covers, forming part of thestandard set for the derivatograph.

The activation energy (Ea) of the degradation process was calculated fromthe TG and DTG curves in the parts of the curves corresponding to a massloss in the range of 20 to 40 mass %. The Gorbachev criterion method [8]was used to determine the type of kinetic function, the value of the mass atthe moment of the maximum process rate being taken as a criterion.Pyrolysis gas chromatography (PGC) was carried out with a Tswett-102chromatograph supplied with a funace-type pyrolyser manufactured by theDzerzhinsk Special Design Bureau of Biological Automatics. The conditionsof pyrolysis were as follows: sample mass 0.5 mg, column size 3000 mm,packing 10 mass% of neopentylglycol succinate on chr oma tone N, flow rateof carde r gas (helium) 44 crn a min -1, heat conductivity detector, current ofdetec tor bridge 190 mA, temperature of detector t hermost at 150 ~ andtemperature of column thermo stat 107 ~

Hydrogen bromide was sorbed with a 0.02 N solution of potassium hyd-roxide and determined by a mercurometric method [9].

D i s c u s s i o n o f r e su l t sWhen the DTA and TG data on PS are compared, attention is immediatelydrawn to a marked effect of the experimental conditions on the shape of the

DTA curves (Fig. 1, curves 1-3) . This fact has previously been considered indetail [10], and here it will only be pointed out t hat these differences areassociated with a considerable contribution of secondary processes to theDTA peaks, viz. oxidation (catalytic oxidation in the case of platinumholders) o f produc ts of PS degradation. These secondary processes havevirtually no e ffect on the shape of the TG curves (Fig. 1, curves 2' and 3').It follows that the degradation of PS in air is evidently limited by diffusionof degradation products in the sample. The same can be said about at-mospheric oxygen acting in the well-known scheme [2] as an initiator offree-radical degradation processes. The replacement of a static air atmos-phere by a flow of 25 1 h -1 increases the removal of degradation products

J . T h e r m a l A n a L 3 3 , 1 9 8 8


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D A U E N G A U E R E T A L . : T H E R M A L D E G R A D A T I O N 1 2 15

T e m p e r o i u r e , ~( 100 300 400 6 0 0 _O0 5 0 O

1 0 - 2 ' 1'2 0 -2

.~ 10(1 -T

F ~ . 1 D T A ( I - 3 ) a n d T G c u r v e s (1 ' - 3 ' ) o f p o l y s t y r e n e- 1 , 1' - c e r a m i c c r u c ib l e s , h e l i u m f l o w , 2 5 h ~- 2 , 2 " - c e r a m i c c r u c i b l e s , s t a t i c a i r- 3 , 3 " - p l a t i n u m c r u c i b l e s , s t a t i c a i r

f r o m t h e s a m p l e s u rf a ce a n d t h e s u p p l y o f o x y g e n t o t h e s u rf a ce , b u t d o e sn o t r e s u l t i n a n y c h a n g e i n t h e T G c u r v e . I t s h o u l d b e n o t e d t h a t P S m e l t sb e l o w t h e t e m p e r a t u r e o f t h e s ta r t o f d e g r a d a t io n , a n d th e r e f o r e t h e p r o -c e ss e s o f t h e r m a l d e g r a d a t i o n o c c u r i n t h e l i q u i d p h a s e , a n d t h e a g g r eg a t es t a t e o f t h e i n i t i a l s a m p l e i s n e g l i g ib l e .

H e n c e , t h e T G d a t a c o r r e s p o n d to t h e t h e r m a l d e g r a d a t i o n o f PS t o ag r e a te r e x t e n t t h a n t h e o b s e r v e d D T A e f f e c t s; t h is f a c t is t a k e n i n t o a c c o u n ti n t h e f u r t h e r d i s c u s si o n .

T h e k i n e t ic p a r a m e t e r s w e r e c a l c u l a te d f r o m t h e d a t a o f t h e r m a l a n a ly s isb y u s i n g th e w e l l - k n o w n e q u a t i o n :

d a E~ = A e x p ( - ) f ( a )d t R Tw h e r e f ( a ) is t h e " k i n e t i c " f u n c t i o n , t h e f o r m o f w h i c h is d e t e r m i n e d b y t h em e c h a n i s m o f a o n e - st a g e p ro c e ss .

I t is s h o w n a b o v e t h a t t h e m a i n p r o c e s s i n t h e t h e r m a l d e g r a d a t i o n o f P Sis it s d e p o l y m e r i z a t i o n . H e n c e , a n a t t e m p t m a y b e m a d e t o d e t e r m i n e t h em e c h a n i s m o f t h e r m a l d e g r a d a t i o n b y s e le c ti n g t h e f o r m o f t h e k i n e t icf u n c t i o n t h a t is i n b e s t a g r e e m e n t w i t h t h e e x p e r i m e n t a l d a ta . T h e m e t h o d -o l o g i c a l p r o c e d u r e o f t h i s a n a l y s i s w a s d e s c r i b e d i n d e t a i l e a r l i e r [ 8 ] . T h er e s u l t s a r e g i v e n i n T a b l e 1 .

3 . T h e r ma l A n a l . 3 3 , 1 9 8 8


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1 2 1 6Table 1

D A U E N G A U E R E T A L . : T H E R M A L D E G R A D A T I O NK i n e t ic p a r a m e t e r s o f t h e r m a l d e g r a d a t i o n o f P S c o m p o s i t i o n w i t h b r o m i n e - c o n t ai n i n g f l a m er e t a r d a n t s ( c o n t e n t - 1 m a s s % b a se d o n b r o m i n e , ca l c u l a t io n - f r o m t h e T G - D T G d a t a )

F l a m e r e t a r d a n t Act ivat ion T y p e o f k i n e t icA t m o s phere e n e r g y E a , funct ionkJ mol i~ - ! f ( o 0

Mechanism of the process

/- air 24 2 [ (~-~--2 /3 - I ] - iH B C D a ir 3 1 6 [ - i n ( 1- a ) ] - IDBDPO a i r 215 [ ( 1 ) 1 /3_ 1 ] -1H B D P a i r 2 9 5 1 - ~- h e l i u m 2 6 2 ( 1 - a ) 2 /3H B C D h e l i u m 3 0 1 ( I _ ~ ) 2 /3D B D P O h e l i u m 2 8 9 ( 1 _ ~ ) 2 /3H B D P he l i um 4 4 4 ( 1_~)2 /3

t h r e e - d i m e n t i o n a l diffusiont w o - d i m e n t i o n a l dif fus ionthree-dimensional dif fusionf i r s t order equation2 / 3 o r d e r2 / 3 o r d e r2 / 3 o r d e r2 /3 order

F i r s t, i t s h o u l d b e n o t e d t h a t , u n l i k e t h e a u t h o r s o f p r e v io u s l y p u b l i s h e dp a p e rs , w e c o u l d n o t c o n f h ' m t h e a s s u m p t i o n t h a t t h e t h e r m a l d e g r a d a t i o no f P S p r o c e e d s a s a f i r s t - o r d e r r e a c t i o n . O n t h e c o n t r a r y , i t f o l l o w s f r o m t h ea n a l y si s o f t h e D T A d a t a g i v e n a b o v e t h a t t h i s p r o c e s s i n a i r i s l i m i t e d b yt h e d i f f u s i o n o f d e g r a d a t io n p r o d u c t s ( a n d , p o s s ib l y , o f a t m o s p h e r i c o x y g e n )i n t h e s a m p l e . T h e t h e r m a l d e g r a d a t i o n o f P S i n h e l i u m o b e y s a n o t h e r m e -c h a n i s m : t h e r e a c t i o n o r d e r is 2 / 3 , w h i c h g e n e ra l l y i n d i c a te s t h a t t h e r ea c t -i o n p r o c e e d s a t t h e i n t e r f a c e . I t m a y b e a s s u m e d t h a t i n t h i s c a s e t h e p r o c e s sis l i m i t e d b y t h e e v a p o r a t i o n o f d e g r a d a t i o n p r o d u c t s f r o m t h e s a m p l es u r fa c e . A s i n d i c a t e d a b o v e , i n t h e c a se o f t h e r m o - o x i d a t i v e d e g r a d a t i o ns e c o n d a r y p r o c e s s e s o f o x i d a t i o n o f t h e d e g r a d a t i o n p r o d u c t s d e v e l o p o nt h e s u r fa c e o f t h e s a m p l e , a n d t h e e v a p o r a t i o n s ta g e n o l o n g e r p l a y s a ni m p o r t a n a t r o l e i n t h e k i n e t i c s o f t h e p r o c es s .

T h e v a l u e s o f Ea f o r t h e t h e r m a l d e g r a d a t i o n o f P S a r e n o t o u t s i d e t h er a n g e s r e p o r t e d i n t h e l i t e r a t u r e [ 5 ]. I f t h e s e v a lu e s a r e c o m p a r e d w i t h t h o s eo b t a i n e d f o r t h e r m o - o x i d a t i v e d e g r a d a t i o n i n t h e p r e s e n c e . of f l am e r e t a rd -a n ts , t h e f o ll o w in g s er ie is o b t ai n ed : P S + D B D P O < P S < P S + H B D P < P S ++ H B S D . T h e f a ct t h a t t h e i n t r o d u c t i o n o f D B D P O i n t o t h e p o l y m e r s li gt hl yd e c r e a s e s E a ' f o r t h e t h e r m a l d e g r a d a t i o n i n a i r, a t f ir s t s i g h t c o r r e s p o n d s t ot h e r e s u l t s p u b l i s h e d i n [ 7 ], a l t h o u g h , s i n c e d i f f u s i o n r e m a i n s t h e l i m i t i n gs ta g e , i t m i g h t b e a s s u m e d t h a t D B D P O d e c re a s es t h e v i s c o s it y o f t h e m e l t ,t h e r e b y f a c i l i t a t i n g t h e d i f f u s i o n o f t h e m o n o m e r ( o r o x y g e n ) i n i t , r a t h e rt h a n a c c e l e r a t i n g t h e p r o c e s s e s o f f r e e -r a d i c a l d e g r a d a t i o n o f P S. I n t h eY. Thermal Anal. 33, 1988


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DAUENGAUER ET AL.: THERMAL DEGRADATION 1217c as e o f t h e o t h e r t w o f l a m e r e ta r d a n t s , a c e r t a in r e t a r d a t i o n o f t h e t h e r m a ld e g r a d a t i o n o c c u r s , a s i n d i c a t e d b y a n i n c r e a se i n Ea a n d c h a n g e s i n t h em e c h a n i s m o f t h e l i m i t i n g s ta g e. O n l y i n t h e c as e o f t h e s y s t e m c o n t a i n i n gH B D P i s a f i rs t o r d e r o b s e r v e d f o r t h e t h e r m a l d e g r a d a t i o n o f P S i n ai r.

T h e v a lu e s o f E a f o r t h e t h e r m a l d e g r a d a t i o n o f P S i n h e l i u m in th ea b s e n c e a n d p r e s e n c e o f f l a m e r e t a r d a n t s f o r m t h e f o l l o w i n g se rie s: P S < P S ++ D B D P O < P S + H B C D < P S + H B D P . I n a ll th e s e c as es i t is p o s s ib l e t o as s u m et h e s a m e m e c h a n i s m o f t h e l im i t i n g s ta g e. F l a m e r e t a r d a n t s h a v e a c e r ta i ni n f l u e n c e o n t h e s u r f a c e e f f e c t s f o r t h e P S m e l t , a n d i n t h i s c a se t h e r e is n or e a s o n t o a s s o c i a te t h e i r a c t i o n w i t h p a r t i c i p a t i o n i n t h e d e g r a d a t i o n p r o c e s s.

~" 70

~. s 8"~ 54-o 50

423~34

3 9

4

6~ 7~ 8~ 9~~mperature,~

Fig. 2 Format ion of styrene upon heating polystyrene pure or containing 15 m a s s % flame retardant(based on bromine) to various pyrolysis t e m p e r a t u r e sI) PS, 2) PS + HBDP, 3) PS + DBDPO, 4) PS + HBCD.

C o m p a r i so n o f t h e c u rv e s o f t h e t e m p e r a t u r e - d e p e n d e n c e o f t h e s t y re n ey i e l d i n p y r o l y s i s ( F ig . 2 ) w i t h t h o s e o f th e i s o l a ti o n o f h y d r o g e n b r o m i d ef r o m t h e c o m p o s i t i o n o f P S w i th b r o m i n e - c o n t a in i n g f la m e r e t ar d a n t s( F ig . 3 ) r e v ea ls a m a r k e d c o r r e l a t i o n i n t h e f o l l o w i n g se r ie s : f o r s t y r e n e y i e l dP S > P S + H B D P > PS + D B D P O > P S + H B C D , a n d f o r h y d r o g e n b r o m i d e e v o l-u t i o n P S + H B C D > P S + D B D P O > P S + H B D P . T h e se d a ta s ug ge st t h a t t h es t ab i li z in g e f f e c t i s in a ll c a se s r e l a t e d t o t h e i so l a t i o n o f h y d r o g e n b r o m i d e ,a n d a ll t h e f l a m e r e t a r d a n t s c o n s i d e r e d h e r e a r e s ta b il iz e rs o f t h et h e r m a ! d e g r a d a t i o n o f P S .

,I . Thermal Ana l . 33 , 1 988


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1 2 18 D A U E N G A U E R E T A L .: T H E R M A L D E G R A D A T I O N

9(3--r 80,..* 70

r

:z: 60'5_ 5O~- 40

302 010

,,, L ~ I _ p4 0 0 6OO 8OO IOO0T e m p e r a t u r e ,~

F i g. 3 F o r m a t i o n o f h y d r o g e n b r o m i d e u p o n h e a t i n g p o l y s t y r e n e c o n t a in i n g 1 5 m a s s % f la m e r e ta r d a n t s(ba s e d on b r om i ne ) t o va r i ous py r o l y s i s t e m pe r a t u r e s1 ) PS + HB CD , 2) PS + DBDPO, 3) PS + HBDP.

H o w e v e r , t h e s e s er ie s d o n o t q u i t e c o i n c i d e w i t h t h o s e o b t a i n e d f r o mt h e r m a l a n a l y s is . T h e o v e r a ll p r o c e s s o f t h e r m a l d e g r a d a t i o n o f P S b o t h i na ir a n d i n h e l i u m i n t h e p r e s e n c e o f f l a m e re t a r d a n t s is p r e s u m a b l y a f f e c t e db o t h b y t h e c h e m i c a l f a c to r s , w h i c h a re p r o b a b l y r e l a te d t o t h e d i r e ctp a r t i c i p a t i o n o f t h e h y d r o g e n b r o m i d e e v o l v e d i n t h e f r ee - ra d ic a l d eg r ad -a t i o n p r o c e s s , a n d b y t h e p h y s i c a l f a c t o r s c h a n g i n g s o m e c h a r a c t e r is t ic s o ft h e p o l y m e r m e l t.

C o n c l u s i o n s1. T h e t h e r m a l d e g r a d a t i o n o f P S in a ir a n d i n a n i n e r t a t m o s p h e r e is l i m i t e d

b y d i f f u s i o n p r o c e s s es o c c u r r i n g a t t h e i n t e r f a c e , re s p e c t iv e l y .2 . T h e i n t r o d u c t i o n o f b r o m i n e - c o n t a i n i n g fl a m e r et a r d a n t s i n t o PS a ff e c ts

t h e k i n e ti c s o f i ts t h e r m a l d e g r a d a t i o n .3 . T h e i n f l u e n c e o f a f la m e r e t a r d a n t o n t h e t h e r m a l d e g r a d a t i o n o f P S i s a

c o m p l e x p r o c e s s , t h e c h e m i c a l a s p e c t s o f w h i c h a re r e l a t e d t o i n h i b i t i o no f t h e c h a i n r e a c t i o n w i t h t h e p a r t i c i p a t i o n o f f r e e r a d i c a l s b y h y d r o g e nb r o m i d e , w h i l e t h e p h y s i c a l a s p e c ts a re r e l a t e d t o t h e c h a n g e s in s o m ec h a r ac t e ri s ti c s o f t h e p o l y m e r m e l t .

J . T h e r m a l A n a l . 3 3 , 1 9 8 8


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DAUENGAUER ET AL.: THERMAL DEGRADATION 1219R e f e r e n c e sl N. Grassie, Chemistry of high polymerdegradation processes, Butterworth, L.,1956, p. 335.2 S. Madorsky, Thermal decomposition oforganic polymers (in Russian), Mir, Moscow,1967. p. 293,3 L. A~ Wall, S. Straus, R F. Florin and F. J.Fetters, J. Res. Nath, Bur, Stand., 77A,(1975) 175.4 R. H. Still, Brit, Polym. J,, 11 (1979) 101.5 H. Nishizaki, J. Yoshida and J. H, Wang, J.

Appl. Plym. Sci., 25 (1980) 2867.6 J. Masarik, J. Svet~ikand Z. Horak, Fire andMatet,ats. 6 (1982) 59.

7 R. V. Petrella, Factors affect ing the com-bustion of polystyrene and styrene. In:Fl~me Retardant Polymeric Materials, ed. byM. Lewin, S. M. Atlas and E. Pearee, N. J.-L., 1978. V. 2, p. 159.8 V. M Gorbachr162 n co/L: Transactions of8th USSR conference on thermal analysis,Kuibyshev, the Kuibyshev PolytechnicalInstitute, 1893, p. 23.9 V. M. Alekseev, Quantitative analysis (inRussian), Nauka, Moscow, 1972, p. 504.10 S.A. Dauengauer, 13. G. Utkina, G. $, Popova

a~d Yu. N. Sazanov, 2. Thermal Anal., 321987) 311.

Zusammenfassung - Die Kinetik des thermischen und thermo-oxidativen Abbaus von Polystyren inGegenwart bromhaltiger Flammschutzmittel wurde untersuch t. Es wird gezeigt, dass die Reaktion dutchdie Diffusion in Luft bzw. dutch die Grenzfl~ichenvorg~inge in Helium begrenzt wird.Die Flammsci:u~zmit~el beeinf/ussen den Abbau yon Polystyren sowoht chemiseh als auch physikalisehund ver~ndern im gewissen Masse auch den Mechanismus des geschwindigkeit sbest immendenSchritts.

PE3IOME ~ H3yqe~a ~m eT~< a TepM~qecKoro ~ TepMooKHcxtltTeJI~ItOrO pacnajxa noJmcTnpona B npH-CyTCTBH~ 6poMcoa;epxcatL~x ~II~H6HTopoB lI/IaMeHtl. YCr~OBJXeHO, trro ~r raxax rrpo~eccoBv aTMocq~epe so3~;yxa ortpe~eylaeTe~l ~jl~y:~rle/~, a s OTMOc~epe r ~ ~ npolleceaM/~ lpoTelc~lOllIl~-Mt~ ~a rpar~t~ue pa~e ~a , I,Lra-a6vrropb~ rtnaMertr~ saTpar~tBato'r d~t3~ec~ea~ ~ xnMt~eer~,i pacrta~ non~-ca ~o .r la H ~to HeKoTopOffl eTeneKlt H3Mee~lOr Mexam ~M onpe / l~ tne ~ r

J. ThermalAnal. 33, 1988

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Thermal and Thermoxidative Degradation of PS in the Presence of Br Containing FRs