New Developments of Crosslinkable Emulsion Polymers

21 N e w Developments of Crosslinkable Emulsion Polymers HENRY WARSON

Downloaded by PRINCETON UNIV on August 20, 2014 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0024.ch021

Solihull Chemical Services, 284 Warwick Rd., Solihull, England, B92 7AF

The application of emulsion thermoplastic polymers into many industries, especially those of coating, textile and paper, saw a major development from about 1958 with the introduction of polymers which could be crosslinked after application. This is achieved by the inclusion of monomers with at least one other reactive group, which is substantially unchanged in the addition polymerisation, but which may later react with itself or another included reactive group either inter- or more probably intra-molecularly. Alternatively the reaction may take place with an added crosslinking agent. Monomers of the first type include N-(methylol) acrylamide or its ethers. A typical added crosslinking agent is hexamethoxymethyl melamine. These processes are now well established, and the author's current volume (1) will be taken as a datum line for a survey of current improvements, this being based on the nature of the reactive groups. Derivatives of Acrylamide NMAM, CH: CHCONHCHOH, available as a 60% aqueous solution, is a highly reactive monomer in copolymerisation, although less so than acrylamide, and copolymerises with most standard monomers, although almost invariably at a high rate. (2) (2A). The ethers, e.g, CHJCHCONHCHÔC^H , formed readily in monomeric condition, or by a secondary reaction with units in a polymer, are equally reactive, as the ether group splits readily, and the longer chain ether groups may assist in improving compatibility with other monomers. In this connection N-(iso-butoxymethyl)acrylamide, CH^C . HCOMECH 0-isoC Η has been introduced recently. It is a colorj less to lighx yellow Clear oil, purity c · Qjfo, density Ο.98, and BP 99 - 100° at 0.03mm. It is water insoluble, but soluble in almost all organic solvents except for aliphatic hydrocarbons*(2B) Difficulties in obtaining even copolymerisation of MâM in emulsion are partly due to unbalanced reactivity ratios, and partly due to its high water solubility. These may result in the formation of *N- (methyloâcrylamide is abbreviated NMAM .| 2

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In Emulsion Polymerization; Piirma, I., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1976.


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i r r e g u l a r o r b r i t t l e copolymer f i l m s , due to i n c o m p a t i b i l i t i e s , w i t h accompanying " f i s h e y e s " and other d e f e c t s . Much current work has been devoted to lowering c u r i n g c y c l e s and temperatures. D i f f i c u l t i e s o f c o p o l y m e r i s a t i o n are most acute with v i n y l a c e t a t e . Whilst e a r l y recommendations i n c l u d e the a d d i t i o n o f methanol to improve c o m p a t i b i l i t i e s , c u r r e n t d i s c l o s u r e s i n c l u d e methods by which NMàM i s added to a p o l y m e r i s i n g emulsion o f v i n y l a c e t a t e . IJMaM, although g e n e r a l l y about 2 · 5 $ of t o t a l monomers, i s r a i s e d to 1 5 $ i n a process i n which the monomers, i n c l u d i n g 0 . 9 $ o f a c r y l i c a c i d , are added to a water phase c o n t a i n i n g t e r t b u t y l hydroperoxide and a b u f f e r e d b i s u l f i t e redox i n i t i a t o r with a f e r r o u s i o n a c t i v a t o r , the process t a k i n g 2 hours. The f i n a l l a t e x i s s u i t a b l e as a base f o r a plywood a d h e s i v e . ( 3 ) Terpolymers o f t h i s type may be mixed with t i n t e t r a c h l o r i d e hydrate o r o t h e r c a t a l y s t to produce an adhesive f o r wood b l o c k s much b e t t e r than p o l y v i n y l acetate a l o n e . ( 4 ) A l t e r n a t i v e processes i n c l u d e the v i n y l e s t e r s o f " V e r s a t i c acid' ( S h e l l Chemicals), with v i n y l a c e t a t e and acrylamide (49*49 . 2 ) , which are added g r a d u a l l y a f t e r conversion to a ρre-emulsion, to an a n i o n i c s u r f a c t a n t s o l u t i o n c o n t a i n i n g a p e r s u l f a t e . Transe parent waterproof f i l m s are formed. Copolymers o f MAM and v i n y l acetate are u s e f u l as s i z e s f o r f i b e r g l a s s i n c o n j u n c t i o n with a s i l a n e and me th ac r y l a to ch ro mi β chloride. Terpolymers o f ethylene, v i n y l acetate and NMA.M are prepared by adding the lafefcer two under constant ethylene p r e s s u r e i n t o an i n i t i a t e d e m u l s i f i e r s o l u t i o n c o n t a i n i n g p o l y v i n y l a l c o h o l , c o n t r o l l i n g the amount o f unpolymerised v i n y l acetate at any one time to be under 3 . 5 $ · T h i s method enables ethylene to be copolymv e r i s e d a t r e l a t i v e l y low p r e s s u r e s . The N1/&M content i s 0 . 5 - 2 $ o f the v i n y l a c e t a t e . The f i n a l l a t e x may be employed as an adhesZ i v e with e x c e l l e n t r e s i s t a n c e to c o l d flow, t h i s being probably imparted lay slow ambient c r o s s l i n k i n g . The l a t t e r i s a s s i s t e d by the i n c l u s i o n o f aluminium c h l o r i d e . ( 7 ) ( 7 A ) A c r y l i c a c i d , a c r y l o n i t r i l e and o p t i o n a l l y t r i a l l y l cyanuiate are a l s o i n c l u d e d i n a copolymer which imparts w r i n k l e r e s i s t a n c e to t e x t i l e s , and a l s o r e s i s t a n t to dry c l e a n i n g so1vents·(8) Vinyl acetate - ethylene - ΉΜΑΜ - d i a l l y l mal eat e copolymers, ' o p t i o n a l l y with i t a c o n i c a c i d , g i v e f i l m s which cure r a p i d l y at 1 3 2 . ( 9 ) · Other copolymers with t h i s a c i d are carpet b a c k s i z e s . 1

N-(isobutoxymethyl)acrylamide (NIBA) · NIBA can be copolymer*; i s e d r e a d i l y with many standard f o r m u l a t i o n s , s i n c e i t i s s o l u b l e i n most monomers. R e a c t i v i t y r a t i o s as determined i n a benzene s o l u t i o n copolymerisation are: methyl a c r y l a t e ( r , ) : NIBA ( r ) 1 . 1 1 : 1.27 e t h y l a c r y l a t e ( r M t NIBA ( r ^ ) 0 . 5 1 : 4 · 98 v i n y l acetate ( r ^ ) : NIBA ( r p 0.015 1 34.00 In comparison with NMA.M copolymers there i s l e s s l i k e l y t o be premature c r o s s l i n k i n g . C r o s s l i n k i n g o f NIBA copolymers may


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occur thermally, a t temperatures o f 150 - 170°, o r under a c i d conditions. Proposed mechanisms are as follows: (2B) CH

2

ÇH -

+

-CH -

CONHCH O R

ÇH

-

NHC«O

2-

X -

0

- BOH'

E

- CH - ÇH - Ν Λ Λ ^ Ν CH - CH COMCH - FCsO (Compound Q) CH OR Compound Q + H O = - ÇH - W A - CH - CH COMiCH 2

2

2

2

2


2

H

+ CH 0 2

+ ROH

In the above R = i s o b u t y l . Many workers i n t h i s f i e l d s t a t e , however, that they have no evidence o f the l i b e r a t i o n o f formaldehyde. A d i f f e r e n t mechanism i s p o s t u l a t e d f o r a c i d c r o s s l i n k i n g , i n v o l v i n g the l i b e r a t i o n o f both isobutanol and i t s formal, u l t i m a t e l y producing c r o s s l i n k e d u n i t s as: - ÇH - Çjtt - ν — ^ - CH - CH 0:C M CH — 0:0 —

—

2

I f a r e a c t i v e substrate i s present i t i s p o s s i b l e that r e a c t i v e groups, e.g, the hydroxyl i n c e l l u l o s e d e r i v a t i v e s , may take p a r t i n the condensation. l a t e x copolymers i n c l u d i n g NIBA have found a p p l i c a t i o n s i n p r o t e c t i v e coatings, binders f o r nonwoven f a b r i c s , water and o i l r e p e l l a n c y , crease r e s i s t a n c e , p r i n t p a s t e s , l e a t h e r f i n i s h i n g , adhesives, paper impregnation, curable t h i c k e n e r s and elastomers. ( 2 B ) . Comonomers i n c l u d e a c r y l i c and methacrylic e s t e r s , a c r y l o ζ n i t r i l e , styrene, and o c c a s i o n a l l y v i n y l acetate o r v i n y l chloride* A c r y l i c Copolymers. l % s t copolymers i n t h i s c l a s s are based on a c r y l i c ( i n c l u d i n g methacrylic; e s t e r s . These produce most o f the r e q u i r e d a p p l i c a t i o n p r o p e r t i e s , a l b e i t a t a premium c o s t . A s o f t , e a s i l y i n t e g r a t e d f i l m may be f i r s t formed, but i t i s r e a d i l y cured. Copolymers o f a c r y l i c esters with NMA.M o r methylene "bisacrylamide Η C(NHC00CH:CH ) improve laminates o f wool with nylon o r acetate f i b e r . (.10) A c r y l i c o r me th a c r y l i c a c i d , a t about 2 - 5$ o f monomers, i s o f t e n a component, h e l p i n g l a t e x s t a b i l i t y , curing and adhesive p r o p e r t i e s . The major monomers are o f t e n present i n q u i t e complex mixtures to s u i t s p e c i f i c a p p l i c a t i o n s . Thus a c r y l o n i t r i l e a s s i s t s solvent r e s i s t a n c e . ( l l ) Hfost o f the m o d i f i c a t i o n s are f o r various aspects o f t e x t i l e f i n i s h i n g . There i s an i n c r e a s i n g i n t e r e s t i n f l o c k i n g adhesives. (12 - 14) Other a c r y l i c l a t i c e s have a s p e c i f i c a p p l i c a t i o n i n the coatings i n d u s t r y . One product based on b u t y l a c r y l a t e and aery l o t n i t r i l e also contains 2.7$ o f i s o b o r n y l methacrylate with 2.84$ o f NM4M. S e l f - e m u l s i f i c a t i o n takes p l a c e with 2-sulfoethyl methac^, r y l a t e and s u r p r i s i n g l y , sodium v i n y l s u l f o n a t e . Coating to metals i s a p p l i e d from an a c i d bath containing f l u o r o b o r i c and hydrofluoric



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a c i d with chromic anhydride and potassium f e r r i c y a n i d e . ( I 5 ) An a l l i e d product i s based on e t h y l a c r y l a t e , NHAJff and a c r y l i c a c i d , e m u l s i f i c a t i o n being nonionic and p o l y m e r i s a t i o n by redàx. A p a i n t at 56^0 pigment - volume - c o n c e n t r a t i o n e x h i b i t e d high scrub resist tance (ASTM-D-2486-66T), and good low temperature c o a l e s c e n c e . ( l 6 j C o l l o i d a l s i l i c a i s i n c l u d e d i n a styrene - methyl methacrylate copolymer with 2.5/° each o f i t a c o n i c a c i d and NMAM. I t i s claimed that heating a t 180° f o r 1 minute g i v e s a water r e s i s t a n t c o a t i n g on aluminium, although some s u r p r i s e must be expressed at t h i s composition forming other than a powder on d r y i n g at ambient o r even elevated temperatures. (17) The ethers, e.g., N-(methoxymethyl)me thacrylami de , i n c o n j u n c t i o n with a c r y l i c o r m e t h a c r y l i c a c i d s are a l t e r n a t i v e s to MAM i n a c r y l i c polymers f o r nonwoven t e x t i l e s , g i v i n g good wet and dry t e n s i l e strength a f t e r c u r i n g , f o r which Î 5 O i s the optimum tempC e r a t u r e , but 110° i s e f f e c t i v e . (18). O f unusual i n t e r e s t i s the d i s c l o s u r e o f a conversion o f an acrylamide - styrene ( l i s 8 9 ) copolymer l a t e x into a Mannich base, i n c l u d i n g u n i t s such as: -(CH CH), thus a f f o r d i n g an ambient c r o s s l i n k . UONHCH N'(CH ) The l a t e x may be added to paper pulp, and a f t e r conversion, the r e s u l t a n t paper has improved b u r s t i n g strength and i n t e r n a l cohesion. ( 1 9 ) An unusual process f e a t u r e s a spun polythene band which has been impregnated with blended a c r y l i c l a t i c e s , e.g, c o n t a i n i n g 1,4-butanedio1 d i a c r y l a t e , e t h y l a c r y l a t e and a c r y l i c a c i d i n 1 component, and 1 , 4 - b u t a n e d i o l d i a c r y l a t e , b u t y l a c r y l a t e , a c r y l i c a c i d and NMA.M i n a second. 1 $ o f the p h o t o s e n s i t i s e r , benzoin i s o p r o p y l ether i s a l s o p r e s e n t . The impregnated band i s drawn across an i r r a d i a t i o n zone w h i l s t r e s t i n g on a t h i n l a y e r o f i c e , thence forming a continuous l e a t h e r - l i k e band. (2θ) N- fο rmyl- N -me t h a c r y l o ylme th y l enedi ami ne, HCX5NHCH NHCH NHOOC^ C(CH ):CH ( 3 . 5 $ ) , and NM&M ( 2 $ ) are copolymerised witE a c r f l o n i t Z rile"? and b u t y l a c r y l a t e (appro χ 1 : 3) to produce a l a t e x which forms tough c r o s s l i n k e d f i l m s when d r i e d a t 9 0 ° · The l a t e x i s u s e f u l f o r coatings, b i n d e r s , and i n t e x t i l e p r i n t i n g . ( 2 l ) F l u o r i n a t e d a c r y l i c monomers, with acrylamide o r NMÂ.M are i n ^ , eluded i n compositions intended f o r imparting o i l and water r e p e l ! l a n c y to t e x t i l e s . (22)(22A) 0

f

External A d d i t i v e s . A roethoxymelamine i s added to a r a t h e r complex a c r y l i c l a t e x i n c l u d i n g methacrylic a c i d , acrylamide, NMAM and d i a l l y l p h t h a l a t e , the product being s u i t a b l e as a f l o c k i n g adhesive. ( 2 3 ) · An a l l i e d product, based on b u t y l aeryIt. ate, a c r y l o n i t r i l e , acrylamide and NMAM i s mixed with a p o l y e s t e r r e s i n , and a p p l i e d to a rayon base, f o l l o w e d by nylon f l o c k . ( 2 4 ) An i n t e r e s t i n g v a r i a t i o n i s a f f o r d e d by the p r i o r r e a c t i o n o f a f u l l y methylolated urea with N- ( 2 , 3 - d i h ydro xyp rop y l ) me thacr y l ami de before copolymerisation takes p l a c e , the r e s u l t a n t l a t e x being a p p l i e d as an imprégnant to a nylon f l e e c e . ( 2 5 ) T h i s type o f condensate may be worthy o f f u r t h e r study. On the other hand, NMaM, with NH^Br c a t a l y s t , may i t s e l f be added t o a high ethylene


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copolymer i n c l u d i n g v i n y l acetate and methacrylic a c i d . The cured l a t e x f i l m enables polypropylene to be h e a t - s e a l e d to aluminium. (26). In a v a r i a t i o n a p o l y e t h y l e n e l a t e x i s used with monomeric MAM and a f i b e r r e a c t i v e agent such as dimethylgloxalmonoureine and a l a t e x c a t a l y s t , the process being o p t i o n a l l y 2-stage. The modified l a t e x features wrinkle and / \ 'wash and wear p r o p e r t i e s . There may be some HoH^CH NcôH d i r e c t g r a f t i n g on to the polythene. ( 2 j ) ( 2 8 ) . \T A r e a c t i v e a c r y l i c l a t e x , i n c l u d i n g e i t h e r acrylamide o r g l y c i d y l methacrylate, i s a p p l i e d as an imprégnant to nylon and p o l y e s t e r t e x t i l e s together with g l y c e r o l d i g l y c i d y l ether o r b i s p h e n o l A. 3 minutes h e a t i n g at 150° i s r e q u i r e d f o r c r o s s e linking. (29)


1

V i n y l Hal i d e s . In copolymerising v i n y l c h l o r i d e with NMAM, the same precautions to ensure even copolymerisation should be taken as with v i n y l a c e t a t e . An NMAM - v i n y l c h l o r i d e copolymer, with a n i t r i l e rubber l a t e x , o p t i o n a l l y carboxylated, and trimethylolmelamine, bonds rayon f l o c k to PVC sheet, and PVC to g a l v a n i s e d s t e e l . ( j l ) A paper c o a t i n g i s based on an ethylene - v i n y l c h l o r i d e NMAM copolymer, pigmented with TiO and c l a y . ( 3 2 ) S i m i l a r t e r C polymers, prepared w i t h delayed a d a i t i o n o f v i n y l c h l o r i d e and NMAM, are a p p l i e d to nonwoven f a b r i c s . Drying a t 1 1 9 ° produces a t e x t i l e o f good s t r e n g t h , handle and drape. ( 3 3 ) The u s e f u l p r o p e r t i e s o f v i n y l i d e n e copolymers i n paper c o a t i n g are f u r t h e r enhanced by i n c l u d i n g NMAM as a comonomer and subsequent c u r i n g . ( 3 4 ) · A l$fo l a t e x , i n c l u d i n g v i n y l i d e n e c h l o r i d e , a c r y l o n i t r i l e ~ a n a c r y l i c e s t e r , acrylamide and NMAM i s u s e f u l as a paper imprégnant, p r o v i d i n g good wet and dry strength a f t e r cure at I 3 5 · ( 3 5 ) L a t i c e s . L a t i c e s are sometimes d e f i n e d as emulsion polymers o r copolymers c o n t a i n i n g a diene. I f they also c o n t a i n a carboxC y l i c a c i d , e.g, i t a c o n i o and/or methacrylic a c i d s , they are u s u a l l y o f the ' s e l f cure type. The cure' o r c r o s s l i n k i n g i s c a t a l y s e d by t r a n s i t i o n metal s a l t s and even by pigments d e r i v e d therefrom. The a c t i o n i s enhanced by i n c l u d i n g NMAM as a monomer. ( 3 6 ) Heat curable foam - forming l a t i c e s are obtained from 1 , 3 butadiene, styrene and NMAM. ( 3 7 ) . L a t i c e s i n c l u d i n g NMAM may be mixed with p o l y i s o c y a n a t e s f o r the production o f foams and f i l m s . ( 3 8 ) . However, o v e r a l l , d i s c l o s u r e s i n c l u d i n g NMAM and a l l i e d r e a c t i v e monomers i n diene l a t i c e s seem to be r a t h e r s c a r c e . 1

1

D i ac e to neacrylami de. D i ac e to ne ac rylamide, Ν- ( 1,1- d i me th y l - 3 - 0 xobut y1)acrylami de has been the subject o f many i n v e s t i g a t i o n s as a comonomer. I t can be modified to a methylol form, but u n l i k e acrylamide, me th v i o l a t i o n takes p l a c e on the carbon atom adjacent to the


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k e t o n i c group and the monomer may he w r i t t e n CH : CEC(o)roc(CH ) ^ CRR C(o)CH where R and R« = H or CH OH. 3$ o f t h i s monomer proves optimum i n ^ f o r m u l a t i o n s , and a d d i t i o n o f HMMM i s advised, a pH o f 3 being optimum f o r a cure, which occurs at ambient temperature i n 4 - 16 hours. V i n y l acetate and a c r y l i c copolymers are quoted i n the l i t e r a t u r e , the l a t t e r even without an a u x i l i a r y c r o s s ^ l i n k i n g agent. The s p e c i a l i n t e r e s t i s i n thermosetting coatings, but formulations are suggested f o r i n t e r i o r g l o s s emulsion p a i n t s . (39)(40). f


The Aminimides. The aminimides(Ashland Chemical Co.), a s e r i e s o f monomers with both p o s i t i v e and negative n i t r o g e n atoms, and which may c o n t a i n unsaturated groups may be t y p i f i e d by the formulas CH sC(CH )C0N~ Ν (CH ) CH CHOHCH . For p r e p a r a t i o n see r e f e . (41 - 44 ) · A f e a t u r e o f these compounds i s that they are i s o Ζ cyanate p r e c u r s o r s , one molecule o f t r i e t h y l a m i n e being l o s t on h e a t i n g . They w i l l thus r e a c t with compounds c o n t a i n i n g a c t i v e hydrogen as an isocyanate, and i n the case o f a polymeric product w i l l g i v e r i s e to c r o s s l i n k i n g . (45) Polymerisation and copolymerisation o f these monomers i s p o s s i b l e i n emulsion with redox systems, although styrene w i l l only copolymerise with the h y d r o c h l o r i d e s o f the aminimides. (47) The major i n t e r e s t seems to be i n metal coatings? s e l f - r e a c t i n g polymers are produced by the copolymerisation o f a c r y l i c compouncfe with a c t i v e hydrogen, e.g, hydroxyethyl a c r y l a t e . At normal curing temperatures the rearrangement o f the aminimides i s v e r y rapids +

RC(0)lT N R"^

>

RNC

+

R'^N

The development o f polymer l a t i c e s and t h e i r pigmentation and a p p l i c a t i o n i s s t i l l at an e a r l y stage. However, an emulsion f o r m u l a t i o n s u i t a b l e as a base f o r p a i n t s has been given. (46) Here a d i f u n c t i o n a l aminimide(below) i s i n c l u d e d at 5$ i n the (CH ) N r 0 C ( C H ) C 0 r Ν ( C H ^ 3

3

2

8

monomers with 10$ o f 2-hydroxyethylacrylate, the balance being a c r y l i c e s t e r s . In some cases the simpler d i f u n c t i o n a l aminimides can be used to c r o s s l i n k other a c r y l i c copolymers which i n c l u d e a c t i v e hydrogen. The water s o l u b i l i t y o f the aminimides should be noted. The epoxide condensation with d i f u n c t i o n a l aminimides produces oxazolidone r i n g s which are u s e f u l i n promoting adhesion and have a suggested a p p l i c a t i o n i n t i r e cord adhesives. (45) Trimethylamine methacrylamide copolymerises w e l l with most standard monomers. The extensive t e c h n i c a l l i t e r a t u r e o f the Ashland Co., i n c l u d i n g patent s p e c i f i c a t i o n s , gives f u r t h e r d e t a i l s of a p p l i c a t i o n s o f these compounds, which should have an i n t e r e s t i n g f u t u r e . Unfortunately i t i s understood (1975) that there has been a setback i n commercialisation due to r e s t r i c t i o n s i n the supply o f unsymmetrical dimethylhydrazine, a key raw


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m a t e r i a l . Some recent developments have been p u b l i s h e d .

(47A)(47B)


Miscellaneous Nitrogen Compounds. The A z i r i d i n e Ring. The a z i r i d i n e r i n g .CH . CH i s analagous i n many ways to the epoxide r i n g and may be used f o r c r o s s l i n k i n g i n r a t h e r s i m i l a r circumstances. Care should be taken both with regard to p o t e n t i a l t o x i c i t y and h y d r o l y t i c s t a b i l i t y o f any expl. erimental compounds. 2 - ( l - a z i r i d i n y l ) e t h y l a c r y l a t e can be οοροζι ymerised d i r e c t l y with a c r y l i c a c i d using a nonionic s u r f a c t a n t , i f the pH o f the emulsion i s lowered w i t h a pKa below 3 · 7 * e.g., phosphoric a c i d o r an organic a c i d such as o x a l i c o r malonic a c i d . ( 4 8 ) The a z i r i d i n e r i n g can open q u i t e r e a d i l y a f f o r d i n g many o p p o r t u n i t i e s f o r c r o s s l i n k i n g with other r e a c t i v e groups. Ethylene - v i n y l acetate - a c r y l i c a c i d terpolymers have been c r o s s l i n k e d with 2 , 4 » 6 - t r i ( 2 - m e t h y l - l - a z i r i d i n y l ) s - t r i a z i n e o r t r i s ( 2 - m e t h y l - l - a z i r i d i n y l ) phosphite oxide. The improvement i n f i l m t e n s i l e strength and the reduced s o l u b i l i t y i n t r i c h l o r ^ ethylene are v e r y marked. (49) Compounds such as t r i s F - ( l - a z i r i d i n y l ) e t h y l \ t r i m e l l i t a t e r e a c t with carboxyl - ended Butadiene polymer, arm might w e l l be an a d d i t i v e to l a t i c e s c o n t a i n i n g carboxyl groups. The o r i g i n a l s p e c i f i c a t i o n quotes 24 hours s t o v i n g at 8 5 · (5£.)#See a l s o ( 5 4 ) Azide D e r i v a t i v e s . Azido format es are prepared from a hydroxy y l - c o n t a i n i n g monomer v i a the chloroformate and sodium a z i d e . G e n e r a l l y h y d r o l y t i c a l l y s t a b l e , they can be used e i t h e r i n direct copolymerisation o r as post - a d d i t i v e s , f u n c t i o n i n g by a secondC a r y r e a c t i o n . In the l a t t e r case the r e a c t i o n i s not r e s t r i c t e d to azoformates o f polymerisable a c i d s . The c r o s s l i n k at 70° p r o d l uces a urethance type l i n k a g e . (51) A number o f v a r i a t i o n s e x i s t i n which a z i d e s , e.g., epoxyaz~ ide compounds o f general formula R

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