Acetal copolymers with backbone bromo functional groups

The invention concerns a method for producing an acetal copolymer containing backbone bromo-functional groups comprising copolymerizing trioxane with 5,6,-dibromo-1,3-dioxepene. The invention also concerns methods of modifying acetal copolymers containing bromo-functional groups and the copolymers produced by the methods of the invention.

BACKGROUND OF THE INVENTION 
Polyacetal copolymers are technically important macromolecules competitive 
with metals, ceramics and nylons in many applications. In the current 
technical processes, they are prepared by copolymerization of trioxane 
with a comonomer such as ethylene oxide, dioxolane or butanediol formal. 
Each such copolymer molecule carries a maximum of two functional groups, 
e.g. hydroxyl end groups. For purposes such as the preparation of graft 
copolymers and polymers with chemically bound stabilizers, it is desirable 
to synthesize polyacetals with higher levels of functional groups. It is 
an object of this invention to prepare polyacetal copolymers of trioxane 
that have stability equivalent to or greater than that of conventional 
resins while at the same time having functional groups which may be useful 
for further modifications or the attachment of additives. 
In conventional acetal resin products, additives such as amidine thermal 
stabilizers and the like tend to reside in the amorphous regions of the 
polymer. Since the distribution of such non-crystalline areas is spatially 
random, the distribution of additives is often not optimal in terms of 
macroscopic properties. If functional sites can be provided at regular or 
semi-regular intervals (e.g. random copolymer) such that stabilizers or 
impact modifiers could be attached at a predetermined locus of points 
within the resin, then superior and more uniform properties could be 
achieved. This approach is particularly advantageous since the crystal 
structure of polyacetal is such that additives may be sterically 
obstructed from the crystalline areas. It therefore may be desirable to 
provide polymer backbone moieties that may disrupt the polymer's crystal 
structure in a controlled manner and provide a locus for attachment of 
additives. 
Polyacetal copolymers with such backbone functional groups would be useful 
in many important applications such as: (a) preparing trioxane copolymers 
with chemically bonded stabilizers; (b) preparing trioxane copolymers with 
chemically attached impact modifiers; (c) preparing grafted copolymers of 
trioxane as compatibilizers with existing commercial acetal copolymer 
blends or with other polymer materials such as glass or minerals; (d) 
preparing copolymers amenable to surface modifications; and (e) preparing 
crosslinked copolymers. 
SUMMARY OF THE INVENTION 
The present invention concerns a method for producing an acetal copolymer 
container backbone halogen functional groups. A preferred embodiment 
concerns a method for producing a copolymer containing bromo-functional 
groups comprising copolymerizing trioxane with 5,6,-dibromo-1,3-dioxepene. 
The invention also concerns the acetal copolymers produced by this novel 
method and the further modifications of these copolymers.

DETAILED DESCRIPTION OF THE INVENTION 
EXAMPLE 1 
(a) Synthesis of monomers 
##STR1## 
1,3-dioxep-5-ene, DXPE 
A mixture of 176 g. (2 moles) of cis-2-butene-1,4-diol, 60 g (2 moles) of 
paraformaldehyde, 25 ml. of benzene and 0.25 g. of p-toluenesulfonic acid 
was refluxed under a Dean-Stark trap until the removal of water was 
completed. Distillation of the reaction mixture after the removal of 
benzene yielded 172 g. of crude 1,3-dioxep-5-ene (b.p. 
120.degree.-126.degree. C.). The crude product containing small amounts of 
water and formaldehyde was purified by redistillation from solid potassium 
hydroxide. Pure 1,3-dioxep-5-ene (b.p.=130.degree. C.) was obtained in the 
amount of 160 g. 
EXAMPLE 2 
5,6-dibromo-1,3-dioxepane 
##STR2## 
A solution of 15.2 g. (0.15 mole) of 1,3-dioxep-5-ene in 20 ml of carbon 
tetrachloride was cooled in an ice bath. A solution of 24 g. (0.15 mole) 
of bromine in 20 ml. of CCl.sub.4 was then added dropwise with stirring. 
The solvent then was removed by distillation and the residue was 
recrystallized from ethanol to give 8.1 g. of 5,6-dibromo-1,3-dioxepane, 
m.p. 37.degree. C. 
EXAMPLE 3 
(b) Copolymerization of Trioxane with 5,6-Dibromo-1,3-dioxepane 
In a dry flask (Kjeldahl, 100 ml.) were placed 10 g. of trioxane and 2.5 g. 
of 5,6-dibromo-1,3-dioxepane. The flask was capped with a serum stopper. 
After removing the air and the dissolved gas under a vacuum from the 
reaction mixture, the flask was flushed with nitrogen. The contents were 
melted and mixed together with a magnetic stirrer in an oil bath 
(60.degree.-65.degree. C.). A volume of 0.2 ul. (microliters) of 
borontrifluoride etherate was then injected through serum stopper into the 
flask. The color of the solution changed from brown to white. Within about 
thirty minutes the solution became immobilized by the growth of the 
polymer throughout the flask. The reaction was allowed to proceed at 
60.degree. C. for 20 hours. At the conclusion of the polymerization, the 
polymer was removed and ground into small chunks. The crude polymer (9.5 
gm) was first washed with 10 ml of a solution of methanol and 2% 
triethanolamine and then with methanol three times. The copolymer was 
dried under vacuum at 40.degree. C. (9 gm). 
This copolymer generates free radical readily upon u.v. irradiation as 
indicated by electron spin resonance absorptions. This photosensitivity 
may be useful for photochemical modifications of the polymer, e.g. surface 
grafting. The invention also contemplates the production of comonomers 
modified with other halogens such as chlorine. Acetal copolymers of 
trioxane containing backbone halogen functions grops such as chlorine can 
also be produced according to the methods of the invention. The 
sensitivity of the bromine and chlorine atoms toward ultraviolent light 
and high energy irradiation combined with the unzipping nature of the 
acetal copolymer itself may make the halogen modified copolymers of this 
invention useful as photoresists for application in intergrated circuits.