Odor removal from polyphenylene ether resins by steam distillation

Low odor polyphenylene ether resin is produced by mixing a polyphenylene ether resin having an odoriferous content in water and bringing the mixture to a boil to distill a portion or all of the water.

The present invention relates to a method for preparing a low odor 
polyphenylene ether resin comprising distilling the resin with steam to 
substantially remove impurities. 
BACKGROUND OF THE INVENTION 
Polyphenylene ethers, also known as polyphenylene oxides, are a class of 
polymers widely used in industry, especially as engineering plastics in 
applications requiring toughness and heat resistance. In recent years, 
there has developed an increasing interest in employing polyphenylene 
ethers in food packaging applications. 
In many of these food packaging applications, it is essential that the 
polyphenylene ether be substantially free from materials which are 
volatile, have undesirable odors, or would otherwise harm the food. 
Various materials of this kind may be present in polyphenylene ether 
resins. They include dialkylamines, such as di-n-butylamine, which are 
components of the catalyst used in the preparation of polyphenylene ethers 
as described hereinafter. Also present may be by-products formed in the 
synthesis of the substituted phenols from which polyphenylene ethers are 
prepared. In the case of poly(2,6-dimethyl-1,4-phenylene ether) these 
frequently include 2,4,6-trimethylanisole (2,4,6-TMA), 
7-methyldihydrobenzofuran (7-MDBF), 2,3-dihydrobenzofuran and 
2,6-dimethylcyclohexanone. Conventionally, polyphenylene ether resins are 
manufactured by polymerizing the monomer in solution with a liquid 
aromatic hydrocarbon solvent. The resin may then be purified by a 
semicontinuous precipitation from the solvent with methanol. 
However, the solvents used in the preparation of PPE and to precipitate it 
are ordinarily recycled, which results in a build up of odor components to 
a steady state level. Also, the methanol used to precipitate the resin 
from the solution is a relatively poor solvent for removing some of the 
odoriferous components. 
Thus, the issue of unpleasant odors associated with polyphenylene ether 
resins has been a long standing problem with many plastics processors and 
has resulted in many attempts to reduce the odoriferous content in the 
resin. 
Banevicius, in commonly assigned U.S. Pat. No. 4,906,700 reduces the 
content of phenolic odoriferous components during the initial production 
stage by distilling the liquid aromatic hydrocarbon reaction solvent prior 
to recycling to the polymerization zone or using fresh solvent. This has 
the effect of reducing the steady state buildup of impurities in the 
solvent and therefore also the polymer resin. 
Other disclosures attempt to reduce the residual amine content by 
devolatilization during extrusion. Kasahara et al., U.S. Pat. No. 
4,369,278; Newmark, U.S. Pat. No. 3,633,880; Banevicius et al., commonly 
assigned U.S. Pat. application, Ser. No. 07/291,534, filed herewith, now 
U.S. Pat. No. 4,992,222 and Bopp, commonly assigned U.S. Pat. application, 
Ser. No. 206,174, filed 6/13/88, now U.S. Pat. No. 5,017,656, all disclose 
various forms of vacuum vented extrusion as a devolatilization technique 
for removing volatile components from polymer resins. In Kasahara et al., 
the patentee teaches the optional use of water injection into the polymer 
melt to aid in devolatilization. Banevicius et al., describes an extrusion 
devolatilization process comprising at least two stages of water or steam 
injection into the polymer melt to effect a more complete removal of 
odoriferous components. However, the above processes require the addition 
of water into the polymer in melt form in a vented extruder. The present 
invention does not involve adding water to the polymer in melt form or an 
extrusion process, but rather adding water to the resin in particulate 
form and then boiling the water to distill a portion of the water and 
substantially all of the odoriferous components. 
Also to be mentioned is Bunting et al. commonly assigned U.S. Pat. 
application, Ser. No. 07/291,563, filed herewith, now U.S. Pat. No. 
4,994,217, which discloses a sequence of devolatilizing apparati, such as 
heat exchanger devolatilizers, to effect a reduction in odoriferous 
content. The patentees teach the injection of high pressure water or steam 
in a stripping zone but do not teach mixing of water and the resin and 
then distillation of the water. 
Surprisingly, it has now been found that where water is admixed with a 
polyphenylene ether resin and a portion of the water is distilled, a low 
odor polyphenylene ether is produced. Distillation of the water from an 
aqueous resin slurry unexpectedly results in the production of 
polyphenylene ether resins exhibiting very low odor in human organoleptic 
tests. 
SUMMARY OF THE INVENTION 
According to the present invention there are provided methods for preparing 
low odor polyphenylene ether resins comprising 
(a) mixing 
(i) a polyphenylene ether resin having a content of odoriferous compounds, 
and 
(ii) water; 
(b) heating the mixture obtained in (a) to distill a portion of said water 
and substantially all of said odoriferous compounds; and 
(c) recovering said polyphenylene ether resin substantially free of said 
odoriferous compounds, from the residue of step (b). 
Preferably, the portion of water distilled is from about 1 to about 99 
percent based on the weight of the water. Especially preferred are 
processes wherein from about 25 to about 75 weight percent of the water is 
distilled. Distillation is preferred to be carried out at temperatures 
ranging from about 50.degree. to about 210.degree. C. at atmospheric, 
super-atmospheric and supra-atmospheric pressures. 
The preferred form of the mixture is a slurry and the preferred methods of 
resin recovery comprise filtering or vacuum filtering, optionally followed 
by a drying process. 
DETAILED DESCRIPTION OF THE INVENTION 
The polyphenylene ethers to which the present invention is applicable are 
known in the art and are described in numerous publications, including 
Hay, U.S. Pat. No. 3,306,874 and 3,306,875, and generally comprise a 
plurality of structural units having the formula 
##STR1## 
In each said units independently, each Q.sub.1, is independently halogen, 
primary or secondary lower alkyl (i.e., alkyl containing up to 7 carbon 
atoms), phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy or 
halohydrocarbonoxy wherein at least two carbon atoms separate the halogen 
and oxygen atoms; and each Q.sub.2 is independently hydrogen, halogen, 
primary or secondary lower alkyl, phenyl, haloalkyl, hydrocarbonoxy or 
halohydrocarbonoxy as defined in Q.sub.1. Examples of suitable primary 
lower alkyl groups are methyl, ethyl, n-propyl, n-butyl, isobutyl, n-amyl, 
isoamyl, 2-methylbutyl, n-hexyl, 2,3-dimethylbutyl, 2-, 3- or 
4-methylpentyl and the corresponding heptyl groups. Examples of suitable 
secondary lower alkyl groups are isopropyl, sec-butyl, and 3-pentyl. 
Preferably, any alkyl radicals are straight chain rather than branched. 
Most often each Q.sub.1 is alkyl or phenyl, especially C.sub.1-4 alkyl, 
and each Q.sub.2 is hydrogen. Suitable polyphenylene ethers are disclosed 
in a large number of patents. The integer n is at least about 50. 
Both homopolymer and copolymer polyphenylene ethers are incuded. Suitable 
homopolymers are those containing, for example, 2,6-dimethyl-1,4-phenylene 
ether units. Suitable copolymers include random copolymers containing such 
units in combination with (for example) 2,3,6-trimethyl-1,4-phenylene 
ether units. Many suitable random copolymers, as well as homopolymers, are 
disclosed in the patent literature. 
Also included are the coupled polyphenylene ethers in which the coupling 
agent is reacted in known manner with the hydroxy groups of two 
polyphenylene ether chains to produce a higher molecular weight polymer 
containing the reaction product of the hydroxy groups and the coupling 
agent. Illustrative coupling agents are low molecular weight 
polycarbonates, quinones, heterocycles and formals. 
The polyphenylene ethers generally possess a number average molecular 
weights within the range of about 3,000 to about 40,000 and a weight 
average molecular weight of about 6,000 to about 80,000, as determined by 
gel permeation chromatography. Its instrinsic viscosity is most often in 
the range of about 0.3-0.6 dl/g as measured in chloroform at 25.degree. C. 
The polyphenylene ethers are typically prepared by the oxidative coupling 
of at least one corresponding, monohydroxyaromatic compound. Particularly 
useful and readily available monohydroxyaromatic compounds are 2,6-xylenol 
(wherein each Q.sub.1 is methyl and each Q.sub.2 is hydrogen), whereupon 
the polymer may be characterized as a poly(2,6-dimethyl-1,4-phenylene 
ether); and 2,3,6-trimethylphenol (wherein each Q.sub.1 and one Q.sub.2 is 
methyl and the other Q.sub.2 is hydrogen). 
A variety of catalyst systems are known for the preparation of 
polyphenylene ethers by oxidative coupling. There is no particular 
limitation as to catalyst choice and any of the known catalysts can be 
used. For the most part, they contain at least one heavy metal compound 
such as a copper, manganese or cobalt compound, usually in combination 
with various other materials. 
A first class of preferred catalyst systems consists of those containing a 
copper compound. Such catalysts are disclosed, for example, in U.S. Pat. 
Nos. 3,306,874; 3,306,875; and 4,028,341. They are generally combinations 
of cuprous or cupric ions, halide ions (i.e., chloride, bromide or iodide) 
and at least one amine. 
Catalyst systems containing manganese compounds constitute a second 
preferred class. They are generally alkaline systems in which divalent 
manganese is combined with such anions as halide, alkoxide or phenoxide. 
Most often, the manganese is present as a complex with one or more 
complexing and/or chelating agents such as dialkylamines, alkanolamines, 
alkylenediamines, omega-hydroxyaromatic aldehydes, o-hydroxyazo compounds, 
beta-hydroxyoximes (monomeric and polymeric), o-hydroxyaryl oximes and 
beta-diketones. Also useful are known cobalt-containing catalyst systems. 
Suitable manganese and cobalt-containing catalyst systems for 
polyphenylene ether preparation are known in the art by reason of 
disclosure in numerous patents and publications. 
The odoriferous impurities, by-products of the monomer and polymer 
synthesis such as aromatic hydrocarbons and oxygen containing compounds 
such as butanone, 2-ethylhex-2-enal and 2,3-dihydrobenzofuran; and amine 
components of the catalyst, such as nitrogen containing compounds such as 
di-n-butylamine, are removed from the polyphenylene ether resin by 
admixing the resin with water and heating to distill a portion of the 
water and essentially all of the odoriferous impurities to produce a 
polyphenylene ether resin essentially free from odoriferous compounds. 
Essentially free from odoriferous compounds is defined to be that level of 
odoriferous compounds which is difficult to detect in human organoleptic 
tests. 
In general, the polyphenylene ether resin, preferably in the form of a 
powder, is suspended in water, preferably to form a slurry-like mixture, 
in any suitable apparatus. The mixture is then heated to boiling, the 
distillation temperature being dependent on the pressure employed. 
Different distillation pressures are contemplated, ranging from below 
atmospheric to above atmospheric, and may be adjusted as desired. 
Distillation is continued until all of the water is distilled or some 
fraction thereof as desired. The polyphenylene ether may then be recovered 
from the remaining mixture by a filtration or vacuum filtration process in 
any conventional apparatus. It is also contemplated that filtration may be 
supplemented by a drying process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following examples illustrate the present invention. They are not to be 
construed to limit the claims in any manner whatsoever. 
EXAMPLE 1 
Polyphenylene ether resin (150 g) was suspended in 1500 ml of deionized 
water. The mixture was heated to reflux and approximately 500 ml of the 
water was distilled. The distillate exhibited a strong odor, while the 
remaining slurry had only a slight odor. The slurry was filtered and the 
filtrate was found to have very little odor. Samples of the distillate and 
filtrate were analyzed using gas chromatography and mass spectometry to 
determine compositions. The distillate showed the presence of butanal, 
toluene and 2,3-dihydrobenzofuran. The filtrate did not contain any major 
amounts of impurities. The polyphenylene ether resin filtered from the 
mixture was air-dried overnight at room temperature and then further dried 
in a vacuum oven at 75.degree. C. for about 16 hours. The melt behavior of 
the isolated powder was compared to the initial polyphenylene ether in a 
Tinius Olsen Plastimeter. Results are shown in Table 1. 
TABLE 1 
______________________________________ 
I.V., dl/g 
Sample Powder Extrudate* 
______________________________________ 
Initial polyphenylene 
0.473 0.595 
ether resin 
Purified powder after air 
0.473 0.587 
drying at room temperature 
for 16 hours 
Purified powder after drying 
0.477 0.614 
in vacuum oven at 75.degree. C. for 
16 hours 
______________________________________ 
*Heated for 2 minutes at 300.degree. C. in a Tinius Olsen Plastimeter 
I.V. = Intrinsic Viscosity 
EXAMPLE 2 
Polyphenylene ether resin (750 g) was suspended in 2250 ml of water and 
heated to reflux until 750 ml of the water was distilled. Samples of the 
distillate were removed at the beginning, middle and end of the 
distillation. The distillate was found to have a strong odor while the 
residual slurry exhibited only a faint smell. The residual slurry was then 
filtered. The filtrate and distillate were then analyzed for odoriferous 
components by gas chromatography/mass spectometry. 
The distillate was found to contain butanal, 2-butanone, toluene, 
2-ethylhex-2-enal, and 2,3-dihydrobenzofuran. At the beginning of 
distillation, the distillate contained all of the odoriferous 
contaminants. In the middle of distillation, butanal, 2-butanone and 
toluene, were observed in the distillate and at the end of distillation 
there was only trace amounts of butanal, 2-butanone and toluene. The 
filtrate was found to comprise trace amounts of toluene only. Analysis of 
the PPO powder showed no apparent decrease in the concentration of 
2,4,6-trimethylanisole. Initial PPO powder was analyzed to comprise 112 
ppm of 7-methyldihydrobenzofuran and 115 ppm in the purified powder. It 
appears that higher temperatures and pressures are required to remove the 
odoriferous 7-methyldihydrobenzofuran and 2,4,6-trimethylanisole. The melt 
behavior of the isolated powder and initial PPO resin is shown in Table 2. 
TABLE 2 
______________________________________ 
Material Time at 300.degree. C.* 
I.V., dl/g 
______________________________________ 
Initial PPO powder 
0 0.471 
Initial PPO powder 
2 0.559 
Isolated Purified PPO 
0 0.483 
Isolated Purified PPO 
2 0.555 
______________________________________ 
*In a Tinius Olsen Plastimeter 
I.V. = Intrinsic Viscosity 
EXAMPLES 3-5 
Example 2 was repeated several times and the results were duplicated. 
Polyphenylene ether resin (750 g) was suspended in water (2250 g) and 
heated to reflux. After distilling 750 g of the water, the mixture was 
cooled and vacuum filtered. The product was air dried for 24 hours. A low 
odor powder was produced. 
EXAMPLE 6 
Example 2 was repeated on a larger scale and the results were duplicated. 
Polyphenylene ether resin (2250 g) was suspended in water (6750 g) and 
heated to reflux. After distilling 2250 g of water, the mixture was cooled 
and vacuum filtered. The filtrate was air dried for 72 hours. A low odor 
powder was produced. 
EXAMPLE 7 
Purified polyphenylene ether resin from Example, 6 was blended with other 
resins and tested for physical properties. A commercial resin composition 
was also tested. The results along with compositional data are set forth 
in Table 3. 
TABLE 3 
______________________________________ 
Example 
7 7** 
______________________________________ 
Composition 
PPO, g (purified*) -- 490 
PPO, g (commercial grade) 
490 -- 
Zytel 101, g 410 410 
Kraton G 1651, g 100 100 
MA, g 3.5 3.5 
Properties 
Tensile Strength, psi 
Yield 8200 8600 
Break 7700 7700 
Elongation, % 
Yield 6.0 6.0 
Break 36.5 36.4 
Notched Izod, ft-lbs/in 
3.72 3.91 
______________________________________ 
* = Example 6 
MA = Maleic Anhydride 
Zytel 101 = A Nylon6,6 (E. I. Dupont) 
PPO = Polyphenylene Ether (General Electric) 
** = Comparative Example 
EXAMPLE 8 
Purified polyphenylene ether resin from Example 6 was blended with a 
high-impact polystyrene and tested for physical properties. A commercial 
comparison resin was also tested. The results along with compositional 
data are set forth below in Table 4. 
TABLE 4 
______________________________________ 
Example 
8 8** 
______________________________________ 
Composition 
PPO, g (purified*) 600 -- 
PPO, g (commercial grade) 
-- 600 
HIPS 400 400 
Properties 
Tensile Strength, psi 
Yield 8900 9200 
Break 7500 7600 
Elongation, % 
Yield 7.4 6.7 
Break 14.9 13.4 
Notched Izod, ft-lbs/in 
2.89 2.84 
______________________________________ 
* = Example 6 
HIPS = High Impact Polystyrene (Huntsman Chemical) 
PPO = Polyphenylene Ether Resin (General Electric) 
** = Comparative Example 
EXAMPLE 9 
1500 g of purified polyphenylene ether resin from Example 6 was extruded at 
300.degree. C. in an extruder equipped with vacuum venting and the 
extrudate tested for physical properties. A commercial comparison was also 
tested. The results are set forth in Table 5 below. 
TABLE 5 
______________________________________ 
Example 
9* 9** 
______________________________________ 
Composition 
I.V. (powder), dl/g 0.46 0.46 
I.V. (extrudate), dlg 
0.60 0.57 
Tensile Strength, psi 
Yield 11,200 11,000 
Break 8500 8300 
Elongation, % 
Yield 6.0 6.0 
Break 14.2 20.4 
Notched Izod, ft-lbs/in 
0.88 0.85 
______________________________________ 
I.V. = Intrinsic Viscosity 
* = Purified PPO Resin 
** = Comparative Example With Unpurified PPO Resin 
The above mentioned patents, patent applications and publications are 
incorporated herein by reference. 
Many variations of the present invention will suggest themselves to those 
skilled in this art in light of the above detailed description. For 
example, instead of poly(2,6-dimethyl-1,4-phenylene ether), 
poly(2,3,6-trimethyl-co-2,6-dimethyl-1,4-phenylene ether) resin can be 
used. Instead of distilling only a portion of the water, almost all or all 
of the water can be distilled. The pressure of distillation may be varied 
to lower or raise the distillation temperature as desired. 
All such obvious modifications are within the full intended scope of the 
appended claims.