Linear hydroquinone phenoxy polymers and process

This invention relates to a process for the preparation of thermoplastic polymers. Specifically it relates to a process for the preparation of a substantially linear, high molecular weight phenoxy resin from substituted hydroquinone, less than 80 mole percent of hydroquinone and optionally up to about 20 mole percent of a second aromatic diol, epichlorohydrin (or another epihalohydrin) and a base, such as sodium hydroxide. Hydroquinone phenoxy resins of this invention are characterized by low permeability to oxygen and carbon dioxide and are, therefore, useful as a gas-barrier layer in multilayer plastic film constructions used in food packaging and beverage bottle applications, for example. For use in such applications, the resin is generally in the form of a thin, uniform film prepared by extrusion, casting, or other such method. It is highly desirable that polymers used in this manner be as free as possible from chain branches or cross-links, as these lead to the formation of gel particles which cause imperfections in the polymer film. These imperfections, in turn, detract from the appearance of the film. Moreover, as is well known, increasing the amount of chain branching in a polymer results in an undesirable reduction of flexibility and toughness.

DESCRIPTION 
1. Technical Field 
This invention relates to new high molecular weight, essentially linear 
hydroquinone phenoxy polymers. It is particularly concerned with polymers 
made from substituted hydroquinone, which may be replaced with up to less 
than 80 mole percent of another aromatic diol such as hydroquinone and an 
epihalohydrin. The polymers are characterized by low permeability to 
oxygen and carbon dioxide and are particularly useful as a gas-barrier 
layer in multilayer plastic film and in beverage bottles. 
This invention also relates to a new process for producing the novel 
hydroquinone polymers, the process involving reacting substituted 
hydroquinone, which may be replaced with up to less than 80 mole percent 
of hydroquinone with about 0.95 to 1.05 equivalents of an epihalohydrin in 
the presence of about 1.0 to 1.1 equivalents of a base and about 1 to 7 
parts by weight of a solvent for the polymer per part polymer. It is 
preferred that water be present in the amount of from about 0.8 to 10 
parts by weight polymer and that a phase transfer catalyst be used. 
The new process results in polymer that is essentially free from chain 
branches or cross-links which lead to gel particles in the polymer. The 
polymer produced by our process is particularly useful for forming films 
which exhibit unusual gas barrier properties and thus are particularly 
suitable in food-package and beverage bottle applications. 
2. Background Art 
Two processes for the preparation of hydroquinone phenoxy resin have been 
disclosed by A. S. Carpenter, E. R. Wallsgrove and F. Reeder (British Pat. 
No. 652,024). In the first process, hydroquinone bis(glycidyl ether) is 
allowed to react with hydroquinone under the influence of a suitable 
catalyst. We have found that this process gives material which is highly 
branched, and in some cases a cross-linked, infusible resin is obtained. 
According to the second procedure of Carpenter et al., hydroquinone phenoxy 
resin is formed directly from hydroquinone, epichlorohydrin, and base 
(e.g., sodium hydroxide) in an ethanol-water reaction medium. Low 
molecular weight polymer precipitates early in the reaction, and its 
molecular weight increases slowly thereafter in a heterogeneous reaction. 
We have found that this reaction gives erratic results because of 
solvent-induced crystallization of the polymer phase. In some cases, 
gelled material is produced, while in other cases only low molecular 
weight polymer is obtained. 
On the other hand, an analogous phenoxy resin, prepared from bisphenol A 
(4,4'-isopropylidenediphenol), may be prepared by several methods similar 
to the above, but which fail when applied to hydroquinone phenoxy resin. 
These methods fail with hydroquinone phenoxy resin because, being 
heterogeneous reactions, they depend upon facile transfer of monomer 
molecules from the solution phase to the semi-solid polymer phase. 
Hydroquinone phenoxy resin, however, becomes crystalline under the 
influence of the water or water/alcohol reaction medium and is no longer 
penetrable by monomer molecules. This results in low average molecular 
weight, broad molecular weight distribution, and in irreproducible 
results. The reaction conditions are suitable for bisphenol A phenoxy 
resin, on the other hand, because this latter resin is not crystallizable 
under the reaction conditions and remains permeable to monomer molecules. 
Bisphenol A phenoxy resin may be prepared directly from bisphenol A, base, 
and epichlorohydrin in an alcohol-water reaction mixture (U.S. Pat. No. 
3,305,528) in a process very similar to the hydroquinone phenoxy resin 
process disclosed in British Pat. No. 652,024 above. It may also be 
prepared in an "interfacial" process in which one phase of the reaction 
medium is aqueous base (e.g., NaOH) and the other phase is the polymer 
itself (U.S. Pat. No. 3,767,618). These methods work for bisphenol A 
phenoxy resin because it does not crystallize under the reaction 
conditions. Because hydroquinone phenoxy resin does crystallize, it cannot 
be prepared by these methods. 
U.S. Pat. No. 3,238,087 discloses laminated structures in which one 
component is a hydroquinone phenoxy resin. However, no process is given or 
suggested which will produce the particular hydroquinone phenoxy polymer 
disclosed in this specification. 
We are not aware of a patent covering the use of a two-phase solvent system 
in which the polymer is soluble in one component. Indeed, U.S. Pat. No. 
3,767,618 teaches that such a system leads to inferior results with the 
bisphenol A resin (cf. their example 4). 
DISCLOSURE OF THE INVENTION 
This invention relates to a process for the preparation of thermoplastic 
polymers. Specifically, it relates to a process for the preparation of a 
substantially linear, high molecular weight phenoxy resin from 
hydroquinone substituted, optionally less than 80 mole percent of 
hydroquinone epichlorohydrin (or another epihalohydrin) and a base, such 
as sodium hydroxide, and the polymer produced thereby. 
In our U.S. application Ser. No. 108,722 filed Dec. 31, 1979, now U.S. Pat. 
No. 4,267,301, we disclosed hydroquinone phenoxy resins or polymers in 
which the aromatic diol component was at least 80 mole percent of 
hydroquinone with the remainder being another aromatic diol. We have found 
that certain aromatic diols substituted with one or two substituents which 
may be chlorine or an alkyl group containing 1-4 carbon atoms used as 
greater than 20 mole percent of the aromatic diol component of the polymer 
result in improved properties over those of the hydroquinone phenoxy 
resins disclosed and claimed in our earlier application. In particular the 
use of substituted hydroquinone derivatives such as chloro or 
dichlorohydroquinone give improved gas barrier properties and methyl 
hydroquinone may be used to provide a polymer with modified crystalline 
properties or solubility. 
The process provides sufficiently mild polymerization conditions to reduce 
the degradation of base-sensitive aromatic diols substituted with one or 
two substituents which may be chlorine or an alkyl group containing 1-4 
carbon atoms while at the same time remaining sufficiently vigorous to 
overcome the steric hindrance to polymerization presented by even 
relatively bulky substituents, such as methyl or tert-butyl groups. The 
process is applicable to mixtures of substituted and unsubstiuted 
hydroquinones in any proportion. 
The hydroquinone phenoxy resins or polymers of this invention are 
characterized by low permeability to oxygen and carbon dioxide and are, 
therefore, useful as a gas-barrier layer in multilayer plastic film 
constructions used in food packaging applications and beverage bottle 
applications, for example. For use in such applications, the resin is 
generally in the form of a thin, uniform film prepared by extrusion, 
casting, or other such method. It is highly desirable that polymers used 
in this manner be as free as possible from chain branches or crosslinks, 
as these lead to the formation of gel particles which cause imperfections 
in the polymer film. These imperfections, in turn, detract from the 
appearance of the film. Moreover, as is well known, increasing the amount 
of chain branching in a polymer results in an undesirable reduction of 
flexibility and toughness. 
In the food packaging and beverage bottling industries, plastic film which 
can be shaped into containers by extrusion blow molding, forging, stretch 
blow molding or other processes is highly desirable. These plastic 
containers must not only be strong but must also have low permeability to 
gases, especially oxygen and/or carbon dioxide, in order to prevent 
spoilage of the contents of the package. In order to provide the optimum 
combination of properties in the most economical way, multiple-layer film 
structures may be produced by lamination, coextrusion, solution casting or 
other such methods in which the layers may consist of different polymers 
or polymer blends chosen to impart specific desirable properties to the 
overall layered film. 
It is necessary that such a film have a low permeability to oxygen and/or 
carbon dioxide. It is also necessary that the layers of the film adhere to 
one another well, preferably when coextruded. The multilayer film and its 
individual components should also possess good thermal stability for ease 
of melt processing. And to enable the reuse of scrap laminated film by 
regrinding and blending of scrap with virgin material, it is desirable 
that all of the components of the multilayer film be compatible when 
re-extruded. Finally the multilayer film must be capable of being formed 
into suitable containers by processes such as stretch blow molding, 
forging, and so on, without loss of its desirable properties. 
It is known that poly(ethylene terephthalate) modified with up to about 35 
mole percent of other diacids or glycols is particularly well suited to 
film extrusion and subsequent thermoforming processes, although its 
permeability to oxygen and carbon dioxide is high. We have found that the 
substituted hydroquinone phenoxy resins of this invention may be combined 
with these polyesters in a multilayer film structure which, surprisingly, 
has excellent adhesion between layers when co-extruded, has good 
compatibility when scrap is re-extruded, has low gas permeability and 
which may be thermoformed without loss of these desirable properties. 
Multilayer constructions may be prepared by various techniques such as 
lamination, solvent casting or co-extrusion, the latter being the 
preferred process from an economic and practical standpoint. In addition 
to flat sheet, the multilayer structure may be in the form of a tube or 
may be formed as part of an extrusion blow molding process. 
The individual layers of the structure may be composed of pure components, 
e.g., polyester or substituted hydroquinone phenoxy resin, or of a blend 
of one or more polyesters and substituted hydroquinone phenoxy resin, such 
as may be produced by the blending of virgin polymer with reground scrap 
multilayer film prior to extrusion. In general it is preferred that the 
multilayer structure contain at least one layer of pure substituted 
hydroquinone phenoxy resin to obtain the optimum gas barrier property for 
the film structure; however, the desirable mechanical properties of the 
polyester are essentially unaffected by blending with substituted 
hydroquinone phenoxy resin. 
We have found that high molecular weight, essentially linear substituted 
hydroquinone phenoxy resin may be prepared by the reaction of a greater 
than 20 mole percent hydroquinone substituted with one or two substituents 
from the group of chlorine or an alkyl group containing 1-4 carbon atoms, 
an epihalohydrin such as epichlorohydrin, and a base such as sodium 
hydroxide, in a reaction medium consisting of water and a polymer solvent, 
such as cyclohexanone. A phase-transfer catalyst such as 
benzyltriethylammonium chloride is used to enhance the transport of 
reagents across the aqueous/organic phase boundary and thereby accelerate 
the reaction rate. 
In contrast to the previously-described methods, this phase-transfer 
solution polymerization is reproducible, suitable for scale-up, and gives 
a product whose ratio of weight-average molecular weight (Mw) to 
number-average molecular weight (Mn) is lower (for a given polymer 
inherent viscosity) than that obtained with other known methods, 
indicating a lower degree of chain branching. 
It is surprising that high molecular weight substituted hydroquinone 
phenoxy resin can be made in the presence of an organic polymer solvent in 
view of the results obtained by T. J. Hairston and W. L. Bressler (U.S. 
Pat. No. 3,767,618) who demonstrated that for bisphenol A phenoxy resin, 
lower molecular weights are obtained when an organic solvent is added to 
the aqueous reaction mixture. Thus, substituted hydroquinone phenoxy resin 
behaves in a manner opposite to that of the closely analogous bisphenol A 
phenoxy resin. 
Broadly the process of our invention for making our novel polymers 
comprises a process for the preparation of high molecular weight linear 
substituted hydroquinone phenoxy polymer from greater than 20 mole percent 
of a hydroquinone substituted with one or two substituents of the group 
chlorine and an alkyl group containing 1-4 carbon atoms, and an 
epihalohydrin, said process comprising reacting the hydroquinone compounds 
with about 0.95 to about 1.05 equivalents of an epihalohydrin in the 
presence of about 1.0 to 1.1 equivalents of a base and about 1 to 7 parts 
by weight solvent for said polymer per part polymer. 
A preferred process of this invention involves reacting chlorohydroquinone 
with epichlorohydrin in the presence of sodium hydroxide, in a reaction 
medium consisting of water, cyclohexanone and benzyltriethylammonium 
chloride as the phase-transfer catalyst at a temperature of about 
50.degree. C. to about 100.degree. C. for a time of about 2 to about 6 
hours. At the end of this time, the polymer may be isolated by any one of 
several procedures well known to the art. 
The novel linear substituted hydroquinone phenoxy polymer of this invention 
which may be prepared from greater than 20 mole percent hydroquinone 
substituted with one or two substituents of the group chlorine and an 
alkyl group containing 1-4 carbon atoms and an epihalohydrin is 
characterized by an inherent viscosity of about 0.45 to 0.9 as determined 
at 25.degree. C. in a 60/40 by volume mixture of phenol/tetrachloroethene 
at a concentration of 0.5 gram/deciliter, a molecular weight 
distribution, as determined by gel permeation chromatography, of 
Mw.sub./.sbsb.Mn .ltoreq. about 4 and Mz.sub./.sbsb.Mn .ltoreq. 10. The 
preferred inherent viscosity is about 0.5 to 0.7 and the preferred 
Mw.sub./.sbsb.Mn is .ltoreq. 3. Shaped objects such as films made from the 
polymer of our invention are particularly useful in a barrier layer in 
films and containers for food packaging applications. 
The reactants include hydroquinone substituted with one or two substituents 
of the group chlorine and an alkyl group containing 1-4 carbon atoms, an 
epihalohydrin, and a base which is capable of effecting deprotonation of 
the aromatic diol and of catalyzing the polymerization. The substituted 
hydroquinone may be replaced with up to less than 80 mole percent of 
hydroquinone. Also the substituted hydroquinone may be replaced with up to 
about 20 mole percent of bisphenol A, tetrachlorobisphanol A, or 
phenolphthalein. Compounds in which the hydroxyl groups are located on 
adjacent carbon atoms of the same aromatic ring such as catechol, however, 
are not preferred because of the possibility of forming a closed-ring 
structure with one molecule of the epihalohydrin component. 
Epihalohydrins which may be used include epichlorohydrin, epibromohydrin 
and epiiodohydrin, the preferred component being epichlorohydrin for 
economic reasons. In addition, 1,3-dihalohydrins, e.g., glycerol 
.alpha.,.gamma.-dichlorhydrin, may be used if an additional equivalent of 
base is used, per equivalent of dihalohydrin, in order to generate the 
epihalohydrin in situ. 
The base used may be any base strong enough to deprotonate the aromatic 
diol to form its mono-anion. Examples of such bases are sodium hydroxide, 
potassium hydroxide, lithium hydroxide, tetraalkylammonium hydroxides, or 
the alkali metal salts of alcohols such as methanol, ethanol, or 
tert-butaneol. Sodium hydroxide is generally the preferred reagent because 
of its low cost. 
The proportions of reactants used are about 0.95 mole to about 1.05 mole of 
epihalohydrin per equivalent of diol (or diol mixture) and about 1.0 to 
about 1.1 mole of base per mole of diol (or diol mixture). It is preferred 
to use about 0.98 mole of epihalohydrin per mole of diol in order to 
minimize chain branching; it is also preferred to use about 1.1 mole of 
base per mole of diol to provide a convenient reaction rate while limiting 
the extent of side reactions. 
The solvent system consists of water and an organic solvent which is 
capable of dissolving the polymer and may or may not be immiscible with 
water. Such solvents include, but are not limited to, cyclohexanone, 
2-butanone, acetophenone, dichloromethane, .gamma.-butyrolactone, 
sulfoane, dimethyl sulfoxide, N-methyl-2-pyrrolidine, N,N-dimethyl 
formamide and triethyl phosphate. The choice of a solvent depends to some 
extent on the solubility characteristics of the polymer being prepared; 
for chlorohydroquinone phenoxy resin, the preferred solvent is 
cyclohexanone. 
The proportion of water may range from about 0.8 part by weight water per 
part polymer to about 10 parts water per part polymer. The amount of 
organic solvent may vary from about 1 part to about 7 parts by weight 
solvent per part polymer. It is preferred to use the minimum amounts of 
water and organic solvents consistent with convenient handling in order to 
enhance the reaction rate. Moreover, it may be desirable to dilute the 
organic phase with additional organic solvent at the end of the reaction 
in order to facilitate the subsequent handling of the polymer solution. 
The phase-transfer catalyst may be any one of several known to the art, 
including quaternary ammonium halides such as methyl tricaprylylammonium 
chloride, benzyltriethylammonium chloride, tetrabutylammonium bromide, 
etc., cyclic polyethers such as cyclic hexamer of ethylene glycol; or 
acyclic polyethers, such as poly(ethylene glycol). The amount of the 
catalyst may vary from about 0.01 to 0.10 mole catalyst per mole of diol. 
Higher amounts may be used, but are uneconomical. The preferred range is 
0.02 to 0.05 mole catalyst per mole of diol; the preferred catalyst is 
benzyltrimethylammonium chloride or benzyltriethylammonium chloride. 
The temperature of the reaction may be from about 50.degree. C. to about 
100.degree. C., the preferred range being from about 80.degree. C. to 
about 90.degree. C. Time of reaction may be from about 2 to about 6 hours 
depending upon the temperature and degree of conversion required. A 
typical reaction time is 4 hours at 90.degree. C. 
At the end of the reaction, the reaction mixture is acidified by the 
addition of acetic acid, phosphoric acid, hydrochloric acid, etc., and the 
aqueous phase is drawn off. If desired, the polymer solution may be 
diluted, washed with water to remove residual sodium chloride, and the 
polymer may be recovered by removal of solvent by means of heat and/or 
vacuum. Alternatively, the polymer may be recovered by coagulation of the 
polymer solution with a polymer nonsolvent, a procedure which is well 
known. 
This invention will be further illustrated by the following examples 
although it will be understood that these examples are included merely for 
purposes of illustration and are not intended to limit the scope of the 
invention. 
Inherent viscosities (I.V.) were determined in a 60/40 (v./v.) mixture of 
phenol and tetrachloroethane at a concentration of 0.5 g./dl., at 
25.degree. C. 
Determination of molecular weight distribution was performed by gel 
permeation chromatography (GPC) on a Waters Associates Model 200 GPC unit 
equipped with Styragel columns (Waters Associates), in m-cresol solvent, 
at a column temperature of 100.degree. C. The columns were calibrated with 
polyethylene terephthalate (PET) standards, and the values of 
number-average, weight-average, and z-average molecular weights (Mn, Mw 
and Mz) were calculated as PET-equivalent weights. An example of the 
calculation is given by N. C. Billingham in "Practical High Performance 
Liquid Chromatography," C. F. Simpson, ed., Heyden and Son Ltd., 1978, 
page 104, incorporated herein by reference.

EXAMPLE 1 
A one-liter resin kettle is charged with 126.81 g. of chlorohydroquinone, 
8.25 g of benzyltrimethylammonium chloride, 200 ml. cyclohexanone, and 230 
ml. water. The kettle is purged with nitrogen and 82.31 g. of 
epichlorohydrin and 77.62 g. of 50% aqueous sodium hydroxide solution are 
added. The kettle is stirred at 80.degree. C. for 5 hours and heated to 
reflux for 2.5 hours. The reaction mixture is acidified with 30 ml. acetic 
acid, the aqueous layer is drawn off, and the polymer solution is washed 
several times with hot water. Removal of solvent under vacuum yields 161 
g. of polymer, PET-equivalent I.V.=0.62 (calculated from GPC data), 
Mw.sub./.sbsb.Mn =2.4 
EXAMPLE 2 
A 500-ml. Morton flask is charged with 45.47 g. 2.5-dichlorohydroquinone, 
2.38 g. benzyltrimethylammonium chloride, 40 ml. cyclohexanone, and 65 ml. 
water. The flask is thoroughly purged with nitrogen and 23.15 g. 
epichlorohydrin and 22.17 g. of a 50% aqueous solution of sodium hydroxide 
are added. The reaction mixture is stirred vigorously at 80.degree. C. for 
5 hours, and additional 20 ml. portions of cyclohexanone are added as 
necessary to maintain good stirring (total amount=100 ml.). The mixture is 
heated under gentle reflux for 2.5 hours, acidified with acetic acid, and 
the aqueous layer is drawn off. The polymer is precipitated by the 
addition of methanol. Yield 55 g. PET-equivalent I.V.=0.52 (calculated 
from GPC data), Mw.sub./.sbsb.Mn =2.6 
EXAMPLE 3 
The procedure of Example 2 is followed, except that the 
dichlorohydroquinone is replaced with 31.22 g. methylhydroquinone. After 
heating at 80.degree. C. for 4 hours, the reaction mixture is heated to 
reflex for 10 hours before acidification. The polymer is isolated by 
removal of solvent under vacuum to yield 39 g. polymer, I.V.=0.45, 
Mw.sub./.sbsb.Mn =2.4. 
EXAMPLE 4--Comparative 
Following the method taught in U.S. Pat. No. 2,602,075, a 500 ml. flask is 
charged with 28.9 g. (0.20 mole) chlorohydroquinone and 64 ml. ethanol. 
The solution is thoroughly purged with nitrogen and a solution of 8.6 g. 
(0.21 mole) sodium hydroxide in 25 ml. water is added, followed by 30 ml. 
water and 44 ml. ethanol. The solution is heated to reflux and 18.5 g. 
(0.20 mole) epichlorohydrin are added slowly. A precipitate of low 
molecular weight polymer forms within 10 minutes and coagulates into a 
soft plastic mass within 3.5 hours. The ethanol/water reaction mixture is 
concentrated by distillation from the reaction, and in an effort to drive 
the reaction to completion, 100 ml. of dimethyl sulfoxide are added to 
dissolve the mass. The polymer solution is stirred at 100.degree. C. for 1 
to 2 hours without further increase in solution viscosity. Isolation of 
the product by precipitation in water gave a brownish polymer, I.V.=0.34 
in phenol/tetrachloroethane solvent. Two repetitions of the above 
procedure gave polymers with I.V.'s of 0.33 and 0.36 respectively; the 
latter polymer also contained insoluble gels. 
EXAMPLE 5--Comparative 
Following the general method of U.S. Pat. No. 3,305,582, a 500 ml. baffled 
flask is charged with 22.8 g. (0.20 mole) hydroquinone, 7.5 g. (0.05 mole) 
chlorohydroquinone, 49 ml. isopropanol, 28 ml. water, and 23.5 ml. (0.25 
mole) epichlorohydrin. After degassing 22.35 g. of a 50% aqueous solution 
of sodium hydroxide (0.28 mole) is added, followed by a solution of 3.67 
g. benzyltriethylammonium chloride in 15 ml. of 55% aqueous isopropanol. 
The mixture is stirred for 16 hours at room temperature, during which time 
a fine voluminous precipitate forms. The mixture is heated to 80.degree. 
C. for 3.5 hours with stirring, and two 15 ml. portions of cyclohexanone 
are added at intervals to maintain good stirring. After 3.5 hours, 2.3 g. 
phenol dissolved in 15 ml. cyclohexanone, followed by 30 ml. 
cyclohexanone, are added and the mixture is stirred a further 3.5 hours. 
The polymeric product obtained is gelled. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.