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Description  |
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This invention relates to the preparation of polymeric materials which are
derived from phenolic compounds.
Novolac resins, which are now very well known materials, may be prepared by
the reaction of a phenolic compound, for example, p-cresol, with
formaldehyde in the presence of an acid catalyst. Such materials are
usually provided in the form of powders which are convertible to the
thermoset or intractable state by further reaction with a basic compound
such as hexamethylene tetramine. It is also known that compounds
containing aromatic nuclei for example benzyl chloride, diphenyloxide and
anthracene may be cross-linked by means of aralkyl halides to form
intractable cross-linked polymers.
We have now found that polymeric materials which may be cross-linked in the
presence of a novolac resin hardening agent, for example hexamethylene
tetramine, to a modified novolac-type resin may be prepared by the
reaction of a phenolic compound and an aralkyl ether or an aralkyl halide.
Accordingly the present invention provides a process for the preparation of
polymers which comprises reacting (1) an aralkyl ether of the general
formula R'[--(CH.sub.2 OR)].sub.a and/or an aralkyl halide of the general
formula R"[--(CH.sub.2 X)].sub.a, wherein R' is a divalent or trivalent
aromatic hydrocarbon or hydrocarbonoxy radical, R" is a divalent or
trivalent aromatic hydrocarbon radical, R' and R" optionally containing
inert substituents in the aromatic nucleus, R is an alkyl radical
containing less than 6 carbon atoms, X is chlorine, bromine or iodine and
a has a value of 2 or 3, with a molar excess of (2) a phenolic compound or
a phenolic compound and a compound containing aromatic nuclei.
The term "phenolic compound" as employed herein includes any compound or
mixture of compounds derived from benzene and containing from one to
three, preferably one or two, hydroxyl radicals attached to the aromatic
nucleus, there being a total of not more than three substituents attached
to carbon atoms in the benzene nucleus. Examples of phenolic compounds for
use in the process of this invention include phenol, p-cresol, resorcinol,
catechol, isopropyl catechol, diphenylolpropane, diphenylolmethane, alkyl
phenols such as p-ethylphenol, p-tert-butylphenol and p-tert-octyl phenol,
p-phenylphenol, m-phenylphenol, p-aminophenol, pyrogallol and
phloroglucinol. When the resinous reaction product is intended for
laminating or moulding applications p-phenylphenol, diphenylolpropane and
phenol are, in general, preferred.
According to the invention the phenolic compound is reacted with an aralkyl
ether of the formula R'[--(CH.sub.2 OR)].sub.a or an aralkyl halide of the
general formula R"[--(CH.sub.2 X)].sub.a. In these general formulae R' may
represent any divalent or trivalent aromatic hydrocarbon or hydrocarbonoxy
radical, for example the phenylene radical, the diphenylene radical, the
diphenylene oxide radical
##STR1##
the radical
##STR2##
or the radical
##STR3##
The R" radical present in the aralkyl halide may be any divalent or
trivalent aromatic hydrocarbon radical, for example the phenylene radical,
the diphenylene radical or the radical
##STR4##
The radical R may be any alkyl radical containing less than six and
preferably less than 4 carbon atoms and X represents a chlorine, bromine
or iodine atom. The preferred compounds (1) for reaction with the phenolic
compounds are those in which a has a value of 2, particularly the
p-xylylene dihalides, for example p-xylylene dichloride, and the
p-xylylene dialkyl ethers for example p-xylyleneglycoldimethylether.
If desired the R' and R" radicals may contain substituents for example
methyl radicals attached to the aromatic nucleus provided the said
substituents are inert under the conditions of the reaction. In fact the
presence of chlorine or fluorine atoms in some or all of the available
positions in the aromatic nucleus has been found advantageous in that it
leads to improved flame resistance in the resulting polymeric products.
Examples of substituted aralkyl ethers and aralkyl halides which may be
employed according to this invention are
2,3,5,6-tetrachloro-1,4-di(methoxymethyl)-benzene.
The reaction between the phenolic compound and the aralkyl ether or aralkyl
halide involves condensation of the alkoxy or halo groups in the aralkyl
compound with nuclear hydrogen atoms in the phenolic compound with the
elimination of an alcohol or a hydrogen halide. Preferably the process of
an invention is carried out in the presence of a catalyst for this
reaction for example certain ball clays or a Friedel Crafts type catalyst
such as stannic chloride, zinc chloride or ferric chloride. The most
preferred catalyst is stannic chloride.
The quantity of catalyst employed is not critical and from about 0.01 to
about 1 percent by weight based on the weight of the reactants (1) and (2)
has been found to be sufficient for most purposes although up to 3 percent
or more may be used if desired. In order to obtain reasonably short
reaction times the reactants are preferably heated to temperatures in the
range from about 150.degree. to 200.degree. C.
If desired organic solvents may be added to the reaction mixture for
example to compatibilise the reaction components or assist in the recovery
of the reaction product. Such organic solvents, if present, should
preferably comprise the high boiling chlorinated aromatic compounds, with
de-activated aromatic rings, for example chlorobenzene.
The time required for the reaction will depend upon such variables as the
nature of the reactants, the type and quantity of the catalyst and the
reaction temperature. Preferably the reaction should be carried to
substantial completion, the alcohol or hydrogen halide liberated being
removed from the reaction mixture by any suitable means.
The products obtained by the reaction of the aralkyl halide or aralkyl
ether with a molar excess of a phenolic compound according to this
invention are generally low molecular weight materials which may be
coloured, viscous liquids at room temperature. As with the conventional
novolac resin compositions these reaction products may be converted to
higher molecular weight materials by the addition thereto of a hardening
agent, usually hexamethylene tetramine, and heating, normally to a
temperature within the range from 100.degree. to 200.degree. C. The extent
of the molecular weight increase and the nature of the resin obtained will
depend on the quantity of hardening agent employed and the duration and
temperature of the heating period. Although the reaction product may be
converted to the solid, infusible, insoluble state in one step by
employing relatively high proportions, for example up to 20 percent by
weight, of hardening agent it is usually preferred to employ a smaller
proportion of the agent to obtain a partially polymerised product. This
partially polymerised product may then be stored if desired and in
application can be further polymerised (or cross-linked) in the presence
of additional quantities of the hardening agent and/or by subjecting it to
a further heating step.
The resinous, partially polymerized (or cross-linked) product obtained on
reaction of the initial reaction product with the hardening agent may be a
viscous liquid or a solid. Generally, the partially polymerised product
will be a solid at this stage, its physical form, depending mainly on the
nature of the phenolic compound employed and on the degree of
cross-linking which has taken place.
As hereinabove described the modified-novolac type reaction products of
this invention may be converted to the infusible, insoluble state by
reaction with, for example, hexamethylene tetramine as the hardening
agent. However, although hexamethylene tetramine comprises the most
preferred material for this purpose it is to be understood that the use of
other known novolac resin hardening agents such as quinone, chloranil,
anhydroformaldehydeaniline and ethylene diamine-formaldehyde are also
included within the scope of this invention.
The phenolic compounds may be employed alone in forming the polymers of
this invention or they may be employed in the reaction in conjunction with
compounds containing aromatic nuclei and not being phenolic compounds as
required by this invention. The additional use of the said aromatic
compounds in the reaction provides a means of modifying the properties of
the product. Suitable aromatic compounds are those capable of condensation
with the aralkyl halide or aralkyl ether and include for example dipenyl
ether, dibenzyl ether, terphenyl, diphenylamine, diphenyl sulphide,
diphenyl, anthracene, naphthalene, diphenyl sulphone, triphenyl phosphate,
octaphenylcyclotetrasiloxane, aryl-substituted borazoles and metal
complexes such as ferrocene. Preferably the compound containing aromatic
nuclei is selected from diphenyl, terphenyl and diphenyl ether. The
proportion of the compound containing aromatic nuclei which may be
incorporated may vary within wide limits but should not be so large as to
prevent satisfactory curing of the reaction product under the action of
the particular novolac hardening agent employed.
Conveniently the compound containing aromatic nuclei is mixed with the
remaining components and the reaction initiated. In some cases however,
particularly where the aromatic compound is of low reactivity, it may be
advantageous to partially react the compound containing aromatic nuclei
with the aralkyl ether or halide prior to incorporating the phenolic
compound in the reaction mixture.
When the compound containing aromatic nuclei is employed it is not then
essential that the phenolic compound should itself be present in molar
excess over the aralkyl halide or aralkyl ether provided that the total of
the phenolic compound and the compound containing aromatic nuclei taken
together represents the required molar excess. As the molar proportion of
the aralkyl halide or aralkyl ether approaches that of the other reactant
the reaction mixture exhibits an increased tendency to gel prematurely.
Generally therefore we prefer to employ 1.3 to 3.0, and more preferably
from 11/2 to 21/2 moles of the phenolic compound, or of the phenolic
compound and the compound containing aromatic nuclei, for every mole of
the aralkyl halide or aralkyl ether.
As is known for the conventional organic novolac resins the resins of this
invention may be further modified by reaction with unsaturated compounds,
in particular the unsaturated oils such as tung oil, linseed oil, perilla
and dehydrated castor oils. Such modification may be carried out, for
example, by reacting the unsaturated compound with the prepared
polymerisable, modified-novolac reaction product.
The modified novolac resins of this invention are heat stable to a degree
which is often superior to that of the conventional organic novolacs. They
may be compounded with organic or inorganic fillers and are suitable for
use in a wide variety of applications for example as binders and in the
preparation of moulding compounds for use in the manufacture of abrasive
grinding wheels and asbestos of fibrous glass reinforced moulded
components, and in the preparation of lamp capping cements. When prepared
in the form of a fine powder the resinous compositions of the invention
are suitable for coating articles by fluidised bed techniques. They may be
dissolved in a suitable solvent, for example methyl ethyl ketone or methyl
cyclohexanone, and used for impregnating for example glasscloth, asbestos
paper and asbestos fabric, which may subsequently be consolidated under
heat and pressure to give laminated or moulded products. Hexamethylene
tetramine is of limited solubility in most common organic solvents. When
preparing resin solutions containing a relatively high proportion of this
hardening agent therefore we prefer to cause partial reaction between
resin and the hexamethylene tetramine and then dissolve the partial
reaction product in the solvent. Further quantities of hexamethylene
tetramine may be added with the solvent although these further quantities
will be limited by the solubility of the hexamethylene tetramine therein.
We have also found that the resinous products of this invention are useful
in the preparation of solid lubricant compositions by incorporating into
the resin prior to the final cross-linking stage a solid lubricant
material such as graphite or molybdenum disulphide. The quantity of solid
lubricant material incorporated into the resin may vary widely but
preferably falls within the range of from 1 to 25 percent by weight. Solid
lubricant compositions prepared in this manner are useful, for example, as
coatings for gear wheels and shafts and in the manufacture of self
lubricating bearings.
The following examples illustrate the invention.
EXAMPLE 1
p-Cresol (2.0 moles, 216 g.) and p-xylylene glycoldimethylether (1.0 mole,
166 g.) were mixed and heated to a temperature of 130.degree. C. with
stirring in order to remove any water from the system. Stannic chloride
(0.001 mole, 0.11 ml.) was then added to the cooled mixture, which was
reheated with stirring and the methanol formed allowed to distil out. The
heating was continued until no further methanol was liberated the reaction
then being substantially complete. The reaction product at this stage was
a brown viscous liquid.
When 50 g, of this liquid were mixed with 5 g. of hexamine (hexamethylene
tetramine) and heated for 40 minutes with continuous agitation at
145.degree. C. a higher molecular weight polymeric material was obtained.
This material was a hard yellowish-brown solid having a melting point of
about 115.degree. C. and which could be crushed to give a fine powder.
When mixed with a further 5% by weight of hexamine and heated to
150.degree. C. the powder was converted to a solid, intractable resin.
EXAMPLE 2
p-Cresol (1.864 moles, 202 g.), diphenyl oxide (0.800 moles, 136 g.) and
p-xylyleneglycoldimethylether (1.336 moles, 222 g.) were heated together
with stirring to 130.degree. C. in order to remove any traces of moisture.
Stannic chloride (0.00134 mole, 0.156 mls.) was then added and the mixture
heated with stirring until the theoretical quantity of methanol had
distilled out. The reaction product obtained was a dark brown viscous
liquid.
A quantity of this liquid (50 g.) was mixed with 1.25 g. of hexamine and
heated with stirring for 45 minutes at 170.degree. C. to give a clear
yellowish-brown liquid which solidified on cooling. This solid had a
melting point of 96.degree. C. and could be easily crushed to give a fine
yellow powder.
In order to examine its thermal stability a quantity of the resin was
heated at 250.degree. C. for 250 hours. The loss in weight of the resin
after this time was only 1.7 percent. A further sample of this resin
prepared from 50 g. of the viscous liquid and 3.25 g. of hexamine
exhibited a weight loss of 4 percent under the same conditions.
When a commercially available conventional phenolic resin was subjected to
this test the weight loss was found to be 18 percent.
EXAMPLE 3
p-tert-butylphenol (1.86 moles, 280 g.) diphenyloxide (0.80 mole, 136 g.)
and p-xylyleneglycoldimethylether (1.34 moles, 221 g.) were heated in the
presence of stannic chloride (0.00134 mole, 0.156 ml.) until the
theoretical quantity of methanol had been liberated. The polymeric
reaction product obtained was found to be a soft, pliable dark solid at
room temperature.
A 25 g. sample of this resin was heated with stirring in an oil bath at
170.degree. C. with 0.625 g. of hexamine, the cross-linking (hardening) of
the resin being allowed to proceed to a stage where stirring became
impossible. The product was then allowed to cool and was found to be a
solid (m.p. 102.degree. C.) which could be ground to a yellow powder
suitable for incorporating in moulding compositions.
A quantity of the initial resinous reaction product (79 g.) was mixed with
hexamine (1 g.) and the mixture heated for 5 minutes with stirring at
150.degree. C. Polymerised tung oil (20 g.) was then added and the system
heated for a further 30 minutes at 150.degree. C. and then for 1 hr. at
175.degree. C. At the end of the heating period the product was completely
homogeneous. A 50% by weight solution of this product in toluene had a
viscosity of 132 cS at 25.degree. C. The resin solution thus obtained was
used for impregnating glasscloth tape by dipping, the resin thereafter
being cured for 30 minutes at 150.degree. C. A further coat of the resin
was applied in a similar manner and cured for a further 1 hr. at
175.degree. C. The coated tape was brown and more flexible than similar
tapes produced with a resin which was not oil modified.
The oil-modified resin was found to cure slowly at 23.degree. C. over a
period of 3-4 days when loaded with metallic driers or combinations of
metallic driers such as lead, cobalt and manganese naphthenates and
exposed to the atmosphere as a thin film.
EXAMPLE 4
Octaphenylcyclotetrasiloxane (0.20 mole, 159 g.) and
p-xylyleneglycoldimethyl ether (0.66 mole, 110 g.) were heated with
stannic chloride (0.00134 mole, 0.156 ml.) until 25 percent by weight of
the theoretical quantity of methanol had been removed. At this point
p-cresol (1.13 moles, 122 g.) was added to the system and the condensation
allowed to continue until the theoretical quantity of alcohol had been
removed. The reaction product obtained was a brown, opaque, tacky solid.
When 25 g. of the resin was heated for 30 minutes at
170.degree.-175.degree. C. with 0.625 g. of hexamine a hard brown opaque
solid was obtained, having a melting point of 99.degree. C.
EXAMPLE 5
p-Cresol (2.0 moles, 216 g.), diphenyloxide (0.8 mole, 136 g.) and
p-xylylene dichloride (1.2 moles, 210 g.) were heated with stannic
chloride (0.0012 mole, 0.14 ml.) until no further hydrochloric acid was
liberated. The reaction product was a dark viscous liquid. This liquid (25
g.), on heating with hexamine (0.76 g.) for 110 minutes at
170.degree.-175.degree. C., was converted to a clear brown solid melting
at 60.degree. C.
EXAMPLE 6
p-phenylphenol (0.20 mole, 24.0 g.), phenol (0.112 mole, 10.56 g.) and
2,3,5,6-tetrachloro-1,4-chloromethylbenzene (0.187 mole, 58.5 g.) were
mixed and heated in the presence of stannic chloride (0.1 ml.) in a
reaction vessel fitted with a stirrer at a temperature of 170.degree. C.
for 4 hours. After this time the reaction mixture had been converted to a
dark coloured material which was a solid at room temperature.
A portion (22.0 g.) of this polymeric reaction product was then heated with
hexamine (0.55 g.) for 3 hours at 130.degree. C. to increase its molecular
weight, the mixture being stirred continuously during the heating step.
The product thus obtained was a dark brown solid having a melting point of
69.degree. C. and which could be crushed to a fine powder.
When 90 parts by weight of the powdered polymeric material was mixed with
10 parts by weight of hexamine and heated for 10 minutes at 200.degree. C.
a hard, intractable resin was obtained.
When exposed to a gas flame this intractable resin burned only very slowly
and reluctantly. For comparative purposes a resin was prepared by exactly
the same method, except that the
2,3,5,6-tetrachloro-1,4-chloromethylbenzene was replaced by
p-xylyleneglycol dimethyl ether. This comparative resin burned strongly
when heated in a gas flame.
EXAMPLE 7
Phenol (0.5 mole, 47.05 g.), p-phenylphenol (0.89 mole, 151.6 g.) and
p-xylylene glycoldimethylether (0.83 mole, 138.5 g.) were mixed and the
mixture heated for one hour at 130.degree. C. to remove any traces of
moisture that might have been present. Stannic chloride (0.38 ml.) was
added to the dried mixture which was then heated with stirring until the
theoretical quantity of methanol had been evolved. The reaction product
obtained was a dark solid.
A quantity (100 g.) of this reaction product was mixed with hexamine (1.5
g.) and the mixture heated with stirring for 1 hour at 170.degree. C. to
give a clear brown solid. This solid was liquified by heating, molybdenum
disulphide (5 g.) dispersed in the liquid and the mixture allowed to cool
to a solid which was then crushed to a fine powder.
The powdered solid could be converted to the intractable, highly
cross-linked state by the addition of hexamine and heating. It was found
to be useful for making moulded articles, such as self lubricating
bearings, with or without the additional presence of filler materials such
as silicas and clays.
EXAMPLE 8
Phenol (1.06 moles, 100 g.) and p-xylylene glycoldimethylether (0.71 mole,
117.6 g.) were mixed and heated to a temperature of 130.degree. C. with
stirring in order to remove any water from the system. The mixture was
cooled stannic chloride (0.0007 mole, 0.081 ml.) added, and the mixture
then heated again with stirring, the methanol formed being allowed to
distil out. Heating was continued until no further methanol was liberated.
When cool the reaction product was obtained as a brown low melting solid.
When 30 g. of the reaction product was mixed with 0.2 g. of hexamine and
the mixture heated for 25 minutes with continuous stirring at 170.degree.
C., a higher molecular weight polymeric material was obtained which could
be crushed to give a fine yellow-brown powder. When mixed with a further
quantity of hexamine and heated again to 170.degree. C. the powder was
converted to an intractable solid.
EXAMPLE 9
Phenol (1.17 moles, 105.4 g.), bis-phenol A, (diphenylolpropane) (0.37
mole, 85.2 g.) and p-xylylene glycoldimethylether (1.0 mole, 166.6 g.)
were heated together to about 130.degree. C. After cooling the mixture
stannic chloride (0.0014 mole, 0.156 ml.) was added and the reaction
mixture heated with continuous stirring until methanol ceased to distil
out. The cooled reaction product was a dark brown low melting solid.
When 20 g. of this polymer was heated at 170.degree. C. with 0.2 g.
hexamine, a higher molecular weight product was formed after 15 minutes
having a melting point of 78.degree. C. When cool this product was crushed
to a fine yellow brown solid which on heating with a total of 10% hexamine
at 200.degree. C. gave a hard intractable solid resin.
EXAMPLE 10
When phenol (0.127 mole, 11.9 g.), diphenylsulphone (0.04 mole, 8.7 g.) and
p-xylyleneglycoldimethylether (0.1 mole, 16.6 g.) were reacted in the
presence of stannic chloride (0.0001 mole, 0.02 ml) according to the
method described in Example 9 the reaction product was a dark brown, low
melting solid.
This solid could be converted to a hard thermoset resin on heating with
hexamine.
EXAMPLE 11
Phenol (5.62 mole, 530 g.) p-hydroxydiphenyl (1.875 mole, 318 g.) and
p-xylyleneglycoldimethylether, were heated together with stannic chloride
(0.005 mole, 0.579 mls.) in the manner described in Example 9 to yield a
dark brown low melting solid.
To a portion of the resin was added 10% by weight of hexamine and the
mixture heated with stirring for 10 minutes at 130.degree. C. to yield on
cooling a yellow brown solid. This solid was crushed to a fine powder and
dissolved in sufficient methyl ethyl ketone to give an approximately 50%
by weight solution. Glass cloth was impregnated with the solution to a
resin solids pick-up of about 40% total weight of glass and resin. The
cloth, after precuring at 135.degree. C. for 12 minutes was used to
prepare 20 ply laminates by pressing for 30 minutes at 175.degree. C.
under a pressure of 1,000 p.s.i. The laminates were post cured by heating
to 250.degree. C. over a period of 24 hours, and then held at 250.degree.
C. for an additional 4 hours. Flexural strength measurements according to
B.S. 2782 were made at 25.degree. C. and 250.degree. C. initially and
after 24 hours and 500 hours heat ageing at 250.degree. C.
The values obtained are shown in the following Table.
______________________________________
Flexural Strength p.s.i.
Condition 25.degree. C.
250.degree. C.
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As prepared 81,000 28,000
After 24 hours 95,000 49,000
at 250.degree. C.
After 500 hours
80,000 45,000
at 250.degree. C.
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The electric strength was measured on 10 ply laminates which had been
similarly prepared and was found to be greater than 800 v/mil. The
laminate was tested again after a heat ageing period of 1,120 hours at
250.degree. C. and the electric strength found to be still greater than
300 v/mil.
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