Curable blends of cyanate esters and polyarylsulphones

A curable polymer composition comprising a polyarylsulphone thermoplastic component and a polymerizable cyanate ester thermoset component.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a polymer composition and more particularly to a 
composition containing a thermosettable cyanate resin precursor and a 
thermoplast effective to make said resin tougher when cured. It relates to 
also such a composition containing reinforcing fibres and to cured resin 
structures made of such a composition. 
2. Description of Prior Art 
Thermoset resins have been used for many years to make strong non-metallic 
structures, but have had somewhat limited fields of application because 
they are brittle. U.S. Ser. No. 253,596, filed Oct. 5, 1988, now 
abandoned, describes a polymer composition providing a useful improvement 
in fracture toughness and briefly reviews earlier attempts to meet this 
requirement. Whereas that U.S. Ser. No. mentions in a general way that the 
thermoset component of its compositions may be a cyanate resin, we have 
now identified particular compositions affording a significant advance in 
performance. 
SUMMARY OF THE INVENTION 
The invention provides in its first aspect a curable polymer composition 
comprising a polymerisable cyanate ester thermoset component and a 
polyarylsulphone thermoplast component containing ether- and/or 
thioether-linked repeating units (PhSO.sub.2 Ph).sub.n and (Ph).sub.a 
where Ph is phenylene, a and n are independently 1 to 2 and may be on 
average fractional and the phenylenes in (Ph).sub.a are linked by a single 
chemical bond. 
In the polyarylsulphone component the relative proportions of the said 
repeating units is such that on average at least two units (PhSO.sub.2 
Ph).sub.n are in immediate mutual succession in each polymer chain present 
and is preferably in the range 1:99 to 99:1, especially 10:90 to 90:10, 
respectively. Typically the ratio is in the range 25-50 (Ph).sub.a, 
balance (Ph SO.sub.2 Ph).sub.n. In preferred polyarylsulphones the units 
are 
I X Ph SO.sub.2 Ph X Ph SO.sub.2 Ph ("PES"); and 
II X(Ph).sub.a X Ph SO.sub.2 Ph ("PEES") 
where X is O or S and may differ from unit to unit; the ratio of I to II 
(respectively) preferably between 10:90 and 80:20 especially between 10:90 
and 55:45. 
The relative proportions of the repeating units of the polyarylsulphone may 
be expressed in terms of the weight percent SO.sub.2 content, defined as 
100 times (weight of SO.sub.2)/(weight of average repeat unit). A 
preferred SO.sub.2 content is at least 22, preferably 23 to 25%. When a=1 
this corresponds to PES/PEES ratios of at least 20:80, preferably in the 
range 35:65 to 65:35. 
The above proportions refer only to the units mentioned. In addition to 
such units the polyarylsulphone may contain up to 50 especially up to 25% 
molar of other repeating units: the preferred SO.sub.2 content ranges (if 
used) then apply to the whole polymer. Such units may be for example of 
the formula 
##STR1## 
in which A is a direct link, oxygen, sulphur, --CO-- or a divalent 
hydrocarbon radical. When the polyarylsulphone is the product of 
nucleophilic synthesis, its units may have been derived for example from 
one or more the following bisphenols and/or corresponding bisthiols or 
phenol-thiols: 
hydroquinone 
4,4'-dihydroxybiphenyl 
resorcinol 
dihydroxynaphthalene (2,6 and other isomers) 
4,4'-dihydroxydiphenyl ether or -thioether 
4,4'-dihydroxybenzophenone 
2,2'-di-(4-hydroxyphenyl)-propane or -methane. 
If a bis-thiol is used, it may be formed in situ, that is, a dihalide as 
described for example below may be reacted with an alkali sulphide or 
polysulphide or thiosulphate. 
Other examples of such additional units are of the formula 
##STR2## 
in which Q and Q', which may be the same or different, are CO or SO.sub.2 
; Ar is a divalent aromatic radical; and n is 0, 1, 2, or 3, provided that 
n is not zero where Q is SO.sub.2. Ar is preferably at least one divalent 
aromatic radical selected from phenylene, biphenylene or terphenylene. 
Particular units have the formula 
##STR3## 
where m is 1, 2 or 3. When the polymer is the product of nucleophilic 
synthesis, such units may have been derived from one or more dihalides, 
for example: 
4,4'-dihalobenzophenone 
4,4' bis-(4-chlorophenylsulphonyl)biphenyl 
1,4 bis-(4-halobenzoyl)benzene 
4,4'-bis-(4-halobenzoyl)biphenyl 
They may of course have been derived partly from the corresponding 
bisphenols. 
The polyarylsulphone may be the product of nucleophilic synthesis from 
halophenols and/or halothiophenols. In any nucleophilic synthesis the 
halogen if chlorine or bromine may be activated by the presence of a 
copper catalyst. Such activation is often unnecessary if the halogen is 
activated by an electron withdrawing group. In any event fluoride is 
usually more active than chloride. Any nucleophilic synthesis of the 
polyarylsulphone is carried out preferably in presence of one or more 
alkali metal carbonates in up to 10% molar excess over the stoichiometric 
and of an aromatic sulphone solvent, at a temperature in the range 
150.degree.-350.degree. C. 
If desired, the polyarylsulphone may be the product of electrophilic 
synthesis. 
The polyarylsulphone preferably contains end groups and/or pendant groups 
of formula --A--Y where A is a divalent hydrocarbon group, preferably 
aromatic, and Y is a group reactive with cyanate groups or with a curing 
agent or with like groups on other polymer molecules. Examples of Y are 
groups providing active hydrogen especially OH, NH.sub.2, NHR or --SH, 
where R is a hydrocarbon group containing up to 8 carbon atoms, or 
providing other cross-linking reactivity especially epoxy, cyanate, 
isocyanate, acetylene or ethylene, as in vinyl, allyl, propenyl or 
maleimide. 
The number average molecular weight of the polyarylsulphone is suitably in 
the range 2000 to 60000. Preferably it is over 5000 especially over 10000 
for example 11000 to 25000 and structurally as well as by chemical 
interaction increases toughness by comparison with that of the thermoset 
resin alone by providing zones of the tough thermoplast between 
cross-linked thermoset zones. Another useful subrange is 3000-11000, 
especially 3000-9000 in which it acts more as a chain-extender for the 
thermoset resin, separating and diluting local cross-link zones and thus 
toughening the structure. Within the above definition of the 
polyarylsulphone those are preferably chosen which are miscible with 
suitable cyanate precursors, have high modulus and Tg and are tough. 
It is convenient to use reduced viscosity (RV), measured on a solution of 
lg of polymer in 100 ml of solution in dimethyl formamide at 25.degree. C. 
as an indication of molecular weight, the correlation being as follows: 
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RV 0.15 0.25 0.45 0.92 
KV (number average) 
5000 13000 20000 60000 
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(Such molecular weights were in fact measured by vapour phase osmometry and 
are of course subject to the usual error range of about 10%). 
The cyanate ester resin component preferably contains cyanate groups linked 
to aromatic nuclei. Suitably it is one or more compounds of general 
formula NCOAr.sub.Z ArOCN, where Ar is an aromatic radical, especially 
paraphenylene, and Z is a linking group. Examples of Z are single-atom 
groups such as O, S, SO, SO.sub.2 and CR.sub.1 R.sub.2 (where R.sub.1 and 
R.sub.2 are hydrocarbon groups containing in all up to 12 carbon atoms and 
are possibly linked externally to form a ring). In other examples .sub.Z 
is larger, for example the residue of a diene such as dicyclopentadiene. 
The term "component" includes monomeric cyanic esters and also oligomeric 
derivatives thereof. 
In curable composition according to the invention a mixture of monomeric 
and oligomeric cyanates, in proportions in the range 0.7:1 to 1.5:1 is 
preferably present. 
The composition may contain a catalyst for curing the cyanate resin, for 
example a compound of a metal such as copper, zinc or cobalt. Such a 
catalyst should be added shortly before curing unless it is of the 
"latent" type, examples of which are cobalt compounds and chelates. 
Hydroxy compounds may also be added. 
The curable composition may, if desired, contain one or more additional 
thermosettable resin components, for example epoxy resin precursors. The 
weight ratio of cyanate to other thermosettable components is suitably in 
the range 4:1 to 10:1. Suitable epoxy resin precursors have 2-4 epoxy 
groups in the molecule. Such additional components may be monomeric or 
partly condensed or a mixture of both. Hardeners and catalysts appropriate 
to such resins may be used. 
The weight proportion of the thermoplast component in the composition is 
typically in the range 10-60, especially 15-40, percent, calculated on the 
non-volatile constituents present after curing the thermoset resin. The 
invention in a second aspect provides the composition in the cured state 
and structures made therefrom. In the cured state the thermoset and 
thermoplast components, the precursors of which were mutually miscible, 
form separate phases. There may be present a distinct continuous phase 
consisting substantially of one of the components, through which particles 
of the other are dispersed. In a preferred composition each component is 
present as a phase elongated in at least one dimension, for example as a 
network in which each extends continuously through any mass of the 
composition. Such a morphology, known also as co-continuous or 
semi-interpenetrating is, in the composition according to the invention, 
preferably the product of spinodal decomposition of the initial mixture as 
the thermoset component, in reacting with itself and any active groups on 
the thermoplast, becomes immiscible with the thermoplast. 
The composition is particularly suitable for fabrication of structures, 
including load-bearing or impact resisting structures. For this purpose it 
may contain a reinforcing agent such as fibres. Fibers can be added short 
or chopped typically of mean fibre length not more than 2 cm, for example 
about 6 mm, typically at a concentration of 5 to 35, preferably at least 
20%, by weight. For structural applications, it is preferred to use 
continuous fibre for example glass or carbon, especially at 30 to 70, more 
especially 50 to 70%, by volume. 
The fibre can be organic, especially of stiff polymers such as poly 
paraphenylene terephthalamide, or inorganic. Among inorganic fibres glass 
fibres such as "E" or "S" can be used, quartz or alumina, zirconia, 
silicon carbide, other compound ceramics or metals. A very suitable 
reinforcing fibre is carbon, especially as graphite. Organic or carbon 
fibre is preferably unsized or is sized with a material that is compatible 
with the composition according to the invention, in the sense of being 
soluble in the liquid precursor composition without adverse reaction or of 
bonding both to the fibre and to the thermoset/thermoplastic composition 
according to the invention. In particular carbon or graphite fibres that 
are unsized or are sized with epoxy resin precursor or thermoplast such as 
polyarylsulphone are preferred. Inorganic fibre preferably is sized with a 
material that bonds both to the fibre and to the polymer composition; 
examples are the organo-silane coupling agents applied to glass fibre. 
The composition may contain for example conventional toughening agents such 
as liquid rubbers having reactive groups, aggregates such as glass beads, 
rubber particles and rubber-coated glass beads, fillers such as 
polytetrafluoroethylene, graphite, boron nitride, mica, talc and 
vermiculite, pigments, nucleating agents, and stabilisers such as 
phosphates. The total of such materials and any fibrous reinforcing agent 
should be such that the composition contains at least 20% by volume of the 
polysulphone/thermoset mixture. The percentages of fibres and such other 
materials are calculated on the total composition after curing at up to 
200.degree. C. 
A further procedure comprises forming incompletely cured composition into 
film by for example compression moulding, extrusion, melt-casting or 
belt-casting, laminating such films to fibrous reinforcing agent in the 
form of for example a non-woven mat of relatively short fibres, a woven 
cloth or essentially continuous fibre in conditions of temperature and 
pressure sufficient to cause the mixture to flow and impregnate the fibres 
and curing the resulting laminate. 
Plies of impregnated fibrous reinforcing agent, especially as made by the 
procedure of one or more of EP-A 56703, 102158 and 102159, can be 
laminated together by heat and pressure, for example by compression 
moulding or by heated rollers, at a temperature above the curing 
temperature of the thermosetting resin or, if cure has already taken 
place, above the glass transition temperature of the mixture, conveniently 
at least 120.degree. C. and typically about 180.degree. C., and at a 
pressure in particular at least 0.1, preferably at least 5,MN/m.sup.2. 
The resulting multi-ply laminate may be anisotropic in which the fibres are 
oriented essentially parallel to one another or quasi-isotropic in each 
ply of which the fibres are oriented at an angle, conveniently 45.degree. 
as in most quasi-isotropic laminates but possibly for example 30.degree. 
or 60.degree. or 90.degree. or intermediately, to those in the plies above 
and below. Orientations intermediate between anisotropic and 
quasi-isotropic, and combination laminates, may be used. Suitable 
laminates contain at least 4 preferably at least 8, plies. The number of 
plies is dependent on the application for the laminate, for example the 
strength required, and laminates containing 32 or even more, for example 
several hundred, plies may be desirable. There may be aggregates, as 
mentioned above in interlaminar regions.

EXAMPLE 1 
A polymer composition was made from the following components: 
25 parts by weight of polyarylsulphone: 
40 mol percent PES, 60 mol percent PEES (a=1) 
100% NH.sub.2 end groups 
RV 0.24; T.sub.g 198.degree. C. 
40 parts by weight of cyanate oligomer derived from the 
phenol-dicyclopentadiene adduct: 
##STR4## 
35 parts by weight of cyanate monomer: 1,1-diphenylethane-4,4'-dicyanate 
The cyanate oligomer was melted at 80-90 deg and the cyanate monomer was 
added. A solution of the polyarylsulphone in methylene chloride was mixed 
in. The solvent was boiled off down to a volatiles level of about 3%. A 
solution of copper acetylacetonate (1% in nonylphenol) providing 63 ppm by 
weight of metal per 100 parts of cyanate resin was stirred in for 5 min at 
80-90 deg C. 
The mixture was cooled to ambient temperature. 
A sample of the mixture was impregnated on to unidirectional carbon fibre 
"HITEX 468b" (supplied by HITCO) at a resin content of 35% by weight and a 
fibre areal weight of 145 g/sq.m. 
The tape was cured in this cycle under 100 psi pressure: 
heat up at 2 deg F. per min 
1 h hold at 250 deg F. 
4 h at 350 deg F.; followed by 
2 h post cure at 428-464 deg F. 
Samples of the impregnated tape were subjected to standard tests. 
The results are set out in the Table 1 following Example 4. A sample of 
neat polymer composition was subjected to the same curing cycle and 
examined microscopically. It was observed to have a co-continuous network 
structure. 
EXAMPLE 2 
Example 1 was repeated subject to the modification that the proportions of 
the three components were 20:50:30 respectively, the fibre was "IM7" 
(supplied by Hercules Inc) and the polymer had RV 0.26, Tg 200.degree. C. 
The results of the standard tests are set out in Table 1 following Example 
4. 
Again a sample of cured neat polymer was observed to have a co-continuous 
network structure. 
EXAMPLE 3 
Example 1 was repeated except that the polyarylsulphone had 100% hydroxy 
end groups and RV 0.32, Tg 203.degree. C., and that the fibre was "IM7". 
Results of mechanical tests are shown in Table 1 following Example 4. 
In cured neat composition a "phase-inverted" morphology was observed, with 
islands of predominantly thermoset resin dispersed in a continuous phase 
of predominantly thermoplast polymer. 
EXAMPLE 4 
A polymer composition was made from the following components 25 parts by 
weight of polyarylsulphone 
80 mol percent PES, 20 mol percent PEES (a=2) 
over 90% OH end groups 
RV 0.25; Mn estimated (from NMR) 9800; Tg 216.degree. C. 
30 parts by weight of cyanate oligomer derived from 
2,2-diphenylpropane(-) 4,4'-dicyanate 
25 parts by weight of cyanate monomer as in Example 1. The procedure for 
mixing impregnation and cure were as in Example 1. A sample of next 
polymer composition was subjected to the same curing cycle and examined 
microscopically. It was observed to have a co-continuous morphology. 
Results of mechanical tests are shown in Table 1. 
TABLE 1 
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Example 
Property 1 2 3 4 
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0.degree. Tensile St Msi 
400 334 341 371 
0.degree. Tensile Mod ksi 
24.2 24.2 19.7 24.5 
0.degree. Tensile Strain 
1.7 1.42 1.7 1.6 
.mu. in/in, % 
CAI, kei after 1300 
37 34 30 31 
in lb/in 
0.degree. Compressive St, ksi 
RT 229 186 167 179 
250.degree. F. 
160 160 158 166 
250.degree. F./wet* 
145 154 150 168 
300.degree. F. 
162 181 132 154 
300.degree. F./wet* 
138 174 138 154 
G.sub.1c, Msi 
RT 0.64 0.65 0.64 0.62 
250.degree. F./wet** 
0.47 0.50 0.43 0.51 
300.degree. F./wet** 
0.42 0.39 0.51 0.39 
550.degree. F./wet** 
-- 0.16 0.26 0.17 
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Notes 
*Wet = 7 days immersion at 160.degree. F. 
**Wet = 65% RH at 150.degree. F. to saturation 
EXAMPLE 5 
Environmental resistance 
Sample of impregnated tape from Examples 1 and 4 were laid up in a +/-45 4 
ply laminate, and subjected to the curing cycle and post-cure described in 
Example 1. 
Specimens were treated as follows: 
JP4 or MEK 6 days' immersion at ambient temperatures 
water 14 days' immersion at 160 deg F. 
then tested for tensile strength and modulus and weight increase results 
are shown in Table 2. 
TABLE 2 
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Control 
JP4 MEK Water 
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Example 1 
Tensile strength, ksi 
25.8 25.3 26.1 20.0 
Tensile modulus, Msi 
2.22 2.08 1.89 1.90 
Weight increase, % 
.. -0.02 0.87 0.65 
Example 4 
Tensile strength, ksi 
21.8 21.3 24.0 16.4 
Tensile modulus, Msi 
2.10 2.11 1.84 2.06 
Weight increase, % 
-- 0 0.71 0.81 
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