Note: Descriptions are shown in the official language in which they were submitted.
lZ11886
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The present invention r~lates to the discovery of a
2 specific class of crosslinking agents for polv~parabanic
3 acid) resins.
4 Poly(parabanic acids), their precursors the poly-
5 (iminoimidazolidinediones) and their methods of preparation
6 are known and described in detail in commonly assigned
7 U.S. Pat. 3,661,859. The poly(parabanic acias) may also be
8 prepared by other processes, such as shown in U.S. Pat. No.
9 3,609,113.
The poly(iminoimidazolidinediones)may be formed by
11 the reaction of hydrogen cyanide with a diisocyanate or mix-
12 ture of diisoc~nates, the reaction of a dicyanoformamide with a di-
13 isocyanate or mixtures of diisocyanates, or the polymerization of a
14 cyanoformamdiyl isocyanate, and contain a 1,3-imidazolidi-
nedione-1,3-diyl ring-of the following structures in the
16 repeating units:
17 0 0
18 C C
19 --N N and/o~ --N N
0=C -- C=NHHN=C C=0
21 wherein NH is in the 4 or 5 position.
22The poly(parabanic acids) also designated as
23 poly(l,3-imidazolidine-2,4,5-triorles) may be prepared,
24 for example, by the acid hydrolysis of poly(iminoimi-
25 dazolidinediones) and contain the imidazolidinetrione
26 ring in the repeating unit.
27 0
28 ~C
29 1 --NN --
30 - 0=C -- C=0
31 U.S. Pat. No. 3,609,113 and German Patent No. 1,770,146
32 describe other methods for preparing polymers which
33contain the poly(parabanic acid) rings.
34The present polymers may be broadly characterized
35as having the repeating unit:
. . ~
36LQ R - _
37 n
'~
~Z11l~86
1 wherein Q is
2 0
3 ",C
4 - N N
0=C - C=O
6 wherein R is an organic moiety which may be aliphatic,
7 alicyclic, aromatic or mixtures thexeof, and n is
8 su~ficiently large to produce a solid product.
The R is the organic moiety of the diisocyanate
when the polymer is produced according to the procedure in
11 U.S. Pat. No. 3,661,859. Thus, the diisocyanates may be
12 selected from a broad group having a large variety of
13 organic moieties. The organic moieties of the diisocyanate
14 may be substituted with groups such as alkyl, aryl,
halogen, sulfoxy, sulfonyl, alkoxy, aryloxy, oxo, ester,
16 alkylthio, arylthio, nitro and the like which do not react
17 with the isocyanate group. Functional groups which have
18 active hydrogen atoms, (e.g., carboxylic acids, phenols,
19 amines, etc.) should not be present. Specific diiso-
cyanates which may be used are set out in the U.S. Pat.21 No. 3,661,859 and other patents, articles or organic
22 textbooks.
23 Some of the parabanic acid polymers have been
23 found to have high glass transition temperatures, and
24 thus are especially suitable as magnetic tapes (where
good dimensional stability at high temperatures is
26 required), films for use in flexible printed circuits,
27 cable wraps, etc., for fibers such as tire cord fibers
28 (where tensile strength and modulus are required), for
29 moldings for electrical connectors, bearings, magnetic
wire insulation, coatings for cable, cookware, glass
31 fabrics, industrial belts (where high temperatures are
32 required) and the like.
33 Generally these polymers are very resistant
34 to thermal decomposition, which does not occur rapidly
until at or above their glass transition temperatures.
1~11886
1 However, the poly(parabanic acid~ polymers are subject to
2 attack by some solvents so that in some applications they
3 can not be used as such but must be thermally crosslinked.
4 Thermal crosslinking is normally conducted at hightemper-
atures, e.g., 225 to 280C for several hours. At these
7 temperatures in air oxidative degradation also occurs with
8 concomitant decrease in some desi~able properties. More-
9 over, the long curing times make the crosslinking econom-
ically unattractive.
11 It is an advantage of the present invention that
12 the present poly(parabanic acid) compositions crosslink in
13 much shorter curing times than previously required for the
14 polymers without the crosslinking agent.
Briefly, the present invention is a crosslinkable
16 composition comprising heterocyclic polymers characterized
17 in the repeating unit by the tri-substituted 1,3-imidazo-
18 lidine-1,3-diyl ring:
19 O
~
21 _ N N
22 O=C C=O
23 specially polyme~s haYing the lepeating unit:
24 ~ Q R ~
n
26 whe~ein Q is
27 O
28 ~ C
29 N N
30 O=C C=O
31 and R is an organic moiety which may be aliphatic,
32 alicyclic, aromatic or mixtures thereof and n is
33 sufficiently large to produce a solid product, and a
34 sufficient amount of a sulfonic acid or derivative
thereof to cause crosslinking. The crosslinked polymer
36 is also an aspect of the present invention as is the
37 method of crosslinking the polymers.
1~i1886
1 More particularly, the polymers may be
2 poly(parabanic acids) characterized by tri-substituted
3 1,3-imidazolidine-3-diyl rings of the following structure:
4 0
~ C
6 - N N -
7 O=C - C=O
8 or more specifically, polymers of the general structure:
9 ~
C
11_ -'' ~ N ~ ~ - respectively,
12 0=C C=0
13 n
14 wherein R and n have the significance given above.
The poly(parabanic acid) polymers are considered
16 to be crosslinked when they are insoluble in their normal
17 solvents. Hence, the term "a crosslinking amount" as that
18 term is used herein is understood to mean an amount of
19 the organic sulfonic acid or derivative which when
.incoroor~t~d in and admi~ed with the polymer will produce
21 upon heating a polymeric material insoluble in solvents
22 for poly(parabanic acid) such as dimethyl formamide.
23 Crosslinking can also be detected in films by a decrease
24 in the tensile elongation; but small amounts of crosslink-
ing are more readily detected by solubility tests.
26 The sulfonic acids are characterized by the
27 presence of the group:
28 HO
29 D S -
O
31 on an organic moiety. The organic moiety may be an
32 aliphatic, cyclic, aromatic or polymeric radical. The
33 organic moiety may be a hydrocarbon which may be substi-
34 tuted with groups which are not detrimental to the
poly(parabanic acid) polymers, such as halogen, sulfoxy,
36 sulfonyl, alkoxy, aryloxy, oxo, ester,thio and nitro
37 groups. Functional groups which have active hydrogens
. .
lZ13L886
1 (e.g., carboxylic acids, phenols, amines, etc.) should not
2 be present. The organic moiety may have more than one
3 -SO2OH group.
4 In addition to the free acid the derivatives of
of the sulfonic acid may be used. Specifically esters
6 (-SO3R) and salts (-SO3M) of the sulfonic acids may be
7 employed to produce the crosslinkable poly(parabanic acids).
8 The R group in the esters may be aliphatic (1 to 4 carbons
9 in length), alicyclic, or aromatic and substituted as
described above.
11 Suitable cations in the salts are alkali metal,
12 alkaline earth metals or metals, preferably from Groups lA,
13 2A, 3A, 4A, 2B, 3B, 6B, 7B and 8 of the Periodic Table,
14 particularly Na, K, Mg, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Ag or
Pb. Reference is to the Periodic Table of Mendeleef as it
16 appears on the front cover leaf of the Handbook of
17 Chemistry and Physics 56th Edition 1975-1976, published by
18 CRC Press Cleveland, Ohio, USA.
19 Some specific crosslinking agents are methyl
sulfonic acid~ ethylsulfonic acid, n-propylsulfonic acid,
21 isopropylsulfonic acid, cyclohexylsulfonic acid, p-toluene-
22 sulfonic acid, 5-nitro-1,3-benzenedisulfonic acid,~ -naph-
23 thalenesulfonic acid, ~ -naphthalenesulfonic acid,
24 anthracene sulfonic acid, 1,5 or 1,8 naphthalenedisulfonic
acid, methyl-p-toluenesulfonate, the free acid form and the
26 sodium and copper salts of sulfonated polysytrene,
27 p-toluene sulfonic acid, 2-hydroxy-4, methoxy-5-sulfo-
28 benzophenone, calcium benzenesulfonate, barium benzene-
29 sulfonate, lead benzenesulfonaté, methyl methyl sulfonate,
ethyl methyl sulfonate, methyl propyl sulfonate and the
31 like. Aromatic sulfonic acids and their derivatives are
32 preferred because of greater compatibility with the
33 polymers.
34 It has been found that very small amounts of the
of the crosslinking agent may be used to obtain the cross-
36 linked polymer and that excessively large amounts of cross-
37 linking agents demonstrated no advantages. The amount of
38 crosslinking agent present to produce a crosslinkable
lZ~1886
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1 product is in the range of 0.25 to 16 weight percent based
2 on the poly(parabanic acid) with a preferred range being
3 about 0.5 wt.% to 8 wt.~. The gist of the present invent-
4 ion, however, is the use of the least amount of crosslink-
ing agent as described to obtain the desired crosslinked,
6 i.e., insoluble, poly(parabanic acid) composition. The use
7 of larger amounts than this are contemplated to be within
8 the scope of the invention, to the extent th~t the cross-
9 linked product is not adversely affected thereby.
For purposes of illustration, the examples illus-
11 trating the invention will be described in specific with
12 respect to a particular polymer. That is, a polyparabanic
13 acid prepared from diphenylmethane diisocyanate in accor-
14 dance with proprietary techniques well described in patents
assigned to Exxon Research and Engineering Company to
16 result in a high performance polymer having the repeating
17 unit shown below:
18 _ _
29 ~ c ~ CH2 ~--
21 O=C - C=O n
22 which Is also designated as poly(l,4-phenylenemethylene-1
23 4-phenylene-1,3-(imidazolidine-2,4,5-trione)) which is
24 also designated in chemical abstracts as poly (2,4,5-tri-
oxo-l, 3 imidazolidinediyl)-1,4-phenylenemethylene-1,4-
26 phenylene) designated PPA-M for convenience. It has a
27 high glass transition temperature of 290 C and can not be
28 extruded or molded.
29 In general, the preferred polymers of the
polymer-plasticizer components are those which have suffi-
31 cient repeating units at room temperature to be solids.
32 In addition to the polymer and crosslinking
33 agent, it is contemplated that other appropriate additives
34 such as those employed to stabilize the polymer against
oxidation or ultraviolet light, flame retardants, pigments,
36 plasticizers, fillers and the like may be present.
37 The present crosslinking agents may be incor-
121~886
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1 porated into the polymers in solution and thereafter cast or
2 coated onto a substrate and cured or may be premixed with
3 polymer powder and thereafter dissolved. When plasticizers
4 are employed in the polymers they may be extruded and subse-
5 quently cured.
6 The curing may be effected by heating the cast or ex-
7 truded polymer containing the crosslinking agent at a temper-
8 ature in the range of 200 to 300C, preferably of 240 to 280
9 C, for about one hour. The curing temperature and time may
10 vary according to the specific poly(parabanic acid) polymer
11 used (i.e., the R group). For example, PPA-M film cast from
12 solutions with various crpsslinking agents present therein at
13 various concentrations crosslinked within one hour at 260C.
14 Very generally, PPA and its precursor are soluble in moderate
15 hydrogen bonding dipolar, aprotic solvents. Suitable solvents include
16 dimethylformamide, dimethylacetamide, dime~hylsulfoxide, hexamethyl-
17 phosphoramide and N-methylpyrrolidone. These may be used in admixture
18 with each other or with other aprotic solvents such as benzene, toluene,
19 xylene, methylacetate, ethylaoetate, anisole, phenetole, butyl benzoate,
chlorobenzene, etc.
21 Hence, the precipitation of the crosslinkable polymer
22 compositions from a suitable solvent either onto a casting
23 surface, from which the crosslinkable film may be removed
24 or onto a substrate to which the film is to be bonded
25 provides a very convenient method of producing the cross-
26 linkable polymer films and coatings. The solution of cross-
27 linkable polymer may be sprayed or brushed onto a surface
28 and the solvent removed to leave a polymer film, which is
29 subsequently cured and crosslinked by heating as described.
.30 This is a particularly useful way to produce electric motor
31 core coated wire.
32 The following examples il}ustrate the present
33 invention.
34 Example 1
This example shows that the presence of methyl
36 p-toluene sulfonate in a film of a poly(parabanic acid)
37 causes the film to become insoluble in dimethyl formamide
121~386
1 when it is exposed to heat for a short period of time.
2 Films (2 mils thick) were cast from each of the
3 following solutions; the poly(parabanic acid) used was
4 PPA-M.
Solution A was prepared by dissolving 600 g. PPA-M
6 and 0.24 g. zelec (a release agent) in 2400 g. dimethyl-
7 formamide.
8 Solution B was prepared by dissolving 600 g. PPA-M,
9 0.24 g. zelec (release agent), and 3.0g. methyl p-toluene-
sulfonate in 2400 g. dimethylformamide.
11 Solution B was prepared by dissolving 600 g. PPA-M, 0.24 g.
12 zelec (release agent), and 3.0 g. m2thyl p-toluenesulfonate in 2400 g.
13 dimethylformamide.
14Solubility in DMF
15 FilmBefore Aging A~ed 1 h~ at 260C
16 A soluble solubl~
17 B soluble insoluble
18Soluble polyme~s become insoluble when
19Soluble polymers become insoluble when they cross-
link; therefore the sulfonate ester caused the polymer to
21 crosslink.
22 Example 2
23 This example shows that the sodium and copper
24 salts as well as the free acid form of sulfonated polysty-
rene caused PPA-M to crosslink when heated.
26 Films which were 80% PPA-M and 20% of one of the
27 sulfonated polystyrene resins shown in the table below
28 were cast from dimethylformamide. For comparisons, a
29 film of PPA-M and film composed of 80~ PPA-M and 20~ poly-
styrene were similarly cast.
31 The solubilities of the films in dimethyl-forma-
32 mide before and after aging 1 hour at 260C are recorded
33 below (see Table). Only the films which contained a sul-
34 fonated polystyrene crosslinked when heated 1 hour at
260C. Unsulfonatedpolystyrene did not cause crosslinking.
121~86
g
1 Solubility in DMF
2 Be~ore After Aging
~ Film No. Polystyrene Aging 1 hr at 260C
4 h None soluble soluble
B 3~ sulfonated, sodium salt soluble insoluble
C 5% sulfonated, sodium salt soluble insoluble
D 2% sulfonated, free acid soluble insoluble
1 E 8% sulfonated, free acid soluble insoluble
t F ~% sulfonated, coppe~ salt soluble insoluble
G not sulfonated soluble soluble
14 Example 3
This example shows that the presence of
16 various sulfonated compounds in PPA-M films causes
17 the films to become insoluble in dimethylformamide
18 after they have been heated only 1 hour at 260C~
19 Solubility in DMF
Refore After Aging
P lm Additive ~wt.~) Aging 1 hr at 26~C
A None soluble soluble
B methvltoluene sulfonate ~1) soluble insoluble
C p-toluene sulfonic acid (1) soluhle insoluble
D 2-hydroxy-4 ~ethoxy-5-sulfo- soluble insoluble
benzophenone ~1)
E 5% sulfonated polystyrene, soluble insoluble
F 8% sulfonated polystyrene, soluble ins
free acid ~1)
