Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates to a thermoplast:ic elastomeric
composition comprising a blend of (~) a high molecular weight
copolymer of ethyl or butyl acrylate or rnixtures thereof with
an ethylenic monomer containing an acid group and (s) a water-
S soluble polyvinyl lactam.
It has previously been proposed to provide thermoplastic
elastomeric compositions in the form of oil extended hydrogenated
block copolymers of styrene and conjugated dienes as described,
for example, in Haefele et al. 3,485,787. Such compositions are
unlike ordinary elastomers in that they possess the necessary
` strength without vulcanization or cross-linking and, therefore,
they permanently retain their thermoplasticity. Acrylic elas-
tomers have been made by chemically cross-linking polymers of
acrylic esters such as polymers of ethyl or butyl acrylate,
which polymers wi-thout cross-linking have inadequate tensile
strcngth for most purposes, but such cross-linking destroys or
greatly decreases the original thermoplasticity of the polymers.
It has also been proposed to react water-soluble poly (N~vinyl
lactams) with polymeric carboxylic acids (including copolymers)
to form water-insoluble compositions useful for a variety of
purposes as described ln Stoner et al. U.S. Patent 2,901,457;
and in Ono et al. U.S. Patent 3,975,570, in which it was proposed
to improve the moisture permeability of conventional pressure-
sensitive adhesives which are copolymers of alkyl acryla-tes
with acrylic or methacrylic acid by blending with them hydroxy-
ethyl cellulose, it was stated tha-t blends of such adhesives
with poly (vinyl pyrrolidone~ did not exhibit improved moisture
`~
- 2
:
permeabilityO It has also been proposed to react water-soluble
poly (N-vinyl lactams) with polymeric carboxylic acids (including
copolymers) to form water-insoluble compositions useful for a
variety of purposes, as described in Stoner et al. U.S. Patent
2,901,457. As pointed out by Stoner et al. at column 4, lines
56-73, the reaction product there described always has sub-
; stantially the same properties and contains the two polymeric
components in the same proportions regardless of the proportions
of the two used to make the product. The compositions of the
; 10 present invention, on the other hand, vary in properties and inproportions of components depending upon proportions of starting
materials.
A pressure-sensitive adhesive composition is known which
is a blend of a poly (N-vinyl lactam) with certain acrylic ester
copolymers of relatively low molecular weight. There are also
described and claimed in U.S. Patent 4,300,820 of Shah, a highly
water-sorptive composition which is a blend of large proportion
of a poly (N-vinyl lactam) with certain copolymers.
It has now been found that high molecular weight
~0 copolymers of ethyl or butyl acrylate or mixtures thereof with
acidic ethylenic monomers in which the acidic group is sulfonic,
phosphonic or carboxylic, which copolymers are thermoplastic, can
be converted into non-tacky, non-adhesive, strong and tough
elastomeric compositions without loss of thermoplasticity by
-- 3 --
`: ~
- blending with the copolymers of poly (N-vinyl lactam), the -total
blend containing from 2 to 15% of poly (N-vinyl lactam) b~
weight.
According to the present invention, therefore, there is
provided a thermoplastic elastomeric composition comprising an
optically clear blend of (A) a high molecular weight copolymer
of ethyl or butyl acrylate or mixtures thereof with from 2 to 10
by weight, based on the weight of the copolymer, of a copoly-
merizable ethylenic monomer containing an acid group and (s) a
water-soluble polymer of a vinyl lactam having the structure
~X~
C=o
N
CH--CH2
in which X represents an alkylene bridge having three to five
carbon atoms, said copolymer having a molecular weight of at
least 600,000 and a glass transition temperature from -10C. to
-50C., and said polymer being present in an amount of 2 to 15%
by weight of the blend and having a molecular weight of at least
10,000.
The copolymers employed in the present invention have
high molecular weights, from about 600,000 to 1,000,000 or more,
have glass transition temperatures from about -10 to about -50C.,
and are copolymers of ethyl or butyl acrylate or mixtures thereof
with ethylenic monomers containing an acid group which is carboxy-
lic, sulfonic or phosphonic, such as acrylic or methacrylic acid,
crotonic acid, maleic acid, 2-sulfoethylmethacrylate, and
l-phenylvinylphosphonic acid. Preferably, the acid group in the
ethylenic monomer is carboxylic, acrylic acid being the acidic
monomer of choice. The amount of copolymerizable ethylenic acid-
containing monomer in the copolymer may vary from 2 to 10~ by
- 4 _
": ~
26~3
- .~
weight of the copolymer, the balance being ethvl or butyl
acrylate.
The N-vinyl lactams, polymers of which can be used in
the present invention include those having the structure
~ X~
/
; ~N
C~l=CH2
in which X represents an alkylene bridge having 3 to 5 carbon
atoms, such as l-vinyl-2-pyrrolidone, 1-vinyl-5-methyl-2-
pyrrolidone, l-vinyl-2-piperidone, and N-vinyl-epsilon-
caprolactam; the polymers may have molecular weights from
10,000 to 1,000,000 or more. Polymers of l-vinyl-2-pyrrolidone,
i.e., those in which X represents -CH2CH2CH2- are preferred.
The amount of polymeric
- 4a -
` :
N-vinyl lactam in the blend can vary Erom 2 to 15~ by weight of
the total blend. Preferably the welght percent oE poly (N-vinyl
lactam) based on the total weight of polymer and copolymer
Y should total from 5 to 15.
- 5 The copolymers employed in the composition of the
present invention can be prepared by conventional polymerization
processes in emulsion, in solu-tion, or in bulk; they may range
from about 600,000 to 1,000,000 or more in molecular weight,
preferably from 750,000 to 1,000,000 or more. The poly (N-vinyl
lactams) which are blended with the copolymers can also be pre-
pared by conventional procedures and are widely available
commercially.
The blended compositions can be made by mixing together
solutions oE the copolymers and of the polymeric N-vinyl lactams
in any desired vehicles or solvents which are miscible with each
other, then removing the vehicle or solvent, as by evaporation.
It is also possible to blend the copolymer with the polymer on
conventional mixing equipment such as a two-roll mill or in an
extruder.
Although different polymers and copolymers are normally
considered to be incompatible with one another when mixed, and
incapable of forming a homogeneous blend having properties
different from either of the components, the blends of the present
invention are optically clear and transparent in the absence of
any fillers or similar additives, indicating that the blends are
homogeneous at least to the extent that no discre-te particles of
`~ either component grea-ter than 4,000 A in diameter are present.
.
; 5
. Because of the thermoplas-ticity of the blended
compositions of the present invention, they can be repea-tedly
formed or shaped simply by heating to elevated temperatures, e.g.,
- 170--200C. and subjecting them to pressure, as for example in a
S mold or in an extruder nozzle. When cooled to room temperature,
the shaped articles made from the blended composition are
transparent, extremely tough, and elastic in nature. They can be
stretched to at leas-t 500~ of their original length, from which
they rapidly regain their original length when tension is
released.
The blended compositions exhibit considerably enhanced
tensile strength and modulus of elasticity, and somewhat decreased
elongation as contrasted to the non-blended acrylate copolymers.
The magnitude of these properties of the blended compositions
depends upon the amount of acidic comonomer, molecular weight of
the copolymer, the relative proportion of poly (N-vinyl lactam) to
copolymer, and the molecular weight of the poly (N-vinyl lactam).
In general, an increase in the magnitude of the above variables
results in increase of tensile strength of the blended composi-
tion.
In order to achieve desirable properties and servicelife of the blended compositions, it may be desirable to include
in the composition in addition to the polymeric N-vinyl lactam
and the copolymer, conventional stabilizers, pigments, fillers
and other compounding agents.
These blended compositions are especially suited for
acceptable performance in an environment where there is exposure
. . .
to sulfur-modified oils at elevated temperatures, under which
conditions the unsaturated rubbers of commerce fail. The ~crylic
~lastomers , as a class, are not recommended for use in water,
steam, or water soluble materials, such as methanol or ethylene
glycol. An important application of these blended compositions is
as seals and gaskets for auto enyines and other machines.
The following specific examples are intended to
illustrate more fully the nature of -the present invention without
acting as a limitation upon its scope.
Examples 1-6
Copolymers of ethyl acrylate with three different
proportions of acrylic acid were prepared by conventional
solution polymerization procedures by dissolving the
desired proportions (40% solids) of monomers in ethyl acetate
; 15 and by employing as the initiator of polymerization a small
amount (0.1% by weight of the monomers) of a free radical
genera-tor such as benzoyl peroxide or 2-t-butylazo-2-cyano
propane. Polymerization was carried out at 80-90C. to a high
degree of conversion. The peak molecular weight as determined
by gel permea'ion chroma-tography and stress strain properties as
determined by ASTM procedure D~412 were as follows:
Ethyl Acrylate Copolymers
Tensile Strenth,
Wt% _ 3 PSI at Ultimate
No. Acrylic Acid I Mp x 10 100% 300% jBreak Elongation, %
1 3 923 38 50 85 1155
2 4 1076 40 71 106 1285
3 5 1076 _ _ 202 670
73
`:
Blends of the copolymers with poly (vinyl pyrrolidone),
grade K-90 (M.w. 360,000), were prepared by dissolving appropriate
amounts of the respective copolymer and the polymer in chloroform
and then heating the resulting solution at 120C. under reduced
pressure to evaporate the solvent and leave a transparent solid
polymeric residue. The dry polymeric blends were then formed
into sheets 2-3 mm in thickness in a press heated at 170C. and
their stress-strain characteristics determined by the same ASTM
procedure as above. The results were as follows:
Blend of Copolymer with Poly(Vinyl pyrrolidone)
Copolymer Wt% of Poly(vinyl Tensile Strength, PSI at Ultima-te
~o.~vrrolidone) 100% 300% BreakElongation, %
~ ............................. _
1 5 63 100 323 706
:- 1 10 76 156 508 778
2 5 67 129 508 1040
; 2 10 90 200 705 738
3 5 106 229 557 ~53
120 312 996 773
Example 7
A copolymer of 97.5% by weight of butyl acrylate and
2.5% by weight of acrylic acid was prepared by polymerizing the
monomers in solution (50% solids) in refluxing ethyl acetate
using the same inltiator as in -the preceding Examples. The
, resulting copolymer was isolated by heating the solution at 120~C.
under vacuum to evaporate volatile materials. A mixture of 8.57
grams of the dry copo].ymer and 0.95 grams of poly (N-vinyl-2-
,
,
-- 8 --
.. . . .. . ...
-' ,
Z~73
pyrro].idone) having a molecular weight of 360,000 was dissolved in
50 ml of chloroform and the solution was heated at 120C. in
vacùum to evaporate the solvent, leaving the solid transparent
blended polymer composition. The blended composition was formed
into a sheet as in the preceding Examples. The formed sheet was
transparent, tough and elastic but more compliant than any of the
blends of Examples 1-6.
B
.
