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TECHNICAL FIELD
This invention relates to anionically-prepared copolymers containing
organometallic-substituted styrene.
BACKGROUND ART
According to Odian, Principles of Polymerization, 2nd Ed.,
Wiley-Interscience, p. 18, (1981) polymers fall into three structural
groups: linear, branched and crosslinked. Branched polymer molecules are
those in which there are side branches of linked monomer protruding from
various central branch points along the main polymer chain and that have
several idealized configurations. Branched polymers are known in at least
three configurations. They may be "comb-like" where each branch is of
equal length, "dendritic" where branches occur on branches (series
branching), or "star-like" where all branches radiate from a single point.
Branching often imparts various desirable properties, for example, branched
polymers have been made that have improved melt flow and processability.
Additionally, appropriate branching disrupts long linear polymer backbones
to thereby reduce crystallinity. In free radical and cationic
polymerization processes, for example in the production of polyethylene,
branching is largely uncontrolled and its extent is dependent on
polymerization variables. In some cases branching can be as high as 15-30
branches per 500 monomer units. In contrast, anionic polymerization
processes yield very narrow molecular weight distributions and a unique
structure. Branched polymer structures produced by anionic polymerization
are generally star shaped (arrayed about a central point or nucleus)
although the structure can be varied by coupling together individually
prepared arms of different structure.
Such polymers are described by St. Clair in U.S. Pat. No. 4,391,949 where
"asymmetric" star block copolymers are prepared by mutually linking
together individually prepared living polymers, which may be represented
by (AB)Li and (C)Li, with polyalkenylaromatic linking reagents. The
structural formula describing the resulting polymer is given as
(A--B).sub.x --Y--(C).sub.z, where x plus z is greater than six. A
statistical distribution of polymer products would be obtained from this
process, where the average structure is equal to the mole ratio of the
respective charges. Further chain growth would only be possible through
the linking nucleus Y.
Crossland, U.S. Pat. No. 4,010,226, has also recognized the problem of
preparing block polymers with an asymmetric configuration and, to avoid
the statistical distribution of polymers obtained by St. Clair, first
coupled a set of polymer arms with divinylbenzene, then continued the
polymerization, utilizing the anionic centers that remain on the
divinylbenzene residue, to produce a different set of arms bound to the
same nucleus. The number of new arms grown would thus equal the number of
arms coupled together, since linking with divinylbenzene (DVB) is a
non-terminating process and each newly grown arm would have an anionic
terminus. Fahrbach, U.S. Pat. No. 4,086,298, discloses star-block
copolymer having a mixture of arms where some arms are formed by first
polymerizing styrene with alkyllithium to form living polymer blocks,
represented by (A)Li, and then adding a mixture of styrene and butadiene
to form a graded copolymer represented by A--B.fwdarw.A' where the arrow
represents a graded segment. Other arms are made up of only the
butadiene-styrene graded copolymer segment. These arms are then linked
together with a polyfunctional coupling agent, such as DVB, to give
star-branched polymers. U.S. Pat. Nos. 4,221,884, 4,248,980, 4,248,982,
4,248,983, and 4,248,984, Bi and Milkovich, describe a similar series of
polymers in which more complex polymer arm segments are linked together
using a polyalkenyl aromatic, such as divinylbenzene, to form an
asymmetric star molecule.
Prudence (U.S. Pat. No. 3,949,020) prepares branched block polymers by a
method wherein divinylbenzene is added with the diolefin monomer to a
polystyryllithium initiator. However, according to Bi and Fetters
(Macromolecules 9, 732-742 [1976]), such a method leads to gelation when
the divinylbenzene/initiator ratio is three or greater.
Martin, in U.S. Pat. Nos. 4,080,400, 4,143,089, 4,148,838, and 4,273,896,
describes a composition obtained from the linking together of anionically
active polymers (from, e.g., styrene) with silanes of the formula,
X.sub.4-a-b Si(R).sub.b (CH.dbd.CH.sub.2).sub.a, where X is a displaceable
group, R is alkyl, a is 1 to 4 and b is 1 to 3. One of the stated objects
of these patents is to couple polymeric carbanions with silanes and then
form new carbanions which can be used to initiate the polymerization of
cyclic silicones or "other unsaturated monomers". No disclosure is
provided directed towards the step of using other unsaturated monomers
except for certain unspecified hydrocarbon/siloxane block polymers.
It has been established [Nametkin, Chemical Abstract Nos. 85:47314a (1976),
87:185046g (1977), and 89:110569n (1978)] that vinylsilanes of the type
described by Martin will copolymerize in an anionic fashion, for example
with butadiene; however, reactivity is very low, with up to 300 hours
required for good conversion. Furthermore, copolymers of vinyl silanes
with dienes initiated by butyl lithium are unimodal but exhibit peak
broadening due to the occurrence of chain termination reactions caused by
spontaneous cleavage reactions producing lithium hydride (Nametkin,
Chemical Abstract No. 93:168679x, 1980). Loss of LiH during anionic
homopolymerization of vinyltrimethylsilane has also been observed and has
been used to explain the poor conversion and spread in molecular weight
distribution observed in these polymers [Nametkin, Dokl. Nauk SSSR, 215,
861 (1974)]. Chaumont [Eur. Poly. J. 15, 537 (1979)] prepared vinylsilyl
terminated polystyrenes via anionic polymerization; however, it was
necessary to cap the polymer anion with diphenylethylene in order to
reduce side reactions.
Chlorosilane-substituted styrenes are well-known compounds and have been
used, for example, to prepare polysiloxane macromolecular monomers
[Kawakami, Polymer J., 14, 913 (1982)]. Chromatography gels have been
described based on poly-.alpha.-methylstyrene dianions and
chlorodimethylsilylstyrene [Greber, Angew. Makromol. Chem. 1971, 16/17,
325]. Compositions for the encapsulation of electrical equipment have been
derived from organosilicon monomers having styrenyl groups (Lewis, U.S.
Pat. No. 2,982,757). Hirao et al. (Macromolecules 1987, 20, 242) has
studied the anionic homopolymerization of (4-alkoxysilyl) styrenes and
reaction of the resultant homopolymer with polystyryllithium.
There has been no disclosure, however, of the use of
organometallic-substituted styrenes, e.g., chlorosilane-substituted
styrenes, in the preparation of condensed phase polymers.
SUMMARY OF THE INVENTION
The present invention provides elastomeric copolymers and block copolymers,
e.g., based upon styrene/isoprene, having a novel condensed phase
structure wherein polymer branches occur along the polymer backbone,
either at a predetermined location or at random locations. The polymers of
the present invention are made by a method which comprises the step of
reacting, under polymerization conditions, hydrocarbyl lithium initiator,
at least one anionically polymerizable compound, and an
organometallic-substituted styrene condensing agent. The reactants may be
added simultaneously to produce a copolymer with polymer branch segments
randomly located along the polymer backbone or sequentially to produce a
copolymer with branches located at the same predetermined location along
the polymer backbone. The resultant polymers may be further reacted with a
linking agent to form multi-arm copolymers. The method of making the
copolymers is claimed in U.S. application Ser. No. 107,262, filed Oct. 9,
1987.
The resultant elastomeric polymers are compatible with any of a wide
variety of known tackifier resins and plasticizers to produce unique
pressure-sensitive adhesive compositions. The pressure-sensitive adhesive
compositions U.S. application Ser. No. 107,289, filed Oct. 9, 1987.
Specifically, the method comprises the step of reacting, under
polymerization conditions, the following:
(a) hydrocarbyl lithium initiator;
(b) at least one anionically polymerizable compound; and
(c) a condensing agent having the general formula
CH.sub.2 =C(R')QY(R).sub.n (X).sub.m I
wherein
Y is tetravalent Si, Ge, Sn or Pb;
X is H, --OR", Cl, Br or F wherein R" is a monovalent lower alkyl group
having from 1 to 6 carbon atoms;
R is hydrogen, a monovalent lower alkyl group having from 1 to 6 carbon
atoms, or phenyl;
Q is phenylene;
R' is hydrogen, a monovalent lower alkyl group having from 1 to 6 carbon
atoms, or phenyl;
m is an integer of 1, 2, or 3; and
n is an integer equal to 3-m, in a mole ratio of (a) to (c) of about (1
+m):1 to form a condensed phase copolymer.
The elastomeric polymers are anionic copolymers comprising at least one
anionically polymerizable monomer and a condensing agent (I) monomer
wherein the mole percentage of condensing agent (I) in each copolymer
segment containing the condensing agent (I) is in the range of about 0.01%
to about 5%.
The polymers of this invention are generally copolymers of the condensing
agent (I) with conjugated diene monomer, or are block copolymers of
conjugated diene and vinyl aromatic monomers (wherein at least one block
is a copolymer of condensing agent monomer and either diene or vinyl
aromatic monomer). The monovinyl aromatic monomer yields a hard polymer
segment having a high T.sub.g, i.e., above 25.degree. C. The conjugated
diene monomer yields a soft (generally elastomeric) polymer segment having
a low T.sub.g, i.e., not greater than about 0.degree. C.
The polymers of the invention are preferably elastomeric anionic polymers
comprised of conjugated diene monomer, typically containing 4 to 12 carbon
atoms, monoalkenyl or monovinyl aromatic monomer and the condensing
reagent (I) wherein the mole percent of condensing reagent in a polymer
segment containing such reagent is about 0.01 to about 5.0, preferably
about 0.02 to about 2.0. Typically, the copolymer contains on a weight
basis from about 50% to about 90% conjugated diene and about 50% to about
10% monoalkenyl or vinyl aromatic monomer.
In one embodiment, branch points are introduced at predetermined loci in
the polymer chain by addition of condensing agent in a sequential fashion,
i.e., after formation of a living polymer segment via conventional anionic
polymerization techniques. Thus, copolymer is prepared by first forming a
living linear polymer segment, then reacting the living polymer segment
with the condensing reagent to form a condensed living copolymer and next
polymerizing therewith additional polymerizable compound to form a
condensed phase block copolymer. Such a block copolymer may be represented
by the following general formula:
(A).sub.x Z.sub.q --B
where:
A is a nonelastomeric polymer segment based on a monovinyl aromatic
compound such as styrene, alpha-methylstyrene, para-methylstyrene, and
t-butyl styrene;
B is an elastomeric polymer segment based on a conjugated diene compound,
such as butadiene, isoprene, and piperylene;
Z is the residue of a condensing reagent having the general formula
CH.sub.2 =C(R')QY(R).sub.n (X).sub.m I
where
X, R, Y, Q, R', m and n have been defined above;
q is an integer from 1 to about 10;
x is an integer from 2 to about 10; and
wherein the mole percentage of Z in the segment (A).sub.x Z.sub.q is in the
range of about 0.1% to about 5%.
The method comprises the further step of contacting the resulting condensed
phase block copolymer of Formula II with a multifunctional linking agent
such as a polyalkenyl aromatic linking agent under reactive thereby
forming a multi-arm condensed phase block copolymer. Such a block
copolymer may be represented by the following general formula:
[(A).sub.x Z.sub.q --B].sub.y L.sub.z III
where:
A, Z, B, x, and q have been defined above;
L is the residue of a multifunctional linking agent;
z is an integer from zero to about 10;
y is an integer from 1 to about 50 and, when y is 1, z is zero;
wherein the mole percentage of Z in the segment (A).sub.x Z.sub.q is in the
range of about 0.1% to about 5%.
The method also comprises first forming a living linear polymer segment,
adding a second polymerizable compound to form a living linear block
copolymer segment, then reacting the living linear block copolymer segment
with the condensing reagent to form a condensed living block copolymer,
and next polymerizing therewith additional polymerizable compound to form
a condensed phase block copolymer represented by the following general
formula:
(A--B(.sub.x Z.sub.q --B IV
where: A, B, Z, x and q are defined above and wherein the mole percentage
of Z in the segment (A--B).sub.x Z.sub.q is in the range of from about
0.01% to about 1%.
The method comprises the further step of contacting resulting block
copolymer IV with a multifunctional linking agent under reactive
conditions thereby forming a multi-arm condensed phase block copolymer
represented by the general formula shown below:
[9A--B).sub.x Z.sub.q --B].sub.y L.sub.z V
wherein: A, B, Z, L, x, q, y and z are defined above and wherein the mole
percentage of Z in the segment (A--B).sub.x Z.sub.q is in the range of
about 0.01% to about 1%.
Other condensed phase block copolymers besides II and IV are also
contemplated and may be linked to form multi-arm condensed phase block
copolymers other than III and V. Such block copolymers, including II, III,
IV, and V, may be represented by the general formula:
[(W).sub.x Z.sub.q --W'].sub.y L.sub.z VI
wherein: W is selected from the group consisting of A, B, BA, and AB, W' is
selected from the group consisting of B, BA and AB, and A, B, Z, L, x, q,
y and z are defined above, and wherein the mole percentage of Z in the
segment (W).sub.x Z.sub.q is in the range of from about to about 5%.
In a second embodiment, randomly placed branch centers are generated on the
polymer chain by polymerization of a mixture of condensing agent and
anionically polymerizable monomer or monomers. The method involves
simultaneously reacting a hydrocarbyl lithium initiator, polymerizable
compound, and condensing reagent to form a living condensed phase
copolymer having a randomly-branched structure which may be represented by
the following general formula:
B/Z VII
wherein B and Z are defined above, and wherein the mole percentage of Z in
the copolymer is from about 0.01% to about 1%.
Copolymer VII may be further reacted with a multifunctional linking agent,
thereby forming a multi-arm condensed phase copolymer. Such a copolymer
may be represented by the general formula:
(B/Z).sub.y L.sub.z VIII
wherein B, Z, L, y and z are defined above, and wherein the mole percentage
of Z in the unlinked copolymer is from about 0.01% to about 1%.
Monovinyl aromatic monomer may be polymerized with condensing reagent to
form a randomly-branched living copolymer which may be further treated by
adding a different polymerizable compound such as butadiene, isoprene, or
piperylene, after completion of the simultaneous reaction and permitting
the different polymerizable compound to copolymerize with the living
copolymer to form a condensed phase block copolymer. The resultant
copolymer may be further reacted with a multi-functional linking agent
thereby forming a multi-arm condensed phase block copolymer. Such block
copolymer may be represented by the general formula:
[(A/Z)--B].sub.y L.sub.z IX
wherein A, B, Z, L, y and z are defined above, and wherein the mole
percentage of Z in the segment A/Z is in the range of from about 0.1% to
about 5%.
In addition, a randomly-branched living copolymer derived from monovinyl
aromatic monomer may be further treated by adding a mixture of a different
polymerizable compound and additional condensing reagent, after completion
of the simultaneous reaction, and permitting the mixture to copolymerize
with the living copolymer to form a block copolymer having "condensed"
structure randomly placed in both blocks. This block copolymer may be
further reacted with a multifunctional linking agent under reactive
conditions thereby forming a multi-arm condensed phase block copolymer.
Such a block copolymer may be represented by the general formula:
[(A/Z)--(B/Z)].sub.y L.sub.z X
wherein A, B, Z, L, y and z are defined above, and wherein the mole
percentage of Z in the segment A/Z is in the range of from about 0.1% to
about 5% and in the segment B/Z is from about 0.01% to about 1%.
Alternatively, a different condensed phase block copolymer may be prepared
by first forming a living linear polymer segment, adding a mixture of a
second polymerizable compound and the condensing reagent, and then
permitting the mixture to copolymerize with the living linear polymer
segment produced by polymerization of the first polymerizable compound.
The resulting block copolymer may be further modified by contacting it
with a multifunctional linking agent under reactive conditions thereby
forming a multi-arm condensed phase block copolymer. Such a block
copolymer may be represented by the general formula:
[A--(B/Z)].sub.y L.sub.z XI
wherein A, B, Z, L, y and z are defined above, and wherein the mole
percentage of Z in the segment B/Z is in the range of from about 0.01% to
about 1%. The unlinked block copolymer may be alternatively modified to
include an additional linear polymer segment to provide a block copolymer
which may be represented by the general formula:
A--(B/Z--A XII
wherein A, B and Z are defined above.
BRIEF DESCRIPTION OF DRAWINGS
Understanding of the invention will be facilitated by reference to the
drawings, wherein:
FIGS. 1 and 2 are graphs depicting the melt viscosity of untackified and
tackified polymers according to the invention and a styrene isoprene
linear triblock copolymer (Shell's Kraton.RTM. 1107) according to the
prior art as a function of shear rate; and
FIG. 3 is a graph depicting the steady shear viscosity of polymer according
to the invention and a styrene isoprene linear triblock copolymer (Shell's
Kraton.RTM. according to the prior art as a function of shear rate.
DETAILED DESCRIPTION
The initiators useful in the preparation of the copolymers of this
invention are known alkyllithium compounds such as methyllithium,
n-butyllithium and sec-butyllithium, cycloalkyllithium compounds such as
cyclohexyllithium, and aryllithium compounds such as phenyllithium,
naphthyllithium and the like.
Useful monoalkenyl aromatic monomers include styrene, ring-substituted
styrenes, and alpha-substituted styrenes. These can be used individually
or as mixtures. Preferred are styrene, alpha-methylstyrene,
paramethylstyrene, and t-butylstyrene. Useful conjugated diene monomers
have 4 to 12 carbon atoms, e.g., 1,3-butadiene, isoprene, piperylene,
myrcene, 2,3-dimethylbutadiene, and the like. These also may be used
individually or as mixtures. Preferred conjugated diene monomers are
1,3-butadiene, isoprene, and piperylene.
The "condensed phase" or branch structure of the copolymers of this
invention is formed by addition of a multifunctional "condensing" reagent
to create points at which two or more polymer segments are connected
together by the reagent. The terminology "condensed" is derived from the
term "polycondensation" which, according to Chemical Kinetics edited by C.
H. Bamford (Elsevier, 1976), is used to denote those polymerization
reactions which proceed by a propagation mechanism in which an active
polymerization site disappears every time one monomer equivalent reacts.
Also, Webster's 7th Collegiate Dictionary defines condensation as a
chemical reaction involving union between atoms in the same or different
molecules often with elimination of a simple molecule to form a more
complex compound of often greater molecular weight. It should be pointed
out that the linking processes that occur with "condensing" reagents and
linking agents such as divinylbenzene are very different. "Condensing"
reagents yield a polymeric species with a single anionic charge, whereas
divinylbenzene joins polymer segments together to give a nucleus
containing a number of anions equal to the number of chains linked
together. Thus, the potential for network formation and gelation
associated with the method of Prudence is avoided by use of "condensing",
rather than linking, agents.
Suitable condensing agents are compounds having dual functionality, the
first derived from at least one anionically polymerizable group and the
second from at least one other group capable of undergoing one or more
nucleophilic displacement reactions. One active chain is terminated by
each nucleophilic displacement reaction. The relative reactivity of the
two groups is unspecified, such that anion addition may be faster or
slower than termination, and the preference of relative reactivity for the
two groups will depend on the final polymer structure desired. The
condensing agent must be compatible with anionic polymerization processes;
i.e., its anionically polymerizable group(s) should be capable of
reinitiating polymerization of itself or other anionically polymerizable
monomers. Useful condensing agents are molecules of the following
structure:
##STR1##
wherein Y is tetravalent Si, Ge, Sn, or Pb;
X is H, --OR", Cl, Br, or F, wherein R" is a monovalent lower alkyl group
having from 1 to 6 carbon atoms;
R is hydrogen, a monovalent lower alkyl group having from 1 to 6 carbon
atoms, or phenyl;
R' is hydrogen, a monovalent lower alkyl group having from 1 to 6 carbon
atoms, or phenyl;
m is an integer of 1, 2, or 3; and
n is an integer equal to 3-m.
The displaced group, X, does not subsequently react in a side reaction with
polymer anions. The alkenylaromatic group may be substituted in the alpha
position with alkyl or aromatic moieties, R', to modify condenser
reactivity. The alkenylaromatic group may also be further substituted on
the aromatic ring with groups such as alkyl, phenyl, alkoxy, dialkylamino,
and the like, which are not reactive toward polymer anions. Preferred
condensing agents are the silylstyrenes for which R is methyl, R' is
hydrogen, Y is silicon, and X is F, Cl, Br, or methoxy, or, most
preferably, X is F or Cl.
The above-described condensing agents are readily prepared via an in situ
Grignard reaction involving, e.g., para-chlorostyrene and
chloroalkylsilane. Other routes for the preparation of these compounds
have been described by Chernyshev (Chemical Abstracts 62:6502c). The
condensing agents are utilized to achieve a branched or condensed phase
polymer structure by addition of 1/n mole of multifunctional condenser per
mole of active polymer anions, where n is the total number of anionically
reactive sites on the condenser molecule. The mole percentage of
condensing agent monomer in any particular polymer segment is generally
within the range of from about 0.01% to about 5%, preferably, within about
0.02% to about 2%. (For monovinyl aromatics, the range is about 0.1-5%,
with about 0.2-2% preferred; for conjugated dienes, the range is about
0.01-1%, with about 0.02-0.2% preferred.)
Conventional anionic polymerization techniques are utilized in preparing
the condensed phase polymers of this invention. Thus, the polymerization
is carried out in an inert atmosphere in the absence of moisture, air, or
other impurities which are known to react with polymer anions. A
temperature between 0.degree. C. and 100.degree. C., more preferably
between 30.degree. C. and 80.degree. C., is maintained. Suitable solvents
are hydrocarbon solvents which may be aliphatic, cycloaliphatic, or
aromatic. Optionally, ethers such as tetrahydrofuran, diethylether, or
other similar solvents, may be used either alone or as mixtures with the
hydrocarbon solvent.
If so desired, linking agents may be used to increase the degree of
branching of the condensed phase copolymers or block copolymers beyond
that achieved via the condensing agent. In this way, symmetrical polymer
architectures such as radial or star structures, etc., can be created, the
final structure being a function of the linking molecule Such
multifunctional linking agents are well-known in the art and are detailed,
e.g., in U.S. Pat. No. 3,985,830. Preferred examples of such compounds are
1,2-dibromoethane, silicon tetrachloride, dichlorodimethyl silane, phenyl
benzoate, and divinylbenzene. The quantity of linking agent used to
further combine the anionically-terminated species of this invention is
derived from the actual content of active polymer chain ends in the
polymerization mixture. Generally, a mole equivalent of linking agent to
chain ends is required when the agent links polymer chain ends by
termination reactions, as is the case for, e.g., dibromoethane and silicon
tetrachloride. When non-terminating agents such as divinylbenzene are
utilized to form star polymers, higher mole ratios are used, generally
within the range of from about 3:1 to about 20:1 or higher. The preferred
range is from about 3:1 to about 8:1.
The molecular weights of the condensed phase polymers may be varied to suit
an individual application. When conjugated diene monomers are utilized,
preferred molecular weights are generally in the range of from about
50,000 to about 200,000. In the case of additional linking of these
copolymers via, e.g., divinylbenzene to form star polymers, molecular
weights may exceed 1,000,000. Condensed phase block copolymers can have
individual segment molecular weights that are typically preferred in the
art, i.e., from about 5,000 to about 50,000 for the glassy or hard
monoalkenyl aromatic phase and from about 50,000 to about 250,000 for the
elastomeric or rubbery conjugated diene phase.
Both the conjugated diene-based condensed phase copolymers and the
condensed phase block copolymers (and linked structures derived from each)
are useful in preparing pressure sensitive adhesive (PSA) compositions.
The block copolymers utilized for this purpose typically have a hard phase
content of from about 10% to about 30% by weight (the remainder
constituting the rubbery phase). The PSA compositions may be formed by
mixing condensed phase copolymer or block copolymer and tackifying resin,
either in solution, as dry granules, or by melt blending. Any of the
resinous (or synthetic) materials commonly used in the art to impart or
enhance the tack of PSA compositions may be used as a tackifier. Examples
include rosin, rosin esters of glycerol or pentaerythritol, hydrogenated
rosins, polyterpene resins such as polymerized .beta.-pinene,
coumaroneindene resins, "C5" and "C9" polymerized petroleum fractions, and
the like. The use of such tack-modifiers is common in the art, as is
described in the Handbook of Pressure-Sensitive Adhesive Technology edited
by Donatas Satas (1982). Tackifying resin is added in an amount sufficient
to provide a tacky composition. This is typically achieved by adding from
about 50 parts to about 300 parts by weight of tackifying resin per 100
parts by weight of condensed phase copolymer.
The tackifier resin is selected to provide the copolymers of the invention
with an adequate degree of tack to maintain in the resultant composition
balanced PSA properties including high shear and peel. As is known in the
art, not all tackifier resins interact with the same base elastomer in the
same manner; therefore some minor amount of experimentation may be
required to select the appropriate tackifier resin and to achieve optimum
adhesive performance. Such minor experimentation is well within the
capability of one skilled in the adhesive art. Along these lines,
selection of the resin should take into account whether the resin
associates with the thermoplastic styrene segment or the rubbery segments.
It is also within the scope of this invention to include various other
components in the adhesive formulation. For example, it may be desirable
to include such materials as plasticizers, pigments, fillers, stabilizers,
and/or various polymeric additives.
The PSA compositions can be applied as solutions, dispersions, or as hot
melt coatings to suitable flexible or inflexible backing materials to
produce PSA-coated sheet materials. Flexible backings may be of any
material which is conventionally utilized as a tape backing or may be of
any other flexible material. Representative examples of flexible tape
backing materials include paper, plastic films such as poly(propylene),
poly(ethylene), poly(vinyl chloride), polyester [e.g., poly(ethylene
terephthalate)], cellulose acetate, and ethyl cellulose. Backings may also
be of woven fabric formed of threads of synthetic or natural materials
such as cotton, nylon, rayon, glass, or ceramic material, or they may be
of a nonwoven fabric such as air-laid webs of natural or synthetic fibers
or blends of these. In addition, the backing may be formed of metal,
metallized polymeric film, or ceramic sheet material. The PSA-coated sheet
materials may take the form of any article conventionally known to be
utilized with PSA compositions such as labels, tapes, signs, covers,
marking indices, and the like.
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