 |
Description  |
|
|
BACKGROUND
1. Preparation of Hydrocarbon Star Polymers
Star polymers derived from unsaturated hydrocarbon monomers, such as
styrene, butadiene and isoprene, have been obtained by preparing
lithium-terminated "living" polymers via anionic polymerization and then
coupling the "living" polymer chains by reacting them with various
polyfunctional linking agents. This has usually produced hydrocarbon star
polymers with relatively few (3-12) arms. Hydrocarbon star polymers with a
larger number of arms (e.g., 15-56) have been obtained by sequential
anionic polymerization of difunctional monomers (e.g., divinylbenzene)
with monofunctional monomers (e.g., styrene) or with monomers that behave
as monofunctional monomers (e.g., isoprene). Both methods of preparing
hydrocarbon star polymers have been reviewed by B. J. Bauer and L. J.
Fetters in Rubber Chem. and Technol. (Rubber Reviews for 1978), Vol. 51,
No. 3, pp 406-436 (1978).
A. Aoki et al., U.S. Pat. No. 4,304,881 (1981), prepared styrene/butadiene
"living" polymers by anionic polymerization and then coupled them by
reaction with silicon tetrachloride to produce a 4-arm star polymer having
a silicon core in Example 4.
H. T. Verkouw, U.S. Pat. No. 4,185,042 (1980), prepared a polybutadiene
"living" polymer by anionic polymerization and then prepared a
silicon-containing 3-arm star by reacting the "living" polymer with
.gamma.-glycidoxypropyltrimethoxysilane in Example 5.
R. Milkovich, U.S. Pat. No. 4,417,029 (1983), prepared a hydrocarbon star
polymer having 10 arms of 2 kinds. Of the 10 arms, 5 were a diblock
copolymer of polystyrene (Mn=12,300) and polyisoprene (Mn=52,450). The
other 5 arms were polyisoprene (Mn=52,450). The hydrocarbon star polymer
was prepared by charging sec-butyllithium, then styrene, them more
sec-butyllithium, then isoprene, then divinylbenzene at a mole ratio of
divinylbenzene to sec-butyllithium initiator of 5.5:1. Subsequent reaction
of the "living" lithium sites in the core with carbon dioxide or ethylene
oxide produced carboxylic acid or hydroxyl groups respectively in the core
in Example 2.
T. E. Kiovsky, U.S. Pat. No. 4,077,893 (1978), suggested reacting
lithium-terminated "living" polymers derived from diene monomers (e.g.,
butadiene or isoprene) with divinylbenzene to form a 4-25 arm star polymer
and then reacting the (still living) star polymer with the same or a
different monomer to grow further polymer chains from the core. Thus, star
polymers having two kinds of arms were proposed in Col. 5, lines 40-58.
W. Burchard and H. Eschway, U.S. Pat. No. 3.975,339 (1976), reacted a
mixture of 50% divinylbenzene and 50% ethylvinylbenzene in toluene with
n-butyllithium to produce a polydivinylbenzene microgel having 270 active
lithium-carbon bonds per molecule. This was subsequently reacted with
styrene to produce a star polymer having 270 arms, each arm having a
weight average molecular weight of 17,500 in Example 1.
H. Eschway, M. L. Hallensleben and W. Burchard, Die Makromolekulare Chemie,
Vol. 173, pp 235-239 (1973), describe the anionic polymerization of
divinylbenzene using butyllithium to produce soluble "living" microgels of
high molecular weight. These microgels were then used to initiate
polymerization of other monomers to produce star polymers. The number of
arms depended on the number of active sites in the "living" microgel,
which in turn depended on the mole ratio of divinylbenzene to butyllithium
initiator. To avoid gellation it was necessary to work at low
concentrations (e.g., 2.5% in benzene).
H. Eschway and W. Burchard, Polymer, Vol. 16, pp 180-184 (March, 1975),
prepared a star polymer having 67 polystyrene arms and 67 polyisoprene
arms by sequential anionic polymerization of styrene, divinylbenzene and
isoprene. Low concentrations of monomer were used to avoid gellation.
2. Preparation of Acrylic Star Polymers
In contrast to hydrocarbon star polymers (which may be prepared having
different arm sizes, different numbers of arms and even with two different
kinds of arms attached to the same core), acrylic star polymers have been
available only in a limited variety of structures.
G. W. Andrews and W. H. Sharkey, U.S. Pat. No. 4,351,924 (1982), prepared
acrylic star polymers having 3 or 4 hydroxyl-terminated arms by coupling
acetal-ended, "living" poly(methyl methacrylate) with
1,3,5-tris(bromomethyl)benzene or 1,2,4,5-tetrabis(bromomethyl)benzene.
O. W. Webster, U.S. Pat. Nos. 4,417,034 (Nov. 22, 1983) and 4,508,880 (Apr.
2, 1985), and W. B. Farnham and D. Y. Sogah, U.S. Pat. Nos. 4,414,372
(Nov. 8, 1983) and 4,524,196 (June 18, 1985) showed that acrylic star
polymers can be prepared via group transfer polymerization by coupling
"living" polymer with a capping agent having more than one reactive site
or by initiating polymerization with an initiator which can initiate more
than one polymer chain. Initiators that could produce acrylic star
polymers with up to 4 arms were demonstrated.
R. J. A. Eckert, U.S. Pat. No. 4,116,917 (1978), describing hydrocarbon
star polymers suggested that small amounts of other monomers (e.g., methyl
methacrylate) may be included (Col. 3, lines 22-28) and that ethylene
dimethacrylate may be used as a coupling agent (Col. 5, lines 22-28). A
similar suggestion is made by T. E. Kiovsky, U.S. Pat. No. 4,077,893,
cited above.
J. G. Zilliox, P. Rempp and J. Parrod, J. Polymer Sci., Part C, Polymer
Symposia No. 22, pp 145-156 (1968), describe the preparation, via anionic
polymerization, of a mixture of star polymers having 3 to 26 polymethyl
methacrylate arms attached to cores of ethylene glycol dimethacrylate. The
mixture also contained linear polymethyl methacrylate. The article says
the lengths of the individual branches were constant but that the number
of branches per star "fluctuates considerably", giving rise to a very high
polydispersity.
3. Uses of Star Polymers
Hydrocarbon star polymers have been used as additives to improve the impact
strength of polyphenylene ether resins--W. R. Haaf et al., U.S. Pat. No.
4,373,055 (1983); dry nylon--W. P. Gergen et al. U.S. Pat. No. 4,242,470
(1980); rubber-modified polystyrene--A. Aoki et al, U.S. Pat. No.
4,304,881, cited above; and chlorinated polyvinyl chloride resins M. H.
Lehr, U.S. Pat. No. 4,181,644 (1980).
Hydrocarbon star polymers have also been added to asphaltic concrete to
improve the service life--C. R. Bresson, U.S. Pat. No. 4,217,259 (1980);
to polyetherester resins to provide a desirable overall balance to
properties--R. W. Seymoure, U.S. Pat. No. 4,011,286 (1977), and to
lubricating oil to improve the viscosity index and act as a dispersant--T.
E. Kiovsky, U.S. Pat. No. 4,077,893 (1978).
Hydrocarbon star polymers have also been used to prepare thermoplastics
having good clarity by blending them with thermoplastic resins such as
methyl methacrylate/styrene/butadiene copolymers, polyester urethanes,
epoxides, acrylics, polycarbonates, polyesters, etc.,--E. L. Hillier, U.S.
Pat. No. 4,048,254 (1977).
Acrylic star polymers, because of the limited selection heretofore
obtainable, have not been put to as great a variety of uses.
SUMMARY OF THE INVENTION
"Living" acrylic star polymers are provided which comprise
a. a crosslinked core comprising a polymer derived from a mixture
comprising one or more monomers having at least two groups
##STR1##
polymerizable by a group transfer polymerization process b. attached to
the core, at least 5 arms comprising polymer chains derived from one or
more monomers polymerizable by a group transfer process, each such monomer
having one group
##STR2##
in each of which R is the same or different and is H, CH.sub.3, Ch.sub.3
Ch.sub.2, CN or CO.sub.2 R' and Z' is O or NR', wherein R' is C.sub.1-14
alkyl, and,
c. attached to the core or to at least some of the arms, "living" group
transfer polymerization sites.
Preferably, these polymers comprise
a. a core comprising a polymer derived from one or more monomers, each
having at least two groups,
##STR3##
b. attached to the core, at least 5 arms comprising polymer chains derived
from one or more monomers, each having one group,
##STR4##
in each of which R is the same or different and is H, CH.sub.3, CH.sub.3
CH.sub.2, CN or CO.sub.2 R' and Z' is O or NR', wherein R' is C.sub.1-4
alkyl.
wherein:
at least 50% of the molecules of such star polymer have from at least 5 to
2,000,000 arms, preferably at least 50, more preferably at least 100 arms.
In a preferred embodiment, such arms are of 1 or more sets of different
types, wherein:
i. the polymer chains comprising one of the types of arms have the same or
different molecular weight and are derived from the same or different
monomers as the polymer chains comprising the other said type of arms,
ii. the polymer chains comprising each type of arms have an arm
polydispersity of 1.0 to 2.0, where said arm polydispersity is the weight
average molecular weight divided by the number average molecular weight of
the polymer chains of that type, and
said star polymers, comprising both core and arms of 1 or more types, have
a molecular polydispersity of 1.0 to 2.0, wherein said molecular
polydispersity is the weight average molecular weight divided by the
number average molecular weight of the molecules.
This can be described as a bimodal or polymodal narrow polydispersity,
wherein each of the star polymer itself and the arms or separate sets of
arms have narrow polydispersities.
Also, preferably the star polymer of this invention is a soluble acrylic
star polymer comprising
a. a crosslinked core comprising a polymer derived from one or more
monomers, each having at least two groups,
##STR5##
b. attached to the core, at least 5 arms comprising polymer chains derived
from one or more monomers, each having one group,
##STR6##
in each of which R is the same or different and is H, CH.sub.3, CH.sub.3
CH.sub.2, CN or CO.sub.2 R' and Z' is O or NR', wherein R' is C.sub.1-4
alkyl,
wherein:
at least 50% of the molecules of such star polymers have a least from 5 to
2,000,000 arms, wherein the ratio of the number of arms to the number of
difunctional acrylic repeat units in the core is less than or equal to
1:1.
Such star polymers are made using a polymerization initiator in a molar
ratio of initiator to difunctional acrylic monomer of less than or equal
to 1:1, giving a crosslinked core and not gelling the reaction mixture. By
"soluble" is meant that nothing separates out from a solution of 1% by
weight stars in 99% solvent (toluene, glyme and/or THF) upon centrifuging
at 17,000 rpm for 30 minutes. Preferably the arms solubilize the core.
Such star polymers of a variety of types are provided that have useful
properties for applications in coatings, films, fibers and plastics. The
star polymers comprise (1) a core derived from a multifunctional monomer
having at least two polymerizable double bonds, (2) at least 5 polymeric
arms attached to the core and preferably (3) "living" group transfer sites
on the core and/or on the arms.
Such "living" star polymers comprise
a. a crosslinked core comprising a polymer derived from one or more
monomers having at least two carbon-carbon double bonds polymerizable by a
group transfer polymerization process, and
b. attached to the core, at least 5 arms comprising polymer chains derived
from one or more monomers polymerizable by a group transfer process, and,
c. attached to the core or to at least some of the arms, "living" group
transfer polymerization sites.
Preferably, in star polymers of the invention, the monomers having one
carbon-carbon double bond polymerizable by a group transfer polymerization
process are selected from
##STR7##
and mixtures thereof wherein: X is --CN, --CH.dbd.CHC(O)X' or --C(O)X';
Y is --H, --CH.sub.3, --CN or --CO.sub.2 R, provided, however, when X is
--CH.dbd.CHC(O)X', Y is --H or --CH.sub.3 ;
X' is --OSi(R.sup.1).sub.3, --R, --OR or --NR'R"; each R.sup.1 is
independently selected from C.sub.1-10 alkyl and C.sub.6-10 aryl or
alkaryl;
R is C.sub.1-20 alkyl, alkenyl, or alkadienyl; C.sub.6-20 cycloalkyl, aryl,
alkaryl or aralkyl; any of said groups containing one or more ether oxygen
atoms within aliphatic segments thereof; and any of all the aforesaid
groups containing one or more functional subsituents that are unreactive
under polymerizing conditions; and each of R' and R" is independently
selected from C.sub.1-4 alkyl.
More preferably, "living" acrylic star polymers of the invention comprise
a. a core comprising a polymer derived from one or more monomers having at
least two carbon-carbon double bonds polymerizable by an initiator, Q--Z,
and
b. attached to the core, at least 5 arms comprising polymer chains derived
from one or more monomers polymerizable by an initiator, Q--Z, and
c. attached to the core and/or to at least some of the arms the groups
Q--Z"--,
where
the group Q-- is the initiating moiety in a "living" group transfer
polymerization initiator, Q--Z, and where the group Z"-- is derived from
an activating substituent, Z, of a group transfer polymerization
initiator, Q--Z, and where the initiator, Q--Z, is capable of reacting
with a monomer having carbon-carbon double bonds to form a "living"
polymer chain having the group, Z"--, attached to one end of the "living"
polymer chain and the group, Q--, attached to the other, "living", end of
the "living" polymer chain and where, the "living" polymer chain is
capable of initiating polymerization of additional monomer, which can be
the same or different from the monomer used to prepare the "living"
polymer chain, to produce a larger "living" polymer chain having a group,
Z"--, attached to one end of the "living" polymer chain and the group,
Q--, attached to the other "living" end of the "living" polymer chain, and
where the group, Z"--, is the same as or an isomer of the group, Z--.
Also preferably in the preparation of star polymers of the invention, the
"living" group transfer polymerization sites are (R.sup.1).sub.3 M--
wherein:
R.sup.1 is selected from C.sub.1-10 alkyl and C.sub.6-10 aryl or alkaryl;
and
M is Si, Sn, or Ge.
Still more preferably, in polymer of the invention, the group, Q--, is
(R.sup.1).sub.3 M-- as defined above.
In such polymers, the group, Z--, is selected from
##STR8##
and mixtures thereof wherein: X' is OSi(R.sup.1).sub.3, --R, --OR or
--NR'R"; each R.sup.1 is independently selected from C.sub.1-10 alkyl and
C.sub.6-10 aryl or alkaryl;
R is C.sub.1-20 alkyl, alkenyl, or alkadienyl; C.sub.6-20 cycloalkyl, aryl,
alkaryl or aralkyl; any of said groups containing one or more ether oxygen
atoms within aliphatic segments thereof; and any of all the aforesaid
groups containing one or more functional substituents that are unreactive
under polymerizing conditions; and
each of R' and R" is independently selected from C.sub.1-4 alkyl
each of R.sup.2 and R.sup.3 is independently selected from H; C.sub.1-10
alkyl and alkenyl; C.sub.6-10 aryl, alkaryl, and aralkyl; any of said
groups except H containing one or more ether oxygen atoms within aliphatic
segments thereof; and any of all the aforesaid groups except H containing
one or more functional substituents that are unreactive under polymerizing
conditions; and
Z' is O or NR';
m is 2, 3 or 4;
n is 3, 4 or 5.
DETAILED DESCRIPTION OF THE INVENTION
In the preparation of the star polymers, use is made of "group transfer"
polymerization. By "group transfer" polymerization, is meant a
polymerization process in which polymerization of monomers having
carbon-carbon double bonds is initiated by certain initiators of the
formula Q--Z where Z is an activating substituent that becomes attached to
one end of the growing polymer molecule and where Q is a group that
continuously transfers to the other end of the growing polymer molecule as
more monomer is added to the growing polymer molecule. Thus,
polymerization of the monomer,
##STR9##
initiated by a group transfer initiator, Q--Z, proceeds as follows:
##STR10##
The group, Q, is thus an active site that can initiate further
polymerization of more monomer. The polymer molecule having the group, Q,
is referred to as a "living" polymer and the group, Q, is referred to as a
"living" group transfer initiating site.
The word "living" is sometimes used herein in quotation marks to indicate
its special meaning and to distinguish it from substances which are alive
in a biological sense.
More particularly, in the preparation of the star polymers, use is made of
the "group transfer" polymerization process of the general type described
in part of W. B. Farnham and D. Y. Sogah, U.S. Pat. No. 4,414,372 and by
O. W. Webster, U.S. Pat. No. 4,417,034, and in continuation-in-part U.S.
Pat. Nos. 4,508,880 Webster, granted Apr. 2, 1985, and 4,524,196 Farnham
and Sogah, granted June 18, 1985, the disclosures of all of which are
incorporated herein by reference. Group transfer polymerization produces a
"living polymer" when an initiator of the formula (R.sup.1).sub.3 MZ is
used to initiate polymerization of a monomer having a carbon-carbon double
bond.
In the initiator, (R.sup.1).sub.3 MZ, the Z group is an activating
substituent that becomes attached to one end of the "living" polymer
molecule. The (R.sup.1).sub.3 M group becomes attached to the other
("living") end of the "living" polymer molecule. The resulting "living"
polymer molecule can then itself act as an initiator for polymerization of
the same or a different monomer to produce a new "living" polymer molecule
having the Z activating substituent at one end and the (R.sup.1).sub.3 M
group at the other ("living") end. The "living" polymer may then be
deactivated, if desired, by contacting it with an active proton source
such as an alcohol. At this point, it might be useful to consider a
specific example--the group transfer polymerization of a specific monomer
(in this case, methyl methacrylate) using a specific group transfer
initiator (in this case 1-trimethylsiloxy-1-isobutoxy-2-methylpropene).
The reaction of 1 mole of initiator with n moles of monomer produces
"living" polymer as follows:
##STR11##
The
##STR12##
group shown on the left side of the "living" polymer molecule is derived
from the activating group, Z, which, in the initiator, was in the form
##STR13##
The --Si(CH.sub.3).sub.3 group on the right side ("living" end) of the
"living" polymer molecule is the (R.sup.1).sub.3 M group. The "living"
polymer molecule can act as an initiator to initiate polymerization of the
same or a different monomer. Thus, if the above "living" polymer is
contacted with m moles of butyl methacrylate in the presence of active
catalyst, the following "living" polymer is obtained:
##STR14##
If the resulting "living" polymer is then contacted with methanol, the
following deactivated polymer is obtained.
##STR15##
The star polymers of the invention are prepared by three different methods,
each making use of the group transfer process described above.
(1) Arm-First Method
In this method, a "living" polymer (the arm) is prepared by contacting a
monomer (A) having a carbon-carbon double bond with a group transfer
initiator, (R.sup.1).sub.3 MZ. The resulting "living" polymer is then
contacted with a multifunctional linking agent (monomer B) having at least
two polymerizable double bonds per molecule of linking agent. This
produces a star polymer having arms of polymerized monomer A attached to a
crosslinked core of polymerized monomer B. The active group transfer sites
in the core can be deactivated by reaction with a proton source.
(2) Core-First Method
In this method, a "living" core is prepared by contacting a group transfer
initiator, (R.sup.1).sub.3 MZ, with a multifunctional linking agent
(monomer B) having at least two polymerizable double bonds per molecule of
linking agent. The resulting "living" core is then contacted with a
monomer (A) to produce a star polymer having arms of polymerized monomer A
attached to a crosslinked core of polymerized monomer B. The active group
transfer sites at the ends of the arms can be reacted with a further
monomer or deactivated by reaction with a proton source.
(3) Arm-Core-Arm Method
In this method, a "living" polymer (the first arm) is prepared by
contacting a monomer (A) having a carbon-carbon double bond with a group
transfer initiator. (R.sup.1).sub.3 MZ. The resulting "living" polymer is
then contacted with a multifunctional linking agent (monomer B) having at
least two polymerizable double bonds per molecule of linking agent. This
produces a star polymer having arms of polymerized monomer A attached to a
crosslinked core of polymerized monomer B and having "living" group
transfer sites in the core. This is then contacted with a third monomer C
to grow arms out from the core. The monomers A and C can be the same or
different and the number of moles of A and C can be the same or different.
Thus, if desired, the two types of arms can have different molecular
weights and/or be derived from different monomers. Using two or more types
of "living" sites in the core, with differently reactible functional
groups on the arms, more than two different types of arms can result.
The multifunctional linking agent referred to above can be any molecule
having at least two polymerizable carbon-carbon double bonds. Examples of
suitable linking agents are:
ethylene dimethacrylate
1,3-butylene dimethacrylate
tetraethylene glycol dimethacrylate
triethylene glycol dimethacrylate
trimethylolpropane trimethacrylate
1,6-hexylene dimethacrylate
1,4-butylene dimethacrylate
ethylene diacrylate
1,3-butylene diacrylate
tetraethylene glycol diacrylate
triethylene glycol diacrylate
trimethylolpropane triacrylate
1,6-hexylene diacrylate
1,4-butylene diacrylate
Other useful ingredients and techniques will be found in the herein
incorporated above-mentioned U.S. Patents, especially U.S. Pat. No.
4,417,034-Webster, in columns 2-9.
INTRODUCTION TO EXAMPLES
The ingredients and procedures used in the examples are outlined below to
aid in understanding the invention.
I. Starting Materials
A. Initiators
Isobutyl Initiator
1-trimethylsiloxy-1-isobutoxy-2-methylpropene
##STR16##
Molecular Weight: 216.39 OH-Blocked Initiator
1-(2-trimethylsiloxyethoxy)-1-trimethylsiloxy-2-methylpropene
##STR17##
Molecular Weight: 276.52
B. Catalysts
TASHF.sub.2
Tris(dimethylamino)sulfonium bifluoride
##STR18##
TBAHF.sub.2 Tetrabutylammonium bifluoride
(C.sub.4 H.sub.9).sub.4 N.sup..sym. HF.sub.2.sup..crclbar.
TBACF
Tetrabutylammonium chlorobenzoate
C. Solvents
Glyme
1,2-dimethoxyethane
CH.sub.3 OCH.sub.2 CH.sub.2 OCH.sub.3
Others
Acetonitrile=CH.sub.3 CN
Xylene
THF=Tetrahydrofuran
##STR19##
D. Monomers
MMA
methyl methacrylate
##STR20##
M.W.=100.12 2EHMA
2-ethylhexyl methacrylate
##STR21##
M.W.=198.29 IEM
2-isocyanatoethyl methacrylate
##STR22##
M.W.=155.14 AMA
allyl methacrylate
##STR23##
M.W.=126.14 EGDMA
ethylene glycol dimethacrylate
##STR24##
M.W.=198.20 TEGDMA
tetraethylene glycol dimethacrylate
##STR25##
M.W.=330.34
II. Reactions
A. Polymerization of MMA with "Isobutyl Initiator"
##STR26##
B. Polymerization of MMA with "OH-Blocked Initiator"
##STR27##
C. Preparation of Star Polymers
Let "IS" represent the initiator, where "I" is the part that remains at the
beginning of the polymer chain (i.e.,
##STR28##
and where "S" represents the part of the initiator that goes to the other
("living") end of the polymer chain and is eventually removed by reaction
with methanol.
Let "M" represent a mono-methacrylate (e.g., MMA).
Let
##STR29##
represent a dimethacrylate (e.g., (EGDMA)
1. Preparation by "Arm First" Method
a. Polymerize "M"
3IS+15M.fwdarw.3 I-M-M-M-M-M-S
b. Add "M M"
##STR30##
c. Add Methanol to Remove "S" Final polymer is:
##STR31##
This star has 3 arms, each arm having been made from 5 monomer molecules.
Calculations:
##EQU1##
where (IS)=moles of initiator
(M-M)=moles of dimethacrylate in above example,
##EQU2##
2. Preparation by "Core First" Method
a. Polymerize "M M"
##STR32##
b. Add "M" and "M M"
##STR33##
c. Add Methanol to Remove "S" Final polymer is:
##STR34##
This star has 3 arms, each arm having been made from 5 monomer molecules.
3. Comparison of "Arm First" and "Core First" Method
a. Calculations are the same.
b. Structures are similar except for point of attachment of initiator
fragment "I".
(1) in "arm first" method, "I" becomes attached to outside ends of arms.
(2) in "core first" method, "I" becomes attached to core. Thus, since "I"
can be made to carry a functional group (e.g., an OH group when the
OH-blocked initiator is used), it is possible to make stars having
functional groups attached to the outside ends of the arms (by the "arm
first" method) or attached to the core (by the "core first" method).
4. Preparation of Giant Stars
Note that the size of the arms can be varied by changing the ratio (M)/(IS)
(where (M)=moles of mono-methacrylate and (IS)=moles of initiator). Long
arms are obtained when (M)/(IS) is large.
Note also that the number of arms can be varied by changing the ratio
(IS)/(M-M) (where (IS)=moles of initiator and (M-M)=moles of
dimethacrylate). A large number of arms results when (IS)/(M-M) is made
close to, but greater than 1.00.
Thus, if 1.05 moles of initiator are used with 1.00 moles of
dimethacrylate, the resulting star will have 21 arms.
##EQU3##
If the ratio (IS)/(M-M) is equal to or less than 1.00, as in a preferred
embodiment of the invention, the equation fails and the number of arms
cannot be calculated. In this case, (e.g., when (IS)/(M-M)=0.25) a
crosslinked core is obtained having a very large number of arms (e.g.,
200). Most of the examples show the preparation of these giant stars.
If a more lightly crosslinked core is desired, monfunctional acrylic can be
substituted for difunctional or higher functionality acrylics. The amount
of substitution can range from a small but effective amount for for the
purpose of decreasing the crosslink density up to 99% by weight
monofunctional ingredients, measured on the basis of total acrylics. Such
small amounts can be less than 1%, even as little as 0.1 or 0.01%, by
weight. Because of the flexibility in designing systems with from much to
little crosslinking in the core, when the claims say "crosslinked", they
mean more or less crosslinked, depending on the proportion of
monofunctional and multifunctional acrylics in the core.
In the examples and elsewhere, parts, percentages and proportions are given
by weight except where indicated otherwise.
EXAMPLE 1
This describes the preparation of a poly(methyl methacrylate) star polymer
by making the arms polymer first and then connecting the arm together.
The polymer is useful as a rheology control agent in high solids paints of
both the unicoat and color coat/clear coat types.
A three-neck round bottom flask fitted with a mechanical stirrer, a reflux
condenser, a rubber septum, a temperature probe and provision for
maintaining a dry nitrogen atmosphere was used as a.reaction vessel. After
purging with dry nitrogen, the flask was charged with the following
initial charge:
Initial Charge
1189.0 g glyme
15.54 g xylene
14.0 g 1-trimethylsiloxy-1-isobutoxy-2-methylpropene
To the initial charge was then added via syringe the initial catalyst:
Initial Catalyst
100 microliters of a 1.0 molar solution of tetrabutylammonium bifluoride
(TBAHF.sub.2) in glyme.
The mixture thus obtained was then stirred continuously under dry nitrogen
while adding the feed compositions shown below at constant rates via
syringe pumps. At the beginning of the first feed, a clock was started and
left running to keep track of the feeds and other steps. The feed
compositions and the clock times (in minutes) at which the additions of
the feed compositions were started and completed were as follows:
______________________________________
Clock Time (Minutes)
Addition Addition
Feed Feed Composition Started Completed
______________________________________
I 300 microliters, 0 90
1.0 M TBAHF.sub.2 and
5.3 g glyme
II 844.4 g methyl methacrylate
0 40
III 55.8 g ethylene glycol
55 70
dimethacrylate
______________________________________
During the additions of the feeds, the temperature gradually rose, reaching
a maximum of 86.degree. C. at a clock time of 30 minutes.
At a clock time of 55 minutes, before the addition of Feed III was started,
a 50 g portion of the reaction mixture (Sample 1) was removed for testing
and quenched by the addition of 2 ml methanol.
At a clock time of 100 minutes, the reaction mixture was quenched by the
addition of quencher:
Quencher
20 g methanol
The resulting clear solution of star polymer had a solids content of 43.1%
(vs 42.45% theoretical).
The arm polymer was present in Sample 1 at a solids content of 37.8% (vs
40.50% theoretical) indicating that about 94% of the methyl methacrylate
had polymerized at the time the sample was taken. Analysis by gel
permeation chromatography (GPC) showed a number average molecular weight
of 11,900 (vs 13,000 theoretical), a weight average molecular weight of
18,100 and a dispersity of 1.52 for the arm polymer.
Light scattering and viscosity measurements on similar star polymers show
molecular weights of about 2.7 million. Thus, the star polymer has on the
order of 200 arms, each having a molecular weight of about 12,000.
EXAMPLE 2
This describes the preparation of a poly(methyl methacrylate) star polymer
having arms terminated with hydroxyl groups.
The polymer can be used as a rheology control agent and is especially
useful in enamels, where the hydroxyl groups allow the star polymer
molecules to become a part of the polymer network making up the
crosslinked enamel film. The polymer can also be used as an enamel binder
polymer by combining it with a polyisocyanate or a melamine/formaldehyde
resin. The polymer can also be used as a precursor for further reactions
(e.g. the introduction of methacrylate functionality as described in
Example 3).
The reaction vessel described in Example 1 was purged with dry nitrogen and
then charged with the following initial charge:
Initial Charge
800.24 g glyme
4.8 g xylene
8.34 g 1-(2-trimethylsiloxyethoxy)-1-trimethylsiloxy-2-methylpropene
To the initial charge was then added via syringe the initial catalyst:
Initial Catalyst
50 microliters of a 1.0 molar solution of TBAHF.sub.2 in glyme.
The mixture thus obtained was then stirred continuously under dry nitrogen
while adding the feed compositions shown below at constant rates via
syringe pumps. The feed compositions and the addition schedules were as
follows:
______________________________________
Clock Time (Minutes)
Addition Addition
Feed Feed Composition Started Completed
______________________________________
I 300 microliters of
0 80
1 M TBAHF.sub.2 and
3.0 g glyme
II 310.18 g methyl 0 30
methacrylate
III 39.62 g tetraethyleneglycol
45 60
dixethacrylate
______________________________________
During the additions of the feeds, the temperature gradually rose, reaching
a maximum of 62.degree. C. at 40 minutes.
At a clock time of 45 minutes, before the addition of Feed III was started,
a 2 g portion of the reaction mixture was (Sample 1) removed for testing
and quenched.
At 110 minutes, the reaction was quenched and the hydroxyl groups unblocked
by the addition of quencher:
Quencher
30.0 g methanol
3.0 g of a 1 molar solution of tetrabutylammonium fluoride in
tetrahydrofuran
The resulting star polymer was isolated by precipitation in methanol and
dried in a vacuum oven. As in Example 1, the star has a large number of
arms, but in this case, the arms have a molecular weight of about 10,000
and each arm is terminated by a hydroxyl group. The star polymer has about
0.0852 milliequivalents OH per gram of solids (or a hydroxyl number of
about 4.78 mg KOH/g polymer).
EXAMPLE 3
This describes the preparation of a star polymer having terminal
methacrylate groups by reaction of the star polymer of Example 2 with
2-isocyanatoethyl methacrylate.
The polymer is useful as a toughening modifier for plastics such as cast
poly(methyl methacrylate) sheet, pigmented, filled such as with hydrated
aluminum oxide, or clear. It may also be used in coatings and in
photopolymerizable systems.
The dry star polymer of Example 2 (150.00 g, 0.0128 equivalents OH) was
dissolved in 300.02 g dry glyme. Then 2.29 g (0.0148 mole)
2-isocyanatoethyl methacrylate and 2 drops of a 10% solution of dibutyltin
dilaurate in methyl ethyl ketone was added and the mixture stirred. After
standing over the weekend, the reaction mixture was found to have lost its
IR band at 2356 cm.sup.-1 (NCO) showing that the reaction was
substantially complete.
The resulting star polymer has a large number of poly(methyl methacrylate)
arms, each having a molecular weight of about 10,000 and each terminated
with a methacrylate group.
EXAMPLE 4
This describes the preparation of a star polymer in which the arms are a
block copolymer of methyl methacrylate and 2-ethylhexyl methacrylate. The
polymer is prepared by making the core first and then polymerizing the
arms onto it.
The polymer can be used as a rheology control agent or toughening agent in
coatings or plastics.
A reaction vessel as described in Example 1 was purged with dry nitrogen
and then charged with the following initial charge:
Initial Charge
88.14 g glyme
1.16 g 1-trimethylsiloxy-1-isobutoxy-2-methylpropene
To the initial charge was then added via syringe the initial catalyst:
Initial Catalyst
50 microliters of a 1.0 molar solution of tris(dimethylamino)sulfonium
bifluoride in glyme.
The mixture thus obtained was then stirred continuously under dry nitrogen
while adding the feed compositions shown below at constant rates via
syringe pumps. The feed compositions and the addition schedules were as
follows:
______________________________________
Clock Time (Minutes)
Addition Addition
Feed Feed Composition Started Completed
______________________________________
I 200 microliters of 1.0 M
0 80
TASHF.sub.2 and 2.0 g
acetonitrile
II 1.02 g ethylene glycol
0 10
dimethacrylate
III 29.57 g methyl methacrylate
20 35
IV 27.73 g 2-ethylhexyl
45 60
methacrylate
______________________________________
During the additions of the feeds, the temperature gradually rose, reaching
a maximum of 48.degree. C. at 45 minutes.
At a clock time of 90 minutes, the reaction was quenched by the addition of
quencher:
Quencher
2.0 g methanol
The resulting star polymer has a core to which is attached very
approximately 25 arms. Each arm has a molecular weight of about 10,700 and
consists of two blocks: a poly(methyl methacrylate block of about 5500
molecular weight attached at one end to the core and a poly(2-ethyl-hexyl
methacrylate) block of about 5200 molecular weight attached at one end to
the other end of the poly(methyl methacrylate) block.
EXAMPLE 5
This describes the preparation of a star polymer having both poly(methyl
methacrylate) arms and poly(2-ethylhexyl methacrylate) arms on the same
star polymer molecule.
The polymer can be used as a rheology control agent or toughening agent in
coatings or plastics.
The poly(methyl methacrylate) arm polymer (a) and the poly(2-ethylhexyl
methacrylate) arm polymer (b) were prepared simultaneously in separate
reaction flasks and, without quenching, were mixed together before
preparing the star polymer (c).
A. POLY(METHYL METHACRYLATE) ARM POLYMER
A reaction vessel as described in Example 1 was purged with dry nitrogen
and then charged with the following initial charge:
Initial Charge
50.25 g glyme
0.65 g xylene
0.55 g 1-trimethylsiloxy-1-isobutoxy-2-methylpropene
To the initial charge was then added via syringe the initial catalyst:
Initial Catalyst
50 microliters of a 1.0 molar solution of tris(dimethylamino)-sulfonium
bifluoride (TASHF.sub.2) in glyme.
The mixture thus obtained was then stirred continuously under dry nitrogen
while adding the feed compositions shown below at constant rates via
syringe pumps. The feed compositions and the addition schedules were as
follows:
______________________________________
Clock Time (Minutes)
Addition Addition
Feed Feed Composition Started Completed
______________________________________
I 50 microliters of 1 M TASHF.sub.2
0 30
and 1.0 g acetonitrile
II 30.42 g methyl methacrylate
0 20
______________________________________
At a clock time of 30 minutes a 1 g portion (Sample A-1) of the reaction
mixture was removed and quenched in methanol.
B. POLY(2-ETHYLHEXYL METHACRYLATE) ARM POLYMER
A reaction vessel as described in Example 1 was purged with dry nitrogen
and then charged with the following initial charge:
Initial Charge
44.13 g glyme
0.52 g xylene
1.16 g 1-trimethylsiloxy-1-isobutoxy-2-methylpropene
Initial Catalyst
50 microliters of a 1.0 molar solution of tris(dimethylamino) sulfonium
bifluoride (TASHF.sub.2) in glyme.
The mixture thus obtained was then stirred continuously under dry nitrogen
while adding the feed compositions shown below at constant rates via
syringe pumps. The feed compositions and the addition schedules were as
follows:
______________________________________
Clock Time (Minutes)
Addition Addition
Feed Feed Composition Started Completed
______________________________________
I 100 microliters of
0 30
1 M TASHF.sub.2
and 1.0 g acetonitrile
II 28.82 g 2-ethylhexyl
0 20
methacrylate
______________________________________
At a clock time of 30 minutes, a 1 g portion of the resulting solution was
removed and quenched in methanol (Sample B-1).
C. STAR POLYMER
A reaction vessel as described in Example 1 was purged with dry nitrogen
and then charged with a mixture of the arm polymer solutions described in
A and B. The initial charge is:
Initial Charge
81.97 g arm polymer solution A
69.61 g arm polymer solution B
The initial charge was then stirred continuously under dry nitrogen while
adding the feed compositions shown below at constant rates via syringe
pumps. The feed compositions and the addition schedule were as follows:
______________________________________
Clock Time (Minutes)
Addition Addition
Feed Feed Composition Started Completed
______________________________________
I 50 microliters of 1 M TASHF.sub.2
30 60
and 1.0 g acetonitrile
II 4.86 g ethylene glycol
30 40
dimethacrylate
______________________________________
At a clock time of 70 minutes, the reaction was quenched by the addition of
quencher:
Quencher
2.0 g methanol.
A portion of the resulting star polymer solution (Sample C-1) was removed
for testing.
Analysis of the sample by HPLC showed the following:
______________________________________
Sample Identification Conversion of Monomer
______________________________________
A-1 MMA arm polymer
69.3%
B-1 2EHMA arm Polymer
98.4%
C-1 Star Polymer 99.75% (MMA)
99.47% (2EHMA)
98.9% (EGDMA)
______________________________________
The resulting star polymer had the following composition by weight.
8% Core
49% MMA arms (Mn=12,000)
43% 2EHMA arms (Mn=5,500)
EXAMPLE 6
This describes the preparation of a star polymer having both poly(methyl
methacrylate) arms and poly(2-ethylhexyl methacrylate) arms on the same
star polymer molecule. In this case, the poly(methyl methacrylate) arm
polymer is made first, then a star polymer is made from it, and finally
poly(2-ethylhexyl methacrylate) arms are grown from the star polymer.
The polymer can be used as a rheology control agent or toughening agent in
coatings or plastics.
A reaction vessel as described in Example 1 was purged with dry nitrogen
and then charged with the following initial charge:
Initial Charge
176.29 g glyme
2.09 g xylene
1.24 g 1-trimethylsiloxy-1-isobutoxy-2-methylpropene
To the initial charge was then added via syringe the initial catalyst:
Initial Catalyst
50 microliters of a 1 molar solution of tetrabutylammonium bifluoride in
glyme. The mixture thus obtained was then stirred c | | |
