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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a process for making acrylic coating
resins and more specifically to superior solvents useful in the synthesis
of high solids acrylic coating resins.
2. Description of the Prior Art
A large variety of acrylic coating compositions are known. Low solids
coatings, i.e., those containing about 18 to 40 wt % solids and the
balance solvents, have heretofore been developed in which the resins
themselves are characterized by high molecular weights, e.g., molecular
weights in the range of 20,000 to 40,000. Such high solvent concentrations
are required with these high molecular weight resins in order to supply
flowability and other properties necessary for ease in applying a uniform
coating. Due to strict air pollution regulations, pollution abatement of
solvents is of paramount importance. To this end, the industry has
expended much effort in an attempt to develop electrostatically sprayable
coatings containing high solids contents; that is, coatings having a lower
amount of solvents in order to satisfy pollution regulations. Attempts to
achieve high solids coatings by merely using more of the conventional high
molecular weight resins in the coatings have not been successful since the
increased solids content using these resins results in an unacceptably
high viscosity, and often the larger amounts of the resins cannot
themselves be dissolved. Efforts at developing a "super solvent" for these
conventional high molecular weight resins have also not proved to be
successful. One prior art approach has been to formulate coatings
containing low molecular weight resins (e.g., of about 1,000 to 7,000
weight average molecular weight) in high solids coatings in order to
reduce the amount of solvents necessary in the blending for coating
applications and, hence, the pollution difficulties associated with the
solvents themselves. After application of these coatings to a surface,
these coatings are cured to form a polymeric network of higher molecular
weight and enhanced physical properties. These high solids acrylic
coatings are useful as exterior finish for automobiles, trucks, metal
furniture, and as an appliance finish.
K. K. Mitra, "Electrostatic Application of Paint", Paint India, vol. 29,
no. 9, pp. 52-56 (1979) indicates that while non-polar solvents (aliphatic
and aromatic hydrocarbons chlorinated solvents, terpenes, etc.) can be
employed in electrostatically sprayable paints to increase bulk and
resistivity, polar solvents are used to control resistivity. The polar
group is said to include ketones, alcohols, esters, ethers, ether
alcohols, and nitro paraffins, etc. The non-polar group is said to include
aliphatic and aromatic hydrocarbons, chlorinated solvents, terpenes, etc.
Also illustrative of prior art, high solids acrylic resins are those
disclosed in U.S. Pat. No. 4,276,212 and in European Patent Applications
27,719; 29,594 and 29,683.
Solvents which are indicated to be typical in these references (e.g., those
mentioned in European Patent Application 29,594) are: Toluene, xylene,
butyl acetate, acetone, methyl isobutyl ketone, methyl amyl ketone, methyl
ethyl ketone, butyl alcohol and other aliphatic, cycloaliphatic and
aromatic hydrocarbons, esters, ethers, ketones, and alcohols.
In a brochure entitled "Hexyl Acetate for the Coatings Industry" (Enjay
Chemical Company), published prior to 1980, use of hexyl acetate as
coating solvent in certain specific low solids acrylic coating
compositions; in urethane coatings in nitrocellulose coatings; and in
baking enamels was disclosed.
U.S. Pat. Nos. 4,075,242 and 4,276,432 disclose the preparation of
acrylic-based resins by use of polymerization media containing certain
high boiling solvents and disclose the use of ethylene and propylene as
co-monomers.
European Patent 29,339 discloses the formation of bifunctional copolymers
in which the monomers comprise from 5 to 25 wt % of monoethylenically
unsaturated monomers having a glycidyl functionality, from 5 to 25% of
monoethylenically unsaturated monomers having hydroxy functionality and 90
to 70 wt % of other monoethylenically unsaturated monomers, with acrylates
as well as mixtures of acrylates and vinyl hydrocarbons being preferred.
Only monovinyl aromatic hydrocarbons are particularly indicated as useful
(e.g., styrene, alpha-methyl styrene, vinyl toluene, t-butyl styrene and
chlorostyrene).
U.S. Pat. No. 4,369,296 relates to the production of methyl methacrylate
homopolymers (or copolymers with certain copolymerizable vinyl monomers;
e.g., styrene and alkyl-substituted styrene) in the presence of from 0.01
to 10 wt % of enol ethers derived from aliphatic or cycloaliphatic
aldehydes and ketones.
U.S. Pat. No. 3,271,375 relates to the use, in combination with a free
radical polymerizable material, of certain unsaturated heterocyclic
organic compounds as molecular weight regulators. The prior art has sought
to control the degree of polymerization via chain transfer content (in the
preparation of acrylic oligomers for high solids coating resins) by use of
relatively inactive solvents such as alkyl aromatics, high boiling ethers
and benzyl alcohol. D. Rhum, et al., J. Coatings Tech'n. Vol. 55, no. 703,
75-79 (August 1983).
U.S. Pat. No. 4,532,294 relates to the preparation of acrylic copolymer
resins employing polymerization solvents comprising certain alkanoic acid
alkyl esters together with hydroxy-substituted alkyl (meth)acrylate and
non-hydroxy substituted alkyl (meth)acrylate monomers, and in optional
presence of additional monomers comprising monovinyl aromatic
hydrocarbons. Among the non-hydroxy substituted alkyl (meth)acrylate
monomers which may be employed are (meth)acrylates as well as mixtures of
acrylates and vinyl hydrocarbons.
U.S. Pat. No. 3,926,925 relates to novel interpolymers containing an olefin
(an alpha-olefin, a 2-alkyl-1-olefin and a vinyl aromatic), polar
monomers, such as an alkyl acrylate, and a fumarate ester or a maleic acid
derivative which are prepared with a catalyst system of an alkyl aluminum
halide and an organic peroxide. U.S. Pat. No. 3,959,225 relates to a
thermally-staged process for preparing alternating interpolymers of one or
more polar monomers and one or more mono- or polyolefins in which a polar
monomer-Lewis Acid complex is reacted with an olefin in the presence of an
active oxygen compound. The olefins discussed as useful in U.S. Pat. No.
3,959,225 are certain Type I olefins and Type III olefins.
U.S. Pat. No. 3,968,148 relates to oligomers of 1-alkenes and derivatives
of acrylic acids.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an improved method for
preparing low molecular weight acrylic copolymer resins is provided in
which the polymerization is conducted in the presence of a polymerization
solvent comprising a mixture of an organic solvent for the resins and at
least one internally olefinically unsaturated aliphatic or cycloaliphatic
hydrocarbon having from 6 to 16 carbon atoms per molecule. The monomers
comprise a mixture of hydroxy-substituted alkyl (meth)acrylates and
nonhydroxy substituted alkyl (meth)acrylates, and the process provides an
improved method for forming low molecular weight acrylic resins which are
useful as components in high solids acrylic coatings suitable for
electrostatic spraying. The internal olefin-containing polymerization
solvent can remain with the resin to become components of the higher
solids coating formulation containing the thus-formed acrylic resins and
can provide surprisingly improved color and odor properties, and can also
provide improved electrical resistivity and solvency and decreased surface
tensions.
It has been further surprisingly found that the process of this invention
permits formation of such improved properties even when the polymerization
is conducted in the presence of a non-inert atmosphere (e.g., air).
In addition, the solvents of this invention provide the low-molecular
weight acrylic resins over a wide range of temperatures. Surprisingly, the
solvents of this invention produce low molecular weight acrylic copolymers
which are characterized by superior molecular weight and viscosity
properties, and are therefore especially suited for use in high solids
coatings. The coatings thereby formulated have excellent flow properties,
higher resistivities than prior art coatings containing ketones and when
applied to surfaces provide high gloss and high impact strength in the
as-applied coating.
DETAILED DESCRIPTION OF THE INVENTION
According to one aspect of the improved process of this invention, improved
acrylic polymers are prepared by contacting under polymerizing conditions
at least one hydroxy-substituted alkyl (meth)acrylate monomer and at least
one non-hydroxy substituted alkyl (meth)acrylate monomer in the presence
of a free radical polymerization catalyst, and a polymerization solvent
comprising an organic solvent for said monomers and at least one internal
olefin having from 6 to 16 carbon atoms per molecule.
The organic solvents which can be employed comprise at least one member
selected from the group consisting of ketones, ethers, glycols, glycol
ethers, esters, keto ethers, ether esters, alcohols, nitrosubstituted
paraffins, aromatic solvents and halocarbon solvents. The organic moiety
to which the ketone, and ether functional groups can be attached includes
alkyl, typically about C.sub.1 to C.sub.20, preferably about C.sub.1 to
C.sub.10, most preferably about C.sub.1 to C.sub.5 alkyl; aryl, typically
about C.sub.6 to C.sub.14, preferably about C.sub.6 to C.sub.10, most
preferably C.sub.6 aryl; cycloalkyl, typically about C.sub.4 to C.sub.20,
preferably about C.sub.6 to C.sub.12, most preferably about C.sub.6 to
C.sub.10 cycloalkyl; aralkyl and alkaryl wherein the alkyl and aryl groups
thereof are described above. Nitro-paraffinic solvents include NO.sub.2
-substituted alkanes of 2 to 5 carbon atoms. Halocarbon solvents include
chloro- and fluorosubstituted saturated hydrocarbons. Alcohol solvents
include alkanols of 4 to 10 carbon atoms, and phenylsubstituted alkanols
of 7 to 10 carbon atoms. Ether alcohols include alkoxy-substituted
alkanols of from 3 to 8 carbon atoms. Glycol solvents include di-hydroxy
substituted alkanes of from 2 to 6 carbon atoms. Glycol ether solvents
include compounds of the formula R'--O--R" wherein R' is alkyl of from 1
to 6 carbon atoms and R" is hydroxy-substituted alkyl of from 2 to 6
carbon atoms.
Suitable ester solvents comprise normally liquid C.sub.1 to C.sub.13 alkyl
esters of alkanoic acids having from 2 to 7 carbon atoms. Prepared ester
solvents are those selected from the group consisting of compounds having
the formula (I):
##STR1##
wherein R.sup.1 is a straight or branched chain alkyl of from 1 to 6
carbon atoms, and R.sup.2 is a straight or branched chain alkyl of from 1
to 13 carbon atoms, with the proviso that R.sup.1 and R.sup.2 together
contain from 6 to 17 carbon atoms, and mixtures thereof. The "R.sup.1 "
group can also comprise C.sub.2 to C.sub.7 alkyl having one carbon
replaced by an ether oxygen (e.g., C.sub.2 H.sub.5 --O--C.sub.2 H.sub.4
--, C.sub.3 H.sub.7 --O--C.sub.2 H.sub.4 --, CH.sub.3 --O--C.sub.2 H.sub.4
--, C.sub.2 H.sub.5 --O--C.sub.3 H.sub.6 --, and the like). Exemplary of
such ester solvents are butyl acetates, pentyl acetates, hexyl acetates,
pentyl propionates, isobutyl isobutyrate, heptyl acetates, methyl
pentanoates, ethyl pentanoates, pentyl pentanoates, ethyl hexanoates,
butyl hexanoates, ethyl neopentanoate, methyl neoheptanoate, octyl
acetates, nonyl nonyl acetates, decyl acetates, undecyl acetates,
acetates, dodecyl acetates, tridecyl acetates and the like. Exemplary of
esters wherein the carboxylic acid moiety is derived from an
ether-containing-containing acid (e.g., acids which are
alkoxy-substituted) are ethyl 3-ethyoxypropionate, butyl
3-butoxypropionate, methyl 2-methoxyacetate, methyl 3-methoxypropionate,
propyl 3-propoxypropionate and the like.
Especially preferred ester solvents of this invention are normally liquid
esters selected from the group consisting of compounds of the formula
(II):
##STR2##
wherein R.sup.3 is a straight or branched-chain alkyl having from 5 to 13
carbon atoms, and mixtures thereof. Exemplary of such preferred ester
solvents herein are pentyl acetates, hexyl acetates, heptyl acetates,
octyl acetates, nonyl acetates, decyl acetates, undecyl acetates, dodecyl
acetates, and tridecyl acetates. The term "normally liquid esters" as used
herein is intended to refer to esters which are in the liquid state at
ambient conditions (25.degree. C., 1 atm).
Suitable ketone solvents include methyl amyl ketone, methyl isobutyl
ketone, methyl propyl ketone, isophorone, cyclohexanone, diethyl ketone,
dibutyl ketone, methyl isopropyl ketone, methyl sec-butylketone,
benzophenone, mixtures thereof, and the like. Suitable ether solvents
include dibutyl ether, tetrahydrofuran, anisole, dioctyl ether,
1,2-dimethoxyethane, 1,4-dimethoxybutane. Suitable halocarbon solvents
include 1,1,2-trichloroethane, tetrachloroethane and the like. Suitable
nitroparaffinic solvents include nitropropane and nitropentane. Suitable
alcohols include 2-ethyl hexanol, diacetone alcohol, n-butyl alcohol,
phenethyl alcohol, benzyl alcohol, amyl alcohol, isobutyl alcohol,
tertiary butyl alcohol, hexyl alcohols, and the like. Suitable glycol
ethers, esters and mixed ether and ester solvents include ethylene glycol
diacetate, propylene glycol diacetate, Cellosolve.RTM. acetate (registered
trademark of the Union Carbide Corporation), butyl Cellosolve, Cellosolve,
the Carbitols.RTM. (registered trademark of the Union Carbide
Corporation), methoxy propyl acetate, ethoxy propyl acetate, and the like.
Suitable keto ethers include molecules of the formula (IIa):
##STR3##
T.sup.1 and T.sup.2 are each hydrocarbyl containing from about 1 to 10
carbon atoms, and T.sup.3 is straight or branched chain alkyl of from 1 to
6 carbon atoms. Illustrative of such keto ethers are CH.sub.3 C(O)CH.sub.2
CH.sub.2 OCH.sub.2 CH.sub.3 ; C.sub.3 H.sub.7 C(O)--C.sub.3 H.sub.6
OC.sub.3 H.sub.7 ; CH.sub.3 C(O)CH.sub.2 C(OCH.sub.3)(CH.sub.3)CH.sub.3 ;
CH.sub.3 C(O)CH.sub.2 C(OC.sub.2 H.sub.5)(CH.sub.3)CH.sub.3 ; C.sub.2
H.sub.5 C(O)CH.sub.2 CH.sub.2 OC.sub.4 H.sub.9 ; and the like. Suitable
aromatic solvents comprise alkyl-substituted benzenes of the formula
(III):
##STR4##
wherein p is an integer of from 1 to 4, and X is in each instance in which
it appears independently selected from the group consisting of straight
and branched-chain alkyl of from 1 to 4 carbon atoms.
Illustrative of suitable alkyl-substituted benzene solvents for use in the
solvent blends of this invention are toluene, xylene, cumene,
alkyl-substituted benzenes in which the alkyl substituent comprises a
total of at least 2 carbon atoms when the benzene ring is mono-alkyl
substituted and of at least 3 carbon atoms when the benzene ring is
substituted by two or more alkyl groups, aromatic groups substituted by a
cyclic aliphatic ring (e.g., tetrahydronaphthalene), ethyl benzene,
isopropyl benzene, n-propyl benzene, 1-methyl-3-ethylbenzene,
1-methyl-4-ethylbenzene, 1,3,5-trimethylbenzene, 1-methyl-2-ethylbenzene,
1,2,4-trimethylbenzene, isobutylbenzene, sec-butylbenzene,
1-methyl-3-isopropylbenzene, 1-methyl-4-isopropylbenzene,
1,2,3-trimethylbenzene, 1-methyl-2-isopropylbenzene, 1,3-diethylbenzene,
1-methyl-3-n-propylbenzene, n-butylbenzene, 1,4-diethylbenzene,
1,3-dimethyl-5-ethylbenzene, 1,4-dimethyl-2-ethylbenzene,
1,3-dimethyl-4-ethylbenzene, 1,2-dimethyl-4-ethylbenzene,
1,2,4,5-tetramethylbenzene, 1,2,3,5-tetramethylbenzene and the like, and
mixtures of the foregoing.
The aromatic solvent component can also contain up to about 50 wt %,
preferably less than about 40 wt %, and more preferably up to about 25 wt
%, of
other hydrocarbon solvents such as C.sub.6 to C.sub.11 aromatic solvents
not satisfying the definition of formula III above, as well as C.sub.6 to
C.sub.11 saturated aliphatic and cycloaliphatic hydrocarbons.
The organic solvents are preferably characterized by a normal boiling point
(at 1 atm) of at least about 100.degree. C., more preferably from about
115.degree. to 250.degree. C., and most preferably from about 150.degree.
to 200.degree. C,. When the thus-polymerized resins are intended for use
as components of electrostatic spray coatings, the organic solvents are
preferably characterized by a resistivity of at least 15 megohms, as
determined by Ransburg resistivity meter, and are also preferably
substantially free of water (more preferably having a water content of
less than 0.5 wt %) and trace metals (more preferably having a trace
metals content of less than 0.004 wt %).
The internal olefins suitable in this invention as a component of the
polymerization solvent comprise normally liquid aliphatic and
cycloaliphatic internal olefins having from 6 to 16 carbon atoms per
molecule. The term "normally liquid", when applied herein to such internal
olefins, is intended to refer to internal olefins which are in the liquid
state at ambient conditions (25.degree. C., 1 atm). Suitable internal
aliphatic olefins are branched and straight chain olefins with internal
olefinic unsaturation, and comprise compounds of the formula (IV):
##STR5##
wherein X.sup.1 and Y.sup.2 are the same or different and H or alkyl of
from 1 to 12 carbon atoms, X.sup.2 and X.sup.3 are the same or different
and are H, alkyl of from 1 to 12 carbon atoms or phenyl, and Y.sup.1 is
alkyl of from 1 to 13 carbon atoms, with the proviso that each molecule of
the olefin contains a total of from 6 to 16 carbon atoms.
A preferred class of olefins for use in this invention are cycloaliphatic
olefins of from 6 to 12 carbon atoms and aliphatic olefins of the formula
(V):
##STR6##
wherein X.sup.4, X.sup.5, X.sup.6 and Y.sup.4 are the same or different
and are H or alkyl of from 1 to 10 carbon atoms and wherein Y.sup.3 is
alkyl of from 1 to 11 carbon atoms, with the proviso that each molecule of
the olefin contains a total of from 8 to 14 carbon atoms.
Such alkyl groups of formulae (IV) and (V) may be branched or straight
chained, and exemplary thereof are methyl, ethyl, n-butyl, iso-butyl,
sec-butyl, tert-butyl, n-pentyl, iso-pentyl, hexyl, heptyl, octyl, nonyl,
decyl, undecyl, dodecyl, tridecyl, and the like. Exemplary of suitable
internal aliphatic olefins, therefore, are 2-hexene, 3-hexene, 2-heptene,
3-heptene, 2-methyl-2-pentene, 3-ethyl2-pentene, 2-, 3- and 4-octene,
3-methyl-2-heptene, 4-propyl-3-heptene, 2-, 3-, and 4-nonene,
2-methyl-4-heptene, 2-, 3-, 4-, and 5-decene, 2-, 3-, 4-, and 5-undecene,
2-, 3-, 4-, 5-, and 6-dodecene, the internally unsaturated tridecenes,
tetradecenes, pentadecenes and hexadecenes, and the like. Such alkyl
groups of formulae (IV) and (V) may also be phenyl-substituted; e.g.,
phenyl methyl, 2-phenyl ethyl, 3-phenyl butyl and the like.
Suitable cycloaliphatic olefins are cycloalkenes of from 6 to 16 carbon
atoms, of which cyclohexene, cyclooctene, cyclodecene, cyclododecene and
the like are illustrative.
Particularly preferred are mixed aliphatic internal olefins commercially
produced by olefin oligomerization, such as mixed octenes, nonenes,
decenes, undecenes, dodecenes, and tridecenes produced by conventional
oligomerization of lower olefin streams (e.g., mixed propylene, butene and
pentene olefins derived from catalytic cracking of petroleum hydrocarbons)
over electrophilic catalysts; e.g., supported phosphoric acid catalysts.
These mixed olefins are predominantly internally unsaturated (e.g., at
least about 80 mol % internally unsaturated) and are highly branched.
The selected internal olefin will preferably be characterized by a normal
boiling point (i.e., at 1 atm) of at least about 100.degree. C., more
preferably from about 115.degree. to 250.degree. C., and most preferably
from about 150.degree. to 200.degree. C. The internal olefin will also
preferably be substantially free of water and trace metals, as discussed
above for the organic solvent, when the resins to be formed are intended
for use as a component of electrostatic spray coatings.
In order to form resins of improved color, it is preferred that the
internal olefin be substantially free of contamination by conjugated
olefinic impurities comprising conjugated diolefins, internally
unsaturated monoolefins in which the olefinic double bond is conjugated
with an aromatic ring (e.g., as in indene) and internally unsaturated
monoolefins which are alpha, beta-unsaturated ketones, esters, amides and
acids. More preferably, the internal olefin contains less than 100 ppm of
the conjugated olefinic impurities.
The polymerization solvent systems of this invention therefore comprise a
mixture of at least one organic (non-olefinically unsaturated) solvent for
the monomers and at least one of the above normally liquid internally
unsaturated olefins. The organic solvent will generally comprise a
majority of the polymerization solvent. More specifically, the
polymerization solvents of this invention will comprise from about 50 to
99 wt %, more preferably from about 60 to 95 wt %, and most preferably
from about 70 to 90 wt % of the non-olefinic organic solvent, and from
about 50 to 1 wt %, more preferably 40 to 5 wt %, and most preferably from
about 30 to 10 wt % of the internal olefin component.
Especially preferred such polymerization solvent mixtures are those wherein
the organic solvent component comprises from about 60 to 95 wt % of a
normally liquid ester of formula (II) above and from about 5 to 40 wt %,
of an internal olefin of formula (V) above.
The hydroxy-substituted alkyl (meth)acrylates which can be employed as
monomers comprise members selected from the group consisting of the
following esters of acrylic or methacrylic acid and aliphatic glycols:
2-hydroxy ethyl acrylate, 3-chloro-2-hydroxypropyl acrylate;
1-hydroxy-2-acryloxy propane; 2-hydroxypropyl acrylate; 3-hydroxypropyl
acrylate; 2,3-dihydroxypropyl acrylate; 3-hydroxy-butyl acrylate;
2-hydroxy-butyl acrylate; 4-hydroxybutyl acrylate; diethylene-glycol
acrylate; 5-hydroxypentyl acrylate; 6-hydroxyhexyl acrylate;
triethyleneglycol acrylate; 7-hydroxyheptyl acrylate
1-hydroxy-2-methacryloxy propane; 2-hydroxy-propyl methacrylate;
3-hydroxypropyl methacrylate; 2,3-dihydroxypropyl methacrylate;
2-hydroxybutyl methacrylate; 3-hydroxy-butyl methacrylate; 2-hydroxyethyl
methacrylate; 4-hydroxybutyl methacrylate; 3,4-dihydroxybutyl
methacrylate; 5-hydroxypentyl methacrylate; 6-hydroxyhexyl methacrylate;
1,3-dimethyl-3-hydroxybutyl methacrylate; 5,6-dihydroxyhexyl methacrylate;
and 7-hydroxyheptyl methacrylate. Although one of ordinary skill in the
art will recognize that many different hydroxy-substituted alkyl
(meth)acrylates including those listed above could be employed, the
preferred hydroxy functional monomers for use in the resin of this
invention are hyroxysubstituted (meth)acrylates, meaning alkyl acrylates
and methacrylates having a total of 5 to 7 carbon atoms, i.e., esters of
C.sub.2 -C.sub.3 dihydric alcohols and acrylic or methacrylic acids.
Most preferably, the hydroxy-substituted alkyl (meth)acrylate monomer
comprises a compound of the formula (VI):
##STR7##
wherein R.sup.4 is hydrogen or methyl and R.sup.5 and R.sup.6 are
independently selected from the group consisting of hydrogen and alkyl of
from 1 to 6 carbon atoms. Illustrative of these particularly suitable
hydroxysubstituted alkyl (meth)acrylate monomers are 2-hydroxy ethyl
methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,
2-hydroxybutyl acrylate and 2-hydroxy propyl methacrylate.
Among the non-hydroxy substituted alkyl (meth)acrylate monomers which may
be employed as monomers are (meth)acrylates (as before, meaning esters of
either acrylic or methacrylic acids). Preferred non-hydroxy unsaturated
monomers are esters of C.sub.1 -C.sub.12 monohydric alcohols and acrylic
or methacrylic acids, e.g., methylmethacrylate, ethylacrylate,
butylacrylate, butylmethacrylate, hexylacrylate, 2-ethyl-hexylacrylate,
lauryl-methacrylate, glycidyl methacrylate, etc.
Particularly preferred non-hydroxy substituted monomers are compounds
selected from the group consisting of monomers of the formula (VII):
##STR8##
wherein R.sup.7 is alkyl of from 1 to 8 carbon atoms and R.sup.8 is
hydrogen or methyl. Exemplary such monomers are butyl acrylate, butyl
methacrylate and methyl methacrylate.
The total monomer mixture can additionally comprise as optional monomers,
monovinyl aromatic hydrocarbons containing from 8 to 12 carbon atoms
(including styrene, alpha-methyl styrene, vinyl toluene, t-butyl styrene,
chlorostyrene and the like), vinyl chloride, vinylidene chloride,
acrylonitrile, methacrylonitrile, vinyl acetate, acrylic acid and
methacrylic acid.
The total monomer mixture passed to the polymerization process step will
generally comprise from about 5 to 40 wt %, and preferably from about 10
to 30 wt %, of the hydroxy-substituted alkyl (meth)acrylate and from about
5 to 95 wt %, preferably from about 30 to 90 wt % of the non-hydroxy
substituted alkyl (meth)acrylate monomer, in addition to any optional
monomers (discussed above). Generally, the non-hydroxy substituted
(meth)acrylate will comprise up to about 90 wt %, more preferably from
about 10 to 60 wt %, of the non-hydroxy methacrylate and from about 5 to
70 wt %, more preferably from about 20 to 50 wt %, of the non-hydroxy
acrylate, all based on the weight of the total monomer mixture. The
non-hydroxy substituted (meth)acrylate will typically comprise a mixture
of methyl methacrylate which will be present in an amount of from about 5
to 60 wt %, more preferably from about 10 to 45 wt %, of the total monomer
mixture, and up to about 60 wt %, more preferably from about 25 to 50 wt
%, of the total monomer mixture of butyl acrylate, 2-ethylhexyl acrylate,
or mixtures thereof.
Where employed, the above optional monovinyl aromatic hydrocarbons will be
generally present in an amount of from about 2 to 60 wt %, preferably from
about 10 to 40 wt % of the total monomer mixture.
In the case of acrylic acid or methacrylic acid, when employed, this
monomer will generally be present in an amount of up to 10 wt %, and more
typically from about 2 to 5 wt %, of the total monomer mixture. The
remaining above-mentioned monomers will generally be present in an amount
of up to 30 wt %, more typically from from 3 to 10 wt %, of the monomer
mixture, where employed.
In preparing the polymers of this invention, the selected monomers,
including the required hydroxy-substituted alkyl (meth)acrylate, and
non-hydroxy substituted alkyl (meth)acrylate, together with any modifying
or other monomers, may be mixed and reacted by conventional free radical
initiated polymerization in such proportions as to obtain the copolymer
desired, this reaction being effected in the presence of the
polymerization solvent of this invention. A large number of organic free
radical initiators are known in the art and are suitable for the purpose.
These include: benzoyl peroxide; lauryl peroxide; t-butylhydroperoxide;
acetylcyclohexylsulfonyl peroxide; di-isobutyryl peroxide;
t-butylperoxypivalate; decanoyl peroxide; azobis-(2-methylpropionitrile);
2-t-butylazo-2-cyanobutane; tertiary butyl perbenzoate, dicumyl peroxide,
ethyl 3,3-(t-amylperoxy)butyrate, ethyl 3,3-di(t-butylperoxy) butyrate,
t-butyl cumyl peroxide, and di(butyl cumyl) peroxide, and di-t-butyl
peroxide, and other dialkyl peroxides, peroxy ketals, and peroxyesters.
The total monomer mixture to be employed in preparing the polymers
according to the process of this invention will generally comprise from
about 30 to 95 wt %, preferably from about 50 to 90 wt %, of the total
mass of monomers and solvent passed to the polymerization reaction vessel.
Thus, the polymerization solvents of this invention will generally
comprise from about 5 to 70 wt %, preferably from about 10 to 50 wt %, of
the total mass of monomers and solvent passed to the polymerization
vessel, with the ranges of organic solvent and internal olefin
concentrations being as set out in the following Table 1:
TABLE 1
______________________________________
Concentrations Relative to Total Mass of
Monomer and Polymerization Solvent Charged
Monomers (wt %)
30-95 50-90
______________________________________
Polymerization Solvent Mixtures
5-70 10-50
(wt %)
a. Preferred -
Organic Solvent (wt %)
2.5-69.3 5-49.5
Internal Olefin (wt %)
0.05-35 0.1-25
b. More Preferred -
Organic Solvent (wt %)
3-66.5 6-47.5
Internal Olefin (wt %)
0.25-28 0.5-20
c. Most Preferred -
Organic Solvent (wt %)
3.5-63 7-45
Internal Olefin (wt %)
0.5-21 0.1-15
______________________________________
The quantity of free radical initiators employed as catalyst in the
reaction can also vary widely and will generally be present in an amount
of from about 0.5 to 10 wt % of the total monomer components charged to
the reaction mixture.
The conditions of temperature and pressure for conducting the
polymerization reaction can vary widely. Generally, the polymerization
will be conducted at a temperature of from about 100.degree. to
240.degree. C., (and preferably from about 130.degree. to 210.degree. C.)
at atmospheric pressure. Pressures of from about 10 to 500 psig are
entirely suitable, although higher or lower pressures can be employed. The
polymerization reaction can be carried out in any of the conventional
equipment employed by the industry for such reactions. Thus, the reaction
vessel can comprise a stirred reactor in which an inert atmosphere (e.g.,
N.sub.2, Ar) is maintained during the polymerization to avoid reactions
with gaseous oxygen which compete, or interfere, with the desired
polymerization reaction. However, the present invention has also be
observed to provide improved high solids resins when the polymerization is
conducted in the presence of air, thereby providing a polymerization
process which is not critically sensitive to equipment leaks or
malfunctions whereby air enters into conventional process equipment.
The polymerization process can be carried out batchwise, semi-continuously,
or continuously. The monomers and solvent system can be premixed or passed
separately to the polymerization vessel alone, or in combination with the
free radical initiators and other components. In addition, the components
of the polymerization solvent may be premixed with each other or with any
other material to be charged (e.g., with any of t | | |
