Emulsion polymerization of vinyl chloride using prehomogenized mixed emulsifier system

A one-step process for the emulsion polymerization of vinyl chloride using a water-soluble initiator and a prehomogenized aqueous emulsifier system of (1) a C.sub.12 -C.sub.18 straight chain alkyl or alkenyl surfactant and (2) a C.sub.16 -C.sub.20 straight chain alkyl or alkenyl alcohol and/or a straight chain saturated hydrocarbon having a carbon content of greater than 18 is disclosed. Suitable examples of straight chain surfactants include sodium lauryl sulfate and sodium oleate. Suitable alcohols include stearyl alcohol, cetyl alcohol and eicosanol. A suitable hydrocarbon is eicosane. The resulting homo- and copolymer latices have excellent mechanical stabilities, particle sizes generally larger than obtainable using only the mixed surfactant system without prehomogenization of the emulsifier system and good thermal stability.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention pertains to a one-step process for the formation of 
vinyl chloride polymers using a water-soluble initiator and a 
prehomogenized aqueous mixed emulsifier system. 
2. Description of the Prior Art 
The use of a straight chain surfactant, e.g., sodium lauryl sulfate, in the 
emulsion polymerization of vinyl chloride will generally result in the 
formation of vary small polymer particles unless the quantity of 
surfactant is carefully controlled by an incremental feed technique. One 
common way in which larger particles of polyvinyl chloride can be obtained 
is by first forming a "seed" particle of the polymer in an initial 
polymerization procedure, followed by a second polymerization or "seed 
growth" step. Some recently issued U.S. patents which relate to this seed 
growth technique are U.S. Pat. No. 3,383,346 to E. S. Smith, U.S. Pat. No. 
3,642,740 to J. K. Pierce, Jr. and U.S. Pat. No. 3,755,225 to J. K. 
Pierce, Jr. et al. The effect of a mixed emulsifier system during only the 
second step of such a process has been studied in the scientific 
literature. J. Ugelstad et al. J. Polymer Sci., Symposium No. 42, 473-485 
(1973). 
In addition to the foregoing prior art, the presence of various alcohols, 
such as stearyl alcohol, as a component in a polymerization reaction 
medium has been studied by other investigators. For example, U.S. Pat. No. 
3,324,097 to G. E. A. Pears and U.S. Pat. No. 3,654,248 to E. Iida et al., 
relate to a polymerization system wherein a homogenized vinyl chloride 
monomer is polymerized in the presence of an oil-soluble catalyst in a 
suspension polymerization procedure. When such a system is used a mixture 
of emulsion and suspension polymerized polyvinyl chloride particles are 
formed. The effect of a mixed emulsifier of surfactant and alcohol in a 
one-shot polymerization of styrene has also been studied: J. Ugelstad et 
al., Die Makromolekulare Chemie, Vol. 175, pp. 507-521 (1974); J. 
Ugelstad, J. Polymer Science, Polymer Letters, Vol. 11, pp. 503-513 
(1973); and A. R. M. Azad et al., ACS Polymer Reprints, Vol. 16, No. 1, 
pp. 131-142 (April 1975). 
Finally, a one-step emulsion polymerization process for forming vinyl 
chloride polymers is described in copending U.S. Ser. No. 740,990, 
entitled "Emulsion Polymerization of Vinyl Chloride Using Mixed Emulsifier 
System", filed on even date herewith in the name of Paul Kraft, wherein a 
mixed emulsifier system of a C.sub.12 -C.sub.18 straight chain alkyl or 
alkenyl surfactant, e.g., sodium lauryl sulfate, and a C.sub.16 -C.sub.20 
straight chain alkyl or alkenyl alcohol and/or a saturated hydrocarbon 
having a chain length of greater than 18 carbon atoms e.g., cetyl alcohol 
is used. Although such a system gives a binodal distribution of polyvinyl 
chloride resins it is difficult to perform in a reproducible manner and 
can yield in successive runs products having vastly different particle 
size distributions. 
It has not, however, been appreciated hitherto that a one-step 
polymerization procedure for vinyl chloride monomer can be achieved using 
a water-soluble initiator and a prehomogenized aqueous mixed emulsifier 
system in order to overcome the deficiencies associated with the prior 
technique of using a mixed emulsifier system. With use of the present 
invention a polydisperse distribution of polyvinyl chloride in the 
particle size range of from about 0.04 to about 1.1 microns is obtained 
with the bulk being in the range of from about 0.6 to about 0.7 microns. 
It has a generally larger amount of larger particles as compared to the 
prior technique and the resin blend has generally superior mechanical 
stability and thermal stability thereby making it more commericially 
desirable as a plastisol or organosol resin. The process is much more 
capable of yielding reproducible particle size results in successive runs 
than is the prior art process. 
SUMMARY OF THE PRESENT INVENTION 
The present invention relates to a one-step emulsion polymerization process 
which comprises the use of a prehomogenized mixed emulsifier of (1) a 
C.sub.12 -C.sub.18 straight chain alkyl or alkenyl surfactant, such as 
sodium lauryl sulfate and sodium oleate, and (2) a C.sub.16 -C.sub.20 
straight chain alkyl or alkenyl alcohol, such as cetyl alcohol, oleyl 
alcohol, stearyl alcohol and eicosanol and/or a straight chain saturated 
hydrocarbon having a carbon content of greater than 18. The resulting 
latices have excellent mechanical stabilities, polydisperse particle sizes 
generally larger than obtainable using a mixed emulsifier system without 
prehomogenization, and good thermal stability. The products are useful as 
plastisol or organosol resins. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The polymerization medium which contains effective amounts for the desired 
polymerization of vinyl chloride monomer (and, optionally, comonomers), a 
water-soluble initiator, a mixed emulsifier which is in the form of a 
pre-emulsion and, if desired, a buffer. 
Vinyl chloride monomer comprises at least 50%, preferably at least 85%, by 
weight of the entire monomeric component. Preferably, it is the sole 
monomer that is present. However, copolymers may be advantageously 
prepared in accordance with this invention. For example, copolymerizable 
mixtures, containing vinyl chloride and up to 49 percent vinyl acetate, 
but preferably in the range of 5 to 10 percent vinyl acetate, may be 
employed. Other monomers copolymerizable with vinyl chloride, which may be 
used in accordance with this invention, include: vinyl esters of other 
alkanoic acids, such as vinyl propionate, vinyl butyrate, and the like; 
the vinylidene halides, such a vinylidene chloride; vinyl esters of 
aromatic acids, e.g., vinyl benzoate; esters of alkenoic acids, for 
example, those of unsaturated mono-carboxylic acids such as methyl, 
acrylate, 2-ethyl hexyl acrylate, and the corresponding esters of 
methacrylic acid; and esters of alpha, beta-ethylenically unsaturated 
dicarboxylic acids, for example, the methyl, ethyl, propyl, butyl, amyl, 
hexyl, heptyl, octyl, allyl methallyl and phenyl esters of maleic, 
itaconic, fumaric acids, and the like. Amides such as acrylamide and 
methacrylamide, and nitriles, such as acrylonitrile, may also be suitably 
employed. Vinyl phosphonates, such a bis(beta chloroethyl)vinylphosphonate 
may also be employed. The water to monomer ratio in the reaction medium 
can be varied widely with values of from about 1.5 to about 2.5:1, 
preferably from about 1.7 to about 2.0:1, being representative. 
The initiator or catalyst which is used in the present invention can be any 
of the well-known water-soluble initiators which are used in the emulsion 
polymerization of vinyl chloride monomer. Oil soluble catalysts cannot be 
used since they yield a mixture of suspension and emulsion particles 
rather than the desired polydisperse product. Such free radical, 
water-soluble initiators as the peroxygen type compounds ammonium 
persulfate, sodium perborate, potassium persulfate, sodium persulfate and 
potassium percarbonate are illustrative of initiators that may be 
employed. If desired, a redox system can be used. Representative of such a 
system is a hydrogen peroxide initiator/ascorbic acid activator 
combination or a potassium persulfate/ascorbic acid combination. 
Combinations of persulfates and bisulfites, as for example, potassium 
persulfate and sodium metabisulfite can also be used. The amount of said 
initiator which is used should be an amount which is effective to 
polymerize the monomers which are present in the reaction medium. 
Generally, from about 0.05% to about 1%, preferably about 0.075% to about 
0.10%, based on the weight of monomers, of initiator or redox system is 
needed. 
The mixed emulsifier system of the present invention contains: (1) a 
C.sub.12 -C.sub.18 straight chain alkyl or alkenyl surfactant and (2) a 
C.sub.16 -C.sub.20 straight chain alkyl or alkenyl alcohol and/or 
saturated hydrocarbon of greater than 18 carbon atom chain length and is 
present in the reaction medium as a prehomogenized blend when the 
polymerization is begun. In such a pre-homogenized blend the surfactant 
and alcohol and/or hydrocarbon are present as a complex which coats the 
individual vinyl chloride monomer droplets and is responsible for the 
particle size distribution of the resin particles which result and their 
desirable physical properties. The use of a mixed emulsifier which has not 
been prehomogenized results in a binodal particle size distribution 
wherein the average particle size of the particles is often lower and 
wherein the resin particles do not possess the characteristics of the 
product of this invention. In such a non-prehomogenized system the 
surfactant and alcohol are uncomplexed so as to allow the alcohol to 
penetrate to the interior of the individual vinyl chloride monomer 
droplets. This allows surfactant micelles to form leading to production of 
a greater portion of smaller resin particles. The use of such a 
non-pre-homogenized polymerization technique also leads to 
irreproducibility problems as described before. 
The C.sub.12 -C.sub.18 straight chain surfactant which is useful in 
practicing the present invention has either the formula ROSO.sub.3 A or 
the formula RC(O)OA, where R is a C.sub.12 -C.sub.18 straight chain alkyl 
or alkenyl group and A is an alkali metal, alkaline earth metal or alkanol 
amine of up to 6 carbon atoms. Representative alkali metal cations are 
sodium, potassium and (for purposes of this invention) ammonium. An 
alkaline earth metal cation is calcium. Exemplary surfactants for use in 
the present invention include sodium lauryl sulfate, sodium tridecyl 
sulfate, sodium myristyl sulfate, sodium cetyl sulfate and sodium stearyl 
sulfate. Also suitable are compounds otherwise similar to any of the 
foregoing but where sodium is replaced by potassium, calcium, ammonium or 
alkanol amines of up to six carbon atoms. Compatible mixtures of any of 
the foregoing surfactants can be used. 
The C.sub.16 -C.sub.20 straight chain alkyl or alkenyl alcohols which are 
to be used in the mixed emulsifier system of the present invention include 
such alcohols as cetyl alcohol, oleyl alcohol, stearyl alcohol and 
eicosanol. A representative saturated hydrocarbon having a chain length of 
greater than 18 carbon atoms is eicosane. Compatible mixtures of any of 
the foregoing second components of the mixed emulsifier can be used. 
It is important to the success of the present invention that the alkyl or 
alkenyl group on the surfactant and other component of the mixed 
emulsifier be a straight chain rather than being either branched or on 
arylalkyl group. It has been found that arylalkyl surfactants, such as the 
alkylaryl sulfonates, and branched chain surfactants, such as 2-ethylhexyl 
sulfate, do not form the desired complex with the other component possibly 
due to steric interference caused by the bulkier branched chain and 
arylalkyl groups. The use of ethoxylated surfactants, such as the 
ethoxylated alkyl phenols and alcohols, should also be avoided since they 
give the surfactant too much of a polar character and tend to inhibit free 
radical polymerization due to the presence of benzoic hydrogens. 
The two components of the mixed emulsifier are first prehomogenized by 
subjecting them to agitation in water when they are both in the liquid 
state in any suitable agitation apparatus until a visually homogeneous 
mixture is formed. The mixture of the two components may have to be heated 
if one or both of the selected components is a solid at ambient 
temperature to above the melting point of each component or components. 
The monomeric reactants and initiator can then be added for the 
polymerization reaction. 
The amount of such mixed emulsifier system which is used must be sufficient 
to maintain a stable emulsion in the reaction environment. Use of smaller 
amounts than described herein will result in coagulation of the latex, 
whereas use of larger amounts will result in undesirable contamination of 
the product without providing any other significant benefit. The weight 
ratio of surfactant to alcohol in the mixture can range anywhere from 
about 1:1 about 1:4, preferably from about 1:2 to about 1:3 in order to 
produce the polydisperse product of the present invention having the 
desirable physical properties associated with the present invention. The 
amount of mixed emulsifier to vinyl chloride monomer (optionally in the 
presence of the copolymerizable monomers) is from about 0.7 to about 3%, 
preferably 0.8% to about 2%, by weight of all such copolymerizable 
monomers. 
The presence of a suitable buffer, e.g., borax, in order to maintain the 
reaction medium at a pH of from about 5 to about 8, preferably from about 
6 to about 7.5, is highly desirable since it will substantially retard any 
hydrolysis of the surfactant, thereby maintaining the integrity of the 
complexed emulsifier system. 
The polymerization process of the present invention is conducted by heating 
the reaction mixture to a temperature of from about 45.degree. C. to about 
70.degree. C. for about 3 hrs. to about 5 hrs.

The foregoing invention is illustrated by the Examples which follows 
EXAMPLE 1 
This Example illustrates a number of polymerizations according to the 
process of the present invention that were conducted in a 2 gallon (7.6 
liter) stainless steel laboratory reactor (Runs 1-6) as well as a 30 
gallon (113.6 liter) pilot plant reactor (Runs 7-9) in a one step process 
in 6 hours. 
The basic polymerization recipe that was used in all runs (unless noted 
otherwise) contained the following ingredients: 
______________________________________ 
Ingredient Amount (in grams) 
______________________________________ 
Deionized water 4500 
Vinyl chloride monomer 
3000 
Stearyl alcohol (available 
from Procter & Gamble) 
67 
Sodium Lauryl Sulfate (30% 
by weight solution - 
"Sipex UB" from Alcolac 
Chemical Corp.) 75 
Potassium persulfate 
initiator 9 
Sodium tetraborate buffer 
1.5 
______________________________________ 
A premix of the mixed emulsifier system was first prepared by adding the 
stearyl alcohol, sodium lauryl sulfate and buffer to the water and was 
homogenized at 250 rpm for 30 minutes at 65.degree. C. in the reactor. 
This temperature is above the melting point of the stearyl alcohol. The 
mixture was then cooled to 30.degree. C. and vinyl chloride monomer and 
initiator were added. This latter temperature is low enough to prevent 
premature reaction of the vinyl chloride monomer. The mixture was agitated 
for an additional 15 minutes to disperse the vinyl chloride monomer 
throughout the reaction medium and the temperature was raised to 
59.degree.-60.degree. C. to initiate the polymerization. 
The molar ratio of stearyl alcohol to sodium lauryl sulfate in the mixed 
emulsifier was 3:1, and the amount of sodium lauryl sulfate, based on 
vinyl chloride monomer, was 0.75%. 
The Table that is given on the page which follows sets forth some typical 
data that were obtained. 
TABLE 
______________________________________ 
Latex Particle 
Run Stability Latex % Dry Size Relative 
No. (min.) pH Coagulum (microns) 
Viscosity 
______________________________________ 
1 14 7.6 0.15 0.10-0.87 
-- 
2 15 8.3 0.23 0.04-1.01 
-- 
3 45 7.8 0.05 0.04-1.02 
1.90 
4 15 8.3 0.38 0.04-1.05 
1.93 
5 7 7.8 1.0 0.04-1.01 
-- 
6 11 8.1 0.19 -- -- 
7 9 4.2 nil 0.06-0.95 
2.26 
8 8 4.2 nil 0.06-0.81 
2.01 
9 15 3.8 nil 0.06-1.09 
-- 
______________________________________ 
Footnotes: 
The latex stability is measured by agitating the product latex in a 
Hamilton Beach laboratory mixer set at low speed. The time required to 
coagulate the product in the mixer is determined by visual inspection. 
This test gives a measure of the time required for a latex to coagulate o 
set-up. Higher times are more desirable. Coagulation adversely affects th 
ease with which latex can be pumped in commercial production environments 
The amount of dry coagulum is based on the weight of the monomer charge. 
Lower amounts of coagulum are desirable since coagulum adversely affects 
commercial operations. 
The relative viscosity is the ratio of the kinematic viscosity of a 
specified solution of the polymer (1% by weight in cyclohexanone at 
25.degree. C.) to the kinematic viscosity of the pure solvent. 
The following changes in procedure were made in Runs 3-9, inclusive: 
Run 3:The sodium lauryl sulfate was obtained from the Richardson Co. and 
15 g. of epoxidized soybean oil ("Paraplex G-62", from Rohm & Haas Co.) 
was added to the reaction. 
Run 4:The sodium lauryl sulfate was the same used in Run 3 and was presen 
at 0.65%, based on the weight of monomer. 
Run 5:The sodium lauryl sulfate was the same used in Run 3 and was presen 
at 0.53%, based on the weight of monomer. 
Run 6:The sodium lauryl sulfate was obtained from Henkel and was present 
at 0.60%, by weight of the monomer. 
Runs 7 to 9:A hydrogen peroxide/ascorbic acid catalyst system was used in 
a 4:1 weight ratio. The largest distribution of particles fell within the 
particle size range of 0.6 to 0.8 microns. 
Runs 1-6 represent laboratory scale batches in which the monomer conversion 
was about 95%. Good mechanical stability, low coagulum and the desired 
particle size of about 1 micron were obtained consistently. Runs 4-6 
represent successful attempts to lower the surfactant level. In Runs 7-9 a 
H.sub.2 O.sub.2 /Ascorbic Acid redox catalyst system was used as opposed 
to the K.sub.2 S.sub.2 O.sub.8 initiator employed in the 2 gallon 
laboratory experiments. This acidic catalyst system would account for the 
low pH values (3.8-4.2) obtained in the resulting latexes. This pH can 
easily be adjusted via an increase in the level of buffer. The mechanical 
stability, coagulum levels and particle sizes in Runs 7-9 were found to be 
comparable to that obtained in laboratory experiments. 
EXAMPLE 2 
This Example illustrates the use of the present process in the synthesis of 
a vinyl chloride/vinyl acetate/bis(betachloroethyl)vinylphosphonate 
terpolymer in a one-step process using the same procedure set forth in 
Example 1. 
The following two reaction mixtures were subjected to emulsion 
polymerization in bottles for 4 hours at a temperature of about 54.degree. 
C. using a cylindrically rotating polymerization bath set at about 16 rpm: 
______________________________________ 
Mixture 
Ingredient A (in g.) B 
______________________________________ 
Vinyl chloride monomer 
127.5 127.5 
Vinyl acetate monomer 
15.0 15.0 
Bis(beta-chloroethyl) 
vinylphosphonate monomer 
7.5 7.5 
1% (1:3 weight ratio) sod- 
ium lauryl sulfate/ 
stearyl alcohol solution 
112.5 150.0 
1% solution of sodium bi- 
carbonate 20.0 20.0 
1% solution of sodium 
persulfate 75.0 75.0 
Deionized water 97.5 60.0 
______________________________________ 
The products from each of the reaction mixtures was tested for mechanical 
stability using a Hamilton Beach test, percent coagulum, particle size and 
percent latex solids. The results are set forth below. 
______________________________________ 
Mech. Particle 
Stab. Coagulum Size Latex Solids 
Mixture 
(sec.) Level (%) (microns) 
(%) 
______________________________________ 
A &gt;4200* 0.13 0.09-2.31 
34 
B &gt;3000* 0.12 0.09-0.93 
36 
______________________________________ 
*neither sample had coagulated at the given time 
The foregoing illustrate certain preferred aspects of the present invention 
and should not be construed in a limiting sense. The claims which follow 
set forth the subject matter on which protection is desired.