Bulk radical polymerization using a batch reactor

The present invention provides a method for the polymerization of free-radically polymerizable vinyl monomers in a batch reactor under essential adiabatic conditions.

FIELD OF THE INVENTION 
The present invention provides a method for the polymerization of 
free-radically polymerizable vinyl monomers in a batch reactor. 
BACKGROUND OF THE INVENTION 
Bulk (i.e. mass) flee-radical polymerization of pure monomer typically 
involves high heat of reaction (i.e. highly exothermic), increasing 
solution viscosity as polymerization progresses and the corresponding 
decrease in heat transfer coefficient of the reacting material. Because of 
these problems, controlling the temperature of bulk polymerization 
processes can be extremely difficult. However, it is well known to those 
skilled in the art that maintaining the desired temperature, is very 
important because of the strong dependence of the flee-radical reaction 
kinetics on the reaction temperature, directly affecting the polymer 
properties such as molecular weight distribution and molecular weight. If 
the heat released from reaction exceeds the heat removal capability due to 
decreasing heat transfer, uncontrolled runaway can result where the rate 
of reaction increases as the temperature escalates due to exothermic 
reaction. 
To circumvent these problems, flee-radical solution polymerization is 
commonly performed where a non-reactive solvent in which the monomer and 
polymer are both soluble is used to reduce the heat load as well as to 
increase the heat transfer coefficient of the reacting mixture to 
facilitate temperature control. Alternatively, the heat load and 
viscosity/heat transfer problems are commonly managed by suspension 
polymerization and emulsion polymerization approaches. Solution 
polymerization, suspension polymerization, and emulsion polymerization 
approaches are disadvantageous in that they require extra equipment and 
extra processing. Solution, suspension, and emulsion polymerization 
provide a decreased yield over bulk polymerization for a specific reactor 
volume. Emulsion and suspension polymerization offer the possibility of 
contaminants being introduced into the polymer from the surfactants and/or 
emulsifiers used in the polymerization process. Contaminants can also be 
introduced through impurities in the solvent in solution polymerization. 
Further, in the case of solution polymerization, solvent handling can be 
dangerous because of the threat of fire and/or explosion. Solvent handling 
can be expensive because extra equipment may be necessary to capture the 
solvent for reuse or other capture method, such as thermal oxidizers, may 
be required to prevent the compounds from being vented to the atmosphere. 
Bulk free-radical polymerization heat transfer difficulties can be often 
managed in continuous processes. For example, reactive extrusion has been 
disclosed (U.S. Pat. Nos. 4,619,979; 4,843,134; and 3,234,303) as a useful 
bulk polymerization process because of the high heat transfer capability 
due to the large heat transfer area per unit reacting volume and the 
extremely high mixing capability. Similarly, a continuous static mixer 
reactor with high heat transfer area for temperature controlled bulk free 
radical polymerization has been disclosed in U.S. Pat. No. 4,275,177. 
As a rule, runaway free-radical polymerization reactions are not practiced 
because of their potentially disastrous consequences (Principles of 
Polymerization, Odian, G., 3rd Edition, Wiley-Interscience, p. 301, 1991). 
Generally, methods are used to control batch bulk polymerization reaction 
temperature to prevent runaway (i.e., U.S. Pat. Nos. 4,220,744, 5,252,662, 
JP 56185709). 
Biesenberger et al. investigate batch runaway polymerization ("A Study of 
Chain Addition Polymerizations with Temperature Variations: I. Thermal 
Drift and Its Effect on Polymer Properties," J. A. Biesenberger and R. 
Capinpin, Polymer Engineering and Science, November, 1974, Vol. 14, No. 
11, "A Study of Chain Addition Polymerizations with Temperature 
Variations: II. Thermal Runaway and Instability--A Computer Study," J. A. 
Biesenberger, R. Capinpin, and J. C. Yang, Polymer Engineering and 
Science, February, 1976, Vol. 16, No. 2, "A Study of Chain Addition 
Polymerizations with Temperature Variations: III Thermal Runaway and 
Instability in Styrene Polymerization--An Experimental Study," D. H. 
Sebastian and J. A. Biesenberger, Polymer Engineering and Science, 
February, 1976, Vol. 16, No. 2, "A Study of Chain-Addition Polymerizations 
with Temperature Variations. IV. Copolymerizations--Experiments with 
Styrene-Acrylonitrile," D. H. Sebastian and J. A Biesenberger, Polymer 
Engineering and Science, February, 1979, Vol. 19, No. 3, "Thermal Ignition 
Phenomena in Chain Addition Polymerizations," J. A. Biesenberger, R. 
Capinpin, and D. Sebastian, Applied Polymer Symposium, No. 26, 211-236, 
John Wiley & Sons, 1975). In Part II of the Biesenberger et al. series, 
potential benefits of runaway polymerization are suggested. However, the 
purpose of the series is to understand runaway polymerization in order to 
prevent it. The series does not teach practical aspects of useful runaway 
polymerization in an industrial setting, as disclosed in the present 
invention. Adiabatic conditions are not employed in the Biesenberger et 
al. runaway polymerizations. 
Continuous flee-radical polymerization processes have been disclosed which 
involve adiabatic polymerization in tubular reactors (U.S. Pat. No. 
3,821,330, DE 4235785A1). These approaches use equipment more complicated 
than a batch reactor. 
Although industrially important, batch (non-continuous) reactors are less 
frequently used for bulk free-radical polymerization. The prime difficulty 
with batch reactors is that the heat transfer area per unit reacting 
volume is poor and becomes increasingly poor with larger reactor size. 
Methods of free-radical polymerization for acrylate pressure sensitive 
adhesive (PSA) production in batch reactors have been disclosed where 
polymerization chemistry is adjusted to slow the reaction rate so that the 
reaction temperature can be controlled (U.S. Pat. No. 5,252,662, JP 
56185709). The difficulty with these approaches is that the heat transfer 
area of the batch reactor is still being relied upon to control reaction 
temperature by removing the heat of reaction and prevent runaway. 
Therefore, these polymerization approaches will not scale up directly 
because of the varying heat transfer capability with batch reactor size 
and they will be difficult to perform in large batch reaction equipment 
because of the increasingly poor heat transfer per unit volume with 
reactor size. Further, in controlling the heat load by slowing the 
reaction rate, the cycle time and thus productivity of a reaction vessel 
is decreased. 
Bach reactors are desirable over continuous reactors in certain instances. 
For example, a specialty chemical manufacturer tends to produce multiple 
products. In this case batch reactors can be beneficial because of their 
multipurpose nature (i.e. not necessarily designed for a particular 
product or chemistry as is often the case with continuous equipment). In 
addition, often the economics of a batch reactor are favorable over that 
for a continuous process because of the relative simplicity of a batch 
reactor equipment. Typically, continuous processes become economical for 
high-volume commodity products (i.e. polystyrene). 
In addition, the use of batch reactors for adhesive production is common 
because of the economics of their typical production volumes. Common 
monomers that are a major contributor to the composition of pressure 
sensitive adhesives (see below) have relatively high boiling points, and 
because of their relatively high molecular weights, have relatively low 
heat of reaction per unit mass. Therefore, the adiabatic temperature rise 
is such that the resulting mixture vapor pressure during reaction remains 
below about 100-300 psig (792.9-2171.8 kPa), pressures handled by common 
batch reactor equipment. 
Advantages of bulk polymerization to produce hot-melt adhesives over other 
conventional polymerization methods are described in U.S. Pat. No. 
4,619,979. 
SUMMARY OF THE INVENTION 
The present invention provides a novel method for producing polymer by bulk 
free-radical polymerization in a batch reactor. The term "polymerization" 
as used herein with respect to the present invention includes also 
telomerizaion. Rather than the conventional approach of directly 
controlling the reaction temperature, the present invention makes use of 
appropriately chosen free-radical initiator(s) and reacting in essentially 
adiabatic runaway reaction cycles. 
As described herein, a "reaction cycle" is defined as a processing sequence 
where initiator(s), monomers (which are not optional in the first reaction 
cycle, but which may be optional in subsequent reaction cycle), and 
optional component(s) are added to the batch followed by one or more 
essentially adiabatic reactions with optional heating between the 
essentially adiabatic reactions. 
As defined herein, by "essentially adiabatic" it is meant that total of the 
absolute value of any energy exchanged to or from the batch during the 
course of reaction will be less than about 15% of the total energy 
liberated due to reaction for the corresponding amount of polymerization 
that has occurred during the time that polymerization has occurred. 
Expressed mathematically, the essentially adiabatic criterion is: 
##EQU1## 
where f is about 0.15, .DELTA.H.sub.p is the heat of polymerization, x 
=monomer conversion=(M.sub.o -M)/M.sub.o where M is the concentration of 
the monomer and M.sub.o is the initial monomer concentration, x.sub.1 is 
the polymer fraction at the start of the reaction and x.sub.2 is the 
polymer fraction due to polymerization at the end of the reaction, t is 
the time. t.sub.1 is the time at the start of reaction, t.sub.2 is the 
time at the end of reaction, and q.sub.j (t), wherein j=1 . . . N is the 
rate of energy transferred to the reacting system from the surroundings 
from all N sources of energy flow into the system. Examples of energy 
transfer sources for q.sub.j (t), wherein j=1 . . . N include, but are not 
limited to, heat energy conducted to or from the batch from the reactor 
jacket, energy required to warm internal components in the reaction 
equipment such as the agitator blades and shaft, and work energy 
introduced from mixing the reacting mixture. In the practice of the 
present invention, having f as close to zero as possible is preferred to 
maintain uniform conditions within a batch during a reaction (i.e., 
maintain homogeneous temperature conditions throughout a batch) which 
helps to minimize batch-to-batch variations in a particular piece of 
equipment as well as minimize batch-to-batch variations when reactions are 
made in batch reactors of differing sizes (i. e., uniform scaleup or scale 
down of reaction). 
Although one essentially adiabatic reaction may be employed, generally two 
or more essentially adiabatic reaction cycles are employed if essentially 
complete conversion of monomer to polymer is desired. There typically is 
cooling between the reaction cycles. Cooling of the reaction mixture 
between reaction cycles typically is performed to prevent the temperature 
of the reaction mixture from increasing to a point where the product is 
unstable. This instability can be manifest by polymer discoloration, 
polymer oxidation, depolymerization to produce undesirable low molecular 
weight oligomers, etc. The temperature necessary to avoid instability 
depends in part on the monomers being used. To avoid such instability the 
temperature of the reaction mixture is generally kept below about 
300.degree. C., preferably below about 250.degree. C. The reaction 
conditions are also typically chosen so that at the end of the final 
reaction cycle, the product viscosity is such that draining from the 
reaction vessel can be performed (Brookfield viscosity at draining 
temperature less than about 500,000 centipoise). 
Optionally, a series of one or more essentially adiabatic reaction cycles 
can be used to provide a syrup of polymer dissolved in monomer, typically 
in the range of about 40-95 weight % based on total weight of monomer(s) 
and polymer where the unreacted monomer can be optionally stripped from 
the polymer to provide the final polymer product rather than running the 
reaction to completion. 
The method of the present invention uses one or more thermal free radical 
initiators that under the increasing reaction temperature profile from 
essentially adiabatic reaction conditions, provide free radicals at a rate 
such that narrow polymer molecular weight distribution is obtained. The 
amount of free radicals generated during the increasing temperature 
profile is controlled by the amounts of each initiator used and the 
temperature decomposition characteristics of the selected initiators. 
Experience has shown that this inventive process is capable of achieving 
polymer molecular weight distributions essentially the same as or narrower 
than isothermal solution polymerization methods. 
As disclosed herein, when appropriately polymerized, essentially adiabatic 
bulk free-radical runaway polymerization in a batch reactor can present 
several advantages: 
1) When adiabatically polymerized, because the reaction equipment is not 
being used to cool the reacting mixture, there is not a significant 
temperature gradient at the walls of the reaction equipment. Such a 
temperature gradient can detrimentally broaden the molecular weight 
distribution of the polymer by making high molecular weight product in the 
cold boundary layer near the reactor wall, because of the free-radical 
reaction kinetics well known to those skilled in the art. For example, 
such high molecular weight components can degrade the coating performance 
of a hot-melt adhesive. 
2) The reaction equipment utilized according to the method of the present 
invention is simple. 
3) Because heat transfer requirements during reaction are eliminated, the 
method of the present invention more readily scales up from lab-scale 
equipment to large production-scale equipment than temperature-controlled 
polymerization methods that rely on available heat transfer area to 
control reaction temperature. 
4) Continuous polymerization reaction equipment contain various degrees of 
"backmixing" where there is a residence time distribution of the reacting 
material in the reaction equipment. Some of the reacting material can 
remain in the reaction equipment for extended periods of time to degrade 
product performance by continued attack by the free-radical initiator to 
form crosslinked polymer. Crosslinked gel particles can degrade product 
performance, such as the coating smoothness of a hot-melt adhesive. 
5) Depending on the polymer and reaction conditions, essentially complete 
conversion of monomer to polymer is possible according to the method of 
the present invention. Based on specific product requirements, it may be 
necessary to react the final 1-15 weight % of monomer slowly (over a 
period of one to several hours) to minimize the formation of low molecular 
weight components as monomer depletes. Residence times of hours in 
continuous reaction equipment, such as an extruder, can be economically 
impractical. 
The present invention provides a method of free radically polymerizing 
vinyl monomers comprising the steps of: 
(a) providing a mixture comprising: 
(i) free radically (co)polymerizable vinyl monomers; 
(ii) optional chain transfer agent; 
(iii) optional crosslinking agent; 
(iv) at least one thermal free-radical initiator; 
(v) optionally a polymer comprising polymerized free radically 
polymerizable monomers; 
in a batch reactor; 
(b) deoxygenating the mixture, wherein step (b) can at least partially 
overlap with step (c); 
(c) heating the mixture to a sufficient temperature to generate sufficient 
initiator free radicals from at least one thermal free radical initiator 
so as to initiate polymerization; 
(d) allowing the mixture to polymerize under essentially adiabatic 
conditions to yield an at least partially polymerized mixture; 
(e) optionally heating the mixture to generate free radicals from some or 
all of any initiator that has not generated initiator free radicals, 
followed by allowing the mixture to polymerize under essentially adiabatic 
conditions to yield a further polymerized mixture; and 
(f) optionally repeating step (e) one or more times. 
Typically, more than one initiator is present in the mixture of step (a). 
More typically, 1 to 5 different initiators are present in the mixture of 
step (a). In some situations, 2, 3, 4 or 5 different initiators are 
present in the mixture of step (a). 
The present invention a method of free radically polymerizing vinyl 
monomers comprising the steps of. 
(a) providing a mixture comprising: 
(i) free radically (co)polymerizable vinyl monomers; 
(ii) optional chain transfer agent; 
(iii) optional crosslinking agent; 
(iv) at least one thermal free-radical initiator; 
(v) optionally polymer comprising polymerized free radically polymerizable 
monomers; 
in a batch reactor; 
(b) deoxygenating the mixture if the mixture is not already deoxygenated, 
wherein step (b) can optionally at least partially overlap with step (c); 
(c) heating the mixture to a sufficient temperature to generate sufficient 
initiator free radicals from at least one thermal free radical initiator 
so as to initiate polymerization; 
(d) allowing the mixture to polymerize under essentially adiabatic 
conditions to yield and at least partially polymerized mixture; 
(e) optionally heating the mixture to generate free radicals from some or 
all of any initiator that has not generated initiator free radicals, 
followed by allowing the mixture to polymerize under essentially adiabatic 
conditions to yield a further polymerized mixture; and 
(f) optionally repeating step (e) one or more times. 
(g) optionally cooling the mixture; 
(h) adding to the mixture in the batch reactor at least one thermal free 
radical initiator wherein the initiator(s) of step (h) can be the same or 
different than the initiator(s) of step (a), optionally free radically 
polymerizable monomers, optionally crosslinking agents, optionally chain 
transfer agent(s), optionally polymer comprising polymerized free 
radically polymerizable monomers, wherein the mixture optionally has a 
temperature below that which would generate initiator free radicals from 
the initiator(s) added in step (h); 
(i) deoxygenating the mixture if the mixture is not already deoxygenated; 
(j) optionally heating the mixture to generate initiator free radicals from 
at least one initiator to further polymerize the mixture if the mixture 
has a temperature below that which would generate initiator free radicals 
from the initiator(s) added in step (h); 
(k) allowing the mixture to further polymerize under essentially adiabatic 
conditions to yield a further polymerized mixture; 
(l) optionally heating the mixture to generate free radicals from some or 
all of any initiator that has not generated initiator free radicals, 
followed by allowing the mixture to polymerize under essentially adiabatic 
conditions to yield a further polymerized mixture; 
(m) optionally repeating step (l) one or more times; 
(n) optionally repeating steps (g) through (m) one or more times. 
Typically, more than one initiator is present in the mixture of step (a) 
and step (h). More typically, 1 or 2 different initiators are present in 
the mixture of step (a), 1 to 5 different initiators are present in step 
(h), and 1 to 5 different initiators are present in each repeat of steps 
(g) through (m) when step (n) is included. Most typically 2 to 5 different 
initiators are present in step (h), and 2 to 5 different initiators are 
present in each repeat of steps (g) through (k) when step (l) is included.

DETAILED DESCRIPTION OF THE INVENTION 
Batch Reactor 
A batch reactor is used in the method of the present invention. By reacting 
batch wise is meant that the polymerization reaction occurs in a vessel 
where product is drained at the end of the reaction, not continuously 
while reacting. The raw materials can be charged to the vessel at one time 
prior to reacting, in steps over time while reacting, or continuously over 
a time period while reacting, and the reaction is allowed to proceed for 
the necessary amount of time to achieve, in this case, polymer properties 
including the desired polymerization amount, molecular weight, etc. If 
necessary, additives can be mixed into the batch prior to draining. When 
the processing is complete, the product is drained from the reaction 
vessel. 
A typical batch reactor for this invention will comprise a pressure vessel 
constructed of material suitable for the polymerization, such as stainless 
steel which is commonly used for many types of free-radical 
polymerization. Typically, the pressure vessel will have ports for 
charging raw materials, removing product, emergency pressure relief, 
pressurizing the reactor with inert gas, pulling vacuum on the reactor 
head space, etc. Typically, the vessel is enclosed partially in a jacket 
through which a heat transfer fluid (such as water) is passed for heating 
and cooling the contents of the vessel. Typically, the vessel contains a 
stirring mechanism such as a motor-driven shaft inserted into the vessel 
to which stirring blades are attached. Commercial batch reaction equipment 
typically is sized in the range of about 10 to about 20,000 gallons (37.9 
to 75,708 liters), and can be custom-built by the user or can be purchased 
from vendors such as Pfaudler-U.S., Inc. of Rochester, New York. 
Safety Considerations 
Extreme caution must be exercised to ensure that the reaction vessel can 
contain the elevated vapor pressure of the reaction mixture, at the 
temperatures that will be encountered, particularly if the reaction should 
proceed faster or further than desired because of an accidental 
overcharge/mischarge of initiator(s). It is also very important to ensure 
the reaction mixture will not decompose at the temperatures encountered to 
form gaseous product that could dangerously elevate the vessel pressure. 
Small-scale adiabatic calorimetric experiments, which one skilled in the 
art would be readily capable of performing, can be used to determine the 
runaway characteristics for particular monomers and initiator mixtures. 
For example, the Reactive System Screening Tool (RSST) or the Vent Sizing 
Package (VSP), both available from Fauske and Associates, Inc. of Burr 
Ridge, Ill., are devices capable of investigating runaway reaction 
characteristics and severity. Additional safety considerations are 
discussed elsewhere herein. 
Free-Radically Polymerizable Vinyl Monomers 
A variety of free radically polymerizable monomers can be used according to 
the method of the present invention. Typical monomers applicable for this 
invention include, but are not limited to, those acrylate monomers 
commonly used to produce acrylate pressure sensitive adhesives (PSA). The 
identity and relative amounts of such components are well known to those 
skilled in the art. Particularly preferred among acrylate monomers are 
alkyl acrylates, preferably a monofunctional unsaturated acrylate ester of 
a non-tertiary alkyl alcohol, wherein the alkyl group contains 1 to about 
18 carbon atoms. Included within this class of monomers are, for example, 
isooctyl acrylate, isononyl acrylate, 2-ethylhexyl acrylate, decyl 
acrylate, dodecyl acrylate, n-butyl acrylate, hexyl acrylate, octadecyl 
acrylate, and mixtures thereof. 
Optionally and preferably in preparing a PSA polar copolymerizable monomers 
can be copolymerized with the acrylate monomers to improve adhesion of the 
final adhesive composition to metals and also improve cohesion in the 
final adhesive composition. Strongly polar and moderately polar 
copolymerizable monomers can be used. 
Strongly polar copolymerizable monomers include but are not limited to 
these selected from the group consisting of acrylic acid, itaconic acid, 
hydroxyalkyl acrylates, cyanoalkyl acrylates, acrylamides, substituted 
acrylamides, and mixtures thereof. A strongly polar copolymerizable 
monomer preferably constitutes a minor amount, e.g. up to about 25 weight 
% of the monomer, more preferably up to 15 weight %, of the monomer 
mixture. When strongly polar copolymerizable monomers are present, the 
alkyl acrylate monomer generally constitutes a major amount of the 
monomers in the acrylate-containing mixture, e.g., at least about 75% by 
weight of the monomers. 
Moderately polar copolymerizable monomers include but are not limited to 
those selected from the group consisting of N-vinyl pyrrolidone, 
N,N-dimethyl acrylamide, acrylonitrile, vinyl chloride, diallyl phthalate, 
and mixtures thereof. A moderately polar copolymerizable monomer 
preferably constitutes a minor amount, e.g., up to about 40 weight %, more 
preferably from 5 weight % to 40 weight %, of the monomer mixture. When 
moderately polar copolymerizable monomers are present, the alkyl acrylate 
monomer generally constitutes at least about 60 weight % of the monomer 
mixture. 
Macromonomers are another monomer useful herein. Described in U.S. Pat. No. 
4,732,808, incorporated by reference herein, is the use of free-radically 
copolymerizable macromonomers having the general formula X--(Y).sub.n --Z 
wherein 
X is a vinyl group copolymerizable with other monomer(s) in the reaction 
mixture; 
Y is a divalent linking group; where n can be zero or one; and 
Z is a monovalent polymeric moiety having a glass transition temperature, 
T.sub.g, greater than about 20.degree. C., and a weight average molecular 
weight in the range of about 2,000 to about 30,000 and being essentially 
unreactive under 
copolymerization conditions. 
These macromonomers are generally used in mixtures with other 
(co)polymerizable monomer(s). The preferred macromonomer described in U.S. 
Pat. No. 4,732,808 may be further defined as having an X group which has 
the general formula 
##STR1## 
wherein R is a hydrogen atom or a --COOH group and R' is a hydrogen atom 
or methyl group. The double bond between the carbon atoms provides a 
copolymerizable moiety capable of copolymerizing with the other monomer(s) 
in the reaction mixture. 
The preferred macromonomer includes a Z group which has the general formula 
##STR2## 
wherein R.sup.2 is a hydrogen atom or a lower alkyl group (typically 
C.sub.1 to C.sub.4), R.sup.3 is a lower alkyl group (typically C.sub.1 to 
C.sub.4), n is an integer from 20 to 500 and R.sup.4 is a monovalent 
radical selected from the group consisting of 
##STR3## 
and--CO.sub.2 R.sup.6 wherein R.sup.5 is a hydrogen atom or a lower alkyl 
group (typically C.sub.1 to C.sub.4) and R.sup.6 is a lower alkyl group 
(typically C.sub.1 to C.sub.4). 
Preferably, the macromonomer has a general formula selected from the group 
consisting of 
##STR4## 
wherein R.sup.7 is a hydrogen atom or lower alkyl group (typically C.sub.1 
to C.sub.4). 
The preferred macromonomer is a functionally terminated polymer having a 
single functional group (the vinyl group) and is sometimes identified as a 
"semitelechelic" polymer. (Vol. 27 "Functionally Terminal Polymers via 
Anionic Methods" D. N. Schultz et al., pages 427-440, Anionic 
Polymerization, American Chemical Society [1981].) Such macromonomers are 
known and may be prepared by the methods disclosed by Milkovich et al. in 
U.S. Pat. Nos. 3,786,116 and 3,842,059, the disclosures of which are 
incorporated herein by reference for the description of the preparation of 
the vinyl-terminated macromonomers. As disclosed therein, vinyl terminated 
macromonomer is prepared by anionic polymerization of polymerizable 
monomer to form a living polymer. Such monomers include those having an 
olefinic group, such as the vinyl-containing compounds. Living polymers 
are conveniently prepared by contacting the monomer with an alkali metal 
hydrocarbon or alkoxide salt in the presence of an inert organic solvent 
which does not participate in or interfere with the polymerization 
process. Monomers which are susceptible to anionic polymerization are well 
known. Illustrative species include vinyl aromatic compounds such as 
styrene, alpha-methylstyrene, vinyltoluene and its isomers or non-aromatic 
vinyl compounds such as methyl methacrylate. Other monomers susceptible to 
anionic polymerization are also useful. 
The purpose of using a copolymerizable macromonomer includes but is not 
limited to enabling hot-melt coating of the PSA, but increasing the 
cohesive strength of the cooled extruded sheet PSA by the interaction of 
the pendant Z moieties on the polymer backbone. The amount of macromonomer 
used is generally within the range of about 1% to about 30%, preferably 1% 
to 7%, of the total weight of monomers. As mentioned previously "monomer" 
is defined herein to include macromonomer. The optional use of such 
macromonomers is included within the scope of the present invention. A 
particular advantage of the present invention is the ability to 
successfully copolymerize said macromonomers into the polymer backbone. In 
conventional, lower-temperature isothermal bulk polymerization, as 
polymerization proceeds, the macromonomer can precipitate out due to the 
immiscability of the macromonomer in the accumulating polymer, preventing 
the necessary polymerization of the macromonomer into the polymer 
backbone. In the practice of the present invention, because of the 
elevated temperatures obtained at high conversion, the successful use of 
free-radically copolymerizable macromonomers has been demonstrated. 
Other monomer(s) for which the inventive method can be expected to be 
applicable include other members of the vinyl family such as monoalkenyl 
aromatic monomers including but not limited to those selected from the 
group consisting of styrene, alpha-methyl styrene, vinyl toluene, 
para-methyl styrene, tertiary butyl styrene, and mixtures thereof. Other 
"acrylic monomers" for which the inventive process is expected to be 
applicable include but are not limited to those selected from the groups 
consisting of methacrylate esters such as methyl methacrylate, N-butyl 
methacrylate, hydroxy ethyl methacrylate, and 
dimethylaminoethylmethacrylate; and methacrylic derivatives, such as 
methacrylic acid, and salts thereof and methacrylonitrile. Other suitable 
nonacrylic ethylenic monomer(s) are expected to include vinyl esters such 
as vinyl acetate and maleic acid. 
Chain Transfer Agents 
Chain transfer agents which are well known in the polymerization art may 
also be included to control the molecular weight or other polymer 
properties. The term "chain transfer agent" as used herein also includes 
"telogens". Suitable chain transfer agents for use in the inventive 
process include but are not limited to those selected from the group 
consisting of carbon tetrabromide, hexanebromoethane, 
bromotrichloromethane, 2-mercaptoethanol, t-dodecylmercaptan, 
isooctylthioglycoate, 3-mercapto-1,2-propanediol, cumene, and mixtures 
thereof. Depending on the reactivity of a particular chain transfer agent 
and the amount of chain transfer desired, typically 0 to about 5 percent 
by weight of chain transfer agent is used, preferably 0 to about 0.5 
weight percent, based upon the total weight of monomer(s). 
Crosslinking 
Crosslinking may also be used in the method of the invention. For example, 
in the art of hot-melt PSA manufacture, PSAs often require a curing step 
after they have been extruded in sheet form in order to give them good 
bond strength and toughness. This step, known as post curing, usually 
comprises exposing the extruded sheet to some form of radiant energy, such 
as electron beam, or ultraviolet light with the use of a chemical 
crosslinking agent. 
Examples of suitable crosslinking agents include but are not limited to 
those selected from the groups consisting of hydrogen abstraction type 
photocrosslinkers such as those based on benzophenones, acetophenones, 
anthraquinones, and the like. These crosslinking agents can be 
copolymerizable or non-copolymerizable. 
Examples of suitable non-copolymerizable hydrogen abstraction crosslinking 
agents include benzophenone, anthraquinones, and radiation-activatable 
crosslinking agents such as those described in U.S. Pat. No. 5,407,971. 
Such agents have the general formula 
##STR5## 
wherein W represents --O--, --N--, or --S--; X represents CH.sub.3 -- or 
phenyl;: Y represents a ketone, ester, or amide functionality; Z 
represents a polyfunctional organic segment that contains no hydrogen 
atoms more photoabstractable than hydrogen atoms of a polymer formed using 
the crosslinking agent; m represents an integer from 0 to 6; "a" 
represents 0 or 1 and n represents an integer 2 or greater. Depending on 
the amount of crosslinking desired and the efficiency of the particular 
crosslinker used, noncopolymerizable crosslinking agents are typically 
included in the amount of about 0% to about 10%, and preferred in the 
range of about 0.05% to about 2%, based on total weight of the monomer(s). 
Examples of suitable copolymerizable hydrogen abstraction crosslinking 
compounds include mono-ethylenically unsaturated aromatic ketone monomers 
free of orthoaromatic hydroxyl groups. 
Examples of suitable free-radically copolymerizable crosslinking agents 
include but are not limited to those selected from the group consisting of 
4-acryloxybenzophenone (ABP), para-acryloxyethoxybenophenone, and 
para-N-(methacryloxyethyl)-carbamoylethoxybenophenone. Copolymerizable 
chemical cross linking agents, are typically included in the amount of 
about 0% to about 2%, and preferred in the amount of about 0.025% to about 
0.5%, based on the total weight of monomer(s). Other useful 
copolymerizable crosslinking agents are described in U.S. Pat. No. 
4,737,559. 
Solvents 
In many cases, free-radical polymerization can take place without solvents, 
i.e., true bulk polymerization where the polymer formed as well as the 
monomers themselves all being miscible. However, the monomers may in some 
cases require a solvent in order to (co)polymerize. For example, 
acrylamides are dissolved in a small amount of solvent in order to make 
them miscible with isooctyl acrylate. Therefore, the inventive process 
includes within its scope the use of solvents which are nonreactive in the 
free radical polymerization being carded out. Such solvents usually 
comprise less than about 20 weight percent based on the total weight of 
the mixture. Useful solvents are those that are miscible in the mixture 
including but not limited to organic solvents such as toluene, hexane, 
pentane, and ethyl acetate. Solvents may also enhance the inventive 
process, so as to reduce the viscosity of the polymer at the end of the 
polymerization to facilitate draining or subsequent processing. Unless 
necessary, however, addition of solvents is not preferred because they can 
present the same disadvantages as solution polymerization, although to a 
lesser degree when the solvent concentration is low. 
Optional Polymer 
Optionally, polymer may be dissolved in the reaction mixture prior to the 
first essentially adiabatic reaction cycle. Alternatively and/or in 
addition the optional polymer may be included in subsequent essentially 
adiabatic reaction cycles. Such polymer may be included to modify the 
molecular weight distribution, molecular weight, or properties of the 
final polymer product after reacting is complete and generally will be 
non-reactive during the polymerization of the inventive process. Although 
it is not required, the polymer generally will be composed of the same 
monomer(s) as that to be reacted in the reaction mixture comprising the 
polymer, monomer(s), initiator(s), optional chain transfer agent(s), etc. 
Polymer dissolved in the monomer(s) prior to the first reaction cycle 
typically will be included in the range of about 0% to about 50% by weight 
and preferably less than about 0% to about 30% by weight, based on total 
weight of monomer(s) plus polymer. The use of polymer syrups to make 
acrylic polymers is explained in U.S. Pat. No. 4,181,752. 
Free-Radical Initiators 
Many possible thermal free radical initiators are known in the art of vinyl 
monomer polymerization and may be used in this invention. Typical thermal 
free radical polymerization initiators which are useful herein are organic 
peroxides, organic hydroperoxides, and azo-group initiators which produce 
free radicals. Useful organic peroxides include but are not limited to 
compounds such as benzoyl peroxide, di-t-amyl peroxide, t-butyl peroxy 
benzoate, and di-cumyl peroxide. Useful organic hydroperoxides include but 
are not limited to compounds such as t-amyl hydroperoxide and t-butyl 
hydroperoxide. Useful azo-group initiators include but are not limited to 
the VAZO.TM. compounds manufactured by DuPont, such as VAZO.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), VAZO.TM. 64 
(2,2'-azobis(2-methylpropanenitrile)), Vazo.TM. 67 
(2,2'-azobis(2-methylbutanenitrile)), and VAZO.TM. 88 
(2,2'-azobis(cyclohexanecarbonitdle)). 
When the initiator(s) have been mixed into the monomers, there will be a 
temperature above which the mixture begins to react substantially (rate of 
temperature rise typically greater than about 0.1.degree. C./min for 
essentially adiabatic conditions). This temperature, which depends on 
factors including the monomer(s) being reacted, the relative amounts of 
monomer(s), the particular initiator(s) being used, the amounts of 
initiator(s) used, and the amount of any polymer and/or any solvent in the 
reaction mixture, will be defined herein as the "runaway onset 
temperature". As an example, as the amount of an initiator is increased, 
its runaway onset temperature in the reaction mixture will decrease. At 
temperatures below the runaway onset temperature, the amount of 
polymerization proceeding will be practically negligible. At the runaway 
onset temperature, assuming the absence of reaction inhibitors and the 
presence of essentially adiabatic reaction conditions, the free radical 
polymerization begins to proceed at a meaningful rate and the temperature 
will start to accelerate upwards, commencing the runaway reaction. 
According to the present invention, a sufficient amount of initiator(s) 
typically is used to carry the polymerization to the desired temperature 
and conversion. If too much initiator(s) is used, an excess of low 
molecular weight polymer will be produced thus broadening the molecular 
weight distribution. Low molecular weight components can degrade the 
polymer product performance. If too little initiator is used, the 
polymerization will not proceed appreciably and the reaction will either 
stop or will proceed at an impractical rate. The amount of an individual 
initiator used depends on factors including its efficiency, its molecular 
weight, the molecular weight(s) of the monomer(s), the heat(s) of reaction 
of the monomer(s), the types and amounts of other initiators included, 
etc. The total initiator amount, that for all initiator(s), typically is 
used in the range of about 0.0005 weight % to about 0.5 weight % and 
preferably in the range of about 0.001 weight % to about 0.1 weight % 
based on the total weight of monomer(s). 
When more than one initiator is used in the reaction, as the first 
initiator depletes during an essentially adiabatic reaction (with the 
corresponding increasing reaction temperature), the second initiator may 
be selected such that it is thermally activated when the first initiator 
is becoming depleted. That is, as the first initiator is depleting, the 
reaction has brought the reaction mixture to the runaway onset temperature 
for the second initiator in the reaction mixture. An overlap is preferred 
such that before one initiator completely depletes another initiator 
activates (reaches its runaway onset temperature). Without an overlap, the 
polymerization rate can slow or essentially stop without external heating 
to bring the mixture to the runaway onset temperature of the next 
initiator in the series. This use of external heating defeats one of the 
benefits of the inventive process by adding the potential for nonuniform 
temperature distribution in the reaction mixture due to the external 
heating. However, polymerization still occurs under essentially adiabatic 
conditions which is an important feature of the invention. 
Until the temperature increases towards the runaway onset temperature for 
an individual initiator in the batch, the initiator is essentially 
dormant, not appreciably decomposing to form free radicals. It will remain 
dormant until the reaction temperature increases towards its runaway onset 
temperature in the reaction mixture and/or until external heat is applied. 
The succession of one initiator depleting and another reaching its runaway 
onset temperature can continue as the temperature rises for virtually any 
number of thermal initiators in the reaction system. In the limit, a 
succession of virtually an infinite number of different initiators could 
be used with nearly complete overlap of the active temperature ranges 
between adjacent initiators in the succession to bring about the 
polymerization and the corresponding adiabatic temperature rise. In this 
case, the amount of each initiator used would need to be virtually 
infinitesimally small so as to not detrimentally broaden the molecular 
weight distribution. 
Practically, to minimize raw material handling requirements, a reasonable 
minimum number of initiators should be used to achieve the desired amount 
of adiabatic polymerization and obtain the necessary polymer properties. 
Typically, 1 to 5 different initiators (more typically 2 to 5) are used 
during a particular reaction cycle. In some circumstances it may be 
advantageous to use 2, 3, 4, or 5 different initiators per reaction cycle. 
To estimate the amount of overlap between successive initiators in a series 
during an essentially adiabatic polymerization, standard polymerization 
modeling techniques can be employed (i.e., W. H. Ray, "On the Mathematical 
Modeling of Polymerization Reactors," J. Macromol. Sci. Macromol. Chem., 
C8(1), 1, 1972) and graphs similar to those shown in FIG. 1a and 1b can be 
made. 
Alternatively, an essentially adiabatic polymerization can be conducted 
(i.e. using a small-scale adiabatic reaction calorimeter) and the 
temperature profile can be measured for a particular set of initiators. 
Based on the known decomposition rates of the initiators and the measured 
temperature profile, the concentration of each initiator versus time can 
be calculated. The calculation involves solving the following differential 
equation for L versus time for each initiator i in the essentially 
adiabatic polymerization (i=1 to n, where n is the number of initiators in 
the reacting system): 
##EQU3## 
Here I.sub.i represents the concentration of initiator i at a given time, 
t represents time, and k.sub.i is the temperature dependent decomposition 
rate constant for initiator i. The rate constant k.sub.i is commonly 
represented by an Arrhenius relationship of the form k.sub.i =k.sub.ref,i 
exp{-E.sub.a,i (1/T-1/T.sub.ref)/R}, where E.sub.a,i is the activation 
energy of the decomposition of initiator i, T is absolute temperature, 
k.sub.ref,i is the decomposition rate coefficient at a chosen reference 
temperature such as T.sub.ref =294 K, and R is the Universal gas constant. 
For clarity, the index i for each initiator will be defined to be numbered 
1 through n ordered by lowest temperature to highest temperature for each 
initiator i which produces a one-hour half life. The constants E.sub.a,i 
and k.sub.ref,i can be estimated from knowing the temperature-dependent 
decomposition characteristics of initiator i, data commonly available from 
commercial manufacturers of free radical initiators. For example, from 
knowing the half-life of initiator i at two different temperatures, 
E.sub.a,i and k.sub.ref,i can be estimated. Once I.sub.i is calculated 
versus time, multiplying I.sub.i at each time by k.sub.i at that time can 
be used to determine 
##EQU4## 
versus time by direct substitution in the rate equation for initiator 
decomposition, Eq. 2. 
Plotting 
##EQU5## 
versus temperature clearly illustrates the temperature overlap ranges of 
each initiator. 
The calculated initiator concentrations shown in FIG. 1a and the 
##EQU6## 
values shown in FIG. 1b were obtained using the measured temperature 
profile of the second reaction cycle of Example 1. The initiator depletion 
rate equation above was solved with the E.sub.a.i and k.sub.ref,i values 
for the Vazo 52, Vazo 88, and di-t-amyl peroxide initiators estimated 
based on half-life data available from the initiator manufacturers (the 
values used are presented in Table 1 below). As a close approximation, Eq. 
2 for each initiator was solved analytically in one-minute intervals as 
though the reaction temperature was constant at the measured value until 
the next temperature measurement was available. This calculation method is 
accurate when solved over sufficiently small time intervals. 
Alternatively, standard numerical solution techniques may be used to 
calculate the estimated initiator concentrations, I.sub.i, based on the 
measured adiabatic polymerization temperature profile and the known 
initiator decomposition rate data (i.e. Carnahan, et at., "Applied 
Numerical Methods", Wiley, 1969). 
TABLE 1 
______________________________________ 
k.sub.ref 
E.sub.a 
Initiator (sec.sup.-1) 
(kcal/mole) 
______________________________________ 
Vazo 52 (i = 1) 1.25e-7 31.0 
Vazo 88 (i = 2) 9.43e-10 31.3 
Di-t-amyl peroxide (i = 3) 
1.10e-12 37.7 
______________________________________ 
In the method of the present invention, a preferred minimum and maximum 
overlap of the active temperature ranges of two or more initiators during 
an essentially adiabatic reaction will be as follows. 
Minimum Initiator Overlap 
It is preferred that prior to the 
##EQU7## 
for at least one (preferably each) initiator i(i&lt;n-1, n&gt;1, where i=1, . . 
. ,n) decreasing to about 10% of its maximum value, the value of 
##EQU8## 
for the next initiator to reach it runaway onset temperature in the series 
will increase to at least about 20% of its maximum value, as the reaction 
temperature increases due to essentially adiabatic polymerization. In 
reacting in this manner, the essentially adiabatic polymerization will 
proceed without the need for heating between the runaway onset 
temperatures of the initiators. 
Maximum Initiator Overlap 
It is preferred that prior to the 
##EQU9## 
for at least one (preferably each) initiator i in a series (i&gt;1, n&gt;1, 
where i=1, . . . ,n) reaching about 30% of its maximum value, the previous 
initiator in the series has already reached its maximum value of 
##EQU10## 
as the reaction temperature increases due to essentially adiabatic 
polymerization. In reacting in this manner, the number of initiators used 
will be kept at a reasonable minimum number. 
A particular initiator used is selected based upon its thermal 
decomposition characteristics. For example, di-cumyl peroxide and 
di-t-amyl peroxide have similar temperature decomposition characteristics 
to produce free radicals (i.e., similar half-lives at various 
temperatures) and may be reasonable substitutes for each other in some 
instances. Apart from the temperature decomposition characteristics, other 
considerations in initiator selection may include an initiator's toxicity, 
cost, and potential side reactions in the polymerization system (such as 
minimizing undesired crosslinking of the polymer). 
Typical initiators, in the order that they become activated as the 
temperature increases, include: Vazo.TM.52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), Vazo.TM. 88 
(2,2'-azobis(cyclohexanecarbonitrile)), di-t-amyl peroxide, and t-amyl 
hydroperoxide. These initiators, for common monomers being reacted, 
typically are "spaced" in their temperature decomposition characteristics 
to overlap sufficiently to perform adiabatic polymerization without the 
need for external heating. Different, or additional, initiators may be 
necessary, depending on the monomer(s) employed. Factors affecting the 
initiator(s) employed include but are not limited to the rate of reaction 
of the monomer(s), the heat of reaction of the monomers, and the heat 
capacity of the reaction mixture. 
In the case that there will be more than one reaction cycle, the 
initiator(s) for the first essentially adiabatic reaction cycle are 
typically selected to bring the reaction to a temperature/conversion level 
where: 
1) The polymerization reaction virtually stops when the initiator(s) have 
essentially depleted (i.e., initiator(s) more than 99% depleted). The 
temperature of the reaction mixture is such that thermal polymerization of 
the monomers (polymerization in the absence of added free radical 
initiators) in the polymer/monomer reaction mixture is practically 
negligible. This is important so that the reaction can be stopped with 
available heat transfer from the reactor jacket (and potentially augmented 
with external cooling such as that from external cooling from pumping the 
reaction fluid through a heat exchanger, etc.). 
2) The solution viscosity is such that when the reaction mixture is cooled 
prior to the next reaction cycle, the next initiator(s), optional chain 
transfer agent, optional additional monomers, optional polymer, etc., can 
be mixed into the batch. This viscosity will be typically less than about 
200,000 centipoise (Brookfield viscosity at mixing temperature) for a 
common batch reactor system. 
Method of the Invention 
Typical reaction(s) with the inventive process proceed as follows. The 
monomer(s) are charged to the reactor in the desired amount(s). The 
temperature of the reaction vessel must be cool enough so that virtually 
no thermal polymerization of the monomer(s) will occur and also cool 
enough so that virtually no polymerization will occur when the 
initiator(s) are added to the batch. Also, care should be taken to ensure 
the reactor is dry, in particular, free of any undesired volatile solvent 
(such as reactor cleaning solvent) which potentially could dangerously 
elevate the pressure of the reaction vessel as the temperature increases 
due to heat of polymerization. The initiator(s), optional chain transfer 
agents, optional polymer, optional crosslinking agents, optional solvent, 
etc., are also charged to the reactor. 
Prior to warming the reaction mixture as described below (or optionally 
simultaneously while warming the batch), after adding all components to 
the batch as described above, the batch is purged of oxygen, a 
free-radical polymerization inhibitor. De-oxygenation procedures are well 
known to those skilled in the art of free-radical polymerization. For 
example, de-oxygenation can be accomplished by bubbling an inert gas such 
as nitrogen through the batch to displace dissolved oxygen. 
After completing the de-oxygenation, the head space in the reactor is 
typically pressurized with an inert gas such as nitrogen to a level 
necessary to suppress boiling of the reaction mixture as the temperature 
rises during reaction. The inert gas pressure also prevents oxygen from 
entering the polymerization mixture through possible small leaks in the 
reaction equipment while polymerization is in progress. 
From heating provided by the jacket on the reactor, the reaction mixture 
temperature typically is raised to or in a range about 1.degree. C. to 
about 5.degree. C. above the runaway onset temperature with sufficient 
mixing in the batch to have an essentially uniform temperature in the 
batch. The batch temperature controller is typically set temporarily to 
maintain the batch at the runaway onset temperature. Once the jacket 
temperature begins to drop as necessary to hold the batch at the runaway 
onset temperature, this indicates that the polymerization has begun. The 
reaction may not proceed immediately when the batch is brought to the 
runaway onset temperature because it may take time to deplete reaction 
inhibitors that are typically shipped with the monomer (to prevent 
unwanted polymerization during shipping and handling), other trace 
impurities, or any oxygen still dissolved in the reaction mixture. As soon 
as the jacket temperature drops, the reactor jacket temperature control 
system is set to track the batch temperature as it increases, due to 
reaction, to facilitate essentially adiabatic reaction conditions. In the 
practice of the inventive process, it has been found beneficial to have 
the jacket track about 1.degree. C. to about 10.degree. C. above the batch 
to warm the reactor walls from the jacket as opposed to warming the 
reactor walls from the heat of reaction of the mixture, making the 
reacting system more adiabatic. Acknowledged is the fact that perfect 
adiabiticity is probably not attainable because there will typically be a 
small amount of heat transferred from the reacting medium to the internal 
agitator blades and shaft as well as the mixing baffles in the reactor. In 
the practice of this invention the effect of heat loss to heating the 
agitator shaft and blades, baffles, temperature probes, etc., has been 
found to be negligible. 
An alternate heating approach would be to gently warm the batch past the 
runaway onset temperature with heat input from the jacket to warm the 
batch at a rate of about 0.1.degree. C./min to about 0.5.degree. C./min 
and continue the heating through the reaction cycle (similar to the 
heating approach above with the jacket tracking about 1.degree. C. to 
about 10.degree. C. above the batch temperature). As in the heating 
approach above, continued heating through the reaction cycle would serve 
to offset the heat loss to the reaction equipment and maintain essentially 
adiabatic reaction conditions. In the practice of the present invention, 
the first heating approach described above appears preferable because it 
ensures the reaction will always commence at the same temperature which 
seems to produce more reproducible product from batch to batch. 
Once the reaction temperature has peaked, due to the depletion of the 
thermal initiator(s) as well as negligible reaction of the monomers from 
thermal polymerization, the polymer content at this point is typically 
about 30-80% by weight based on the total weight of monomer(s) and 
polymer. 
If desired, the polymerization cycles can be stopped at this point and the 
unreacted monomer stripped from the reaction mixture or further 
polymerized in other equipment. Stripping apparatuses for the purpose of 
removing residual monomer are well known to those skilled in 
polymerization art. One potential stripping apparatus is an 
extractor-extruder operating with sections vented to vacuum chambers 
wherein the monomer can be condensed and optionally reused in subsequent 
polymerizations. Typical extractor-extruders are referred to in Modern 
Plastics Encyclopedia, Volume 45, October 1968 and Volume 46, October 
1969, both published by McGraw-Hill. 
A potential benefit of stopping the polymerization without reacting to 
completion is that the molecular weight distribution has been found to 
broaden as conversion increases towards completion. Product property 
requirements could warrant the extra effort and cost of stripping versus 
reacting to completion. Another reason to cease the polymerization process 
at partial conversion would be to limit the solution viscosity at 
manageable levels. For example, as the polymer molecular weight increases, 
the solution viscosity will increase. If high molecular weight polymer is 
to be produced and the 100% conversion melt viscosity is not manageable, 
i.e. greater than about 200,000 to about 500,000 centipoise (Brookfield 
viscosity at temperature), stopping the reaction at less than 100% 
conversion could be beneficial. 
When the reaction system is to be further polymerized in one or more 
essentially adiabatic reaction cycles, the batch temperature typically is 
cooled prior to beginning the next reaction cycle. Generally the batch is 
cooled about 5.degree.-20.degree. C. below the runway onset temperature of 
the initiator used in the next reaction cycle. If more than one initiator 
is used the batch temperature is typically cooled at least about 
5.degree.-20.degree. C. below the runaway onset temperature of the 
initiator having the lowest runaway onset temperature. 
As the partially polymerized reaction mixture cools, its viscosity will 
increase. Optionally, if necessary, additional monomer(s) can be added to 
the batch before it has fully cooled to compensate for the increasing 
viscosity. Typically, if necessary, a relatively small amount will be 
added. Charging additional monomer in the amount less than about 30 weight 
% of the amount of monomer added in the first reaction cycle is preferred. 
While the batch is cooling or when it has cooled to the desired 
temperature, optionally more monomer(s) can be added to adjust monomer 
ratios to compensate for unequal reactivity ratios of the monomers in the 
previous reaction cycle. Similarly, monomer(s) not included in an earlier 
reaction cycle can be added to tailor the polymer properties as needed. 
Monomer addition may also be performed as an in-process correction to 
compensate for slight batch-to-batch variations in the amount of reaction 
conversion obtained in a previous reaction cycle. 
When the batch has cooled to the desired temperature, the additional 
initiator(s) are added to the batch. Optionally, additional chain transfer 
agent(s) can be added. Adjusting the amount of chain transfer agent can 
provide an in-process correction for the product molecular weight obtained 
from the previous reaction cycle. Other additives, including optional 
photocrosslinking agents, optional polymer, optional solvent, etc., can 
also be added at this time. 
The batch is de-oxygenated, warmed to the runway onset temperature of the 
initiator having the lowest runaway onset temperature, and reacted 
essentially adiabatically as described above for the previous reaction 
cycle. 
If necessary, additional reaction cycles can be performed to continue 
increasing conversion to the desired level. 
Optionally, when all of the reaction cycles are complete, unreacted monomer 
can be stripped from the batch by pulling vacuum on the hot reaction 
product in the batch reactor by external vacuum equipment such as a vacuum 
pump and optionally condensing monomer vapors in an external heat 
exchanger with cooling. 
Optionally additives including but not limited to those selected from the 
group consisting of plasticizers, tackifiers, antioxidants, stabilizers, 
and mixtures thereof, can be added at this time by mixing one or more of 
them into the molten polymer product. The identity and relative amounts of 
such components are well known to those skilled in the art. For example, 
the antioxidant/stabilizer Irganox.TM. 1010 
(tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane), 
manufactured by Ciba-Geigy Corporation, can be mixed into the polymer to 
increase the temperature stability of the polymer. Antioxidant is 
typically used in the range of about 0.01% to about 1.0% based on the 
total weight of the polymer product. 
The reaction mixture's viscosity at the temperature at the end of the final 
reaction cycle is preferably less than about 200,000 to about 500,000 
centipoise (Brookfield viscosity at draining temperature) to permit 
draining of the molten polymer from the reactor and optionally mixing 
additives into the batch. Typically, inert gas (such as nitrogen) pressure 
in the head space of the reactor can be used to hasten the draining of the 
product from the reactor. 
After the reaction mixture is drained, an apparatus such as an 
extractor-extruder can be used to strip unreacted monomer and/or any 
solvent that optionally was added to the batch, or further process the 
polymer by mixing in additives comprising plasticizers, tackifiers, 
antioxidants and/or stabilizers, and extruding the polymer into the 
physical form that it is intended to be used (i.e. in sheet form for a 
PSA). 
The invention will be further clarified by consideration of the following 
examples which are intended to be purely exemplary. All parts, 
percentages, ratios, etc., in the examples and elsewhere herein are by 
weight unless indicated otherwise. 
Preparation of Sample for Adhesion Test 
The copolymers made for PSA were dissolved in ethyl acetate 50% by weight 
of polymer plus ethyl acetate. The solutions were knife coated on 38 
micrometer thick primed polyester film to about a 25 micrometer dried 
coating thickness (exact thickness is reported in the examples below). The 
copolymer PSAs thus coated were immediately dried for ten minutes in a 
65.degree. C. oven followed by optional exposure to ultraviolet light (UV) 
for post curing of the adhesive (see "UV Curing Equipment" below) and then 
aging for about sixteen hours at 22.degree. C. and 50% relative humidity 
prior to testing. The coated sheet thus prepared was ready for testing as 
described under "Peel Adhesion Test". 
UV Curing Equipment 
Two different pieces of equipment were used as sources of UV radiation for 
curing the adhesive samples in the examples below. They were the PPG UV 
processor, PPG Industries, Inc., Blainfield, Ill., and the Fusion Systems 
Curing Unit, Fusion Systems Corp., Rockville, Md. The PPG UV processor is 
equipped with two medium pressure mercury lamps which have a spectral 
output between 240 and 740 nm with emissions primarily in the 270 to 450 
nm output range. The Fusion Systems Curing Unit use UV lamps having a 
power supply of 300 watts/inch (118.1watts/cm). The "H" bulbs available 
from Fusion Systems Corp. were used. The UV radiation dose amount was 
controlled by the power settings on the respective device, the conveyor 
speed setting, and the number of passes of the adhesive under the 
ultraviolet light. 
Peel Adhesion Test 
Peel adhesion is measured as the force required to remove a coated flexible 
sheet material from a test panel, measured at a specified angle and rate 
of removal. The details of this test are given in "Test Methods for 
Pressure Sensitive Tapes", Eighth Edition, Revised August 1980. The 
procedure is summarized as follows: 
1. A 12.7 mm width of coated sheet is applied to the horizontal surface of 
a clean glass test plate with at least 12.7 lineal centimeters in firm 
contact. A 2 kg hard rubber roll is used to apply the strip. 
2. The free end of the coated strip is doubled back nearly touching itself 
so the angle of the removal is 180.degree.. The free end is attached to 
the adhesion tester scale. 
3. The glass test plate is attached to the table of an IMASS.TM. adhesion 
testing machine manufactured by Instrumentors, Inc. which is capable of 
moving the table away from the scale at a constant rate of 2.3 meters per 
minute. 
4. The force required for the removal is reported as an average of a range 
of numbers recorded by the testing apparatus. This value is reported as 
Newtons per 100 millimeters (N/100 ram) of width according to PSTC-1. 
Shear Strength-Holding Power Test 
(PSTC No. 7--Eight Edition--1985) 
This test measures the time required to pull a PSA tape from a standard 
flat surface in a direction parallel to that surface under the stress of a 
standard, constant load. The value is expressed in units of time (minutes) 
per unit area. It is a measure of the cohesive strength of the polymeric 
material. The conditions under which the examples in this application were 
measured follows: 
1. Surface=stainless steel panel 
2. Tape area=12.7 mm by 12.7 mm 
3. Panel area=178.degree. * 
4. Constant Load=1 kilogram *2.degree. less than 180.degree. to negate any 
peel forces thereby insuring that only shear forces are measured. 
PSTC No. 7 is found in "Test Methods", Pressure Sensitive Tape Council, 
1800 Pickwick Ave., Olenview, Ill. 60025 (August 1985). 
Molecular Weight and Molecular Weight Distribution 
The characterization oft he molecular weight distribution of polymers has 
been done by size exclusion chromatography, also known as gel permeation 
chromatography (GPC). GPC test methods are explained in Modern Size 
Exclusion Liquid Chromatography, Practice of Gel Permeation 
Chromatography, John Wiley & Sons, 1979. 
In the examples, the term M.sub.w means weight-average molecular weight, 
and the term M.sub.n means number-average molecular weight both of which 
are terms well understood in the polymer art. The term polydispersity is 
the ratio of M.sub.w /M.sub.n. 
Samples were prepared for GPC as follows: 
(1) The polymer sample was dissolved at a concentration of 20 mg/ml in 
tetrahydrofuran at room temperature to make a total of about 10 ml of 
solution. 
(2) If the polymer contained acrylic acid, then the solution was treated 
with saturated diazomethane in diethyl ether by adding 5 ml of such 
solution drop-wise while stirring. If no acrylic acid is present in the 
polymer, proceed directly to Step 5 below. 
(3) The resulting mixture was reduced to about 1 ml volume by evaporation 
under a stream of air. 
(4) Tetrahydrofuran was added to bring sample volume to 10 ml. 
(5) The resulting fluid was filtered through a 0.45 micrometer Teflon.TM. 
filter in a syringe to prevent plugging of the GPC column by the sample. 
(6) The resulting filtrate was used for chromatographic analysis. 
A Waters model 150-C ALC/GPC, available from Millipore Corp., Milford, 
Mass., operated at 45.degree. C. with a tetrahydrofuran carder stream 
flowing at 1 ml/min (200 microliter sample injection volume) was used for 
GPC analysis. A refractive index detector was used. Polystyrene standards 
from Polymer Laboratories, Ltd., were used in the range molecular weight 
range of 162 to 3,150,000. Six columns (Phenogel.TM. columns made by 
Phenomenex Co.) with pore sizes from 100 .ANG. to 10.sup.6 .ANG. were 
used. 
Monomer Conversion to Polymer 
In the examples below, extent of polymerization, or the amount of 
conversion of monomer to polymer was measured by one of two methods: gas 
chromatography (GC) or by a solids measurement. Two different GC methods 
were employed. One GC method was used when only %IOA (% isooctyl acrylate 
monomer in the sample by weight) is reported, and a different GC method 
was used when both %IOA and AA (% acrylic acid monomer in the sample by 
weight) are reported. 
%IOA 
A Hewlett-Packard Model 5890 gas chromatograph was used for measuring the 
weight percent of unreacted isooctyl acrylate (%IOA) with the following 
conditions: 
Column--Type: stainless steel 
Length: 12 foot (3.658 m) 
Inner Diameter: 1/8 inch (0.3175 cm) 
Packing manufactured by Supelco Co. of Bellefonte, Pa. 
(Liquid phase 20% SP2100, Solid support 80/100 mesh Supelcoport) 
Oven Temperature--210.degree. C. (Isothermal) 
Detector--Thermal Conductivity (TCD) 
Sensitivity Setting: High 
Injector Temperature--250.degree. C. 
Detector Temperature--300.degree. C. 
Sample size--3 microliters 
Run time--5 minutes 
Carrier Gas--Helium 
An internal standard solution containing the monomer (e.g. isooctyl 
acrylate) to be detected and a substance determined to have a similar 
detector response and a non-similar elution time, called the internal 
standard spiking compound (ISSC) is prepared in a vial. The concentration 
in the standard of the monomer being tested and that of the ISSC are both 
1.00% by weight in a suitable solvent. 
The standard is injected. The area under the analyte peak and under the 
ISSC peak in the time versus detector response plot of the chromatographic 
run of the standard are then measured. Calculations are then made to 
determine the relative detector response factors for the two compounds. 
An aliquot of the sample of unknown residual monomer is diluted to 10% by 
weight with a suitable solvent to reduce the viscosity of the sample. The 
ISSC is added to the mixture in a weight equal to 5% of the weight of the 
sample before diluting with the solvent. The sample is injected. 
The area under the analyte peak and under the ISSC peak in the time versus 
detector response plot of the chromatographic run of the diluted sample 
are then measured. Calculations are then made to determine the residual 
levels of the monomers in the sample using the measured areas and the 
relative response factors previously determined. 
%IOA and %AA 
A Hewlett-Packard Model 5890 gas chromatograph was used for measuring the 
weight percent of unreacted isooctyl acrylate (%IOA) and unreacted acrylic 
acid (%AA) with the following conditions: 
Column--Type: Capillary 
Length: 15 meter 
Inner Diameter: 0.53 millimeter 
Liquid phase: HP-FFAP (manufactured by Hewlett-Packard) 
Film Thickness: 3 micrometer 
Split Flow--80 ml/min at 50.degree. C. 
Oven Temperature Program: 
Initial Temperature--50.degree. C. 
Initial Time--0.5 minutes 
______________________________________ 
Final Temperature 
Final Time 
Rate (.degree.C./minute) 
(.degree.C.) (minutes) 
______________________________________ 
Level 1 
20 100 0 
Level 2 
30 250 2 
______________________________________ 
Detector--Flame Ionization FID) 
Injector Temperature--250.degree. C. 
Detector Temperature--300.degree. C. 
Sample size--1 microliters 
Run time--5 minutes 
Carrier Gas--Helium--10 ml/min at 50.degree. C. 
An aliquot of a sample of unknown residual monomer levels is diluted to 10% 
by weight with acetone to reduce the viscosity of the sample. 
An external standard solution containing the residual monomers (e.g. 
isooctyl acrylate, acrylic acid) at known concentrations in acetone are 
prepared in a vial. The concentrations of the monomers in the standard are 
selected close to the expected concentrations of the monomers in the 
diluted sample of unknown residual monomers. 
Equal volumes of the standard solution and the diluted sample are injected 
under identical conditions. The areas under the analyte peaks in the time 
versus detector response plot of the chromatographic run of the standard 
solution and of the diluted sample are then measured. Calculations are 
then made to determine the residual levels of the monomers in the sample. 
Solids Measurement 
About 0.5-1.0 gm of polymer sample was placed in a small tin. The 
polymer-containing tin was placed in a convection oven at 
120.degree.-130.degree. C. for at least three hours, or until weight loss 
by evaporation could not be measured any longer. By the measured weight 
loss of evaporated monomer, the amount of monomer converted to polymer can 
be calculated (expressed in percent in the examples below). 
Inherent Viscosity 
The inherent viscosities (IV) reported herein were obtained by conventional 
methods used by those skilled in the art. The IVs were obtained using a 
Cannon-Fenske #50 viscometer in a water bath controlled at 25.degree. C., 
to measure the flow time of 10 ml of a polymer solution (0.2 g per 
deciliter polymer in ethyl acetate). The test procedure followed and the 
apparatus used are described in detail in Textbook of Polymer Science, F. 
W. Billmeyer, Wiley-Interscience, Second Edition, 1971, Pages 84 and 85. 
EXAMPLE 1 
This example illustrates the use of the inventive process to produce a 
hot-melt acrylate pressure sensitive adhesive (isooctyl acrylate/acrylic 
acid monomer ratio: 90/10). Two essentially adiabatic reaction cycles are 
used in combination with a vacuum strip of residual unreacted monomer 
after the reaction cycles are completed. 
The following components were charged to a 75-gallon (284 liter) stainless 
steel batch reactor: 414.0 lbs. (187.78 kg) of isooctyl acrylate (IOA), 
5.0 grams of Vazo.TM.52 (2,2'-azobis(2,4-dimethylpentanenitrile)), 208.7 
grams of carbon tetrabromide, 1605.0 grams of a 26 weight % solids mixture 
of 4-acryloxy benzophenone (ABP) in ethyl acetate, and 46.0 lbs. (20.87 
kg) of acrylic acid (AA). With the mixture held at 75.degree. F. 
(23.89.degree. C.), nitrogen was bubbled through the solution for 20 
minutes to displace oxygen from the mixture and the reactor head space 
(volume of reactor not occupied by reaction mixture). The reactor was 
pressured to about 50 psig (448.16 kPa) with nitrogen and sealed. With the 
reactor's agitator (a 3-blade, retreating blade agitator) turning at about 
75 revolutions per minute, the temperature of the mixture was raised to 
150.degree. F. (65.56.degree. C.) by temperature-controlled water 
circulating through the jacket on the reactor. Once the polymerization had 
begun, the temperature control system was set to cause the temperature of 
the water circulating through the jacket to track 10.degree. F. 
(5.56.degree. C.) above the batch temperature to facilitate adiabatic 
reaction conditions. About 3 minutes into the reaction, as a final oxygen 
purge, the reactor pressure was vented to 5 psig (137.89 kPa) and then 
pressured back to about 50 psig (448.16 kPa) with nitrogen. As shown in 
FIG. 2, after about 10 minutes into the reaction, the batch temperature 
reached about 286.degree. F. (141.11 .degree. C) and the jacket 
temperature control system was unable to keep pace with the rate of batch 
temperature rise. At this point the jacket was drained and the reaction 
temperature kept climbing. Seven minutes later, the reaction temperature 
peaked at 298.degree. F. (147.78.degree. C.) at which time cooling was 
applied to the jacket on the reactor. 
A sample was taken of the reaction mixture. The polymer IV was 0.51 dl/gm 
and the unreacted IOA in the mixture was 61 weight % based on the total 
weight of the mixture. 
Once the batch temperature cooled to 125.degree. F. (51.67.degree. C.), the 
nitrogen pressure on the reactor was vented. Next, using external steam 
ejectors, the pressure on the reactor head space was reduced (vacuum 
pulled on reactor head space) to an absolute (as opposed to gauge 
pressure) of about 7.5 psi (51.71 kPa) and the reactor was sealed. Then 
the following mixture was vacuum charged to the reaction mixture (sucked 
into the reactor) through a dip tube into the reaction mixture: 10.0 grams 
of Vazo.TM. 52 (2,2'-azobis(2,4-dimethylpentanenitrile)), 6.0 grams of 
Vazo.TM. 88 (2,2'-azobis(cyclohexanecarbonitrile)), 10.0 grams of 
di-t-amyl peroxide, 30.0 grams of carbon tetrabromide, dissolved in 5 lbs. 
(2.27 kg) of IOA. As a charge line flush, 5 more lbs. (2.27 kg) of IOA was 
vacuum charged to the reaction mixture through the dip tube. 
The reactor temperature control system was set to raise the batch 
temperature to 150.degree. F. (65.56.degree. C.). While the batch was 
warming to 150.degree. F. (65.56.degree. C.), with the agitation set at 
about 75 revolutions per minute, the reaction mixture was purged of oxygen 
using the following procedure: a vacuum was pulled on the reactor head 
space to cause vigorous bubbling of the reaction mixture caused by trapped 
nitrogen from the first reaction cycle to be liberated from the mixture 
for about 30 seconds. 
Then the reactor pressure was raised to about 3 psig (124.11 kPa) with 
nitrogen and held for about 1 minute. Again a vacuum was pulled to cause 
trapped nitrogen to degas from the reaction mixture for about 30 seconds. 
Next the reactor head space was pressured to 50 psig (448.16 kPa) and held 
for about 1 minute. The reactor pressure was vented to about 3 psig 
(124.11 kPa) and held for about 1 minute. Finally, the reactor pressure 
was raised to 50 psig (448.16 kPa) with nitrogen the reactor was sealed. 
Once the mixture reached 150.degree. F. (65.56.degree. C.), and the 
polymerization had begun, the temperature control system was set to cause 
the temperature of the water circulating through the jacket to track 
10.degree. F. (5.56.degree. C.) above the batch temperature to facilitate 
adiabatic reaction conditions. The batch temperature rose over a period of 
about an hour as shown in FIG. 2. Once the batch temperature peaked at 
about 328.degree. F. (164.44.degree. C.), the jacket was drained and steam 
at a pressure of about 110 psig (861.84 kPa) was applied to the jacket to 
hold the reaction mixture at about 330.degree. F. (165.56.degree. C.) for 
about 40 more minutes (the temperature of the jacket past the point where 
direct steam was applied is not shown in FIG. 2 because the temperature 
probe was not properly positioned in the jacket piping to measure the 
jacket temperature when using direct steam). 
At this point 208.7 grams of Irganox.TM. 1010 thermal 
stabilizer/antioxidant (tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydr 
ocinnamate))methane), manufactured by Ciba-Geigy Corporation, dissolved in 
400 grams of ethyl acetate was pressure-charged through a dip tube into 
the reaction mixture. A charge line flush of 200 more grams of ethyl 
acetate was next pressure charged to the reaction mixture through the dip 
tube. The reactor head space pressure was vented to about 5 psig (137.89 
kPa). The batch was mixed at 330.degree. F. (165.56.degree. C.) with about 
75 revolutions per minute agitation for about 12 hours (this is longer 
than necessary to mix the thermal stabilizer into the batch, but because 
of a 2-shift operation in our pilot plant, the processing was on hold 
overnight). 
Next, the unreacted residual monomer and residual ethyl acetate was 
stripped from the reaction mixture under reduced vacuum at 
330.degree.-340.degree. F. (165.56.degree.-171.11.degree. C). Vapors were 
condensed in an external heat exchanger. At this point, the polymer 
product Brookfield viscosity (measured at 180.degree. C.) was about 60,000 
centipoise. 
The product readily drained from the reactor with a slight nitrogen 
pressure on the head space. The resulting polymer product had the 
following properties: 
unreacted IOA: 2.1 weight % based on total weight of the mixture 
unreacted AA:0.2 weight % based on total weight of the mixture 
IV: 0.61 dl/gm 
M.sub.n : 15,000 
M.sub.w : 270,000 
M.sub.w /M.sub.n ; 18 
To test the adhesive properties of the polymer product, adhesion and shear 
tests were conducted with the coated product adhesive (25 micrometer dried 
coating thickness). The adhesive coating was very smooth, with a 
glass-like finish, free of any visible polymer gel particles. The adhesive 
was post cured by exposure to ultraviolet radiation. Three different 
levels of UV radiation were used to cure the adhesive as shown in Table 2. 
A control, without any post cure, is also included in the results in Table 
2. 
TABLE 2 
______________________________________ 
UV Dose Adhesion (N/100 mm) 
Shear (min) 
______________________________________ 
0 (control) 62.0 13 
100 mJ/cm.sup.2 
65.2 3002 
200 mJ/cm.sup.2 
65.7 4271 
400 mJ/cm.sup.2 
62.0 7656 
______________________________________ 
EXAMPLE 2 
This example illustrates the use of the inventive process to produce a 
hot-melt acrylate pressure sensitive adhesive (isooctyl acrylate/acrylic 
acid monomer ratio: 93/7). Two essentially adiabatic reaction cycles are 
used without a vacuum strip of residual unreacted monomer. 
The following components were charged to the same 75-gallon (284 liter) 
stainless steel batch reactor used for Example 1:427.8 lbs. (194.05 kg) of 
isooctyl acrylate (IOA), 5.0 grams of Vazo.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), 80.0 grams of 
isooctylthioglycoate, 1605.0 grams of a 26 weight % solids mixture of 
4-acryloxy benzophenone (ABP) in ethyl acetate, and 32.2 lbs. (14.61 kg) 
of acrylic acid (AA). The reaction mixture was purged of oxygen and the 
polymerization reaction was started in a manner similar to that for 
Example 1. The reaction was started at 150.degree. F. (65.56.degree. C.) 
and after about 15 minutes of reaction time, with the jacket water 
temperature tracking the batch temperature in a manner similar to Example 
1, the peak batch temperature obtained was 297.degree. F. (147.22.degree. 
C.). 
A sample was taken of the reaction mixture. The polymer IV was 0.62 dl/gm 
and the unreacted IOA in the mixture was 47 weight % based on total weight 
of the mixture. 
As an in-process correction to adjust the polymer solids down to about 50 
weight %, 25.9 pounds of isooctyl acrylate and 1.9 pounds of acrylic acid 
were added to the batch. 
The reaction mixture was cooled similar to Example 1. Once the batch 
temperature reached about 130.degree. F. (54.44.degree. C.), the following 
components were charged to the batch: 10.0 grams of Vazo.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), 6.0 grams of Vazo.TM. 88 
(2,2'-azobis(cyclohexanecarbonitrile)), and 12.0 grams of di-t-amyl 
peroxide, 20.0 grams of isooctylthioglycoate, and 10.0 lbs. (4.54 kg) of 
isooctyl acrylate. 
The mixture was agitated at about 100 revolutions per minute while heating 
to 150.degree. F. (65.56.degree. C.). The batch was purged of oxygen 
similar to the method used in Example 1 at this stage of the processing. 
The head space of the reactor was pressured to about 50 psig (448.16 kPa) 
with nitrogen for the reaction. The reaction procedure was the same as 
that in Example 1: the reaction was started at 150.degree. F. 
(65.56.degree. C.) and after 30 minutes of reaction time, with the jacket 
water temperature tracking the batch temperature in a manner similar to 
Example 1, the peak batch temperature obtained was approximately 
340.degree. F. (171.11.degree. C.). After a two-hour hold while mixing the 
batch at approximately 340.degree. F. (171.11.degree. C.), 208.7 grams of 
Irganox.TM. 1010 
(tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane), 
dissolved in 400 grams of ethyl acetate was added to the batch similar to 
Example 1. A line flush of 200 grams of ethyl acetate was subsequently 
added to the batch. Next the mixture was stirred at about 80 revolutions 
per minute for approximately 4 hours at about 340.degree.-50.degree. F. 
(171.11.degree.-76.67.degree. C.). No unreacted residual monomer was 
stripped from the batch, as was the case in Example 1. The product was 
readily drained from the reactor through an 16-mesh screen with 10 psig 
(172.37 kPa) nitrogen pressure on the reactor head space. 
The resulting product drained had the following properties: 
unreacted IOA: 0.4 weight % based on total weight of the mixture 
unreacted AA: 0.1 weight % based on total weight of the mixture 
IV: 0.69 dl/gm 
M.sub.n ; 10,300 
M.sub.w : 312,300 
M.sub.w /M.sub.n : 30 
To test the adhesive properties of the polymer product, adhesion and shear 
tests were conducted with the coated product adhesive 25 micrometer dried 
coating thickness). The adhesive coating was very smooth, with a 
glass-like finish, free of any visible polymer gel particles. The adhesive 
was post cured by exposure to ultraviolet radiation. Two different levels 
of UV radiation were used to cure the adhesive as shown in Table 3. A 
control, without any post cure, is also included in the results in Table 
3. 
TABLE 3 
______________________________________ 
UV Dose Adhesion (N/100 mm) 
Shear (min) 
______________________________________ 
0 (control) 71.6 4.0 
200 mJ/cm.sup.2 
62.0 619 
400 mJ/cm.sup.2 
59.8 852 
______________________________________ 
EXAMPLE 3 
This example illustrates the use of the inventive process to produce a 
hot-melt acrylate pressure sensitive adhesive (isooctyl acrylate/acrylic 
acid monomer ratio: 90/10). Five essentially adiabatic reaction cycles are 
used in combination with a vacuum strip of residual unreacted monomer 
after the reaction cycles are completed. 
The following components were charged to the same 75-gallon (284 liter) 
stainless steel batch reactor used for Example 1:360.0 lbs. (163.29 kg) of 
isooctyl acrylate (IOA), 4.5 grams of Vazo.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), 181.4 grams of carbon 
tetrabromide, 1047.0 grams of a 26 weight % solids mixture of 4-acryloxy 
benzophenone (ABP) in ethyl acetate, and 40 lbs. (18.14 kg) of acrylic 
acid (AA). The reaction mixture was purged of oxygen and the 
polymerization reaction was started in a manner similar to that for 
Example 1. The reaction was started at 150.degree. F. (65.56.degree. C.) 
and after 12 minutes of reaction time, with the jacket water temperature 
tracking the batch temperature in a manner similar to Example 1, the peak 
batch temperature obtained was 287.degree. F. (141.67.degree. C.). 
A sample was taken of the reaction mixture. The polymer IV was 0.54 dl/gm 
and the unreacted IOA in the mixture was 63 weight % based on total weight 
of the mixture. 
The reaction mixture was cooled similar to Example 1. Once the batch 
temperature reached about 120.degree. F. (48.89.degree. C.), the following 
components were charged to the batch: 10.0 grams of Vazo.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), 3.0 grams of Vazo.TM. 88 
(2,2'-azobis(cyclohexanecarbonitrile)), and 14.0 grams of dicumyl 
peroxide, 10.0 grams of carbon tetrabromide, 40.0 lbs. (18.14 kg) of 
isooctyl acrylate, 4.4 lbs. (2.00 kg) of acrylic acid, and 116.2 grams of 
a 26 weight % solids mixture of 4-acryloxy benzophenone (ABP) in ethyl 
acetate. 
The mixture was agitated at about 100 revolutions per minute while heating 
to 150.degree. F. (65.56.degree. C.). The batch was purged of oxygen by 
pressuring to about 50 psig (448.16 kPa) and venting to about 2 psig 
(117.21 kPa) three times. The head space of the reactor was pressured to 
about 50 psig (448.16 kPa) with nitrogen for the reaction and sealed. The 
reaction procedure was the same as that in Example 1: the reaction was 
started at 150.degree. F. (65.56.degree. C.) and after about 35 minutes of 
reaction time, with the jacket water temperature tracking the batch 
temperature in a manner similar to Example 1, the peak batch temperature 
obtained was approximately 323.degree. F. (161.67.degree. C.). 
After a 30-minute hold while mixing the batch at approximately 320.degree. 
F. (160.00.degree. C.), a sample was taken of the reaction mixture. The 
polymer IV was 0.59 dl/gm and the unreacted IOA in the mixture was 19.5 
weight % based on total weight of the mixture. 
Fifty minutes after taking the sample above, a mixture of 8.0 grams of 
di-t-amyl peroxide dissolved in 400.0 grams of ethyl acetate was pressured 
into the batch followed by a 200.0 gram line flush of ethyl acetate. The 
batch was de-oxygenated by venting to about 20-30 psig (241.31-310.26 kPa) 
and pressuring to about 50 psig (448.16 kPa) with nitrogen 2 times. The 
reactor was pressured to about 50 psig (448.16 kPa) and sealed for 
continued polymerization. During continued reaction, the batch temperature 
rose from about 323.degree. F. (161.67.degree. C.) to about 336.degree. F. 
(168.89.degree. C.). 
After an hour, a sample was taken of the reaction mixture. The polymer IV 
was 0.58 and the unreacted IOA in the mixture was 12.2 weight % based on 
total weight of the mixture. 
Fifty minutes after taking the sample above, a mixture of 10.0 grams of 
di-t-amyl peroxide dissolved in 400.0 grams of ethyl acetate was pressured 
into the batch followed by a 200.0 gram ethyl acetate line flush. The 
batch was de-oxygenated by venting to about 20-30 psig (241.31-310.26 kPa) 
and pressuring to about 50 psig (448.16 kPa) with nitrogen 2 times. The 
reactor was pressured to about 50 psig (448.16 kPa) and sealed for 
continued polymerization. The batch temperature remained at about 
335.degree. F. (168.33.degree. C.) during this reaction cycle. 
Forty minutes after adding the above 10-gram initiator charge, a mixture of 
6.0 grams of di-t-amyl peroxide dissolved in 400.0 grams of ethyl acetate 
was pressured into the batch followed by a 200.0 gram ethyl acetate line 
flush. The batch was de-oxygenated by venting to about 20-30 psig 
(241.31-310.26 kPa) and pressuring to about 50 psig (448.16 kPa) with 
nitrogen 2 times. The reactor was pressured to about 50 psig (448.16 kPa) 
and sealed for continued polymerization. The batch temperature remained at 
about 335.degree. F. (168.33.degree. C.) during this reaction cycle. 
After an hour, a sample was taken of the reaction mixture. The unreacted 
IOA in the mixture was 6.3 weight % based on total weight of the mixture. 
After two more hours, 201.6 grams of Irganox.TM. 1010 
(tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane), 
dissolved in 400 grams of ethyl acetate was added to the batch similar to 
Example 1. A line flush of 200 grams of ethyl acetate was subsequently 
added to the batch. The batch was mixed at about 320.degree. F. 
(160.00.degree. C.) with about 50-60 revolutions per minute agitation. 
After nine hours, a sample was taken of the reaction mixture. The unreacted 
IOA in the mixture was 4.4 weight % based on total weight of the mixture. 
The unreacted residual monomer and residual ethyl acetate were next 
stripped from the reaction mixture under reduced vacuum at 310.degree. F. 
(154.44.degree. C.). Vapors were condensed in an external heat exchanger. 
The resulting product readily drained from the reactor with a slight 
nitrogen pressure on the head space. The product drained had the following 
properties: 
unreacted IOA: 2.8 weight % based on total weight of the mixture 
unreacted AA: 0.3 weight % based on total weight of the mixture 
IV: 0.56 dl/gm 
M.sub.n : 17,900 
M.sub.w : 284,000 
M.sub.n /M.sub.n : 16 
To test the adhesive properties of the polymer product, adhesion and shear 
tests were conducted with the coated product adhesive 25 micrometer dried 
coating thickness). The adhesive coating was very smooth, with a 
glass-like finish, free of any visible polymer gel particles. The adhesive 
was post cured by exposure to ultraviolet radiation. Two different levels 
of UV radiation were used to cure the adhesive as shown in Table 4. A 
control, without any post cure, is also included in the results in Table 
4. 
TABLE 4 
______________________________________ 
UV Dose Adhesion (N/100 mm) 
Shear (min) 
______________________________________ 
0 (control) 59.8 12 
160 mJ/cm.sup.2 
57.1 515 
320 mJ/cm.sup.2 
63.9 7444 
______________________________________ 
EXAMPLE 4 
This example illustrates the use of the inventive process to produce a 
hot-melt acrylate pressure sensitive adhesive (isooctyl acrylate/acrylic 
acid monomer ratio: 90/10). One essentially adiabatic reaction cycle is 
used to produce a polymer syrup which can be stripped of unreacted monomer 
to produce a hot-melt acrylate pressure sensitive adhesive. 
The following components were charged to the same 75-gallon (284 liter) 
stainless steel batch reactor used for Example 1:414.0 lbs. (187.79 kg) of 
isooctyl acrylate (IOA), 5.0 grams of Vazo.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), 135.0 grams of 
isooctylthioglycoate, 1605.0 grams of a 26 weight % solids mixture of 
4-acryloxy benzophenone (ABP) in ethyl acetate, and 46.0 lbs. (20.87 kg) 
of acrylic acid (AA). The reaction mixture was purged of oxygen and the 
polymerization reaction was started in a manner similar to that for 
Example 1. The reaction was started at 150.degree. F. (65.56.degree. C.) 
and after about 12 minutes of reaction time, with the jacket water 
temperature tracking the batch temperature in a manner similar to Example 
1, the peak batch temperature obtained was 293.degree. F. (145.00.degree. 
C.). 
The resulting polymer product properties were analyzed and found to be: 
Polymer solids: 42.9 weight % based on total weight of the mixture (from 
solids measurement) 
Viscosity@25.degree. C.: approximately 30,000 centipoise (Brookfield 
viscosity) 
IV: 0.62 dl/gm 
M.sub.n : 104,000 
M.sub.w : 375,000 
M.sub.w /M.sub.n : 3.6 
At this point in the processing, the monomer can be stripped from the 
polymer using techniques and equipment known to those skilled in the art. 
To test the adhesive properties of the polymer, the 42.9 weight % solids 
polymer syrup was knife coated to a 23.75 micrometer dried coating 
thickness using the methods described above. The adhesive coating was very 
smooth, with a glass-like finish, free of any visible polymer gel 
particles. The adhesive was post cured by exposure to ultraviolet 
radiation. Two different levels of UV radiation were used to cure the 
adhesive for testing the adhesive properties as shown in Table 5. A 
control, without any post cure, is also included in the results in Table 
5. 
TABLE 5 
______________________________________ 
UV Dose Adhesion (N/100 mm) 
Shear (min) 
______________________________________ 
0 (control) 70.3 45 
200 mJ/cm.sup.2 
65.0 10,000+ 
400 mJ/cm.sup.2 
63.3 10,000+ 
______________________________________ 
EXAMPLE 5 
A Reactive System Screening Tool (RSST) was used to perform polymerization 
reactions for this example and several examples below. The RSST is a small 
calorimeter available from Fauske and Associates, Inc., Burr Ridge Ill., 
in which samples of about 10.0 ml can be reacted very nearly 
adiabatically, apart from a small constant heat input which increases the 
sample temperature in the test cell a minimum of 0.25.degree. C./min. It 
has been found that in heating non-reactive samples, the RSST temperature 
controller does a very good job of maintaining the desired heat rates-the 
heater automatically increases its power to counterbalance heat losses to 
the surroundings and the desired heat rate is followed closely. However, 
in the practice of the present invention, when a sample is heated and it 
begins to react exothermically, the heater does not increase its power 
exactly to counterbalance the heat losses as the sample temperature 
increases, particularly for reactions which start fast and gradually slow 
at elevated temperatures. The heater power slightly lags the heat losses 
to the surroundings which increase in proportion to the temperature of the 
material in the test cell. For example, when a polymerization is conducted 
in the RSST and the heater is set to its minimum heat rate of 0.25.degree. 
C. /min, when the polymerization finishes due to the depletion of 
initiator, the temperature of the test cell momentary quits increasing, 
often slightly cooling a few .degree. C, until the heater power is 
increased by the RSST temperature control program to eventually continue 
heating the non-reacting sample at 0.25.degree. C. /min. Therefore, to 
maintain reaction conditions as close to adiabatic as possible, the heater 
was set in the range of 0.25.degree. C. /rain to 0.5.degree. C. /min at 
reaction temperatures above 135.degree. C. to increase the heater input 
power to more accurately offset the heat losses during reaction to 
facilitate adiabatic polymerization. The higher heat rate is used for 
faster reactions. This heat program procedure with the RSST has been 
verified by comparing temperature profiles of RSST polymerizations and 
75-gallon polymerizations where the reactor jacket water temperature is 
set to closely track the batch temperature. The particular version of the 
RSST used for the examples herein contained a double bottom heater and a 
stainless steel sheath thermocouple for the temperature measurements. 
This example illustrates the use of the inventive process to produce a 
hot-melt acrylate pressure sensitive adhesive (isooctyl acrylate/methyl 
acrylate/acrylic acid monomer ratio: 75/20/5). Two essentially adiabatic 
reaction cycles are used without a vacuum strip of residual unreacted 
monomer. 
The following mixture was charged to the RSST test cell: 5.92 grams of 
isooctyl acrylate, 0.40 grams of acrylic acid, 1.62 grams of methyl 
acrylate, 0.010 grams of isooctylthioglycoate, 0.092 grams of a 26 weight 
% solids mixture of 4-acryloxy benzophenone (ABP) in ethyl acetate, and 
0.08 grams of 0.20 grams of Vazo.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitfile)) dissolved in 100 grams of 
isooctyl acrylate. 
Once the RSST test cell was charged with the reaction mixture, it was 
sealed in the RSST containment vessel. With agitation from a magnetic stir 
bar, the reaction mixture was de-oxygenated by pressuring the containment 
vessel to about 300 psig (2171.84 kPa) with nitrogen, holding for about 
one minute, venting to about 5 psig (137.89 kPa), and holding for about 
one minute. Pressuring and venting was repeated a total of five times. 
Next the RSST containment vessel was pressured to about 100 psig (792.89 
kPa) with nitrogen to suppress boiling of the unreacted monomers as the 
reaction temperature increased. 
The RSST heater was programmed to automatically ramp the test cell 
temperature up from room temperature to 55.degree. C. at 1.degree. C./min 
and then heat at 0.25.degree. C. /min. The polymerization began at about 
60.degree. C. (indicated by a gradually increasing rate of temperature 
rise) and over a period of about 27 minutes, the temperature increased to 
and peaked at about 160.degree. C. At this point, the RSST heater was 
turned off and the sample was cooled to about 30.degree. C. 
To the reaction product from the first reaction cycle was mixed 1.40 grams 
of isooctyl acrylate, 0.10 grams of acrylic acid, 0.40 grams of methyl 
acrylate, 0.023 grams of grams of a 26 weight % solids mixture of 
4-acryloxy benzophenone (ABP) in ethyl acetate, and 0.10 grams of the 
following mixture: 100.0 grams isooctyl acrylate, 0.38 grams Vazo.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), 0.28 grams Vazo.TM. 88 
(2,2'-azobis(cyclohexanecarbonitrile)), 0.05 grams di-t-amyl peroxide, 
0.15 grams t-amyl hydroperoxide. The test cell was placed in the RSST 
containment vessel again and de-oxygenated using the same procedure as 
that for the first reaction cycle and pressured to about 100 psig (792.89 
kPa) for reaction. 
For this reaction cycle, the RSST was set to automatically ramp the test 
cell's temperature up to 55.degree. C. at 1.degree. C./min, up to 
60.degree. C. at 0.5.degree. C. /min, up to 135.degree. C. at 0.25.degree. 
C. /min, up to 180.degree. C./min, and finally up to 185.degree. C. at 
0.25.degree. C. /min. As the reaction mixture warmed, when it reached 
about 65.degree. C., polymerization began. After about 90 minutes the 
reaction temperature peaked at about 165.degree. C. At this point 
adiabatic reaction conditions were abandoned, and by the pre-programmed 
temperature profile described above, the sample continued to warm to 
185.degree. C. and was held at this temperature for 360 minutes. The 
properties of the resulting polymer were analyzed and were found to be: 
Polymer solids: 96.0 weight % based on total weight of the mixture (from 
solids measurement) 
IV: 0.52 dl/gm 
M.sub.n : 13,900 
M.sub.w : 222,200 
M.sub.w /M.sub.n : 16.0 
To test the adhesive properties of the polymer product, adhesion and shear 
tests were conducted with the coated product adhesive 25 micrometer dried 
coating thickness). The adhesive coating was very smooth, with a 
glass-like finish, free of any visible polymer gel particles. The adhesive 
was post cured by exposure to ultraviolet radiation. Two different levels 
of UV radiation were used to cure the adhesive as shown in Table 6. A 
control, without any post cure, is also included in the results in Table 
6. 
TABLE 6 
______________________________________ 
UV Dose Adhesion (N/100 mm) 
Shear (min) 
______________________________________ 
0 (control) 79.3 1.32 
200 mJ/cm.sup.2 
60.0 897 
400 mJ/cm.sup.2 
55.9 1261 
______________________________________ 
EXAMPLE 6 
This example illustrates the use of the inventive process to produce a 
hot-melt acrylate pressure sensitive adhesive. The use of a 
methacrylate-terminated styrene macromonomer as one of the monomers being 
polymerized is demonstrated, eliminating the need for post curing the 
adhesive to build up internal strength of the adhesive (isooctyl 
acrylate/styrene macromonomer/acrylic acid monomer ratio: 87/6/7). 
The following mixture was added to the RSST test cell: 8.88 grams of the 
following mixture: 79.06 grams of isooctyl acrylate, 7.00 grams of acrylic 
acid, 0.127 grams of isooctylthioglycoate, and 2.50 grams of a solution of 
0.05 grams of Vazo.TM. 52 (2,2'-azobis(2,4-dimethylpentanenitrile)) 
dissolved in 90.0 grams of isooctyl acrylate. Also 1.14 grams of a 52.5 
weight % solution of a methacrylate-terminated styrene macromonomer 
dissolved in isooctyl acrylate was added to the test cell. The 
methacrylate-terminated styrene macromonomer had weight average molecular 
weight of about 10,000, a polydispersity of about 1.0, and was prepared in 
the manner described in Example M-1 of U.S. Pat. No. 4,732,808. 
Once the RSST test cell was charged with the reaction mixture, it was 
sealed in the RSST containment vessel. With agitation from a magnetic stir 
bar, the reaction mixture was de-oxygenated by pressuring the containment 
vessel to about 300 psig (2171.84 kPa) with nitrogen, holding for about 
one minute, venting to about 5 psig (137.89 kPa), and holding for about 
one minute. Pressuring and venting was repeated a total of five times. 
Next the RSST containment vessel was pressured to about 100 psig (792.89 
kPa) with nitrogen to suppress boiling of the unreacted monomers as the 
reaction temperature increased. 
The RSST was set to ramp the test cell temperature up from room temperature 
to 55.degree. C. at 1.0.degree. C./min and then ramp the temperature up 
0.25.degree. C./min after passing 55.degree. C. The polymerization began 
at about 64.degree. C. and over a period of about 23 minutes, the 
temperature increased to and peaked at about 133.degree. C. The heater of 
the RSST was then turned off and the sample was cooled to about 30.degree. 
C. 
To the reaction product from the first reaction cycle was mixed 0.10 grams 
of the following mixture: 100.0 grams isooctyl acrylate, 0.4792 grams 
Vazo.TM. 52 (2,2'-azobis (2,4-dimethylpentanenitrile)), 0.2815 grams 
Vazo.TM. 88 (2,2'-azobis(cyclohexanecarbonitrile)), and 0.1220 grams 
di-t-amyl peroxide. The test cell was placed in the RSST containment 
vessel again and de-oxygenated using the same procedure as that for the 
first reaction cycle and pressured to about 50 psig (448.16 kPa) for 
reaction. The RSST was set to automatically ramp the test cell's 
temperature up to 55.degree. C. at 1.degree. C./min, up to 60.0.degree. C. 
at 0.5.degree. C./min, and up at 0.25.degree. C./min past 60.0.degree. C. 
As the reaction mixture warmed, when it reached about 65.degree. C., 
polymerization began. After about 133 minutes the reaction temperature 
peaked at 160.degree. C. 
The polymer product was found to have an IV value of 0.53 dl/gm. 
To test the adhesive properties of the polymer product, adhesion and shear 
tests were conducted with the coated product adhesive (21 micrometer dried 
coating thickness). The adhesive coating was very smooth, with a 
glass-like finish, free of any visible polymer gel particles. The adhesive 
was not post cured by exposure to ultraviolet radiation. The adhesive 
properties obtained were adhesion of 60.7N/100 mm and a shear value of 
1577 minutes. Compared to other adhesive samples prepared in the examples 
presented herein, this shear value is much higher than the other 
non-ultraviolet radiation cured control samples. 
EXAMPLE 7 
This example illustrates the application of the inventive process to make a 
polymer using octadecyl acrylate/isooctyl acrylate/N,N-dimethyl acrylamide 
with a monomer ratio: 50/14.3/35.7. 
The following components were charged to a 10-gallon (37.9 liter) stainless 
steel batch reactor: 17.7 lbs. (8.03 kg) octadecyl acrylate, 5.1 lbs. 
(2.31 kg) isooctyl acrylate, 12.7 lbs. (5.76 kg) N,N-dimethyl acrylamide, 
0.47 gm Vazo.TM. 52 (2,2'-azobis (2,4-dimethylpentanenitrile)), and 79.4 
grams of 3-mercapto-1,2-propanediol. The reaction mixture was purged of 
oxygen by bubbling nitrogen through the reaction mixture for 20 minutes 
with the reactor's 2-blade, anchor-type agitator set at about 75 
revolutions per minute. The reactor head space next was pressured to 50 
psig (448.16 kPa) with nitrogen and sealed for reaction. The batch was 
heated to 140.degree. F. (60.degree. C.) and when the reaction began, the 
temperature of the water in the jacket of the reactor was set to track the 
temperature of the batch. After 27 minutes of reaction, the batch 
temperature peaked at 276.degree. F. (135.5.degree. C.). The batch was 
then cooled to 125.degree. F. (51.7.degree. C.). Next, after venting the 
nitrogen pressure, the following components were added to the reactor: 
1.08 grams of Vazo.TM. 52 (2,2'-azobis(2,4-dimethylpentanenitrile)), 0.60 
grams Vazo.TM. 88 (2,2'-azobis (cyclohexanecarbonitrile)), 0.51 grams of 
di-t-amyl peroxide, 100.0 grams of octadecyl acrylate, 28.6 gm isooctyl 
acrylate, and 71.4 gm N,N-dimethyl acrylamide. Next, to purge oxygen from 
the reaction mixture, a slight vacuum was pulled on the head space to 
cause trapped nitrogen to bubble out of the reaction mixture for about 20 
seconds. The batch was then pressured to about 2 psig (117.21 kPa). Again 
a slight vacuum was pulled on the head space to cause trapped nitrogen to 
bubble out of the reaction mixture for about 20 seconds. Finally, the 
reactor head space was pressured to about 50 psig (448.16 kPa). Next the 
reaction mixture was warmed to 150.degree. F. (65.56.degree. C.) and when 
the reaction began, the temperature of the water in the jacket of the 
reactor was set to track the temperature of the batch. After 55 minutes of 
reaction, the batch temperature peaked at 294.degree. F. (145.5.degree. 
C.). The reaction mixture was held at about 280.degree. F.-290.degree. F. 
(137.8.degree. C.-143.3.degree. C.) for the next four hours. The polymer 
product, at about 270.degree. F. (132.2.degree. C.) readily drained 
through a 40-mesh screen with essentially no hang-up in the reactor. The 
properties of the resulting polymer were analyzed and were found to be: 
Polymer solids: 98.9 weight % based on total weight of the mixture (from 
solids measurement) 
M.sub.n : 16,300 
M.sub.w : 43,600 
M.sub.w /M.sub.n : 2.81 
EXAMPLE 8 
This example illustrates the application of the inventive process to make a 
polymer using octadecyl acrylate/ethyl acrylate/methyl methacrylate with a 
monomer ratio: 30/33.4/36.6. 
10.0 grams of the following mixture was charged to an RSST test cell: 30% 
octadecyl acrylate, 33.4% ethyl acrylate, and 36.6% methyl methacrylate 
(all based on weight percent). Also charged to the test cell were 0.05 
grams of 3-mercapto-1,2-propanediol and 0.10 grams of a mixture of 0.3 
grams of Vazo.TM. 52 (2,2'-azobis (2,4-dimethylpentanenitrile)) and 0.3 
grams of Vazo.TM. 67 (2,2'-azobis(2-methylbutanenitrile)) dissolved in 
25.0 grams of methyl methacrylate. 
Once the RSST test cell was charged with the reaction mixture, it was 
sealed in the RSST containment vessel. With agitation from a magnetic stir 
bar, the reaction mixture was de-oxygenated by pressuring the containment 
vessel to about 300 psig (2171.84 kPa) with nitrogen, holding for about 
one minute, venting to about 5 psig (137.89 kPa), and holding for about 
one minute. Pressuring and venting was repeated a total of five times. 
Next the RSST containment vessel was pressured to about 50 psig (448.16 
kPa) with nitrogen to suppress boiling of the unreacted monomers as the 
reaction temperature increased. 
The RSST was set to ramp test cell temperature up to 55.degree. C. at 
1.0.degree. C./min and then ramp the temperature up 0.35.degree. C./rain 
above 55.degree. C. The polymerization began at about 65.degree. C. and 
over a period of about 49 minutes, the temperature increased to and peaked 
at about 149.degree. C. The heater of the RSST was turned off and the 
sample was cooled to about 30.degree. C. 
Next, 0.10 grams of the following mixture was mixed into the reaction 
product from the first reaction cycle: of 0.3 grams of Vazo.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), 0.3 grams of Vazo.TM. 67 
(2,2'-azobis(2-methylbutanenitrile)), and 0.3 grams of Vazo.TM. 88 
(2,2'-azobis(cyclohexanecarbonitdle)) dissolved in 25.0 grams of methyl 
methacrylate. The test cell was place in the RSST containment vessel again 
and de-oxygenated using the same procedure as that for the first reaction 
cycle and pressured to about 50 psig (448.16 kPa) for reaction. The RSST 
was programmed to ramp the test cell's temperature up to 55.degree. C. at 
1.degree. C./min and then ramp at 0.35.degree. C./min up to 140.degree. C. 
As the reaction mixture warmed, when it reached about 74.degree. C., 
polymerization began. After about 30 minutes the reaction temperature 
peaked at 140.degree. C. At this point the sample was held at 140.degree. 
C. for 180 more minutes. The properties of the resulting polymer were 
analyzed and were found to be: 
Polymer solids: 94.5 weight % based on total weight of the mixture 
(from solids measurement) 
M.sub.n : 17,946 
M.sub.w : 43,390 
M.sub.w /M.sub.n : 2.42 
EXAMPLES 9,10,11 
A series of methyl methacrylate (MMA) polymerizations was performed in the 
Reactive System Screening Tool (RSST). In each case the test cell was 
charged with methyl methacrylate, n-octyl mercaptan, Vazo.TM. 52 
(2,2'-azobis(2,4-dimethylpentanenitrile)), Vazo.TM. 88 
(2,2'-azobis(cyclohexanecarbonitrile)), and di-t-amyl peroxide in the 
amounts shown in Table 7. The methyl methacrylate was used as supplied 
from ICI Acrylics, St. Louis, Mo., with 10 ppm MEHQ inhibitor 
(4-methoxyphenol). 
TABLE 7 
______________________________________ 
Exam- n-octyl Vazo .TM. 
Vazo .TM. 
di-t-amyl 
ple MMA mercaptan 52 88 peroxide 
______________________________________ 
9 10.0 gm 0.01 gm 0.001 gm 
0 gm 0 gm 
10 10.0 gm 0.01 gm 0.001 gm 
0.001 gm 
0 gm 
11 10.0 gm 0.01 gm 0.001 gm 
0.001 gm 
0.0006 gm 
______________________________________ 
Once the RSST test cell was charged with the reaction mixture, it was 
sealed in the RSST containment vessel. With agitation from a magnetic stir 
bar, the reaction mixture was de-oxygenated by pressuring the containment 
vessel to about 300 psig (2171.84 kPa) with nitrogen, holding for about 
one minute, venting to about 5 psig (137.89 kPa), and holding for about 
one minute. Pressuring and venting was repeated a total of five times. 
Next the RSST containment vessel was pressured with nitrogen to suppress 
boiling of the unreacted MMA as the reaction temperature increased. The 
RSST was pressured to about 50 psig (448.16 kPa) for Examples 9 and 10 and 
it was pressured to about 100 psig (792.89 kPa) for Example 11. 
The RSST was set to ramp test cell temperature up from room temperature to 
55.degree. C. at 1.0.degree. C./min and then ramp the temperature up 
0.25.degree. C. /min above 55.degree. C. The temperature of the reaction 
mixtures during warming and during polymerization are shown in FIG. 3. In 
each case, once the rate of temperature rise dropped to about 0.25.degree. 
C., the heater of the RSST was turned off. In each case, the 
polymerization reaction began at about 58.degree.-60.degree. C. (where the 
rate of temperature rise increased above 0.25.degree. C./rain). 
The conversions determined from solids measurements, GPC data, and IV data 
for each experiment are presented in Table 8. The conversion values shown 
are weight percent polymer in the final reaction mixture. Because the GPC 
was calibrated with poly(styrene) standards, the molecular weights shown 
in Table 8 are not meant to be absolute values. 
TABLE 8 
______________________________________ 
Sample Conversion M.sub.n M.sub.w p IV 
______________________________________ 
Example 9 
20.4% 92,500 201,000 2.18 0.31 
Example 10 
48.5% 82,900 175,800 2.12 0.37 
Example 11 
74.5% 72,700 164,300 2.26 0.35 
Standard 
-- 31,700 83,600 2.64 -- 
______________________________________ 
As shown in Table 8, the polydispersity values obtained are quite low. In 
fact they are close to the minimum value of 2.0 obtainable with 
free-radical polymerization of MMA (Ray, W. H., "On the Mathematical 
Modeling of Polymerization Reactors," J. Macromol. Sci. Macromol. Chem., 
C8(1), 1, 1972). A poly(methyl methacrylate) secondary standard was 
measured for comparison. The secondary standard was from Scientific 
Polymer Products, Inc. Its M.sub.w indicated on the sample jar was 93,300 
and its M.sub.n indicated on the jar was 46,400. The measured 
polydispersities of the examples were all less than that for the secondary 
standard which had a polydispersity of 2.01. 
MMA isothermal polymerization is known to exhibit an autoacceleration of 
the polymerization rate with an accompanying increase in molecular weight 
and a broadening of the molecular weight distribution. This 
autoacceleration can become pronounced as low as 20 weight % polymer 
content in the monomer for isothermal polymerization (Principles of 
Polymer Chemistry, P. J. Flory, Cornell University Press, 1953). Because 
the molecular weight distributions remained at a polydispersity of about 
2.0 with increasing conversion, this indicates that the increasing 
temperature profile made the autoacceleration phenomenon negligible, 
enabling the attainment of a narrow molecular weight distribution. 
Theoretically, temperature-controlled free-radical polymerization, in the 
absence of significant gel effect, must employ a decreasing temperature 
profile to minimize the broadening of the molecular weight distribution as 
polymerization progresses (Sacks et al., "Effect of Temperature Variations 
Molecular Weight Distributions: Batch, Chain Addition Polymerizations," 
Chem. Eng. Sci., 28, 241, 1973). A decreasing temperature profile would be 
counter productive in this case because the viscosity would become 
increasingly unmanageable as the temperature decreased, particularly in 
combination with the increasing polymer content from reaction. 
While this invention has been described in connection with specific 
embodiments, it should be understood that it is capable of further 
modification. The claims herein are intended to cover those variations 
which one skilled in the art would recognize as the chemical equivalent of 
what has been described here.