JP2529632C - - Google Patents

Description

Description: FIELD OF THE INVENTION [0001] The present invention relates to a suspension of a solid free radical generating initiator in water, and to prepare such a suspension.
And methods for using such suspensions in polymerizations
You. [0002] The polymerization of ethylenically unsaturated monomers such as vinyl chloride is often carried out in aqueous suspensions.
Free radical-forming compounds that are soluble in monomers, such as organic peroxides or
Is initiated by thermal decomposition of an azo compound. Aqueous including small particles of solid initiator
It is often advantageous to charge the initiator in the form of a suspension. [0003] Peroxide suspensions for the production of PVC are described, for example, in W.S. F. Bell Helst (
W. F. Verhelst et al., "Production of PVC using a peroxide suspension."
"Synthetic material (Kunststoff) 70 (1980) 4, 224-228 pages
Page. Peroxide suspensions, their manufacture and composition,
It is also disclosed in several patents. British Patent No. 2068009 describes various non-I
Disclosed are aqueous suspensions of solid free radical generating initiators, including on-emulsifiers.
EP 106627 describes peroxides, protective colloids, surfactants and water.
Mixing the water at a temperature equal to or higher than the melting point of the peroxide;
A method for the preparation of an aqueous suspension is described. [0004] The main requirement for initiator suspensions is that they are easy to handle and adequate.
Must be able to be stored stably in the
Is that it must not have a negative effect on the polymer produced. In addition, suspension
It is important to note that the actual process for the production of
It is important. SUMMARY OF THE INVENTION According to the present invention, while maintaining a large amount of residual active initiator, a smaller particle size and narrower particle size distribution than previously obtainable. Initiator suspension with
It was found that a suspension was obtained. The initiator suspension of the present invention has excellent stability
And the initiator in the suspension has a small particle size and a narrow particle size distribution.
Allows rapid and uniform distribution of initiator during monomer drop during polymerization
Become like As a result, the resin particles in the produced polymer have a very equal particle size.
And the polymer shows a very low fisheye number. The present invention relates to a solid free radical generating initiator, water, as defined in the claims.
An improved method for producing an aqueous suspension. The method is as follows:
(A) heating the initiator to its melting point; and (b) preferably one or more emulsifiers and one or more protective colloids.
Finely splits the initiator in water while the initiator is in the molten state in the presence of
(C) quenching the initiator so that the time in which the initiator is in a molten state does not exceed 5 minutes.
And [0007] Preferably, the initiator should not be in the molten state for more than 3 minutes. Initiator 1
It is in a molten state for a time not exceeding 30 minutes, especially for a time not exceeding 30 seconds.
Particularly preferred. In addition, the initiator was cooled by about 20 ° C. below its melting point in degrees Celsius.
It is also suitable to cool to a lower temperature, especially about 30 ° C lower. [0008] The short time in the molten state means that when the initiator is finely divided in water,
No time for the resulting droplets to coalesce before solidifying by cooling
That results. With rapid cooling, the droplets are finely divided in water.
It is usually appropriate to solidify within 2 minutes, preferably within 1 minute
. Cooling is performed in such a way that the droplets solidify within 30 seconds, especially within 20 seconds.
Is particularly preferred. However, these times are approximate and depend, inter alia, on the efficiency of the emulsifier in the system. The initiator is
It must be in a molten state when it is finely divided by
It is preferred that the initiator is in a molten state for as short a time as possible. Initiator
The shortest time that must be in the molten state depends on the efficiency of the equipment used
. [0009] The short time in the molten state is also a very small amount of active initiator
It also means that only the heat is lost by pyrolysis. Melting point or lower
Properly adjust the time in the above temperature not more than 2%, preferably more than 1%
Only insignificant amounts of active initiator material are degraded during the above treatment.
Adjust the time at the melting point or above it, not more than 0.5%,
In particular, only an amount of active initiator not exceeding 0.2% is decomposed during the above treatment.
It is particularly preferred that this is done. The decomposition of free radical generation initiator, especially peroxide, is 1
It is well known that the following rate law is generally followed, which means that the following equation approximately applies:
Means Kt = −ln (P _t / P ₀ (I) where k is the reaction rate constant, t is time, P _t Is the amount of initiator at time t, P ₀ Is open
It is the initial amount of initiator. Therefore, some portion x of the initiator remains at some temperature
The time t is t = t _h Given as ln x / ln 2 (II), where t _h Is the half-life of the initiator at the temperature in question.
With respect to the stability of the initiator, the time at or above the melting point is x
The time t calculated from equation (II) as 0.98, preferably 0.99, suitably exceeds
Should not be. The above time is calculated by setting X to 0.995 and sometimes 0.998.
It is particularly preferred that the calculated time is not exceeded. For example, if the melting point is about 30 minutes
If less than about 1% of the initiator with half-life is to be degraded,
X is about 0.99 and t _h If is about 30 minutes, the time at melting point is about
It can be said that it should not exceed 30 seconds. If the initiator has a half-life of about 4 hours, for stability, the above time should not exceed about 3.5 minutes
Is enough. The solid initiator is first suitably mixed with water to form a coarse suspension, and then the mixture is
Heat to the melting point of the initiator. Emulsifier and protective colloid are before its heating
Or can be added later. Amount of at least one part of emulsifier and protective colloid
Is suitably added before the above heating. The release released when the initiator decomposes
Heat is distributed throughout the mixture, so uncontrolled rises in temperature and acceleration of the initiator
Disintegration is prevented. Fine division of the initiator homogenizes the coarse suspension in the heated state
Properly, for example by flowing through narrow passages and
Emulsions are formed by / or ultrasound. A suitable average of the heated coarse suspension
The pressure drop is suitably from about 3000 to about 150,000 kPa,
About 10,000 to 30,000 kPa, and this pressure drop
Or one or several gaps, spanning several gaps in series,
Alternatively, flowing through a valve is included. Suitable gap homogenizer
Are commercially available, for example, APV Gaulin:
Registered trademark). Control the required speed and temperature during heating and cooling
For example, these operations can be performed, for example, on media such as hot and cold water, respectively.
It is preferably carried out by heat exchange in a rate type heat exchanger. Therefore, a particularly preferred method for producing a suspension according to the invention comprises the following steps:
(A) an initiator, an emulsifier, a protective colloid and water to form a coarse suspension
(B) heating the coarse suspension to the melting point of the initiator; (c) mixing the heated mixture to form an emulsion, preferably with a gap or
Comprises homogenizing by passing through a valve homogenizer; and (d) quenching the emulsion to form a suspension of solid initiator. [0013] The suspension according to the invention is a solid free radical generating initiator, for example, preferably at about 25 ° C. or lower.
Above, particularly preferably a melting point of about 30 ° C. or more, more preferably about 40 ° C. or more
A peroxide, suitably an organic peroxide (eg, dialkyl or dialal)
Kill peroxide, aromatic or aliphatic diacyl peroxide, perester, perke
Tar, ketone peroxide or peroxydicarbonate)
it can. Suitable initiators in the methods and suspensions of the present invention have a melting point of about 3
It has a half-life longer than 0 minutes, especially longer than about 60 minutes. In addition, the initiator is 0 ° C
It is also preferred that they are inherently stable, but if not,
Dropping additives may be used in the suspension. Dialkyl peroxydicarbonate
Salts such as dimyristyl-, dicetyl-, distearyl-, dicyclohexyl
Ru-, di-4-tert-butylcyclohexyl- and didecyl-peroxydical
Bonates form a particularly suitable group of peroxides. Other suitable peroxides
Some of the products include -dilauroyl peroxide, -bis (o-methylbenzoyl), -bis
(M-methylbenzoyl), -ddecanoyl, -1,1'-dihydroxydicyclyl
Rohexyl and -dicumyl, 2,5-dihydroxy-peroxy-2,5-di
Methylhexane and di-t-butyl peroxyisophthalate may be mentioned.
Wear. The dialkyl esters of monoperoxyoxalic acid are another suitable peracid
Form groups of compounds, which are preferably members of the perester portion of the molecule.
Alkyl groups are tertiary alkyl groups having 4-8 carbon atoms, while other alkyl groups are
The kill group is a primary having from 18 to 28 carbon atoms, preferably having from 18 to 24 carbon atoms.
It is such that it is a straight chain alkyl group. These peroxides are available from the European Patent Application
No. 271,462 A2 discloses such dialkyl
Examples of esters include the following compounds: octadecyl (t-butyl)
Loxy) oxalate, octadecyl (t-pentylperoxy) oxalar
Octadecyl (t-hexylperoxy) oxalate, octadecyl (t
-Heptylperoxy) oxalate, octadecyl (t-octylperoxy)
) Oxalate, octadecyl (2,4,4-trimethyl-2-pentylperiod)
Xy) oxalate, octadecyl (1-methyl-1-cyclohexylperoxy) oxalate, and the alkyl group in the ester portion of the molecule are each
Corresponding compounds, which are kosyl, docosyl and tetracosyl groups, may be mentioned.
it can. Particularly suitable such dialkyl esters are octadecyl (t-butyl).
Tylperoxy) oxalate, eicosyl (t-butylperoxy) oxala
, Eicosyl (t-pentylperoxy) oxalate, docosyl (t-butyl)
Tylperoxy) oxalate, docosyl (t-pentylperoxy) oxala
, Docosyl (t-hexylperoxy) oxalate, docosyl (t-hepta)
Tylperoxy) oxalate, docosyl (t-octylperoxy) oxala
, Docosyl (2,4,4-trimethyl-2-pentylperoxy) oxala
And docosyl (1-methyl-1-cyclohexylperoxy) oxalar
It is. Among the above-mentioned initiators, diacyl peroxide, dialkyl peroxydioxy
Use of dialkyl esters of carbonate and monoperoxyoxalic acid
Is preferred. Particularly suitable initiators are dilauroyl peroxide, dicetyl peroxy
Dicarbonate, dimyristyl peroxydicarbonate, di- (4-t-butyl
Rucyclohexyl) peroxydicarbonate and docosyl (t-butylper)
Oxy) oxalate. The initiator was prepared such that the resulting suspension had an active oxygen content of about 0.
Suitable in an amount to contain 3 to about 4% by weight, especially about 0.5 to about 3% by weight of active oxygen
Which usually means that the suspension has about 10 to about 60 initiators.
Suitably it means from about 20 to about 45% by weight. An emulsifier is suitably added in an amount of about 0.1 to about 20% by weight based on the suspension.
And particularly preferably in an amount of about 0.2 to about 10% by weight. In this case, the non-ionic field
Surfactants such as ethoxylated fatty alcohols, fatty acids, alkylphenols
Knol or fatty acid amide, or ethoxylated or ethoxyl
Glycerol esters or sorbitan esters of unmodified fatty acids
It is preferably used. Anionic surfactants such as sulfuric acid, sulfonic acid, ether
Sulfuric acid, phosphoric acid or ether phosphate alkyl or alkyl aryl
Or the mono- or diesters of sulfosuccinic acid may also be used.
it can. Cationic and amphoteric surfactants can also be used. The emulsifier can be used alone or in a mixture, but it can be used with an anionic surfactant.
It cannot be mixed with a cationic surfactant. Among the usable protective colloids, polyvinyl alcohol, polyvinylpyrroli
Acrylic acid with don, polyacrylic acid, acrylamide or acrylate
Luic acid copolymers, such as hydroxyethyl- and hydroxypropyl-cellulose.
Water-soluble cellulose derivatives such as methylhydroxypropyl- and ethylhydro
Xyethyl-cellulose, methyl- and carboxymethyl-cellulose, zera
Chin, starch and the like. The amount of protective colloid is emulsifier and initiator
In order to obtain a suitable viscosity, preferably 100 r. p. m. ,
Measured at 20 ° C. with a Brookfield RVT viscometer
It is selected to obtain a viscosity of about 20 to about 600 cp. Based on the suspension
From about 0.001% by weight, usually from about 0.05 to about 10% by weight, preferably from about 0.2 to
About 5% by weight of the protective colloid is added. [0016] The present invention relates to a free radical-producing opener which can be produced by the above-described method of the present invention.
It also relates to an aqueous suspension of the initiator. At least 50% by weight of the initiator particles are greater than 5 μm
Small, and at least 90% by weight of the initiator particles are smaller than 10 μm
A diacyl peroxide, a dialkyl peroxydicarbonate,
Or selected from the group consisting of dialkyl esters of monoperoxyoxalic acid
It has been found that a suspension of the solid free radical generating initiator in water is obtained. Initiator
Preferably at least 50% by weight of the particles are smaller than 3 μm, particularly preferably smaller than 2 μm
And at the same time at least 90% by weight of the initiator particles are preferably 5 μm, particularly preferably
Is smaller than 4 μm. Essentially all initiator particles in the suspension are smaller than 20 μm
Particularly preferably, it is smaller than 10 μm. Particle size is defined by laser diffraction
Mean measured value. The average amount of active initiator in each particle is greater than 90% by weight
Preferably, it can be obtained according to the invention, and the suspension is active oxygen
It preferably contains from about 0.3 to about 4% by weight. The suspension is very stable
If, for example, the peroxide itself has sufficient chemical and thermal stability, the suspension can be separated or separated at room temperature (about 20 ° C.) for one or several months without problems.
It can be stored without any other physical changes. The above suspension
Preferably also contain an emulsifier and a protective colloid. Suitable and good
Suitable initiators, emulsifiers and protective colloids, as well as their amounts,
Reference is made to the disclosure relating to the preparation of a suspension according to Ming. The invention also relates to a plant for producing a suspension according to the invention, which plant
Means for heating the initiator, means for finely dividing the initiator in water (preferably
Phomogenizer), and means for quenching the finely divided mixture
Claims 1. A plant for producing an aqueous suspension of a solid according to claim 1.
is there. The plant also mixes the solid initiator with water, emulsifier and protective colloid.
Means are also suitably included. An embodiment of the plant according to the invention is illustrated in more detail in the accompanying drawings.
1 and 2 schematically show two types of plants for carrying out the method of the present invention.
FIG. 3 schematically shows a side cross section of a detail of a usable gap homogenizer.
Is shown. FIG. 1 shows a heat exchanger connected to a mixing tank 1, a pump 2, and a heating medium such as hot water.
Exchanger 3, preferably a heated gap homogenizer 4, in a cooling medium such as cold water.
A heat exchanger 5 connected thereto and a pump having an outlet 8 for the manufactured product.
Shows a runt, the means of which are connected in series. Heat exchangers 4 and 5
Preferably a plate heat exchanger to achieve very rapid heating and cooling
be able to. The homogenizer 4 is preferably a high-pressure pump, for example a piston pump
And a gap, preferably an essentially ring-shaped gap with adjustable width
And In the preparation of the suspension according to the invention, water, initiators, emulsifiers and
And protective colloids are mixed continuously or batchwise in tank 1
Make a suspension. In the heat exchanger 3, the coarse suspension is heated, for example, by hot water,
The initiator reaches a molten state. The mixture is then sent to a homogenizer 4, which exits in the form of an emulsion and is quenched in a heat exchanger 5, for example by cold water.
Thus, a suspension of solid initiator particles is obtained. According to the disclosed plant, the flow and
Cooling may be performed when the initiator is at a suitable time, for example, from about 5 or about 10 seconds to about 30 seconds.
Can be maintained in a molten state for up to about 60 seconds. FIG. 2 shows a heat exchanger in which the outlet from the homogenizer 4 is connected to a cooling medium.
5 shows a deformation plant guided to a circulation system 6 with 5 and a pump 7. Circulation above
After the heat exchanger 5 in the system there is an outlet 8 for the manufactured product. Other parts are
FIG. 1 corresponds to the part of the plant. The production of the suspension according to the invention relates to FIG.
It is performed in the same manner as disclosed above, except that the homogenizer 4
Is mixed with the circulated cooled suspension from the circulation system 6 and then mixed with the heat exchanger 5
, So that very efficient cooling is obtained. About 50 to about 9 of flow rate
0% is circulated, for example, through system 6, while the remainder is passed through outlet 8 as product
Be taken out. FIG. 3 schematically shows a partial side cross section of the gap homogenizer 4. H
The high pressure port is attached to the ring-shaped support 21 forming the ring-shaped gap 24 together with the
A pump (not shown) communicates through the tube 20 and the width of the gap 24 is
Adjusted by 22 axial movements. The gap 24 is provided with a hole leading to the outlet 25.
The space 23 has a ring shape. Homogenizer 4 may also include means for heating, for example,
An electric heating coil can also be provided, thereby providing an essentially uniform temperature at outlet 2.
5 can be maintained on the entire path. The above homogenizer is used
And the heated coarse suspension flows from the high pressure pump through tube 20 and gap 24.
It is. The substantial increase in velocity and turbulence obtained there is due to the
In which the result is that an essentially homogeneous emulsion is obtained. Axis of head 22
The directional position is the desired pressure drop at the gap 24, for example from about 3000 to about 1
It is adjusted to obtain 50,000 kPa. Finally, the invention relates to an aqueous system by charging a solid free-radical-forming initiator soluble in the following monomers into the system in the form of a suspension according to claim 1 Etch in
The present invention relates to a method for polymerizing a len-based unsaturated monomer. Examples of monomers that can be polymerized include vinyl
Aromatic compounds (eg, styrene and substituted styrenes such as p-chlorostyrene).
Ene), esters of aliphatic α-methylene carbonate (preferably methyl acrylate,
Lower alcohols such as ethyl acrylate, methyl methacrylate or ethyl methacrylate
Alkyl esters), nitrile acrylates, vinyl esters (eg, acetates),
Vinylated vinyl, vinyl ether (eg vinyl methyl ether), vinyl chloride
Includes den, and lower alkenes (eg, butadiene). The present invention is known
Polymerization of vinyl chloride or salt by the method of suspension polymerization or microsuspension polymerization
Vinyl chloride and up to about 20% by weight of alkene,
Nyl, vinylidene chloride, acrylic acid, methacrylic acid, acrylate, methacrylic acid
Acid salts, acrylonitrile, methacrylonitrile, vinyl esters, etc.
Particularly useful for polymerization with polymerizable monomers. Suspensions are usually based on monomers.
The active initiator is added in an amount of about 0.01 to about 2% by weight. In the suspension according to the invention, the initiator particles are small and within a narrow particle size distribution range.
This provides important advantages in the polymerization. Above particle size and narrow particle size
Rapid and uniform distribution of initiator during all monomer drops depending on range
Which results in a uniform initiator concentration and, consequently, a uniform particle size.
New resin particles are obtained and the number of fish eyes in the resin becomes very small.
At the same time the initiator will be used more efficiently. As quick as above
And evenly distributing also allows the reaction mixture to be preheated to the polymerization temperature.
It is possible to charge the initiator as the last component, thereby allowing the polymerization reactor
Can be used more efficiently. Removes all oxygen before charging reactor
Reaction mixture preheated by heating one or more components
Products can be manufactured. The present invention will be described in more detail with reference to the following examples. All amounts are by weight unless otherwise indicated. Examples 1 to 12 In a test plant corresponding to the plant shown in FIG. 1, 12 kinds of suspensions were produced.
Built. The heat exchangers 3 and 5 are plate-type heat exchangers and have a gap homogenizer.
The user 4 uses an APV Gaulin® style, L
It was of the AB100-5 TBS type. In each test, dicetyl peroxy
Coarse suspension consisting of dicarbonate (melting point 52 ° C), emulsifier, protective colloid and water
Mix 4 liters of the suspension at 20 ° C. in tank 1 and then add with warm water at 80-90 ° C.
It was pumped to the heated heat exchanger 3 and brought to a temperature of about 50-55 ° C. Then heated
The mixture was pumped through a gap homogenizer 4 maintained at a temperature of about 52 ° C.
However, at that time, the pressure drop in the gap was about 18,000 kPa. in addition
The emulsion thus produced is cooled in a heat exchanger 5 with cooling water at a temperature of about 2-4 ° C.
Cool to a temperature of 〜１０10 ° C. The flow through the device is about 1.7 l / min
The average residence time between the two heat exchangers 4,5 was about 10 seconds. Each suspension
Was measured with a Cilas (registered trademark) particle size meter 850. Each manufactured
The viscosity of the suspension was measured using a Brookfield® RV
Using a T-type, spindle 3 viscometer, 20 ° C., 100 r. p. m. Measured with
. Each of the above suspensions was stored at 20 ° C. for one month.
There was no separation. The following substances were used as emulsifiers. That is, the ethoxylation step is essentially
Berol 08, which is allyl alcohol (HLB = 18.5)
: Registered trademark), also essentially ethoxylated stearyl alcohol (HLB = 1
8.5) Lutensol AT 80: Lutensol AT 80
Registered trademark), essentially ethoxylated stearyl alcohol (HLB = 18.0)
A certain Lutensol AT 50 (Lutensol AT 50: registered trademark),
And consisting essentially of glycerin mono and distearate (HLB = 3.2)
Atmos 150 (Atmos 150). The following are protective colloids
Was used. That is, Gosenol KH, which is essentially a high molecular weight polyvinyl alcohol and has a degree of hydrolysis of about 78.5 to 81.5 mol%
20 (Ghosenol KH20®) and essentially low molecular weight
Alkanol having a degree of hydrolysis of about 71.5 to 73.5.
Cos. 72.5 (Alcotex 72.5: registered trademark). 12 tests
The composition in weight percent of each suspension in Table 1 is shown in Table 1 below. Rest to 100%
Is essentially water. [Table 1] Table 2 below shows that 50 and 90% by weight of the particles, respectively, were larger than the given particle size.
The particle size of small is shown in μm, and the viscosity is shown in cp. [Table 2] Example 13 In a test plant as disclosed in Examples 1-12, dilauroyl peroxide (melting point
56 ° C.). The conditions during the process are as follows.
To a temperature of 4 to 59 ° C. and a homogenizer at a temperature of about 56 ° C.
And the pressure drop at the gap was about 17000 kPa,
The conditions were the same as those used in the production of suspensions 1 to 12. The suspension produced is composed of 30% by weight of initiator, ethoxylated stearyl alcohol milk.
Berol 08 (registered trademark) (HLB = 18.5) 0.8
%, And a protective colloid (Alcotex 72.5)
: 1% by weight (registered trademark). In the suspension produced, 50% by weight of the particles have a particle size of not more than 2.04 μm
And 90% had a particle size of 4.22 μm or less. Of the suspension at 20 ° C.
The viscosity was 120 cp. The suspension was stored at 20 ° C. for 1 month,
Alternatively, no sedimentation or separation occurred. Example 14 In a test plant as disclosed in Examples 1-12, docosyl (t-butylpe
A suspension of (loxy) oxalate (mp 42 ° C) was prepared. Conditions during the process
The heat in the heat exchanger 3 is heated to a temperature of about 40 to 45 ° C.
And keeping the homogenizer at a temperature of about 42 ° C.
Production of suspensions 1 to 12 except that the pressure drop at about 21,000 kPa
The conditions were the same as those used in. [0030] The suspension produced is composed of 25% by weight of initiator, ethoxylated stearyl alcohol.
Emulsifier Berol 08 (registered trademark) (HLB = 18.5)
8%, and a protective colloid (Alcotex 72.5).
5: 1% by weight). In the suspension produced, 50% by weight of the particles have a particle size of not more than 2.28 μm.
And 90% had a particle size of 4.56 μm or less. Viscosity of suspension at 5 ° C
The degree was 91 cp. The above suspension was stored at 5 ° C. for one month,
No sedimentation or separation occurred.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of one type of plant for implementing the method of the present invention. FIG. 2 is a schematic diagram of another type of plant for performing the method of the present invention. FIG. 3 is a side sectional view of a usable gap homogenizer. [Description of Signs] 1: Mixing tank, 2: Pump, 3: Heat exchanger, 4: Gap homogenizer, 5: Heat exchanger, 6: Circulation system, 7: Pump, 8: Outlet.

Claims (1)

Claims: 1. At least 50% by weight of the initiator particles are smaller than 5 µm;
And a solid free radical generating initiator selected from the group consisting of diacyl peroxides, dialkyl peroxydicarbonates or dialkyl esters of monoperoxyoxalic acid, wherein at least 90% by weight of the initiator particles are smaller than 10 μm. Suspension in water. 2. The suspension according to claim 1, wherein essentially all of the initiator particles are smaller than 20 μm. 3. The initiator is dilauroyl peroxide, dicetyl peroxy dicarbonate, dimyristyl peroxy dicarbonate, di- (4-t-butylcyclohexyl) peroxy dicarbonate or docosyl (t-butyl peroxy) oxalate. The suspension according to claim 1 or 2, characterized in that: 4. The following steps: (a) heating the initiator to its melting point; (b) splitting the initiator in water while the initiator is in a molten state; 2. A plant for producing an aqueous suspension according to claim 1, comprising the steps of: cooling the initiator; means (3) for heating the initiator; and means (4) for finely dividing the initiator. Means for quenching the mixture such that the time that the initiator is in the molten state does not exceed 5 minutes (5)
The above-mentioned plant, comprising: 5. A process for the polymerization of ethylenically unsaturated monomers by charging a solid free-radical generating initiator into the system in the form of a suspension according to claim 1. 6. The method of claim 5, wherein essentially all of the initiator particles are smaller than 20 μm. 7. The method according to claim 1, wherein the initiator is dilauroyl peroxide, dicetyl peroxydicarbonate, dimyristyl peroxydicarbonate, di- (4-t-butylcyclohexyl) peroxydicarbonate or docosyl (t-butylperoxy) oxalate. 7. The method according to claim 5, wherein: