Polymerization processes and products

Beads are made from water-soluble monomer or monomer blend by reverse phase bead polymerization by extruding aqueous monomer beads into or onto the top of an upflowing column of non-aqueous liquid and the beads polymerise as they float downwardly through the column during a period of at least 1/2 minute. The resultant beads can have a very narrow particle size distribution.

This invention relates to beads which have a narrow size range distribution
 and which are formed of water soluble or water swellable polymeric
 material, and to methods of making these beads by reverse phase bead
 polymerization.
 High molecular weight water soluble or water swellable polymers are
 currently made mainly by either the gel polymerization and comminution
 process or by reverse phase polymerization.
 In the gel process, an aqueous solution of the monomer or monomer blend is
 polymerised in bulk to form a rigid gel, which is then dried and
 comminuted. The product has a wide particle size distribution of
 irregularly shaped particles and includes a large amount of fines.
 The reverse phase polymerization process comprises forming droplets of an
 aqueous solution of water-soluble ethylenically unsaturated monomer or
 monomer blend and polymerising the monomer or monomer blend, while the
 droplets are suspended in a non-aqueous liquid, to form aqueous polymer
 droplets. If the droplets are very small the product is a reverse phase
 emulsion. If the droplets are beads, the bead polymerization process is
 completed by drying the resultant polymer beads and separating the polymer
 beads from the non-aqueous liquid.
 The usual way of performing a reverse phase bead polymerization process
 comprises charging a reaction vessel with non-aqueous liquid and
 dispersing the aqueous monomer or monomer blend in bulk into the liquid
 with sufficient agitation to form the aqueous monomer beads, and
 conducting the polymerization while stirring the suspension vigorously so
 as to keep the beads suspended in the non-aqueous liquid. The resultant
 particle size distribution is much narrower, and the amount of fines is
 much less than when the polymer is made by the widely used gel
 polymerization and comminution process and this is advantageous. However
 the reverse phase bead polymerization process does have a tendency to
 produce beads having a wider size distribution than would be desired
 including fines and some mis-shapen beads. This is due to the inevitable
 collisions and shearing forces applied to the monomer droplets and to the
 polymerising beads, especially in large scale commercial processes.
 Although the product can be sieved or otherwise classified according to
 size, this inevitably still leads to a product having a fines fraction and
 a significant spread of particle sizes. For instance fines become trapped
 on the surface of larger beads and sieving does not separate them.
 Attempts to obtain a narrower size distribution by sieving to a very
 narrow size range are not practicable on a large commercial scale (for
 instance above 1 kg or above 10 kg) and again the final product still
 contains fines.
 The products, contaminated with fines, have been widely used on a
 commercial scale and are considered satisfactory for many purposes. For
 instance water soluble beads are used on a large scale for dissolution in
 water to form a flocculant or viscosifying solution and cross linked,
 water swellable, beads are used for delivering, by a sustained release
 mechanism, active ingredient distributed through the beads. Because of
 their more regular shape and narrower size distribution and lower fines
 production, they are often preferred over products made by gel
 polymerization and comminution. However it would be desirable to produce
 beads which have better performance properties, for instance handling and
 dissolution or release properties.
 It is known to conduct oil-in-water emulsion and bead polymerization
 processes, using water-insoluble monomer or monomer blend dispersed in
 water, under conditions whereby collisions between the beads during
 polymerization can be reduced. For instance in GB 1,124,610 it is proposed
 to form a monomer emulsion, having a particle size below 5 .mu.m, and to
 feed this into a simple tubular loop reactor in which the tubular reactor
 has an upwardly extending tubular leg which leads, at its top, into a
 downwardly extending tubular leg. Monomer emulsion is fed into the base of
 the upwardly extending leg and polymer emulsion is taken, when
 appropriate, from the base of the downwardly extending leg. The upward and
 downward movement of the emulsion is due, at least in part, to changes in
 specific gravity as the polymerization proceeds. The polymerization period
 is suggested as 0.5 to 20 hours, preferably 1 to 10 hours.
 In U.S. Pat. No. 3,922,255 a blend of water-insoluble monomers is fed
 through orifices (to form non-aqueous beads) into the base of a vertical
 column along with an aqueous medium containing a stabiliser such as
 gelatin. This aqueous medium and the non-aqueous monomer beads travel
 together upwardly through the column and thereby form a dispersion of
 beads in water in the column. In an example, the time of travel through
 this column averages 3.5 minutes. The dispersion is taken from the top of
 this column through a line and fed to the top of a downwardly extending
 column heated to a temperature at which polymerization is initiated.
 Accordingly there is no initiation of polymerization until a considerable
 period after contact of the beads with the continuous phase, including
 passage through a feed line. The beads and the aqueous medium are caused
 to flow slowly down this column, with a residence time of 150 minutes in
 an example. The resultant slurry of partially polymerised beads is taken
 from the base of the column, some of the aqueous medium recycled to the
 top of the column, and the beads and the remainder of the aqueous medium
 are fed to a reactor where they are subjected to further reaction for, in
 an example, four hours.
 In EP 67,415, water-insoluble monomer is fed through a droplet generator
 into an aqueous suspension medium containing a stabiliser so as to form a
 suspension of droplets in the aqueous medium. This suspension is then fed
 through a line to the top of a column where polymerization is initiated
 and the aqueous medium flows downwardly at a rate such that the droplets
 initially reside at the top of the column but sink, concurrent with the
 downflowing liquid, as polymerization progresses. In an example, the
 residence time in this column is 170 minutes. The aqueous medium and the
 droplets are then reacted under plug flow conditions in another reactor,
 and the resultant suspension of partially polymerised beads in aqueous
 medium is then fed into a third reactor which is another column and
 wherein aqueous medium flows upwardly and the polymer beads, when they are
 completely polymerised, sink to the base of the column and are recovered.
 The total polymerization time is around 5 hours in an example.
 Other disclosures of polymerising water-insoluble is monomer beads include
 JP 51-150592, EP 271,922 and U.S. Pat. No. 4,579,718.
 In U.S. Pat. No. 4,444,961 a particular system is described for forming a
 dispersion of monomer beads in an immiscible liquid, This comprises a
 perforated plate separating a monomer supply from a vertical column of the
 immiscible liquid, and a vibrating pump for pulsing beads through the
 perforated plate into the column. In the preferred embodiments, the
 monomer is water-insoluble monomer and the beads are pulsed into the base
 of an upwardly flowing column of water. However it is also proposed that
 the beads could move countercurrent to the flow of the column. It is also
 proposed that a water-soluble monomer blend could be pumped as beads into
 a column of water-immiscible liquid, in similar manner. The monomer
 droplets flow through this column and emerge from it as a dispersion in
 the immiscible liquid, after about 100 seconds in an example. The
 dispersion is then passed through a line into a separate vessel in which a
 vessel which is separate from the column in which the agitation is
 provided to maintain a dispersion of the droplets and polymerization is
 initiated.
 None of these methods are capable of giving the improvement that we desire
 in the bead polymerization of a water-soluble monomer or monomer blend or
 in the properties of the resultant beads. For instance in U.S. Pat. No.
 4,444,961 the agitation during polymerization will cause bead collisions,
 and in all the described processes the transport of the beads in an
 immiscible liquid before they are exposed to polymerization conditions and
 before they enter the first polymerization vessel will again result in
 undesirable bead collisions.
 Ruckenstein and Hong in Polymer, Volume 36, Number 14, pages 1857 to 1860
 have described a method of making highly cross linked beads by a manual
 method in a test tube. In three runs this method gave beads having a mean
 particle size of 1.3 to 2.5 mm and a relative standard deviation of 5 to
 5.6%, but in a fourth run the starting monomer beads were formed more
 rapidly and then had a particle size of 0.46 mm and a relative standard
 deviation of 34%. Thus, the attempt to increase the rate of production is
 shown to result in very poor product quality. Further, even the slow
 small-scale method was stated to require large amounts of cross linking
 agent, at least 13000 ppm, in order to prevent coalescence of the beads.
 In this small scale, slow, process for making cross linked beads, beads of
 aqueous monomer including sufficient cross linking agent are ejected onto
 the top of a 35 cm column of non-aqueous liquid from a syringe which is
 shown as being positioned a considerable height above the top of the
 column. The liquid in the column is heated to a temperature at which
 polymerization will occur in the beads. The beads gradually sink through
 the column of heated liquid as they polymerise. It is stated that the time
 for the beads to fall from the top of the column to the base is 7 to 9
 seconds. Partial gelation had occurred by the time the beads reached the
 base of the column, and they were left in the base of the column for two
 hours in order to complete polymerization. If inadequate cross linker is
 used, coalescence occurs. Accordinagy the process is not applicable to
 more lightly cross linked beads of the type conventionally used in some
 supersorb polymers (e.g., below 5000 ppm and often below 2000 ppm) and it
 is not applicable to water soluble flocculants, viscosifiers or other
 beads which are wholly or substantially free of cross linking agent. Also
 speeding up the process is shown to give poor results, and scaling that
 process up to be capable of commercial production is not practicable
 because of the inevitable collisions that would occur during the short
 fall down the column if large amounts of monomer are introduced and due to
 the apparent tendency for stickiness at the bottom of the column unless
 the beads are very highly cross linked. Further, it would give a very wide
 particle size distribution.
 This process also results in mis-shapen beads or fines due to distortion
 and fragmentation of the monomer beads when they drop down onto the
 surface of the liquid column.
 Accordingly no process is available which is capable, on a commercial
 scale, of producing polymer beads of water soluble monomer or monomer
 blend and which have a size distribution which is significantly different
 from that which is obtained by conventional bead polymerization processes,
 and discussed above. Further, no beads are available which are water
 soluble or which contain active ingredient and which do not suffer from
 the disadvantages of such beads which are made by existing techniques.
 According to one aspect of the invention, a reverse phase bead
 polymerization process for the manufacture of polymer beads comprises
 forming aqueous monomer beads of an aqueous solution of water soluble
 ethylenically unsaturated monomer or monomer blend and polymerising the
 monomer or monomer blend in the presence of initiator to form aqueous
 polymer beads while suspended in a non-aqueous liquid and then recovering
 the dry polymer beads, wherein the process comprises
 providing in a substantially upright vessel a substantially continuously
 upflowing, substantially non-disruptive, substantially vertical column of
 the non-aqueous liquid wherein the column extends upwardly between a
 discharge point at its base and a monomer feed point at its top,
 extruding the aqueous monomer or monomer blend as aqueous monomer beads
 through orifices into, or non-shatteringly onto, the non-aqueous liquid in
 the presence of initiator and at a temperature whereby polymerization
 initiates substantially immediately upon contact between the beads and the
 non-aqueous liquid, the extrusion of the beads into or on to the liquid
 being conducted at a position which is the monomer feed point or which is
 in substantially non-turbulent non-aqueous fluid communication with the
 monomer feed point,
 allowing the polymerising beads to flow downwardly, countercurrent to the
 upflowing liquid, to the discharge point,
 selecting the initiator and the rate of upflow of the column such that the
 polymerising beads are substantially non-coalescent when they reach the
 discharge point and such that the time for the beads to fall from the feed
 point to the discharge point is at least about 1/2 minute,
 removing a suspension of the non-coalescent beads in non-aqueous liquid
 from the column at the discharge point, and recovering dry, water soluble
 or superabsorbent polymer beads from the suspension.
 Generally the beads in the suspension which is removed from the column at
 the discharge point are maintained under bead polymerization conditions
 while polymerization is completed prior to the final recovery of the dry
 beads.
 In one preferred process of the invention the polymer which is obtained is
 water soluble. Generally this is made by conducting the polymerization in
 the absence of added cross linker. Accordingly the process is particularly
 valuable for the manufacture of polymeric flocculants and viscosifiers.
 In other processes of the invention an active ingredient is included in the
 aqueous solution of monomer, whereby the active ingredient is distributed
 throughout the polymeric beads. Accordingly, by this means, it is possible
 to provide beads from which the active ingredient can be released under
 predetermined conditions. The beads can be soluble in water, but generally
 are swellable rather than soluble, for instance as a result of having been
 polymerised in the presence of added cross linking agent. The amount of
 cross linking agent can be selected between values which are relatively
 low and values which are high (e.g., 100 to 500 ppm up to 3000 to 10,000
 ppm), according to whether rapid or slow release of the active ingredient
 is required.
 In other preferred processes we add very small amounts (e.g., 5 to 200 ppm)
 of cross linking agent and in particular in some instances it is desirable
 to add moderate amounts (e.g., 200 to 1000 or even 2000 ppm) of cross
 linking agent such that the beads are superabsorbent. By superabsorbent we
 mean that the beads will absorb more than 30 grams, and often more than 70
 or more than 100 grams, deionised water per gram dry weight of bead. The
 quoted amounts of cross linking agent are appropriate when it is a
 polyethylenically unsaturated cross linking agent. If other types of cross
 linking agent are incorporated different amounts may be required in order
 to achieve similar properties in the final polymers.
 In other processes, the amount of polyethylenic or other cross-linker can
 be much higher, e.g., up to 1%, 5% or even 20 or 30% by weight (based on
 monomer). In particular the invention can be used to make gel permeation
 chromatography (GPC) beads, for instance formed by polymerization with 5
 to 30%, often 10 to 20%, by weight polyethylenically unsaturated cross
 linking agent. They can have a mean size within the range of sizes typical
 for GPC beads.
 In the invention, the aqueous monomer or monomer blend is extruded into, or
 non-shatteringly onto, the non-aqueous liquid as individual monomer beads
 having a desired size, polymerization is initiated substantially
 immediately the beads enter the liquid, and the beads fall gradually and
 independently through a substantially non-disruptive, substantially
 vertical, upwardly flowing column of the non-aqueous liquid.
 The flow of the upwardly flowing column of non-aqueous liquid must be
 substantially non-disruptive, that is to say it must not disrupt the
 individual integrity of the monomer beads which are flowing downwardly.
 Thus the flow should be sufficiently non-turbulent that it does not cause
 unacceptable collisions of the monomer beads while they are still sticky
 and falling through the column, and it must be sufficiently non-disruptive
 that it does not cause shearing of the beads into smaller particles while
 they are flowing down through the column. Conveniently therefore the flow
 can be considered to be substantially non-turbulent. Preferably the flow
 is sufficiently non-turbulent (i.e., substantially laminar) that beads
 falling through the upflowing liquid will follow a substantially
 rectilinear downward path and will not encounter forces having a
 sufficient transverse component as to promote significant coalescence of
 the beads as they fall.
 The column is usually wholly vertical but it can be slightly inclined
 provided the flow profile is such that the beads do not significantly
 impact on to and coalesce against the walls of the column.
 The column is formed in any suitable upright vessel which is itself usually
 a tubular substantially vertical reaction vessel. The vessel must be free
 of baffles or other devices that would render the flow disruptive and
 turbulent. Thus preferably the column is substantially free of baffles or
 other turbulence-inducing features. Preferably the walls of the column are
 substantially smooth and parallel or taper outwardly or inwardly at an
 angle which is sufficiently low to avoid promoting turbulence.
 The column of non-aqueous fluid flows upwardly at a rate which controls the
 rate of fall of the beads to a period which is within the range about 1/2
 or 1 minute to about 30 minutes and which is sufficient (having regard to
 the initiator and the other polymerization conditions) for the beads to be
 substantially non-coalescent when they reach the foot of the column.
 The rate of flow must be sufficient that the duration of fall is at least
 about 1/2 minute, and usually at least 1 minute, for two reasons. First,
 it is necessary to ensure that sufficient time is given for the
 polymerization to proceed sufficiently, before the beads reach the foot of
 the column, for the beads to be substantially non-coalescent by the time
 they reach the foot of the column. Second, it is desirable to conduct the
 process using a polymerization which takes a significant time to go to
 completion, rather than a polymerization which goes to near completion
 almost instantaneously, within a few seconds. This is because, as a
 generality, improved polymer properties are obtained with slower
 polymerizations than with quicker polymerizations, especially when making
 high molecular weight water soluble polymers or other useful polymers in
 accordance with this invention. In particular, if the duration of fall is,
 for instance, significantly less than about half a minute then it is
 inevitable either that significant coalescence is likely to occur at the
 base of the column or that the polymerization will have to be arranged to
 go sufficiently fast to make an inferior polymer, or both.
 In the invention, the ultimate bead size of the polymer beads is
 substantially determined as a result of the choice of extrusion conditions
 (e.g., the size of the orifices), and as a result of avoiding shattering
 of the beads by extrusion into or closely onto the liquid, and the
 avoidance of substantial coalescence. The substantially immediate
 initiation of polymerization and the countercurrent non-turbulent flow
 allows optimisation of the polymerization while maintaining the bead size
 as the beads fall independently and non-turbulently and substantially
 without coalescence through the column of upflowing liquid.
 The monomer beads are introduced into the upflowing column of non-aqueous
 liquid at the monomer feed point which is at or near the top of the
 column. Non-aqueous fluid may flow upwardly above the monomer feed point,
 for instance as a result of a monomer feed extrusion device being provided
 in the centre of the upright vessel and non-aqueous fluid flowing up
 around it. Often, however, the monomer feed point is at the top of the
 upflowing column in that the non-aqueous liquid is deflected at this point
 from a substantially vertical flow to a lateral flow or other direction
 which allows it to be removed from the vessel.
 The discharge of the aqueous monomer beads into or onto the non-aqueous
 liquid may be at this monomer feed point or it may be at some position
 distant from it provided that position is above and is in sufficiently
 close and substantially non-disruptive non-aqueous fluid communication
 with the monomer feed point. Thus the monomer feed point may be a point at
 which the upflow is deflected laterally and there can be a short vertical
 column above this in which little or no upflow occurs but down which the
 beads can fall through non-aqueous liquid in a substantially non-turbulent
 manner without coalescence.
 The extrusion of the aqueous monomer or monomer blend as monomer beads
 through orifices may be conducted in any manner suitable for forming a
 plurality of beads of predetermined size from a fluid liquid. The orifices
 generally have a diameter in the range 0.05 to 2 mm. There may be a
 plurality of extrusion needles each of which is provided with a pulsed
 supply of liquid or there may be a perforated grid provided with a pulsed
 supply of liquid.
 The frequency of pulsation will be selected having regard to the rheology
 of the aqueous monomer bead and the non-aqueous liquid. The frequency can
 be determined by routine optimisation for any particular feed and needle
 or grid assembly. Preferably the frequency of pulsation is from 20 to 100
 Herz, most preferably from 50 to 80 Herz. For instance the pulsed
 extrusion can be achieved by the needles discharging from a supply chamber
 which is subjected to pulsed variations in pressure. For instance part of
 the chamber may be defined by a diaphragm which is caused to vibrate at
 the desired frequency, for instance by means of electromagnetic vibration.
 The size of the aqueous monomer beads is selected so as to provide final
 dry polymer beads of whatever size is desired, for instance having a
 weight average size in the range 30 .mu.m to 3 mm, and often between 0.1
 mm and 2 mm. Usually all the orifices are of substantially the same size
 and usually all discharge from a single supply chamber, and thus all
 discharge under the same pressure. Accordingly the initial aqueous monomer
 beads are preferably all of substantially the same size. In general, the
 ejected aqueous monomer beads are usually as uniform as possible, for
 instance at least 90% by weight within 15 to 30% of the weight average
 size. Often the size distribution is significantly less than this, for
 instance as discussed in more detail below.
 It is generally preferred that the extrusion orifices are located in the
 surface or beneath the surface of the non-aqueous liquid, i.e., so that
 the monomer beads are extruded direct from the extrusion orifices into the
 non-aqueous liquid. Extrusion in this manner facilitates the formation of
 beads of the controlled size, and it also minimises the risk of distortion
 or other malformation of the monomer beads, which can occur when the beads
 drop down on to the surface of the non-aqueous liquid. Extrusion from
 orifices above the non-aqueous liquid can, however, be tolerated provided
 the drop distance is sufficiently small that the beads do not shatter or
 otherwise significantly distort when they impact on the surface of the
 non-aqueous liquid. Generally the extrusion orifices should not be located
 more than 20 mm, and preferably not more than 10 mm, above the surface of
 the liquid.
 The process is facilitated by the presence of amphipathic polymeric
 stabiliser in the non-aqueous liquid. The amount can be less than the
 amount which is normally required for a conventional bead polymerization
 and the amount of active polymeric stabiliser is generally in the range
 0.01 to 0.5% based on the weight of non-aqueous liquid. Suitable polymeric
 stabilisers are copolymers of water soluble ethylenically unsaturated
 monomers, such as methacrylic or acrylic acid or dialkylaminoalkyl (meth)
 acrylate salt, and water insoluble ethylenically unsaturated monomers such
 as styrene and/or fatty alkyl acrylates or methacrylates. Block copolymers
 such as the copolymer of polyethylene glycol and hydroxy stearic acid can
 be used, all as is conventional for bead polymerization of water soluble
 or swellable polymers.
 The non-aqueous liquid can be any conventional hydrocarbon or other
 non-aqueous liquid such as any of those known for use in reverse phase
 polymerizations. For instance it may be an aliphatic, cycloaliphatic or
 aromatic hydrocarbon, typically having a boiling point of between
 150.degree. C. and 350.degree. C., or an ester or ether or other water
 immiscible liquid.
 The time required for the monomer beads to polymerise sufficiently that
 they become non-coalescent, while still dispersed in the fluid, is
 dictated by the choice of the monomer blend, the initiator system and the
 polymerization conditions in the vessel, such as the temperature.
 The rate of descent of the beads, and thus their times of travel, depends
 on the size and composition of the beads, the rate of upflow, and the
 choice of upflowing liquid (especially the differential between the
 specific gravities of the beads and the liquid. Viscosifier can be
 included to increase the viscosity of the liquid but this is usually
 avoided.
 The rate of upflow and the relative specific gravities on the one hand and
 the polymerization conditions on the other are selected in known manner
 such that the monomer beads polymerise to a substantially non-coalescent
 state before they reach the bottom of the column and in a period which is
 preferably not more than 30 minutes and is usually less than 15 or 20
 minutes. It is generally undesirable to polymerise too fast (because of
 the impact this has on ultimate molecular weight) and so it is normally
 preferred that the beads need to polymerise for at least one minute before
 they become non-coalescent and often the polymerization has to be
 conducted for 11/2 or 2 minutes, often at least 5 minutes, before the
 non-coalescent state is achieved.
 If there is a substantially static column of non-aqueous fluid down through
 which the beads fall before reaching the monomer feed point, this flow
 will itself occupy a few seconds, for instance up to 10 or even 20 seconds
 or more in some processes, and so this will add to the total
 polymerization time.
 The rate of upflow of the non-aqueous liquid through the column is usually
 at least 0.2, and preferably at least 0.5, cm/sec. Preferably it is not
 more than 3 cm/sec but speeds of up to 10 cm/sec or higher can be suitable
 in some processes. A particular advantage of the invention is that it is
 easily possible to adjust the speed of upflow (merely by adjusting the
 rate of pumping of the non-aqueous fluid through the apparatus) and
 thereby it is easily possible to change the polymerization conditions
 according to variations in the feed (for instance changes in the monomer
 or monomer blend or in the initiator or temperature) or rate of supply of
 monomer feed or desired end product (for instance molecular weight).
 It is generally preferred that the rate of upflow at the top of the column
 (and down through which the monomer droplets fall) should be less than the
 race of upflow throughout the main length of the column. Thus there can be
 a static head of fluid at the top of the column or, more usually, the rate
 of upflow in the topmost section of the column is less than 90% and often
 less than 70% of the rate of upflow throughout the central part of the
 column. Usually it is at least 20% of the rate of upflow through the
 central part of the column, for instance above 40%. The reason for having
 a static or slower upflow at the top of the column is that the monomer
 droplets have a lower specific gravity than the droplets once
 polymerization has progressed significantly. By arranging for the upflow
 to be less at the top, sedimentation of the beads occurs at the top of the
 column even though the rate of upflow lower down the column (selected to
 give the desired sedimentation of the polymerising beads) is sufficiently
 high that it would (if applied to the monomer beads) be liable to carry
 the monomer beads upwardly and out of the column.
 The length of the slower top portion of the column can be selected
 according to the rate of specific gravity change that is desired. Usually
 it is at least 3% and usually at least 5% of the total length of the
 column. It can be as much as, for instance, 20% or more but usually it is
 less than 10% of the total length of the column. If desired, the column
 can be tapered downwardly over substantially all its length, but this is
 usually unnecessary.
 By saying that the polymerization initiates substantially immediately upon
 contact of the aqueous monomer beads with the non-aqueous liquid, we mean
 that all the components necessary to initiate polymerization are present,
 but of course measurable polymerization may not occur immediately since
 there is usually a significant induction period before it can be seen that
 measurable polymerization has occurred.
 Generally part of a redox initiator system is in the non-aqueous liquid and
 the other part is in the monomer droplets in known manner, and/or the
 non-aqueous liquid is at a temperature sufficient to activate a thermal
 initiator in the monomer beads.
 The polymerization temperature, and in particular the temperature of the
 non-aqueous liquid column and the non-aqueous liquid in the final
 polymerization, is generally in the range 50 to 90.degree. C., usually
 around 65 or 70.degree. C. up to 80 or 85.degree. C.
 The column leads downwardly to a discharge point at which the beads collect
 after they have reached the non-coalescent state. For instance a
 substantially non-coalescing skin will have formed around each bead or the
 entire bead will have become non-coalescing. Accordingly by the time the
 beads reach the discharge point, it is possible to expose them to
 turbulence and agitation (in contrast to the substantially non-turbulent
 and non-disruptive conditions which they have encountered previously)
 without significant risk of coalescence between the beads. It is often
 convenient for the rate of upflow of the non-aqueous liquid to be slower
 adjacent the discharge point than above it, so as to facilitate settling
 of the beads out of the liquid. Accordingly the bottom of the column can
 be dimensioned so as to produce a slower rate of upflow. For instance the
 rate of upflow over the bottom 3 to 20%, usually 3 to 10%, of the total
 length of the column can be less than at higher points in the column
 (e.g., below 90% and preferably 20-70% of the rate of upflow at higher
 points).
 The suspension of non-coalescent beads which is removed from the column at
 the discharge point can be a suspension of fully polymerised beads, in
 which event the final beads can be recovered from it, but generally the
 beads are subjected to further bead polymerization conditions in a
 suitable polymerization vessel, This may be at the base of the column but
 can be any suitable vessel to which the suspension can be transferred.
 Transfer may be by pumping or by merely dropping into the vessel. If full
 polymerization is to be achieved in the column, the fall time in the
 column must be sufficiently long to permit this. Generally the fall time
 in the column is not more than 30 minutes, and a post-polymerization stage
 is then usually desirable.
 The bead polymerization conditions to which the beads are exposed in the
 post polymerization stage (after discharge from the column) can be
 conventional conditions in which the suspension of beads in non-aqueous
 liquid is subjected to agitation in conventional manner so as to keep the
 beads in dispersion in the non-aqueous liquid.
 The overall polymerization conditions are generally such that the total
 period between introducing the monomer into the non-aqueous liquid and
 completion of polymerization is between about 1/4 hour and 3 hours, more
 usually between about 1/2 hour and 1 or 11/2 hours.
 The process can be conducted substantially continuously with the result
 that there is a substantially uniform residence time in the process for
 all the material which is being polymerised. Often, however, it is more
 convenient to conduct the process batchwise, wherein during each batch
 there is continuous addition of monomer until all the monomer has been
 added, there is continuous upflow of non-aqueous liquid until all the
 beads have fallen through it, and the final polymerization is conducted
 for sufficient time to ensure that full polymerization has occurred of the
 beads which were introduced last.
 The non-aqueous liquid usually needs to be purged with nitrogen during the
 process and conveniently this is conducted during the recycle of the
 non-aqueous liquid from the top of the column back to the base of the
 column.
 The recovery of dry beads from the final polymerization suspension involves
 removing the water and separating the beads from the non-aqueous liquid.
 Preferably it also involves removing unreacted monomer. Preferably the
 final suspension (ie after the final polymerization) of beads in
 non-aqueous liquid is subjected to azeotropic distillation (i.e.,
 distillation which removes both water and non-aqueous liquid). After
 distillation to reduce the water content to, for instance, below 10% by
 weight of the beads they may then be separated from the residual
 non-aqueous liquid by filtration or centrifugation and may then be
 subjected to further drying, for instance fluid bed drying.
 The monomers which can be used for making the polymers of the invention can
 be any of those conventionally used for the production of water soluble or
 superabsorbent polymer beads from ethylenically unsaturated material. The
 monomers are usually acrylic monomers.
 A preferred non-ionic monomer is acrylamide.
 Preferred anionic monomers are ethylenically unsaturated carboxylic acids
 (such as acrylic acid) or sulphonic acid (such as AMPS) Often they are in
 the form of sodium, ammonium or other water soluble salts.
 Ethylenically unsaturated cationic monomers include dialkylaminoalkyl
 (meth) -acrylates and -acrylamides and their acid addition and quaternary
 ammonium salts, such as dimethylaminoethyl (meth) acrylate quaternary
 salts, and quaternary diallyl dialkyl monomers such as diallyl dimethyl
 ammonium chloride (DADMAC).
 When the beads are to be superabsorbent, the monomers are usually anionic
 (for instance acrylic acid or salt such as sodium acrylate) or a blend
 thereof with acrylamide. When the polymer is to be water soluble, it may
 be non-ionic (for instance polyacrylamide homopolymer) or anionic or
 cationic and is often formed from a blend of acrylamide or other water
 soluble non-ionic monomer with ionic monomer.
 Water soluble bead polymers are typically used as viscosifiers or
 flocculants, including retention aids for paper making. They can be
 anionic, cationic or non-ionic. Typically they have intrinsic viscosity
 (IV), measured by a suspended level viscometer at 25.degree. C. in 1N
 sodium chloride solution buffered to pH7, of at least 4 dl/g although
 lower IV beads (e.g., IV 1-4 dl/g) of cationic polymers such as poly
 DADMAC can also be made by this process and used as coagulants. The IV
 will usually always be above about 0.5 dl/g since lower molecular weight
 polymers tend to be difficult to put into satisfactory dry bead form.
 Gel permeation chromatography beads may be formed of acrylamide or blends
 of acrylamide with other monomers and sufficient polyethylenic cross
 linker to restrict their swelling in water to 0.2 to 2 times their weight,
 e.g., 15 to 30%.
 When active ingredient is included in the aqueous monomer feed, that active
 ingredient will be dispersed in the final matrix of the polymer in each
 polymer bead. The active ingredient may be, for instance, an enzyme. The
 invention is of particular value therefore in the immobilisation of
 enzymes, for instance for use in a chemical reaction, since it is possible
 to provide beads having a very uniform size and therefore a very uniform
 availability of enzyme. Other active ingredients which can be trapped in
 the beads in this manner include agriculturally and horticulturally useful
 active ingredients such as fertilisers, nutrients, herbicides, pesticides
 (including fungicides).
 These beads may either be linear or cross linked. For instance the gel
 immobilisation beads for enzymes are usually cross linked. The mean
 particle size is usually between 0.5 and 2 mm.
 The distribution of sizes of polymer beads can, in the invention, be
 controlled primarily by the distribution of sizes of the extrusion
 orifices and the extrusion conditions. If (as is usual) all the orifices
 have substantially the same size then it is possible in the invention to
 obtain beads which are substantially all of the same size. Accordingly the
 invention is useful both where a narrow size range is desirable (e.g., as
 flocculant or viscosifier) and where it is essential for optimum
 performance (e.g., in a slow release composition).
 According to a second aspect of the invention we provide novel beads of
 water soluble or water swellable polymeric material. These beads are
 obtainable by the process of the invention. They are formed from a water
 soluble ethylenically unsaturated monomer or monomer blend and have a mean
 particle size generally in the range 0.05 to 5 mm, preferably 0.1 to 3 mm,
 and at least 95% by weight of the beads have a size at least 50% of the
 mean particle size. Usually at least 98%, and generally at least 99%, by
 weight of the particles have a size at least 50% of the mean particle
 size. In particular, preferred beads of the invention have at least 95%,
 usually at least 98% and preferably at least 99% by weight of the beads
 having a size at least 70% and usually at least 80 to 90% of the mean
 particle size.
 These values indicate that the proportion of fines is extremely low and
 indeed it is usually substantially zero. Often the beads have 99.9% by
 weight of the particles with a size above 50% and often above 80% of the
 mean particle size.
 The standard deviation of the beads, from the mean particle size, is
 preferably below 0.1, and most preferably is below 0.05. Usually it is
 above 0.01. These standard deviations are extremely narrow and indicate a
 very narrow particle size distribution.
 The relative standard deviation is usually below 5% and preferably below
 3%. It can be as low as 0.5% but is usually at least 1%.
 The narrow size distribution in the invention is obtainable in the direct
 product of the described process, and thus it is not necessary to sieve or
 otherwise fractionate the bead product to obtain this distribution.
 In one aspect of the invention, the novel beads are provided in relatively
 large quantities, for instance containers containing at least 1 kg and
 usually at least 10 kg of the beads. This is commercially convenient and
 possible in the invention because of the ease of manufacturing the novel
 beads by the novel process.
 In another aspect of the invention the beads are of water soluble polymeric
 material.
 In another aspect of the invention the beads contain an active ingredient
 distributed substantially uniformly through the polymeric material, which
 is often a cross linked material.

The apparatus of FIG. 1 comprises an upright vessel 1 which defines a
 substantially vertical column 2 of non-aqueous liquid. This column extends
 between a discharge point 3 at the base of the column and the vessel and a
 monomer feed point 4 at the top of the column. A side arm 5 leads from the
 vessel whereby fluid from the column 2 moving up through the vessel is
 diverted into a collector 7. The vessel extends upwardly to define a short
 substantially static column of liquid.
 A nitrogen purge 8 is provided in the collector 7 whereby fluid can be
 purged with nitrogen prior to being recycled through line 9 by pump 10 and
 column 11 into reaction vessel 12 into which the discharge point 3
 discharges.
 Aqueous monomer is fed by pump 13 through a pulsed ejection system 14 by
 which it either drops down through a distance h on to the upper surface 15
 of the liquid in the part 6 of the vessel or, more usually, is ejected
 under the surface 15 of the liquid.
 Non-aqueous liquid is pumped down vessel 11, through reactor 12 and up
 through vessel 1, thereby forming an upwardly moving vertical column 2 of
 non-aqueous liquid extending between the points 3 and 4. The flow is
 substantially non-turbulent in that there are no baffles in the column 2
 and the beads of polymerising material drop down through the column
 following a substantially linear path.
 In the apparatus of FIG. 2 the column 2 is supplied with a flow of
 non-aqueous liquid (the direction of flow being shown by broken arrows) by
 a pump 20 from a reservoir 21. The incoming non-aqueous liquid enters the
 column at a point 22 which is above the discharge point 3 and below a neck
 23 where the column splays outwardly. Accordingly the rate of flow of the
 non-aqueous liquid increases as it passes through the neck and up into the
 main length of column, which is narrower. The liquid flows upwardly to a
 weir 24 (as shown in FIG. 3) and overflows at the weir into a surrounding
 collector 25 from which it discharges by pipe 26.
 The top portion 27 of the column has a larger diameter than the main length
 so that the rate of upflow decreases as the column diameter increases, and
 is connected to the main length of the column by a tapering collar 34.
 Monomer is extruded into the non-aqueous liquid by needles 28 having
 orifices 29 positioned just beneath the level 30 of the top of the liquid.
 These needles communicate between the orifices 29 and a supply chamber 31
 into which the aqueous monomer feed 27 is pumped. One side 32 of the
 supply chamber is defined by a diaphragm which is caused to vibrate with a
 vertical motion by an electromagnetic vibrator 33.
 Monomer is discharged from these needles into the upflowing liquid and
 falls downwardly as polymerising beads, the direction of movement being
 shown by solid arrows. The downflow accelerates as the liquid passes the
 collar 34 and subsequently decelerates as the liquid passes the collar 23
 and the beads accumulate at the discharge point 3 at the base of the
 column. From here they may be pumped as a slurry up through duct 36 and
 discharged from valve 37 into one of the reactor vessels 39. Each of these
 is provided with a stirrer shown diagrammatically as 40 and with suitable
 outlet means 41 for removing sedimented beads from the base. Non-aqueous
 liquid falls over a weir and returns to reservoir 21 via ducting 42.
 Product is removed from vessels 39 via drain or other outlet means 41
 prior to distillation in other equipment.
 Appropriate means for purging the non-aqueous liquid with nitrogen in the
 reservoir 21 and, when necessary, in the reactor vessels 39 are provided
 but, for simplicity, are not shown.
 The following are examples of the invention.
 EXAMPLE 1
 An anionic water soluble monomer mixture consisting of

Acrylamide (50% aqueous solution) 58 g
 Sodium Acrylate (50% aqueous solution 25 g
 50% neutralised)
 Sodium Hydroxide (46% aqueous solution) 5 g
 Urea (100%) 0.9 g
 Water 12 g
 was prepared, and adjusted to pH 6.0. The solvent phase as Exxsol D240/270,
 trade mark for a dearomatised hydrocarbon solvent of boiling range
 242.degree. C. to 270.degree. C. and flashpoint of 118.degree. C.
 Amphipathic stabiliser was added at a level of between 0.05% and 1% on
 weight of solvent phase.
 Thermal initiators were then added to the aqueous monomer phase typically
 between 0.001% and 0.1% on monomer phase. These could typically be a
 di-azo compound such as 2,2'-Azobis [2-(2-imidazolin-2-yl)propane]
 dihydrochloride, 2,2'-Azobis(2-amidinopropane) dihydrochloride or
 4-4'-Azobis (4-cyanopentanoic acid), or a peroxy compound such as ammonium
 persulphate, singularly or in combination.
 The solvent phase was purged of O.sub.2 prior to the addition of the
 aqueous monomer phase by bubbling N.sub.2 at a flow rate of 1 litre per
 minute. The N.sub.2 was then continuously bubbled through the solvent
 phase whilst monomer transfer took place.
 The solvent was heated to and maintained at a temperature of 80.degree. C.
 whilst being pumped around the system at a flowrate of approximately 500
 mls per minute.
 The aqueous monomer phase was introduced into the solvent phase through a
 vibrating 5-nozzle assembly at a flow rate of 5 ml per minute per nozzle.
 The nozzle assembly was oscillated at a frequency of 60 to 80 Hz. The
 nozzle diameter was 0.51 mm.
 The counter current solvent flow was controlled in order to allow the
 polymerising aqueous phase a minimum time of 1 minute to "skin over"
 before it reached the column bottom. This was to ensure that coalescence
 would not occur. The resultant slurry of non-coalescent beads was
 transferred to a holding vessel and subjected to further polymerization at
 80.degree. C. for 1/2 hour.
 By this process it was possible to obtain beads having a mean particle size
 of 1.49 mm, a minimum of 1.42 mm, a maximum of 1.55 mm, a standard
 deviation of 0.04 and a relative standard deviation of 2.68%.
 EXAMPLE 2
 An aqueous, cationic, water soluble, monomer mixture consisting of

Acrylamide (50% aqueous solution) 79 g
 Adipic Acid (100%) 3 g
 Methacryloyloxy ethyl trimethyl ammonium 1.4 g
 chloride (70% aqueous solution)
 Acryloyloxy ethyl trimethyl ammonium 15 g
 chloride (70% aqueous solution)
 Urea (100%) 1.8 g
 was prepared and adjusted to pH 4.0. The solvent phase was Exxsol D240/270.
 Amphipathic stabiliser was added at a level of 1000 ppm on weight of
 solvent phase.
 Thermal initiators were then added as in Example 1 and the solvent phase
 was purged as in Example 1.
 The solvent was heated to and maintained at a temperature of 67.degree.
 C.-71.degree. C. whilst being pumped around the system at a flowrate of
 approximately 330 mls per minute.
 The aqueous monomer phase was introduced into the solvent phase through a
 vibrating 5 nozzle assembly at a flow rate of 5 ml per minute per nozzle.
 The nozzle assembly was oscillated at a frequency of 60 to 80 Hz. The
 nozzle diameter was 0.51 mm.
 The counter current solvent flow was controlled in order to allow the
 polymerising aqueous phase a minimum time of 2 minutes to "skin over"
 before it reached the column bottom. This was to ensure that coalescence
 would not occur. The resultant slurry was subjected to further
 polymerization at 67 to 71.degree. C. for 1/2 hour.
 By this means it was possible to obtain beads having a mean diameter of
 1.44 mm, a minimum of 1.33 mm, a maximum of 1.47 mm, a standard deviation
 of 0.03 and a relative standard deviation of 2.08%.
 EXAMPLE 3
 A cross linked monomer mixture consisting of

Acrylic Acid (80% solution) 36 g
 Sodium Hydroxide (46% solution) 26 g
 Water 38 g
 was prepared and adjusted to pH 4.0. The solvent phase, purging and
 initiator were as in Example 1.
 Amphipathic stabiliser was added at a level of 500 ppm on weight of solvent
 phase.
 Cross linking agent was added to the aqueous monomer phase in the form of
 Tetrallylammonium chloride or Methylene-Bis Acrylamide, typically at a
 level of 0.05% to 0.2% on monomer phase.
 The solvent was heated to and maintained at a temperature of 90.degree. C.
 whilst being pumped around the system at a flowrate of approximately 500
 mls per minute.
 The aqueous monomer phase was introduced into the solvent phase through a
 vibrating 5 nozzle assembly at a flow rate of 5 ml per minute per nozzle.
 The nozzle assembly was oscillated at a frequency of 20 to 100 Hz. The
 nozzle diameter was 0.26 mm.
 The counter current solvent flow was controlled in order to alow the
 polymerising aqueous phase a minimum time of 1 minute to "skin over"
 before it reached the column bottom. This was to ensure that coalescence
 would not occur. The slurry was then subjected to further polymerization
 at 90.degree. C. for 1/2 hour.
 By this means it was possible to obtain beads having a mean diameter of
 0.78 mm, a minimum of 0.74 mm, a maximum of 0.82 mm, a standard deviation
 of 0.01 and a relative standard deviation of 1.28%.