Method and apparatus for delaying polymerisation

Abstract

The present invention relates to a method of and an apparatus for extending the shelf life of an initiated monomer mixture, the method comprising the prevention of premature free radical polymerisation by introducing oxygen or oxygen-containing gas into a container of the initiated monomer mixture and providing mechanical agitation to the container, wherein said introduction and agitation are performed in a temperature and pressure controlled environment.

Claims

1. A method of extending the shelf life of an initiated monomer mixture comprising the prevention of premature free radical polymerization during a storage period prior to use of the initiated monomer mixture to form a polymeric article, by introducing oxygen or oxygen-containing gas into a container of the initiated monomer mixture during the storage period and providing mechanical agitation to the container during the storage period, wherein the initiated monomer mixture comprise a mixture of ethylenically unsaturated compounds and radical initiator, and wherein the volume of the container is larger than the volume of initiated monomer mixture contained therein thereby providing space in the container above the initiated monomer mixture.

2. The method as claimed in claim 1, wherein air is introduced into the container as said oxygen or oxygen-containing gas.

3. The method of claim 2, further comprising filtering or drying the air before introducing the air into said container.

4. The method of claim 2, further comprising filtering and drying the air before introducing the air into said container.

5. The method as claimed in claim 1, wherein said method is automated and performed in a closed environment with controlled temperature.

6. The method as claimed in claim 5, wherein the method comprises sparging said oxygen or oxygen-containing gas into the container.

7. The method as claimed in claim 1, wherein said method is carried out at a temperature of about 15° C.

8. The method as claimed in claim 1, wherein said introduction of oxygen or oxygen-containing gas and said mechanical agitation occur simultaneously.

9. The method of claim 1, wherein the shelf life of the initiated monomer mixture is extended to at least four days.

10. The method of claim 9, wherein filtered and dried air is introduced into the container simultaneously with the mechanical agitation, and wherein the method is automated and performed in cycles in a closed environment, wherein conditions of the closed environment are controlled and monitored by an electronic controller, the electronic controller controlling one or more of pressure, temperature, rate of agitation, duration of agitation, frequency of introduction of oxygen or oxygen-containing gas cycles and frequency of agitation cycles.

11. The method of claim 1, which is automated and performed in cycles in a closed environment, wherein conditions of the closed environment are controlled and monitored by an electronic controller.

12. The method of claim 11, wherein the electronic controller controls one or more of pressure, temperature, rate of agitation, duration of agitation, frequency of introduction of oxygen or oxygen-containing gas cycles and frequency of agitation cycles.

13. The method of claim 1, wherein the initiated monomer mixture is a mixture for the preparation of polymeric contact lenses, and the prevention of premature free radical polymerization is during a storage period prior to use of the initiated monomer mixture to form a polymeric contact lens.

14. The method of claim 13, further comprising polymerizing the initiated monomer mixture after the storage period and forming a polymeric contact lens.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1a and 1b respectively show front and side views of a preferred apparatus for performing the method according to the invention loaded with containers;

(2) FIG. 1 c shows an exploded view of the apparatus of FIGS. 1a and 1 b.

(3) FIG. 2 is a flowchart showing a process for delivering oxygen to contact lens monomer mixtures in accordance with the invention; and

(4) FIG. 3 is an example of an input screen for an apparatus carrying out the method according to the invention.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWING FIGURES

(5) Referring to the drawings, there is shown an apparatus for automated sparging of oxygen or oxygen-containing gas into a container of initiated monomer mixture while providing mechanical agitation to the container.

(6) FIGS. 1a, 1b and 1c show a preferred apparatus 1 for performing the method according to the invention. The preferred apparatus 1 has a plurality of containers 2 spaced over three shelves 3. Each container 2 is located in its own gripping nest 4 which is mounted on a rotating platform 5. Above the front access door 6 of the apparatus there is a user interface screen 7 and operator control buttons 8. The refrigeration control interface 9 is located to the left of the user interface screen 7.

(7) Drive motors for shelf agitation are located underneath each shelf 3 within an aluminium housing. This rotates the rotating platform to induce a sloshing motion in the initiated monomer mixture at a rate which is variable from the operator user interface screen 7 (between approximately 2 and 4 Hz (between about 10 and 200 rpm).

(8) A door switch is provided on the front access door 6 to detect the status of the door 6 (open or closed). In addition, this door 6 is locked by a solenoid bolt while agitation is taking place to prevent accidental opening. In an alternative embodiment, a sensor may be provided to detect when the door is opened and to send a signal which causes rotation of an platform which is in the rotation part of the cycle to cease until the door is closed. All pneumatic components reside in the pneumatic enclosure 10 at the rear of the machine. This panel 10 contains the air service unit, air dryer with pre-filter (0.01 μm), flow controller, pressure regulator and valves/distribution manifolds (not shown).

(9) The air dryer operates on a duty-standby arrangement with desiccant media carrying out the drying function. From the outlet of the air dryer air then enters the precision pressure regulator. This regulator is intended to reduce the pressure experienced by the containers 2 (5-30 psi or approximately 34-207 kPa). The value of this pressure is measured by the flow controller downstream. This flow controller regulates the mass flow delivered to each agitator shelf (0-2 slpm). Finally, air leaving the flow controller is distributed between three manifold blocks, one per shelf 3. Each manifold block is isolated by a 2/2 shutoff valve (normally closed). A final filter (0.5 μm) is placed between the valve and manifold to prevent any possibility of particles shed from the valve entering the air stream. All exhaust (return) air from the containers 2 is piped to the exhaust manifold in the bottom right of the panel 10. This air can then be removed by the exhaust port on the outside of the panel 10.

(10) Once air has been cleaned and prepared in the pneumatic panel 10 it is then piped out to the containers 2 on each agitator shelf 3 via hard wall tubing. Each shelf 3 has twelve pipes routed to it: six pressurised inlet air lines and six exhaust air lines (not shown). These lines are fitted to the cap 11 that is provided for each container 2.

(11) The shaking mechanism used to agitate the containers is designed in such a way as to mitigate most if not all vibration associated with the rotation of an off balance load. All six nests 4 are aligned so as to always have two opposing containers 2 directly counterbalancing each other when their respective centres of gravity are moving. When a particular nest 4 is not in use, the quick connect fittings for that nest 4 should be coupled together to form a direct flow path between the pressure line and the exhaust line.

(12) To start the system, the operator must first ensure the correct running parameters have been entered and press the Start Button on the user interface screen.

(13) FIG. 2 is a flowchart showing the preferred steps of the process cycle according to the method of the invention. In this preferred method, the steps of distributing dried and filtered air and shaking the monomer mixture are performed in cycles at a duration and rate determined by the operator and pre-programmed into the electronic controller.

(14) The oxygenation/aeration cycle A1-A5 is automatically initiated based on the operator input. The first step of this cycle after initiation A1 is a check that the environment is at the correct temperature (A2a and A2b). Then access ports are checked to see if they are closed and secure (A2). Incoming air is then filtered and dried to ensure quality and the pressure thereof is reduced to control the pressure experienced by each container (A3). Data regarding the pressure entering each container is provided to the electronic controller and this data is used to control the aeration flow rate (A4 and A5). At the same time the agitation cycle B1-B5 takes place. Here checks for motor errors are made (B2), the mixing speed is set (B3) and each container is mixed for a time determined by the apparatus timer based on the operator input (B5).

(15) After the containers have been aerated and agitated for the predetermined time, each cycle begins again.

(16) Should any of the checks fail the electronic controller alarms and an operator or technician is summoned. The user interface screen is capable of allowing for users with sufficient access to change critical parameters for adding air to the monomer mixtures.

(17) An example of a user interface screen is shown in FIG. 3. Here the cycle is set to repeat every 6 hours, the duration of agitation (mixing time) is 10 minutes and the rate of agitation (‘mixing speed’) is 130 rpm (2.167 Hz).

EXAMPLES

Example 1

Preparation of Initiated Monomer Mix

(18) During development of the nesofilcon A monomer formulation (the monomer formulation utilised in production of Biotrue ONEday lenses), it was observed that introduction of oxygen to the formulation greatly improved stability of the monomer mixture resulting in extended shelf life. On average, nesofilcon A monomer mix utilised in the Biotrue ONEday lens has a shelf life of approximately two days when no re-oxygenation process is utilised.

(19) Uninitiated nesofilcon A monomer mix was prepared containing the following ingredients:

(20) TABLE-US-00001 ACTIVE INGREDIENT N-vinyl pyrrolidone t-Butyl-hydroxycyclohexyl Methacrylate 1,2-propanediol 2-Hydroxyethyl Methacrylate Ethylene Glycol Dimethacrylate Allyl Methacrylate 2-[3-(2H-Benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate Poloxomer 407 Dimethacrylate In-Monomer Visibility Tint (RD-322))

(21) Formulation requirements were used to calculate the amount of each ingredient required for manufacture of 2 L and 10 L sized batches. Individual ingredients were metered into the formulation using a minimum accuracy of two decimal places.

(22) Initiation of Nesofilcon a Monomer Mix:

(23) TABLE-US-00002 ACTIVE INGREDIENT 2,2′-Azobisisobutyronitrile (AIBN)

(24) The amount of initiator needed was calculated using the following equation:

(25) Monomer net weight in grams×0.00418=Grams of Initiator Required. The amount of initiator added was weighed using a tolerance of ±0.20%.

(26) In a dry air environment the calculated amount of 2,2-azobisisobutyronitrile (AIBN) initiator was added to the mix, the container was sealed, returned to a refrigerator at 15° C. (+/−3° C.), and stirred for 1 hour, (±5 minutes), at 15° C. (+/−3° C.). Approximately 2100 g of monomer was immediately transferred into a 3.0 L HDPE plastic container leaving approximately 1 L of free space to assure adequate headspace to inhibit polymerisation. Transfer into the larger container was carried out in a dry air environment. The mix was stored at 15° C. (+/−3° C.) until use with daily regeneration of the headspace in the HDPE container.

Example 2

Regeneration: Manual Method

(27) A container containing the initiated mix from Example 1 (approximately 2100 g of initiated monomer, container capacity of 3.0 L) was opened for 30 seconds, (±10 seconds), in ambient atmosphere. The container was then sealed the shaken for 10 seconds. A log was kept with the lot number of the mix and the time and date of headspace regeneration.
The initiated mix was stored at 15° C. (+/−3° C.) without premature polymerisation for up to 7 days.

Example 3

Regeneration: Automated Method

(28) 18 bottles containing initiated mix from Example 1 (approximately 2100 g L of initiated monomer, container capacity of 3.0 L) were loaded into a Sanyo LabCool refrigerator modified to accommodate three agitation shelves; each shelf consisting of six bottle receptacles aligned so as to always have two opposing bottles directly counterbalancing each another when their respective centres of gravity are moving.

(29) Each bottle was located in its own gripping nest mounted on a rotating platform shaking mechanism.

(30) Every 2.5 hours the system agitated a shelf for 10 minutes at 2.167 Hz (130 rpm). This agitated the bottles to induce a sloshing motion in the monomer mixture.

(31) During the first 30 seconds of this 10-minute mix/agitation cycle, air was sparged in at a volume flow rate of approximately 3.33E−05 m.sup.3/sec (or 2 slpm, i.e. 2 standard litres per minute, a standard litre being a litre that has been corrected to represent standard temperature and pressure). This amounts to 0.33 litres of air per 2 litres of monomer during a mixing cycle.

(32) Assuming approximately 21% of air is oxygen, this equated to 0.0693 litres of oxygen per 2 litres of monomer per mixing cycle. The agitation cycles for each shelf were offset from each other by 50 minutes to prevent all of the shelves mixing at once and putting too great of a vibrational load on the fridge skeleton.

(33) Air which has been filtered (40 μm filtration) and dried (water separation) to air to purity class 2.1.1 (as outlined by IS08573-1) was piped to the refrigeration compartment and into the bottles at an air pressure set to 700 kPa via pressurised inlet air lines. These lines and exhaust air lines were fitted to each bottle cap provided for each bottle. The cap of each bottle allowed free rotation of the stainless steel core while tightening the cap ring.

(34) The initiated mix was stored at 15° C. (+/−3° C.) without premature polymerisation for up to 7 days.

Example 4

Stability Testing

(35) 9 batches of the initiated mix from Example 1 were left to cure and the time taken for the mix to start curing was visually assessed.

(36) As seen in Table 1 below, three batches (1, 2 and 3) were treated with the manual method of Example 2. Three batches (4, 5 and 6) were not treated at all and three batches (7, 8 and 9) were treated with the automated method of Example 3. This data is representative of results the inventors have seen during development (i.e. during protocols to investigate different aspects of the manufacturing process). These shelf lives mentioned below were observed again and again.

(37) TABLE-US-00003 TABLE 1 Method used to Batch Shelf Life* increase shelf life 1 4 Days Manual 2 4.5 Days Manual 3 4 Days Manual 4 46 hours None 5 51 hours None 6 53 hours None 7 8 Days Automated 8 7.5 Days Automated 9 8 Days Automated *Time taken for contents of container to begin to gel

Example 5

Stability Testing

(38) A single 10 L batch of initiated mix according to Example 1 was split into ten identical 2 L glass bottles such that each bottle contained an identical volume and weight (1.00 kg) of initiated mix. Each bottle had an identical volume of free space (approximately 1 L). As each 2 L bottle was decanted from the same 10 L batch, all of the raw material components were identical.

(39) Each of the 2 L bottles were stored at 15° C. (+/−3° C.) according to Table 2:

(40) TABLE-US-00004 TABLE 2 Bottle Bottle Manual Automated number unopened method .sup.b method .sup.c 1 √ 2 √ 3 √ 4 √ 5 √ 6 √ 7 √ 8 √ 9 √ 10 √

(41) In each case, the conditions were as follows for the duration of study: Bottle unopened: Each 2 L bottle (bottles 1 to 4) was placed in controlled temperature environment and unopened. Manual method: Each 2 L bottle (bottles 5 to 7) was placed in controlled temperature environment, opened to atmosphere once per day for 30 seconds, recapped and shaken vigorously by hand for a minimum of 2 minutes. Automated method: Each 2 L bottle (bottles 8 to 10) was placed in controlled temperature environment and connected to an automated system which initiated a cycle every 150 minutes consisting of agitation for 10 minutes at 2.167 Hz coupled with 30 seconds sparging in of dried air at a volume flow rate of approximately 3.33E−05 m.sup.3/sec.

(42) Each bottle was visibly assessed regularly, i.e. a minimum of once every 24 hours, for signs of premature polymerisation characterised by visual increase of monomer viscosity, presence of solid materials in the solution, change in consistency of monomer and colour changes.

(43) Table 3 outlines the times noted for onset of premature curing of each bottle:

(44) TABLE-US-00005 TABLE 3 Bottle Time to premature number curing 1 47 hours 2 52 hours 3 50 hours 4 48 hours 5 3.5 days 6 4 days 7 4 days 8 >9 days* 9 >9 days* 10 >9 days* *No premature curing noted after a storage time of 9 days. At 10 days, some curing had begun.

(45) Like Example 4, Example 5 shows that the use of air to regenerate the headspace of a container of initiated monomer mix improves the shelf life and is preferable to sealed storage. Furthermore, the automated method improves the shelf life more than the manual method.

Example 6

(46) A monomer mixture is prepared by mixing the following ingredients: N-vinyl pyrrolidone (90 weight percent), 4-t-butyl-hydroxycyclohexyl methacrylate (10 weight percent), Pluronics® F127 Dimethacrylate (5 weight percent), ethylene glycol dimethacrylate (0.15 weight percent), allyl methacrylate (0.15 weight percent) and 2-hydroxypropyl methacrylate (2 weight percent). 0.5 weight percent of AIBN is added and the mixture is treated with the automated method of Example 3.
The initiated monomer mix does not begin to cure for at least 8 days.

(47) As the monomer started to react, the viscosity of the liquid increased. This occurred slowly (over the course of 2-3 hours) with the mix becoming less ‘water like’ and more ‘honey like’.

(48) As the gelation proceeded, the monomer hardened—typically from the bottom of the container upwards (as this is the monomer that is furthest away from the air present in the container). Once this hardening happened, the cured monomer resembled a solid mass and was no longer mobile. As the reaction reached completion all of the available liquid monomer slowly became solid.

(49) All of the trials were carried out in the same lab, under the same conditions. 2 L of monomer was placed in a 3 L HDPE container (leaving 1 L approximately of air space). The bottles were initiated and stored in the same 15° C. environment and monitored over several days. The batches were said to have gelled when gelation was visually reported by an operator. For the batches that were not treated, the bottles were not opened once initiation had occurred. Without treatment (whether manual or automated), the usable shelf life of this monomer was less than 46 hours. Any longer (and even if no signs of viscosity increase are present) the reaction had already commenced. If monomer which had started to react was added to moulds for lens manufacture, this would lead to severe issues in manufacturing.

(50) With manual or automated treatment the shelf life of the monomer was approximately 7 days. A slight increase in the shelf life was observed when using the automated method over the manual method.

Preferred Embodiments

(51) Disclosed in certain preferred embodiments of the invention herein is:

(52) 1. A method of extending the shelf life of an initiated monomer mixture comprising the prevention of premature free radical polymerisation by introducing oxygen or oxygen-containing gas into a container of the initiated monomer mixture and providing mechanical agitation to the container.

(53) 2. The method of preferred embodiment 1, wherein said oxygen-containing gas is air.

(54) 3. The method of preferred embodiment 2, wherein said air is filtered and/or dried before being introduced into said container.

(55) 4. The method of preferred embodiment 1, wherein said method is automated and performed in cycles in a closed environment and wherein the conditions of the environment are controlled and monitored by an electronic controller which enables an operator to set one or more of the pressure, the temperature, the rate of agitation, the duration of agitation, the frequency of the introduction of oxygen or oxygen-containing gas cycles and the frequency of agitation cycles.

(56) 5. The method of preferred embodiment 4, wherein the method comprises sparging said oxygen or oxygen-containing gas into the container.

(57) 6. The method of preferred embodiment 5, wherein said oxygen-containing gas is air.

(58) 7. The method of preferred embodiment 6, wherein said air is filtered and/or dried before being introduced into said container.

(59) 8. The method of preferred embodiment 1, wherein said method is carried out at a temperature of about 15° C.

(60) 9. The method of preferred embodiment 4, wherein said method is carried out at a temperature of about 15° C.

(61) 10. The method of preferred embodiment 1, wherein said introduction of oxygen or oxygen-containing gas and said mechanical agitation occur at least partially simultaneously.

(62) 11. The method of preferred embodiment 4, wherein said introduction of oxygen or oxygen-containing gas and said mechanical agitation occur at least partially simultaneously.

(63) 12. The method of preferred embodiment 11, wherein said oxygen-containing gas is air.

(64) 13. The method of preferred embodiment 12, wherein said air is filtered and/or dried before being introduced into said container.

(65) 14. The method of preferred embodiment 1, wherein said introduction of oxygen or oxygen-containing gas and said mechanical agitation are each independently performed at least once every 1 to 24 hours.

(66) 15. The method of preferred embodiment 4, wherein said introduction of oxygen or oxygen-containing gas and said mechanical agitation are each independently performed at least once every 1 to 24 hours.

(67) 16. The method of preferred embodiment 15, wherein said oxygen-containing gas is air.

(68) 17. The method of preferred embodiment 16, wherein said air is filtered and/or dried before being introduced into said container.

(69) 18. The method of preferred embodiment 1, wherein mechanical agitation of the container takes place at a predetermined rate and/or for a predetermined duration.

(70) 19. The method of preferred embodiment 4, wherein mechanical agitation of the container takes place at a predetermined rate and/or for a predetermined duration.

(71) 20. The method of preferred embodiment 19, wherein every 2.5 hours a shelf is agitated for 10 minutes at 130 RPM (2.167 Hz) and during the first 30 seconds of this 10-minute mix air is sparged in at 2 slpm (approximately 3.33E−05 m.sup.3/sec).

(72) 21. The method of preferred embodiment 20, wherein said air is filtered and/or dried before being introduced into said container.

(73) 22. An apparatus for extending the shelf life of an initiated monomer mixture, the apparatus comprising: refrigeration means; means for introducing oxygen or oxygen-containing gas into a container of initiated monomer mixture; means for evacuating exhaust gas generated by reaction of oxygen with the mixture; means for mechanical agitation of the container; and an electrical controller for controlling the refrigeration temperature, the agitation and the introduction of oxygen or oxygen-containing gas.

(74) 23. The apparatus of preferred embodiment 22, wherein said means for introducing oxygen or oxygen-containing gas is sparging means.

(75) 24. The apparatus of preferred embodiment 22, wherein the introducing means comprises an air service unit, an air dryer with pre-filter, and optionally a flow controller, a pressure regulator and valves/distribution manifolds.

(76) 25. The apparatus of preferred embodiment 24, wherein said introducing means is sparging means.

(77) 26. The apparatus of preferred embodiment 22, wherein the electrical controller is adapted to monitor the length of time the dryer has been in use and to display this information on a user interface screen.

(78) 27. The apparatus of preferred embodiment 26, wherein the status of each of the process indicators temperature, agitation duration, agitation rate, oxygen or oxygen-containing gas flow rate and/or pressure can be checked from the user interface screen.

(79) 28. The apparatus of preferred embodiment 26, wherein all apparatus functions are operated from the user interface screen.

(80) 29. The apparatus of preferred embodiment 26, wherein the user interface screen is capable of allowing operators to change one or more critical parameters for adding oxygen or oxygen-containing gas to the initiated monomer mixtures.

(81) 30. The apparatus of preferred embodiment 22, wherein the refrigeration means has at least one shelf and drive motors for shelf agitation are located underneath each shelf.

(82) 31. The apparatus of preferred embodiment 22, wherein the refrigeration means has a front access door and a door switch provided on the front access door to detect whether the door is open or closed.

(83) 32. The apparatus of preferred embodiment 31, wherein the door is locked while agitation is taking place to prevent accidental opening.

(84) 33. An electronic controller for an agitation and oxygenating or aerating refrigeration apparatus comprising: means for receiving and displaying process information relating to the rate and duration of introducing oxygen or oxygen-containing gas into a container and the rate and duration of agitation of the container; means for displaying and setting the temperature of the apparatus; and means for displaying and setting on and off time periods for the apparatus.

(85) 34. The electronic controller of preferred embodiment 33, wherein the status of each of the process indicators temperature, agitation duration, agitation rate, oxygen or oxygen-containing gas flow rate and/or pressure can be checked from the user interface screen.

(86) 35. The electronic controller of preferred embodiment 33, wherein all apparatus functions are operated from a user interface screen.

(87) 36. The electronic controller of preferred embodiment 35, wherein the user interface screen is capable of allowing operators to change one or more critical parameters for adding oxygen or oxygen-containing gas to the initiated monomer mixtures.

(88) 37. A system for extending the shelf life of an initiated monomer mixture, the system comprising: one or more containers of initiated monomer mixture; one or more shelves for the containers; refrigeration means; an access door; means for introducing oxygen or oxygen-containing gas into the container; means for evacuating exhaust gas generated by reaction of oxygen with the mixture; means for mechanical agitation of the container, the means attached to a shelf; and an electrical controller for controlling the temperature of the system, the agitation and the introduction of oxygen or oxygen-containing gas; a user interface screen which displays process information relating to the system; and operator control buttons for controlling one or more of: the temperature, the agitation and the introduction of oxygen or oxygen-containing gas.

(89) 38. The system of preferred embodiment 37, wherein a cycle is performed every 2.5 hours in which the system agitates a shelf for 10 minutes at 130 RPM (2.167 Hz) and air is sparged in at 2 slpm (approximately 3.33E−05 m.sup.3/sec) during the first 30 seconds of this 10 minute mix cycle.

(90) 39. The system of preferred embodiment 37, wherein a plurality of containers are spaced over the one or more shelves.

(91) 40. The system of preferred embodiment 37, wherein each container is located in its own gripping nest which is mounted on the means for mechanical agitation.

(92) 41. The system of preferred embodiment 37, wherein the rate of agitation is variable from the operator user interface screen.

(93) 42. The system of preferred embodiment 37, wherein said means for introducing oxygen or oxygen-containing gas is sparging means.

(94) 43. The system of preferred embodiment 37, wherein said container is at least 20% larger than the volume of initiated monomer mixture contained therein.

(95) 44. The system of preferred embodiment 37, wherein the introducing means comprises an air service unit, an air dryer with pre-filter, and optionally a flow controller, a pressure regulator and valves/distribution manifolds.

(96) 45. The system of preferred embodiment 44, wherein said means for introducing oxygen or oxygen-containing gas is sparging means.

(97) 46. The system of preferred embodiment 37, wherein the electrical controller is adapted to monitor the length of time the dryer has been in use and to display this information on the user interface screen.

(98) 47. The system of preferred embodiment 37, wherein the status of each of the process indicators temperature, agitation duration, agitation rate, oxygen or oxygen-containing gas flow rate and/or pressure can be checked from the user interface screen.

(99) 48. The system of preferred embodiment 37, wherein all apparatus functions are operated from the user interface screen.

(100) 49. The system of preferred embodiment 37, wherein the user interface screen is capable of allowing operators to change one or more critical parameters for adding oxygen or oxygen-containing gas to the initiated monomer mixtures.

(101) 50. The system of preferred embodiment 37, wherein the refrigeration means has at least one shelf and drive motors for shelf agitation are located underneath each shelf.

(102) 51. The apparatus of preferred embodiment 37, wherein the refrigeration means has a front access door and a door switch provided on the front access door to detect whether the door is open or closed.

(103) 52. The apparatus of preferred embodiment 51, wherein the door is locked while agitation is taking place to prevent accidental opening.

(104) Aspects of the present invention have been described by way of example only and it should be appreciate that additions and/or modifications may be made thereto without departing from the scope thereof as defined in the appended claims.