GB1588625A - Graft copolymers - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO GRAFT COPOLYMERS (71) I, THE SECRETARY OF STATE FOR DEFENCE, LONDON, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention is concerned with the production of graft copolymers.

Graft copolymers are so called because a further monomer is caused to react and polymerise on the polymer chain of an already existing polymer. The polymeric substrate may be either an addition or a condensation polymer and any conventional method of polymerisation initiation may be used although irradiation is a preferred method.

Conventional graft copolymerisation processes consist essentially of copolymerising a polymeric substrate in contact with a suitable monomer (in solution or in bulk). Copolymerisation is generally achieved by irradiation which generates.active sites on the polymeric substrate or in the monomer and it is also normal to add inhibitors of known type to the reaction mixture in order to minimise homo-polymerisation reaction of the monomer. The degree of graft copolymerisation depends upon the intensity of the irradiation, length of time during which the reaction is allowed to continue and reaction temperature. When the reaction has reached the desired stage the graft copolymer is removed from the monomer and thoroughly washed to remove 2lnreacted monomer and any homopolymer that may have:been produced despite the use of an inhibitor.

In accordance with the present .invention a process for the production .of a graft copolymer includes the steps -of-(a) exposing .a preformed polymeric:substrate in vacuo or in an inert gas to a source of.high .energetic radiation of sufficient energy to generate free radical sites on andlor in the substrate (b), passing the activated substrate into contact with a comonomer while a substantial proportion of the generated -free radical sites remain active and (c) maintaining control between the activated substrate and the monomer for a time sufficient to produce a desired degree of graft copolymerisation, the free radical generation step and the copolymerisation step being carried out in the absence of oxygen and other reactive impurities, which tend to react with free radicals or to give unwanted side reactions, and wherein the substrate is in the form of a moving web and steps (a) and (b) are applied simultaneously to different portions of the web as it moves.

Suitable radiation sources for the practice of the present invention include electron sources, for example a linear accelerator, a Van de Graaff generator, or a resonant transformer or alternatively an X-ray target may be fitted in the electron path to produce X-rays which will generate the desired free radical sites. Electron sources such as those defined above are preferred and advantageously electron energies above 200 KeV preferably above 1 MeV, are used in the practice of the present invention.

The criterion for the minimum energy is that free radical sites must be generated on and/or in the substrate. The upper energy limit theoretically possible is the one at which the polymer substrate starts to be degraded, say in the region of 20 MeV but for practical reasons energies much greater than 10 MeV are seldom encountered in practice and we have found that the range 1 to 5 MeV is optimum.

In the present specification the term "inert gas" is used to mean a gas which is non-reactive toward free radicals so that it does not diminish the radical yield in the free radical generation step and particularly oxygen is excluded.

Typical inert gases include nitrogen (oxygenfree), and argon.

The preformed polymeric substrate used in the present invention may be in the form of fibre, film, sheet, foil or laminate and may be, for example, any of polyolefins orcopolyolefins, for example polyethylene (low, medium or high density), polypropylene, poly 4-methylpentene-l (and copolymers of these polyolefins), products of other vinyl polymerisations, for example polyvinylacetate and plyvinylalcohol as well as the halogen containing vinyl polymers or copolymers and. other halogen containing polymers, for example polyvinylchloride, chlorinated rubbers, polytetrafluoroethylene and polychiorofluoroethylene, polyamides or copolyamides and products of other condensation polymerisations, for example the saturated and the un-saturated polyesters, or a mixture of any of these polymers. The physical and chemical form of the base polymers may be as is convenient to the process of manufacture and does not preclude the presence of additives such as filler particles, reinforcing fibres and/or other additives such as thermal or oxidation stabilisers, dyes, and pigments and also includes material which are semi-permeable by virtue of having micropores introduced by mechanical treatment. We have found polyethylene and polyproplylene particularly suitable for the practice of the present invention.

Graft comonomers that can be used in the process of the present invention are those that can be polymerised by free radical reaction and include reactive polar vinyl monomers for example acrylonitrile, vinyl pyridine, vinyl pyrrolidone, ethylenic carboxylic acids, for example acrylic acid, methacrylic acid, itaconic acid, ethylenic carboxylic acid amines, for example acrylamide and methacrylamide, and ethylenic carboxylic acid amines, for example butylamine acrylate, and the most advantageous results have been obtained using acrylic acid.

The degree of grafting is determined, inter alia, by the length of time during which the activated substrate is in contact with the copolymerisation solution. In a continuous process this is achieved by controlling the residence time of the activated substrate in the copolymerisation solution, short residence time leading to a relatively light graft. Other factors which influence the degree of grafting include the extent of activation, the more intense the activation the greater the number of free radicals generated and therefore the relatively heavier the graft, also favoured by rapid passage from activation to copolymerisation; the extent of penetration of the activated substrate by the monomer, which may be assisted by the presence of one or more swelling agents for the substrate polymer in the copolymerisation reaction mixture. The temperature of the copolymerisation also affects the extent of grafting, high temperatures tending to favour heavy grafts, all other parameters remaining constant.

The process of the present invention is particularly adapted to the production of graft copolymer by a continous process and apparatus suitable for the practice of the present invention will now be described with reference to the drawings filed with the Provisional Specification in which: Figure 1 is a schematic cross-section of apparatus adapted to batch operation, and Figure 2 is a schematic cross-section of apparatus adapted to continuous operation.

With reference to Figure 1 the apparatus consists of a hermetically sealable container 10 having a removable top 11 which houses a motor 12 and a feed roll 13. The container 10 is divided by a horizontal partition 14 into an upper section 15 which houses a series of rollers 16 arranged in two rows and lower section 17 which contains a grafting solution 18 and a take-up roller 19 arranged to be driven in operation by the motor 12 through a belt drive 20. A linear accelerator 21 (shown only schematically) is mounted opposite a 17p aluminium window 22 in the upper section 15 as electron source and the apparatus is provided with an entry port 23 in the removable top 11 and a porous sintered tube 24 supplied by an entry port 25 under the level of the grafting solution by which the apparatus may be purged by inert gas (source not shown), generally oxygen-free nitrogen, excess gas being removed through exit port 26.

In operation the feed roll 13 is charged with a roll of preformed polymer film 27 interleaved with a layer of porous non-woven material, the double layer being passed over the rollers 16 and the end attached to the take-up roll 19, the lower container 18 charged with the appropriate grafting solution, and the apparatus sealed. The apparatus is then purged by passing inert gas, normally nitrogen (oxygen-free into the apparatus through ports 23 and 25. Deleterious effect of insufficient purging include peroxidation of the polymer, detectable by infra-red spectroscopy, and reduced graft levels, all other parameters remaining constant. The period of purging required can be determined by trial and error experiments to determine the period of time that eliminates these effect.

When the oxygen content of the exhaust gases (port 26) has dropped to an acceptably low level, the electron source 21 and the motor 12 are started so that the polymer film 27 is drawn over the bank of rollers 16, being irradiated in passing, and then into the take-up roll 19 under the surface of the grafting solution 18 in the lower section 17. Grafting is then allowed to continue for a desired length of time after which the apparatus is opened and the grafted film removed from the take-up roller, washed in distilled water and dried.

The electron dose rate can be varied by altering the operating parameters of the linear accelerator 21, or its distance from the container 10, or alternatively the dose rate received by the film 27 can be varied by altering the number of passes made by the film through the electron path. Measurement of the electron dose is carried out by attaching Perspex (Trade Mark) dosimeters as described in Phys Med Biol, 14, (1969) p585-596 to a film and running it through the apparatus without the presence of grafting solution.

Figure 2 illustrates an apparatus which is designed to carry out the process described above continuously.

The apparatus comprises consecutively a feed chamber 40, an irradiation chamber 41, a grafting chamber 42, a washing chamber 43, and a drying chamber 44. Each of the feed chamber 40, irradiation chamber 41 and grafting chamber 42 are provided with entry ports 45, 46 and 47 respectively and exit ports 48, 49 and 50 respectively by means of which each of these chambers can be purged with inert gas.

Two sets of airlock nip rollers, upper 51 and lower 52, provide sealed or sealable access from the feed chamber 40 to the irradiation chamber 41 and further sets of airlock nip rollers provide access from the irradiation chamber 41 to the grafting chamber 42, reference 53, from the grafting chamber 42 to the washing chamber 43, reference 54, from the washing chamber to the drying chamber, reference 55, exit from the washing chamber to the outside, reference 56, and exit from the drying chamber 44 to the outside 57. The feed chamber includes an upper feed roll 58 and lower feed roll 59 arranged to provide film material to the upper nip rollers 51 and the lower nip rollers 52 respectively feeding into the irradiation chamber 41. Each of the chambers 41,42,43 and 44 is provided with two staggered rows of rollers 60 arranged so that film material 61 may be passed in a zig-zag manner through them. There are also provided an upper 62 and lower 63 take-up roll arranged to take up film material from nip rollers 57 and 56 respectively. A linear accelerator 64 (shown only schematically) is provided as a source of energetic electrons opposite a suitable window 65 in the irradiation chamber 41. An appropriate grafting solution 66 is provided in the grafting chamber 42 and a washing liquid 67 in the washing chamber 43. Drying in the drying chamber is by means of warm air (supply not shown).

Operation is broadly as described for Figure 1, so far as purging the apparatus and measuring the electron dose is concerned. The film material to be grafted 68 is supplied from upper feed roll 58 through upper nip rollers 51 and across rollers 60 in the irradiation chamber 41 which it leaves through nip roller 53. At this point it is brought together with porous nonwoven absorbent material 69 supplied from lower feed roll 59 through nip rollers 52. The composite film material 61 then passes through the grafting solution 66 in the grafting chamber 42, through the nip rollers 54 into the washing chamber 43 in which the two films are separated. The absorbent film 69 passes through nip rollers 56 and is taken up on lower roll 63 and the grafted material is washed and then passes through nip rollers 55 into the drying chamber 44 after which it passes through nip rollers 57 and is taken up on upper roll 62.

In one possible embodiment of the invention the apparatus of Figure 1 may be arranged so that the lower set of rollers 16 are immersed in the grafting solution 18 so that the activation and grafting processes proceed alternately. The apparatus of Figure 2 could be similarly modi fied.

As well as varying residence times by varying the throughput speed the time of residence in individual chambers may be varied independently, within limits, by varying the number of zig-zags within that chamber.

Although the apparatus is illustrated with absorbent material 69 in contact with only one surface of the substrate material 68, it will be apparent that it only requires a minor modification to provide absorbent material on both surfaces if required.

The present apparatus illustrates take up of the product after drying but it is obvious that the material could be subjected to other processes after or below the drying and/or the washing stages.

It will also be apparent that the apparatus of Figure 2 can be readily adapted to run continuously for an indefinite period by provision of means for changing rolls of feed material and means for replenishing the grafting and other solutions employed, whilst the apparatus is running without recourse to stopping the apparatus.

The irradiation chamber 41 in this embodiment is described as being continuously purged with inert gas but it will be readily apparent that with minor adjustment it could be arranged to operate in vacuo.

The process of the present invention will now be illustrated by way of example only using the apparatus described above.

In the following the degree of grafting is defined as ( (WF-WI)/WF ) Xl 00% where WF is final weight of polymer and WI is initial weight of polymer.

EXAMPLE 1 This is a batch process using the apparatus of Figure 1.

Low density polythene film (supplied by Translantic Plastics) 3500mm long, 150mm wide and 40u thick was interleaved with a nonwoven viscose felt material supplied by Johnson & Johnson and loaded into the apparatus. The lower section 17 was filled to the desired level with a grafting solution made up as follows: Glacial acrylic acid 30%-v/v Distilled water 70% v/v Ferrous sulphate "Analar" (Trade Mark) 0.0155 mole/litre The apparatus was sealed and then purged with nitrogen (oxygen free) at a flow rate of 1 litre/min for 60 mins.

Irradiation was carried out by energetic electrons from a 4.3 MeV Linear Accelerator (reference 21 in Figure 1) with the apparatus 840mm from the accelerator flight tube. In this position with the accelerator set at a pulse repetition rate of 200 per second the incident dose rate was 1.10 Megarads per minute. After a 45 minute irradiation during which the film was drawn through the apparatus at a linear speed of 40mm per min the apparatus was sealed from the purging gas and from the atmosphere and left for 2.5 hours.

The prepared grafted copolymer film was then removed, washed twice with distilled water and air dried at 200 C. Spectrophotomeric analysis at 800cm-1 and 1410cm indicated a graft level of 40% + 2% over a linear length of 1650mm in that part of the film which received uniform treatment.

Electrical resistivity was determined using the method outlined by Falk & Salkind in "Alkaline Storage Batteries" published by John Wiley and Sons in 1969 p258.

At 25 C in a 30% aqueous potassium hy droxide solution the electrical resistivity was 0.20+0.01 Ohms cm2, indicating complete penetration of the monomer into the polymer matrix.

Ater reflux in xylene at 136 0C for 2 hours the sample had a gel fraction of 0.6 showing that there was probably a degree of intermolecular linking during copolymerisation.

Boiling for 2 hours under reflux in a 20% v/v methanol/distilled water mixture reduced the sample weight by less than 1% pointing to a very small amount of entrapped homopolymer and a stable graft.

EXAMPLE 2 The process described in Example 1 was repeated using low density polyethylene film 5000mm ling 150 mm wide and 12u thick, except that the apparatus was purged for 1.4 hours prior to electron irradiation.

The grafted film was removed from the tank washed twice and dried. Degree of graft was determined as 35%~2% uniformly over a length 2992mm.

Electrical resistivity of the granted film was 0.05i0.01 Ohms cm2 at 25 C in 30% aqueous potassium hydroxide. Boiling under reflux in xylene again indicated inter-molecular linking and boiling in a 20% v/v methanol/distilled water revealed little homopolymer and a stable graft.

EXAMPLE 3 5000mm of a 150mm and 38p thick, low density polyethylene film (designated "Dio thene" and supplied by Metal Box Co Ltd) was interleaved with absorber and placed in the apparatus as described in Example 1. The graft ing solution was also as described in Example 1.

Nitrogen (oxygen free) was passed through the system for 1.0 hours prior to irradiation.

After a 60 min irradiation at the same dose rate as in Example 1, during which the film was moved through the apparatus at 40mm/min, the time allowed for grafting was 2.8 hours.

Analysis of the washed and dried copolymer film showed a degree of graft of 40So+1 10/o over a length of 1900mm. Electrical resistivity of the film over the same area was 0.19 Ohms cm2 at 250C in a 30% aqueous potassium hydroxide electrolyte.

EXAMPLE 4 5500 mm of 100 mm wide 'Diothene" low density polyethylene was placed in the apparatus along with a grafting solution, as described in Example 1.Purging with nitrogen (oxygen free) was for 1.3 hours at a flow rate of 1 litre per min.

The electron dose rate was 1.3 Megarads per minute; the film transport speed was 90mm/ minute. Following irradiation 2.5 hours was allowed for grafting to the desired degree. The degree of graft obtained was 37%+2% over a length of 4000mm. Electrical resistivity measurements as described in Example 1 gave a value of 0.18 Ohms cm2.

EXAMPLE 5 5500mm of an oriented polyproplyene film 100mm wide 14u thick with an orientation ratio 8:1 in the machine to transverse modes, was interleaved with absorber and wound onto the apparatus as described in Example 1. The grafting solution was as in Example 1 and was purged for 1.3 hours at 1.2 litres/min prior to irradiation. The film was transported through the apparatus at 90mm/min during the irradiation at an incident dose rate of 1.3 Megarads per minute. Grafting time after irradiation was 2 hours.

The degree of graft obtained was 27%+2% over a length of 3200mm and the electrical resistivity was 300 Ohms cm2.

EXAMPLE 6 5500mm of a 100mm wide sample of a microporous polypropylene film (designated "Celgard 2400" (Trade Mark) and supplied by Celanese Corporation) was irradiated in the manner as described in Example 4, purging taking place at 1.2 lit/min for 1.5 hours. 2 hours was then allowed for the grafting reaction at the end of which the film was shown to have a degree of graft at 40%+2% and an electrical resistivity of 0.02 Ohms cm2 compared with 190 Ohms cm2 for the untreated film. Wettability of the film as demonstrated by contact angle measurements was also greatly increased.

WHAT I CLMM :- 1. A process for the production of a graft copolymer which includes the steps of (a) exposing a preformed polymeric substrate in vacuo or in an inert gas to a source of highly energetic radiation of sufficient energy to generate free radical sites on and/or in the substrate, (b) passing the activated substrate into contact with a monomer while a substantial proportion of the generated free radical sites remain active, and (c) maintaining contact between the activated substrate and the monomer for a time sufficient to produce a desired degree of graft copolymerisation, the free radical generation step and the copolymerisation step being carried out in the absence of oxygen and other reactive impurities which tend to react with free radicals or to give unwanted side reactions, and wherein the substrate is in the form of a moving web and steps (a) and (b) are applied simultaneously to different portions of the web as it moves.

2. A process as claimed in Claim 1 and wherein the radiation source is an electron source selected from a linear accelerator, a Van de Graaff generator and a resonant transformer or an electron source with an X-ray target fitted in the electron path.

3. A process as claimed in Claim 1 or Claim

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (16)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   1650mm in that part of the film which received uniform treatment.

   Electrical resistivity was determined using the method outlined by Falk & Salkind in "Alkaline Storage Batteries" published by John Wiley and Sons in 1969 p258.

   At 25 C in a 30% aqueous potassium hy droxide solution the electrical resistivity was 0.20+0.01 Ohms cm2, indicating complete penetration of the monomer into the polymer matrix.

   Ater reflux in xylene at 136 0C for 2 hours the sample had a gel fraction of 0.6 showing that there was probably a degree of intermolecular linking during copolymerisation.

   Boiling for 2 hours under reflux in a 20% v/v methanol/distilled water mixture reduced the sample weight by less than 1% pointing to a very small amount of entrapped homopolymer and a stable graft.

   EXAMPLE 2 The process described in Example 1 was repeated using low density polyethylene film 5000mm ling 150 mm wide and 12u thick, except that the apparatus was purged for 1.4 hours prior to electron irradiation.

   The grafted film was removed from the tank washed twice and dried. Degree of graft was determined as 35%~2% uniformly over a length 2992mm.

   Electrical resistivity of the granted film was 0.05i0.01 Ohms cm2 at 25 C in 30% aqueous potassium hydroxide. Boiling under reflux in xylene again indicated inter-molecular linking and boiling in a 20% v/v methanol/distilled water revealed little homopolymer and a stable graft.

   EXAMPLE 3 5000mm of a 150mm and 38p thick, low density polyethylene film (designated "Dio thene" and supplied by Metal Box Co Ltd) was interleaved with absorber and placed in the apparatus as described in Example 1. The graft ing solution was also as described in Example 1.

   Nitrogen (oxygen free) was passed through the system for 1.0 hours prior to irradiation.

   After a 60 min irradiation at the same dose rate as in Example 1, during which the film was moved through the apparatus at 40mm/min, the time allowed for grafting was 2.8 hours.

   Analysis of the washed and dried copolymer film showed a degree of graft of 40So+1 10/o over a length of 1900mm. Electrical resistivity of the film over the same area was 0.19 Ohms cm2 at 250C in a 30% aqueous potassium hydroxide electrolyte.

   EXAMPLE 4

   5500 mm of 100 mm wide 'Diothene" low density polyethylene was placed in the apparatus along with a grafting solution, as described in Example 1.Purging with nitrogen (oxygen free) was for 1.3 hours at a flow rate of 1 litre per min.

   The electron dose rate was 1.3 Megarads per minute; the film transport speed was 90mm/ minute. Following irradiation 2.5 hours was allowed for grafting to the desired degree. The degree of graft obtained was 37%+2% over a length of 4000mm. Electrical resistivity measurements as described in Example 1 gave a value of 0.18 Ohms cm2.

   EXAMPLE 5 5500mm of an oriented polyproplyene film 100mm wide 14u thick with an orientation ratio 8:1 in the machine to transverse modes, was interleaved with absorber and wound onto the apparatus as described in Example 1. The grafting solution was as in Example 1 and was purged for 1.3 hours at 1.2 litres/min prior to irradiation. The film was transported through the apparatus at 90mm/min during the irradiation at an incident dose rate of 1.3 Megarads per minute. Grafting time after irradiation was 2 hours.

   The degree of graft obtained was 27%+2% over a length of 3200mm and the electrical resistivity was 300 Ohms cm2.

   EXAMPLE 6 5500mm of a 100mm wide sample of a microporous polypropylene film (designated "Celgard 2400" (Trade Mark) and supplied by Celanese Corporation) was irradiated in the manner as described in Example 4, purging taking place at 1.2 lit/min for 1.5 hours. 2 hours was then allowed for the grafting reaction at the end of which the film was shown to have a degree of graft at 40%+2% and an electrical resistivity of 0.02 Ohms cm2 compared with 190 Ohms cm2 for the untreated film. Wettability of the film as demonstrated by contact angle measurements was also greatly increased.

   WHAT I CLMM :- 1. A process for the production of a graft copolymer which includes the steps of (a) exposing a preformed polymeric substrate in vacuo or in an inert gas to a source of highly energetic radiation of sufficient energy to generate free radical sites on and/or in the substrate, (b) passing the activated substrate into contact with a monomer while a substantial proportion of the generated free radical sites remain active, and (c) maintaining contact between the activated substrate and the monomer for a time sufficient to produce a desired degree of graft copolymerisation, the free radical generation step and the copolymerisation step being carried out in the absence of oxygen and other reactive impurities which tend to react with free radicals or to give unwanted side reactions, and wherein the substrate is in the form of a moving web and steps (a) and (b) are applied simultaneously to different portions of the web as it moves.
2. 2. A process as claimed in Claim 1 and wherein the radiation source is an electron source selected from a linear accelerator, a Van de Graaff generator and a resonant transformer or an electron source with an X-ray target fitted in the electron path.
3. 3. A process as claimed in Claim 1 or Claim

   2 and wherein the radiation source is an electron source generating electrons having an energy within the range 200 KeV to 10 MeV.
4. 4. A process as claimed in any one preceding claim and wherein radiation source is an electron source generating electrons having an energy within the range 1 MeV to 5 MeV.
5. 5. A process as claimed in any one preceding claim and wherein the inert gas is oxygen-free nitrogen, or argon.
6. 6. A process as claimed in any one preceding claim and wherein the preformed polymeric substrate is in the form of fibre, film, sheet, foil, or laminate.
7. 7. A process as claimed in any one preceding claim and wherein the polymeric substrate is a polyolefin or copolyolefin which may or may not contain a halogen, a vinyl polymer or copolymer which may or may not contain a halogen, or a condensation polymer or copolymer, or a mixture of these polymers.
8. 8. A process as claimed in Claim 7 and wherein the condensation polymer is a nylon or a saturated or unsaturated polyester or a mixture thereof.
9. 9. A process as claimed in any one preceding claim excluding Claim 8 and wherein the polymeric substrate is a low, medium or high density polyethylene, polypropylene, poly4methylpentene-l, polyvinylacetate, polyvinyl alcohol, polyvinyl chloride, a chlorinated rubber, polytetrafluoroethylene, or polychlorofluoroethylene.
10. 10. A process as claimed in any one preceding claim excluding Claim 8 and Claim 9 and wherein the polymeric substrate is a polyethylene or a polypropylene.
11. 11. A process as claimed in any one preceding claim and wherein the graft comonomer is a reactive polar vinyl monomer.
12. 12. A process as claimed in any one preceding claim and wherein the graft comonomer is acrylonitrile, vinyl pyridine, vinyl pyrrolidone, acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacrylamide or butylamine acrylate.
13. 13. A process as claimed in any one preceding claim and wherein the graft comonomer is acrylic acid.
14. 14. A process substantially as hereinbefore described and with particular reference to Figure 1 of the drawings filed with the Provisional Specification.
15. 15. A process substantially as hereinbefore described and with particular reference to Figure 2 of the drawings filed with the Provisional Specification.
16. 16. A graft copolymer when produced by a process as claimed in any one preceding claim.