The present invention relates to a process for the production of polymers via suspension polymerisation. The invention also relates to polymers obtained via such process.

The production of polymers via suspension polymerisation is a well-known process that is used for the production of a variety of polymers. For example, it is known to be used for the production of certain polymers using monomers comprising vinyl moieties. Examples of such monomers are styrene, vinyl chloride, vinyl acetate, methyl methacrylate, acrylonitrile or combinations thereof. In particular, the production of PVC by suspension polymerisation of vinyl chloride is a well-established process.

In such suspension polymerisation processes, a quantity of monomer is suspended in a medium. Commonly, this suspension is conducted using one or more suspending agents. Such suspending agents ensure a desired degree of colloidal stability of droplets formed from the monomer in the suspension.

The medium used in the suspension polymerisation reactions of monomers comprising vinyl moieties may for example be water. After the polymerisation reaction is terminated, the polymer product is separated from the medium. The medium obtained from such separation commonly comprises water and a certain quantity of the suspending agents.

This medium stream may be disposed of as a wastewater stream. However, the suspending agents present in this wastewater stream need to be removed from the stream to ensure the water can be used again. This removal may for example take place via purification steps such as ultrafiltration or membrane filtration. However, during such purification steps, the suspending agents may agglomerate and result in blocking of the purification process.

For that reason, there is a need to provide a process for suspension polymerisation of monomers comprising vinyl moieties where the suspension shows the desired degree of colloidal stability of the monomer droplets, with improved reusability of the wastewater resulting from the process.

This has now been achieved by a process according to the present invention comprising suspension polymerisation of monomers comprising vinyl moieties using a reaction mixture comprising:

• a quantity of a reaction medium;

• a quantity of a monomer wherein the monomer comprises at least one vinyl

moiety; and • a quantity of a comonomer wherein the comonomer comprises at least one acrylate moiety and at least one hydroxyl moiety.

Such process results in the reduction of the quantity of suspending agents in the wastewater resulting from the process, whilst still ensuring the suspension has the desired degree of colloidal stability.

In a suspension polymerisation processes, such as suspension polymerisation processes for the production of polymers in which styrene, vinyl chloride, vinyl acetate, methyl

methacrylate, acrylonitrile or combinations thereof are used as monomers, polyvinyl alcohols (PVA) and mixtures of such PVA ^' s are commonly used as suspending agents. Such PVA's may be used to ensure the desired dimensions and colloidal stability of the monomer droplets that a formed during the polymerisation process and which are during the process converted into the desired polymers. However, the use of such PVA's has a disadvantage in that they remain in the reaction medium that is utilised in the suspension polymerisation process. Commonly, water may be selected as the reaction medium.

The process according to the present invention results in a reduction of the quantity of PVA ^' s that are discarded from the process via the medium as the need for use of such PVA ^' s is reduced and may even be eliminated.

A further disadvantage of the use of PVA ^' s as suspending agents in suspension polymerisation processes is that such process needs to comprise unit operations to provide the PVA ^' s in the required form to be used in suspension polymerisation. The PVA ^' s need to be brought into solution prior to dosing to the suspension polymerisation. This influences the overall process economics. By reducing or even eliminating the need for using such PVA ^' s, the process configuration may be simplified and the process economics may be improved.

The process according to the present invention may in certain embodiments be operated such that wherein the reaction mixture further comprises a quantity of one or more suspending agent(s). For example, the reaction mixture may comprise one or more suspending agents selected from polyvinyl alcohols, cellulosics, and polyvinyl acetates or combinations thereof. Such one or more suspending agents may for example comprise polyvinyl alcohols. For example, the one or more suspending agents may comprise a quantity of a polyvinyl alcohol having a degree of hydrolysis of < 60%. Further, the one or more suspending agents may comprise a quantity of a polyvinyl alcohol having a degree of polymerisation of 60-75%. Even further, the one or more suspending agents may comprise a quantity of a polyvinyl alcohol having a degree of hydrolysis of 85-90%.

The one or more suspending agents may for example be a combination of different polyvinyl alcohols each having a different degree of polymerisation. For example, the one or more suspending agents may comprise a quantity of a polyvinyl alcohol having a degree of hydrolysis of < 60% and a quantity of a polyvinyl alcohol having a degree of hydrolysis of 60- 75%. More preferably, the one or more suspending agents comprise a quantity of a polyvinyl alcohol having a degree of hydrolysis of 50-60% and a quantity of a polyvinyl alcohol having a degree of hydrolysis of 65-75%.

Alternatively, the one or more suspending agents may comprise a quantity of a polyvinyl alcohol having a degree of hydrolysis of < 60%, a quantity of a polyvinyl alcohol having a degree of hydrolysis of 60-75% and a quantity of a polyvinyl alcohol having a degree of hydrolysis of 85-90%.

In a preferred embodiment, the one or more suspending agents comprise a quantity of a polyvinyl alcohol having a degree of hydrolysis of 50-60% and a quantity of a polyvinyl alcohol having a degree of hydrolysis of 65-75%, and are added to the reaction medium in a quantity of 500-5000 ppm with regard to the weight of the monomer, more preferably 500-3000 ppm, or 500-2000 ppm.

The degree of hydrolysis of the polyvinyl alcohols (PVA) may for example be determined in accordance with ISO 15023-2 (2003).

In the process according to the invention, the reaction medium may for example comprise water. In a specific embodiment, the reaction medium consists of water.

The invention also encompasses as one of its embodiments a process wherein:

• the reaction medium is water; and

• the monomer is selected from vinyl chloride, styrene, vinyl acetate, methyl

methacrylate, acrylonitrile, or combinations thereof.

In particular, an embodiment is encompassed wherein the comonomer is a compound according to formula I:

Formula I wherein:

· R1 is CH ₃ or H;

• R2 is a moiety comprising 1 -10 carbon atoms; and

• n is an integer from 1 -10.

The comonomers according to formula I are believed to interact with the monomers selected from vinyl chloride, vinyl acetate, styrene, methyl methacrylate, acrylonitrile, or combinations thereof in such way during the polymerisation that a suspension of fine droplets is formed where the comonomers are positioned on the surface of the droplets, and wherein the monomers are to a certain degree contained within the droplets.

In a preferred embodiment, R1 is CH3. In another preferred embodiment, R2 comprises at least one hydroxyl moiety, more preferably R2 comprises at least two hydroxyl moieties, more preferably R2 comprises at least one hydroxyl moiety and n is 1 .

R2 may for example be selected from:

-CH ₂ -CH(CH ₃ )-,

-CH ₂ -CH(OH)-CH ₂ -,

-CH ₂ -(CH(OH)) ₂ -CH ₂ -,

-CH ₂ -(CH(OH)) ₃ -CH ₂ -,

-CH ₂ -(CH(OH)) ₄ -CH ₂ - ,

-0-CH2-CH ₂ -[-0-CH2-CH ₂ -] _m -, or

-0-CH ₂ -CH2-CH2-[-0-CH2-CH2-CH ₂ -]m- where m is an integer from 1 -10.

For example, R2 is -CH ₂ -CH(OH)-CH ₂ -. Preferably, R1 is CH3 and R2 is selected from:

-CH ₂ -CH(CH ₃ )-,

-CH ₂ -CH(OH)-CH ₂ -,

-CH ₂ -(CH(OH)) ₂ -CH ₂ -,

-CH ₂ -(CH(OH)) ₃ -CH ₂ -,

-CH ₂ -(CH(OH)) ₄ -CH ₂ - ,

-0-CH2-CH ₂ -[-0-CH2-CH ₂ -]m-, or

-0-CH ₂ -CH2-CH2-[-0-CH2-CH2-CH ₂ -]m- where m is an integer from 1 -10.

Preferably, R1 is CH ₃ and R2 is -CH ₂ -CH(OH)-CH ₂ -. In an embodiment of the invention, the comonomer is selected from glycerol

(meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, tetritol mono(meth)acrylate, xylitol mono(meth)acrylate, sorbitol mono(meth)acrylate,

polyethyleneglycol (meth)acrylate, polypropyleneglycol (meth)acrylate, or combinations thereof. It is preferred that the comonomer is selected from glycerol (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate. Alternatively, the comonomer may be selected from glycerol methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, or sorbitol monomethacrylate.

More preferably, the comonomer is glycerol methacrylate.

The use of such comonomer has as one of its advantages that there is no need for the preparation of a solution prior to introduction into the reactor as these compounds are stable at room temperature.

The reaction mixture may for example comprise≥ 1000 ppm of the comonomer with regard to the weight of the monomer in the reaction mixture. Alternatively, the reaction mixture may comprise > 2000 ppm of the comonomer, or≥ 4000 ppm. For example, the reaction mixture may comprise < 15000 ppm of the comonomer, or < 12000 ppm. Preferably, the reaction mixture comprises≥ 2000 ppm and < 15000 ppm, alternatively > 4000 ppm and < 12000 ppm of the comonomer with regard to the total weight of the monomer in the reaction mixture. The reaction mixture may for example comprise > 1000 ppm of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is selected from glycerol methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, or sorbitol monomethacrylate. The reaction mixture may for example comprise > 1000 ppm of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is glycerol methacrylate.

The reaction mixture may for example comprise≥ 1000 ppm and < 15000 ppm of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is selected from glycerol methacrylate, 2-hydroxyethyl methacrylate, 2- hydroxypropyl methacrylate, or sorbitol monomethacrylate. The reaction mixture may for example comprise > 1000 ppm and < 15000 of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is glycerol methacrylate.

The reaction mixture may for example comprise > 4000 ppm and < 12000 ppm of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is selected from glycerol methacrylate, 2-hydroxyethyl methacrylate, 2- hydroxypropyl methacrylate, or sorbitol monomethacrylate. The reaction mixture may for example comprise > 4000 ppm and < 12000 of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is glycerol methacrylate. The use of such quantity of comonomer results in the desired effect of droplet stabilisation being achieved, whilst not negatively influencing the product properties of the polymer obtained from the process.

The reaction mixture may for example comprise > 1000 ppm of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is selected from glycerol methacrylate, 2-hydroxyethyi methacrylate, 2-hydroxypropyl methacrylate, or sorbitol monomethacrylate, and wherein the monomer is selected from vinyl chloride, styrene, vinyl acetate, methyl methacrylate, acrylonitrile, or combinations thereof. The reaction mixture may for example comprise≥ 1000 ppm of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is glycerol methacrylate and wherein the monomer is vinyl chloride.

The reaction mixture may for example comprise≥ 1000 ppm and < 15000 ppm of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is selected from glycerol methacrylate, 2-hydroxyethyl methacrylate, 2- hydroxypropyl methacrylate, or sorbitol monomethacrylate, and wherein the monomer is selected from vinyl chloride, styrene, vinyl acetate, methyl methacrylate, acrylonitrile, or combinations thereof. The reaction mixture may for example comprise 1000 ppm and < 15000 of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is glycerol methacrylate and wherein the monomer is vinyl chloride.

The reaction mixture may for example comprise > 4000 ppm and < 12000 ppm of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is selected from glycerol methacrylate, 2-hydroxyethyl methacrylate, 2- hydroxypropyl methacrylate, or sorbitol monomethacrylate, and wherein the monomer is selected from vinyl chloride, styrene, vinyl acetate, methyl methacrylate, acrylonitrile, or combinations thereof. The reaction mixture may for example comprise > 4000 ppm and < 12000 of the comonomer with regard to the weight of the monomer in the reaction mixture, wherein the comonomer is glycerol methacrylate and wherein the monomer is vinyl chloride. In an embodiment of the invention, the process is conducted using a reaction mixture comprising:

• a quantity of a reaction medium comprising water;

• a quantity of one or more suspending agents comprising a quantity of a polyvinyl alcohol having a degree of hydrolysis of < 60 % and a quantity of a polyvinyl alcohol having a degree of hydrolysis of 60-75%;

• a quantity of monomer comprising vinyl chloride; and

• a quantity of comonomer comprising glycerol methacrylate.

In a particularly preferred embodiment, the process is conducted using a reaction mixture comprising:

• a quantity of a reaction medium comprising water;

• < 2000 ppm of one or more suspending agents comprising a quantity of a polyvinyl alcohol having a degree of hydrolysis of < 60 % and a quantity of a polyvinyl alcohol having a degree of hydrolysis of 60-75%;

· a quantity of monomer comprising vinyl chloride; and

• > 500 ppm of comonomer comprising glycerol methacrylate;

wherein the ppm quantity of the suspending agents and the comonomer are expressed as ppm by weight with regard to the weight of the monomer. The polymerisation may for example be performed at a temperature of 20-70 'C, alternatively 50-60 C. The polymerisation may for example be performed at a pressure of 5-10 bar, alternatively 7-9 bar. The polymerisation may for example be performed during a reaction period of 200-500 min, alternatively 300-400 min.

The polymerisation may for example be performed at a temperature of 20-70 C, and at a pressure of 5-10 bar. Preferably, the polymerisation is performed at a temperature of 20-70 C, at a pressure of 5-10 bar, and during a reaction period of 200-500 min. More preferably, the polymerisation is performed at a temperature of 50-60 C, at a pressure of 7-9 bar, and during a reaction period of 300-400 min.

The process may be a batch polymerisation process. Preferably, the process is a batch polymerisation process in which the duration of the polymerisation is 200-500 min.

In a further particular embodiment of the invention, the product obtained from the process is subjected to a separation step to obtain a polymer stream and a waste stream comprising the medium, wherein the waste stream comprises < 1000 ppm of poiyvinylalcohol with regard to the total weight of the waste stream.

It is further preferred that the polymer obtained via the process according to the invention comprises≥ 1000 ppm of polymeric units derived from the comonomer comprising at least one acrylate moiety and at least one hydroxyl moiety with regard to the total weight of the polymer.

The present invention will now be illustrated by the following non-limiting examples.

Polymerisation experiments were performed in a stainless steel closed reactor having a volume of 4.35 I. The reactor was equipped with an agitator with two blades and four baffles. Water was used as reaction medium. In each experiment, 2100 g of water, mixed with a quantity of suspending agents and comonomers as listed in table 1 , was introduced into the reactor. Table 1 : Suspending agents and comonomers

Experiment PVA72 PVA88 PVA55 MC comonomer

1 1200 0 250 120 GMA: 4000

2 1200 800 250 120 GMA: 10993 3(C) 1200 800 250 120 0

4 1200 800 250 120 HEMA: 1 1333

5 1200 400 250 120 HEMA: 6000

6 1200 800 250 120 SMA: 1 1333

The quantities in table 1 are expressed as ppm by weight with regard to the weight of the total quantity of vinyl chloride introduced to the reactor.

Experiments 1 and 2 and 4-6 present examples according to the present invention.

Experiment 3 is included for comparative purposes.

The materials that were used in the experiments are:

• PVA72: polyvinyl alcohol having a degree of hydrolysis of 72 mol%,

• PVA88: polyvinyl alcohol having a degree of hydrolysis of 88 mol%,

• PVA55: polyvinyl alcohol having a degree of hydrolysis of 55 mol%,

• MC: hydroxypropyl methylcellulose

• GMA: glycerol methacrylate

• HEMA: 2-hydroxyethyl methacrylate

• SMA: sorbitol monomethacrylate

The degree of hydrolysis of the polyvinyl alcohol (PVA) may be determined in accordance with ISO 15023-2 (2003).

Sodium carbonate was introduced into the reactor as a buffer, in a quantity of 237 ppm with regard to the weight of the vinyl chloride. After charging the mixture of water, suspending agents and comonomers to the reactor, the atmosphere in the reactor above the reaction medium was purged with nitrogen three times. Subsequently, a vacuum was applied to the reactor, and kept for 5 minutes under agitation at 400 rpm. The agitator was stopped and 1500 g vinyl chloride was changed to the reactor. The agitator was started again and agitation was maintained at a speed of 900 rpm. The reactor contents were heated to 54 C. 200 ppm of di(2- ethylhexyl)peroxydicarbonate and 562 ppm 3-hydroxy-1.1 ^' -dimethyl butyl peroxyneodecanoate with regard to the weight of the vinyl chloride were added as initiators to start the reaction. After 1 hour, further water dosing at a rate of 1 .8 g/min was started to compensate the volume shrinkage due to the consumption of the vinyl chloride and the formation of the polyvinyl chloride polymer. After the respective polymerisation times of 300 min (ex. 1 ), 340 min (ex. 2) and 350 min (ex. 3), reflecting a 80% conversion of vinyl chloride, the reactor was vented, and the reactor contents subjected to a temperature of 90 C for 150 min to remove volatile components including unreacted vinyl chloride. Subsequently, the reaction medium was separated from the obtained polymer, and the polymer was dried in a fluidized bed dryer at 90 C to obtain a PVC polymer comprising < 0.3 wt% moisture.

The PVC polymer particles obtained in each of the experiments 1 -3 were subjected to material properties testing. The obtained results are presented in table 2.

Table 2: Material properties of PVC obtained in experiments 1 -3.

Wherein:

• Dio, Dso and Dgo present the particle size dimension where respectively 10%, 50% and 90% by volume of the particles in the sample have a diameter of less than the presented value, as determined in accordance with ISO 9276-2 (2014); · Bulk density is determined in accordance with ASTM D-1895 96 (2010); and

• Porosity is determined as the quantity of di(2-ethylhexyl)phthalate in ml absorbed by 1 g of polymer upon subjecting the polymer at 23 C to vacuum, submerging in di(2-ethylhexyl)phthalate for 10 min, and subsequently centrifuging at 2000 rpm for 45 min.

· T _g is the glass transition temperature as determined via DSC in accordance with with ISO 1 1357-2 (2013).

The obtained samples were analysed using Fourier transform infrared spectroscopy (FTIR) to analyse the extent to which the comonomer was incorporated into the polymers during the suspension polymerisation process. The obtained data are presented in table 3. Table 3: FTIR data

The absorbance ratio 1730 cnr ¹ / 4325 cm ^'1 is an indicator for the presence of carbonyl groups in the tested polymer; the absorbance ration 3590 cnr ¹ / 4325 cnr ¹ is an indicator for the presence of hydroxyl groups in the tested polymer.

The incorporated comonomer is presented as % by weight with regard to the total weight of the polymer sample.

From the examples presented above, it becomes apparent that the process according to the present invention has a desired degree of colloidal stability of the suspension to result in a polymer having the desired properties such as expressed by the particle size, bulk density, glass transition temperature and porosity, whilst allowing for a reduction of the consumption of suspending agents, resulting in a reduction of the suspending agents discarded of with the wastewater of the process. The function of the comonomer comprising at least one acrylate moiety and at least one hydroxyl moiety, such as GMA, as a reactive suspending agent is also reflected by the fact that the reactor vessels showed a clean inside wall upon visual inspection after the polymerisation experiments, ensuring no undesirable deposition of any of the material from the reaction mixture or from the reaction products.