EXP AND ABLE POLYMERS FIELD OF THE INVENTION

The present invention relates to expandable polymers.

BACKGROUND

Foaming of polymers often requires the use of environmentally unfriendly and/or flammable foaming agents. For instance, foaming of polystyrene ( PS ) is generally done by mixing an organic blowing agent, such as pentane, under pressure into the polystyrene melt, using a conventional extruder. Upon expansion at the die ex it, the polymer foams and the formed cellular structure is vitrified.

Water would be an attractive alternative as foaming agent. How ever, water does not dissolve in polystyrene, requiring additional efforts to suitably disperse water into the polystyrene. Past efforts have only seen limited success, however.

For further background on w ater-expandable polystyrene (WEPS), see, e.g., Crevecoeur et al . in ' ^" Water expandable polystyrene ^" . Polymer 40 ( 1999) p. 3685- 3689; US Patent 7456227; and US Patent 6387968. All three references are hereby incorporated in their entirety by reference.

SUMMARY

in an embodiment, the present invention provides expandable polymers comprising surface-modi fled particles. In an embodiment, the polymers comprise water as expansion agent. In an embodiment, the present invention provides using surface- modi fied particles in the synthesis of polymers.

Additional objects, advantages and features of the present invention are set forth in this specification, and in part will become apparent to those skilled in the art on examination of the following, or may be learned by practice of the invention. The inventions disclosed in this appl ication are not limited to any particular set of or combination of objects, advantages and features. It is contemplated that various combinations of the stated objects, advantages and features make up the inventions disclosed in this application.

DETAILED DESCRIPTION

The present invention provides the use of surface-modified particles in preparing expandable polymers, e.g. water ex andable polymers. In an embodiment, the polymer is a thermoplastic polymer, e.g. polystyrene, styrene copolymers, e.g.

styrenic maleic anhydride copolymers, polyphcnylenc oxide, polystyrene- polyphenylene oxide blends, pol yoxymethylene, poly( -methyl, methacrylate), methyl methacrylate copolymers, polyethylene, polypropylene, ethylene-propylene copolymers, polyvinyl ch loride, polycarbonate, polyethylene terephthalate, crosslinked variations thereof, rubber-modified versions thereof, blends thereof, and interpenetrating networks thereof, e.g. polyethylene and polymerized vinyl aromatic resins, such as polystyrene. In an embodiment, the expandable polymer is water expandable polystyrene.

In an embodiment, the surface-modified particles, for instance hydrophobizcd particles, assist in incorporation of water droplets in the polymer, e.g. during suspension polymerization. In an embodiment, the amount of water and the size of the water droplets can be controlled by the amount of surface-modified part icles.

The particles may be organic or inorganic particles. In an embodiment, the particles are metal oxides. In an embodiment, the particles are a salt. In an embodiment, the particles are silica, alumina, and/or titania particles. In an embodiment, the particles are tricalciumphosphate particles ( Ca;(PO i b ). In an embodiment, the amount of particles in the WE PS is, relative to the total weight of WE PS, polystyrene is less than 1.5wt%, e.g. less than 1 wt%, less than 0.5 wt%, or less than 0.25wt%. In an embodiment, the amount of particles in the WEPS is, relativ e to the total weight of W'EPS, at least 0.05wt%, e.g. at least 0. 1 wt% or at least 0.2 wt%. In an embodiment, the particle size is in a range of 10- l OOOnm.

In an embodiment, the surface of the particles is modified. In an embodiment, the surface of the particles is made more hydrophobic. In an embodiment, surface modification is effected by grafting molecules onto the particles. In an embodiment, alky I- or po 1 y d i m et h y 1 s i 1 ox a n e chains arc grafted onto the particles. In an

embodiment, the surface-modified particles are hydrophobic fumed silica. In an embodiment, surface modification is effected through creation of a salt, e.g. between the particle and an amphiphilic molecule. In an embodiment, the molecular weight of the amphipil ic molecule is less than 1000 g/mol, e.g. less than 500 g/mol, less than 250 g/mol. or less than 1 50 g mol. In an embodiment, the molecular weight of the amphiphil ic molecule is at least 75 g/mol, e.g. at least 125 g/mol. In an embodiment, the amphiphilic molecule is valeric acid or hexyl amine.

Further examples of surface modification, surface modification agents, and particles are disclosed in EP 2361679, which is hereby incorporated in its entirety by reference.

In an embodiment, the WE PS comprises, relative to the total weight of the WE PS, at least 0.5 wt% of water, e.g. at least 1 wt%, at least 2 wt%, at least 5 wt% w ater, at least 7 wt%, at least 1 0 wt, or at least 1 5 wt%. In an embodiment, the WEPS comprises, relative to the total weight of the WEPS, less than 5 wt% water, e.g. less than 25 wt%, less than 20 wt%, less than 1 5 wt%, less than 1 0 wt%, less than 5 wt%, less than 3 wt%, or less than 2 wt%.

In an embodiment, the diameter of the droplets in the WEPS is less than 200 micron, e.g. less than 100 micron, less than 75 micron, less than 50 micron, or less than 25 micron. In an embodiment, the diameter is at least 1 micron, e.g. at least 10 micron. In an embodiment, the diameter is about 1 5 micron.

In an embodiment, the present invention prov ides a process comprising:

(a) prov iding a mi ture of styrene and surface-modified particles to form a first mi ture;

(b) mixing the first mixture with water to form a second mixture;

(c) mix ing the second mixture with water, an emulsifier (e.g. polyvinylalcohol, "PVA"), an initiator (e.g. a perox ide, for instance d i benzoyl perox ide ), and styrene to form a third mixture.

(d) polymerizing styrene in the third mixture. In an embodiment, the present invention provides a process where part of the particles are used for creating surface-modified particles and part of the particles are used to act as emulsifier. In an embodiment, a "one pot" process is provided for creating expandable polymers, e.g:

(a) providing a mixture comprising monomer (e.g. styrene), initiator (e.g. a peroxide), particles, surface-modified particles, and water;

(b) polymerizing the monomer in the mixture.

In an embodiment, the particles in the mixture consist essentially of one type of particles (e.g. silica and surface modified silica; or tricalciumphosphate and surface- modified t i ca I c i 11 m phosphate ) .

In an embodiment, a process is provided comprising:

(a) mi ing monomer, initiator, particles, water, and surface-modifier, wherein the amount of surface-modifier is insufficient to effectively surface modify all particles;

(b) polymerizing the monomer.

In an embodiment, the present invention provides water-expandable polymers, wherein the water-expandable polymer, when heated from 30 C to 200°C at a rate of 2°C minute, displays a weight loss that is less than the water content in the water- expandable polymer.

In an embodiment, the present invention provides water-expandable polymers, wherein the water-expandable polymer, when heated from 30 C to 200°C at a rate of 2°C/minute, displays a weight loss of less than 1.5 wt%, relative to the total weight of the water-expandable polymer, e.g. less than 1 wt%.

Additional embodiments are set forth in numbered clauses below:

1 . Polystyrene com rising particles, the particles consisting essentially of surface- modified particles.

2. The polystyrene of clause 1, further comprising water.

3. The polystyrene according to any one of clauses 1-2, wherein said particles include silica particles. 4. The polystyrene according to any one clauses 1-3, wherein said particles are su rf ace-mod i fi ed with hexylamine.

5. A bead comprising the polystyrene according to any one of clauses 1 -4.

6. A foam comprising the polystyrene according to any one of clauses 1 -4.

7. Water-expandable polystyrene, the water-expandable polystyrene displaying less than 1% weight loss, relative to the total weight of the water-expandable polystyrene, when heated from 30°C to 200°C at a rate of 2°C/min.

8. Water-expandable polystyrene, the water-expandable polystyrene, when heated from 30°C to 200 C at a rate of 2°C/minute, displaying a weight loss that is less than the water content in the water-expandable polystyrene.

9. The water-expandable polystyrene of any one of clauses 7-8, further comprising surface-modified particles.

10. The water-expandable polystyrene according to any one of clauses 7-9, comprising at least 2wt% water, relative to the total weight of the water-expandable polystyrene.

1 1. The water-expandable polystyrene according to any one of clauses 7- 1 0, comprising less than 25wt % water, relative to the total weight of the water- expandable polystyrene.

1 2. Use of surface-modified particles in the synthesis of water-expandable polystyrene.

13. A process comprising:

(a) prov iding a mixture of styrenc and surface-modified particles to form a fi st mixture:

(b) mix ing the first mixture with water to form a second mixture;

(c) mixing the second mixture w ith water, a stabilizer, an initiator, and styrcne to form a third mixture.

(d) polymerizing styrene in the third mixture.

14. A process comprising foaming a water-expandable polymer, the water- expandable polymer comprising surface-modified particles. 1 5. The process of clause 14. wherein the polymer is polystyrene.

16. Polystyrene foam comprising surface-modified particles.

1 7. The polystyrene foam of clause 16, further comprising water.

18. A process comprising:

(a) providing a mixture comprising monomer, initiator, particles, surface-modified particles, and water;

(b) polymerizing the monomer in the mixture.

19. The process of clause 18, wherein the particles in the mixture consist essentially of one type of particles.

20. The process according to clause 1 , wherein the one type of particles is t ri cal c i u m phosphate.

21. A process comprising:

(a) mixing monomer, initiator, particles, water, and surface-modifier, wherein the amount of surface-modifier is insufficient to effectively surface modify all particles:

(b) polymerizing the monomer.

EXAMPLES

The following examples are given as particular embodiments of the invention and to demonstrate the practice and advantages thereof It is understood that the examples arc given by way of illustration only and are not intended to limit the specification or the claims that follow in any matter.

Materials

The styrene monomer (>99% pure, Sigma-Aldrich Chemie GmbH, Germany ) was used without distillation of the inhibitor tert-butylcatechol ( 1 0 1 5 ppm ). The initiators, d ibenzoyl perox ide (active content, 75%; water, 25%) was supplied by ABCR GmbH & Co. KG, Karlsruc Germany. The emulsifier PVA with molecular weight 72 000 was suppl ied by Fluka and used as received.

Inorganic metal oxide particles used in the experiments were: (1 ) α-ΑΚΟ » powder (Ceralox HPA-0.5, 99.99% A1 ₂ 0 ₃ , Sasol North America Inc., Tucson, AZ, USA ) w ith 2

average particle diameter, dso, of 200 nm, specific surface area of 1 0 m g and density of 3.98 g/cm ³ ; (2) The Si0 ₂ powder was Tixosil 365.

The short amphiphilic molecules used for particle modification were valeric acid (>99 % pure, Sigma-Aldrich ( ^' hemic GmbH, Germany) for (t-ANO;. and hexyl amine (>99% pure, Fiuka AG, Buchs. Switzerland) for Si() ₂ .

Double deionized water with an electrical resistance of 18MW cm was used in the experiments (Nanopure water system, Barnstcad, USA).

Preparation of suspensions of modified particles In styrene ("styrene

suspension")

The styrene colloidal suspensions with 10 vol% resp. 15 vol% alumina as well as those with 4 vol% resp. 6 vol% silica by adding the particles to styrene containing the desired amount of amphiphile (vol% being relative to the volume of styrene in the styrene suspension, i.e. vol% particles + vol% styrene in the styrene suspension = 1 00 vol%). De-agglomeration and modification of the colloidal particles was performed by ball-mill ing the suspensions in polyethylene bottles for 22 hours using alumina milling balls ( 1 0 mm diameter).

Preparation and characterization of "master-batches"

Emulsification. was performed by vigorously stirring the styrene suspension with water for 3 minutes, using a household mixer at full power (Multimix 350 W, Braun, Spain ). The mixtures prepared in this manner are referred to as "master-batch" (that were later diluted with styrene to obtain the reaction mixture for the final

polymerization to WEPS). The volume fraction of water referred to in the examples is relative to the total volume of the master-batch.

Polymerization

First, PVA (0.2 wt%) was dissolv ed in water at 100°C, and subsequently cooled down to 90°C. Then, d i benzoyl pero idc was dissolv ed in styrene at room temperature, after which the water-in-styrene master-batch was added, until the desired water concentration in the final reaction mixture was obtained. Suspension polymerization of the reaction mixture was performed in a suspension reactor of 1 1. The ratio R of the reaction mixture styroi+water to PVA-solution medium was 1/3 (w/w). The reaction mixture was added to the 90"C PVA-water solution in the reaction vessel during constant stirring, leading to an emulsion of water-in-styrene droplets in the PVA solution. At this temperature, polymerization of styrene started and was continued for 6 h at 90"C under continuous stirring. Finally, the suspension was cooled to room temperature and the spherical beads were filtered and w ashed with water. After drying, the beads were stored in closed polyethylene flasks.

Analytical Methods

- Thermographic Analysis (TGA) was performed using a TGA system from Mettier (Switzerland), by heating a sample from 25°C to 800°C at a rate of 2°C/min under a flow of 50 ml/min air. Weight loss of a sample between 30°C and 200°C was taken as indicative of the water content in the sample.

- Differential Scanning Caiorimetry (DSC) analysis was performed using a system from ettier (Switzerland). The heat flow normalized to sample weight as a function of tem erature was recorded at a heating rate of 10°C/min.

- Foaming of WEPS beads was performed by immersing the beads in boil ing water for 3 minutes.

COMPARATIVE EXAMPLE A

0,6 g PVA(0,2 wt%) was completely dissolved in 300ml boil ing water to form a water mixture. 0,6 g dibenzoylperoxide (0,4 wt%) was dissolved in 1 50ml of styrene at room temperature to from a styrene mixture. Subsequently, polymerization was started by adding the styrene mixture to the water mixture in a the reaction vessel at 90"C under constant stirring. Suspension polymerization was continued for 6 h at 90' C while stirring. Finally, the suspension was cooled to room temperature and the spherical PS beads were filtered and washed with water.

The onset glass-transition temperature of the PS beads was 102°C, as measured by DSC. M icroscopic analyses revealed minor amounts of water in the PS-beads, which might be due to the stirring during the polymerization in the water-PVA mixture. TGA analysis showed a weight loss at 200°C of about 3.5 wt% (relative to the total weight of the beads), indicative of a similar water content. Foaming was poor.

COMPARATIVE EXAMPLE B A suspension was prepared by adding alumina powder to styrene in an amount of 10 vol% alumina powder and 90 vol% styrene. Homogenization took place on a ball mill during 20 hours. This suspension was then mixed with 195ml of water (80 vol%) using a household mixer at full power (Multimix 350 W, Braun, Spain) for 3 minutes, result ing in a styrene-in- water emulsion master-batch (instead of a water-in-styrene emulsion).

0,6 g PVA(0,2 wt%) was completely dissolved in 300ml boiling water. A reactor mixture consisting of 0.6 g d i benzoyl perox ide, 20 g of the master-batch and 130ml of styrene at room temperature was added to the PVA solution at 90 C under constant stirring to start the emulsion polymerization. Suspension polymerization was continued for 6 h at 90' C while stirring. Finally, the suspension was cooled to room temperature and the spherical PS beads were filtered and washed with water.

Microscopic analyses revealed minor amounts of water in the PS-beads. TGA analysis indicated the amount of water in the PS beads to be about 3.5wt% (relative to the total weight of the beads).

COMPARATIVE EXAMPLE C

A suspension comprising 4 vol % of silica powder (Ti osil 365 ) was prepared by adding the powder to styrene. Homogenization was performed on a ball mill during 20 hours. This suspension was then mixed with 62.7 ml of water (50 vol%) using a household mixer at full power (Multimix 350 W, Braun, Spain ) for 3 minutes to obtain a styrene-in-water emulsion master-batch (instead of a water-in-styrene emulsion).

0,6 g PVA(0,2 wt%) was completely dissolved in 300ml boiling water. A reactor mixture consist ing of 2.4 g dibenzoyl peroxide, 15 g of the master-batch and 1 35 ml of styrene at room temperature was added to the PVA solution at 90°C under constant stirring to start the emulsion polymerization. Suspension polymerization was continued for 6 h at 90°C while sti ring. Finally, the suspension was cooled to room temperature and the spherical PS beads were filtered and washed with water. Microscopic analyses revealed minor amounts of water in the PS-beads. TGA analysis indicated the amount of water in the PS beads to be about 2.4 wt%. Foaming was poor.

EXAMPLE 1

A styrene suspension comprising 10 vol% of alumina powder w ith a mean particle size of 200 nm was prepared by adding the powder to styrene containing 0,15 mol/1 of Valeric Acid. Homogenization took place on a ball mill during 20 hours. This styrene suspension was then mixed with 1 5ml of water (80 vol%) using a household mixer at full power (Multimix 350 W, Braun, Spain ) for 3 minutes to obtain a master-batch water-in-styrene emulsion. A droplets size of about 30- 100μηι in the emulsion was determined by l ight microscopy.

0,6 g PVA(0,2 wt%) was completely dissolved in 300ml boiling water. A reactor mixture consisting of 0,6 g dibenzoyl eroxide (0.4 wt%) , 20 g of master-batch water- in-styrene emul sion and 1 30ml of styrene at room temperature was added to the PVA solution at 90°C under constant stirring to start the polymerization. Suspension polymerization was continued for 6 h at 90"C while stirring. Finally, the suspension was cooled to room temperature and the spherical PS beads were filtered and washed with water.

The onset glass-transition temperature of the PS beads was 101 C, as measured by DSC. The PS beads were evaluated by l ight microscopy, revealing large amounts of water droplets. TGA analysis indicated a water content of about 1 1 wt% (relative to the total weight of the beads). Foaming was good.

EXAMPLE 2

A styrene suspension comprising 10 vol% of alumina powder w ith a mean particle size of 200 nm was prepared by adding the powder to styrene containing 0, 1 5 mol/1 of Valeric Acid. Homogenization took place on a ball mill during 20 hours. This suspension was then mixed with 195ml of w ater (80 vol%) using a household mixer at full power (Multimix 350 W, Braun. Spain ) for 3 minutes to obtain a alumina- stabilized master-batch water-in-styrene emulsion. A droplets size of about 30- 1 ΟΟμπτ in the emulsion was determined by light microscopy.

0,6 g PVA(0,2 wt%) was completely dissolved in 300ml boiling water. A reactor mixture consisting of 0,6 g dibenzoyl peroxide, 10 g of master-batch water-in-styrene emulsion and 140ml of styrene at room temperature was added to the PVA solution at 90°C under constant stirring to start the polymerization. Suspension polymerization was continued for 6 h at 90°C while stirring. Finally, the suspension was cooled to room temperature and the spherical PS beads were filtered and washed with water.

The onset glass-transition temperature of the PS beads was 102°C, as measured by DSC. The PS beads were evaluated by light microscopy, revealing large amounts of water droplets. TGA analysis indicated a water content of about 6 wt% (relative to the total weight of the beads). Foaming was good.

EXAMPLE 3

A suspension comprising 15 vol% of alumina powder (Ceralox) with the mean particle size of 200 nm was prepared by adding the powder to styrene containing 0,2 mol l of Valeric Acid. Homogenization took place on a ball mill during 20 hours. This suspension was then mixed with 195ml of water (80 vol%) using a household mixer at ful l power (Multimix 350 W, Braun, Spain ) for 3 minutes to obtain a alumina- stabil ized master-batch water-in-styrene emulsion. The droplets size of about 10-40 μηι in the emulsion was determined by light microscopy.

0,6 g PVA(0,2 wt%) was completely dissolved in 300ml boiling water. A reactor mixture consisting of 0,6 g dibenzoylperoxide, 10 g of the new master-batch water-in- styrene emulsion and 140ml of styrene at room temperature was added to the PVA solution at 90°C under constant stirring to start the polymerization. Suspension polymerization was continued for 6 h at 90°C while stirring. Finally, the suspension was cooled to room temperature and the spherical PS beads were filtered and washed with water.

The onset glass-transition temperature of the PS beads was 102°C, as measured by DSC. The PS beads w ere evaluated by light microscopy, revealing large amounts of water droplets. TGA analysis indicated a water content of about 1 5 wt%. Foaming was good.

EXAMPLE 4

A styrene suspension comprising 6 vol % of silica powder (Tixosil 365) was prepared by adding the powder to styrene containing 0,6 mol/1 of Hexyl amine.

I lomogenization took place on a ball mill during 20 hours. This suspension was then mixed with 57.8 ml water (50 vol%) using a household mixer at full power (Miiltimix 350 W, Braun, Spain ) for 3 minutes to obtain a sil ica-stabilized master-batch water- in-styrenc emulsion. The droplets size varied from 1 - 1 0 μηι to 10-50 μπι in the emulsion as determined by light microscopy.

0,6 g PVA (0,2 wt%) was completely dissolved in 300ml boiling water. A reactor mixture consisting of 2.4 g d i benzoyl perox idc. 30 g of master-batch water-in-styrenc emulsion and 120 ml of styrene at room temperature was added to the PVA solut ion at 90°C under constant stirring to start the polymerization. Suspension polymerization was continued for 6 h at 90"C while stirring. Finally, the suspension was cooled to room temperature and the spherical PS beads were filtered and washed with water.

The onset glass-transition temperature of the PS beads was 101°C, as measured by DSC. The PS beads were evaluated by light microscopy, revealing large amounts of tiny water droplets. Foaming was good. TGA analysis revealed substantially no weight loss before the onset of total degradation at 400°C, indicative of a stable and finely dispersed inclusion of water in the beads.

Hav ing described specific embodiments of the present invention, it will be understood that many modifications thereof will readily appear or may be suggested to those skilled in the art, and it is intended therefore that this invention is l imited only by the spirit and scope of the following claims.