MXPA00004964A - Extrusion process for enhancing the melt strength of polypropylene - Google Patents

Abstract

The invention relates to a process for enhancing the melt strength of polypropylene comprising the steps of:mixing the polypropylene with at least one peroxydicarbonate;reacting said polypropylene and peroxydicarbonate at a temperature between 150°C and 300°C, with the proviso that the peroxydicarbonate is not in the form of an aqueous dispersion.

Description

EXTRUSION PROCEDURE TO INCREASE THE RESISTANCE TO THE FUSION OF POLYPROPYLENE DESCRIPTIVE MEMORY The invention relates to a process for increasing the melt strength of polypropylene by mixing a peroxydicarbonate with the polypropylene and heating the polypropylene mixture. peroxydicarbonate Such a process is known from EP-B-0 384 431. This reference discloses a process for preparing polypropylene (PP) with a branched index of at least 1 consisting of (1) mixing a decomposition peroxide at a low temperature, such as the peroxydicarbonate, with the PP, (2) heating or maintaining the resulting mixture at a temperature from room temperature to 120 ° C, and then (3) heating the PP to a temperature of 130 to 150 ° C to deactivate substantially all the radicals free present in said PP. The PP obtained has a significant amount of long chain branches and has an increased weight average molecular weight giving the polymer a significant elongational viscosity during stress hardening. In step (3) it is mentioned that the heating must be done by extrusion or in a fluidized bed. Furthermore, it is established that at a temperature higher than 120 ° C, an essentially linear polymer with few branches or without branches is obtained.

Apparently, the significant elongational viscosity during hardening is related to the improvement of the melt strength of the obtained PP due to the long chain branching. It is only mentioned in this publication that step (3) of this procedure can be performed by extrusion; In the examples, the entire procedure is carried out in a sealed reaction vessel. A disadvantage of this method is that it comprises three steps, which is undesirable in practice. DE-A-4340194 (US 5,416,169) describes a process for preparing PP having a high melt strength and a chain branching coefficient of 1, by mixing bis (2-ethylhexyl) peroxydicarbonate with a linear, crystalline PP, followed of a heating at 70 to 150 ° C. In a subsequent step, the PP is removed from the reaction vessel and the molten material is emptied to be molded. The peroxydicarbonate is dissolved in an inert solvent before being added to the PP. It is established that other peroxydicarbonates having a similar decomposition temperature can not be used for this purpose. A disadvantage of this method is that it can only be carried out using a specific peroxide, i.e., bis (2-ethylhexyl) peroxydicarbonate. Another disadvantage is that the process is carried out in two steps, which is undesirable and not economical in practice.

The object of the present invention is to provide a process that does not have the aforementioned disadvantages and that the process of the PP yields have good melt strength. For this purpose, the present invention provides a method for increasing the melt strength of polypropylene by covering the following steps: - polypropylene is mixed with at least one peroxydicarbonate; - said polypropylene and peroxydicarbonate are reacted at a temperature between 150 ° C and 300 ° C, with the proviso that the peroxydicarbonate is not in the form of an aqueous dispersion within a polar medium with at least 90% by weight of the particles initials being smaller than 50 μm and at least 99% by weight of the initial particles being smaller than 65 μm. The reaction conditions are chosen in such a way that more than 50% by weight, preferably more than 70% by weight, but even better, more than 80% by weight of the peroxide is still present when the mixture of the peroxide and the polymer reaches a temperature of 120 ° C, preferably 150 ° C. In the previously unpublished patent application now published as WO 97/49759 a method is described for increasing the melt strength of polypropylene, wherein a dispersion of the initiator, such as peroxydicarbonate, in a polar medium, for example, water, and with a particle size distribution in particular, is in contact with the polypropylene and the resulting mixture is heated. This procedure can be carried out using an extruder. The process according to the present invention is a process that provides PP, which has an increase in melt strength. Since PP processing often involves the ejection of the PP, or to form pellets in the case of storage and transport or for further processing, that is, the formation of a final product, it is an additional advantage that the process of invention is an extrusion process, which allows the modification of the PP, to increase the resistance to melting, so that it is combined with said step of the process. The term "polypropylene" ("PP") refers to polymers or blends of polymers containing at least 50% by weight of polymerized propylene. The polymerization catalysts can be Ziegler-Natta, metallocene or other types that give a stereospecific polymerization of propylene. In connection with this, propylene homopolymers can be used; or random, alternating or block copolymers; or random, alternating or block terpolymers of propylene and another olefin. Generally, a propylene copolymer or terpolymer will contain one or more olefins, such as ethylene, butene, pentene, hexene, heptene or octene, but may also contain another olefinically unsaturated monomer or combinations thereof, such as acrylates, styrenes, styrene derivatives , acrylonitrile, vinyl acetate, vinylidene chloride and vinyl chloride. Here it is preferred to limit the content of olefins other than propylene to 30% by weight of the copolymer. Especially suitable for use are propylene homopolymers, copolymers of propylene and ethylene or mixtures of polypropylene and polyethylene containing not more than 10% by weight of the polymerized ethylene. The melting point of the commercially available normally solid PP is 160-170 ° C. The melting point of the propylene copolymers and ter-copolymers in general may be lower. The process of the invention is preferably carried out at a temperature in the range of 150 ° C to 300 ° C, most preferably 160 to 250 ° C, most preferably still 170 ° C to 225 ° C. The molecular weight of the PP used can be selected from a wide range. Indicative of the molecular weight is the molten material flow index (MFI). A PP having an MFI of 0.1 to 1000 g / 10 min (230 ° C, 21.6 N) can be used. Preferably, a PP containing 0.5 to 250 g / 10 min is used. The process according to the present invention is suitably carried out in a molten material mixing equipment, known to a person skilled in the art. Preferably an extruder or a kneader is used. Most preferably, a single or double screw extruder is used. An internal mixer such as a Banbury mixer, optionally associated with an extruder, can also be used. The peroxydicarbonate can be mixed first with the PP and then the mixture can be extruded. Alternatively, the peroxydicarbonate can be added to the extruder containing the PP by injection or spray, or it can be added together with the PP. It is preferred to introduce a peroxydicarbonate together with the PP into the extruder, for example by means of a feeder.

The state of the temperature of the extruder should allow the PP to melt, for example above 150 ° C. The screw speed is typically about 25 to 500 rpm. The normal residence time in the extruder is 15 seconds to 30 minutes. Larger residence times can be achieved using static additional mixers, etc. The extruded strand must be further processed, as is known, by a specialist in the area. Normally, the extruded strand is fed through a water bath and granulated using a granulator.

Alternatively, the extruded modified PP is formed directly in the desired final product. It is preferred to carry out the process of the present invention in an atmosphere of inert gas, such as nitrogen or argon.

Preferably nitrogen is used. Both solid and liquid peroxydicarbonates can be used in the process according to the present invention. A solution of peroxydicarbonate in an inert solvent, such as Sododecane, or in frozen flakes. Suitable inert solvents are known to a person skilled in the art. It is preferred to use a solid peroxydicarbonate, for example, in the form of flakes, finely divided particles (powder) or a liquid peroxydicarbonate, optionally adsorbed on or adsorbed on a suitable carrier, such as silica or polypropylene powder or fine spheres. The use of solid peroxydicarbonate allows a higher storage and processing temperature. This higher temperature is beneficial when the peroxydicarbonate is introduced into the extruder using feeders (weight loss). The peroxydicarbonates used in the process of the present invention have a half-life of one hour at a temperature of about 65 ° C. Suitable examples of peroxydicarbonates have the formula R1-OC (O) OOC (O) O-R2, where R1 and R2 are independently selected from the group consisting of CH3, 2-Y-C3H7O-C6H4, C2H5CH (CH3), 4-CH3-C6H4, Cl3CC (CH3) 2, C7H-i5, cC 6HnCH2, 3-t-C4H9-C6H5_ CI3Si (CH2) 3, C6H5, CH3CH (OCH3) CH2CH2I C6H5OCH2CH2, C6H5CH2, Z-C8H17CH = CH (CH2) 8, 2-CH3-C6H4, ( CH3) 2CHCH2CH (CH3), 3,4-di-CH3-C6H3, CI3C, CHCH (CI), CICH2, [C2H5OC (O)] 2CH (CH3), 3,5-d1-CH3-C6H3, C8H17, C2H5, C18H37, 2-0X0-1, 3-dioxolan-4-CH2, C2H5CH (CI) CH2, 4-CH30-C6H4, -C4H9, CH3SO2CH2CH2, C12H25, C6H5CH (CI) CH2, H2C = CHC (0) OCH2CH2, 4-NO2-C6H4, C4H9, C10H21, C4H9CH (C2H5) CH2, H2C = CHCH2, 2-CI-c-CeH? O, H2C = C (CH3) CH2, c-C6H .., CICH2CH2, 4- [C6H5-N = N] -C6H4CH2, C16H33, 1-naphthyl, 4-t-C4H9-C6H10, 2,4,5-tri-CI-C6H2, CI (CH2) 3, C H29, 9-fluorenyl, 4 -N02-C6H4CH2 2-i-C3H7-C6H4, CH3OCH2CH2, H2C = C (CH3), 3-CH3-C6H4, BrCH2CH2 > 3-CH3-5-C3H7-C6H3, Br3CCH2, C2H5OCH2CH2, 4-CH3OC (O) -CSHU, H2C = CH, i-C3H7, 2-C2H5CH (CH3) -C6H4, CI3CCH2, C5H11, C-C12H23. 4- t-C4Hg-C6H4, C6H13, C3H7, CH3? CH2CH2, C6H- | 3CH (CH3), CH3OC (CH3) 2CH2CH2, C3H7OCH2CH2, CH3OCH2CH (CH3) 2-i-C3H7-5-CH3-c- C6H9, C4H9OCH2CH2, t-C4H9, (CH3) 3CCH2 > where i = iso, t = tertiary, Z = cis, 5 c = cyclic. Preferred are bis (4-tert-butylcyclohexyl) peroxydicarbonate, dicetyl peroxydicarbonate, and dimyristyl peroxydicarbonate, which are solid peroxides at room temperature, and diisopropyl peroxydicarbonate, di-n-butyl peroxydicarbonate, and bis (2-ethylhexyl) peroxydicarbonate. ), which are liquids at room temperature, either in pure form or as a solution in isododecane. Optionally, a combination of peroxydicarbonates or peroxydicarbonates and other peroxides can be used to influence the flow rate of the molten material of the (co) polymer and / or increase the degree of modification of the (co) polymer. The amount of peroxydicarbonate to be used will depend of the desired degree of modification of PP and PP used. Preferably peroxydicarbonate concentrations are used in the range of 0.1 to 10 meq (= milliequivalents = millimoles of peroxide) per 100 g of PP, most preferably 0.25 to 5 meq / 100 g of PP. In another embodiment of the present invention, the method of The modification is carried out in the presence of a coagent to influence the melt flow rate of the (co) polymer and / or increase the degree of modification of the (co) polymer. By coagent is generally meant a polyfunctional reagent additive such as a polyunsaturated compound that will rapidly react with polymer radicals, overcome the steric hindrance effects and minimize undesirable side reactions. More information about the coagents is found in Rubber Chemistry and Technology, Vol 61 pp.238-254 and W Hofmann, Progress in Rubber and Plastics Technology, Vol. 1, No. 2, March 1985, p. 18-50. The term "coagent" has the same meaning as given in those publications. A wide variety of useful coagents are commercially available, including di- and triallyl compounds, di- and tri (meth) acrylate compounds, bismaleimide compounds, divinylbenzene, 1,3-diisopropenylbenzene and its oligomer, vinyltoluene, vinylpyridine, paraquinone dioxime, 1, 2 cis-polybutadiene and its derivatives. Particularly preferred coagents include triallyl cyanurate, triallyl isocyanurate, ethylene glycol dimethacrylate, and trimethylolpropane trimethacrylate. The incorporation of an effective amount of one or more of these coagents into the (co) polymer, before or during the reaction with the present compound tends to influence the melt flow rate and molecular weight of the modified (co) polymer. Although the process of the present invention can be carried out as an intermittent internal mixer (Banbury) process, it is preferably carried out as a continuous process. The PP obtained using the process according to the present invention, can be processed to a final product without additional adaptations if desired. The modified PP can be processed into the desired final product in all ways known to those skilled in the art, the processing conditions being generally dependent on the material and equipment used. Optionally, the modified PP can be purified, modified or molded in one or several steps, before its final processing. In addition, it can be further modified using another polymer or monomer in order to increase the compatibility of the final product with other materials. Alternatively, the modified PP can be degraded, or conversely, slightly interlaced, to increase its processing and / or application capacity. Generally, to obtain the desired final conventional adjuvants, in an amount known to one skilled in the art, such as antioxidants, UV stabilizers, lubricants, antidegradants, foaming agents, nucleating agents, fillers, pigments and / or antistatic agents are added to the PP . These adjuvants can be added to the PP before, during or after the modification step according to the invention. For example, an agent can be added which blows or gas can be injected into the extruder, before, during or after the modification, in order to produce foamed PP. Preferably, a stabilizer, for example one or more antioxidants, is added to render them harmless to any free radicals that are still present in the PP obtained as well as any radicals that could be subsequently formed from unreacted peroxide and / or subsequent processing under air / oxygen In a typical experiment, 0.01 to 1.0 parts per hundred parts of PP of an antioxidant are used. The PP obtained by the process of the invention does not show a substantial difference in the weight average molecular weight. It has been found that only the peroxydicarbonates give the increased melt strength desired in the process of the present invention. The diacyl peroxides and peresters did not give such an improvement in the melt strength of PP. Although you do not want to be limited by any particular theory, it is believed that the improvement in the fusion force is caused by modification of PP due to the formation of adducts alkylcarbonate polymers, the alkylcarbonate groups originating from the peroxydicarbonate used. The PP obtained by the process according to the present invention must be further processed, for example, by foaming, foam molding, extrusion, injection molding, blow molding, extrusion coating, profile extrusion or thermoforming. The modification reaction with peroxide can also be performed during such processing. The invention is illustrated by means of the following examples.

Experimental section The following materials and methods are used in the examples: Polypropylene: Hostalen® PPN 1042 polypropylene copolymer (granules), ex. Hoechst.

Novolen® 3200 HX random polypropylene (granules), ex. BASF.

Peroxides: Trigonox® EHP-C75 75% bis solution of (2-ethylhexyl) peroxydicarbonate in isododecane, ex. Akzo Nobel. Trigonox® NBP- 50% solution of dibutyl peroxydicarbonate in 50% isododecane C50, eg Akzo Nobel. Perkadox® 16 Bis (4-tert-butylcyclohexyl) peroxydicarbonate (pure), eg Akzo Nobel. Perkadox 26 Dimyristyl peroxydicarbonate (90%) ex. Akzo Nobel. Liladox® 90P Dicetyl peroxydicarbonate (90%) ex. Akzo Nobel.

Various components: Perkalink® 300 triallyl cyanurate (coagent), ex. Akzo Nobel Irganox® 1010 antioxidant, ex. Ciba Geigy Procedure A Mixing procedure The appropriate amount of the peroxydicarbonate and antioxidant was added to 300 g of polypropylene powder in a 3 liter bucket and mixed by hand stirring for 5 minutes at room temperature. The compounds were extruded immediately after mixing.

Procedure of the components All the compounds were modified by extrusion melting with a Haake extruder "TW100" of twin screws with intensive mixing screws attached to a "Rheocord System 40" Haake. During the experiment, the nitrogen was passed countercurrently from the hopper to the feeder. The extruder comprised a cylinder that included four consecutive temperature chambers, in which the first chamber had a temperature of 170 ° C; the second, 180 ° C; the third, 180 ° C; and the fourth chamber, 190 ° C. The screw speed was 50 rpm. The extruded strand was fed through a water bath and granulated with an automatic granulator "ASG5".

Procedure B Modification procedure The modification experiments were carried out in a 150 ml Buchi laboratory autoclave (special type BEP280). The initiator was diluted to 33% with isododecane and Primol® 352. The autoclave was filled with 50 grams of polymer / antioxidant mixture and after closing it, it was flushed with nitrogen (3 bars) followed by vacuum suction (3 times) to avoid the presence of oxygen. Then, the autoclave was heated (continuous flow of nitrogen, speed of the anchor stirrer: 150 rpm). At a polymer temperature of 155 ° C (measured by means of a PT100 thermocouple, directly inside the polymer), the appropriate amount of peroxide / solvent was injected into the autoclave. The autoclave was subsequently heated above 230 ° C for 5 minutes. The reaction mixture was then melted for about 15 minutes (total experimental time) as measured by the torque increase. Then, the reaction mixture was removed, cooled and granulated.

Procedure C The appropriate amount of the peroxydicarbonate and the antioxidant were added to the polypropylene homopolymer powder and mixed at room temperature. This mixture was combined with the PP homopolymer powder and dosed to the extruder or dosed separately together with the PP copolymer granules. All compounds were modified under melt extrusion in a twin screw extruder Werner & Pfeiderer ZSK 30. The extruder comprised a cylinder that included four consecutive temperature chambers, wherein the first chamber had a temperature of 100 ° C; the second and third, 180 ° Cm; and the fourth chamber, 190 ° C. The compounds were fed to the first chamber of the extruder. During the experiment the nitrogen was passed countercurrently from the hopper to the feeder. The screw speed was 200 rpm. The extruded strand was fed through a water bath and granulated with an automatic granulator "ASG5".

Test procedures The MFI (index of flow of molten material) that characterized the flow behavior of a molten PP, was measured with a Góttfert melt indicator (model MP-D) according to DIN 53735 and ASTM 1238 (230 ° C, load 21.6 N) The swelling in the die, ie the degree to which the extruded material is inflated in a direction perpendicular to the direction of extrusion after leaving the die, due to the elasticity of the molten PP, was determined by measuring the thickness of the strand leaving the melt indicator and subtracting the diameter of the nozzle (2.1 mm) and is the average value of ten measurements in mm. In the evaluation of the modified polypropylene, it was found that the swelling in the die was proportional to the melting strength. Resistance to fusion, for example, the ability of a molten PP to resist a taut elongation or narrowing without breaking, was measured using a Gottfert Reotens attached to a Rheograph capillary rheometer Gottfert (190 ° C, speed 0.5 mm / sec, acceleration 24 mm / sec2, length of the strand 70 mm). In tables 1 and 2 the data are presented in the comparative examples AG, preparation of PP without using a peoxidicarbonate, and examples 1-17 according to the process of the present invention (comparative examples C and D are controls with solvent without peroxide ). The amounts of peroxide are used as milliequivalents (mmoles of peroxide groups) of peroxide per one hundred grams of PP (meq / 100 g PP). The examples show an increase in die swelling and melt strength compared to PP prepared without using a peroxydicarbonate. The increase in swelling in the die is always related to the improvement of the elastic viscosity and the resistance to fusion. In table 2, the data on examples of homo-PP, co-PP and random PP, are shown as those obtained in the following procedure C (example 15-17, Comparative Examples F-G).

In procedure C, where a twin screw extruder Werner & Pfleiderer ZSK 30, an extrusion process of PP in scale production was simulated in which in a time of 30 seconds of residence the compounds are modified by fusion. During the extrusion process the temperature of the compound is increased from about 20 ° C (hopper) to about 190 ° C at the end of the extruder. In this procedure, the peroxydicarbonate is decomposed according to the Arrhenius equation depending on the temperature and residence times in the different temperature chambers of the extruder.

Arrhenius equation: Kd = _ e "-Ea / RT where: Kd = Constant rate for dissociation in sec "1 A = Arrhenius frequency factor in sec" 1 (for Liladox 90P: 3.02 E + 15) Ea = The activation energy for the peroxydicarbonate in J / mol (for Liladox 90P: 124.3E + 3) R = 8.3142 J / mol.KT = Temperature in K The concentration of the initiator at any time can be calculated by the equation: [l] = [lo] e Kd t where: [lo] = The original concentration of the initiator [I] = The concentration of initiator in time tt = the time in seconds Table 3 shows the amount of reacted peroxydicarbonate as a function of the temperature and residence time in the extruder, as calculated using the aforementioned equations. The temperature of the compound is taken as the average cylinder temperature and a linear profile temperature (20 ° C to 190 ° C in 30 seconds). In this process, more than 80% w / w of the peroxydicarbonate reacts with the PP above 120 ° C. Therefore, the increase in melt strength of PP, as a result of the reaction of peroxydicarbonate with PP, in an extrusion process occurs mainly above 120 ° C. The invention is not limited to the aforementioned description; rather, the required rights are determined by the following claims.

TABLE 1 vO TABLE 2 Comparative examples C-G and examples 13-17 OR TABLE 3 * Temperature of the compound in the hopper (time = 0) ts5

Claims (10)

NOVELTY OF THE INVENTION CLAIMS

1. A method for increasing the melt strength of polypropylene comprising the single step of reacting polypropylene with at least one peroxydicarbonate, in a reaction vessel at a temperature higher than 150 ° C and above 300 ° C, with the condition that the peroxydicarbonate is not in the form of an aqueous dispersion in a polar medium with at least 90% by weight of initiator particles, these being less than 50 μm and at least 99% by weight of the initiator particles being less than 65. μm, where the melting strength of the polypropylene is increased and by removing the reaction vessel a modified polymer is obtained at the melting point, suitable to form a final product.

2. The process according to claim 1, further characterized in that the peroxydicarbonate is reacted with molten polypropylene.

3. The process according to claim 1 or 2, further characterized in that the process is conducted in an extruder.

4. The method according to claim 2, further characterized in that the temperature is 160 to 250 ° C.

5. - The method according to claim 4, further characterized in that the temperature is 170 to 225 ° C.

6. The process according to any of the preceding claims, further characterized in that the peroxide comprises a peroxycarbonate.

7. The method according to any of the preceding claims, further characterized in that the peroxydicarbonate has the formula R1-OC (0) OOC (0) 0-R2, where R1 and R2 are independently selected from the group consisting of CH3, 2 -i-C3H70-C6H4, C2H5CH (CH3), 4-CH3-C6H4, CI3CC (CH3) 2, C7H15, cC 6H. .CH2) 3-t-C4H9-C6H5, CI3Si (CH2) 3, C6H5, CH3CH (OCH3) CH2CH2, C6H5OCH2CH2, C6H5CH2) Z-C8H17CH = CH (CH2) 8, 2-CH3-C6H4, (CH3) 2CHCH2CH ( CH3), 3,4-di-CH3-C6H3, CI3C, CHCH (CI), CICH2, [C2H5OC (O)] 2CH (CH3), 3,5-di-CH3-C6H3, C8H17, C2H5, C18H3, 2-oxo-1,3-dioxolan-4-CH2, C2H5CH (CI) CH2, 4-CH3O-C6H4, I-C4H9, CH3SO2CH2CH2l C12H25, C6H5CH (CI) CH2l H2C = CHC (O) OCH2CH2, 4-N02-C6H4, C4H9, C? 0H21, C4H9CH (C2H5) CH2, H2C = CHCH2, 2-CI-c-C6H10, H2C = C (CH3) CH2, c-C6Hn, CICH2CH2, 4- [C6H5-N = N] -C6H4CH2, C6H33, 1-naphthyl, 4-t-C4H9-C6H10, 2I4.5-tri-CI-C6H2, CI (CH2) 3, C? 4H29, 9-fluorenyl, 4-N02-C6H4CH2 2-i-C3H7-C6H4, CH3OCH2CH2, H2C = C (CH3), 3-CH3-C6H4, BrCH2CH2, 3-CH3-5-C3H7-C6H3, Br3CCH2, C2H5OCH2CH2) 4-CH3OC (0) -C6H4, H2C = CH, i-C3H7, 2-C2H5CH (CH3) -C6H4, Cl3CCH2, C5H11, cC? 2H23, 4-t-C4H9-CeH4, C6H13, C3H7, CH3? CH2CH2, C6H13CH (CH3), CH3OC (CH3) 2CH2CH2) C3H7OCH2CH2, CH3OCH2CH (CH3) 2-i- C3H7-5-CH3-c-C6H9, C4H9OCH2CH2) t-C4H9, (CH3) 3CCH2, where i = iso, t = tertiary , Z = cis, c = cyclic.

8. The method according to claim 7, further characterized in that the R1 and R2 are independently selected from the group consisting of CH3? C6H5OCH2CH2, 4-t-C4H9-C6H10, C16H33, (CH3) 3CH2CH (CH3) CH2CH2? Ci3H37, C4H9, c-CßH-ii, CH3CH (OCH3) CH2CH2, C3H7, i-C3H7 / C2H5CH (CH3), C10H2, C2H5, Ci4H29? C2HsCH (CH3), C6HsCH2? C-? 8H37, and C4H9CH (C H5) CH2

9. The process according to claim 8, further characterized in that the peroxydicarbonate is selected from the group consisting of bis (4-tert-butylcyclohexyl) peroxydicarbonate, dicetyl peroxydicarbonate. and dimyristyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-n-butyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, bis (2-ethylhexyl) peroxydicarbonate.

10. The process according to any of claims 7 to 9, further characterized in that the peroxydicarbonate is a liquid or preferably a solid at room temperature. 1. The process according to claim 10, further characterized in that the liquid is a peroxydicarbonate solution in an inert solvent, and is preferably bis (2-ethylhexyl) peroxydicarbonate or dibutyl peroxydicarbonate in isododecane. 12. The method according to any of the preceding claims, further characterized in that at least one co-agent is present in the reaction mixture when the polypropylene reacts with peroxydicarbonate. 13. Polypropylene having an increased melting strength that can be obtained using the method according to any of the preceding claims. 14. A process for producing an extrusion, spinning or blowing material under melting, molding, thermoforming or foaming based on a polypropylene, in which the polypropylene according to claim 13 is used.