DE102019115580B4 - Mixture of an organic matrix, low-molecular substances and at least two fractions of surface-modified polymer particles with different mean particle diameters and different particle size distributions, and methods for influencing the rheology of such a mixture - Google Patents

Abstract

Mixture containing an organic matrix, low molecular weight substances and at least two fractions of surface-modified polymer particles with different mean particle diameter and different particle size distribution, the polymer particles having a surface modification whose polarity, expressed as log POW1000, lies between the polarity of the polymer particles and the organic matrix and the polymer particles take up the low-molecular substances from the organic matrix in a controlled and time-controlled manner, in particular adsorb them, or release them to the organic matrix, in particular desorb them, and from the time the surface-modified polymer particles are added to the organic matrix, a time-controlled modification of the material properties of the matrix, in particular their rheological properties, within an absorption or adsorption time dependent on the glass transition temperature and the particle diameter of the polymer particles on time (time of absorption or adsorption, tA) or within a desorption time (time of desorption, tD), with the absorption or adsorption time (tA) and the desorption time (tD) being shorter than a technologically specified response time (tP), within which the material properties of the matrix adjust to a stable equilibrium after the addition of the polymer particles.

Description

The invention relates to a mixture containing an organic matrix, low-molecular substances and at least two fractions of surface-modified polymer particles with different average particle diameters and different particle size distributions, according to the preamble of claim 17, and a method for influencing the rheology, in particular the viscosity, of a mixture , which comprises an organic matrix, at least one polymer composition of surface-modified polymer particles and low-molecular substances.

When processing formulated materials, e.g. an organic matrix, the composition of the mixture is crucial. For example, the rheology (viscosity, thixotropy, shear thinning, rheopexy and dilatancy) of formulated materials can be altered by a wide variety of additives, organic or inorganic, soluble or insoluble. The viscosity can be reduced by adding soluble low molecular weight additives or by chemically reducing the molecular weight. The viscosity can be increased by adding soluble high molecular weight additives or by chemically increasing the molecular weight. As an undesirable side effect of these measures, other material properties of the formulated material, such as strength, elasticity, toughness, creep behavior, fracture behavior, are usually negatively influenced.

The addition of insoluble particulate additives to adjust the rheology is widely known. The rheological effect of particulate systems is due to their affinity to each other, which creates a temporary particle network in the matrix, which influences the rheology of the matrix. Examples of an aqueous matrix are dispersed sheet silicates or nanocellulose, and organically modified montmorillonite for an organic matrix. Micronized PTFE, for example, has a positive influence on the flow behavior of polymer melts. The particulate additives generally have a negative effect on the mechanical properties of the formulated material.

Furthermore, it is known that the rheology of organic matrices can be influenced by reducing the proportion of low-molecular substances, e.g. by extraction. Low-molecular substances from organic matrices can also be removed by particulate additives due to adsorption. A disadvantage of this method is the associated adsorption time and adsorption capacity.

From the DE 44 30 819 C1 discloses a bitumen mixture and a method for its production, the bitumen mixture containing powdered rubber and/or granulated rubber.

In "Construction and Building Materials 34(2012)", pages 83-90, an article entitled "Surface modified ground rubber tire by grafting acrylic acid for paving applications" has appeared, in which a surface modification of ground rubber tire particles in two different sizes (40 mesh and 300 mesh) is described by a polymerization of acrylic acid.

The object of the present invention is to reduce the adsorption time and thus the time it takes to achieve a desired rheology, in particular a desired viscosity, of a composition composed of an organic matrix and core-shell polymer particles introduced therein as a particulate additive.

According to the invention, this object is achieved in that, in the production of a composition which contains an organic matrix with low-molecular substances, core-shell polymer particles are introduced into the matrix in a multimodal particle size distribution. The low-molecular substances of the matrix are taken up, in particular adsorbed, by the core-shell polymer particles within a reaction time (adsorption time) that depends on the diameter of the individual core-shell polymer particles, so that the uptake, in particular the adsorption of the low-molecular substances on the fractions of the Core-shell polymer particles with different particle size distribution takes place within different adsorption times. By adding the core-shell polymer particles to the matrix in the form of several fractions with different particle size distributions, a time-controlled modification of the rheology of the composition can take place because of the adsorption times that are dependent on the diameter of the core-shell polymer particles. Thus, by adding the core-shell polymer particles with a multimodal particle size distribution, the establishment of a stable state with desired rheological properties of the composition can take place faster than with a monomodal particle size distribution of the core-shell polymer particles and in particular at least twice as fast.

Surprisingly, it was found that the adsorption time and the adsorption capacity of the core-shell polymer particles for a given organic matrix by a bimodal or multimodal particle size distribution in conjunction with a targeted selection of the polymer type of the core and the shell of the core-shell polymer particles to the Material properties and processing conditions of the organic matrix can be adjusted. The adsorption behavior is determined by the polymer type of the core. Due to the smaller polymer particles, the short-term adsorption of the low-molecular fractions from the organic matrix takes place in the initial phase, and the larger polymer particles determine the long-term adsorption capacity. The modification of material properties can be controlled over time by the ratio of the particle fractions of the core-shell polymer particles to one another. The shell of the core-shell polymer particles ensures the adaptation of the particle surface and connection to the organic matrix, which avoids a negative effect on other material properties.

1. a) einer organischen Matrix, die niedermolekulare Stoffe enthält, sowie
2. b) wenigstens zwei Fraktionen von Core-Shell-Polymerpartikeln mit unterschiedlicher Partikelgrößenverteilung, so dass die Core-Shell-Polymerpartikel in einer multimodalen, mindestens bimodalen Partikelgrößenverteilung vorliegen, wobei die Partikel beliebige Geometrie aufweisen können.

The invention thus discloses a composition consisting of the components

1. a) an organic matrix containing low molecular weight substances, and
2. b) at least two fractions of core-shell polymer particles with different particle size distributions, so that the core-shell polymer particles are present in a multimodal, at least bimodal particle size distribution, it being possible for the particles to have any geometry.

The invention also discloses a method for influencing the rheology, in particular the viscosity, of a composition consisting of the above components a) and b), the core-shell polymer particles being introduced into the matrix in a multimodal particle size distribution. In particular, the core-shell polymer particles in the process according to the invention are present in several fractions, each with a different particle size distribution, the particle size distributions of the several fractions differing from one another in each case by a different relative maximum of the particle size distribution. The relative maximum is understood to be the mean value of the particle size (mean radius or diameter) of the respective fraction. The particle size distribution of the individual fractions of the core-shell polymer particles has a Gaussian distribution around the mean value of the particle size.

Depending on the application, the composition can also contain customary additives.

In comparison to the addition of core-shell polymer particles with a unimodal particle size distribution into a matrix containing organic, low-molecular substances, the low-molecular substances of the matrix are taken up more quickly by the core-shell polymer particles in the composition according to the invention. The invention thus enables the rheological parameters, in particular the viscosity, of the composition to be influenced and adapted more quickly.

Is provided by the present invention, a composition of core-shell polymer particles with bimodal or multimodal particle size distribution of any geometry, the controlled low molecular weight substances from an organic matrix to which the polymer particles are added, can take up, whereby a time-controlled modification of material properties, in particular the rheology and above all the viscosity of the composition is achieved. The core-shell polymer particles have a core and a shell, with the core acting as an adsorbent and the shell adapting the particle surface and connecting it to the organic matrix. The smaller polymer particles (i.e. the polymer particles of the fractions with a small mean diameter) result in rapid, short-term adsorption of the low-molecular fractions from the organic matrix in the initial phase, and the larger polymer particles (i.e. the polymer particles of the fractions with a larger mean diameter) cause adsorption determines the long-term adsorption capacity. The modification of the material properties, in particular the rheology parameters such as viscosity, can be temporally controlled and in particular accelerated by the ratio of the particle fractions of the core-shell polymer particles to one another.

Advantageous developments, configurations and applications of the invention are specified in the dependent claims.

The invention is described below with reference to detailed embodiments.

The core-shell polymer particles according to the invention, also referred to below as polymer particles for short, can consist of one or more different polymers and can be crosslinked or uncrosslinked, filled or unfilled, filler-reinforcing or non-reinforcing, and of any geometry (dimension, dimensions and form factor (aspect ratio ), length-to-thickness ratio).

Core-shell polymer particles (or also called core-shell polymer particles) are understood to mean particles with a core made of a polymer material and a shell made of another polymer material or a polymer material that is mixed with another organic or inorganic material.

Polymer material in this sense are, for example, polymeric hydrocarbons such as polyolefins, halogenated derivatives thereof, elastomers such as caoutchouc, rubber etc., epoxy resins, polyurethanes, polyesters, polycarbonates, polyureas, polyimides, acrylic resins, alkyd resins, and others.

The polymer particles can be produced by known methods, such as suspension or dispersion polymerization, and brought into particle form by grinding, precipitation, spray drying, sieving, fractionating, centrifuging, etc.

Separating agents of any nature and size can be added to enable pourability or flowability during storage, transport, processing, dosing, etc.

The matrix of the compositions according to the invention consists of organic material, in particular a formulated material which contains low-molecular substances. The matrix can be, for example, plastics, especially plastic mixtures, caoutchouc, adhesives or the like. The organic matrix can serve as a coating, adhesion promoter, adhesive, printing ink, etc. The organic material of the matrix can be mixed with other substances, for example with a polymer material, and contain silicon dioxide, talc, montmorillonite, bentonite, kaolin, soot, fine polymer powder, color pigments, or wax particles.

An organic matrix within the meaning of the invention can be a fluid at room temperature or at an elevated temperature of 100-200° C. or 150-300° C. or 200-400° C. which contains low-molecular fractions. The organic matrix is generally present as a mixture, dispersion, suspension, emulsion or mixed forms thereof, with a fluid component preferably having a lower kinematic viscosity at the intended application temperature, in particular the low-molecular component, than the entire organic matrix. As a result, the organic matrix is able to interact with the core-shell polymer particles via the low-molecular fraction. Examples of such organic matrices are bitumen, adhesives, synthetic resins, fluid plastics, paint binders, tars, pitches, rubbers, natural resins, adhesion promoters, printing ink, etc., all of which can optionally have additives and fillers added to them.

In order to obtain fractions of the polymer particles with different particle sizes or different particle size distributions, the core-shell polymer particles can be classified after their production. As an alternative to this, during the production of the polymer particles, a comminution process can be set from the outset in such a way that fractions with a desired particle size distribution are already produced during the production process.

The particle fractions obtained in this way with different particle size distributions can then be mixed in the desired ratio. In this way, a mixture of particle fractions, each with a different particle size distribution, can be produced, which has a multimodal particle size distribution. If, for example, two fractions with different particle size distributions and in particular with different mean particle size values (mean diameter or radius) are mixed, a bimodal particle size distribution is obtained. Correspondingly, a mixture of particle fractions with a multimodal particle size distribution can be obtained if more than two fractions with different particle size distributions are mixed.

The particle fractions with different particle size distributions can be mixed before or during introduction into the organic matrix.

Exemplary particle sizes are in a bimodal distribution in the range from 50 to 150 μm for the smaller particle size and in the range from 180 to 250 μm for the larger particle size. Preferred lies the value of the average particle size in a bimodal distribution for the smaller particle fraction at least 100 µm and for the larger particle fraction at least 200 µm.

In the case of a bimodal particle size distribution of the core-shell polymer particles, the particle size distribution contains a first and a second relative maximum of the (mean) particle size, the ratio of the second relative maximum to the first relative maximum preferably being at least 2.

The first derivative of the particle size distribution curve determined by laser diffraction of a representative sample (fraction of polymer particles) changes sign at least three times over the entire course (from + to - to + to -), whereas the second derivative of the particle size distribution curve passes through zero at least three times, i.e. two maxima and a minimum in between. With a multimodal distribution, the number of maxima and minima increases accordingly.

The distance between a minimum and the two neighboring maxima (= peak height) should be significant and be at least 5% of the distance between the zero line and the highest maximum.

As described above, a bimodal or multimodal distribution of polymer particles can be achieved by suitable process control in situ during the production of the polymer particles or by subsequent mixing or post-processing. According to the invention, the resulting mixtures of several fractions of polymer particles with different particle size distributions (bi- or multimodal) are introduced into the matrix.

The proportion by weight of the core-shell polymer particles introduced into the matrix, based on the total weight of the composition, can be between 0.1 and 90% by weight, preferably between 0.5 and 70% by weight and particularly preferably between 1 and 50% by weight. % lie. The fraction of the core-shell polymer particles introduced into the matrix, which has a particle size distribution with the smallest relative maximum, can expediently have a weight fraction of 0.1 to 99.9%, preferably 5 to 95% and particularly preferably 10 to 90 % exhibit.

As stated above, a surprising reduction in adsorption time is achieved through the use of a multimodal particle size distribution of the core-shell polymer particles.

wobei $${\text{D}}_{\text{P}}={10}^4*\text{EXP}\left[\left(-\mathrm{0,06}*{\text{T}}_{\text{g}}+2\right)-\mathrm{0,1351}*{1000}^{2/3}+\mathrm{0,003}*1000-10545/\text{T}\right]{\text{in cm}}^2/\text{s}$$

The adsorption time (t _A in seconds) of the core-shell polymer particles for low-molecular substances (with a reference molecular weight of the low-molecular fraction of 1000 g/mol) results from the particle diameter (d in cm ² - determined, for example, via laser diffraction), the polymer type, described by its glass transition temperature (Tg in °C) and temperature (T in K) as follows: $${\text{t}}_{\text{A}}={\left(\text{i.e}/2\right)}^2/\left(6*{\text{D}}_{\text{P}}\right)$$

whereby $${\text{D}}_{\text{P}}={10}^4*\text{EXP}\left[\left(-0.06*{\text{T}}_{\text{G}}+2\right)-0.1351*{1000}^{2/3}+0.003*1000-10545/\text{T}\right]{\text{in cm}}^2/\text{s}$$

Nichtpolymere Bestandteile, z.B. anorganische Feststoffe oder niedermolekulare Stoffe mit einem Molekulargewicht < 1000 g/mol, werden bei der Berechnung der Glasübergangstemperatur der Polymermischung nicht berücksichtigt, d.h. der polymere Anteil stellt das Bezugsgewicht dar und die Gewichtsanteile der n Polymeren werden darauf bezogen.If the polymer particles consist of a polymer mixture, ie a number of n polymers, the glass transition temperature of the mixture is calculated from the glass transition temperatures of the n polymers and their proportion by weight (x _n ) as follows: $$\frac{1}{T_G}=\frac{x_1}{T_{G\mathrm{,1}}}+\frac{x_2}{T_{G\mathrm{,2}}}+\cdots +\frac{x_n}{T_{G,n}}$$

Non-polymeric components, e.g. inorganic solids or low-molecular substances with a molecular weight < 1000 g/mol, are not taken into account when calculating the glass transition temperature of the polymer mixture, ie the polymer component represents the reference weight and the weight components of the n polymers are based on this.

Another relevant parameter for the material system to be considered is the adsorption capacity. The adsorption capacity results from the amount of polymer particles added and the distribution equilibrium of the low-molecular substances between the organic matrix and the polymer particles.

One of the objects of the present invention is to reduce the settling time, ie to achieve the desired material property in the shortest possible time. The response time (t _P in s) is therefore the time up to which certain material properties defined for technological reasons for the intended application are to be achieved.

The shell (shell) of the core-shell particles can be achieved, for example, by surface modification using one or more polymers with a molecular weight (weight average) of at least 1000 g/mol with functional segments that interact with both the polymer particles and the organic matrix can occur into which they are introduced. The polarity of the surface modification, expressed as the octanol/water partition coefficient Kow, lies between the polarity of the particle surface and the polarity of the organic matrix, but is closer to the polarity of the particle surface than to the polarity of the organic matrix. That is, the affinity K _P,M of the surface modification (OM) is greater for the particle surface (P) than for the organic matrix (M).

For example, the software EPI-Suite of the US Environmental Protection Agency (www.epa.gov) can be used to calculate the octanol/water partition coefficient. The SMILES notation is generated from the chemical structure of the segment or partial area and transferred to the EPI-Suite software. This then calculates the corresponding octanol/water partition coefficient.

The octanol/water partition coefficient of polymers or surfaces is calculated from a segment or sub-area with a molecular weight that is closest to 1000 g/mol.

In the case of heterogeneous polymers, e.g. block copolymers with a number of n segments (S), the octanol/water partition coefficient is calculated for each chemically uniform segment and weighted using the weight fraction (x _n ) as follows: $$lOG{P}_{O/W}^P=x_1\ast lOG{P}_{O/W}^{P_{S1}}+x_2\ast lOG{P}_{O/W}^{P_{S2}}+\cdots +x_n\ast lOG{P}_{O/W}^{P_{Sn}}$$

If the segments have a molecular weight of less than 1000 g/mol, the polymer is considered to be homogeneous with statistically distributed functional groups and the octanol/water partition coefficient is calculated for a representative segment.

Die Affinität K_P,M der Oberflächenmodifikation (OM) zu der Partikeloberfläche (P) und zu der organischen Matrix (M) berechnet sich wie folgt: $$K_{P,M}=\frac{{\left(log{P}_{O/W}^P-log{P}_{O/W}^{OM}\right)}^2}{{\left(log{P}_{O/W}^{OM}-log{P}_{O/W}^M\right)}^2}$$

Die Oberflächenmodifikation kann in einem oder mehreren Schritten als Feststoff, aus Lösung oder Dispersion, durch Sprühen, durch Bedampfen oder dergleichen aufgebracht werden. Dazu gehört auch die Modifikation der Partikeloberfläche durch mechanische, thermische, chemische oder energetische Behandlung, wodurch sich eine Oberflächenmodifikation ergibt und geeignete Core-Shell-Polymerpartikel erzielt werden können. Die Oberflächenmodifikation kann vernetzt oder unvernetzt sein, um eine bessere Anbindung an die Partikeloberfläche zu gewährleisten.In the case of heterogeneous surfaces, e.g. polymer particles with different fillers, some of which are on the surface, with a number of n sub-areas (F), the octanol/water distribution coefficient is calculated for each chemically uniform sub-area and the area proportion (f _n ) weighted as follows: $$lOG{P}_{O/W}^P=f_1\ast lOG{P}_{O/W}^{P_{f1}}+f_2\ast lOG{P}_{O/W}^{P_{f2}}+\cdots +f_n\ast lOG{P}_{O/W}^{P_{fn}}$$

The affinity K _P,M of the surface modification (OM) to the particle surface (P) and to the organic matrix (M) is calculated as follows: $$K_{P,M}=\frac{{\left(lOG{P}_{O/W}^P-lOG{P}_{O/W}^{OM}\right)}^2}{{\left(lOG{P}_{O/W}^{OM}-lOG{P}_{O/W}^M\right)}^2}$$

The surface modification can be applied in one or more steps as a solid, from solution or dispersion, by spraying, by vapor deposition or the like. This also includes the modification of the particle surface by mechanical, thermal, chemical or energetic treatment, which results in a surface modification and suitable core-shell polymer particles can be achieved. The surface modification can be crosslinked or uncrosslinked in order to ensure better attachment to the particle surface.

In order to be able to process the core-shell polymer particles obtained in this way more easily, they should remain free-flowing. In order to achieve this, release agents such as calcium carbonate, talc, starch or cellulose or mixtures thereof can be used and added to the polymer particles.

The invention is explained below using an example of a bitumen/rubber powder system, the matrix being formed by a bitumen mixture into which polymer particles in the form of rubber particles are introduced according to the invention.

Example:

Ground rubber particles from scrap tires with surface modification in bitumen

Ground rubber particles, which can be obtained from used tires, for example, essentially consist of synthetic rubber, natural rubber, carbon black, silica, oil and processing aids such as crosslinkers, accelerators, stabilizers or lubricants.

A bimodal particle size distribution with relative maxima of the average size of the rubber particles at 800 μm and 400 μm is provided by grinding with suitable comminution devices (e.g. by cryo-grinding or the like) or by separating methods such as sieving or classifying.

Due to the mechanical grinding, the rubber particles essentially consist of a rubber core and a carbon black shell surrounding the core.

After grinding, the surface of the rubber particles is modified with polyoctenamer. The affinity of the cis double bond in the polymer chain of the polyoctamer for the carbon black particles adhering to the particle surface plays an important role.

The viscosity of bitumen is too low in some road construction applications (e.g. split mastic asphalt, porous asphalt). In order to prevent the bitumen from running out of the hot asphalt mix, the viscosity of the bitumen must be increased. Traditionally, this is achieved by adding finely ground cellulose fibers.

A comparative test has shown that when rubber particles are added in a monomodal particle size distribution with a (mean) diameter of 800 µm, it takes about 1 hour for the viscosity to increase sufficiently through adsorption of the low-molecular substances in the bitumen on the rubber particles. This period of around 60 minutes is far too long for practical applications, e.g. in road construction. However, if according to the invention, in addition to the fraction of rubber particles with a particle size distribution around the mean of 800 μm, a further fraction of rubber particles with a particle size distribution around a mean diameter of <400 μm is added, the viscosity of the bitumen increases sufficiently within 5 minutes Scope. The resulting shorter adjustment time of approx. 5 minutes thus meets the typical requirements for asphalt mixing times in road construction.

The adsorption of the low-molecular substances from the bitumen matrix on the rubber particles continues over the larger particle fraction of the two rubber particle fractions both during and after the laying of the asphalt and leads to a more stable and resilient asphalt pavement than without the addition of rubber particles or rubber particles in a monomodal particle size distribution.

Claims (24)

Mixture containing an organic matrix, low molecular weight substances and at least two fractions of surface-modified polymer particles with different mean particle diameter and different particle size distribution, the polymer particles having a surface modification whose polarity, expressed as log P _OW ¹⁰⁰⁰ , lies between the polarity of the polymer particles and the organic matrix and the polymer particles take up the low-molecular substances from the organic matrix in a controlled and time-controlled manner, in particular adsorb them, or release them to the organic matrix, in particular desorb them, and from the time the surface-modified polymer particles are added to the organic matrix, a time-controlled modification of the material properties of the matrix, in particular their rheological properties, within an absorption or adsorption range dependent on the glass transition temperature and the particle diameter of the polymer particles option time (time of absorption or adsorption, t _A ) or within a desorption time (time of desorption, t _D ), the absorption or adsorption time (t _A ) and the desorption time (t _D ) being less than a technologically specified response time ( t _P ) is within which the material properties of the matrix adjust to a stable equilibrium after the addition of the polymer particles. blend after claim 1 , wherein the particle size distribution of the polymer particles has at least two maxima, the mean particle diameters of the at least two maxima being apart by a factor of at least 1.2. Mixture according to one of the preceding claims, wherein the fraction of the polymer particles with the smallest mean particle diameter has a weight fraction of 0.1 to 99.9% by weight, preferably 5 to 95% by weight and particularly preferably 10 to 90% by weight in the mixture of polymer particles. Mixture according to one of the preceding claims, wherein the polymer particles have any geometry. Mixture according to one of the preceding claims, wherein the proportion by weight of the polymer particles in the total weight of the mixture is between 0.1 and 90% by weight, preferably 0.5 to 70% by weight and particularly preferably 1 to 50% by weight . Mixture according to one of the preceding claims, wherein the mixture contains release agents, whereby the polymer particles are free-flowing. Mixture according to one of the preceding claims, in which the low-molecular substances are originally contained in the surface-modified polymer particles or are attached to them and migrate into the matrix by diffusion and have become embedded therein. Mixture according to one of the preceding claims, in which the low-molecular substances are originally contained in the matrix and have been accumulated, in particular adsorbed or incorporated, by diffusion on or in the polymer particles. Mixture according to one of the preceding claims, characterized in that the surface-modified polymer particles contain a core made of a first polymer material and a shell surrounding the core made of a second polymer material different from the first polymer material. Mixture according to one of the preceding claims, characterized in that the particle size distribution of the polymer particles has at least a first and a second relative particle size maximum, the ratio of the particle size of the second relative maximum to the first relative maximum being at least 2. Mixture according to one of the preceding claims, characterized in that the particle size distribution of the polymer particles has a bimodal or multimodal particle size distribution with a plurality of relative maxima of the (average) particle size, the smallest relative maximum of the fractions of the polymer particles with different particle size distribution being in the range from 50 to 150 µm and in particular 100 µm or more. Mixture after one of Claims 10 or 11 , the relative maximum following the smallest relative maximum being in the range from 180 to 250 μm and in particular 200 μm or more. Mixture according to one of the preceding claims, characterized in that the particle size distribution of the polymer particles has at least a first and a second relative maximum, the first relative maximum being in the range from 50 to 150 µm and in particular at 100 µm and the second relative maximum above 200 µm lies. blend after Claim 13 , where the distance between the peak height of a relative minimum and the peak height of the two relative maxima surrounding the minimum is at least 5% of the value of the peak height of the highest relative maximum. Mixture according to one of the preceding claims, wherein the fraction of the polymer particles which has a particle size distribution with the smallest relative maximum of the mean particle diameter has an area percentage of 0.1 to 99.9% based on the total area of the curve of the particle size distribution and preferably an area percentage of from 5 to 95% and more preferably from 10 to 90%. Mixture according to one of the preceding claims, in which the matrix is a bitumen mixture and the polymer particles are ground rubber particles. Method for influencing the rheology, in particular the viscosity, of a mixture which comprises an organic matrix, at least one polymer composition of surface-modified polymer particles and low-molecular substances, characterized in that the surface-modified polymer particles are in the form of at least two fractions of surface-modified polymer particles with different mean particle diameters and different particle size distribution are introduced into the matrix, the polymer particles having a surface modification whose polarity, expressed as log P _OW ¹⁰⁰⁰ , lies between the polarity of the polymer particles and the organic matrix and the polymer particles take up low-molecular substances from the organic matrix in a controlled manner, in particular by adsorption, or deliver to the organic matrix, in particular by desorption, starting from the point at which the surface-modified polymer particles are added to the organic matrix, a time-controlled modification of the material properties of the matrix, in particular its rheological properties, within an absorption or adsorption time (time of absorption or desorption, t _A ) dependent on the glass transition temperature and the particle diameter of the polymer particles or within a desorption time (time of desorption, t _D ) takes place, with the absorption or adsorption time (t _A ) and the desorption time (t _D ) being less than a technologically specified response time (t _P ), within which the material properties of the matrix are stable after the addition of the polymer particles adjust balance. procedure after Claim 17 , wherein the low-molecular substances originally contained in the surface-modified polymer particles or are attached thereto and migrate into the matrix by diffusion and become embedded therein. procedure after Claim 17 , wherein the low-molecular substances are originally contained in the matrix and, after diffusion from the matrix, are absorbed on or in the polymer particles, in particular adsorbed or embedded. procedure after Claim 17 , characterized in that the low-molecular substances are originally contained in the matrix and are taken up by diffusion on or in the polymer particles, in particular adsorbed or embedded, with the uptake of the low-molecular substances taking place on the different fractions of the polymer particles with different particle size distributions within different uptake times. procedure after Claim 17 , characterized in that the low-molecular substances are originally contained in the surface-modified polymer particles or are attached thereto and migrate into the matrix by diffusion and become embedded therein, with the diffusion of the low-molecular substances from the different fractions of the polymer particles with different particle size distributions taking place within different diffusion times. Procedure according to one of claims 17 until 21 , wherein a release agent is added to the polymer particles in order to make the polymer particles free-flowing. procedure after Claim 17 , characterized in that a first fraction has a particle size distribution with a first relative maximum at a first mean particle size and a second fraction has a particle size distribution with a second relative maximum at a second mean particle size, the second mean particle size being at least twice as large as that first mean particle size. Procedure according to one of claims 17 until 23 , where the matrix is a bitumen mixture and the polymer particles are ground rubber particles.