DD300170A7 - Process for the preparation of porous suspension polymers of Vc - Google Patents

Abstract

The invention relates to a process for the preparation of porous vinyl chloride suspension polymers in the K value range of 58 to 72, independently of the polymerization temperature used, using a secondary dispersant combination having a degree of increase in the porosity of the PVC powders of * kg of secondary dispersant per 100 kg Vinyl chloride allowed at the same time improved morphological homogeneity and advantageous stability against thermooxydative degradation. As a secondary dispersant is a mixture of a partially saponified polyvinyl acetate having a content of free hydroxyl groups of 0.45 to 0.55 mol / mol with a K value of Fikentscher 35-45, as 20 to 30% alcoholic solution * and calcium Stearoyl-lactoyl-lactate (II) in a total concentration of both components from 0.00001 to 0.008 kg / kg VC are used. The mixing ratio of I to II is 1: 0.05 to 1: 8, depending on the secondary dispersant concentration. At a total concentration of the mixture of 0.00001 to 0.0014 kg / kg of VC, the ratio of I (based on a 25% alcoholic solution) to II is 1: 0.6 to 8, at 0.0015 to 0.0029 kg / kg VC 1: 0.4 to 3, at 0.003 to 0.0049 kg / kg VC 1: 0.2 to 1.2 and at 0.005 to 0.008 kg / kg VC 1: 0.05 to 0.6. {polyvinyl chloride; suspension; dispersants; Hilfsdispergatoren; Sekundaerdispergatorkombination; polyvinyl acetate; partially saponified polyvinyl acetate; Calcium stearoyl-lactoyl-lactate; dispersant concentration}

Description

In said DE-PS are mixed esters of hydroxycarboxylic acids having up to 6 carbon atoms and partial esters of saturated or olefinically unsaturated monomycarboxylic acids and polyols having defined chain lengths and OH group contents or their esters with hydroxycarboxylic acids in the presence of known Prirnärdispergatoren, preferably cellulose ethers and Polyvinylalkohoien than Dispersing aid for the VC polymerization used to increase the porosity. The disadvantage of this method is, on the one hand, that strong grain / coarsening occurs and, on the other hand, the resulting polymers have a pronounced tendency to electrostatic charge. In addition, the porosity and plasticizer absorption decreases again at comparatively low increases in concentration. The resulting polymers are thus greatly limited in their applications due to their property picture. Finally, the disadvantage of the comparatively high proportion of extraneous, easily traceable and migratable constituents in the PVC is mentioned, which has a detrimental effect especially in the application of the processing products in the Lebensnv ttelindustrie and medicine (DD 213105).

Attempts have been made to eliminate some of these negative side effects by using surfactants with particular molecular and structural makeup. Thus, it is known that when using glyceride esters of different composition containing a certain proportion of unsaturated constituents (DD 141316), the shell formation can be suppressed and the thermal stability of the PVC can be improved. The disadvantage of these compounds, however, is that they reduce the rate of polymerization and thus lead to a reduction in the space-time yield. Also, the efficiency of these glycoride esters on porosity is not very high. By using glyceride esters of mixtures of hydrogenated fatty acids on an animal basis with a defined concentration of the Cu-Cje fraction and an iodine number = s 5 (DD 202879), although the space-time yield is increased and the peroxide consumption is lowered, but only rates of increase in the porosity of 1-2.5%, based on an adjuvant concentration of 0.10 kg, based on 100 kg of vinyl chloride achieved. The problem of the high proportion of low molecular weight products in the PVC and the tendency for increased shell formation can not be solved either. DD 200024 adds ethylene-propylene oxide adducts of defined structure and composition for the polymerization, which at the same time increase the porosity and suppress foam formation. However, at higher concentrations, this type of compound leads to a drastic increase in the thermal and thermo-oxidative degradation of the PVC chain and to an impermissible grain coarsening. The morphological uniformity of the grain is not as high as, for example, when using sorbitan fatty acid esters. Also, the rate of increase in porosity, especially at low K values of the PVC, can not meet higher demands. In DD 218105 citric acid esters are used which have a defined content of α-monoglyceride, citric acid and free double bonds in order to simultaneously solve the problem of the medical suitability of the PVC processing products. However, these esters are very low in their porosity promoting effect. The same drawback occurs when sorbitol esters are added which have a solid consistency at room temperature and are liquid under polymerization conditions (DE 2740 209) or, as in DE 2701971, dialkyl esters having a C number of the alcohol component of 1-12 be used as a secondary disperser. The effects of adding sugar esters of aliphatic acids, although mixtures of mono-, di- and triesters may also be used, as described in DE 2509998, and those of using a polyacrylate-based anionic surfactant (DE 2648833) are likewise not so great. It is equally possible for high and low K values of the PVC to produce PVC powders with sufficient porosity, comparable high morphological homogeneity, sufficient thermostability and a low content of oversize and undersize.

It is known from DE 3047164 to use water-insoluble soaps of higher carboxylic acids with at least one double bond in order to achieve a high increase in porosity with comparatively low bulk density drop and low material input, with the actual active ingredient only forming "in situ" shortly before or during the polymerization. The levels of use required to increase the porosity are very low, but as a result, there are significant problems in evenly distributing the components, and it is not possible to produce processed products with a small number of specks in the porosity, morphological homogeneity and demonomerizability of products of different K values (DD 229704) can not be almost eliminated In order to improve the distribution of the secondary dispersant, the organic components in DE 304 7164 dissolved in xylene. However, this practice leads to a load on the wastewater and the VC recovery system. On the other hand, the PVC primary particles from XyIo! swelled, which in turn partially counteract the increase in porosity and the ease of demonomerizability. Higher use concentrations of the compounds described in DE 3047164 lead to an unacceptably high retardation of the polymerization, to strong coarsening phenomena of the grain mixture and to a disproportionately low rise in porosity or even to a decrease in porosity. Although the use of alternative secondary dispersants based on macromolecular surface-active compounds (wit) the addition of low-saponified polyvinyl acetate (DE 2 950 294, DE 2633087, EP 30048, GB1524492) causes a comparatively high increase in porosity at low K values, the efficiency is, however, measured that of sorbitol esters, but not so pronounced at high K values. Disadvantages are also a deterioration of the thermal stability with increase of the use concentration, an increased occurrence of flotation phenomena in the polymerization reactor, as a result of which dreaded lumping or at low output leads to coarsening phenomena in the solid suspension and charging phenomena in the dried powder, resulting in a reduction or in extreme cases may even lead to a loss of flowability. Since the partially hydrolyzed polyvinyl acetates must be added in organic solution, an increase in the total concentration inevitably leads to a higher load on the wastewater. The morphological uniformity is good, but it also does not meet very high requirements for separate applications of PVC. It is known to modify VAc polymers by copolymerization of vinyl acetate with N-containing monomers and to use inter alia in combination with ethylene-propylene oxide adducts to increase porosity, wherein the speckling and the content of residual monomers are reduced (DE 3003778). However, the production of these products is considerably more expensive. The bulk density drop is comparatively large, the grain size distribution is wider. In order to increase the effects on the formation of a favorable morphology for the application and processing of the PVC, without cumbersome and costly methods for the synthesis of novel particle dispersants are required and adversely affect the grain formation process has been tried in the past, known secondary dispersants in Use combination with each other. Either are, as with the

Mixture of partially hydrolyzed high-acetate polyvinyl acetates and fatty acid esters of sorbitan, the components are highly incompatible with one another, so that there are signs of segregation, as a result of increased precipitation and deposit formation occurs, which can lead to complete instability of the dispersion, or give the Sekundärdispergatormischungen PVC qualities in which the positive and negative influences of the individual components are additive. The use of such mixtures is then not interesting for the practice, since the technological effort is unnecessarily increased and a separate storage, metering and quality input control of the individual components is required. In case of deviations of the PVC quality characteristics from the given standard beyond an assignment of the possible influencing factors is difficult. In DE 2683025, partial esters and ethers of polyhydric alcohols and waxes of oligomeric ethylene oxide adducts are added to the polymerization, thereby achieving both a reduction in shell formation in the reactor and also an improvement in the processing of the PVC powder. However, these blends hardly cause an increase in porosity, there are large differences in morphological homogeneity between low and high K PVC powders, and thermal stability is also compromised by the use of the secondary dispersant blend.

Object of the invention

The aim of the invention is the material-economical production of porous and morphologically homogeneously constructed suspension polymers of the VC for a broad molecular weight range.

Defection of the essence of the invention

The invention has for its object to provide a process for the preparation of porous, homogeneously constructed suspension polymers of the VC for a K value range of 58 to 72, which tion at a technically permissible pressure up to 14atü without further Polymeri tion is adjustable by temperature control, under Using a Sekundärdispergatorkombination that regardless of the polymerization temperature used a degree of increase in the polymer porosity of> 4% / 0.1 kg secondary dispersant, based on 100 kg of VC, and at a given Sekundärdispergatorkonzentration a 20% higher internal porosity with improved morphological homogeneity and homogeneity advantageous stability to thermo-oxidative degradation and narrower particle size distribution than at the same concentration of the individual components of the Sekundärdispergatormischung causes.

According to the invention the object is achieved in that as a secondary dispersant, a mixture of a partially saponified polyvinyl acetate having a content of free hydroxyl groups of 0.45 to 0.55 mol / VoI as 20 to 30% strength alcoholic solution

(I) with a Kik value of 35-45 according to Fikentscher and calcium saeoyl-lactovl-lactate (II) in a total concentration of both components of 0.00001 to 0.008 kg / kg of VC, wherein the mixing ratio of I to Il is 1: 0.05 to 1: 8 and is set differently depending on the secondary dispersant concentration.

The calcium stearyl lactoyl lactate is characterized by a saponification number of 260 to 280 mg KOH / g, an acid number of 110 to 118 mg KOH / g and an iodine number of S 2.

At a total use concentration of the secondary dispersant mixture of 0.00001 to 0.0014 kg / kg of VC, the ratio of I (based on 25% alcoholic solution) to II is 1: 0.4-8, at a concentration of 0.0015-0 , 0029kg / kg VC 1.0.4-3, at a concentration of 0.003-0.0049kg / kg VC1: 0.2-1.2 and at a concentration of 0.005-0.008kg / kg VC 1: 0.05-0 ,. 6

The K value of the partially hydrolyzed polyvinyl acetate is determined in 4% solution of a 1: 1 mixture of H ₂ O and isopropanol. The internal porosity of the PVC grain is determined alternatively by means of Hg Porosimeter Carlo-Erba and by determining the maximum possible plasticizer (DOP) uptake at normal temperature. To assess the morphological homogeneity of the PVC powder two different methods are used. On the one hand, the desorption of a PVC powder applied with a constant amount of vinyl chloride is monitored and from this the proportion of particularly compact, hardly demonomerizable particles and the mean diffusion layer thickness are determined.

On the other hand, the PVC powder is added under defined conditions with an oil and the penetration of the oil into the powder by the different levels of brightness are converted into spectral colors, followed over time. From the measured values, the proportion of grain that is not penetrated by the oil can be determined very accurately at arbitrary times and thus make statements about the homogeneity of the powder.

Of particular importance when using the solution according to the invention is that it is possible to realize a diffusion rate of the vinyl chloride from or an oil or plasticizer in the PVC Kor η, which at K values 60 60 comparable to those of the K values a70, which is not possible with previously known solutions.

If the concentrations and concentration ratios of the two components according to the invention are maintained, a high basic stability of the PVC compared with thermo-oxidative degradation is also achieved. Detection is carried out by determining the total stability time or the incubation time until the measurable discharge of HCl from the PVC.

embodiments example 1

The free-radical polymerization of the vinyl chloride in suspension takes place in a pressure reactor equipped with an impeller stirrer, flow-conducting devices and temperature and pressure measuring devices.

135Tl are used. Demineralized water, 78.6Tl. Vinyl chloride, 0.056Tl. _NaHCO3 and 4,5Tl. a 1% aqueous solution of a 1: 1 mixture of a commercially available methylhydroxypropylallulose (DSmh = 1.8, MSp ₀ - 0.21 and e _2% = 54c Pa) and a partially hydrolyzed polyvinyl acetate (VAc content 0.25 mol / mol, KW = 42).

As a secondary dispersant is a mixture of 0.126Tl. a 25% strength methanol solution of a partially hydrolyzed polyvinyl acetate (residual acetate content 0.46 molar, KW = 38.8) (I) and 0.0786Tl. Ca-stearoyl-lactoyl-lactate (II) used. The free-radical formers used are 0.01 TI. Di-lauroyl peroxide and 0.024 part. Di-Cetylperoxidicarbonat. The total mixture is thoroughly pre-dispersed for 15 minutes and then brought to a polymerization temperature of 71 ⁰ C. 270 min after reaching the set temperature, the pressure drop starts. From this time on, polymerization is continued for a further 30 minutes and the reactor is subsequently depressurized. Under standard conditions, the removal of the unreacted vinyl chloride from the aqueous suspension and the drying of the powder.

The characteristic data of the PVC powder are compiled in Tab. Despite the low molecular weight, the product has high internal porosity, excellent morphological homogeneity, favorable desorption behavior, balanced thermal stability and narrow particle size distribution (Table 2).

Example 2 The polymerization is carried out analogously to Example 1. In a modification to Example 1, the Total secondary dispersant concentration to 0.34 part. (0.004 kg / kg VC) while increasing the ratio of components I to Il changed to 1: 0.47. After the polymerization and workup, a PVC powder is obtained, which compared to Example 1, a further increased porosity

and plasticizer adsorption capacity, and despite the low K value for all morphological

Properties comparable to the product described in Comparative Example E with a K value of 70, the Application of previously known solutions with sorbitan monolaurate has been prepared as a secondary dispersant (Table 2). Example 3

The polymerization is carried out analogously to Example 1. In a modification to Example 1, the polymerization is carried out at -51 ⁰ C. As a radical generator are 0.036Tl. Di-Cetylperoxidicarbonat eingesezt. The total secondary dispersant concentration is 0.0019 kg / kg VC and the ratio of components I to II is 1: 1.37. The example documents that, while maintaining the secondary dispersant concentration and composition according to the invention, it is also possible to realize above-average porosities while maintaining the granulometric properties.

Example 4 The experimental procedure corresponds to Example 1. In contrast to Example 1, only a partially hydrolyzed primary dispersant

water-soluble polyvinyl acetate having a residual acetate content of 0.288 mol / mol and a K value of 45 used. Used are 5.2Tl. a 1% aqueous solution.

The polymerization is carried out at 63 ° C, the amount of the radical generator to 0.08Tl. Di-lauroyl peroxide and 0.03 part. Di-cetyl peroxydicarbonate is changed. The secondary dispersant is 0.0157 TI. Component I i> nd 0.0393Tl. the Component II used. The example documents the variability of the solution according to the invention with regard to the use of the invention Primary disperser, the desired K value of the PVC and the concentration and the ratio of the individual components of the Sekundärdispergatorgemisches.

Belsplel5

The polymerization process is analogous to Example 1. In a modification to Example 1, the polymerization is carried out at 55 ° C and

as suspension stabilizer a water-soluble partially saponified polyvinyl acetate having a CW of 42 and a residual acetate content of 0.25 mol / mol in an amount of 8Tl. a 1% solution used. The radical formers serve 0.036Tl.

Di-Cetylperoxidicarbonat. The total secondary dispersant concentration is 0.001 kg / kg VC and the ratio of Components I to II 1: 1.5. The example is direct in terms of total secondary dispersant concentration and other polymerization conditions

Comparable with Comparative Example H, in the Ca-stearoyl-lactoyl-lactate (component II) analogous to the procedure in the

DE 3011645, Example 8, is used without further addition. The morphological and granulometric properties in Tab. 2 reveal the clear advantages in all investigated parameters when using secondary dispersant mixtures

the composition of the invention over the individual components of the same use concentration.

Comparative Example A

Polymerization procedure and work-up conditions correspond to those of Example 1. In a modification to Example 1, only the component I of the Sekundärdispergatorgemisches is used, wherein the concentration is selected so that it corresponds to the total concentration of components I and II in Example 1 (Table 1). The analysis of the PVC powder obtained shows that the rate of increase of the porosity is remarkably lower. In addition, the product has a lower morphological and granulometric homogeneity.

Comparative Example B

The polymerization is carried out analogously to Example 1. With regard to the total concentration of the secondary dispersant, Comparative Example B is directly comparable to Example 1 and Comparative Example A. In contrast, however, only the component II is used. The product is characterized by significantly lower internal porosity due to a higher morphological heterogeneity and an inadmissibly high proportion of coarse grain.

Comparative Example C

Experimental procedure and polymerization conditions correspond to those of Example 2, as well as the used Sekundärdispergatorkonzentration (0.0044 kg / kg VC). However, the ratio of components I to II is shifted to 1 to 2.14 so that for this total concentration it is outside the limits of the invention. The characteristic data of the PVC powder are summarized in Tab. 2. The example shows that, despite the use of relatively high secondary dispersant concentrations, high rates of increase in porosity can not be achieved if the prescribed ratio between components I and II is not retained.

Vergielchsbeisplel D

The experimental procedure is analogous to Example 1. In a modification to Example 1, the component II of the secondary dispersant mixture with 0.134 part. a sorbitol monolaurate combined. It is obtained a very coarse PVC grain, the porosity and morphological homogeneity is »lower than in Example 1. The product is prone to charging phenomena (Table 2).

Comparative Example E

Experimental procedure and polymerization conditions are directly comparable to Example 3. In contrast to Example 3 are used as secondary disperser only 0.204Tl. Sorbitan monolaurate used. A PVC powder is obtained which, despite an increased secondary dispersant concentration in the porosity, does not come close to the product of the same K value prepared in Example 3 (Table 2).

Vergnchsbelspiel F

The experimental procedure is comparable to Example 1. In a modification to Example 1, a Sekundärdispergatorgemisch of 0.102Tl. Component I and 0.102Tl. Sorbitan monolaurate used. The polymerization must be stopped prematurely, since a strong deposit formation on the reactor wall and the reactor is formed, which leads to a huge impairment of mixing.

Verglelchsbelsplel G

The experimental procedure is comparable to Example 1. In contrast to Example 1, only the component I is used as a secondary dispersant and in concentrations that are required to achieve the same grain porosity as in Example 1 with 0.0026 kg / kg VC. The result was 0.354Tl. of component I for a plasticizer adsorption of 25.8kg / 100kg PVC. That is more than 73% secondary dispersant requirement more than in example 1. With the component II of the secondary dispersant mixture it was not possible at all for the same K value to realize a plasticizer adsorption of 25.8%.

Verglelchsbelsplel H

Polymerization sequence, Pm temperature, Primärdispergatorart and concentration and Sekundärdispergatorgefamtkonzentration correspond to Example 5, wherein instead of the Sekundärdispergatormischung only Ca-stearo Mactoyl-lactate is used. The conditions are thus, as far as the information about the chemical nature of the polyvinyl alcohols and the hydrodynamic apparatus sizes ever adjustable, largely comparable to Example 8 in DE 3011645.

Table 2 shows the consistently poorer morphological and granulometric properties of the PVC powder compared to Example 5.

Table 1: Polymerization conditions

at Sekundärdispergatoren * - Komp.il/kg-kg-'VC relationship total Konzen Other polymers - polymerized game Comp. I / kg kg "'VC I / II tration sationshilfsstoffe / - sations- 0.0016 0.0010 kg kg "'VC kg kg "'VC temperature ° C 1 0.0016 0.0014 1: 0.62 0.0026 - 71 2 0.0030 0.0045 0.0011 1: 0.47 0.0044 - 71 3 0.0008 0 0.0005 1: 1.37 0.0019 - 54 4 0.0002 0.0006 1: 2.50 0.0007 - 63 5 0.0004 - 1: 05.01 0.001 55 A 0.0026 0.0026 1: 0 0.0026 - 71 B - 0.0030 0: 1 0.0026 - 71 C 0.0014 0.0009 1: 2.4 0.0044 - 71 D - - 0.0026 0.0017 sorbitan 71 - monolaurate e - 0.0019 0.0019 sorbitan 54 - monolaurate F - 0.0026 0.001 sorbitan 71 - monolaurate G 0.001 - 0.0045 71 H 0: 1 0.001 55

K value relative Soft 0.41 25.8 powder VC-desorption middle Unaufge -6- 300 170 inner doer 0.34 20.1 porosity compact diffusion connected porosity admission anstiegpro shares layer thickness shares Thermo grain kg / 100 kg PVC 0.1 kgsecondary kg / kg PVC pm after 5 ' stable proportion of Table 2: Characteristic data of the PVC disperg. 0.7 kg / kg PVC formality 200 pm at 68.4 0.41 25.8 100 kg PVC 0,008 0.6 0,018 O ₂ at ' % game 58.4 0.47 33.4 6.90 0,008 0.5 0,013 17O ⁰ C min 70.0 0.53 42.5 4.40 0,007 0.8 0,012 25 0.4 62.8 0.40 24.2 7.60 0.011 0.6 0,017 22.4 0.5 69.4 0.42 25.6 8.80 0,007 4.2 0,013 30 0.6 1 58.4 0.34 19.8 9.4 0.064 4.5 0.078 28.5 0.5 2 58.5 0.31 16.0 2.20 0.072 3.8 0,110 32 0.5 3 58.4 0.35 20.4 0.08 0.057 2.3 0,039 20.1 0.4 4 58.1 0.36 22.3 1.45 0,021 1.1 0,049 19.1 12.6 5 69.8 0.44 32.0 3.19 0,012 0,018 23.1 3.5 A Demolition of the trial 1.05 1.6 24.7 26.3 B 58.4 0,017 1.2 0,052 27.8 1.3 C 69.4 2.6 0.22 0.043 D 3.9 17.5 0.3 e 26 8.7 F G H

Claims (2)

1. A process for the preparation of porous suspension polymers of vinyl chloride for a broad molecular weight range corresponding Fikentscher K values between 58 and 72 in the presence of known primary and secondary dispersants, characterized in that a mixture of a partially saponified polyvinyl acetate containing free hydroxyl groups as secondary dispersant from 0.45 to 0.55 mole / mole and Fikentscher K value of 35 to 45, as 20 to 30% alcoholic solution (I), and calcium stearoyl lactoyl lactate (II) in a total concentration of both Components of 0.00001 to 0.008 kg / kg of vinyl chloride is added, wherein the mixing ratio of I to Il to be maintained 1: 0.05 to 1: 8 and is adjusted differently depending on the Sekundärdispergatorgesamtkonzentration. 2. The method according to claim 1, characterized in that the ratio of the components I, based on a 25% ipe alcoholic solution, to II at a total use concentration of the secondary dispersant mixture of 0.00001 to 0.0014 kg / kg of vinyl chloride 1: 0.6 to 8, at a concentration of 0.0015 to 0.0029 kg / kg of vinyl chloride 1: 0.4 to 3, at a concentration of 0.003 to 0.0043 kg / kg of vinyl chloride 1: 0.2 to 1.2 and at tiner concentration 0.005 to 0.008kg / kg of vinyl chloride 1: 0.05 to 0.6. For this 1 page drawing Field of application of the invention The invention relates to a process for the preparation of porous, homogeneously constructed suspension polymers of vinyl chloride (VC) of different molecular weights using known primary and secondary dispersants. Characteristic of the known technical solutions The preparation of porous suspension polymers of the VC by addition of so-called secondary dispersants, which are low and high molecular weight, preferably oil-soluble, surface-active substances understood that "light or only to a limited extent to form stable adsorption layers capable and thus not stabilize the dispersion alone can, is known (DE 2659103, DE 2740209, DE 3003776). Their effect on the grain formation process is very complex, can only be determined empirically and thus can not be predicted or predicted with mathematical or physicochemical methods. Thus, it is well known that low molecular weight surfactants of the partial ester of glycerol, pentaerythritol and sorbitan with long-chain fatty acids (DT-OS 2603025, DT-OS 1946348, DT-OS 2121393, DT-OS 2310431, DD 141424, DE 2041372, DE 707,259) by preferentially incorporating them into the interface, but not themselves contributing to the stability of the droplets, lead to macroagglomeration phenomena, thereby entrapping an increased interstitial volume between the individual individuals of the grain, ultimately resulting in a higher porosity of the grain. Another mechanism of action of these surfactants is that they have the ability to form multiple dispersions, in that water is introduced into the dispersed organic phase, which leaves cavities after the workup and drying of the f-VC grain, also has a higher overall porosity reached. Finally, the ability of oil-soluble surfactants to stabilize the primary particles and agglomerates which precipitate inside the monomer droplets, resulting in a loose structure of the inner PVC structural units in the nm range, is added. Further effects are due to phase breakthroughs and kinetic effects. All factors taken together, ultimately, by superimposing in a confusing way, the increase of the internal pore volume of the grain. The effect of the secondary dispersants is therefore always on the type and concentration of the applied, actual suspension stabilizer, also referred to in the literature as a primary dispersant, and on the Polymorisationstempsratur dependent, the porosity or the porosity increasing effect decreases dramatically with increase in temperature. The secondary dispersant addition is associated with more or less negative effects on the polymerization process and other morphological, granulometric and / or molecular properties of the PVC. It is thus known that the use of sorbitan fatty acid esters leads to increased shell formation on the vessel wall, increase of foaming in the polymerization and work-up phase-in particular in the demonomerization process-and to a higher thermal and thermo-oxidative degradation of the PVC (DD 229704). Thus, the concentration of surfactants with the aim of achieving high rates of increase in porosity, can not be increased arbitrarily, as well as the negative side effects accumulate. Among other things, when the concentration is increased, the grain coarsening tendency increases. Nor is it possible to increase the absolute inner pore volume proportionally with further increase in concentration of the secondary dispersant, d. h., It will be achieved with increasing Sekundärdispergatorkonzentration only low efficiencies in terms of porosity increase. Especially at high polymerization temperatures, a high additional concentration leads only to a low rate of increase, with some surfactants even to a drop (DE 3011645) of the porosity.