RU2336282C1 - Method of suspension polyvinylchloride synthesis - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: synthesis of suspension polyvinylchloride is realised by polymerisation of vinylchloride by heating in presence of initiating system, which consists of initiators, which differ by temperature of period of half-life: peroxydicarbonates and acyl peroxides, and emulsifying system based on methyloxypropylcellulose and secondary polyvinyl alcohol, which are introduced at the beginning of process; after drop of pressure, temperature of polymerisation is raised on 6-10°C from heating temperature, and reaction mass is exposed during 40-60 minutes. Suspension polyvinylchloride can be used for production of plasticised materials such as, cable and medical plasticates, films.

EFFECT: obtaining efficient method of suspension polyvinylchloride synthesis.

2 tbl, 8 ex

Description

The invention relates to the chemistry of macromolecular compounds and can be used in the synthesis of suspension polyvinyl chloride, intended for the production of plasticized materials, such as cable and medical plastic compounds, films.

In the known method (Japanese application No. 411606, publ. 16.01.92, class MKI 5 C08F 14/06), vinyl chloride polymers and copolymers thereof with other vinyl monomers are prepared by polymerization by radical initiators, the initiator being proposed to be introduced in two portions: at the beginning of the process about two-thirds of the total amount, and after an hour another third when monomer conversion is 10-30%. Using the method of phased introduction of the initiator complicates the technology for the synthesis of polyvinyl chloride and requires the installation of an additional device for dosage of the initiator.

To reduce the duration of the water-suspension polymerization of vinyl chloride in US patent No. 4826940, publ. 05/02/89, MKI ⁴ C08F 2/20, recommend that after the conversion of vinyl chloride more than 10% raise the temperature gradually or stepwise within 10-80 ° C. In the above example, the temperature begins to rise at a constant speed of 0.045 ° / min from 47 ° to 63 ° C, which creates serious inconvenience during the process.

In some sources (Japanese application No. 1110511, MKI C08F 14/06, publ. 04/27/1989), polyvinyl chloride is synthesized in two stages in the presence of a mixture of initiators: the first with a half-life of 10 hours at a temperature not exceeding 35 ° C, for example, diisobutyl peroxide, and the second - with a decomposition temperature not lower than 50 ° C, for example 2,2'-azodiisobutyronitrile. In the first stage, vinyl chloride is polymerized at a low temperature of 20-30 ° C to a conversion of 60-85%, in the second stage, the polymerization temperature is 50-80 ° C. In French patent No. 2100789, MKI C08F 14/06, publ. 03.24.1972, the first stage of polymerization of vinyl halides, in particular vinyl chloride, proceeds at 35-55 ° C, then at a conversion of 10-60% the temperature is raised to 60-80 ° C and the polymerization process is completed at the indicated temperature. In both cases, there is a large difference in the temperature range, which will inevitably lead to a large variation in the Fikentcher constant K _f , which is a relative criterion for the molecular weight of polyvinyl chloride, and therefore will lead to a wide molecular weight distribution of the polymer.

It is known that in order to increase the polymerization rate of the vinyl chloride monomer, at least one additional organic initiator is added to the polymerizable mixture at the reaction temperature at the moment when the pressure in the polymerization reactor begins to drop (application EP 1375529, published 02.01.2004). As any additional initiators, any kind of organic peroxides with a half-life from 0.0001 to 1 hour at the polymerization temperature that differs from those used in the polymerization process before the pressure drop can be used. The additional input of the initiator can be either periodic or continuous, which greatly complicates the technology, since in order to use this technique, the polymerization reactor must be equipped with an appropriate piping system and several entry points located at different positions along the periphery of the reactor to ensure faster distribution of the initiator. In addition, the supply of additional initiator is carried out either in solution (alcohols, isodecane, etc.), or in an emulsion or suspension. It is obvious that the introduction of solvents or surfactants is undesirable.

The closest is the synthesis method of suspension polyvinyl chloride, in which the initiating system and emulsifying system are introduced at the beginning of the synthesis process, and after the pressure drop the polymerization temperature is raised by 8-12 ° C and the reaction mass is maintained for 1 hour (RU 2155775 C2, op. 10.09 .2000). But this invention uses a redox system, the components of which - potassium persulfate, phthalimide, alkyl betaine - have good solubility in water, which can lead to the occurrence of suspension and emulsion polymerization at the same time, which significantly increases the fraction of the fine fraction and worsens the flowability of the polymer.

The technical result of the invention is to increase the degree of conversion of the synthesis of polyvinyl chloride while maintaining all the quality indicators of the polymer without installing additional equipment.

For this, the authors propose to use an initiating system for the synthesis of suspension polyvinyl chloride by polymerization of vinyl chloride by heating, which includes initiators with different half-life temperatures: peroxydicarbonates, for example di-2-ethylhexylperoxydicarbonate (PDEG), at 40-53 ° С and acyl peroxides, for example, lauroyl peroxide (PL), at 55-65 ° С, and an emulsifying system based on methoxypropyl cellulose and recycled polyvinyl alcohol, which are introduced at the beginning of the process, and after the pressure drop the polymerization temperature is raised by 6-10 ° C from the heating temperature and the reaction system is held for 40-60 minutes. More complete information on the effect of temperature on the breakdown of initiators is presented in Table 1 (Reference Akzo Nobel, 2002, p. 10, 12).

Table 1 Initiator Half-life temperature, ° С in 0.1 h in 1 h in 10 hours PDEG 83 64 47 Sub 99 79 61

The synthesis is carried out in two stages: in the first stage, a more active PDEG initiator works at 48-49 ° С, and in the second stage, starting from the moment the pressure in the reactor drops, the temperature of the reaction mixture is increased by 6-10 ° С and is active at this temperature lauroyl peroxide (PL). The beginning of the pressure drop in the reactor corresponds to a 75-80% conversion, and the implementation of the second short stage (40-60 min) at a higher temperature increases the yield, practically without changing the previously achieved set of properties of polyvinyl chloride. So, for example, the Fikentcher constant for polymers synthesized using only one stage and both stages varies within 71 ± 1. Along with the initiating system, the authors propose using an emulsifying system based on methyloxypropyl cellulose (MOCC) and secondary polyvinyl alcohol (PVA). It is proposed to use polyvinyl alcohol with a degree of hydrolysis of 25-70% as a secondary protective colloid.

The combination of initiating and emulsifying systems leads to a soft course of the polymerization process, provides favorable conditions for the formation of polymer grains and, ultimately, the preservation of the properties of polyvinyl chloride at a higher monomer conversion.

The following examples illustrate the invention.

Example 1. In a special steel reactor with a volume of 3.5 l, equipped with an impeller mixer, a breakwater and a steam bath, the initiator is lauroyl peroxide initiator (PL) in an amount of 0.0045% by weight of vinyl chloride (BX); PDEG initiator in an amount of 0.09% by weight of monomer; diphenylolpropane antioxidant in an amount of 0.001% by weight of VX; 1600 g of demineralized water with a pH regulator dissolved in it — sodium carbonate in an amount of 0.0056% by weight of water and an emulsifying system (0.18% by weight of MOC water and 0.07% by weight of secondary PVA water). The reactor is closed, the stirrer is turned on, and after 800 g of BX are introduced, heating is started. The polymerization is carried out at a temperature of 49 ° C. After the start of the pressure drop in the reactor, the second stage is carried out - depolymerization, for which the temperature is raised to 59 ° C and maintained at this level for 1 hour. At the end of the depolymerization stage, the contents of the reactor are cooled and the non-polymerized BX is blown off. The suspension is discharged, the polymer is separated from the mother liquor on a Buchner funnel, washed with water and dried in an oven at 55-60 ° C. The yield of PVC is determined gravimetrically, and its main qualitative characteristics (K _f , absorption mass of plasticizer (MPP), dispersion) - according to GOST 14332-78. The resulting polymer powders are evaluated visually under a microscope (magnification 7) to determine defective particles.

The experimental data are summarized in table 2.

Example 2. It differs from example 1 in that the initiator of the PL is introduced in an amount of 0.03% by weight of BX.

Example 3. It differs from example 1 in that the initiator of the PL is introduced in an amount of 0.045% by weight of BX.

Examples for comparison.

Example 4. It differs from example 2 in that there is no secondary PVA in the composition of the emulsifying system.

Example 5. It differs from example 3 in that there is no stage of depolymerization.

Example 6. It differs from example 2 in that in the polymerization formulation there are no PL, PVA and no depolymerization stage.

Example 7. It differs from example 2 in that the depolymerization is carried out for 1 hour at a given process temperature of 49 ° C.

Example 8. It differs from examples 1-3 in that there is no initiator of the submarine.

Examples 1-3 indicate that the use of an initiating system consisting of components operating at different temperatures, in combination with the depolymerization stage and the mandatory introduction of a modifier of the morphological structure of PVC grain - secondary polyvinyl alcohol into the emulsifying system provides a high polymer yield (86-92, 5%) and allows you to maintain its quality even at high degrees of conversion. The obtained polymers are characterized by a very narrow range of fluctuations of the Fikentcher constant (70.5-71), good reproducibility in dispersion, a quite satisfactory MPP value (24-28.1 g of dioctyl phthalate / 100 g of PVC) and a relatively low content of defective particles (glassy and with closed porosity).

The exclusion from the composition of the emulsifying system of PVA (examples 4 and 6) leads to a significant deterioration in the adsorption capacity of PVC (MPP is 16.6 and 18 g DOP / 100 g PVC) and a very significant increase in the number of defective particles.

The absence of a depolymerization step (Examples 5 and 6) predetermined a relatively low polymer yield (78.8-81.2%).

In example 7, the polymerization process is carried out without a second, higher temperature stage, however, the duration is increased by one hour, but at a constant temperature of the whole reaction 49 ° C. A comparison of example 7 with example 2 gives a clear idea of the advantage of the proposed invention (yield 85.6 and 90.6%, respectively).

The use of only one PDEG initiator without PL (comparison of example 8 with examples 1-3) provides a yield of 83.5%, while the introduction of PL in a concentration of 0.0045-0.045% by weight of VC allows to obtain a yield in the range 86-92.5% .

table 2 Example No. The concentration of the components of the initiating system,% by weight VX The presence in the emulsifying system of PVA The presence of the second stage Polymerization time (total), h Exit, % PVC properties K _f MPP, g DOF / 100 g PVC Dispersion (sifting through a sieve 0315),% The number of defective particles,% Glassy Closed porosity PDEG Sub At 20 ° C At 95 ° C one 0.09 0.0045 + + 7.5 86 70.5 24 66,4 2,3 17 13.3 2 0,03 7.2 90.6 71 24 65,4 2,5 fifteen 10 3 0,045 6.9 92.5 70.8 28.1 62.3 3,7 10 8.9 four 0.09 0,03 - + 7.3 89.7 70.8 16.6 45.0 5.8 71,4 40.5 5 0,045 + - 6.2 81.2 70.5 24.8 68,2 3.8 12 10 6 - - - 6.8 78.8 71.5 eighteen 70.6 4.4 53 28 7 0,03 + 1 hour increase in synthesis time 7.5 85.6 70.7 24.1 57.8 4.0 25 fourteen 8 - + + 7.4 83.5 70.6 20.5 66,4 - - -

Claims (1)

A method for the synthesis of suspension polyvinyl chloride by polymerization of vinyl chloride by heating in the presence of an initiating system consisting of initiators that differ in half-life temperature: peroxydicarbonates and acyl peroxides, and an emulsifying system based on methoxypropyl cellulose and secondary polyvinyl alcohol, which are introduced at the beginning of the process, and after the pressure drops, the temperature the polymerization is raised by 6-10 ° C from the heating temperature and the reaction mass is maintained for 40-60 minutes.