RU2469049C1 - Method for suspension polymerisation of vinyl chloride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method for suspension polymerisation of vinyl chloride is realised while heating in the presence of an initiating system consisting of at least peroxycarbonate and hydrazine in ratio 1:0.0043-0.4 and an emulsifying system. The peroxycarbonate used can be at least di-2-ethylhexyl peroxycarbonate and dicetyl peroxycarbonate. The emulsifying system used is at least a combination of derivatives of methylcellulose and polyvinyl alcohols. A post-polymerisation step is allowed when after pressure begins to drop in the reaction apparatus, reaction temperature is raised by not more than 10°C relative operating parameters and kept at that level for a certain period of time, e.g., 1 hour.

EFFECT: high polymer output while maintaining its quality.

4 cl, 1 tbl, 16 ex

Description

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

It is known that in the chemistry of high molecular weight compounds, redox initiating systems are widely used.

So, in particular, in patent RU 2155775, publ. 09/10/2000, the process of suspension polymerization of vinyl chloride is carried out in the presence of an oxidizing agent: di-2-ethylhexyl peroxydicarbonate (PDEG) and a water-soluble reducing agent: potassium persulfate, phthalimide or alkyl betaine, taken in a mass ratio of from 1: 0.67 to 1: 0.8.

A known method of obtaining homo - or copolymers of vinyl or vinylidene halides, patent US 4269954, publ. 05/26/1981, in the presence of a radical initiator and activator such as sodium nitrite and sodium tetrahydroborate.

The synthesis of suspension polyvinyl chloride, known from patent RU 2336282, publ. 10.20.2008, taken as a prototype, is carried out in the presence of an initiating system consisting of initiators with different half-life temperatures: peroxydicarbonates and acyl peroxides.

The objective of the claimed invention is to develop a method of suspension polymerization of a monomer, for example vinyl chloride. The problem is solved in that the suspension polymerization of vinyl chloride is carried out by heating using hydrazine and peroxydicarbonate, which is part of the initiator system, in the presence of an emulsifying system. The ratio of peroxydicarbonate and hydrazine is 1: 0.0043 ÷ 0.4. As peroxydicarbonate, at least di-2-ethylhexylperoxydicarbonate and dicetylperoxydicarbonate can be used.

To prevent the negative impact on the quality of polyvinyl chloride temperature and high degrees of conversion, it is necessary to use an emulsifying system. As an emulsifying system, at least a combination of methyl cellulose derivatives and polyvinyl alcohols can be used.

It is allowed to use the depolymerization stage when, after the start of the pressure drop in the reaction apparatus, the reaction temperature is increased by no more than 10 ° C relative to the operating parameters and maintained at this level for a certain time, for example, for 1 hour.

The use of hydrazine as a reducing agent of peroxydicarbonate, which is part of the initiating system, can increase the degree of conversion of vinyl chloride.

The introduction of water-soluble hydrazine virtually eliminates the polymerization process in the aqueous phase, since the initiating system will work only after diffusion of hydrazine into a drop of vinyl chloride, in which the initiator, peroxydicarbonate, is in a dissolved state. Diffusion occurs throughout the polymerization process.

The following examples illustrate the essence of the invention.

EXAMPLE 1

Into a 3.5-liter reactor equipped with an impeller mixer with a rotation speed of 220 rpm, a breakwater and a steam-water bath, enter: di-2-ethylhexylperoxydicarbonate (PDEG) in an amount of 0.09% by weight of vinyl chloride, 1600 g of demineralized water with sodium carbonate previously dissolved in it in an amount of 0.0056% by weight of water, methoxypropyl cellulose in an amount of 0.18% by weight of water, polyvinyl alcohol (PVA) with a degree of hydrolysis of 45% in an amount of 0.07% by weight of water and hydrazine with the mass ratio of PDEG: hydrazine equal to 1: 0.025, 800 g of vinyl chloride.

Suspension polymerization of vinyl chloride is carried out at a temperature of 48 ÷ 52 ° C. After the start of the pressure drop in the reactor, the depolymerization stage is carried out - the reaction temperature rises to 60 ° C and is maintained at this level for 1 hour. At the end of the prepolymerization stage, the contents of the reactor in order to terminate the polymerization process are sharply cooled to a temperature of 20 ÷ 25 ° C. After removal of residual vinyl chloride, the contents of the reactor in the form of an aqueous suspension are discharged.

The aqueous suspension is filtered on a Buchner funnel to separate the polyvinyl chloride from the mother liquor. The wet polymer is washed with water and dried in a heating cabinet at a temperature of 55 ÷ 60 ° C. The yield of polyvinyl chloride is determined by weighing the dried polymer, and its main qualitative characteristics - “Plasticizer Absorption Mass” (MPP), “Fikentcher Constant” (K _F ), “Residue after sifting on sieve No. 0315” are determined according to GOST 14332-78. The degree of contamination with polymer deposits of the working surface of the autoclave and mixing devices (mixer, breakwater) is visually assessed.

The experimental data of example 1 and the following examples are shown in the table.

EXAMPLE 2

It differs from example 1 in that hydrazine is loaded at a mass ratio of PDEG: hydrazine as 1: 0.4.

EXAMPLE 3

It differs from example 1 in that hydrazine is loaded at a mass ratio of PDEG: hydrazine as 1: 0.0043.

EXAMPLE 4

It differs from Example 3 in that PDEG, lauroyl peroxide (PL) and hydrazine are loaded at a mass ratio of PDEG: PL: hydrazine as 1: 0.5: 0.4. The polymerization temperature of vinyl chloride is 62 ° C. The prepolymerization step is not carried out.

EXAMPLE 5

It differs from Example 4 in that it is loaded with PDEG, lauroyl peroxide and hydrazine at a mass ratio of PDEG: PL: hydrazine as 1: 0.5: 0.025.

EXAMPLE 6

It differs from Example 4 in that lauroyl peroxide and hydrazine are loaded at a mass ratio of PDEG: PL: hydrazine as 1: 0.5: 0.0043.

EXAMPLES FOR COMPARISON

EXAMPLE 7

Differs from example 1 in that the step of the prepolymerization is not carried out.

EXAMPLE 8

It differs from example 2 in that PVA with a degree of hydrolysis of 45% is absent.

EXAMPLE 9

Differs from example 1 in that hydrazine is absent.

EXAMPLE 10

It differs from Example 1 in that PDEG and hydrazine are loaded at a mass ratio of PDEG: hydrazine as 1: 0.6.

EXAMPLE 11

It differs from Example 1 in that PDEG and hydrazine are loaded at a mass ratio of PDEG: hydrazine as 1: 0.0025.

EXAMPLE 12 (prototype)

It differs from Example 1 in that hydrazine is absent and PL is used as a co-initiator to PDEG at a ratio of PDEG: PL as 1: 0.33.

EXAMPLE 13

It differs from example 4 in that it is loaded with PDEG, lauroyl peroxide and hydrazine at a mass ratio of PDEG: PL: hydrazine as 1: 0.5: 0.0025.

EXAMPLE 14

It differs from Example 4 in that PDEG, lauroyl peroxide and hydrazine are loaded in a mass ratio of PDEG: PL: hydrazine as 1: 0.5: 0.6.

EXAMPLE 15

It differs from example 5 in that PVA with a degree of hydrolysis of 45% is absent.

EXAMPLE 16

Differs from example 4 in that hydrazine is absent.

Examples 1 ÷ 3 indicate that the use of the redox system peroxydicarbonate - hydrazine (mass ratio 1: 0.0043 ÷ 1: 0.4), an emulsifying system based on methyl cellulose derivatives and the synthesis of PVC with a Fikentcher constant equal to 70 ÷ 73 polyvinyl alcohols with varying degrees of saponification in combination with the depolymerization stage provides a high polymer yield (93.6 ÷ 95.4%) while maintaining its quality even at high degrees of conversion and slight crust formation on the working surface of the polymerization ionic equipment.

Examples 4–6 indicate that the use of the redox system peroxydicarbonate: PL: hydrazine (mass ratio 1: 0.5: 0.0043 ÷ 1: 0.5: 0, in the synthesis of PVC with a Fikentcher constant equal to 58 ÷ 60) 4) and an emulsifying system based on methyl cellulose derivatives and polyvinyl alcohols provides a high polymer yield (90.1 ÷ 92.2%) while maintaining its quality even at high degrees of conversion and slight crust formation on the working surface of the polymerization equipment.

The increase in examples 10 and 14 of hydrazine leads to an inhibition of the polymerization process, and therefore, to an extension of the polymerization process and a sharp decrease in the degree of conversion of vinyl chloride. However, there has been an increase in the number of operations between cleanings of the reaction equipment.

The resulting polymers are characterized by a very narrow range of fluctuations in the molecular weight of the polymer (Quality Index "Fikentcher Constant"), which does not depend on the amount of hydrazine used.

The reduction in examples 11 and 13 of the mass of hydrazine used reduces the conversion of vinyl chloride and leads to an increase in polymer deposits on the working surface of the polymerization equipment, which reduced the number of operations between cleaning the reaction equipment.

The replacement of hydrazine with PL in experiment 12, although it provides a high level of vinyl chloride conversion, leads to a sharp increase in crust formation on the working surface of polymerization equipment.

The exclusion in experiments 8 and 15 of the secondary protective colloid from the composition of the emulsifying system leads to a significant deterioration in the adsorption capacity of PVC (quality index “Plasticizer absorption mass”) and an increase in the proportion of coarse polymer particles (quality indicator “Screening through sieve No. 0315”).

The absence of the stage of additional polymerisation during the synthesis of PVC (Example 7) reduces the degree of monomer conversion from 93.6 ÷ 95.4 to 88.3%.

The absence of hydrazine in examples 9 and 16 leads to an even more significant decrease in the degree of conversion of the monomer, as well as to a decrease in the number of operations between cleanings.

Claims (4)

1. The method of suspension polymerization of vinyl chloride by heating in the presence of an initiating system and an emulsifying system, characterized in that the initiating system contains at least peroxydicarbonate and hydrazine in a ratio of 1: 0.0043 ÷ 0.4. 2. The method according to claim 1, characterized in that at least di-2-ethylhexyl peroxydicarbonate or dicetyl peroxydicarbonate can be used as peroxydicarbonate. 3. The method according to claim 1, characterized in that, as an emulsifying system, a combination of at least methyl cellulose derivatives and polyvinyl alcohols is used. 4. The method according to claim 1, characterized in that after the start of the pressure drop in the reaction apparatus, the reaction temperature is increased by no more than 10 ° C relative to the initial polymerization temperature and maintained at this level for a certain time, for example 1 hour