CS255664B1 - The method of radiation grafting of polyolefins - Google Patents

Abstract

The present invention relates to a process for the grafting of polyolefins in a swollen solution of a graft monomer selected from the group consisting of acrylic acid, methacrylic acid and their reactive derivatives, characterized in that the grafting is carried out in the presence of effective radical polymerization inhibitors from the group of polyvalent phenols. in the presence of effective chain transfer agents from the group of halogenated aliphatic hydrocarbons and mercapto compounds.

Description

The invention relates to the radiation grafting of polyolefins with free methacrylic or acrylic acid and their polymerization with capable derivatives sufficiently soluble in the medium used, such as anhydrides, halides or easily extensible esters. The medium is typically a hydrocarbon such as benzene or toluene having a low or medium transfer constant. Solvents as well as monomers grafting are usually used in a pure state free of inhibitors and other substances with high chain constant. Known processes yield graft copolymers with relatively long but not very numerous side chains of (methacrylic acid) or poles (of acrylic acid) and / or chains based on polymerizable (meth) acrylic acid derivatives such as anhydrides, halides or esters which allow additionally easy release of acidic groups by hydrolysis or saponification.

The present invention provides a process for the radiation grafting of polyolefins in a swollen state of a graft monomer solution selected from the group consisting of acrylic acid, methacrylic acid, and reactive derivatives thereof, comprising grafting in the presence of potent radical polymerization inhibitors of the polyvalent phenol group. the presence of efficient chain transfer agents from the group of halogenated aliphatic hydrocarbons and mercapto compounds.

The invention is based on the assumption that, in particular for dialytic and electrodialysis membranes and hollow fibers, the graft copolymer structure is more favorable in which there are very numerous but short, often single-membered side chains of said acids. The graft copolymer thus acquires a much more regular structure without too large hydrophobic and hydrophilic domains, such that the backbones can optionally be arranged in parallel and partly form a crystalline structure, giving the graft copolymers in swollen state a higher strength with the same acid side group content.

According to the invention, this is achieved in that the radiation grafting of the solvent-swollen polyolefins and the monomer to be grafted is carried out in the presence of effective radical polymerization inhibitors such as hydroquinone or a target. butylpyrocatechol, which prevents the formation of long chains both grafted and free from the monomer present and at the same time in the presence of an efficient chain transfer agent such as halogen aliphatic hydrocarbons or substances with the -SH free group. Examples include carbon tetrachloride, chloroform and bromoform, optionally thiacetic acid or ethyl bromide.

It is advantageous to select such a shoe. a solvent in which the homopolymer that is possibly formed from the grafted monomer on the surface of the grafted polymer does not dissolve or poorly dissolve. In the case of free methacrylic acid, such a solvent is, for example, benzene or toluene. The resulting homopolymer then forms a fine powder on the surface of the graft polymer or copolymer, which can be easily removed in the dry.

Polymers and copolymers of ethylene, propylene, vinyl bromide, vinyl chloride and vinyl fluoride may also be used as base materials, optionally with other co-monomers such as acrylonitrile, hydroxyethyl methacrylate, methacrylic esters with lower aliphatic alcohols, etc.

The less crystalline and / or more swellable the base polymer or copolymer, the more monomer can be grafted onto it. Thus, for example, high pressure polyethylene is more suitable than low pressure, ethylene-propylene copolymer is more suitable than polypropylene, various vinylfluoride copolymers are more suitable than poles (vinylfluoride), and the like.

It is preferable to carry out radiation grafting as usual with the exclusion of molecular oxygen.

Any device producing shortwave UV radiation (preferably with the addition of benzoin or its derivatives), X-ray radiation and gamma-rays, e.g.

He did

A 25 x .mu.m film of high pressure polyethylene was immersed in a container containing a nitrogen purged mixture of 70 parts by weight. of anhydrous benzene, 5 parts of carbon tetrachloride and 25 parts of methacrylic acid, inhibited by 200 ppm hydroquinone and dried. The vessel was hermetically sealed and after 2 hours swelling at 20 ° C irradiated with 20,000 rad / hr Co 2 ® emitter with a total dose of 0.85 Mrad.

After opening the container, the film was removed and dried. After removal of the polymethacrylic acid adhering to the film as a white powder, the film was swelled in 5% aqueous potassium hydroxide solution at 70 ° C for 2 hours. Thereafter, the film of prana was spent 24 hours in exchanged distilled water and dried. The amount of grafted methacrylic acid reached 65% by weight. based on the original weight of polyethylene. The film has a membrane potential of -14.7 mV in the 0.2 / 0.1 mol KCl system, which corresponds to a potassium ion transport number of 0.957 and a permselectivity of 91.6%. The sheet resistance in 0.5 moles of NaCl is 340 m <cm ² .

Example 2

Hollow fibers of ethylene-propylene copolymer (10 w / w) were swollen to equilibrium with a solution of 20 parts methacryloyl chloride in 75 parts toluene and 5 parts bromoform in the presence of 300 ppm tert-butylpyrocatechol for 1 hour at 25 ° C. The skein was then removed from the bath and irradiated as in Example 1. After evaporation of the solvents and treatment with 5% potassium hydroxide solution, washing and drying the fibers contained 48 wt. % of grafted methacrylic acid, based on the starting weight of the fibers.

Example 3

A 30 [mu] m thick film of high pressure polyethylene was immersed in a container containing a nitrogen purged mixture of 70 parts by weight. anhydrous benzene, 5 parts dodecyl mercaptan and 25 parts methacrylic acid inhibited by 150 ppm hydroquinone and dried.

After hermetic sealing and 2 hours swelling, the container was irradiated with a Co ⁶⁰ emitter of 20,000 rad / h with a total dose of 0.9 Mrad. After opening the vial, the film was removed and dried and swelled in 5% aqueous sodium hydroxide solution at 70 ° C for 2 hours. The film was then washed for 24 hours in changed distilled water and dried. The amount of grafted methacrylic acid reached 55% by weight. based on the original weight of polyethylene.

The film exhibits a membrane potential of -15.2 mV and a permselectivity of 92.3% in the 0.2 / 0.1 mol KCl system.

The surface evaporation of the film in 0.5 mol NaCl is 330 mft / cm.

Claims (1)

A process for the radiation grafting of polyolefins in a swollen state of a graft monomer solution selected from the group consisting of acrylic acid, methacrylic acid, and reactive derivatives thereof, characterized in that grafting is carried out in the presence of effective radical polymerization inhibitors of the polyvalent phenol group. groups of halogenated aliphatic hydrocarbons and mercapto compounds.