V.Ya. Kabanov

Preparation of permeability-controlled track membranes on the basis of ‘smart’ polymers

The modification of polymer track membranes from polyethylene terephtalate (PET) and polypropylene (PP) was performed by radiation-induced graft polymerization of thermosensitive poly-N-isopropylacrylamide (poly-NIPAAM). The opening and closing of the pores was controlled by temperature and studied by the electric conductivity and water flow methods. The structure of the grafted membranes was investigated by scanning electron and atomic force microscopy.

THE USE OF RADIATION-INDUCED GRAFT POLYMERIZATION FOR MODIFICATION OF POLYMER TRACK MEMBRANES

Abstract Track membranes (TM) made of poly(ethylene terephtalate) (PET) and polypropylene (PP) films have a number of peculiarities as compared with other ones. They have high mechanical strength at a low thickness, narrow pore size distribution, low content of extractables. However, TM have some disadvantages such as low chemical resistance in alkaline media (PET TM), the low water flow rate due to the hydrophobic nature of their surface. The use of radiation-induced graft polymerization makes it possible to improve the basic characteristics of TM. In this communication our results on the modification of PET and PP TM are presented. The modified membranes were prepared by radiation-induced graft polymerization from the liquid phase. Three methods of grafting were used: (a) the direct method in argon atmosphere; (b) the pre-irradiation of TM in air followed by grafting in argon atmosphere; (c) pre-irradiation in vacuum followed by grafting in vacuum without contacting oxygen. The aim of the work was to investigate some properties of TM modified by grafted poly(methylvinyl pyridine) (PMVP) and poly(N-isopropylacrylamide) (PNIPAAM). It was shown that the modification of TM with hydrophilic polymer results in the growth of the water flow rate. In the past few years many works have been devoted to the synthesis of new polymers – the so-called “intelligent” materials – such as PNIPAAM. However, it is very difficult to make thin membranes of this polymer. Recently, it has been proposed to manufacture composite membranes by grafting stimulus-responsive polymers onto TM. Following this principle, we prepared thermosensitive membranes by the radiation-induced graft polymerization of N-isopropylacrylamide (NIPAAM) onto PET TM. PET TM with the pore size of about 1 μm and pore density of 106 cm−2 were first inserted into a solution of NIPAAM containing inhibitor of homopolymerization (CuCl2) and then exposed to the γ-rays from a 60Co source. The transport properties of the grafted TM were investigated. The permeation of water through the TM was controlled by temperature. The grafted TM exhibited almost the same transition temperature (about 33°C) as that of PNIPAAM.

Modification of Polymers by Radiation Graft Polymerization (State of the Art and Trends)

The state of the art polymer modification by radiation graft polymerization is surveyed. The mainstream of research in this field is elucidated. Data published within the last five–ten years are summarized.

The heavy ion tracks in polymers investigation by means of high-effective liquid chromatography and atomic-force microscopy

Abstract The method of heavy high-energy ions latent tracks structure in polymers investigations have been proposed. This method includes the irradiated polymer preliminary treatment with water, then with week alkali solution for different track area visualization and investigation. The products of polyethylene terephthalate radiolysis from the track areas were investigated by means of inverse-phase chromatography. Atomic-force microscopy was used for surface change of initial and developed polymer investigation. It was shown that the latent track has complicated structure and consists of different areas. For Xe-irradiated PET-sample 3 areas (with diameters 7, 17 and 50– 150 nm ) were found. Such track structure allows to explain the discrepancy between the data, previously obtained by using different methods.

Radiation chemistry of polymers

Results of basic and applied research in radiation chemistry of polymers in Russia and Belarus for the last 5–10 years are presented.

UV- and γ-sensitization of latent tracks in polyethylene terephthalate

Photosensitization of polymer polyethylene terephthalate (PET) bombarded with swift heavy ions (Xe) was studied. Ultraviolet (UV)- and γ-irradiation were used for sensitization. Infrared spectroscopy (IR) and reversed-phase high-performance liquid chromatography (HPLC) were used to study the radiolysis products in latent tracks (directly in the sample or in the etching solution). It was found that the exposure of the sample to ultraviolet light results in the transformation of the radiolysis products formed in the tracks into terephthalic acid. Surface defects, detected by AFM, were found to correspond to tracks; their form (cavities and hillocks) and size changing reflect the changing of latent track state. It was found that UV irradiation destroyed the cross-linked regions in the tracks. This process (photodecomposition) was shown to be the key stage of the UV sensitization and the main cause of etching rate increase. The γ-irradiation effect on track etching was found to be almost the same.

Radiation chemistry of smart polymers (A Review)

Radiation chemistry methods used to prepare smart polymers are surveyed. The properties of these polymeric materials are considered. The benefits of radiation-chemical procedures for manufacturing smart polymers are discussed. The areas of their practical use are outlined

Present status and development trends of radiation-induced graft polymerization

Abstract A review of present status and world trends in practical use of radiation-induced grafting is given. Experience in the last 15–20 years of application of this method worldwide is generalized. Its advantages and drawbacks are discussed.

A structural-morphological study of radiation grafted copolymers of polyethylene with polyacrylic acid☆

Abstract A structural-morphological study of radiation-grafted copolymers of PE with PAA has been carried out. It was shown that as well as the permeation of the PAA into the polymer, an increase in the PAA concentration in the grafted phase occurs, the rate of the subsequent process being about 1·5 times greater than that of the first one. Under given conditions, the process rate is not diffusion-controlled. It was shown that grafting is accompanied by breakdown of the para -crystalline structure of the PE. The conditions for complete covering of the PE surface with a grafted layer have been established.

Properties of polymer track membranes modified by grafting with poly(2-methyl-5-vinylpyridine) and poly(N-isopropylacrylamide)

The properties of track membranes (TM) based on poly(ethylene terephthalate) (PETP) and polypropylene (PP) and modified by radiation-induced graft polymerization of 2-methyl-5-vinylpyridine (MVP) andN-isopropylacrylamide (NIPAA) were studied. The rate of grafting and the limiting degree of grafting increase linearly as the pore diameter of TM increases. The gasdynamic and hydrodynamic pore diameters of modified TM were determined. The dependence of water permeability of TM modified by grafting with poly(2-methyl-5-vinylpyridine) (PMVP) on the degree of grafting passes through a maximum, which, according to the data of wetting angle measurements, corresponds to the maximum hydrophilicity. The negative χ-potential of TM changes sign after modification by grafting with PMVP. Thermosensitive TM based on PETP and PP were prepared by radiation-induced graft polymerization of NIPAA. The structure of modified TM was studied by electron microscopy and atomic force microscopy.