The surface of poly(ethylene terephthalate) (PET) track etched membranes (TMs) was covered with thermo-responsive poly(N-vinylcaprolactam) (PVCL) by a photochemical immobilization method. First, a photo-reactive azidophenyl group was incorporated into the thermo-responsive PVCL chains. Secondly, the polymers were cast on the PET membrane followed by irradiation with UV light. Characterization by X-ray photoelectron spectroscopy and FT-ATR-IR demonstrated that the thermo-responsive polymer chains are effectively grafted on the membrane surface. Scanning electron microscopy and atomic force microscopy on the dry composite membranes demonstrated that the pore size diameter decreases and the surface roughness increases with increasing amount of grafted polymer chains on the TM. The water permeation through the modified TM drastically increases when the cloud point (Tcp) of the grafted PVCL-chains is reached. The permeability of a mixture of dextrane molecules is not only controlled by the molecular weight of the individual macromolecules but also strongly by temperature. This last observation opens the possibility to use the same membranes for the separation of macromolecular mixtures over a broad molecular weight range.

Copolymers with both pH- and thermo-responsiveness were synthesized by free radical copolymerization of N-vinylcaprolactam with small amounts of acrylic acid. The copolymers have been prepared in various solvents and characterized by gel permeation chromatography, Fourier-transform infrared (FTIR) spectroscopy and titration. The phase separation behaviour of these copolymers was studied in water and buffered solutions at a variety of pH values and temperatures by means of attenuated total reflectance FTIR and cloud-point measurements. The aqueous solutions of the copolymers showed a temperature, pH and molecular weight dependent phase-separation behaviour. (C) 2003 Society of Chemical Industry.

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.

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.

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.

Environmentally responsive polymeric track membranes were prepared. Polypropylene (PP) and poly(ethylene terephthalate) (PETP) track membranes with a pore size ranging from 0.03 to 1 mu m were modified by radiation grafting of thermally responsive poly(N-isopropylacrylamide). The microstructure of grafted membranes was examined by electron microscopy. The modified membranes are able to reversibly respond to a temperature change in the range 32-34 degrees C, increasing or decreasing the pore size.

Modified membranes have been prepared by radiation-induced grafting of hydrophilic polymer onto polypropylene track membranes (PPTMs). The change in morphology and surface properties of graft membrane were investigated. The thickness of PPTMs grows linearly with grafting yield. Water contact angle on the original and modified membranes has been measured and it was shown that it decreases with grafting yield until the last will be equal to 5–7%. It is noteworthy that properties of graft membranes were unchanged during their storage under ambient conditions more than half a year.

The effect of temperature on the kinetics of radiation-induced graft polymerization of styrene onto poly(ethylene terephthalate) (PETP) nuclear membranes with varying parameters (pore diameter, pore density and average distance between the pores) and onto PETP films of different thickness has been studied. Graft polymerization was carried out by preirradiation in air and in vacuum. The overall activation energy of grafting and the activation energy of swelling of PETP in toluene have been obtained. It was found that for preirradiation in vacuum, an Arrhenius plot has two linear ranges for the initial grafting rate. The activation energy in the low temperature range correlates with the activation energy for PETP swelling. The activation energy in the high temperature range is determined by the kinetics of graft polymerization. For preirradiation in air, the Arrhenius plot of the initial grafting rate gives an activation energy which approximately corresponds to the initiation of grafting by oxy radicals. The dependence of the critical thickness of the PETP matrix on temperature has also been obtained for preirradiation in vacuum. The form of this dependence is identical to that of the rate of graft polymerization.