Poly(ethylene terephthalate) (PET) is one of the most widely used synthetic materials in the world. Its high crystallinity and high melting point are responsible for its toughness and its excellent fiber-and film-forming properties. In these two forms it has found many industrial, biomedical and domestic applicationsas a base film of magnetic tape, photographic films, and photorecording medium, as textiles, packaging, in biomedical engineering as a material for artificial blood vessels, tendons, hard tissue prostheses, surgical thread and many others. As are most synthetic polymers, PET is relatively inert and hydrophobic without functional groups able to take part in covalent enzyme immobilization. To overcome this drawback chemical modifications have been attempted to alter the surface properties of the material.
Many methods of modification of PET surface have been proposed, among them are controlled, chemical breaking of ester bonds [1-15], surface grafting polymerization [16][17][18][19][20][21][22][23][24][25][26] and plasma treatment [27][28][29][30][31][32][33]. The first group of methods includes reaction of PET with low molecular weight substances containing hydroxyl, carboxyl or amine groups thus incorporating corresponding functionalities onto the surface. Such action increased the hydrophility of the polymer and created the anchor functionalities for subsequent reactions. The main problem however is to find the proper parameters of these processes, parameters that do not cause high degradation or significant decrease of the mechanical properties of the sample. The same processes but in much more severe conditions are applied also for chemical recycling of PET [34,35].
Primary amine groups are often introduced by thermally induced aminolysis, which is reaction of an organic amine agent with the ester bonds along a polymer chain. Among the most often used amines are hydrazine [13,15], ethylenediamine [6][7][8][9][10][11][12]15] and 1,6-diaminohexane [2,4,11].
The expected applications of modified polyester are diverse-in electronic devices [27,33], in water-fuel separation process [32] or in textile industry to improve properties of fabric (dyeing) [1]. However, the most often pointed out goal of all those modification is to gain biocompatible and bioactive surfaces for biomedical applications of PET. Most researchers try to develop anti-adhesive and antibacterial [2,4,16,23,24] properties or improve biocompability (cell attachment and growth, antithrombic properties) [3,5,15,[17][18][19]21,24,26,28,29] of polymeric materials.
Functional groups created during modification processes can serve as anchor sites for covalent immobilization of various