ИСТИНА

Our recent investigations have shown that in acidic medium polyacrylic acid (PAA) forms thermo-sensitive complexes with polycations, such as poly(diallyldimethylammonium chloride), poly(1,2-dimethyl-5-vinylpyridinium methylsulfate), poly(ethylene imine). The complex formation is due to ion-dipole interactions between non-ionized carboxylic groups of PAA and positively charged functional groups of polycation. Now we turn from the study of homopolymers in mixtures to the copolymers study. The copolymers of various microstructure based on 4-vinyl pyridine (4-VP) and acrylic acid (AA) have been synthesized by means of reversible addition – fragmentation chain transfer (RAFT) polymerization and characterized using GPC and 1H NMR. The symmetrical triblock-copolymer poly(4-VP)-block-poly(AA)-block-poly(4-VP) contains 60 units of 4-VP and 150 units of AA, while the content of AA units in the polymeric chain of gradient copolymer of closer average composition increases from the tails of macromolecule to its centre. As well as quaternized samples of the above copolymers were studied. First of all we have studied the influence of chain architecture on the properties of obtained copolymers in aqueous solutions. Using Dynamic Light Scattering technique we found that in acidic medium (0.1 M HCl) both copolymers formed aggregates of average hydrodynamic radius about 80 – 90 nm. Static Light Scattering measurements showed that aggregates consist of 26 - 37 macromolecules depending on the chemical structure of copolymer. The driving force of aggregation is presumably ion-dipole interaction between the positively charged units of 4-VP and carboxylic groups of AA. This assumption was proved by the investigation of the influence of temperature on the aggregation numbers. Since all copolymers contain considerable excess of AA units, we assume the following structures of aggregates: triblock-copolymer forms micelle-like aggregates with core of poly(4-VP) – poly(AA) complex and corona of excess poly(AA) blocks; gradient copolymer aggregates contain 4-VP and AA units in the interior, as well as at the surface. The study of solutions phase state shows that chain microstructure affects the aggregative stability of copolymers in solution. The influence of chain microstructure on the kinetics and mechanism of adsorption of amphiphilic copolymers onto nylon membrane has been studied. It was shown that poly(AA) is incapable of adsorbing onto nylon memabrane, however for all copolymers the adsorption was observed, which might be caused by 4-VP interaction with membrane.The mechanism of adsorption for gradient copolymers is similar to that for block-copolymers. It was found that for triblock-copolymers as well as for gradient copolymers the initial portion of adsorption isotherm is described by Langmuir equation, while the final part – by Freundlich equation. However both adsorption constants and limiting adsorption values are different for the above samples. The difference in adsorption parameters of the copolymers studied is associated with difference of their micro-structure, that is, the distribution of the monomeric units in the polymeric chain.