Semi-interpenetrating networks based on POLY(N-isopropyl acrilamide) and POLY(N-vinylpyrrolidone)

Abstract

Three series of semi-interpenetrating polymer networks based on cross-linked poly(N-isopropylacrylamide), PNIPA, and 1, 2 and 3 wt% of linear poly(N-vinylpyrrolidone), PVP, were synthesized in order to improve the mechanical properties of PNIPA gels. The effect of the incorporation of the linear PVP polymer into the temperature responsive networks on the phase transition temperature, swelling behavior and mechanical properties was studied. Polymer networks with four different crosslinking densities were prepared with various molar ratios (25/1 to 100/1) of the monomer (N-isopropylacrylamide) to the cross linker (N,N'-methylene-bisacrylamide). The hydrogels were characterized by determination of the equilibrium degree of swelling at 25 °C, the dynamic shear modulus and the effective crosslinking density, as well as the ultimate hydrogel properties, such as the tensile strength and elongation at break. Furthermore, the deswelling kinetics of the hydrogels was also studied by measuring their water retention capacity. The inclusion of the linear hydrophilic PVP in the PNIPA networks increased the equilibrium degree of swelling, the highest values of which were obtained for samples with 2 and 3 wt% of PVP and the NIPA/MBA molar ratio of 75/1 and 100/1. The highest reinforcement effect, evaluated from the ratio of G'red(semi-IPN) to G'red(PNIPA), was obtained by incorporation of 2 wt% PVP. The tensile strength of the semi-IPNs reinforced with linear PVP was higher than that of the PNIPA networks. The elongation at break of these semi-IPNs varied between 22 and 55%, which are 22-41% larger than those for single PNIPA networks. The tensile measurements confirmed that the presence of 2 wt% of the linear polymer significantly reinforced the PNIPA network.

Tri serije semi-interpenetrirajućih polimemih mreža, semi-IPN, na bazi umreženogpoli(N-izopropilakrilamida), PNIPA, i 1, 2 i 3 mas. % linearnog poli(N-vinilpirolidona), PVP, sintetisane su sa ciljem da se poboljšaju mehanička svojstva PNIPA gelova. Ispitivan je uticaj prisustva različite količine linearnog hidrofilnogpolimera na temperaturom indukovani pseudo-fazni prelaz, proces bubrenja, kao i na mehanička svojstva hidrogelova. Polimerne mreže sa četiri različite gustine umreženosti dobijene su variranjem molskog odnosa monomera (N-izopropilakrilamid) i umreživača (N,N'-metilenbisakrilamid, MBA) od 2511 do 100/1. Hidrogelovi su karakterisani određivanjem ravnotežnog stepena bubrenja, dinamičkog modula na smicanje, efikasnosti umreženja, zatezne čvrstoće i izduženja do kidanja. Uvođenjem linearnog hidrofilnog PVP-a u PNIPA mrežu ravnotežni stepen bubrenja raste i kreće se u opsegu od 7 do 16,5. Najveće vrednosti ravnotežnog stepena bubrenja pokazuju semi-IPN sa 2 i 3 mas. % PVP i molskim odnosom NIPA/MBA od 75/1 i 100/1. U odnosu na PNIPA hidrogelove ravnotežni stepen bubrenja kod ovih uzoraka veći je za 25-38%. Najveći efekat ojačanja, izračunat iz odnosa G'red(semi-IPN)/G'red'(PNIPA), postignut je uvođenjem 2 mas. % PVP-a. Vrednosti zatezne čvrstoće semi-interpenetrirajućih mreža ojačanih linearnim PVP-om veće su od vrednosti za PNIPA mreže i kreću se u intervalu od 5-12 kPa. Izduženje do kidanja za ove semi IPN je između 22 i 55%, što je za 22-41 % veće od vrednosti za PNIPA mreže. Ispitivanja mehaničkih svojstava na istezanje pokazala su (i potvrdila) da prisustvo 2 mas. % linearnog PVP polimera, značajno ojačava PNIPA mrežu.