| Popis: |
Prepletene polimerne mreže (IPN) definiramo kot kombinacijo polimernih mrež, kjer je vsaj ena sintetizirana in/ali zamrežena v prisotnosti druge polimerne mreže. V razvoju in raziskavah pa postajajo zelo popularni dinamični polimeri, ki lahko pod specifičnim vplivom izmenjujejo kemijske vezi in tako spremenijo topologijo svoje strukture. Sinteza IPN se običajno izvede na sekvenčni način. Z ustreznimi monomeri, ki polimerizirajo po ločenih mehanizmih, pa jih lahko pripravimo tudi na simultani način. V našem raziskovalnem delu smo pripravili tako sekvenčne kot simultane full-IPN, v katerem sta bili obe polimerni komponenti zamreženi. Ena polimerna mreža je bila nedinamična in sicer na osnovi stirena, kopolimeriziranega z divinil benzenom. Druga polimerna mreža pa je bila na osnovi ε-kaprolaktona, kopolimeriziranega z 4,4'-bioksepanil-7,7'-dionom, ki je predstavljala dinamično mrežo zaradi možnosti reorganizacije mreže preko reakcije transesterifikacije. Raziskovali smo kako način sinteze, gostota zamreženja in hitrost polimerizacije z odpiranjem obroča ε-kaprolaktona vplivajo na termične in mehanske lastnosti materiala, ki smo jih določili z DSC ter DMA. Full-IPN smo nadalje uporabili za pripravo poroznih struktur polistirena, tako da smo PCL degradirali pod pogoji hidrolize ter porozni skelet analizirali s SEM. Full-IPN vzorci, pripravljeni na sekvenčni način, imajo ne glede na količino difenil fosfata kot katalizatorja za polimerizacijo z odpiranjem obroča CL, praktično identične mehanske in termične lastnosti. Zelo podobne lastnosti imajo tudi full-IPN vzorci pripravljeni na simultani način z večjo količino DPP. Po drugi strani pa vzorci pripravljeni na simultan način z manjšo količino katalizatorja, pri katerih je gel nastal pred fazno separacijo, izkazuje boljšo mehansko trdnost v območju nad temperaturo tališča PCL. Pokazali smo, da je, ob enaki gostoti zamreženja, kristaliničnost PCL-a rahlo večja ob hitrejši polimerizaciji. Porozna struktura PS je pokazala, da imajo full-IPN pri večji količini DPP večje polimerne domene zaradi obsežnejše fazne separacije. Pokazali smo, da je struktura full-IPN odvisna tako od hitrosti nastanka obeh polimernih mrež, kot tudi od možnosti reorganizacije dinamične mreže z izmenjavo kemijskih vezi. Interpenetrating polymer networks (IPN) are defined as a combination of polymer networks, where at least one network is synthesized and/or cross-linked in the presence of the other. In research and development of polymer materials, a relatively new topic of dynamic polymers is getting extremely popular, because of their ability to exchange bonds under specific conditions which gives them the power to alter the topology of their structure. IPN synthesis is usually performed sequentially, but with the right monomer selection, where each one polymerizes by a different mechanism, we can also prepare them simultaneously. In our work, we prepared sequential and simultaneous full-IPNs, where both polymer components were cross-linked. One polymer network, based on styrene and copolymerized with divinylbenzene, was static. The other polymer network, which was based on ε-caprolactone and copolymerized with 4,4'-bioxepanyl-7,7'-dione, represented a dynamic network, because it has the ability to reorganize its structure through transesterification reaction. By tuning the cross-linking density and kinetics of ɛ-caprolactone polymerization, we investigated how these changes affect the thermal and mechanical properties of the final material, which we determined by DSC and DMA. Further, we used IPNs as precursors for porous PS structure by degrading PCL under hydrolytic conditions, so we could analyse the porous skeleton by SEM. Sequential full-IPNs exhibited identical mechanical and thermal properties no matter the amount of DPP catalyst for ring-opening polymerization of ε-caprolactone. Simultaneous full-IPNs with higher DPP amount display similar characteristics. On the other hand, simultaneous samples with lower amount of catalyst, where gel point occurs before phase separation, demonstrate higher mechanical strength above PCL melting temperature. We have shown that the PCL crystallinity slightly arises with faster polymerization process for samples with the same cross-linking degree. The porous PS structure revealed that full-IPNs have larger domains due to greater extent of phase separation, when larger amount of DPP was used. Finally, we showed that full-IPN structure depends on the formation rate of both polymer networks and the ability of a dynamic network to alter its structure by dynamic bond exchange reaction. |
