Mikro struktura polihipe polimerov dosežena s sinerezo, hiperzamreženjem in graftiranjem : doktorska disertacija

slovenian

doktorska dela

2020

hypercrosslinking   polyHIPE materials   RAFT grafting from the surface of polyHIPE materials   RAFT polymerization   syneresis

Univerza v Mariboru, Fakulteta za kemijo in kemijsko tehnologijo

Within the doctoral dissertation, styrene-based polymers with multilevel porosity were prepared. A well-defined porous structure was achieved by combining different techniques to introduce porosity into the polymers. By polymerizing the continuous phase of a high internal phase emulsion, macroporous polymers with an open cell interconnected polyHIPE structure were formed. Micropores were obtained using a Friedel-Crafts hypercrosslinking reaction, and by syneretic phase separation using a mixture of solvents. Multilevel pore size distribution is advantageous when using polymeric materials in flow systems where macropores allow convective mass transfer and reduce back pressures, while smaller meso- and micropores increase the specific surface area.%Highly porous poly (styrene-co-divinylbenzene) polymers were prepared by polymerizing the continuous phase of a high internal phase emulsion. Monoliths were synthesized by free radical and RAFT (reversible addition-fragmentation chain transfer) polymerization. In both polymerization types, the polymers had a typical polyHIPE structure. The polymers were then hypercrosslinked with the radical initiator di-tert-butyl peroxide to obtain micro- and mesopores, and consequently to raise the BET specific surface area (3 to 4 fold increase). The microstructure of the polyHIPE materials was also affected by the type of polymerization. Compared to the polymers prepared using free radical polymerization, the specific surface areas of non-hypercrosslinked polyHIPE materials prepared with RAFT polymerization were 4-5 times higher, which indicates increased formation of micropores in the case of RAFT crosslinking mechanism. %Furthermore, poly (styrene-co-4-vinylbenzyl chloride-co-divinylbenzene) polyHIPE materials with a typical open cellular polyHIPE structure were prepared at different initial crosslinking degrees (2, 5 and 10%). The addition of styrene to the monomer mixture dilutes the functional groups and enables the study of the effect of dilution on the Friedel-Crafts hyperlinking reaction. The hypercrosslinking reaction introduces micropores into the macroporous polyHIPE materials which results in high BET specific surfaces (up to 731 m2/g). At 57-63 mol% of STY the dilution of the functional groups is too intense to enable effective hypercrosslinking which results in a drastic drop in specific surface areas and a lack of micropores, compared to samples with higher concentrations of functional groups.%In continuation, glycidyl methacrylate was grafted from the surface of macroporous poly (4-vinylbenzyl chloride-co-divinylbenzene) monoliths which were prepared by the radical polymerization of the continuous phase of the high internal phase emulsion. In order to increase the specific surface area the highly porous (80% porosity) polyHIPE materials were hypercrosslinked by Friedel-Craft reaction and further functionalized with branched tris (2-aminoethyl) amine. The free amino groups of the branched amine were used to immobilize a suitable RAFT agent for glycidyl methacrylate grafting from the surface. High surface density of the glycidyl methacrylate molecules on the surface was obtained by surface grafting of the polyHIPE materials with bound RAFT reagent. Grafting was performed only on the hypercrosslinked materials, as these achieved higher conversions in the reaction with the amine and RAFT reagent, due to the greater accessibility of the reactive sites. The efficiency of the grafting reaction was confirmed by gravimetry, scanning electron microscopy and infrared spectroscopy. The RAFT polymerization also improved the mechanical properties of the poly (4-vinylbenzyl chloride-co-divinylbenzene) polyHIPE materials.%In the second part of the doctoral work, syneretic phase separation was used as the tool for porosity induction in the synthesis of poly (4-vinylbenzyl chloride-co-divinylbenzene) beads using suspension polymerization. The monomer phase was diluted with toluene or with a

07.08.2023