Studies On The Preparation,Modification And UV-Shielding Performance Of Maleic Anhydride Copolymer Microspheres

Compared to inorganic UV-shielding agents,organic UV absorbers show more efficient UV-shielding performance.However,these small additive molecules have raised considerable concern in recent years due to photodegradation when exposed to UV light irradiation and migration during the processing or use of polymer materials.Grafting small molecular UV absorbers to micro-or nano carriers and directly constructing UV-shielding polymer particles are effective methods to improve the stability of these small additive molecules.UV-shielding micro-and nano particles can not only act as a chemical UV filter to absorb UV light,but also scatter and reflect UV light,thus illustrate better UV-shielding performance.A lot of UVshielding micro and nano particles have been reported,but there still exists some problems including complicated preparation process,use of highly toxic organic solvents and single function.In this paper,maleic anhydride copolymer microspheres were prepared via a simple and efficient self-stabilized precipitation polymerization method,and were used as a UVshielding agent in the polymer matrix after functional modification,which provided new ideas for design and fabrication of UV-shielding polymer particles.The specific research contents are as follows:1.Monodispersed ternary polymer microspheres with broadband UV-shielding performance were successfully prepared through the self-stabilized precipitation polymerization(2SP)of vinyl acetate(VA),maleic anhydride(MA)and a commercial vinyl UV absorber 2-(2’-hydroxy-5’-methacryloxyethylphenyl)-2H-benzotriazole(NB),using 2,2’-azobisisob-utyronitrile(AIBN)as an initiator.The effects of solvent,monomer feed ratio,initiator concentration,monomer concentration,reaction temperature and reaction time on the morphology,particle diameters,size distribution and UV-blocking performance of the resultant polymeric microspheres were investigated systematically.The experimental results indicated that the mixed solvent of ethyl benzoate and n-heptane with 7:3 volume ratio was the optimal solvent for preparation of monodispersed poly(VA-co-MA-co-NB)(PVMN)microspheres via2 SP process.The diameters and UV-blocking performance of the polymeric microspheres can be easily controlled by facile change of reaction conditions.With the increase of ratio of UV absorber NB,initiator concentration,monomer concentration and reaction temperature,the size of the polymeric microspheres increased while still keeping well dispersity.In addition,the established preparative strategy can be potentially extended to other UV-absorbant vinylic monomer and use as a versatile method for fabricating stable polymer UV absorber.2.Crosslinked maleic anhydride-α-methylstyrene copolymer microspheres(PMAS)were synthesized by self-stabilized precipitation polymerization,and then the fluorescent whitening agent VBL was grafted onto PMAS microspheres through esterification to obtain VBLfuntionalized PMAS microspheres(PMAS-VBL),finally the PMAS-VBL microspheres were incorporated into polyvinyl alcohol matrix to develop a transparent blue light emitting and UVshielding film.The results showed that VBL was successfully grafted onto the surface of PMAS microspheres.Compared with PMAS microspheres,the UV absorption efficiency of PMASVBL microspheres was significantly improved.At the same time,the PMAS-VBL microspheres displayed excellent fluorescence properties.The introduction of PMAS-VBL microspheres can effectively improve the UV-shielding performance of PVA films.With only1 wt% PMAS-VBL microspheres in PVA,the average transmittance of the composite films in the UV region decreased from 79.7% to 30.6% while visible light transmittance is still close to pure PVA.The rhodamine B degradation experiment further proved that the composite films have excellent UV-shielding properties.Under the protection of PVA/PMAS-VBL composite films,the degradation rate of rhodamine B solution was significantly reduced.Meanwhile,the films also showed excellent photostability and high quantum yield(QY),and the QY of the PVA7 film is as high as 74.26%.In addition,the thermal stability of the films was also effectively enhanced with the introduction of PMAS-VBL microspheres into PVA.Therefore,as transparent UV-shielding films that can emit blue light,the composite PVA/PMAS-VBL films have great application potential in fields of greenhouse agriculture,photovoltaic materials and so on.3.The prepared crosslinked styrene-maleic anhydride copolymer microspheres(PSM)were aminated with ethylenediamine,and then modified with caffeic acid via EDC/NHSmediated amidation reaction to obtain antioxidative UV-shielding copolymer microspheres(PSM-CA),and finally the PSM-CA microspheres were introduced into PVB to prepare composite films.The experimental results showed that caffeic acid was successfully grafted on the surface of PSM microspheres,and every 1000 mg PSM-CA microspheres contains 40.67 mg caffeic acid.The results showed that the introduction of PSM-CA microspheres not only endowed the PVB matrix with a good capacity to scavenge radicals,but also effectively improve its UV-shielding efficiency.The PVB films containing 5 wt% PAM-CA microspheres can block 100% of UVC and UVB,as well as 99% of UVA,with radical scavenging activity up to 89.2%.Photodegradation measurement of Rhodamine B solution also confirmed the improved UV-shielding performance of PVB films after introducing PSM-CA microspheres.In addition,the PVB composite films exhibited excellent photostability in the whole UV region with wavelength from 200 to 400 nm,which still remained low UV transmittance after irradiation for 8 h.Moreover,PSM-CA microspheres the incorporation of a small amount of PSM-CA microspheres has no obvious effect on the thermal stability and mechanical properties of the films,but excessive addition would lead to a decrease of in the elongation at break.