Self-Stabilized Precipitation Polymerization Of Vinyl Chloride-Maleic Anhydride And Itaconic Anhydride And Its Application In Oil-Water Separation

Self-stabilized precipitation polymerization（2SP）is a highly efficient and environmentally friendly technique which is widely used to prepare functional polymer microspheres with well-defined morphology and uniform particle size using low-toxic esters or ketones as reaction medium without any surfactants or stabilizers.Poly（vinyl chloride）is the largest chlorine-consuming product in the chlorine-alkali industry.The preparation of functional vinyl chloride-based microspheres with regular morphology and clean surface through copolymerization of vinyl chloride with other functional monomers is of great significance to broaden the application of vinyl chloride polymers in many fields and new scenarios.Maleic anhydride（MAH）and itaconic anhydride（ITA）with double bonds and hydrophilic anhydride groups are often used as important monomers for the modification of other polymer materials.Therefore,it is of great significance to prepare multifunctional vinyl chloride-based microspheres and anhydride-based microspheres,which can be applied for the functional modification of other polymer materials.Based on the 2SP polymerization technology,the copolymerization of VCM-MAH and the homo-polymerization of ITA were designed and implemented.A series of anhydride-based polymer microspheres with well-defined morphology and uniform particle size were synthesized by simply adjusting the polymerization conditions.The anhydride groups on the surface of these microspheres provide a platform for further functional modifications.Surface precipitation light-grafting polymerization（S2P）technology was developed by combining the 2SP polymerization technique with the surface light-grafting method.It provides a new idea for constructing asymmetric wettability membrane.Additionally,based on the inherent UV shielding effect of PET,S2P polymerization exclusively takes place on the illuminated side of PET,effectively fabricating PET with unique asymmetric wettability.Moreover,the potential application of these asymmetric wettability membranes in wastewater treatment,including oil-water separation,heavy metal adsorption,and dye removal,has been comprehensively investigated.The main contents are as follows:1.The 2SP copolymerization of VCM and MAH was studied in detail.The impact of the reaction solvent,concentration of monomers and initiators,as well as the ratio of monomer feed on the morphology,size and dispersibility of the VCM-MAH copolymer（PVM）microspheres were systematically evaluated.The results showed that the mixed solvent system of n-hexane/isoamyl acetate performed exceptionally well as a reaction medium for the 2SP copolymerization of VCM and MAH.Specifically,when the solubility parameter ranged from 15.92 to 16.22 MPa^1/2,PVM microspheres with well-defined morphology and uniform particle size were obtained.The number average particle size（D_n）of PVM microspheres ranged from 185 to 335 nm,with a narrow particle size distribution（PSD）ranging from 1.02 to 1.05,while the number average molecular weight（M_n）of PVM copolymer ranged from14400 to 21400.Elemental analysis indicated that VCM and MAH tended to alternately copolymerize at different feeding ratios during polymerization process.Additionally,SEM was employed to characterize the morphology and particle size of PVM microspheres obtained at various stages of polymerization,elucidating the progress of nucleation and growth of the PVM microspheres.Moreover,PVM microspheres were further used to modify PET non-woven fabrics,which can significantly enhance the hydrophilicity of PET,leading to a decrease in its surface contact angle from 112.3°to 0°（after 50 s）.In water/hexane oil-water separation,the modified PET non-woven fabric exhibited high throughput(50012±2003 L·m^-2·h^-1)and high separation efficiency（99.95%）,demonstrating excellent performance for water/light oil separation applications.2.The 2SP polymerization technology was successfully extended to the homo-polymerization of itaconic anhydride（ITA）.Highly reactive carbon-carbon double bond and anhydride group enable the synthesis of anhydride-based polymer microspheres with reduced particle size.Firstly,a systematic screening was conducted to identify the suitable reaction medium for 2SP polymerization of ITA.Poly（itaconic anhydride）（PITA）microspheres with small size,regular morphology and narrow dispersity can be prepared in isoamyl acetate and n-hexane（mass ratio of 1/14）mixed solvent.The resulting microspheres had a minimum D_n of 139 nm,PSD of 1.03,and M_n of 1400 g/mol.Furthermore,the impact of various polymerization factors such as monomer concentration,temperature,as well as initiator concentration and type on the morphology,particle size,yield and M_n of the microspheres were comprehensively investigated.The morphology of microspheres during different stages of polymerization was tracked using SEM.It was observed that the microspheres grew rapidly in the early stage（6 h）,but the growth rate slowed down later.In order to make the particle size smaller,a low content（1wt%）of divinylbenzene（DVB）or ethylene glycol dimethacrylate（EGDMA）cross-linking agents were incorporated into the polymerization system,resulting in the PITA microspheres with an average particle size of 95 nm.Alternatively,when the content of DVB cross-linking agent increased to 10 wt%,PITA microspheres with a larger particle size of 125 nm could be obtained with a higher yield（54.0%）.3.Inspired by the above-mentioned strategy for the preparation of microsphere,the surface precipitation photo-grafting（S2P）polymerization technology was developed by combining the 2SP polymerization technology with surface photo-grafting techniques.The influence of a series of reaction conditions such as reaction medium,monomer and initiator concentration,irradiation time on the S2P polymerization system of ITA were systematically studied,and PITA microspheres were successfully grafted onto the surface of PET nonwoven fabric.The results demonstrate that,due to PET’s inherent UV light shielding effect,surface photo-grafting polymerization solely occurs on the illuminated side,resulting in hydrophilic surface of the illuminated side while the unilluminated side remains hydrophobic.This process enables the fabrication of an asymmetric structure for PET non-woven membrane.Furthermore,the alkaline hydrolysis of the anhydride group of PITA was performed,leading to the introduction of more hydrophilic carboxylic groups and micro-nano structure.This process enabled the construction of a PET-g-ITA-alk film with special asymmetric wettability.The illuminated side surface of the obtained PET-g-ITA-alk exhibited superhydrophilicity（WCA～0°）and underwater superhydrophobicity（UOCA～153°）,while the backlight side surface demonstrated intrinsic hydrophobicity and underwater superlipophilicity.By leveraging the special asymmetric wettability of the membrane,on-demand separation of water/light oil and heavy oil can be achieved with a permeation flux as high as 97207±172 L·m^-2·h^-1 and a separation efficiency of 99.8%.Moreover,the PET-g-ITA-alk also exhibits exceptional wear resistance,acid-base resistance,and reusability,which has outstanding application value in the field of oil-water separation.This straightforward and innovative preparation method offers novel insights for developing membrane materials with special asymmetric wettability.4.To further enhance the durability of the PET membrane and improve its separation performance,particularly for oil-water emulsion separation efficiency,an asymmetric structure was created by cross-linking reaction using DVB as a cross-linking agent.Subsequently,crosslinked PITA microspheres（CL-PITA）were successfully grafted onto the illuminated side of the PET through S2P polymerization of PITA and DVB.The surface of PET-g-ITA/DVB-cat was then functionalized with polyethylene imine（PEI）,followed by protonation with hydrochloric acid to prepare a multifunctional PET-g-ITA/DVB-cat membrane.The effects of grafting times,M_n of PEI,and DVB content on the morphology,grafting rate,and wettability of the CL-PITA microspheres were investigated to determine optimal reaction conditions.The results demonstrated a significant correlation between grafting times and the enhancement of both particle size and grafting efficiency of the microspheres.Furthermore,the incorporation of DVB greatly enhanced the dimensional stability of CL-PITA and improved solvent resistance of the PET-g-ITA/DVB-cat membrane.After 10-times water/n-hexane separation experiments,the PET-ITA/DVB_（10）-cat membrane exhibited a slightly lower flux decay（14.6%）than PET-ITA/DVB_（0）-cat membrane（46.4%）.Moreover,as the DVB content increased from 0 to 10 wt%,the separation efficiency of water/xylene emulsions using PET-g-ITA/DVB-cat membranes improved from 98.7%to 99.6%.Additionally,the PET-g-ITA/DVB-cat membrane can also effectively remove dyes and heavy metal ions.The rejection rates of PET-g-ITA/DVB_（10）-cat for Congo red,methylene blue,Cu²⁺,and Co²⁺heavy metal ions at a concentration of 5 mg/L were significantly higher than those achieved by PET-g-ITA/DVB_（0）-cat,with values of 90.3%,10.0%,91.7%,and 90.7%,respectively.This efficient,multifunctional,and sustainable PET-g-ITA/DVB-cat membrane enables effective separation of oil-water mixtures,water-oil emulsions,organic dyes,and heavy metal ions,showing great potential for diverse applications in complex wastewater treatment.