Controlled Preparation, Structure And Performance Of Novel Fluorinated Copolymers Via A(R)GET ATRP

Fluorinated polymer is a kind of excellent material with high thermal stability, superb chemical resistance, superior weatherability, oil and water repellence and low flammability. Poly(fluoroalkyl acrylate)s with long perfluoroalkyl groups (≥8) are known as the perfect polymer materials with extremely low surface energy. However, their degradation products, perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), cause severe environmental problems such as bioaccumulation and reproductive toxicity. Besides, PFOA and PFOS cannot naturally degrade. So the usage of poly(fluoroalkyl acrylate)s has been limited. Alternative fluorinated materials which are environmentally friendly and nontoxic are needed to replace the traditional fluoroalkyl polymers.It’s been reported that poly(perfluoroalkyl acrylate)s containing chains of six or less perfluorinated carbon atoms (PFA-C<6) do not bioaccumulate in the human body, but their surface properties are not as good as those with eight perfluorinated carbon atoms (PFA-C8) because their alkyl side chains are hard to crystallize or create stable arrangement of structure. So PFA-C<6 is not practical. However, if space group is introduced to PFA-C<6, it can improve the surface properties of PFA-C<6, especially oil and water repellence.In this work, we introduced a polar sulfonamido space group between the main chain and side chain of PFA-C6 to improve its surface properties, and [N-methyl-perfluorohexane-1-sulfonamide] ethyl (methyl) acrylate (C6S(M)A) was synthesized. The introduced spaced group improve the stability of the alkyl side chain of C6S(M)A. Homopolymers of C6S(M)A were synthesized via traditional free radical polymerization, and their surface properties were tested. Test results show that these homopolymer have excellent oil and water repellence. And then copolymers of C6S(M)A and MMA or PEGMA were synthesized via atom transfer radical polymerization (ATRP) to obtain designed polymer. The activities of C6S(M)A, copolymerization rules and properties of copolymers were investigated and characterized. Based on the work mentioned above, inorganic-polymeric composite materials were surface-initiated polymerization via ’grafting from’ approach on surface modified nano-silica particles, and their structures and properties were characterized.In this work, several conclusions are drawn as followings:1. Synthesis and characterization of environmental fluorinated monomers C6S(M)A(1) Two fluorinated monomers with polar space group (-N(CH3)SO2-), C6SA and C6SMA, were synthesized using Perflurohexane sulphonyl fluoride as raw material through amination, alchoholization and esterification. The yield of C6S(M)A were about 75%, and the structures of intermediates and products were characterized by FTIR and 1H-NMR.(2) The reactivity ratios between C6SA and MMA, PEGMA were determined via Kelen-Tiidos method during ATRP in solution. The results are as follows:r(C6SA)= 0.34, r(MMA)=1.42; r(C6SA)=0.11, r(PEGMA)= 1.12, and it can be seen that the relative reactivity of C6SA is lower than MMA and PEGMA.2. Synthesis and surface properties of statistical copolymers PC6S(M)A/MMA via A(R)GET ATRP(1) Catalyst is the key factor to control A(R)GET ATRP. When Sn(EH)2 and Cu2+/PMDETA are added stoichiometrically to reaction system, copolymerization is living/controllable. When reducing agent was excess, it was hard to control the A(R)GET ATRP of C6S(M)A with PMDETA as ligand. When high reactive Me6TREN was used as ligand, it was able to control the copolymerization of C6S(M)A efficiently using low catalyst concentration ([Cu(Ⅱ)]≤200ppm) and excess Sn(EH)2, and fast reaction rate was achieved.(2) Besides catalyst, the composition of comonomers, reaction temperatures, the concentration of initiator and designed degree of polymerization also have effects on the reaction rate and controllability. When the concentration of Cu(Ⅱ) is 100ppm (VS. monomer) and the reaction temperature is higher than≥100℃, polymerization is uncontrollable. And expected reaction rate and controllability are achieved when the reaction temperature is between 50-90 ℃.(3) The copolymerization of C6SMA and MMA is ideal, the static contact angle of P(MMA-co-C6SMA) increases linearly as the content of C6SMA increases. A lowest surface energy of 17.5mN/m was achieved when C6SMA content was 55%wt.(4) Copolymer tends to form statistical structure during ATRP due to the big difference between the reactivity ratios of C6SA and MMA. As copolymer chain grows, the accumulated content of C6SA increases, while MMA content decreases. Thus gradient copolymer forms. A lowest surface energy of 11.1mN/m was achieved when C6SA content was 60%wt.3. Synthesis and properties of diblock copolymers PMMA-b-C6SA via A(R) GET ATRP(1) PMMA-Br macromolecular initiators with different molecular weights can be controllably synthesized via both AGET ATRP and ARGET ATRP, and all the PDIs are lower than 1.3 with a high conversion rate of 98%. When these initiators are used in the polymerization of C6SA, initiators prepared via AGET ATRP show almost no initiating activity, while initiators prepared via ARGET ATRP show good initiating activity and give a high conversion rate of over 95%. This result indicats when catalyst concentration is lower than 100ppm, the fuctional groups -Br at the end of macromolecular initiators can be well reserved.(2) As mentioned before, PMMA-Br macromolecular initiators with different molecular weights prepared via ARGET ATRP show good initiating activity, and they can be used to synthesize PMMA-b-PC6SA copolymers with different chain lengths. Diblock copolymers synthesized using PMMA-Br with high molecular weight as initiator have lower surface energies when same C6SA content is used. It’s observed that there is micropase separation phenomenon on the surface of the diblock copolymers membrane in AFM. When the DP of PC6SA segment reaches 15, the surface energy of diblock copolymers tends to stablize at a level about 10.7mN/m. The water static contact angle is about 120°, and the HD static contact angle is about 75°.4. Synthesis and performance of P(MMA-b-C6SA) on the surface of nano silica particles via’grafting from’approach(1) Spheral nano silica particles (particle size:100nm) were prepared using Stober method with TEOS as raw material. And then SiO2-NH-Br, a ATRP initiator, was synthesized through two-step method.(2) SiO2-NH-Br was used to initiate ARGET ATRP, and a macromolecular initiator SiO2-PMMA-Br was synthesized. And then this macromolecular initiator was used to initiate the block copolymerization with C6SA, and a organic/inorganic nano composite fluorinated copolymer SiO2-P(MMA-b-PC6SA) was prepared.(3) SiO2-P(MMA-b-PC6SA) has a rough surface with micro-nano hierarchial structure, and the roughness reaches 4.2nm. The water static contact angle is as large as 143°, and the HD static contact angle is 90°. After theoretical analysis on this rough surface, it’s concluded that the superio oil and water repellence of SiO2-P(MMA-b-PC6SA) is achieved through modification using low-surface-energy fluorinated copolymer and rough surface.