Non-fluorine-segment Length Fluorinated Poly Butyl Methacrylate Block Copolymer Surface Structure Constructed

Excellent surface performance of fluorinated block copolymer depends on the packed CF3 groups formation on its surface. Up to the present time, the improvement of surface performance of fluorinated copolymer is to increase the content of expensive fluorinated monomer. Hence, it become a research focus how to architect the excellent surface structure with lower content of fluorine.A series of diblock copolymers poly(butyl methacrylate)-b-poly(perfluoro- octylethyl methacrylate) (PBMAm-b-PFMAn) and triblock copolymers (PFMAn-b -PBMAm-b-PFMAn) were synthesized by atom transfer radical polymerization (ATRP). Effect of degree of polymerization of PBMA on the air/solution interfacial structures of copolymers was systematically investigated by surface tension measurement and surface-sensitive sum frequency generation vibrational spectroscopy (SFG). Surface structures on copolymer solid films were architected, proceeding from the air/solution interfacial structures. And then the relation between surface structures and air/solution interfacial structures were studied in detail. Some conclusions were obtained as follows:(1)Surface tension of PBMAm-b-PFMAn and PFMAn-b-PBMAm-b-PFMAn copolymers in toluene solution increased with increasing of PBMA block length. When the length of PBMA block was long enough, surface tension of copolymers approached to the surface tension of PBMA toluene solution. SFG result reveals that no fluorinated component was absorbed on the air/solution interface. When the length of PBMA block was short, PFMA block was absorbed at the solution interface and the toothbrush structure was formed, which results in great decrease of surface tension compared to PBMA homopolymer solution. It might be related to stability of micelle formed in toluene solution.(2)The length of PFMA block also influenced the surface tension of copolymer toluene solution. As to PBMAm-b-PFMAn toluene solution, when the length of PBMA block was equal to or less than 308, surface tension of copolymer solution decrease with increasing of the length of PFMA block. While the length of PBMA block was greater than 308, surface tension of copolymer solution increased with increasing the length of PFMA block. The explanation was as follows: when the length of PBMA block was short, the micelle formed in toluene solution was instable and PFMA block was helpful to adsorb at air/solution interface. When the length of both PBMA block and PFMA block were long, the stable micelle was formed which would stop PFMA component from adsorbing at air/solution interface.(3)When the length of PBMA block was short, the surface tension of PFMAn-b -PBMAm-b-PFMAn toluene solution was much lower than the surface tension of PBMAm-b-PFMAn copolymers. SFG result reveals that more PFMA block was absorbed and denser structure was formed at PFMAn-b-PBMAm-b-PFMAn toluene solution/air interface than PBMAm-b-PFMAn in toluene solution. This was due to the looser micelle, which is helpful for adsorption of PFMA segments, in PFMAn-b- PBMAm-b-PFMAn toluene solution. When the length of PBMA block was long enough, the surface tension of PFMAn-b-PBMAm-b-PFMAn and PBMAm-b-PFMAn copolymers solution approached to that of PBMA solution. The results show that more PBMA segments was absorbed on the air/solution interface.(4)When the length of PBMA block was short, and the PFMA block length was about 1.0, surface tension of their cyclohexanone solution was much lower than that of toluene solution for PBMAm-b-PFMAn. As the PFMA block length was about 4.0 or 6.0, PBMAm-b-PFMAn in toluene solution had a lower surface tension. This was attributed to that solubility parameters of toluene is closer to FMA. When the block length of PFMA and PBMA are short, the micelle formed in solution was instable. Cyclohexanone, which is of high polarity, promote PFMA segments adsorbing at air/solution interface. But the stability of micelle is enhenced in cyclohexanone solution with increasing of PFMA block length. When the length of PBMA block is long, surface tension of PBMAm-b-PFMAn solution approached to that of PBMA solution. SFG result revealed that no fluorinated component was absorbed at the air/solution interface. This was attributed to the stable micelle formed in solution as the PBMA block is long enough. (5)The surface structures of the films were determined by the air/solution interfacial structures of the copolymers when the film was prepared by spin-coating. This might be attributed to the rapid evaporation of the solvent. The structure at air/solution interface was freezed in this way. So the surface structure of spin-casting films have close relation with interface structures of solution.(6)The structure at air/solution interface have no significant effect on surface structures of the films prepared by casting. The content of PFMA at surface of casting films increased with increasing of the length of PBMA block. When the block length of PBMA was as long as 512, the content of PFMA at surface of casting films was maxmum value, and the perfluoroalkyl side chain were tightly packed at the surface. This may be attributed to that the free energy of PFMA components of surface enrichment was influence by PMMA block length. As to casting film, evaporation of the solvent was so slow that there were enough time to enrich surface with more PFMA segments. Hence, the air/solution interfacial structures have no significant effect on surface structure of casting films.