Vapor-based Fabrication Of Isocyanate-based Polymer Coatings And Their Applications

As an indispensable branch of functional thin films,barrier and protective films have played an important role in industrial production and daily life.The rapid development of technology has lead the research of barrier and protective films towards facile manufacture methods that can prepare films with maximized functionalities and enhanced durability.Polymer barrier films are considered to have wider applications than their inorganic counterparts,due to the advantages such as flexibility,lightness,ease of manufacture,and low cost.However,the traditional liquid-phase preparation methods often require a large amount of organic solvent,thus not applicable to solvent-sensitive materials and pose potential damages to both the operator and environment.In addition,the complex reaction environment in the liquid phase can also lead to uncontrollable polymerization and film formation processes,and the prepared films usually have rather poor inherent barrier performance and durability.In this work,initiated chemical vapor deposition(iCVD)was used to copolymerize bifunctional isocyanate monomer with functional monomers baring primary amino group and short fluorinated side chain,leading to highly transparent flexible gas barrier coatings and durable hydrophobic protective coatings,respectively.The obtained results are as follows:1.Transparent flexible polymer barrier coatings consisting of poly(isocyanate ethyl methacrylate-co-4-aminosterene)(pIEM-AS)were fabricated by copolymerizing isocyanatoethyl methacrylate(IEM)and 4-aminostyrene(AS)using iCVD on polystyrene film.The highly reactive isocyanate group from IEM reacted with primary amino groups from AS upon deposition,inducing self-crosslinking.The resultant coatings were smooth and uniform,with light transmittance over99%.The compositional ratio of the copolymer can be easily adjusted by changing the feed ratio of precursors.Subsequent annealing maximized the crosslinking degree of the coatings,and reduced possible internal strains.Copolymer coating with optimized composition(pIEM-AS₂)exhibited oxygen permeability as low as 4.2×10^-3 Barrer,which is 26 times and 8 times lower than commercially available PET and PVDF barrier films,respectively.The pIEM-AS₂ coating also exhibited excellent mechanical strength with Young's modulus of 11.7 GPa and hardness of 0.41GPa,superior than most conventional polymer materials.In addition,the pIEM-AS₂ coating on polycarbonate film substrate remained intact after folding test,indicating its high flexibility.The achieved barrier performance was attributed to the highly crosslinked structure consisting of rigid benzene rings and flexible IEM side chains,which effectively reduced the free space volume and improved the gas barrier properties;whereas the mechanical strength and flexibility was attributed to the annealing process which alleviated the internal strain,and the low average connectivity number which provided high freedom of the atoms within the network.The reported copolymer coating system is thus expected to be used in various fields ranging from flexible electronic encapsulation to food packaging and corrosion protection.2.Environmental-friendly hydrophobic coatings,poly(perfluorooctyl acrylate-co-isocyanate ethyl methacrylate)(pC6-IEM),were prepared using iCVD,followed by subsequent annealing under high humidity.The isocyanate groups react with water vapor in the air,inducing crosslinking within the coating.The obtained crosslinked network effectively limited the rearrangement of fluorinated chains on the surface;thereby greatly improved the dynamic hydrophobicity of the coating.When the content ratio of perfluorooctyl acrylate(C6)to IEM in the copolymer was about 0.43,coating on flat Si wafer substrate exhibited a minimum water sliding angle(WSA)of 24°.Annealing-induced crosslinking also enhanced the structural stability and mechanical properties of the coating,rendering high resistance to different organic solvents and prolonged ultrasonication.The achieved pC6-IEM coating also exhibited high flexibility,as well as excellent mechanical strength with Young's modulus and hardness of 9.7 GPa and 0.32 GPa,respectively.When deposited on fabrics,the hydrophobic coating imparted superhydrophobicity to the fabric with water contact angle higher than155?and WSA as low as 3?.The superhydrophobicity of the coated fabric was maintained surviving harsh durability tests,such as 1000 cycless of abrasion and 100 cycles of rigorous washing.In summary,this thesis demonstrates the application of iCVD coatings containing isocyanate groups in the field of barrier and protection,indicating that the iCVD method has great potential in fabricating functional polymer coatings.