Study On Chemical Modification And Optical Properties Of Polymethacrylates

In this thesis,through molecular design method,poly(meth)acrylates were modified by copolymerizing with isobornyl methacrylate or fluorinated methacrylate,chemical crosslinking and changing topological structure.The effect on thermal properties,solvent resistance,hydrophobicity and optical properties of polymer films has been studied systematically by chemical composition,fluorine content,crosslinking degree and topological structure change of polymers.The resuls show that crosslinking network structure and star-shaped topological structure effectively decrease the optical birefringence of polymer film;the formation of crosslinking network significantly enhances glass transition temperature(Tg),thermal decomposition temperature and solvent resistance of material by restricting molecular chain segment movement;the introduction of perfluorinated alkyl group improve hydrophobicity of polymer film,especially the fluorinated segments are more easily enriched on the film surface due to the star-shaped structure,vwhich further improve hydrophobicity of material beneficial to maintain performance stability of optical devices under humid conditions.The detailed contents of this thesis are summarized as below:4,4'-isopropylidenediphenol dimethacrylate(BD)was synthetized as crosslinking agent and copolymerized with isobornyl methacrylate and butyl acrylate to obtain crosslinked(meth)acrylate copolymer films.The crosslinked films exhibit good thermal stability with initial weight loss over 300 ? and high glass transition temperature over 200 ?.The film forming condition was determined.The effect of crosslinking agent content on thermal and optical properties was also studied.The film refractive indices were tunable along with BD contents in the range from 1.47 to 1.54.The films exhibit relatively low birefringence and good thermal properties attributed to the three-dimensional crosslinking network structure.Methylacryloyloxyl-2-hydroxypropyl perfluorooctanoate(FGOA)was synthesized and copolymerized with methyl methacrylate(MMA)to obtain linear fluorinated methacrylate random copolymers.Then the hydroxyl of fluorinated pendant group was esterified to introduce cross-linkable vinyl groups,and cross-linked polymer films were acquired after heat treatment.The effect of crosslinking network structure on film properties was also studied by comparison of thermal properties,surface morphology,hydrophobicity and optical properties of linear copolymer films with crosslinked copolymer films.Both kinds of copolymer films exhibited low birefringence and the refractive indices decrease and thermo-optical coefficients increase with the incremental fluorine content.The crosslinking density grew up along with the increase of fluorinated segment content,endowing the crosslinked films with good thermal properties and excellent solvent resistance.The Tgs of cross-linked copolymer films are above 111 ? and 11-88 ? higher than linear copolymer films.The introduction of fluorinated monomer can improve hydrophobicity of polymer films;decrease the effect on stability of material by humid environment and lower absorption loss of material in the communication band for the hydrocarbon bond replaced by fluorocarbon bond.Tetrakis(4-(1-bromoethyl)phenyl)silane(BTES)was synthesized as the novel tetrafunctional ATRP initiator,and its kinetics of polymerization initiating MMA monomer was also studied.Star-shaped fluorinated block copolymers were synthesized from MMA and FGOA monomers initiated by BTES in sequence with tetraphenyl silicon structure as core and FGOA as the end-capping segments.It is studied that the effect by star-shaped block structure on thermal properties,surface morphology,hydrophobicity and optical properties of copolymer films.The obtained star-shaped fluorinated block copolymers(F-PMMA)readily dissolve in common organic solvents and show good film-formation,with the polydispersity indices<1.30,Tgs in rang of 11.0-120 ? and extremely low birefringence(nearly 0 at 1550 nm).Then the hydroxyl of star-shaped fluorinated block copolymers was esterified to introduce cross-linkable vinyl groups,and cross-linked star-shaped fluorinated block copolymer films(CF-PMMA)were finally obtained after heat treatment.The Tgs of CF-PMMA films were not observed below 150 ?.The CF-PMMA film shows good hydrophobicity as well as significantly improved thermal properties and solvent resistance,for the fluorinated segments located at the end of the molecular chains lower the adverse effect on their migration by cross-linked structure.