Study On The Titanium Compound In-situ Formed During The Synthesis Of PET

Organic-inorganic hybrid materials have promisingly potential of application since they could combine the good properties of organic and inorganic materials.The in-situ sol-gel process is one of the important methods for preparation of organic-inorganic hybrid materials.In recent twenty years,researchers paid much attention to effectively combine the sol-gel process and polymer synthesis, process and application in order to develop high performance polymer based nanocomposites.The method of in-situ blending precursor and polymer,the method of in-situ blending sol and polymer and the method of in-situ polymerization of sol and polymer monomers have been intensively studied.However,there have little reports about the method of in-situ polymerization with precursors except from our research group.Polyesters,such as PET,PBT and aliphatic polyester,are the important raw materials of plastics,fibers, coatings etc.Therefore,it has important academic and industrial significance to study the structure change of precursor during the PET synthesis and its mechanism.In this dissertation,the bis（2-hydroxyethyl）terephthalate（BHET） /titanium compound nanocomposites and poly（ethylene terephthalate） （PET）/titanium compound nanocomposites were synthesized by the method of in-situ polymerization with TBOT.The various factors during direct esterification which affected the morphology and structure of in-situ formed titanium compound had been paid much attention to.It was found that the butyl alcohol is distilled out at the beginning of the esterification process and titanium compound had already been formed when the degree of esterification reached 32%. The temperature of esterification and proportion of raw materials were main factors which affected the morphology and structure of in-situ formed titanium compound.The in-situ formed titanium compound synthesized at higher temperature e.g.260℃in esterification was round particle.However,the in-situ formed titanium compound synthesized at lower temperature e.g.240℃in esterification showed slice-like morphology.Meanwhile,the slice-like titanium compound was easier to be formed at the lower concentration of PTA and the monodisperse titanium compound with less size could be formed at the higher stirring speed.By WAXD patterns,it was indicated that the in-situ formed titanium compound had unique crystalline structure with new diffraction peaks between 2-theta 6°and 11°.Moreover,it was found that the slice-like titanium compound could also be in-situ formed during the process of transesterification,which revealed that the in-situ hydrolysis of TBOT was not necessary for forming slice-like titanium compound.The BHET based composites with slice-like titanium compound were also synthesized by the method of in-situ polymerization with Ti sol and Ti-Si sol.It was found that slice-like titanium compound with unique crystalline structure could also be in-situ formed at lower temperature in esterification by the method of in-situ polymerization with Ti sol.The Ti-Si sol owing the potential to form Ti core-Si shell structure at vacuum dryness was prepared.The composites obtained by the method of in-situ polymerization with Ti-Si sol were characterized by SEM,FTIR and WAXD.It was shown that slice-like and granular materials were formed,the granular materials increased and the intensity of new diffraction peaks between 2-theta 6°and 11°decreased with the increase of Si content in the sol.It would be deduced that it was the titanium component in Ti-Si sol contributed to form the slice-like materials.The structure change of in-situ formed titanium during heat treatment was examined.It was shown that the product of the PET/titanium compound composite calcined at 420℃became almost amorphous.However,the products of the PET/titanium compound composite calcined at 550℃and 800℃had unique crystalline structures with obvious differences from TiO₂,and the crystalline structure changed with the increase of calcining temperature.By SEM,it was found that some granular materials were formed and some slice-like shapes constructed by granular materials appeared.The almost same results were obtained from BHET/titanium compound composite calcined at different temperature.The in-situ formed titanium compounds were obtained by centrifugal separation from BHET/titanium compound composites and PET/titanium compound composite.Their structure was characterized and their formation mechanism was concluded.It was shown that the granular titanium compound owned almost amorphous diffraction pattern.Its chemical structure was TiO₂ with partial organic component and it was consistent with the references. The slice-like titanium compound from BHET based composites and from PET based composite both had unique crystalline structures with obvious difference from TiO₂.It was indicated by FTIR and NMR that the slice-like in-situ formed titanium compound was titanium organics with phenyl,carbonyl and methylene.Therefore,it was the competition between hydrolyze/condensation of precursor and the reaction between the precursor（or its partial hydrolysate）and monomers that resulted in different morphology and structure of in-situ formed titanium.At lower temperature in esterification,the reaction between the precursor（or its partial hydrolysate）and monomers appeared to become prior to hydrolyze/condensation of precursor and the slice-like titanium organics was formed.It was inspired that BHET/titanium compound nanocomposite would act as the catalyst for the polycondensation of PET and PBT. The physicochemical properties of the PET resin obtained almost reached the standard of the first grade commercial PET resins.It had good spinnability and the broken strength of fibers from it could reach 3.78 cN/dtex as the draw ratio is 4.0.