Synthesis Of Hyperbranched Polyesters By Noncoupling-bimonomer Methodology And Its Phase Modulation Structure Construction And Properties In Epoxy Resin

Hyperbranched polymers are a novel kind of three dimensional torispherical irregular and functional characteristics macromolecules having highly branched architectures,and the controllable polymerization and molecular designing have significant effects on their application in catalytic reaction,self-assembly technique and material modification.It has long been a hot and frontier topic in materials science about the preparation of advanced functional composites with good integrated performance by ingenious aggregation structure adjustment of multi-component thermosetting blend system.In order to solve the prone to cause gel of noncoupling-bimonomer methodology,we put forward a novel gel theory and success in realizing controllable synthesis of hyperbranched polyester,and then the hyperbranched polyester has been applied in catalytic polymerization,design and control of micro-interfaces and toughness of epoxy resin.The nano-structure,vesicle structure and macroscopic phase separation structure of thermosetting resin were prepared by utilizing the self-assembly,catalytic effect of hyperbranched polyester,the transition of solubility parameter,and change of kinetics and thermodynamics caused by solidification.We have focused on formation mechanism of different morphology,structure-properties relationships,toughening mechanism and catalytic mechanism.The main results are shown as fellow:(1)Controllable synthesis of hyperbranced polyester based on noncoupling-bimonomer methodologyWe successfully synthesized ester-terminated polyester(HBPE)by employing the "One Pot,Three Step" method and "Azeotropic Molecular Sieves Dehydration" process.We presented here an innovative gel point forecasting model by modifying Flory's theory,which can make an accurate prediction and synthesis hyperbranched polymers with higher reaction degree but not gel in(k+1)A3+kB2(k?1)system by noncoupling-bimonomer methodology.Then,by adjusting feed ratio and controlling acid value,we synthesized a series of carboxylic-terminated polyester(HBPE-PA)and ester-terminated polyester(HBPE-AA),and systematically measured and analyzed the structure and properties of HBPE,HBPE-PA and HBPE-AA by utilizing Fourier transform infrared spectroscopy(FT-IR),1H-NMR,13H-NMR,Gel permeation chromatography(GPC),Differential scanning calorimetry(DSC),and Thermogravimetry(TG).The results shown that the molecular weight and polydispersity indexes of HBPE increased with the decreasing of acid values,the Tg and thermostability as well;the HBPE and its terminal modified molecular could dissolve in aprotic organic solvent,the polarity of HBPE-PA,HBPE and HBPE-AA decrease in turn;the HBPE and its terminal modified molecules are in high-elastic state in room temperature,and the initial degradation temperature increased with increasing of molecular weight and the degree of terminal group modification.(2)Adjustment of phase structure and formation mechanism of different phase behaviorsBy adjusting the dissolution of HBPE in epoxy precursor and curing process of the epoxy system,we obtained the nanostructure,vesicle structure and macroscopic phase separation structure of thermosetting resin.The dissolution behavior of epoxy/HBPE blends and epoxy/MOCA/HBPE system was investigated by DSC,hot stage polarized optical microscopy(HSPOM)and hot stage phase contrast microscope(HSPCM).The phase behavior and morphology of the MOCA-cured epoxy/HBPE were investigated by field emission scanning electron microscopy(FESEM),atomic force microscope(AFM)and dynamic mechanical thermal analyses(DMTA).The results shown that,among the experimental condition,the dissolution HBPE in epoxy precursor was controlled by both of the chemical reaction and diffusion,and the process was time-dependence.In addition,before the completely dissolved,the HBPE can self-assemble into compound vesicles and the solubility of HBPE in DGEBA/MOCA could be enhanced by the strong intermolecular hydrogen bonding;the terminal group could catalyzed and accelerated the curing reaction,and then a strong kinetics and thermodynamic competition would form between the acceleration of the curing reaction and the dissolution of HBPE,and we could balance the competition by adjusting solidifying program and finally realize the controllable of morphology;the formation of the nanostructure with long-rang order is controlled by the reaction induce separation mechanism,formation of the "bubble in bubble" likely double-deck large compound vesicles phase is based on self-assembly mechanism,and formation of the macroscopic phase separation structure is depended on rapidly squeezing.(3)Structure-property relationship and toughening mechanismWe have made comparison on structure-properties relationships of the vesicle structure and nanostructure and studied on the toughening mechanism.The damping property of vesicle structure epoxy firstly decreased and then increased with the increasing of HBPE,and the descending rate of Tg and storage modulus of vesicle structure epoxy were lower than nanostructure epoxy.It was found that the fracture toughness of the thermosetting blends increases gradually with decreasing HBPE content,and the best improvement comes with the blends HBPE containing 6-9%HBPE.The mechanical properties of vesicle structure epoxy were better and KIC and GIc increased by 130%and 497%respectively when the amount of HBPE was 9%.And the dramatical increased impact strength of vesicle structure epoxy could get the same prediction.Furthermore,under different failure condition(strain rate and cyclic failure)and temperature(77 K and 383 K),the mechanical properties of the vesicle structure epoxy are better than nanostructure epoxy as well.The improvement of hydrophilic properties and shear strength prove that the addition of HBPE can improve the polarity of the epoxy matrix.The fracture surface and crack tip damage zone of different failure types of cured epoxy blends with HBPE were measured by optical microscope(OM),SEM and FESEM,the mainly toughening mechanisms in nanostructure toughened epoxy have been identified to be nano-cavitation induced by plastic deformation and the effect of matrix shear banding in the second position.The cavitation of matrix has a lot to do with deformability,state of aggregation of nanophase and the rate of stress rupture of epoxy matrix.The toughening of vesicle structure relies on the cooperation effect of limited shear yielding and crack deflection caused by the compound vesicle structure.At the same time,the change of gradient of local cross-linking density of vesicle caused by the HBPE's catalytic action played a key role in toughening vesicle structure epoxy.(4)Catalytic mechanism and curing kineticsWe dealt with the study of curing kinetics of HBPE/epoxy blends in order to give a comprehensive account about the effect of adding HBPE on the reaction rate of the network formation and the catalytic mechanism and curing-phase structure relationship.Our study indicated that the cure reaction was accelerated by incorporation a small amount of HBPE and the catalysis of HBPE was a lot to the dosage.When the DGEBA/MOCA contained more than 6wt%of HBPE,the curing reaction would be significantly accelerated and the exothermal curve were divided into two exothermal peak.The matrix composition was varied,and some differences about the hydrogen bonding interactions and chemical reaction resulting from the cross-linked network structures were observed.The catalytic properties of HBPE to the acceleration of curing reaction could be ascribed to the polyester's terminal hydroxyls and hydrogen bonding between hydroxyl groups and a small amount of carboxyl groups.This catalytic behavior was also corroborated by FTIR analyses.The competition of the curing rate and the phase separation had played a decisive role in the formation of different phasestructures.The kinetic parameters of the curing process were determined by Malek method and the results indicated that Sestak-Berggren model is fairly coincident with the experimental data;the reaction order of m was 0.389 and n 1.547,respectively.The Sestak-Berggren equation was also found to be adequate to describe of reaction of DGEBA/MOCA with 6%HBPE,and the reaction mechanism shown an increasing reaction rate-dependent and insufficient in depicting the diffusion-controlled kinetics of the this curing system.The activation energy was calculated based on NLV Vyazovkin isoconversional method,and the results showed that Ea of both two curing systems changed from 35 to 95 kJ/mol,and the values increased with curing degree.The catalysis of HBPE could reduce the apparent activation energy of the reaction at the early stage,however,the dilution effect and diffusion control enhanced by the HBPE would hinder the reaction and increase the apparent activation energy.(5)The degradation kinetic and thermodynamic analysesThe non-isothermal degradation process of neat epoxy and epoxy contained HBPE were invested with thermogravimetric analysis(TGA)and derivative thermogravimetry(DTG).The "model free" method(Vyazovkin' method)and "model fitting" methods(Coats-Redfern method,Malek method and ABS differential method)were both applied to analyze and compare the decomposition of cured pure epoxy and HBPE epoxy mixture,and the relationship between pre-exponential factor(lnA)and reaction activation energy(Ea)were established by using kinetic compensation parameter method.The linear dependence was also established between the change of the ?S and Ea for the formation of the activate complex from the reagents.The heat resistance parameters of mixture indicated the thermal stability could be almost retained and the main decompose reaction could be slightly accelerated in perspective of transition state theory.By combining the analysis of CR method,"Master"cures analysis,RSS method,and F-test,the neat epoxy and epoxy contained HBPE degradation under nitrogen atmosphere could be described by F2 and the F3 reaction kinetics,respectively.