Phase Behaviors,Structures And Properties Of Polycarbonate/Reactive Plasticizer Blends And Their Nanocomposites

As bisphenol-A polycarbonate(BAPC)possesses good optical,thermal and mechanical properties,it has been widely used in building,automobile,medical devices and so on.However,it needs a processing temperature as high as 280 °C,which makes it easy to occur oxidation decomposition and hydrolysis,and finally lower its molecular weight and properties.Nowadays,though non-reactive plasticizers are always used to lower the processing temperature of polymers,their migration and evaporation not only lower the performance of products,but also bring the problem of environmental pollution.For the past few years,the reactive plasticizers,which not only lower the processing temperature but also maintain the properties of the polymer matrix,have been drawn widely attention.As the addition of reactive plasticizer to polymer matrix not only brings the fundamental physical problems,i.e.,compatibility and crystallization,but also chemical reactions and related issues in physical chemistry,this dissertation mainly focuses on the miscibility between BAPC and reactive plasticizer,the phase transition behaviors of BAPC/reactive plasticizer blends,the crystallization behavior of BAPC,the relationship between polymerization kinetics and microstructures of the blends,as well as the microstructures and properties of BAPC/reactive plasticizer/nanofillers composites.The aim of this dissertation is to lower the processing temperature of BAPC and maintain or enhance the transparency,heat resistance and mechanical properties of BAPC.Firstly,the films of BAPC/DAP-DCP(diallyl phthalate-dicumyl peroxide)blends were prepared through solution cast.Only one glass transition temperature(Tg)could be observed in each differential scanning calorimetry(DSC)heating curve of BAPC/DAP blends,and it decreased with the increasing of DAP content,which obeyed the Fox equation.During increasing the temperature of BAPC/DAP-DCP blends,the thermally induced phase separation between BAPC and DAP,the cold crystallization of BAPC,the polymerization of DAP and the melting of BAPC crystals took place in sequential.A bi-continuous structure was formed in the blends with DAP content higher than 10 wt.% after the thermal treatment at 130 °C for 1 h.Furthermore,the polymerization of DAP in the blends not only maintained the thermal resistance and optical properties of the BAPC,but also enhanced the flowability and mechanical properties,especially for the blends with 10 wt.% and 15 wt.% poly(DAP).Compared with pure BAPC,the BAPC/poly(DAP)blends with 10~15 wt.% of poly(DAP)possessed similar glass transition temperature,tensile strength and ~80% of optical transmittance in the wavelength range of 600~800 nm,as well as an increase of 64~68% for moduli and 100~135% for melt flow index.Secondly,BAPC crystal with a unique peanut-like crystalline structure was obtained in the solution-cast films of BAPC/plasticizer blends.Furthermore,concentric black dotted rings were also observed within the peanut-like crystals.The peanut-like morphology had no selectivity to the kinds of plasticizer and the casting temperature.The development of these peanut-like crystals was ascribed to the local orientations of BAPC chains,which were induced by the concentration fluctuation during solvent evaporation and further fixed by the quick drying process.The concentric black dotted rings within the peanut-like crystals should be attributed to the driving effect of BAPC crystalline lamellae and phase separation between plasticizers and BAPC.Next,the isothermal and non-isothermal cold crystallization behaviors of BAPC in the BAPC/DAP blends were studied through Avrami equation.DAP greatly accelerated the crystallization rate of BAPC in BAPC/DAP blends and lowered the activation energy.The melting point of BAPC crystals formed through isothermal cold crystallization did not increase with the increasing of temperature,which deviated from Hoffman-Week theory.It might be due to that the phase behavior did effect on the cold crystallization process.Thirdly,the polymerization rate of DAP in BAPC/DAP blends increased with the increasing of polymerization temperature,while the double bond conversion increased firstly and then decreased.The Avrami-Erofeev equation,which has been widely used for the phase transitions in solid,was adopted to describe the relationship between polymerization kinetics and microphase structure in the blends.When the value of exponent n was larger than 1.73,the poly(DAP)was a thin fiber-like three-dimensional network in BAPC/poly(DAP)blends;when the value of n was between 1 and 1.73,the poly(DAP)showed a partial connected spherical-like network;while the value of n was less than 1,the poly(DAP)appeared as a perfect spherical-like three-dimensional network.For the BAPC/DAP blend with 25 wt.% DAP,its final microstructure was dominated by the initial viscosity when the polymerization temperature was lower than 150 °C,and by the polymerization rate as the polymerization temperature was higher than 150 °C,respectively.Finally,in order to improve the UV-resistance of BAPC,the nano-TiO2 and nanoTiO2@SiO2 nanoparticles were added into the BAPC and BAPC/DAP.Compared with nanoTiO2,nano-TiO2@SiO2 lowered the thermal catalytic degradation effect on BAPC,enhanced the heat resistance and transparency of BAPC,and slightly decreased the UV absorption ability.The nano-TiO2@SiO2 in BAPC/poly(DAP)/nano-TiO2@SiO2 composites not only enhanced the UV absorption properties and glass transition temperature of BAPC/poly(DAP)blends,but also affected the microstructure of the composites.