The Glass Transition Behavior And Crystallization Of Polymer Blends And Block Copolymer System

The confinement of polymers in nanoscales show peculiar behaviors characterized by dramatic changes in many physical properties compared to the bulk.Such changes make significant effects on the nanofabrication field.Therefore,the properties,especially the glass transition behavior of polymers under confinement has been controversially and dynamically discussed in past two decades.The increase,reduction,as well as the unchanged of polymer glass transition temperature(Tg)compared to the bulk have been reported in numerous work.However,most of the confinement is polymer thin film and nanoscale media,which is to some extend hard to analyze the detailed characteristics.In this thesis,by taking the advantages of the fast scanning rate of the ultra fast differential scanning calorimetry(UFDSC),we applied block copolymer as template to study the confined polymer glass transition behavior.We also study the crystallization of polymers using UFDSC technique,and discussed the crystallization of polymers confined in polymer blends.Firstly,we investigated a series of diblock copolymer polydimethylsiloxane-bpoly {2,5-bis[(4-methoxyphenyl)-oxycarbonyl]} styrene(PDMS-b-PMPCS)synthesized by atom transfer radical polymerization(ATRP).Lamellae(LAM),hexagonally packed cylinders(HEX)and double gyroid(GYR)phases of diblock copolymer are obtained by controlling PMPCS length and the thermal annealing condition.This provides us a system to study the glass transition of polymers under the well-defined confining geometries and interfacial physicochemical properties.By taking advantage of ultrafast diferential scanning calorimeter(UFDSC),the glass transition temperature(Tg)of PDMS in the confined state is measured without destroying the nanophase structures sustained by the rigid PMPCS domains.Depending on the detailed confinement geometry,the Tg of PDMS shows a difference of as high as 20 K.We propose that the Tg is firstly correlated to ?D,the local density of PDMS,which can be calculated based on the small-angle X-ray scattering(SAXS)results and the symmetry consideration of various geometries.Besides ?D,the interfacial curvature effect on the Tg of PDMS is also observed clearly:for the PDMS block with a fixed ?D,its Tg increases when the interfacial curvature changes from negative(in GYR),to zero(in LAM)and to positive(in HEX).Secondly,we investigated the secondary crystallization of poly vinyldene flouride(PVDF)by UFDSC.Compared to the conventional DSC,we have one advantage to avoid the changed of PVDF crystallization behavior during the scanning program due to the fast scanning rate provided by UFDSC.We first studied the temperature dependence of PVDF crystallization by annealing the sample at different temperatures,we found the temperature region of forming the secondary crystallization.Then we investigated the time dependence of the secondary crystallization of PVDF by annealing at different times.We found the the crystal grew rapidly at the very beginning of the annealing,then became slowly as time moved on,finally to equilibrium.By analyzing the UFDSC results,we propose that there exists two steps in forming the secondary crystallization of PVDF:the growth rate of the crystal decreases as the annealing temperature increases at the first step;while the the growth rate of the crystal remains a constant in no correlation with the annealing temperature at the second step.We also investigated a series of poly vinyldene flouride/poly ethyl methacrylate(PVDF/PEMA)blends with various composition.We found the condition of forming the ?-phase of PVDF crystal through melting-annealing-quench(as-quenched)treatment,the amorphous PEMA promotes the growth of ?-phase of PVDF crystal.However,because of the amorphous PEMA restrains to some extend the overall PVDF crystallization,therefore,both major and minor fraction of amorphous PEMA restrain the growth of ?-phase of PVDF crystal.We also proposed that the PVDF/PEMA blends after as-quenched treatments can form more stable ?-phase of PVDF crystal during the heating progress,mainly duo to the melting-recrystallization process of ?-phase of PVDF crystal,the stability of such crystal is in consistent with the pure PVDF.At last,a series of the block copolymers polystyrene-b-poly ethylene oxide(PS-bPEO)with various molecular weight and composition was simply investigated.We first analyze the effect of the amorphous PS on the crystallization of PEO.We also discussed the microphase separation of block copolymer in correlation with the molecular weight and composition.The order-disorder transition of the microphase separation has also been characterized qualitively.