In this study, it was examined whether the dynamics of polymer chains at a surface is different from that in thebulk, and if so, to what extent they differ in terms of surface glass transition temperature and diffusio...In this study, it was examined whether the dynamics of polymer chains at a surface is different from that in thebulk, and if so, to what extent they differ in terms of surface glass transition temperature and diffusion coefficient. Obtainedresults clearly indicate that surface chains can travel for a relatively large distance in comparison with the characteristiclength scale of usual segmental motion even at a temperature below its bulk glass transition temperature, T_g^b. This isconsistent with our previous results that the surface glass transition temperature is much lower than the corresponding T_g^b.Also, it was experimentally revealed that there was a gradient of molecular motion in the surface region.展开更多
To tailor properties of polymer composites are very important for their applications.Very small concentrations of nanoparticles can significantly alter their physical characteristics.In this work,molecular dynamics si...To tailor properties of polymer composites are very important for their applications.Very small concentrations of nanoparticles can significantly alter their physical characteristics.In this work,molecular dynamics simulations are performed to study the thermodynamic and structural properties of polystyrene/C60(PS/C60)composites.The calculated densities,glass transition temperatures,and coefficient of thermal expansion of the bulk PS are in agreement with the experimental data available,implying that our calculations are reasonable.We find that the glass transition temperature Tg increases accordingly with an added concentration of C60 for PS/C60 composites.However,the self-diffusion coefficient D decreases with increase of addition of C60.For the volumetric coefficients of thermal expansion(CTE)of bulk PS and PS/C60 composites,it can be seen that the CTE increases with increasing content of C60 above Tg(rubbery region).However,the CTE decreases with increasing content of C60 below Tg(glassy region).展开更多
The synthesis of pseudo- and semi-interpenetrating polymer networks (IPNs) based on polydimethylsiloxane (PDMS) and polystyrene (PS) is described. IPNs were obtained by simultaneous and in situ sequential synthesis pr...The synthesis of pseudo- and semi-interpenetrating polymer networks (IPNs) based on polydimethylsiloxane (PDMS) and polystyrene (PS) is described. IPNs were obtained by simultaneous and in situ sequential synthesis procedure. The preliminary studies on IPNs properties such as transition temperature, microphase separation and mechanical behaviors have been carried out by using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The experimental evidence clearly showed that semi-IPNs obtained by sequential synthesis procedure have higher interpenetrating extent than pseudo-IPNs synthesized by simultaneous procedure. Over the full composition, the PDMS/PS IPNs are immiscible. The pseudo-IPNs microphase separation can be greatly subdued through the formation of grafting bonds between two networks as well as the kinetic rate-matching of the individual network crosslinking.展开更多
A two-stage transition upon crossing the glass transition of polystyrene with increasing temperature was precisely determined and interpreted by using solid-state nuclear magnetic resonance （SSNMR）, 1H-XH dipolar co...A two-stage transition upon crossing the glass transition of polystyrene with increasing temperature was precisely determined and interpreted by using solid-state nuclear magnetic resonance （SSNMR）, 1H-XH dipolar couplings based double quantum-filtered （DQF） and dipolar filter （DF） experiments and 13C chemical shift anisotropy （CSA） based centerband-only detection of exchange （CODEX） experiment are used to fully characterize the time scale of molecular motions during the glass transition. While differential scanning calorimetry （DSC） and CODEX experiment predicted the first stage of glass transiton, DQF and DF experiments provided the evidence for the second stage transition during which the time scale of molecular motions changed from very slow （t 〉 ms） to very fast （t 〈 Its）. The first stage of glass transition begins with the occurrence of remarkable slow re-orientation motions of the polymer backbone segments and ends when the degree of slow motion reaches maximum. The onset and endpoint of the conventional calorimetric glass transition of polystyrene can be quantitatively determined at the molecular level by SSNMR. In the second stage, a subsequent dramatic transition associated with the melting of the glassy components was observed. In this stage liquid-like NMR signals appeared and rapidly increased in intensity after a characteristic temperature Tf （-1.1Tg）. The signals associated with the glassy components completely disappeared at another characteristic temperature Tc （-1.2Tg）.展开更多
The effect of different sulfonation degree on properties of sulfonated syndiotactic polystyrene(S s PS) was investigated by 1H NMR, 13 C NMR,FTIR,DSC and WAXD.The results of 13 C NMR showed that a peak at δ =145 5 ap...The effect of different sulfonation degree on properties of sulfonated syndiotactic polystyrene(S s PS) was investigated by 1H NMR, 13 C NMR,FTIR,DSC and WAXD.The results of 13 C NMR showed that a peak at δ =145 5 appeared in all S s PS spectra,which proved that the syndiotactic structure of syndiotactic polystyrene( s PS) still existed in S s PS.With increasing degree of sulfonition,the chemical shifts of C 1 and C\|3 for sulfonated benzene ring turned out to be wider. 1 H NMR spectra showed that C\|3 for sulfonated benzene ring had a chemical shift of 7 66.FTIR spectra showed that sulfonic acid groups were introduced on the para position of benzene rings and with increasing sulfonation degree,the absorption strength of 612/1600 cm 1 ,834/1600cm -1 increased,but the absorption strength of 1078/1600cm -1 decreased.The absorption of ～1030cm -1 ,～1179cm -1 ,～1217cm -1 appeared when the sulfonation degree was higher that 6%. s PS and S s PS H 2 2 had absorption at 975 and 943cm -1 and also had double peaks around ～1175cm -1 ;DSC showed that with increasing sulfonation degree, the glass transition temperature increased, the melt temperature,crystallization temperature and crystallization degree decreased;S s PS couldn’t crystallize when sulfonation degree was higher that 6mol%;WAXD proved that s PS had the α and β crystal types, however,S s PS with 2 2% sulfonation degree only had the β crystal type, and S s PS with 6 1% sulfonation degree didn’t crystallize.展开更多
The polymerization of styrene in the media of MCM-41 is carried out by means of host-guest polymerization of styrene in MCM-41 mesoporous material with the aim to investigate the effects of interface and confinement o...The polymerization of styrene in the media of MCM-41 is carried out by means of host-guest polymerization of styrene in MCM-41 mesoporous material with the aim to investigate the effects of interface and confinement of MCM-41 on host-guest interactions. Detailed physical properties of the mesoporous MCM-41 material containing polystyrene is characterized by XRD(X-ray diffraction), FT-IR(Fourier transform infrared), TGA(thermal gravimetric analysis), and nitrogen adsorption-desorption isotherms. We also find a great increase in the glass transition temperature of guest polystyrene influenced by the confined geometry of the host by differential scanning calorimetry(DSC).展开更多
基金This work was in part supported by a Gran-in-Aid for Scientific Research (A)(#13355034) from the Ministry of Education, Science, Sports, and Culture, Japan.
文摘In this study, it was examined whether the dynamics of polymer chains at a surface is different from that in thebulk, and if so, to what extent they differ in terms of surface glass transition temperature and diffusion coefficient. Obtainedresults clearly indicate that surface chains can travel for a relatively large distance in comparison with the characteristiclength scale of usual segmental motion even at a temperature below its bulk glass transition temperature, T_g^b. This isconsistent with our previous results that the surface glass transition temperature is much lower than the corresponding T_g^b.Also, it was experimentally revealed that there was a gradient of molecular motion in the surface region.
基金Project supported by the National Natural Science Foundation of China(Grant No.11704329)the Scientific Research Fund of Sichuan Provincial Education Department of China(Grant No.15ZB293)+1 种基金the Pre-Research Project of Yibin University of China(Grant No.2019YY06)the Open Research Fund of Computational Physics Key Laboratory of Sichuan Province at Yibin University of China(Grant No.JSWL2014KF02).
文摘To tailor properties of polymer composites are very important for their applications.Very small concentrations of nanoparticles can significantly alter their physical characteristics.In this work,molecular dynamics simulations are performed to study the thermodynamic and structural properties of polystyrene/C60(PS/C60)composites.The calculated densities,glass transition temperatures,and coefficient of thermal expansion of the bulk PS are in agreement with the experimental data available,implying that our calculations are reasonable.We find that the glass transition temperature Tg increases accordingly with an added concentration of C60 for PS/C60 composites.However,the self-diffusion coefficient D decreases with increase of addition of C60.For the volumetric coefficients of thermal expansion(CTE)of bulk PS and PS/C60 composites,it can be seen that the CTE increases with increasing content of C60 above Tg(rubbery region).However,the CTE decreases with increasing content of C60 below Tg(glassy region).
文摘The synthesis of pseudo- and semi-interpenetrating polymer networks (IPNs) based on polydimethylsiloxane (PDMS) and polystyrene (PS) is described. IPNs were obtained by simultaneous and in situ sequential synthesis procedure. The preliminary studies on IPNs properties such as transition temperature, microphase separation and mechanical behaviors have been carried out by using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The experimental evidence clearly showed that semi-IPNs obtained by sequential synthesis procedure have higher interpenetrating extent than pseudo-IPNs synthesized by simultaneous procedure. Over the full composition, the PDMS/PS IPNs are immiscible. The pseudo-IPNs microphase separation can be greatly subdued through the formation of grafting bonds between two networks as well as the kinetic rate-matching of the individual network crosslinking.
基金financially supported by the National Science Fund for Distinguished Young Scholars(No.20825416)the National Natural Science Foundation of China(No.21374051)+2 种基金973 program(No.2012CB821503)PCSIRT(No.IRT1257)CERS-1-61.A.C.S.acknowledges the support of the Natural Science and Engineering Council(NSERC)of Canada
文摘A two-stage transition upon crossing the glass transition of polystyrene with increasing temperature was precisely determined and interpreted by using solid-state nuclear magnetic resonance （SSNMR）, 1H-XH dipolar couplings based double quantum-filtered （DQF） and dipolar filter （DF） experiments and 13C chemical shift anisotropy （CSA） based centerband-only detection of exchange （CODEX） experiment are used to fully characterize the time scale of molecular motions during the glass transition. While differential scanning calorimetry （DSC） and CODEX experiment predicted the first stage of glass transiton, DQF and DF experiments provided the evidence for the second stage transition during which the time scale of molecular motions changed from very slow （t 〉 ms） to very fast （t 〈 Its）. The first stage of glass transition begins with the occurrence of remarkable slow re-orientation motions of the polymer backbone segments and ends when the degree of slow motion reaches maximum. The onset and endpoint of the conventional calorimetric glass transition of polystyrene can be quantitatively determined at the molecular level by SSNMR. In the second stage, a subsequent dramatic transition associated with the melting of the glassy components was observed. In this stage liquid-like NMR signals appeared and rapidly increased in intensity after a characteristic temperature Tf （-1.1Tg）. The signals associated with the glassy components completely disappeared at another characteristic temperature Tc （-1.2Tg）.
文摘The effect of different sulfonation degree on properties of sulfonated syndiotactic polystyrene(S s PS) was investigated by 1H NMR, 13 C NMR,FTIR,DSC and WAXD.The results of 13 C NMR showed that a peak at δ =145 5 appeared in all S s PS spectra,which proved that the syndiotactic structure of syndiotactic polystyrene( s PS) still existed in S s PS.With increasing degree of sulfonition,the chemical shifts of C 1 and C\|3 for sulfonated benzene ring turned out to be wider. 1 H NMR spectra showed that C\|3 for sulfonated benzene ring had a chemical shift of 7 66.FTIR spectra showed that sulfonic acid groups were introduced on the para position of benzene rings and with increasing sulfonation degree,the absorption strength of 612/1600 cm 1 ,834/1600cm -1 increased,but the absorption strength of 1078/1600cm -1 decreased.The absorption of ～1030cm -1 ,～1179cm -1 ,～1217cm -1 appeared when the sulfonation degree was higher that 6%. s PS and S s PS H 2 2 had absorption at 975 and 943cm -1 and also had double peaks around ～1175cm -1 ;DSC showed that with increasing sulfonation degree, the glass transition temperature increased, the melt temperature,crystallization temperature and crystallization degree decreased;S s PS couldn’t crystallize when sulfonation degree was higher that 6mol%;WAXD proved that s PS had the α and β crystal types, however,S s PS with 2 2% sulfonation degree only had the β crystal type, and S s PS with 6 1% sulfonation degree didn’t crystallize.
基金Supported by the National Natural Science Foundation of China(No.20173039)and the Key Laboratory of Catalysis.China National Petroleum Corporation
文摘The polymerization of styrene in the media of MCM-41 is carried out by means of host-guest polymerization of styrene in MCM-41 mesoporous material with the aim to investigate the effects of interface and confinement of MCM-41 on host-guest interactions. Detailed physical properties of the mesoporous MCM-41 material containing polystyrene is characterized by XRD(X-ray diffraction), FT-IR(Fourier transform infrared), TGA(thermal gravimetric analysis), and nitrogen adsorption-desorption isotherms. We also find a great increase in the glass transition temperature of guest polystyrene influenced by the confined geometry of the host by differential scanning calorimetry(DSC).
