The polymorphic transition of trans-1,4-polyisoprene(TPI) during stretching was investigated by in situ wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The influences of the initial structure...The polymorphic transition of trans-1,4-polyisoprene(TPI) during stretching was investigated by in situ wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The influences of the initial structure, stretching temperature, and strain rate on the contents of different crystal modifications(α, β) were explored. The results confirm that the α-β transition occurs during stretching of TPI that only contains αcrystal(α-TPI). When the stress is relaxed, the β crystal formed during stretching remains, which indicates that the transition is irreversible. On the other hand, stretching of TPI that only contains β crystal(β-TPI) results in orientated β crystal. No β-α transition occurs during stretching. The different structures of stretched α-TPI and β-TPI exclude the previously proposed "melting-recrystallization mechanism". The α-β transition depends significantly on temperature and strain rate, indicating the transition is governed both by thermodynamics and kinetics. Our results support a solid-solid transition mechanism rather than a melting-recrystallization mechanism. The irreversible nature of the transition is attributed to the metastability of the β phase in the unstretched state. Different from the "β phases" that appear in polymers with stress-induced reversible transitions, e.g. poly(butylene terephthalate) and poly(butylene succinate), the stability of β phase in TPI is high that can be long-lived.The strain rate dependence of α-β transition hinders the determination of critical stress for the transition. It further indicates that the local stress within the sample is more heterogeneous at higher strain rates.展开更多
Synthesis of telechelic trans-1,4-polyisoprenes（TPI： trans-structure ＆gt; 95%） was evaluated based on two different methods of oxidative cleavage（indirect cleavage： first epoxidation of TPI, then the selective c...Synthesis of telechelic trans-1,4-polyisoprenes（TPI： trans-structure ＆gt; 95%） was evaluated based on two different methods of oxidative cleavage（indirect cleavage： first epoxidation of TPI, then the selective cleavage of epoxidized units in epoxidized trans-1,4-polyisoprene（ETPI） and direct cleavage of isoprene units in TPI）. The influence of solvents and the ratio of oxidative agents was investigated by 1H-NMR and 13C-NMR. A series of well-defined telechelic TPI with double terminated functional groups and less side reaction（molecular weight distribution range： 1.96？2.26） were synthesized by indirect cleavage in chloroform. Telechelic TPI showed similar crystallization behavior with TPI and interesting cold crystallization behavior characterized by DSC.展开更多
Although bioinspired sacrificial bonds have been demonstrated to be efficient in improving the mechanical properties of polymer materials, the effect of binding energy of a specific dynamic bond on the ultimate mechan...Although bioinspired sacrificial bonds have been demonstrated to be efficient in improving the mechanical properties of polymer materials, the effect of binding energy of a specific dynamic bond on the ultimate mechanical performance of a polymer network with dual-crosslink remains unclear. In this contribution, diamine and sulfur curing package are introduced simultaneously into a sulfonated cis-1,4-polyisoprene to create dually-crosslinked cis-1,4-polyisoprene network with sulfonate-aminium ionic bonds as the sacrificial bonds. Three diamines （primary, secondary and tertiary） with the same spacer between the two nitrogen atoms are used to create the ionic bonds with different binding energies. Although the binding energy of ionic bond does not affect the glass transition temperature of cis-1,4-polyisoprene （IR）, it exerts definite influences on strain-induced crystallization and mechanical performance. The capabilities of diamine in dissipating energy, promoting strain-induced crystallization and enhancing the mechanical performance are in the same order of secondary diamine 〉 primary diamine 〉 tertiary diamine. The variations in mechanical performances are correlated to the binding energy of the ionic bond, which is determined by pKa values.展开更多
Trans-1,4-polyisoprene（TPI） nanofibers have been fabricated successfully through electrospinning technology.Through the control of electrospinning parameters, highly crystallized TPI fresh fibers composed mainly of ...Trans-1,4-polyisoprene（TPI） nanofibers have been fabricated successfully through electrospinning technology.Through the control of electrospinning parameters, highly crystallized TPI fresh fibers composed mainly of β phase were produced. Morphology and diameter of TPI nanofibers can be controlled by adjusting the electrospinning conditions. The in situ observations of FTIR spectra revealed that the crystallinity of the TPI fibers decreased with aging. While for TPI nanofibers aging at 45 °C for 24 h, a decrease in crystallinity as well as β to a transformation was observed with aging and these changings happened in the first 50 h during aging. The mechanism for β-TPI formation during electrospinning process and the reduced crystallinity with aging were proposed.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos. 21922308 and 22005196)the Youth Innovation Promotion Association of CAS (No. Y201908)。
文摘The polymorphic transition of trans-1,4-polyisoprene(TPI) during stretching was investigated by in situ wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The influences of the initial structure, stretching temperature, and strain rate on the contents of different crystal modifications(α, β) were explored. The results confirm that the α-β transition occurs during stretching of TPI that only contains αcrystal(α-TPI). When the stress is relaxed, the β crystal formed during stretching remains, which indicates that the transition is irreversible. On the other hand, stretching of TPI that only contains β crystal(β-TPI) results in orientated β crystal. No β-α transition occurs during stretching. The different structures of stretched α-TPI and β-TPI exclude the previously proposed "melting-recrystallization mechanism". The α-β transition depends significantly on temperature and strain rate, indicating the transition is governed both by thermodynamics and kinetics. Our results support a solid-solid transition mechanism rather than a melting-recrystallization mechanism. The irreversible nature of the transition is attributed to the metastability of the β phase in the unstretched state. Different from the "β phases" that appear in polymers with stress-induced reversible transitions, e.g. poly(butylene terephthalate) and poly(butylene succinate), the stability of β phase in TPI is high that can be long-lived.The strain rate dependence of α-β transition hinders the determination of critical stress for the transition. It further indicates that the local stress within the sample is more heterogeneous at higher strain rates.
基金financially supported by the Natural Science Foundation of Shandong Province(No.ZR2014BQ022)the National Natural Science Foundation of China(No.51273100)a Project of Shandong Province Higher Educational Science and Technology Program(No.J14LA12)
文摘Synthesis of telechelic trans-1,4-polyisoprenes（TPI： trans-structure ＆gt; 95%） was evaluated based on two different methods of oxidative cleavage（indirect cleavage： first epoxidation of TPI, then the selective cleavage of epoxidized units in epoxidized trans-1,4-polyisoprene（ETPI） and direct cleavage of isoprene units in TPI）. The influence of solvents and the ratio of oxidative agents was investigated by 1H-NMR and 13C-NMR. A series of well-defined telechelic TPI with double terminated functional groups and less side reaction（molecular weight distribution range： 1.96？2.26） were synthesized by indirect cleavage in chloroform. Telechelic TPI showed similar crystallization behavior with TPI and interesting cold crystallization behavior characterized by DSC.
基金financially supported by the National Basic Research Program of China(No.2015CB654700(2015CB654703))the National Natural Science Foundation of China(Nos.51673065,51703064,51473050 and 51333003)Fundamental Research Funds for the Central Universities(No.2017PY006)
文摘Although bioinspired sacrificial bonds have been demonstrated to be efficient in improving the mechanical properties of polymer materials, the effect of binding energy of a specific dynamic bond on the ultimate mechanical performance of a polymer network with dual-crosslink remains unclear. In this contribution, diamine and sulfur curing package are introduced simultaneously into a sulfonated cis-1,4-polyisoprene to create dually-crosslinked cis-1,4-polyisoprene network with sulfonate-aminium ionic bonds as the sacrificial bonds. Three diamines （primary, secondary and tertiary） with the same spacer between the two nitrogen atoms are used to create the ionic bonds with different binding energies. Although the binding energy of ionic bond does not affect the glass transition temperature of cis-1,4-polyisoprene （IR）, it exerts definite influences on strain-induced crystallization and mechanical performance. The capabilities of diamine in dissipating energy, promoting strain-induced crystallization and enhancing the mechanical performance are in the same order of secondary diamine 〉 primary diamine 〉 tertiary diamine. The variations in mechanical performances are correlated to the binding energy of the ionic bond, which is determined by pKa values.
基金financially supported by the National Basic Research Program of China(Nos.2015CB654700(2015CB654706))the National Natural Science Foundation of China(No.51473083)+3 种基金Special Foundation of Taishan Mountain Scholar Constructive ProgramShandong Provincial Key R & D program(No.2015GGX102019)Shandong Provincial Natural Science Fund for Distinguished Young Scholars(No.JQ201213)the Yellow River Delta Scholar program(Office of National University Science & Technology Park Administrative Committee(China University of Petroleum)
文摘Trans-1,4-polyisoprene（TPI） nanofibers have been fabricated successfully through electrospinning technology.Through the control of electrospinning parameters, highly crystallized TPI fresh fibers composed mainly of β phase were produced. Morphology and diameter of TPI nanofibers can be controlled by adjusting the electrospinning conditions. The in situ observations of FTIR spectra revealed that the crystallinity of the TPI fibers decreased with aging. While for TPI nanofibers aging at 45 °C for 24 h, a decrease in crystallinity as well as β to a transformation was observed with aging and these changings happened in the first 50 h during aging. The mechanism for β-TPI formation during electrospinning process and the reduced crystallinity with aging were proposed.
