Co-reporter:Jun Shao, Jingru Sun, Xinchao Bian, Yunchun Zhou, Gao Li and Xuesi Chen
CrystEngComm 2013 vol. 15(Issue 33) pp:6469-6476
Publication Date(Web):07 Jun 2013
DOI:10.1039/C3CE40748A
The poly(D-lactide)/poly(L-lactide) (PDLA/PLLA) blends with low molecular weights were cast from solution. After heating to above the melting temperature, followed by cooling at various rates, DSC, WAXD and FTIR studies revealed that a mesomorphic phase developed in the PDLA/PLLA 90/10 and 80/20 (or 10/90 and 20/80) specimens when the temperature window spanned from 80 °C to 110 °C. The mesophase melted and reorganized into crystallites after the temperature increased to ∼130 °C. Although the formation and transition of the mesophase was observed at lower temperatures in partially crystallized specimens, the mesophase could exist steadily when the temperature did not exceed 100 °C. The content of the mesophase was proven to be strongly dependent on the cooling rate, the D/L weight ratio and the molecular weights in the blends. The formation of the mesophase could be explained by the fact that the crystallization of the PLA matrix was disturbed by the addition of small amount of enantiomeric PLA.
Co-reporter:Lidong Feng, Xinchao Bian, Zhiming Chen, Gao Li, Xuesi Chen
Polymer Degradation and Stability 2013 Volume 98(Issue 9) pp:1591-1600
Publication Date(Web):September 2013
DOI:10.1016/j.polymdegradstab.2013.06.025
Two novel biodegradable copolymers, including poly(ethylene glycol)-succinate copolymer (PES) and poly(ethylene glycol)-succinate-l-lactide copolymer (PESL), have been successfully synthesized via melt polycondensation using SnCl2 as a catalyst. The copolymers were used to toughen PLA by melt blending. The DSC and SEM results indicated that the two copolymers were compatible well with PLA, and the compatibility of PESL was superior to that of PES. The results of tensile testing showed that the extensibility of PLA was largely improved by blending with PES or PESL. At same blending ratios, the elongation at break of PLA/PESL blends was far higher than that of PLA/PES ones. The elongation maintained stable through aging for 3 months. The moisture absorption of the blends enhanced due to the strong moisture absorption of PEG segments in PES or PESL molecules, which did not directly lead to enhance the hydrolytic degradation rate of the PLA. The PLA blends containing 20–30 wt% PES or PESL were high transparent materials with high light scattering. The toughening PLA materials could potentially be used as a soft biodegradable packaging material or a special optical material.
Co-reporter:Lidong Feng;Xinchao Bian;Yi Cui;Zhiming Chen;Xuesi Chen
Macromolecular Chemistry and Physics 2013 Volume 214( Issue 7) pp:
Publication Date(Web):
DOI:10.1002/macp.201200696
Co-reporter:Jun Shao, Jingru Sun, Xinchao Bian, Yi Cui, Yunchun Zhou, Gao Li, and Xuesi Chen
Macromolecules 2013 Volume 46(Issue 17) pp:
Publication Date(Web):August 22, 2013
DOI:10.1021/ma400938v
The crystallization and melting behaviors of polylactide (PLA) homochiral polymer under the confinement of stereocomplex crystallites were studied in the linear and three-armed poly(d-lactide)/poly(l-lactide) (PDLA/PLLA and 3PDLA/3PLLA) solution casting blends. WAXD results showed that novel modified crystallites formed when PLA homopolymer crystallized from the melting state. And the modified crystallites formed in 3PDLA/3PLLA blends (M-A) were less stable than that formed in similar PDLA/PLLA blends (M-B) after specimens cooled at a specific rate. Although these modified crystallites differed from PLA α crystallites (M-C), both of them transformed into α crystallites during heating. The transitions among different crystallites revealed the multiple melting behaviors in DSC measurement. The type of PLA homochiral crystallites and their contents mainly depended on the D/L compositions, annealing conditions, molecular weights, and architectures of the polymers in the blends. The formation of these modified crystallites should be ascribed to the confinement of PLA stereocomplex and steric hindrance of polymers, and PLA homopolymer could not charge into lattice orderly during rapid crystallization.
Co-reporter:Kaixuan Ren, Yilong Cheng, Chaoliang He, Chunsheng Xiao, Gao Li, Xuesi Chen
Polymer 2013 Volume 54(Issue 9) pp:2466-2472
Publication Date(Web):19 April 2013
DOI:10.1016/j.polymer.2013.02.038
The solid state and melt nanoscale structures of a series of poly(ethylene glycol)-block-poly(γ-alkyl-l-glutamate)s (PEG-b-PALG) copolymers bearing different alkyl side groups, i.e., n-butyl, n-hexyl, n-octyl, and n-dodecyl, have been investigated in the present work. An interesting effect of alkyl side groups on the secondary conformation of polypeptide block, crystallization of PEG segments and morphology of the copolymers was observed. With increasing the length of alkyl side groups or raising the temperature, the predominant secondary structure gradually changed from α-helix to β-sheet conformation. Differential scanning calorimetry, wide-angle X-ray diffraction analysis and polarized optical microscopy indicated that the crystallization and morphology of PEG segments were markedly restricted by the polypeptide block. Therefore, the alkyl side groups not only exhibited significant influence on the conformation of polypeptide block, but also affected the crystallization of PEG segments. The secondary structure, crystallization and spherulite morphology of these synthetic biomaterials, which were significantly influenced by alkyl side groups, may play an important role in their physicochemical properties, such as self-assembly, as well as in some biomedical applications.
Co-reporter:Jingru Sun, Jun Shao, Shaoyong Huang, Bao Zhang, Gao Li, Xianhong Wang, Xuesi Chen
Materials Letters 2012 Volume 89() pp:169-171
Publication Date(Web):15 December 2012
DOI:10.1016/j.matlet.2012.08.129
A particular crystallization behavior of PLA stereocomplex was observed when the poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA) (50/50) was subjected to specific melting conditions. The effect of the holding temperature in the melt state of PLLA/PDLA samples on the nonisothermal melt crystallization process and on the structure have been investigated by means of DSC, and wide angle X-ray diffraction. In the moderate melting condition, residual ordered domains act as athermal nuclei and a single crystallization process via a predetermined nucleation mechanism was observed. The survived nuclei favor high temperature polymer crystallization, correspondingly, a high melting temperature (TmH) of PLA stereocomplex, of 244.9 °C with the fusion enthalpy 87.0 J/g were obtained. Such a Tm result of PLA stereocomplex is much higher than that of the reported previously.Graphical abstractHighlights► The crystallization behavior of the PLA stereocomplex depends on its initial melt state. ► When higher temperature than 240 °C was applied, stereocomplexation is strongly depressed. ► While in the mild melting condition, the survived nuclei favor high temperature polymer crystallization. ► A high melting temperature (TmH) of PLA stereocomplex, of 244.9 °C with the fusion enthalpy 87.0 J/g was obtained.
Co-reporter:Jun Shao, Jingru Sun, Xinchao Bian, Yi Cui, Gao Li, and Xuesi Chen
The Journal of Physical Chemistry B 2012 Volume 116(Issue 33) pp:9983-9991
Publication Date(Web):July 31, 2012
DOI:10.1021/jp303402j
Stereocomplex poly(lactide)s (sc-PLAs) were obtained from solution blending of 3-armed poly(l-lactide) (3PLLA) and linear poly(d-lactide) (PDLA) and between enantiomeric 3PLAs. Differential scanning calorimetry and wide-angle X-ray diffraction results indicated that racemic crystallites were preferentially produced in all the binary blends. The melting temperature and fusion enthalpy of racemic crystallites were remarkably different through varying the structure, constituent, and molecular weight of PLA. Through this investigation, higher melting temperatures were obtained in the middle molecular weight binary blends, and the highest melt temperature of racemic crystallites reached to 246 °C, it was the highest reported value until now. In similar molecular weight blends (or the linear PLA was similar to each branch of 3PLA enantiomers), with the composition of 3PLA increasing, the phase separation molecular weight decreased gradually (Mlinear/linear blends > Mlinear/3-armed blends > M3-armed/3-armed blends). The structure distinction between 3PLA and linear PLA induced different thermal properties and phase behaviors of the 3PLLA/PDLA and 3PLLA/3PDLA blends. The thermal properties of these mixtures and its variations provided basic data for their industrial applications.
Co-reporter:Ting Zhao;Jijun Cui;Yunchun Zhou;Leijing Liu;Junliang Yang;Enle Zhou;Xuesi Chen
Journal of Polymer Science Part B: Polymer Physics 2006 Volume 44(Issue 22) pp:3215-3226
Publication Date(Web):12 OCT 2006
DOI:10.1002/polb.20886
The confined crystallization behavior, melting behavior, and nonisothermal crystallization kinetics of the poly(ethylene glycol) block (PEG) in poly(L-lactide)–poly(ethylene glycol) (PLLA–PEG) diblock copolymers were investigated with wide-angle X-ray diffraction and differential scanning calorimetry. The analysis showed that the nonisothermal crystallization behavior changed from fitting the Ozawa equation and the Avrami equation modified by Jeziorny to deviating from them with the molecular weight of the poly(L-lactide) (PLLA) block increasing. This resulted from the gradual strengthening of the confined effect, which was imposed by the crystallization of the PLLA block. The nucleation mechanism of the PEG block of PLLA15000–PEG5000 at a larger degree of supercooling was different from that of PLLA2500–PEG5000, PLLA5000–PEG5000, and PEG5000 (the numbers after PEG and PLLA denote the molecular weights of the PEG and PLLA blocks, respectively). They were homogeneous nucleation and heterogeneous nucleation, respectively. The PLLA block bonded chemically with the PEG block and increased the crystallization activation energy, but it provided nucleating sites for the crystallization of the PEG block, and the crystallization rate rose when it was heterogeneous nucleation. The number of melting peaks was three and one for the PEG homopolymer and the PEG block of the diblock copolymers, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3215–3226, 2006
![Poly[oxy[(1S)-1-methyl-2-oxo-1,2-ethanediyl]], α-hydro-ω-hydroxy-, ester with α-methyl-ω-hydroxypoly(oxy-1,2-ethanediyl), diblock](http://img.cochemist.com/ccimg/473300/473266-61-4.png)
![Poly[oxy[(1S)-1-methyl-2-oxo-1,2-ethanediyl]], α-hydro-ω-hydroxy-, ester with α-methyl-ω-hydroxypoly(oxy-1,2-ethanediyl), diblock](http://img.cochemist.com/ccimg/473300/473266-61-4_b.png)
![2-CHLORO-N-[1-(2-FLUOROBENZOYL)PIPERIDIN-4-YL]ACETAMIDE](http://img.cochemist.com/ccimg/56100/56090-54-1.png)
![2-CHLORO-N-[1-(2-FLUOROBENZOYL)PIPERIDIN-4-YL]ACETAMIDE](http://img.cochemist.com/ccimg/56100/56090-54-1_b.png)
![Poly[oxy(1,4-dioxo-1,4-butanediyl)oxy-1,4-butanediyl]](http://img.cochemist.com/ccimg/26300/26247-20-1.png)
![Poly[oxy(1,4-dioxo-1,4-butanediyl)oxy-1,4-butanediyl]](http://img.cochemist.com/ccimg/26300/26247-20-1_b.png)
](http://img.cochemist.com/ccimg/27000/26913-06-4.png)
](http://img.cochemist.com/ccimg/27000/26913-06-4_b.png)
![2-METHYL-2-PROPANYL 4-[(4-AMINOPHENYL)CARBAMOYL]-1-PIPERIDINECARB<WBR />OXYLATE](http://img.cochemist.com/ccimg/25200/25191-15-5.png)
![2-METHYL-2-PROPANYL 4-[(4-AMINOPHENYL)CARBAMOYL]-1-PIPERIDINECARB<WBR />OXYLATE](http://img.cochemist.com/ccimg/25200/25191-15-5_b.png)
![POLY[OXY[(1R)-1-METHYL-2-OXO-1,2-ETHANEDIYL]]](http://img.cochemist.com/ccimg/27000/26917-25-9.png)
![POLY[OXY[(1R)-1-METHYL-2-OXO-1,2-ETHANEDIYL]]](http://img.cochemist.com/ccimg/27000/26917-25-9_b.png)
![Poly[oxy[(1S)-1-methyl-2-oxo-1,2-ethanediyl]]](http://img.cochemist.com/ccimg/26200/26161-42-2.png)
![Poly[oxy[(1S)-1-methyl-2-oxo-1,2-ethanediyl]]](http://img.cochemist.com/ccimg/26200/26161-42-2_b.png)