MACROMOLECULES
·
2011
·
IF 4.838
Yanwu Zhou,Junpo He,Changxi Li,Linxiang Hong,Yuliang Yang
The thermal decomposition of different classes of RAFT/MADIX agents, namely dithioesters, trithiocarbonates, xanthates, and dithiocarbamates, were investigated through heating in solution. It was found that the decomposition behavior is complicated interplay of the effects of stabilizing Z-group and leaving R-group. The mechanism of the decomposition is mainly through three pathways, i.e., β-elimination, α-elimination, and homolysis of dithiocarbamate (particularly for universal RAFT agent). The most important pathway is the β-elimination of thiocarbonylthio compounds possessing β-hydrogen, leading to the formation unsaturated species. For the leaving group containing solely α-hydrogen, such as benzyl, α-elimination takes place, resulting in the formation of (E)-stilbene through a carbene intermediate. Homolysis occurs specifically in the case of a universal RAFT agent, in which a thiocarbonyl radical and an alkylthio radical are generated, finally forming thiolactone through a radical process. The stabilities of the RAFT/MADIX agents are investigated by measuring the apparent kinetics and activation energy of the thermal decomposition reactions. Both Z-group and R-group influence the stability of the agents through electronic and steric effects. Lone pair electron donating heteroatoms of Z-group show a remarkable stabilizing effect while electron withdrawing substituents, either in Z- or R-group, tends to destabilize the agent. In addition, bulkier or more β-hydrogens result in faster decomposition rate or lower decomposition temperature. Thus, the stability of the RAFT/MAIDX agents decreases in the order where R is (with identical Z = phenyl) −CH2Ph (5) > −PS (PS-RAFT 15) > −C(Me)HPh (2) > −C(Me)2C(═O)OC2H5 (7) > −C(Me)2Ph(1) > −PMMA (PMMA-RAFT 16) > −C(Me)2CN (6). For those possessing identical leaving group such as 1-phenylethyl, the stability decreases in the order of O-ethyl (11) > –N(CH2CH3)2 (13) > –SCH(CH3)Ph (8) > −Ph (2) > −CH2Ph (4) > −PhNO2 (3). These results consort with the chain transfer acitivities measured by the CSIRO group and agree well with the ab initio theoretical results by Coote. In addition, the difference between thermal stabilities of the universal RAFT agents at neutral and protonated states has also been demonstrated.
研究领域:
化学
·
材料科学
✓ 已验证
产品关联
DOI
高影响因子
EUROPEAN POLYMER JOURNAL
·
2014
·
IF 3.242
Houluo Cong,Jingang Li,Lei Li,Sixun Zheng
In this contribution, we reported the synthesis of poly(N-isopropylacrylamide)- block -poly(N-vinylpyrrolidone)- block -poly(N-isopropylacrylamide) (PNIPAM- b -PVP- b -PNIPAM) triblock copolymers through sequential reversible addition–fragmentation chain transfer/macromolecular design via the interchange of xanthate (RAFT/MADIX) process. The triblock copolymers have been characterized by means of 1 H nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). This ABA triblock copolymer displayed a typical thermoresponsive gelation behavior. In this work, the thermoresponsive gelation behavior was investigated by means of rheological measurements, micro-differential scanning calorimetry (Micro-DSC) and small angle X-ray scattering (SAXS). The thermoresponsive gelation behavior could endow the triblock copolymers with the potential application as injectable hydrogels.
研究领域:
高分子化学
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材料科学
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生物医学工程
✓ 已验证
产品关联
DOI
高影响因子
POLYMER
·
2013
·
IF 3.379
Houluo Cong,Lei Li,Sixun Zheng
In this work, we reported the synthesis of poly(N-isopropyl acrylamide)- block - poly(N-vinylpyrrolidone)- block -poly(N-isopropylacrylamide) triblock copolymer (PNIPAAm- b -PVPy- b -PNIPAAm) via reversible addition-fragmentation chain transfer polymerization/macromolecular design via the interchange of xanthate (RAFT/MADIX) process. This approach was further employed to prepare the PNIPAAm- b -PVPy block copolymer networks with N,N′-methylenebisacrylamide as the crosslinker. The results of small angle X-ray scattering (SAXS) indicate that the PNIPAAm- b -PVPy block copolymer networks were microphase-separated, in which PVPy was dispersed into PNIPAAm matrix as the microdomains. The architecture of block copolymer networks allows investigating the effect of the blocked permanently hydrophobic chains ( viz. PVPy) on the deswelling and reswelling behavior of the PNIPAAm hydrogels. It was found that the diffusion of water molecules in PNIPAAm- b -PVPy block copolymer networks was in a non-Fickian and accelerating manner. The swelling ratios of the PNIPAAm- b -PVPy hydrogels were significantly higher than that of control PNIPAAm hydrogel. Compared to control PNIPAAm hydrogel, the PNIPAAm- b -PVPy hydrogels displayed an accelerated response to the external temperature changes in terms of deswelling and reswelling tests. The accelerated thermoresponsive properties is ascribed to the presence of the PVPy blocks in the PNIPAAm- b -PVPy block copolymer networks, which could act as the hydrophilic tunnels to facilitate the diffusion of water molecules in the PNIPAAm networks.
研究领域:
材料科学
·
高分子化学
·
生物材料
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF SUPERCRITICAL FLUIDS
·
2017
·
IF 2.991
Lei Bao,Shuyi Fang,Dongdong Hu,Yuan Zong,Ling Zhao,Weikang Yuan,Tao Liu
Several amphiphilic nonfluorinated polymers, poly(vinyl acetate)-block-poly(dimethylaminoethyl methacrylate) (PVAc -b- PDMAEMA) and poly(vinyl acetate- alt -diethyl maleate) (PVDBM) -b- PDMAEMA with different ratios of CO 2 -philic and hydrophilic groups, were synthesized using RAFT/MADIX polymerization and ATRP. Stability measurements revealed that PVDBM 8 -b- PDMAEMA 22 could emulsify 80% CO 2 in H 2 O, with stable CO 2 -in-water (C/W) emulsions observed for more than 48 h under 20.0 MPa at 25 °C, which was 20 times longer than PVAc -b- PDMAEMA did. The optimal degree of polymerization (DP) for CO 2 -philic groups in PVDBM- b -PDMAEMA was 8, because increasing the DP of PVDBM increased the CO 2 -philicity, whereas increased molecular weight limited the miscibility in water. Molecular dynamics simulations were applied to determine the hydrophilic/CO 2 -philic balance (HCB). It was found that enhanced CO 2 -philic tails widened the HCB range, and the optimal range of the HCB was varied with CO 2 -philic tail types. Both experimental and simulation results demonstrated that enhancing the CO 2 -philicty of surfactant tails can improve the stability of C/W emulsions.
研究领域:
材料科学
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化学工程
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高分子化学
✓ 已验证
DOI
高影响因子
Polymers
·
2019
·Vol. 11
·期 9
·1440
·
IF 3.164
Dan Lu,Hu Wang,Ru-Ke Bai
An alternating fluorinated copolymer based on chlorotrifluoroethylene (CTFE) and butyl vinyl ether (BVE) was synthesized by RAFT/MADIX living/controlled polymerization in the presence of S-benzyl O-ethyl dithiocarbonate (BEDTC). Then, using the obtained poly(CTFE-alt-BVE) as a macro chain transfer agent (macro-CTA), a block copolymer was prepared by chain extension polymerization of vinyl acetate (VAc). After a basic methanolysis process, the poly(vinyl acetate) (PVAc) block was transferred into poly(vinyl alcohol) (PVA). Finally, a novel fluorinated polyurethane with good surface properties due to the mobility of the flexible fluorinated polymer chains linked to the network was obtained via reaction of the copolymer bearing the blocks of PVA with isophorone diisocyanate (IPDI) as a cross-linking agent.Keywords:fluorinated polyurethane;fluorinated polymer;chlorotrifluoroethylene
研究领域:
高分子化学
·
材料科学
✓ 已验证
产品关联
DOI
PubMed
高影响因子
危险品化学品经营许可证（带存储）