Thermo-responsive Diblock Copolymer Worm Gels in Non-polar Solvents

被引:269
作者
Fielding, Lee A. [1 ]
Lane, Jacob A. [1 ]
Derry, Matthew J. [1 ]
Mykhaylyk, Oleksandr O. [1 ]
Armes, Steven P. [1 ]
机构
[1] Univ Sheffield, Dept Chem, Sheffield S3 7HF, S Yorkshire, England
基金
英国工程与自然科学研究理事会;
关键词
RAFT DISPERSION POLYMERIZATION; BLOCK-COPOLYMER; BENZYL METHACRYLATE; NANO-OBJECTS; IN-SITU; EFFICIENT SYNTHESIS; ETHYLENE-OXIDE; MICELLES; VESICLES; NANOPARTICLES;
D O I
10.1021/ja501756h
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Benzyl methacrylate (BzMA) is polymerized using a poly(lauryl methacrylate) macromolecular chain transfer agent (PLMA macro-CTA) using reversible addition-fragmentation chain transfer (RAFT) polymerization at 70 degrees C in n-dodecane. This choice of solvent leads to an efficient dispersion polymerization, with polymerization-induced self-assembly (PISA) occurring via the growing PBzMA block to produce a range of PLMA-PBzMA diblock copolymer nano-objects, including spheres, worms, and vesicles. In the present study, particular attention is paid to the worm phase, which forms soft free-standing gels at 20 degrees C due to multiple interworm contacts. Such worm gels exhibit thermo-responsive behavior: heating above 50 degrees C causes degelation due to the onset of a worm-to-sphere transition. Degelation occurs because isotropic spheres interact with each other much less efficiently than the highly anisotropic worms. This worm-to-sphere thermal transition is essentially irreversible on heating a dilute solution (0.10% w/w) but is more or less reversible on heating a more concentrated dispersion (20% w/w). The relatively low volatility of n-dodecane facilitates variable-temperature theological studies, which are consistent with eventual reconstitution of the worm phase on cooling to 20 degrees C. Variable-temperature H-1 NMR studies conducted in d(26)-dodecane confirm partial solvation of the PBzMA block at elevated temperature: surface plasticization of the worm cores is invoked to account for the observed change in morphology, because this is sufficient to increase the copolymer curvature and hence induce a worm-to-sphere transition. Small-angle X-ray scattering and TEM are used to investigate the structural changes that occur during the worm-to-sphere-to-worm thermal cycle; experiments conducted at 1.0 and 5.0% w/w demonstrate the concentration-dependent (ir)reversibility of these morphological transitions.
引用
收藏
页码:5790 / 5798
页数:9
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