According to the new method of preparing core-shell nanospheres developed by our group, by using two monomers, 2-hydroxypropyl
methacrylate(HPMA) and vinyl acetate(VAc), two kinds of core-shell nanospheres with poly(ɛ-caprolactone) (PCL) as the core
and crosslinked poly(2-hydroxypropyl methacrylate) (PHPMA) or poly(vinyl acetate) (PVAc) as the shell were successfully prepared
under similar conditions. After degrading the PCL cores of the two kinds of nanospheres by lipase, the corresponding crosslinked
poly(methyl acrylic acid) hollow spheres and crosslinked poly(vinyl alcohol) hollow spheres were obtained. Results indicate
that the new method we proposed for preparing core-shell polymeric nanospheres via in-situ polymerization can be generalized to a certain extent, and it is suitable for many systems provided the monomer used is soluble
in water, while its corresponding polymer is insoluble in water.
Translated from Chemical Journal of Chinese University, 2006, 27(9): 1762–1766 [译自: 高等学校化学学报] 相似文献
This article briefly describes some new approaches to stimuli-sensitive polymeric micelles and hollow spheres, which were
developed in the authors’ laboratory in recent years. (1) Self-assembly of component polymers to non-covalently connected
micelles (NCCM) driven by specific interactions. For example, in water, PCL and PAA formed core-shell nanospheres due to interpolymer
hydrogen bonding. After crosslinking the PAA shell and removing the PCL core, “nanocages” made of PAA network were obtained.
This hollow structure shows perfect reversible size-pH dependence. (2) Simultaneous in-situ polymerization of monomers and
self-assembly of the polymers. In this approach, PNIPAM network was formed by radical polymerization covering PCL particles.
Hollow spheres of PNIPAM network were then obtained by biodegradation of the PCL core. Both the core-shell spheres and hollow
spheres show reversible size dependence on temperature change because of the phase transition of PNIPAM around 32°C. (3) Complexation-induced
micellization and transition between the micelles and hollow spheres. Graft copolymers of hydroxylethyl cellulose (HEC) and
PAA were prepared by free radical polymerization. The copolymers showed pH dependent micellization, i.e., micelles formed
when pH of the graft copolymer solution decreased to around 3. The micellar structure could be locked by crosslinking the
PAA grafts. The resultant cross-linked micelles undergo pH-dependent transition between the micelles and hollow spheres, which
accompanies a remarkable particle size change. Both the micellization and the structure transition were found to be reversible
and associated with H-bonding complexation between the main chain and grafts.
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Translated from Acta Polymerica Sinica, 2005, 650(5) (in Chinese) 相似文献
A one-step sequential method for preparing AgCl@polypyrrole-chitosan core-shell nanoparticles and subsequently the formation of polypyrrole-chitosan hollow nanospheres is reported. The formation of the core and the shell is performed in one reaction medium almost simultaneously. Transmission electron microscopy (TEM) images show the presence of core-shell nanoparticles and hollow nanospheres. Ultraviolet-visible (UV-vis) studies reveal that AgCl was formed first followed by polypyrrole. X-ray diffration (XRD) and UV-vis studies show that AgCl was present in the core-shell nanoparticles and could be removed completely from the core. 相似文献
According to our "block-copolymer-free" strategy for self-assembly of polymers, noncovalently connected micelles (NCCM) with poly(epsilon-caprolactone) (PCL) as the core and poly(acrylic acid) (PAA) as the shell in aqueous solutions were attained due to specific interactions between the component polymers. The micellar structure was then locked in by the reaction of PAA with diamine. Afterward, hollow spheres based on PAA network were obtained by either core degradation with lipase or core dissolution with dimethylformamide of the cross-linked micelles. The cavitation process was monitored by dynamic light scattering, which indicated a mass decrease and size expansion. The hollow structure is confirmed by transmission electron microscopy observations. The resultant hollow spheres are pH- and salt-responsive: there is a substantial volume increase when pH changes from acid to base, and vice versa. The volume change takes place dramatically over the pH-range from 5.8 to 7.5. Furthermore, this volume-pH-dependence is found to be completely reversible provided the effect of ionic strength is excluded. The volume change can be adjusted by changing the shell thickness and the cross-linking degree of the hollow spheres. The salt effect on the hollow sphere size depends on pH: with increasing salt concentration the size shows an increase, a decrease, and a little change in acidic, basic, and neutral media, respectively. 相似文献
Summary: This work reports a new type of poly(ε‐caprolactone) (PCL) robust hollow sphere with controllable biodegradability, produced by grafting PCL shells from the surface of silica sphere cores and removing the template cores. Bis(ε‐caprolactone‐4‐yl) (BCY) composed of two ε‐caprolactone molecules was used as the crosslinker, which not only greatly strengthened the PCL hollow spheres but also brought hardly any non‐biodegradable component into the system. Solubility experiments and biodegradation tests show that the crosslinked PCL hollow spheres were robust both in water and acetone, and were completely biodegradable with characteristics of controllable biodegradability according to the content of the BCY. The Rhodamine release test indicated that the release rate of encapsulated drugs in the PCL hollow spheres was controlled by diffusion and the biodegradability of the PCL molecules, and the latter mechanism will dominate when more enzymes are involved.
Reaction scheme for synthesis of linear and crosslinked hollow poly(ε‐caprolactone) spheres. 相似文献
Silver-coated poly(methyl acrylic acid) (PSA) core-shell colloid particles were prepared by an in situ chemical reduction method. Crystalline silver/titania composite hollow spheres were obtained by coating the as-prepared PSA/silver particles with an amorphous titania layer and subsequently calcining in Ar atmosphere. SEM and TEM investigation indicated that the size of the as-prepared PSA/silver and PSA/silver/TiO(2) core-shell particles and silver/titania composite hollow particles was fairly uniform and the wall thickness of the hollow spheres was in the range of 40-80 nm. UV-vis absorption spectra were recorded to investigate their optical properties. 相似文献
We report herewith the synthesis of hollow Pt nanospheres by using bis(p-sulfonatophenyl)phenylphosphine to selectively remove the Ag cores of Ag-Pt core-shell nanoparticles. Core-shell Ag-Pt nanoparticles were first obtained by the successive reduction method with a discontinuous Pt shell to allow the BSPP passage. Transmission electron microscopy imaging of the core-shell Ag-Pt nanoparticles before and after BSPP dissolution showed little changes in the particle size, indicating that the removal of the Ag cores had occurred isomorphously. The hollow Pt nanospheres, together with the predecessor Ag-Pt core-shell particles of the same size, were transferred from water to toluene and surface modified by dodecylamine in toluene. This allows the catalytic activities of solid and hollow Pt particles in room temperature methanol oxidation reaction to be compared under conditions of identical particle size and the same surface environment. The measured higher specific activity of the Pt hollow nanospheres could then be attributed unambiguously to the larger specific surface area prevalent in the porous hollow structure. 相似文献
