Summary: A series of thermally responsive dendritic core-shell polymers were prepared based upon dendritic polyamidoamine (PAMAM), modified with carboxyl end-capped linear poly(N-isopropylacrylamide) (PNIPAAm-COOH) in different ratios via an esterification process to obtain PNIPAAm-g-PAMAM. The graft ratio of PNIPAAm could be adjusted by changing the feed ratio of PAMAM-OH to PNIPAAm-COOH and was verified by 1H NMR and gel penetration chromatography (GPC). The lower critical solution temperature (LCST) of PNIPAAm-g-PAMAM evaluated by UV-vis spectrophotometer was about 32 °C. Indomethacin (IMC) as a model drug was loaded in the thermosensitive polymer-grafted dendrimer derivative and its release behavior was studied below and above its LCST (27 °C vs 37 °C). Results showed that the LCST of PNIPAAm-g-PAMAM was around 32 °C compared with that of the pure PNIPAAm. The release behavior of the indomethacin entrapped in the internal cavities of the PNIPAAm-g-PAMAM showed that almost 77% of the drug was cumulatively released at 27 °C after 10 hours, whereas only 20% was released at 37 °C. The release rate of IMC from the IMC/PNIPAAm-g-PAMAM complex at 37 °C is significantly slower than that at 27 °C, which indicates that the PNIPAAm chains grafted on the surface of PAMAM dendrimer could act as a channel switching on-off button through expending or contracting in response to the temperature variation and could control the drug release by varying the surrounding temperature. 相似文献
Summary: After synthesizing both hard poly(organophosphazenes), which acted as strong hydrogels at a temperature below 37 °C, and soft poly(organophosphazenes), which displayed the opposite properties, we blended the polymers. When these polymers were blended at an appropriate ratio, the blended aqueous solution changed into a transparent hydrogel with improved mechanical properties at a temperature of 37 °C. According to DSC and IR measurements, the two polymers blended homogeneously and exhibited a behavior characteristic of a completely different copolymer.
An aqueous poly(organophosphazene) solution at room temperature (left) is reversibly and rapidly transformed into a transparent hydrogel at body temperature (right) when a hard poly(organophosphazene) is blended with a soft one at an appropriate ratio. 相似文献
A novel thermo-responsive diblock copolymer of poly(N-vinyl-2-pyrrolidinone)-block-poly(N-isopropylacrylamide) (PNVP-b-PNIPAM) was synthesized. FT-IR, 1H-NMR and SEC results confirmed the successful synthesis of PNVP-b-PNIPAM diblock copolymer via anionic polymerization. The polymeric micelles formed from PNVP-b-PNIPAM copolymer in aqueous solution were developed and characterized as a potential thermo-responsive and biocompatible drug delivery system. Micellization of the diblock copolymer in aqueous solution was characterized by dynamic laser scattering (DLS), turbidity measurement, tension measurement and transmission electron microscopy (TEM). The thermo-responsive polymeric micelles with the size ranges of 200 to 260 nm and thickness of 30 nm are localized, selected and targeted for drug release, having a great potential in response to external-stimulus such as temperatures from 35 to 39°C. The critical micellization concentration (cmc) of PNVP-b-PNIPAM in aqueous solution is 0.0026 wt% determined by turbidity measurement. The size of micelles determined by DLS increased from 163 to 329 nm with increasing concentration of PNVP-b-PNIPAM from 0.25 to 0.5 wt% in aqueous solution at 40°C, which is determined by DLS. 相似文献
The synthesis of diblock copolymers of poly(N-isopropylacrylamide) (PNIPAM) and poly(vinyl acetate) (PVAc) was performed by macromolecular design via interchange of xanthates (MADIX) process. Following the preparation of methyl (isopropoxycarbonothioyl) sulfanyl acetate (MIPCTSA) as chain transfer agent, it was reacted with vinyl acetate to obtain PVAc macro-chain transfer agent. Then, block copolymerization was completed by successive addition of N-isopropylacrylamide (NIPAM). 1H NMR spectroscopy confirmed the presence of both blocks in the copolymer structure, with the expected composition based on the feed ratio. Size Exclusion Chromatography (SEC) was used to investigate the relative values of molecular characteristics. Only 20% of PVAc was converted to block copolymer. The resultant block copolymer structures were further examined in terms of their morphologies as well as critical micelle concentration (CMC) by using ESEM and Fluorescence Excitation Spectroscopic techniques, respectively. Morphological characterization confirmed amphiphilic block copolymer formation with the existence of mainly ca. 100 nm well distributed micelles. The thermo responsive amphiphilic behavior of the block copolymer solutions were followed by Dynamic Light Scattering (DLS) technique. 相似文献
Narrowly distributed polystyrene-g-p(N-isopropylacrylamide) (PSt-g-PNIPAM) was prepared by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide using the brominated polystyrene as macroinitiator and CuCl combined with hexamethyltriethylenetetramine as catalyst. Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy confirmed the structure of PSt-g-PNIPAM. The gel permeation chromatography (GPC) showed that the graft copoly- mer had a single distribution peak with molecular weight, Mn (g/mol) of 19815 g/mol (using polystyrene as the standard). Differential scanning calorimetry (DSC) revealed that due to both effects of hydro- phobic isopropyl groups and hydrogen bonds in the amide group, the glass transition temperature (Tg) of PSt-g-PNIPAM enhanced 16.0 ℃ compared to the Tg of the polystyrene. 相似文献
Poly(N-isopropylacrylamide) (PNIPAAm) is a well-known thermosensitive polymer. It shows the lower critical solution temperature (LCST) of about 32℃ in aqueous solution. Many PNIPAAm containing amphiphilic copolymers have been reported. The most frequentl… 相似文献
