Although photoluminescence of tertiary aliphatic amines has been extensively studied, the usage of this fundamental chromophore as a fluorescent probe for various applications has unfortunately not been realized because their uncommon fluorescence is easily quenched, and strong fluorescence has been observed only in vapor phase. The objective of this study is how to retain the strong fluorescence of tertiary amines in polymers. Tertiary amines as branching units of the hyperbranched poly(amine-ester) (HypET) display relatively strong fluorescence (Φ = 0.11-0.43). The linear polymers with tertiary amines in the backbone or as the side group are only very weakly fluorescent. The tertiary amine of HypET is easily oxidized under ambient conditions, and red-shifting of fluorescence for the oxidized products has been observed. The galactopyranose-modified HypET exhibits low cytotoxicity and bright cell imaging. Thus, this study opens a new route of synthesizing fluorescent materials for cell imaging, biosensing, and drug delivery.
Drug delivery systems (DDS) based on functionalized polymeric nanoparticles have attracted considerable attention. Although great advances have been reported in the past decades, the fabrication efficiency and reproducibility of polymeric nanoparticles are barely satisfactory due to the intrinsic limitations of the traditional self-assembly method, which severely prevent further applications of the intelligent DDS. In the last decade, a new self-assembly method, which is usually called polymerization-induced self-assembly (PISA), has become a powerful strategy for the fabrication of the polymeric nanoparticles with bespoke morphology. The PISA strategy efficiently simplifies the fabrication of polymeric nanoparticles (combination of the polymerization and self-assembly in one pot) and allows the fabrication of polymeric nanoparticles at a relatively high concentration (up to 50 wt%), making it realistic for large-scale production of polymeric nanoparticles. In this review, the developments of PISA-based polymeric nanoparticles for drug delivery are discussed.
Mesoporous silica nanoparticles (MSNs) are considered for potential scaffoldings in drug delivery due to their good biocompatibility and large pore volume, and it is the focus to find a suitable gatekeeper for the mesopores. In this paper, a reliable and versatile method of surface-initiated atom transfer radical polymerization (SI-ATRP) has been employed to prepare the hybrid poly(2-(diethylamino)ethyl methacrylate)-coated MSNs (MSN-PDEAEMA). The resultant hybrid nanoparticles with pH-sensitive polymer shell and MSN core were characterized by a series of techniques including high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, and nitrogen adsorption isotherms. The pH-responsive PDEAEMA brushes anchored on MSNs could serve as a switch to control the opening and closing of the pores. Release of guest molecules was conducted at different pHs, and the results showed rapid release in acidic aqueous solution but very little leakage in alkaline solution. By adjusting the pH of the solution repeatedly, the release of encapsulated molecules could be switched on and off at will. We envision that this nanosystem should have potential applications in sited release of anticancer drug and gene delivery.
The self-assembly of block copolymers attracts wide interest due to many potential applications of the polymeric aggregates. Great effort has been made to realize the convenient fabrication of abundant polymeric materials with well-defined nanostructures. This review introduces the development of the in situ preparation of block copolymer aggregates by heterogeneous polymerization. Great emphasis is put on discussing the formation mechanism of aggregates with different morphologies. Some important factors that influence the morphologies are illustrated when different polymerization methods are employed. By demonstrating some recent advances and existing problems in this area, more attention and effort should be paid to this field to facilitate its further progress.
The reversible addition-fragmentation transfer (RAFT) polymerizations of 4-vinylpyridine (4VP) in tetrahydrofuran (THF) and in cyclohexane with RAFT agent, dithiobenzoate-terminated polystyrene (PS-SC(S)Ph), involve one polymerization rate (R p ) 0.083 mol L -1 h -1 ) and two stages of polymerization (R p ) 0.164 and 0.0024 mol L -1 h -1 before and after 5 h), respectively. The polymerization of 4VP and divinylbenzene (less than 10% relative to 4VP) in THF led to gelation, but the polymerization in cyclohexane displayed clear solution consistently throughout polymerization, and kinetic studies showed sudden decrease of polymerization rate and sharp increase of molecular weight at around 5 h. Polymerization was followed by gel permeation chromatography (GPC) and the combination of GPC and multiangle laser light scattering (MALLS). The results show the formation of micelles with PS as shell and poly(PVP-co-DVB) as core by microphase separation; the micelles' size increased fast around 5 h polymerization, and then the micelles grew slowly with progress of polymerization. A series of experiments were made to look for reasons for the decrease of polymerization rate at around 5 h of polymerization, and the possible reasons are the restriction of diffusion and higher concentration of dithiobenzoate groups in the cores of micelles. The effects of molecular weight of RAFT agent and the content of DVB in the mixture of 4VP and DVB on the polymerization and the formation of micelles were also investigated. 1 H NMR, dynamic and static light scattering (DLS, SLS), transmission electron micrograph (TEM), and atomic force microscopy (AFM) were used to characterize the micelles, and the micelles with less than 50 nm in diameter and narrow size distribution were obtained. Thus, an efficient synthetic method of stable micelles was developed in comparison with the self-assembling of block and graft polymers in selective solvents, and one advantage of this method is that the polymerization, micellization, and cross-linking reactions occur in one pot, forming stable, narrow micelles with functional cores.
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