China
Africa
Explore chapters and articles related to this topic
Manufacturing Techniques for Nanoparticles in Drug Delivery
Published in Yasser Shahzad, Syed A.A. Rizvi, Abid Mehmood Yousaf, Talib Hussain, Drug Delivery Using Nanomaterials, 2022
Daniel Real, María Lina Formica, Matías L. Picchio, Alejandro J. Paredes
Like ATRP and NMP, RAFT is another reversible-deactivation radical polymerization technique but is more versatile and allows for better control over molecular weights and polydispersity (Keddie, 2014). This polymerization method relies on adding a chain transfer agent (RAFT agent) to a conventional free radical polymerization medium. RAFT polymerization is characterized by four different steps: initiation, addition–fragmentation, reinitiation, and equilibration. In the first step, free radicals are generated from the initiator, and the subsequent addition of monomer creates active polymer chains (Pn•). In the addition-fragmentation step, the polymer chains combine with the RAFT agent, giving an active intermediate and releasing a homolytic leaving group (R•). This step is reversible, and the active intermediate can lose either the cleavable group (R•) or the polymeric chain (Pn•). Re-initiation can start with R• by addition of a monomer and forming a new active polymer (Pm•). This active chain goes through the addition–fragmentation or equilibration steps. Active polymer chains (Pn• and Pm•) are in equilibrium between the active and dormant (bound to the thiocarbonyl compound) stages. Thus, when one polymer chain is in the dormant stage, the other chain is active in polymerization.
Controlled Polymerization
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
In recent years, RAFT has grown to be a very popular approach to controlled radical polymerization, due to an attractive combination of breadth of accessible monomers and solvents, tolerance of functional groups, and general ease of use. The principal distinction between RAFT polymerization on the one hand, and ATRP or SFRP on the other, is that RAFT polymerization involves a reversible chain transfer, whereas the other two involve reversible chain termination. The key player in the RAFT process is the chain transfer agent (CTA) itself. A general structure of a RAFT CTA [4.II] is shown below:
Design of Bioresponsive Polymers
Published in Deepa H. Patel, Bioresponsive Polymers, 2020
Anita Patel, Jayvadan K. Patel, Deepa H. Patel
Subsequent to NMRP and ATRP, RAFT polymerization is the advanced living radical polymerization (LRP) method [25]. Through reversible addition and fragmentation chain transfer procedure, the free radical polymerization demonstrates living distinctiveness in the existence of RAFT agent. Homopolymers, plus block copolymers branched as well as ascent polymers with tapered polydispersities can effortlessly be organized via RAFT polymerization, [26]. In addition, it is entirely consistent with conventional free radical polymerization. The broad range of monomers that possibly will be simply polymerized with RAFT technique, primarily carboxyl monomers is the major benefit of this technique contrary to ATRP and NMRP polymerization [18, 19, 27].
Atom transfer radical polymerization initiated by activator generated by electron transfer in emulsion media: a review of recent advances and challenges from an engineering perspective
Published in Journal of Dispersion Science and Technology, 2023
Mohammed Awad, Ramdhane Dhib, Thomas Duever
The CRP technique can take place according to three different reaction schemes: 1) Atom transfer radical polymerization (ATRP), 2) Nitroxide – mediated radical polymerization (NMRP), and 3) reversible addition-fragmentation chain transfer polymerization (RAFT). Dynamic equilibrium reaction between dormant species and active radicals is the standard of all three CRP techniques, this is to synthesize a wide range of polymers with a low polydispersity index (Ð) under mild conditions. The equilibrium reaction helps reduce the termination reaction by providing a low concentration of radicals and simultaneously allowing a slow growth of polymer chains.[12,21,22] The achievement of reasonable chemical control over the reaction extent is governed by the fast reciprocity between the dormant and active species, as well as the instantaneous and rapid initiation of all chains. Consequently, this may not occur unless the initiator has high efficiency and negligible chain breaking reactions. In fact, the same lifetime of the propagating radicals will result from a similar chain length in all polymer chains, which indicates a Ð close to unity. In other words, during the chain growth the propagation reaction is slowed down by the dynamic equilibrium reaction, which results in a narrow Ð of the polymer chains.[23]
Synthesis and characterization of phenylboronic acid-containing polymer for glucose-triggered drug delivery+
Published in Science and Technology of Advanced Materials, 2020
Guihua Cui, Kunming Zhao, Kewei You, Zhengguo Gao, Toyoji Kakuchi, Bo Feng, Qian Duan
In the previous research, most of the polymer preparation of GA used amino group for reaction, and most of the polymers were synthesized by free radical polymerization. However, in this study, we retained the amino of GA, which is better for retaining the activity of GA. We synthesized polymer by atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT), so the reaction is more controllable. Meanwhile, europium fluorescence system is adopted in this study, which can be directly used for determination in the future. In a previous work of our team, a series of thermo-sensitive GA terminated-PNIPAM polymers (GA-PNIPAM) had been developed in our team by ATRP [21,22], and which could coordinate with Eu(III) ions to form the (GA-PNIPAM)/Eu(III) complexes with amino. To explore the novel PBA-based glucose-sensitive drug delivery, in this work, the thermo-sensitive phenylboronic acid PBA-containing block copolymer poly(N-isopropylacrylamide)-block-poly(3-acrylamidophenylboronic acid) (PNIPAM136-b-PAPBA16) were fabricated by RAFT. Then, the addition of a GA-containing complexes (GA-PNIPAM)/Eu(III) resulted in the formation of core-shell complex micelles based on the cross-linking between PBA- and GA-containing blocks as shown in Scheme 1. The results of the transmission electron microscopy (TEM) and dynamic light scattering (DLS) revealed the complex micelles were excellent nanoparticles which may be a promising candidate for glucose-responsive drug delivery for diabetes treatment.
Synthesized of glucose-responsive nanogels labeled with fluorescence molecule based on phenylboronic acid by RAFT polymerization
Published in Journal of Biomaterials Science, Polymer Edition, 2019
RAFT polymerization provides opportunities for preparing polymers with controlled molecular weights/lengths, architectures and precise location of functional groups. By rationally designing targeted polymers, nanogels can be prepared with a higher degree of control of structures, properties and functions using RAFT polymerization [36]. Glycopolymer nanogels p(AAPBA-AGA-BODIPYMA) were synthesized via RAFT polymerization method (Scheme 1). The monomers of AAPBA, AGA and BODIPYMA were used to obtain the glucose-sensitive, biocompatible and fluorescent nanogels. RAFT agent was used to control the molecular weight and avoid the molecular weight too large during the polymerization. Figure 1A showed the 1H NMR spectra of monomers and p(AAPBA-AGA-BODIPYMA). Compared with the spectra of AAPBA and AGA, signals of double bonds in AAPBA (5.7, 6.3 and 6.5 ppm) and AGA (5.2, 5.8 and 6.3 ppm) spectra disappeared and protons on the newly formed main chain generated signals at 1.0-2.2 ppm in the spectrum of p(AAPBA-AGA-BODIPYMA). Both typical signals of phenyl (6.8-7.8 ppm) in AAPBA and sugar residue (3.0-3.8 ppm) in AGA were preserved in the spectrum of p(AAPBA-AGA-BODIPYMA). These results imply that p(AAPBA-AGA-BODIPYMA) was successfully prepared. Figure 1B shows FT-IR spectrum of p(AAPBA-AGA-BODIPYMA) nanogels that exhibited a broad absorption band with a range of 3200 to 3600 cm−1, which was attributed to hydrogen bonds formed between hydroxyls of carbohydrate moieties. The peak absorptionband of 3310 cm−1 was attributed to N-H stretching. The amide I band assigned to C = O stretching resulted in an absorption band of 1664 cm−1, while amide II band assigned to N-H bending vibration of a secondary amide at an absorption band at 1545 cm−1). The band in 1040 to 1240 cm−1 region resulted from the C-O stretching and corresponded to alkoxy bonds in the carbohydrate moieties. Expect for the broad absorption band and C-O stretching band that reflected the presence of carbohydrate moieties, the absorption bands in the range of 1340 to 1610 cm−1 were typical of the phenyl ring in AAPBA.