Evaluation of the clenbuterol imprinted monolithic column prepared by reversible addition-fragmentation chain transfer polymerization

To make more homogenous organic monolithic structure, reversible addition-fragmentation chain transfer （RAFT） process was employed in the synthesis of the clenbuterol imprinted polymer. In the synthesis, the influence of synthetic conditions on the polymer structure and separation efficiency was studied. The result demonstrated that the imprinted columns prepared with RAFT process have higher column efficiency and selectivity than the columns prepared with conventional polymerization in the present study, which may result from the higher surface area, smaller pore size and the narrower globule size distribution in their structures. The result indicated that RAFT polymerization provided better conditions for the clenbuterol imprinted monolithic polymer preparation. 2009 Xiang Chao Dong. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Polyisoprene Bearing Dual Functionalized Mini-blocky Chain-ends Prepared from Neodymium-mediated Coordinative Chain Transfer Polymerizations

Through neodymium-mediated coordinative chain transfer copolymerizaiton(CCTcoP),polyisoprenes bearing dual hydroxylated mini-blocky chain-ends were prepared via a three-step strategy.Kinetic studies revealed that,the polymerization demonstrated typical features of CCTcoP across the whole polymerization process,i.e.,quasi-living polymerization characteristic,tunable molecular weights,narrow molecular weight distributions,and atom economies.Comparing to previously reported CCTP homopolymerization systems,the presence of oxygen-containing IpOAl polar comonomer slowed down chain transfer rates obviously,rendering slightly higher molecular weights of the resultant PIps and smaller Np(number of polymer chains per Nd atom)values.Moreover,to mimic the structure of natural rubber,the hydroxyl end groups can be facilely modified into phosphonate,amide,and UPy,whose structures were further confirmed by NMR spectra.Incorporation these functionalities could greatly improve the hydrophilic properties of the polymers,as revealed from the significantly reduced static water contact angles.

Lanthanide complexes mediated coordinative chain transfer polymerization of conjugated dienes

Tremendous advances has been witnessed in the past few years in the lanthanide complexes mediated coordinative chain transfer polymerization(CCTP) of conjugated dienes. CCTP features catalyst economy, well-controlling over both microstructure and architecture of the resulting polymers, and accessibility for novel(co)polymers. This review highlights the recent progresses made in the field of CCTP of dienes. After a brief introduction, the body of this review is divided into three parts:(1) principle of CCTP;(2) coordinative chain transfer homopolymerization of dienes;(3) coordinative chain transfer copolymerization of dienes.At the end, we present some challenges remaining in this area and our personal opinion regarding where this field should continue to develop. CCTP represents a novel strategy to prepare polydiene synthetic rubbers with controlled high molecular weight and narrow molecular weight distribution, which has reached the practical industrial application level, demonstrating a great potential in industrialization.

Synthesis of Thermoresponsive Poly( diethyleneglycol methacrylate-co-6-Ovinyladipoyl-D-glucopyranose) Glycopolymer via RAFT Polymerization

The monomer 6-O-vinyladipoyl-D-glucopyranose( VAG)was synthesized by lipase catalyzed trans-esterification of divinyladipate with D-glucopyranose. A novel double hydrophilic glycopolymer poly( diethyleneglycol methacrylate-co-6-Ovinyladipoyl-D-glucopyranose)( P( DEGMA-co-VAG)) with narrow polydispersity( PDI) and thermosensitivity was prepared by reversible addition-fragmentation chain transfer( RAFT)polymerization. P( DEGMA-co-VAG) was characterized by1 H NMR,FTIR and gel permeation chromatography( GPC). The characterization of UV-visible spectroscopy showed that the micelles from glycopolymer P( DEGMA-co-VAG) were thermo-responsive and the low critical solution temperature( LCST) could be controlled by the molar ratio of monomers. When the molar ratio of DEGMA and VAG was 2∶ 1,the LCST of P( DEGMA-co-VAG) was36 ℃ in aqueous solution,which could form nano micelles in the human body environment. It was found that P( DEGMA-co-VAG)was non-toxic at 0. 1-1 mg / m L concentrations when incubated with pig iliac endothelial cells( PIECs) for 24 h. Thus,the synthesized glycopolymers has great potential as drug delivery carriers.

Simulation of Rate Retardation in RAFT Polymerization of Styrene with Low RAFT-Initiator Ratio

Bulk polymerizations of styrene (St) were carried out in the presence of three reversible addition fragmentation chain transfer (RAFT) agents benzyl dithiobenzoate (BDB), cumyl dithiobenzoate(CDB), and 1-phenylethyl dithiobenzoate (PEDB) under low ratio of RAFT agent to initiator. The kinetic model was developed to predict polymerization rate, which indicates that the RAFT polymerization of St is a first-order reaction. In the range of experimental conversions, the plots of -ln(1-x) against time t are approximately linear (x is monomer conversion). The kinetic study reveals the existence of strong rate retardation in RAFT polymerization of styrene. A coefficient K_r is defined to estimate the rate retardation in the RAFT system considering the assumption that the retardation in polymerization rate is mainly attributed to slow fragmentation of the intermediate radicals. K_r relates to the structure of RAFT agents as well as the concentrations of RAFT agent and azobis isobutyronitrile (AIBN). For a certain RAFT agent, the value of K_r is enhanced by the increase in the initial concentration of RAFT agent and the higher ratio of RAFT to AIBN. With the same recipe for different RAFT agents, the increasing trend for the values of K_r is BDB<PEDB<CDB.

Reversible Chain Transfer Catalyzed Polymerization with Alkyl Iodides Generated from Alkyl Bromides by in Situ Halogen Exchange

Reversible chain transfer catalyzed polymerization(RTCP)is a practical and efficient process for the precise synthesis of polymers with special architecture by using simple phenols(2,4,6-trimethylphenol,TMP)or hydrocarbons(xanthene,XT)as efficient organocatalysts.Herein,alkyl iodide(R-1),which was gen erated from in situ bromine-iodine transformation of alkyl bromide(R-Br)with sodium iodide(Nal),was served as initiator to mediate RTCP with TMP or XT.MMA and other functional methacrylates,including GMA,DEAM,DMAEMA and BzMA,were successfully initiated by combining orga no catalysts and azo in itiators to yield polymers with low-polydispersity(M_(w)/M_(n)=1.1-1.5)and ideal mono mer conversions(50%-90%)at moderate temperature.More over,3-armstar polymers were also obtained by this method.The high chain-end fidelity of the obtained poly(methyl methacrylate)with iodine as chain-end group(PMMA-I)was confirmed by chain-extension reaction.The en vironme ntally frie ndly initiators and orga no catalysts exhibit powerful polymerization properties toward RTCP,providing a sign ificant method to synthesize functional polymers.

Enzyme-assisted Photoinitiated Polymerization-induced Self-assembly in Continuous Flow Reactors with Oxygen Tolerance

Polymerization-induced self-assembly(PISA)is an emerging method for the preparation of block copolymer nano-objects at high concentrations.However,most PISA formulations have oxygen inhibition problems and inert atmospheres(e.g.argon,nitrogen)are usually required.Moreover,the large-scale preparation of block copolymer nano-objects at room temperature is challenging.Herein,we report an enzyme-assisted photoinitiated polymerization-induced self-assembly(photo-PISA)in continuous flow reactors with oxygen toleranee.The addition of glucose oxidase(GOx)and glucose into the reaction mixture can consume oxygen efficiently and constantly,allow the flow photo-PISA to be performed under open-air conditions.Polymerization kinetics indicated that only a small amount of GOx(0.5 μmol/L)was needed to achieve the oxygen tolerance.Block copolymer nano-objects with different morphologies can be prepared by varying reaction conditions including the degree of polymerization(DP)of core-forming block,monomer concentration,reaction temperature,and solvent composition.We expect this study will provide a facile platform for the large-scale production of block copolymer nano-objects with different morphologies at room temperature.

Molar Mass Dispersity Control by lodine-mediated Reversibledeactivation Radical Polymerization

Dispersity(D)of polymers has a great effect on the properties of polymeric materials,and therefore how to control θ is very important but still a huge challenge in polymer synthesis,especially for reversible-deactivation radical polymerization(RDRP)strategy.Herein,we successfully developed a novel strategy to adjust D of polymers by visible light-controlled reversible complexation mediated living radical polymerizatio n(RCMP)and combi nation of single-electron transfer-degenerative chain tran sfer living radical polymerization(SET-DTLRP)at room temperature.In RCMP system,2-iodo-2-methylpropionitrile(CP-I)and ethyl 2-iodo-2-phenylacetate(EIPA)were used as alkyl iodide initiators,by using methyl methacrylate(MMA)as the model monomer and n-butylacrylate(BA)as the end-capping reagent to regulate D of polymers.Subsequently,we successfully prepared the block copolymer PMMA-b-PBA with adjustable D by reactivating the polymer end-chains via SET-DTLRP in the presence of copper wire,fully dem on strati ng that it is a promising strategy that can keep the"living"feature of polymers while regulating their molar mass dispersities easily.

Recent Advances of CuAAC Click Reaction in Building Cyclic Polymer

Cyclic polymers have attracted more and more attentions in recent years because of their unique topological structures and characteristic properties in both solution and bulk state. There are relatively few reports on cyclic polymers, partly because of the more demanding synthetic procedures. In recent years, 'click' reaction, especially Cu(I)-catalyzed azide-alkyne cycloaddition(CuAAC), has been widely utilized in the synthesis of cyclic polymer materials because of its high efficiency and low susceptibility to side reactions. In this review, we will focus on three aspects:(1) Constructions of monocyclic polymer using CuAAC 'click' chemistry;(2) Formation of complex cyclic polymer topologies through CuAAC reactions;(3) Using CuAAC 'click' reaction in the precise synthesis of molecularly defined macrocycles. We believe that the CuAAC click reaction is playing an important role in the design and synthesis of functional cyclic polymers.