The direct polymerization of acrylic acid (AA) in aqueous solution for high molecular weight by means of living radical polymerization is still difficult. Here, AA was polymerized homogeneously in water by a reversible addition-fragmentation transfer polymerization (RAFT) in the presence of a water-soluble trithiocarbonate as a RAFT agent. Various ratios [AA]:[RAFT agent] were investigated to aim at different molecular weights. The polymerization exhibited living free-radical polymerization characteristics at different ratios [AA]: [RAFT agent]: controlled molecular weight, low polydispersity and well-suited linear growth of the number-average molecular weight, Mn with conversion. The chain transfer to solvent or polymer was suppressed during the polymerization process, thus high linear PAA with high molecular weight and low PDI can be obtained. Moreover, using the generated PAA as a macro RAFT agent, the chain extension polymerization of PAA with fresh AA displayed controlled behavior, demonstrated the ability of PAA to reinitiate sequential polymerization. 相似文献
Atom transfer radical polymerization (ATRP) of styrene catalyzed by cuprous (CuX)/1, 10-phenanthroline (Phen)and CuX/CuX_2/Phen was conducted in an aqueous dispersed system. A stable latex was obtained by using ionic surfactantsodium lauryl sulfonate (SLS) or composite surfactants, such as SLS/polyoxyethylene nonyl phenyl ether (OP-10),SLS/hexadecanol and SLS/OP-10/hexadecanol. Among which SLS and SLS/OP-10/hexadecanol systems established betterdispersed effect during the polymerization. It was found that Phen was a more suitable ligand than N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA) to maintain an appropriate equilibrium of the activator Cu(I) and the deactivatorCu(II) between the organic phase and the water phase. The effect of several initiators (such as EBiB, CCl_4 and 1-PEBr) andthe temperature on such a kind of ATRP system was also observed. The number-average molar mass (M_n) of polystyrene (PS)increased with the conversion and the molar mass distribution (M_w/M_n) remained narrow. These experimental data show thatthe polymerization could be controlled except for the quick increase of monomer conversion and the number-average molarmass of PS in the initial stage of polymerization. Furthermore, the initiator efficiency was found to be low (~57%) inCuX/Phen catalyzed system. To overcome this problem, Cu(II)X_2 (20 mol%-50 mol% based on CuX) was introduced intothe polymerization system. In this case, higher initiator efficiency (60%-90%), low M_w/M_n of PS (as low as 1.08) wereachieved and the molar masses of the PS fit with the theoretical ones. 相似文献
The synthesis of poly(acrylic acid) (PAA) of low molar mass under safe conditions is difficult due to the high polymerization rate of acrylic acid (AA) and the fast heat generation. The aqueous‐solution “semibatch” polymerization of non‐ionized AA in almost starved conditions involves high initiator loads when low molar masses are required. This article proposes the simultaneous feeding of AA and nonconventional chain transfer agents (CTA) as a strategy aimed at controlling both the molar masses and the generated heat rate. Three CTAs are investigated: 2‐mercaptoethanol, thioglycolic acid, and isopropyl alcohol. Even when PAA of relatively low molar mass can be produced by adequately selecting the flow rates and concentrations of both AA and CTA, it is found that the nature of CTA can have a significant effect on the polymerizations kinetics. The mechanisms responsible for these effects are discussed with the help of a representative mathematical model.
Di‐ and triblock copolymers of styrene and butyl acrylate with controlled molar masses (Mn up to ≈ 105) were sequentially prepared by radical atom transfer polymerization in a homogeneous medium using chlorine end capped polymers as initiators and the copper(I) chloride/bipyridine complex as catalyst, in the presence of dimethylformamide. Random poly(styrene‐co‐butyl acrylate) was synthesized and the cross‐over reactions between Cl end capped polystyrene and poly(butyl acrylate) to the opposite monomers were examined. 相似文献
A new amphiphilic graft copolymer containing hydrophilic poly(acrylic acid) backbone and hydrophobic poly(vinyl acetate) side chains was synthesized via sequential atom transfer radical polymerization (ATRP) followed by selective hydrolysis of poly(methoxymethyl acrylate) backbone. Grafting‐from strategy was employed to synthesize PMOMA‐g‐PVAc graft copolymer (Mw/Mn=1.64) via ATRP. The final PAA‐g‐PVAc amphiphilic graft copolymer was obtained by selective acidic hydrolysis of PMOMA backbone in acidic environment without affecting the side chains. The critical micelle concentrations (cmc) in aqueous media were determined by a fluorescence probe technique. The micelle morphologies were found to be spheres. 相似文献
Ultra-high molecular weight polyethylene (UHMWPE) fibrous adsorbents with different molar content of amidoxime (MAO) and acrylic acid (MAA) were prepared by graft polymerization of acrylonitrile (AN) and acrylic acid (AA), followed by amidoximation. Uranium adsorption experiments in both artificial and natural seawater were carried out to investigate the effect of MAO and MAA on the uranium adsorption capacity of UHMWPE fibrous adsorbents. Adsorption results showed that the UHMWPE fibrous adsorbent with MAO = 4.27 and MAA = 4.64 mmol/g-ads exhibited better uranium adsorption capacity in both artificial (7.01 mg-U/g-ads) and natural (0.77 mg-U/g-ads) seawater.
A doubly hydrophilic triblock copolymer poly(acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) (PAA-b-PEO-b-PAA) with Mw/Mn = 1.15 was synthesized by atom transfer radical polymerization of t-butyl acrylate (tBA), followed by acidolysis of the PtBA blocks. The pH-sensitive micellization of PAA-b-PEO-b-PAA in acidic solution was investigated by potentiometric titration, fluorescence spectrum, dynamic light scattering and
zeta potential. The pKa was 6.6 and 6.0 in deionized water and in 0.1 mol/L NaCl solution, respectively. The copolymer formed micelles composed of
a weakly hydrophobic core of complexed PAA and PEO and a hydrophilic PEO shell in 1 mg/mL solution at pH < 5.5 due to hydrogen
bonding. The critical micelle concentration was 0.168 mg/mL at pH 2.0. At pH < 4.5, steady and narrow distributed micelles
were formed. Increasing pH to 5.0, unsteady and broad distributed micelles were observed. At pH > 5.5, the micelle was destroyed
owing to the ionization of the PAA blocks. 相似文献
Polysiloxanes with high molecular weight (Mn > 100 000, Mw/Mn < 2.2) containing various quantity of trifluoroethylene aryl ether groups were prepared by anion ring opening polymerization (AROP) in the presence of promoters including N,N‐dimethylformamide (DMF) and N‐methyl pyrrolidone (NMP). The structures of monomers and polymers were characterized by FTIR and NMR. It was found that the addition of promoter could significantly increase the polymerization rate, decrease the polymerization temperature, and increase the molecular weight of the polymer. When DMF as the promoter, the optimal conditions for polymerization were as follows: The polymerization temperature is 100°C, the amount of catalyst is 2.0%, and the molar ratio of promoter to catalyst is 160:1. The optimal conditions for polymerization using NMP as the promoter were as follows: The polymerization temperature is 75°C, the amount of catalyst is 2.0%, and the molar ratio of promoter to catalyst is 70:1, which indicated that NMP is more effective on AROP than DMF. Thermogravimetric analysis (TGA) showed that the polymer has good heat temperature resistance. Differential scanning calorimetry (DSC) showed that the introduction of NMP in bulk polymerization could improve the randomness of polymer structure, which leads to the disappearance of crystal peak and improve the low temperature resistance of polymer. 相似文献
The γ-radiation-induced crosslinking polymerization of methyl methacrylate (MMA), methacrylic acid (MAA), 2-hydroxyethyl methacrylate (HEMA), methyl acrylate (MA), and acrylic acid (AA) was carried out in bulk. The polymerization rates of AA and HEMA were much larger than those of other monomers. Acetylene had no influence on the polymerization rate in the initial stage, and the rate was dependent only on the kinds of monomers. In the absence of acetylene, gelation took place in PMA, PAA, and PHEMA obtained at complete conversion, but not in PMMA and PMAA. By the addition of acetylene, complete gelation of PMMA was observed, but no gel formation was observed for PMAA. Volume and weight swelling ratios were measured for PMA, PAA, PHEMA, and PMMA with complete gelation. It was found that by the addition of acetylene the molar concentration of crosslinks increased as much as about twice for PMA and PHEMA, and over about one hundred times for PMMA AND PAA. The relation between volume Sv and weight swelling ratio Sw was studied theoretically. Sv was expressed by the the equation, Sv = (pp /p+)Sw+ (1 -pp/ps), as a function of Sw and the densities of pure polymer (pp) and solvent (ps) in swollen polymer. 相似文献
The anionic homopolymerization of 2,5‐dimethylhexa‐1.5‐dien‐3‐yne (DMDEY) was investigated by utilizing butyllithium, sec‐butyllithium, diphenylmethylsodium, and naphthalene/sodium as initiators. Soluble polymers with molecular weights up to 50 000 g/mol corresponding to Mw/Mn of 1.05 were obtained through homopolymerization with diphenylmethylsodium as initiator in THF at low temperatures. The homopolymers consist of 1,2‐linked monomer units with pendant 3‐methylbut‐3‐en‐1‐yne groups. 相似文献