The polymerization of several (meth)acrylamides [N,N-dimethylacrylamide, N-tert-butylacrylamide, and N-(2-hydroxypropyl)methacrylamide] by atom transfer radical polymerization (ATRP) was attempted. When initiating systems containing ligands commonly used in ATRP, such as linear amines or bipyridines, were employed, very low conversions were noticed in either bulk or solution, after more than 20 h at 90 °C. However, the use of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me4Cyclam) as a ligand provided polymers in high yields in a short time, but the polymerization was not controlled. This was attributed to the slow deactivation rate of the catalytic system. Experiments using model compounds for the active chain ends indicated that the low conversion obtained in the polymerization of (meth)acrylamides when linear amines or bipyridines are used as ligands may be explained by a slow activation in conjunction with a fast deactivation. The loss of bromine end groups during the polymerization through a cyclization reaction could have a contribution to the poor control in the ATRP of (meth)acrylamides. Additionally, poly(meth)acrylamides may competitively complex copper and form species with lower catalytic activity. Even though the ATRP of (meth)acrylamides was not a controlled process, by using the Me4Cyclam-based catalyst system and macroinitiators prepared by ATRP, poly(methyl acrylate-b-N,N-dimethylacrylamide) (M n = 48 600, M w/M n = 1.33) and poly[butyl acrylate-b-N-(2-hydroxypropyl)methacrylamide] (M n = 34 000, M w/M n = 1.69) block copolymers were synthesized.

Halide anions have been used as complexing ligands in iron-mediated ATRP, in both direct and reverse ATRP. In direct ATRP, iron(II) bromide complexed with ammonium and phosphonium chloride, bromide, or iodide salts has been shown to catalyze the polymerization of both styrene and (meth)acrylates in a controlled manner under appropriate conditions. The experimental molecular weights increased linearly with monomer conversion and were close to the calculated values. The polymerization rates and polydispersities (Mw/Mn ) 1.1-1.4) were dependent on the monomer employed. Reverse ATRP, initiated by AIBN/FeBr3/onium salts, led to a controlled polymerization of both methyl methacrylate and methyl acrylate, while for styrene uncontrolled molecular weights and high polydispersities were obtained, presumably due to the involvement of the cationic polymerization. It is suggested that different iron complexes may be involved in ATRP, depending on the onium salt/FeBr3 ratio. Because of their ionic nature, the iron complexes could be removed easily from the reaction mixture by washing the polymerization mixture with water.

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Poly(n-butyl acrylate)-graft-branched polyethylene was successfully prepared by the combination of two living polymerization techniques. First, a branched polyethylene macromonomer with a methacrylate-functionalized end group was prepared by Pd-mediated living olefin polymerization. The macromonomer was then copolymerized with n-butyl acrylate by atom transfer radical polymerization. Gel permeation chromatography traces of the graft copolymers showed narrow molecular weight distributions indicative of a controlled reaction. At low macromonomer concentrations corresponding to low viscosities, the reactivity ratios of the macromonomer to n-butyl acrylate were similar to those for methyl methacrylate to n-butyl acrylate. However, the increased viscosity of the reaction solution resulting from increased macromonomer concentrations caused a lowering of the apparent reactivity ratio of the macromonomer to n-butyl acrylate, indicating an incompatibility between nonpolar polyethylene segments and a polar poly(n-butyl acrylate) backbone. The incompatibility was more pronounced in the solid state, exhibiting cylindrical nanoscale morphology as a result of microphase separation, as observed by atomic force microscopy.

Four different methods of block copolymerization, combining atom transfer radical polymerization (ATRP) and conventional radical polymerization, were studied. The first two methods employed azo compounds containing activated halogen atoms. 2,2‘-Azobis[2-methyl-N-(2-(4-chloromethylbenzoyloxy)ethyl)propionamide] (AMCBP) was used to initiate the polymerization of vinyl acetate (VAc) at 90 °C. The resulting pVAc with a Cl terminal group (M n = 47 900; M w/M n = 2.21) was subsequently used as a macroinitiator for styrene (St) to yield pVAc-b-pSt (M n = 91 600; M w/M n = 1.80). In the second method, 2,2‘-azobis[2-methyl-N-(2-(2-bromoisobutyryloxy)ethyl)propionamide] (AMBEP) was first used to polymerize n-butyl acrylate (BA) at 30 °C in the presence of CuBr/tris[2-(dimethylamino)ethyl]amine (Me6-TREN). The pBA (M n = 7500; M w/M n = 1.15) with the preserved central azo unit was dissolved in VAc and extended to a block copolymer (M n = 41 800; M w/M n = 3.56). Alternatively, ATRP has been combined with a redox initiated system. VAc was polymerized in the presence of CCl4/Fe(OAc)2/N,N,N‘,N‘ ‘,N‘ ‘-pentamethyldiethylenetriamine (PMDETA) to yield pVAc with trichloromethyl end groups (M n = 3600; M w/M n = 1.81). The polymer obtained was dissolved in styrene and block copolymerized by ATRP to form pVAc-b-pSt (M n = 24 300; M w/M n = 1.42). In the last method, pBA with a bromine end group (M n = 2460; M w/M n = 1.32) as prepared by ATRP was dissolved in VAc together with CuBr/1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me4-cyclam) to initiate VAc polymerization. A block copolymer with M n = 4450 and M w/M n = 2.58 was prepared. In the presence of 20 mol % of CuBr2, the polydispersity was further reduced to 1.73.

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New slow-release agrochemical formulations based on cross-linked poly(acrylic acid) hydrogels and liquid fertilizers (LF) were prepared by free radical copolymerization of acrylic acid (AA) and N,N′-methylenebisacrylamide directly in the LF solution. Two NPK liquid fertilizer compositions containing urea and potassium and ammonium phosphates were employed. For comparison, AA was also polymerized under identical conditions in distilled water. The resulting products were characterized by FTIR spectroscopy and scanning electron microscopy, and their water absorption and slow-release properties were determined. The results showed that the swelling degree (SD) of the hydrogels synthesized depended on the overall concentration of reactants (monomers and initiator), LF composition and cross-linking agent, and initiator concentrations. By appropriately combining these reaction parameters, superabsorbent hydrogels with SDs in distilled water ranging from a few hundred to 1000 g of water/g of xerogel can be obtained. The fertilizer-containing hydrogels displayed slow-release properties in still distilled water at room temperature. These slow-release formulations will be tested in the future for their effect on corn and sunflower crops.

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