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Seven star polymers with degrees of polymerization (DPs) of the arms from 10 to 100 and dimensions in the nanometer range were prepared using sequential group transfer polymerization of 2-(dimethylamino)-ethyl methacrylate (DMAEMA, hydrophilic positively ionizable monomer) and ethylene glycol dimethacrylate (hydrophobic neutral cross-linker). The polymers were characterized in tetrahydrofuran by gel permeation chromatography and static light scattering to determine the molecular weights and the weight-average number of arms for each sample. The number of arms of the star polymers varied from 20 to 72. Aqueous solutions of the star polymers were studied by turbidimetry, hydrogen ion titration, and dynamic light scattering to determine their cloud points, pKs, and hydrodynamic diameters. The cloud points of the larger star polymers, with arm DP 30-100, were found to be 29-34 °C, almost independent of the DP of the arms. Similarly, the pKs of all star polymers were calculated to range between 6.7 and 7.0, again independent of the arm DP. In contrast, the hydrodynamic diameters of the star polymers strongly depended on the DP of the arms. In particular, by increasing the DP of the arms from 20 to 100, the hydrodynamic diameters in water increased from 7 to 31 nm. All star polymers were evaluated for their ability to transfect human cervical HeLa cancer cells with the modified plasmid pRLSV40 with the enhanced green fluorescent protein as the reporter gene. Our results showed that as the DP of the arms of the DMAEMA star homopolymers increased from 10 to 100, the overall transfection efficiency decreased, with the star polymer with DP of the arms of 10 emerging as the best transfection reagent. Systematic variation of the amounts of star polymer and plasmid DNA used in the transfections led to an optimization of the performance of this star polymer, yielding overall transfection efficiencies of 15%, comparable to the optimum overall transfection efficiency of the commercially available transfection reagent SuperFect of 13%. © 2004 American Chemical Society. 5 6 2221 2229 Tradenames: Superfect Manufacturers: Aldrich, Germany Cited By :98

Linear homopolymers and randomly cross-linked homopolymer networks of 2-(dimethylamino)ethyl methacrylate of various molecular weights (MWs) were synthesized by group transfer polymerization in the bulk. 1-methoxy-1-(trimethylsiloxy)-2-methyl propene was used as the initiator, while tetrabutylammonium bibenzoate served as the catalyst. Ethylene glycol dimethacrylate was the cross-linker used for the network synthesis at an 8-fold molar excess with respect to the initiator. Gel permeation chromatography in tetrahydrofuran was used to characterize the linear homopolymers in terms of their MW and molecular weight distribution (MWD). Although the experimental MWs did not match the theoretical MWs, they were reasonably close to them. The MWDs were rather broad with polydispersity indices ranging between 1.5 and 1.9. The monomer conversion was relatively high, ranging from 97% to 74% for theoretical degrees of polymerization (DPs) from 5 to 500. No polymerization was observed for an attempted DP of 1000. Networks with molar ratios of monomer to initiator (nominal DPs) from 5 to 200 were prepared, while an attempted synthesis with a nominal DP of 500 did not yield a network. The networks were characterized in terms of their degree of swelling in water and the effects of DP, pH, salt concentration and temperature were investigated. © 2002 Elsevier Science Ltd. All rights reserved. 39 3 609 616 Cited By :7

Randomly cross-linked homopolymer networks of 2-(dimethylamino)ethyl methacrylate (DMAEMA) of various average degrees of polymerization (DPs) between cross-links were synthesized by group transfer polymerization (GTP) in tetrahydrofuran (THF), using 1-methoxy-1-(trimethylsiloxy)-2-methyl propene (MTS) as the initiator, ethylene glycol dimethacrylate (EGDMA) as the cross-linker (eight-fold molar excess with respect to the initiator), and tetrabutylammonium bibenzoate (TBABB) as the catalyst. Networks with monomer-to-initiator molar ratios of 5, 10, 20, 50, 100 and 200 were synthesized successfully, while an attempted synthesis with a monomer-to-initiator molar ratio of 500 did not produce a network. The networks were characterized in terms of their degree of swelling (DS) in water and the effects of DP, pH, salt concentration and temperature were investigated. Moreover, the aqueous degrees of swelling determined in this study of random networks were compared to the aqueous degrees of swelling of model networks also synthesized by GTP and using a similar procedure. © 2001 Elsevier Science Ltd. All rights reserved. 42 22 9205 9209 Cited By :16

The equilibrium constants of various candidates for the crosslinking reaction between chromium(III) and partly hydrolysed polyacrylamide have been calculated. For this purpose use has been made of a) the crosslinking index in gels to calculate the concentration of crosslinks, b) pH-dependent concentrations of various hydrolysis products of Cr3+ ions and c) pH-dependent concentration of free carboxylic acid anions. The conclusion is that the crosslinks consist of two carboxylic acid anions coordinated with the dimerisation product of the Cr3+ ions. 171 189 200 Cited By :11

A series of hydrophilic model networks based on homopolymers of a weak base were prepared using group transfer polymerization (GTP) and characterized in terms of their aqueous degree of swelling as a function of pH. This constitutes the first reported example of cationic hydrogels in which the length of segments between cross-links is kept constant. The synthesis involved the GTP of 2-(dimethylamino)ethyl methacrylate (DMAEMA, weak base monomer) in tetrahydrofuran (THF, solvent) using the bifunctional initiator, 1,4-bis(methoxytri-methylsiloxymethylene)-cyclohexane (MTSMC) and the subsequent in situ cross-linking with the addition of 8-fold mole excess with respect to the initiator of the difunctional monomer ethyleneglycol dimethacrylate (EGDMA). Four different model networks with degrees of polymerization (DP) of the linear segments between cross-links of 10, 20, 50 and 100 were prepared. The molecular weight (MW) and molecular weight distribution (MWD) of the linear segments were measured using gel permeation chromatography (GPC) in THF. The degree of swelling of all model networks was measured in water as a function of the solution pH. The conditions of gel synthesis were optimized with respect to cross-linker loading and monomer concentration using the results of a parallel study on the synthesis of star polymers of DMAEMA. The star polymers were also prepared by GTP of DMAEMA and linking (to stars) with EGDMA, but a mono-functional initiator, 1-methoxy-1- trimethylsiloxy-1-methyl-propene (MTS), was used rather than MTSMC. The star polymers were analyzed by GPC which revealed the percentage of free homopolymer relative to star polymer. The optimal conditions were identified as those under which the percentage of unlinked (free) homopolymer is minimized-the same conditions were adopted for the synthesis of the networks. (C) 2000 Elsevier Science Ltd. 41 24 8523 8529 Cited By :41

Group transfer polymerization (GTP) was applied to prepare model networks based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate (MMA). The flexibility of GTP allowed the synthesis of three isomeric networks with different architecture of the segments between crosslinks. The networks were characterized in terms of their aqueous degree of swelling as a function of pH, and the effect of chain architecture on the swelling behavior of the amphiphilic networks. 33 8 3176 3179 Cited By :68

Experimental isoelectric points and amine acid compositional data for 58 proteins were compiled and organized. The experimental isoelectric points correlated well with the acidic to basic amino acid molar ratio. This agreement proved the usefulness of a recently presented analytical expression correlating explicitly protein isoelectric point to acid-base composition. Regressed acidic and basic dissociation constants were determined to be pKa = 4.9 and pKb = 10.0, in fair agreement with the expected values of pKa = 4.2 and pKb = 11.2. Theoretical isoelectric points determined by a more complete computational procedure were on the average in as good an agreement with the experimental values as those calculated via the theoretical approximation using the regressed dissociation constants. Thus, the analytical approximation is a powerful tool for the convenient and accurate calculation of protein isoelectric point from the amine acid composition. © 1995 Academic press. Inc. 231 1 82 91 Cited By :65

Cationic star polymers of 2-(dimethylamino)ethyl methacrylate (DMAEMA) were prepared via the "arm-first" method under group transfer polymerization (GTP) conditions, and were interconnected using a novel, hydrophilic, positively ionizable dimethacrylate cross-linker which is essentially the cyclic dimer of DMAEMA, thus ensuring that the building units of the arms and the core of the star polymers were identical. After their physicochemical characterization, these star-like polyamines were evaluated for their ability to transfer small interfering RNA (siRNA) to murine myoblast cells. Suppression efficiency was found to increase with polymer loading and star branch size, attaining sufficiently high values, comparable to that observed with standard non-viral siRNA transfection systems, while cytotoxicity was kept reasonably low. © 2012 Elsevier Ltd. All rights reserved. 48 8 1422 1430 Cited By :15