Four well-defined end-linked triblock polyampholyte conetworks composed of positively ionizable 2-(dimethylamino)ethyl methacrylate (DMAEMA) repeating units and negatively ionizable methacrylic acid (MAA) repeating units were synthesized using one-pot, sequential reversible addition–fragmentation chain transfer (RAFT) polymerization, by employing 1,4-bis[2-(thiobenzoylthio)prop-2-yl]benzene (1,4-BTBTPB) as the chain transfer agent, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. From the four end-linked conetworks, three were based on ABA triblock polyampholytes with polyDMAEMA midblocks with a constant degree of polymerization (DP) and polyMAA end-blocks of different DPs. The fourth end-linked polyampholytic conetwork was based on an equimolar BAB triblock polyampholyte with a polyMAA midblock. Furthermore, two polyampholyte networks were also prepared: one based on an end-linked equimolar statistical polyampholyte, and one with a randomly cross-linked, rather than an end-linked, architecture. Finally, the two homopolymer networks based on the DMAEMA and the MAA monomers were also synthesized. The MAA units were introduced in the (co)networks via the polymerization of 2-tetrahydropyranyl methacrylate (THPMA) followed by its acid hydrolysis after (co)network formation. The linear precursors to the (co)networks were found to have molecular weights and compositions close to the expected values, whereas the extractables from the (co)networks were determined to be lower than 30%. In water, the degrees of swelling (DS) of all the polyampholyte (co)networks presented a characteristic minimum at intermediate pH values, around the (co)network isoelectric point (pI), while they increased at acidic and basic pHs. The pI values of the ampholytic (co)networks were estimated as the midpoints of the regions of reduced swelling and ranged between 5.3 and 6.8, decreasing with the increase of the MAA content in the (co)networks. Finally, small-angle neutron scattering (SANS) studies of the polyampholyte (co)networks swollen in D2O provided SANS profiles without any peaks but broad shoulders whose location was consistent with the spacing of the cross-linking cores.

Four cationic hydrophilic star homopolymers based on the novel hydrophilic, positively ionizable cross-linker bis(methacryloyloxyethyl)methylamine (BMEMA) were synthesized using sequential group transfer polymerization (GTP) and were, subsequently, evaluated for their ability to deliver siRNA to mouse myoblast cells. The nominal degrees of polymerization (DP) of the arms were varied from 10 to 50. For the polymerizations, 2-(dimethylamino)ethyl methacrylate (DMAEMA) was employed as the hydrophilic, positively ionizable monomer. For comparison, four linear DMAEMA homopolymers were also synthesized, whose nominal DPs were the same as those of the arms of the stars. The numbers of arms of the star homopolymers were determined using gel permeation chromatography with static light scattering detection, and found to range from 7 to 19, whereas the hydrodynamic diameters of the star homopolymers in aqueous solution were measured using dynamic light scattering and found to increase with the arm DP from 13 to 26 nm. The presence of the hydrophilic BMEMA cross-linker enabled the solubility of all star homopolymers in pure water. The cloud points of the star homopolymers in aqueous solution increased with the arm DP from 23 to 29 °C, while the cloud points of the linear homopolymers were found to decrease with their DP, from 42 to 32 °C. The effective pK values of the DMAEMA units were in the range of 6.9 to 7.3 for the star homopolymers, whereas they ranged between 7.3 and 7.4 for the linear homopolymers. Subsequently, all star and linear homopolymers were evaluated for their ability to deliver siRNA to the C2C12 mouse myoblast cell line, expressing the reporter enhanced green fluorescent protein (EGFP). All star homopolymers and the largest linear homopolymer presented significant EGFP suppression, whereas the smaller linear homopolymers were much less efficient. For all star homopolymers and the largest linear homopolymer both the EGFP suppression and the cell toxicity increased with polymer loading. The siRNA-specific EGFP suppression, calculated by subtracting the effect of cell toxicity on EGFP suppression, slightly increased with star polymer loading for the two smaller stars, whereas it presented a shallow maximum and a decrease for the other two stars. Moreover, the siRNA-specific EGFP suppression also increased slightly with the DP of the arms of the DMAEMA star homopolymers. Overall, the EGFP suppression efficiencies with the present star homopolymers were at levels comparable to that of the commercially available transfection reagent Lipofectamine.

One-pot, sequential reversible addition−fragmentation chain transfer (RAFT) polymerization was employed for the preparation of five end-linked semifluorinated amphiphilic polymer conetworks based on 2,2,2-trifluoroethyl methacrylate (TFEMA, hydrophobic monomer) and 2-(dimethylamino)ethyl methacrylate (DMAEMA, hydrophilic monomer). 1,4-Bis[2-(thiobenzoylthio)prop-2-yl]benzene (1,4-BTBTPB) was used as the chain transfer agent, while ethylene glycol dimethacrylate (EGDMA) served as the cross-linker. Three of the end-linked conetworks were based on ABA triblock copolymers with polyDMAEMA midblocks with degrees of polymerization (DPs) of 50 and polyTFEMA end-blocks with overall polyTFEMA DPs of 25, 50, and 75. The fourth end-linked amphiphilic polymer conetwork was based on an equimolar BAB triblock copolymer with a polyTFEMA midblock and an overall copolymer DP of 100. The last end-linked conetwork was based on a statistical copolymer. A randomly cross-linked conetwork was also prepared by the simultaneous terpolymerization of the two comonomers (equimolar) and the cross-linker. The molecular weights and compositions of all the polymer precursors to the conetworks were characterized using gel permeation chromatography and 1H NMR spectroscopy, respectively. The conetworks were characterized in terms of their degrees of swelling (DS) in THF and in water as a function of the solution pH. All conetworks swelled more in acidic than in pure water due to the ionization of the DMAEMA units in acidic water. The low pH aqueous DS of the statistical copolymer-based end-linked conetwork was higher than those of its triblock copolymer counterparts due to lack of microphase separation within the former conetwork. Finally, the microphase separation of the amphiphilic conetworks in deuterium oxide was investigated using small-angle neutron scattering which indicated a distance between the hydrophobic scattering centers of about 15 nm.

Whilst hydrogels and hollow particles both continue to attract much attention in the literature there are few examples of hydrogel composites containing hollow particles. Here, we study composite polyacrylamide (PAAm) hydrogels containing micrometer-sized pH-responsive shell-crosslinked hollow particles (abbreviated as HPXL) based on poly(methylmethacrylate-co-methacrylic acid) functionalised with glycidyl methacrylate (GMA). The HPXL particles were prepared using our scaleable emulsion template method and inclusion of GMA was found to promote spherical hollow particle formation. The pendant vinyl groups from GMA enabled shell-crosslinked hollow particles to be prepared prior to formation of the PAAm/HPXL composite gels. The morphologies of the particles and composite gels were studied by optical microscopy, confocal laser scanning microscopy and scanning electron microscopy. Dynamic rheology measurements for the composite gels showed that the modulus variation with HPXL concentration could be described by a percolation model with a HPXL percolation threshold concentration of 4.4 wt% and a scaling exponent of 2.6. The composite gels were pH-responsive and largely maintained their mechanical properties over the pH range 4.0 to 8.0. Because the composite gels had tuneable mechanical properties (with modulus values up to 530 kPa) and were pH-responsive they are potential candidates for future wound healing or membrane applications.

We present two novel, homologous, pyridinebased monomers, 2-(pyridin-2-yl)ethyl methacrylate (PyEMA) and (pyridin-2-yl)methyl methacrylate (PyMMA), which, despite their structural similarity, the former can be readily thermolyzed to methacrylic acid, while the latter remains intact under the same conditions. This was most dramatically demonstrated in the present work, where PyEMA and PyMMA were randomly terpolymerized with a dimethacrylate cross-linker using reversible addition−fragmentation chain transfer polymerization to yield weakly double-cationic polyelectrolyte hydrogels of three different compositions which, upon thermal treatment, they were readily converted to polyampholyte hydrogels. While the parent double-cationic polyelectrolyte hydrogels exhibited a swelling response only to low-pH conditions, the daughter polyampholyte hydrogels presented swelling responses to both high-and low-pH conditions. Owing to the relative values of the effective pK a 's of the weakly acidic and weakly basic units, with the latter being lower than the former ("inverse polyampholyte" behavior), the swelling profiles of the daughter hydrogels were insensitive to polyampholyte composition.