New ground for organic catalysis: a ring-opening polymerization approach to hydrogels.

Herein, we describe an organocatalytic living polymerization approach to network and subsequent hydrogel formation. Cyclic carbonate-functionalized macromolecules were ring-opened using an alcoholic initiator in the presence of an organic catalyst, amidine 1,8-diazabicyclo[5.4.0]undec-7-ene. A model reaction for the cross-linking identified monomer concentration-dependent reaction regimes, and enhanced kinetic control was demonstrated by introducing a co-monomer, trimethylene carbonate. The addition of the co-monomer facilitated near-quantitative conversion of monomer to polymer (>96%). Resulting poly(ethylene glycol) networks swell significantly in water, and an open co-continuous (water-gel) porous structure was observed by scanning electron microscopy. The organocatalytic ring-opening polymerization of cyclic carbonate functional macromonomers using alcoholic initiators provides a simple, efficient, and versatile approach to hydrogel networks.

Synthesis of well-defined hydrogel networks using click chemistry.

New PEG-based hydrogel materials have been synthesized by Click chemistry and shown to result in well-defined networks having significantly improved mechanical properties; the selectivity of the azide/acetylene coupling reaction also allows for the incorporation of various additives and functional groups leading to chemical tailoring of the hydrogels.

New phenoxyketimine titanium complexes: combining isotacticity and living behavior in propylene polymerization.

A series of titanium bis(phenoxyketimine) olefin polymerization catalysts were synthesized and screened for propylene polymerization. The phenoxyketimine ligands contain pentafluorophenyl N-aryl groups and ortho-phenol substituents of varying size. Catalysts with ortho-phenol substituents of intermediate size produce living, substantially isotactic polypropylene. The living nature of these catalyst systems is demonstrated through the synthesis of block copolymers with narrow molecular weight distributions.

Gel permeation chromatography as a combinatorial screening method: identification of highly active heteroligated phenoxyimine polymerization catalysts.

A number of mixed-ligand bis(phenoxyimine) titanium catalysts were screened using a pooled combinatorial approach. Gel permeation chromatography (GPC) was used to analyze polypropylene mixtures, leading to the identification of highly active catalysts. Complexes with only one ortho-fluorinated ligand are significantly more active than homoligated complexes for the syndiospecific polymerization of propylene.