Novel oligo[poly(ethylene glycol) fumarate] (OPF) hydrogels functionalized with cell adhesion peptides were prepared, and the effects of incorporated peptide density and macromolecular structure of hydrogels on attachment and morphology of marrow stromal cells (MSCs) were evaluated. Poly(ethylene glycol) (PEG; number average molecular weight of 930, 2860, and 6090) was used to synthesize OPF. A model peptide, Gly-Arg-Gly-Asp (GRGD), was incorporated into OPF hydrogels after being coupled to acrylated PEG of molecular weight 3400. The increase of incorporated peptide concentration enhanced MSC attachment to OPF hydrogels of PEG of molecular weight of 930 and 2860. However, the number of attached MSCs to OPF hydrogels of PEG (molecular weight 6090) remained constant regardless of the peptide density. The length of PEG in OPF also influenced cell attachment. When 1 micromole peptide/g hydrogel was incorporated into the OPF hydrogels, the degree of cell attachment at 12 h relative to the initial seeding density was 93.9 +/- 5.9%, 64.7 +/- 8.2%, and 9.3 +/- 6.6% for OPF hydrogels prepared with PEG of molecular weights of 930, 2860, and 6090, respectively. However, the crosslinking density of hydrogels did not significantly affect cell attachment. The interaction was sequence specific, in that MSC attachment to GRGD-modified hydrogels was competitively inhibited when cells were incubated in the presence of 0.5 mM soluble GRGD before cell seeding. These results suggest that we can modulate MSC attachment to OPF hydrogels by altering the peptide density and the molecular structure of OPF hydrogels.

Modulation of marrow stromal osteoblast adhesion on biomimetic oligo[poly(ethylene glycol) fumarate] hydrogels modified with Arg-Gly-Asp peptides and a poly(ethylene glycol) spacer

Complex-radical alternating copolymerization

The effect ofN-substituents on the radical polymerization ofN-substituted maleimides (RMI) was investigated. The polymerization reactivities, i.e. yield and molecular weight of the polymers, were found to change depending on the structure of theN-substituents. The poly(RMI)s bearing a bulkyN-substituent were confirmed to be semiflexible poly(substituted methylene)s which were soluble in many organic solvents, but did not melt below their decomposition temperatures. From thermogravimetric analysis determined in a nitrogen stream, no weight-loss of poly(RMI) was observed at temperature below 300°C, and the maximum decomposition temperature was 400–440°C, except forN-tert-alkyl substituted derivatives which decomposed at 240–280°C via a two-step reaction.

Reactivity in radical polymerization of N -substituted maleimides and thermal stability of the resulting polymers

Polymerization of alkyl diazoacetates [N2CHCO2R:  R = Et (1a) and Me (1b)] mediated by PdCl2 in the presence of an amine gave poly(alkoxycarbonylmethylene)s [(CHCO2R)n:  R = Et (2a,b), Me (3a,b)] bearing an ester group on every carbon atom of their main chains. MALDI−TOF−MS analyses of the polymers 2a and 3b indicated that the degree of polymerization of the polymers extended up to nearly 100. The Pd-mediated polymerization of 1a and 1b in the presence of pyridine afforded the polymers quantitatively after reprecipitation from CHCl3 into n-hexane. A mechanism of the polymerization initiated with a Pd-assisted nucleophilic attack of an amine to the monomers is proposed.

Palladium-Mediated Polymerization of Alkyl Diazoacetates To Afford Poly(alkoxycarbonylmethylene)s. First Synthesis of Polymethylenes Bearing Polar Substituents

ESR spectroscopic studies of radical polymerization

Di-tert-butyl fumarate (DtBF) was found to homopolymerize easily with 1,1′-azobisisobutyronitrile and benzoyl peroxide as radical initiators at 50~80°C to give a nonflexible rod-like polymer, poly(tert-butoxycarbonylmethylene) with number-average molecular weight of more than 100,000. The colorless powderlike polymer thus obtained was soluble in benzene, toluene, carbon tetrachloride and tetrahydrofuran, and gave a transparent film or fiber from its toluene solution. This polymer did not melt, but it underwent degradation with a quantitative elimination of isobutene at 180~190°C. The remaining polymer was confirmed to be a pure poly(fumaric acid), poly(hydroxycarbonylmethylene). Therefore, the degradation of poly(DtBF) in solution at 180~190°C was found to be a new route for synthesizing of a high molecular weight poly(fumaric acid).

Radical high polymerization of di-tert-butyl fumarate and novel synthesis of high molecular weight poly(fumaric acid) from its polymer

Radical copolymerization of dialkyl fumarates (DRF) with various vinyl monomers was carried out in benzene at 60°C. The monomer reactivity ratios, r1 and r2, were determined from the comonomer-copolymer composition curves. The relative reactivity of DRFs with various ester substituents toward a polystyryl radical was revealed to depend on both steric and polar effects of the ester groups. It has also been clarified that α-substituents of the polymer radical have a significant role in addition of DRF, from the comparison of the monomer reactivity ratios determined in copolymerizations with monosubstituted and 1,1-disubstituted ethylenes. The absolute cross-propagation rate constants were also evaluated and discussed. © 1992 John Wiley & Sons, Inc.

Effect of the substituents on radical copolymerization of dialkyl fumarates with some vinyl monomers

Monomer-isomerization radical polymerization of Di-tert-butyl maleate to high molecular weight poly(di-tert-butyl fumarate)

Determination of absolute rate constants for radical polymerization of diisopropyl fumarate based on a quantitative scavenge of propagating radical

Radical polymerization of fumarates bearing different alkyl ester groups (DRF) on the same molecules was investigated. In bulk polymerization of DRF at 60°C initiated with 2,2′-azobis(isobutyronitrile), it was confirmed that the polymerization reactivity depended on the structures of both alkyl ester groups. The introduction of bulky alkyl groups increased the polymerization rate and molecular weight of the polymer because of retardation of bimolecular termination rates. The effect of the ester substituents on the termination was examined by electron spin resonance spectroscopy. The copolymerization reactivities of DRF with styrene were also investigated. © 1993 John Wiley & Sons, Inc.

Kohei Shiraishi

Papers

Radical high polymerization of di-tert-butyl fumarate and novel synthesis of high molecular weight poly(fumaric acid) from its polymer

Effect of the substituents on radical copolymerization of dialkyl fumarates with some vinyl monomers

Monomer-isomerization radical polymerization of Di-tert-butyl maleate to high molecular weight poly(di-tert-butyl fumarate)

Determination of absolute rate constants for radical polymerization of diisopropyl fumarate based on a quantitative scavenge of propagating radical

Radical polymerization and copolymerization reactivities of fumarates bearing different alkyl ester groups