Amino Acid Pendant Research Articles

Functionalization of a styrene/butadiene random copolymer by radical addition of l-cysteine derivatives

The functionalization of a styrene/butadiene (20/80) random copolymer (SBR) is performed by radical-mediated addition of l-cysteine derivatives to the macromolecules' double bonds. The reaction carried out in solution and in the melt leads to SBR chain bearing amino and carboxylate functionalities through thiol addition to the vinyl double bonds of the 1,2-butadiene units with anti-Markovnikov regioselectivity. The addition yield (up to 5wt%) and the occurrence of the crosslinking side reaction are investigated with reference to feed conditions and process parameters. The optical rotation of the reaction products confirms the addition of l-cysteine to SBR chain and provides a simple route to prepare optically-active polymers containing pendant amino acid residues.

MALDI-TOF Detection of Olefin Structural Isomerization in Metathesis Chemistry

MALDI-TOF mass spectrometry has been employed to examine polymers generated via acyclic diene metathesis (ADMET) polymerization using a ruthenium metathesis catalyst at 50 °C, a study which targets the analysis of ADMET polymers having amino acid pendant groups placed at specific positions along the polyolefin backbone. The MALDI spectra clearly delineate olefin isomerization chemistry which competes with propagation when catalyst 2 is employed, the result being loss of precise control of polymer structure. The distribution of peaks in the MALDI spectra matches the distribution pattern of gas chromatography (GC) peaks obtained for other ADMET polymers, leading to the following conclusions. First, structural isomerization and metathesis occur concurrently rather than in any kind of sequence. Second, the relative amount of isomerized chains produced dominates over the amount of nonisomerized products. In contrast to GC, MALDI analysis unequivocally identifies the mass of the oligomeric chains, allowing for increased confidence in assignment of the possible chain structures.

The spatial effect of hydrophobic groups in pendant amino acid monomers on the thermal volume phase transition of hydrogels

A series of hydrogels containing each of the regioisomers, methacryloyl l-valine methyl ester (MA-ValOMe) and methacryloyl l-alanine isopropyl ester (MA-AlaOiPr), were prepared by radiation-induced polymerization. The regioisomers have both methyl and isopropyl groups but at different positions in the side chain of the hydrogels. We estimated the effect of the hydrophobic position in the side chain (spatial effect) on the volume phase transition temperatures (VPTT) of the hydrogels. When methacryloyl l-alanine methyl ester (MA-AlaOMe) hydrogel, showing a VPTT of 23°C, was used as a co-monomer, the VPTTs of copolymer hydrogels exhibited a prominent decrease when the MA-ValOMe and MA-AlaOiPr compositions were increased. In this case, the MA-ValOMe component, which has a hydrophobic group near the main chain of the hydrogels, decreased the VPTT more efficiently than Ma-AlaOiPr. The relationship between the VPTT and the co-monomer composition exhibited a linear correlation at temperatures above 0°C. Thus, the apparent VPTTs of homopolymer hydrogels, MA-ValOMe and MA-AlaOiPr, were estimated to be −78 and −25°C, respectively, by extrapolating 100% of the composition of the monomers from the linear VPTT versus the composition plot.

New Chemical Modification of Polymers with Pendant Chloromethyl Groups Using 1,8-Diazabicyclo-[5.4.0]-7-undecene

The esterification reaction of poly[(p-chloromethyl)styrene] (PCMS) with benzoic acid and acetic acid proceeded very smoothly to give the corresponding polymers with pendant ester residues using 1,8-diazabicyclo-[5.4.0]-7-undecene (DBU) as an organic base even at 30°C in aprotic polar solvents such as N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone, and dimethyl suloxide (DMSO). The reaction of poly(2-chloroethyl vinyl ether) (PCEVE) and poly(epichlorohydrin) (PECH) with benzoic acid in the presence of DBU in DMF also gave corresponding polymers with pendant benzoate moieties. However, the reactivities of PCEVE and PECH were lower than that of PCMS. Furthermore, the reaction of PCMS with N-protected amino acids such as Boc-L-alanine, Cbz-L-alanine, and Bz-DL-alanine afford corresponding polymers with pendant amino acid residues in high conversions using DBU in DMSO. From these results, it was concluded that DBU is the extremely useful organic base for the esterfication reaction of the pendant chloromethyl groups in the polymers with carboxylic acids under mild reaction conditions.

Photochemical reaction of a polymer containing vinyl ether moieties with thiol compounds

AbstractThe photochemical addition reaction of poly(oxy‐1‐methyleneethylene‐co‐oxy‐1‐chloromethylethylene) (1), a polymer containing vinyl ether groups and synthesized by partial elimination reaction of poly(epichlorohydrin)Poly(oxy‐1‐chloromethylethylene). , with methyl 3‐mercaptopropionate was carried out using benzophenone (BP) as a photosensitizer. The addition reaction proceeds with high conversion in benzene, toluene and tetrahydrofuran (THF). However, the degree of addition in both 1,4‐dioxane and N‐methyl‐2‐pyrrolidone (NMP) is relatively low, and the reaction does not proceed in dimethyl sulfoxide (DMSO) under the same reaction conditions. An optically active polymer containing pendant amino acid moieties was also synthesized by the photochemical reaction of polymer 1 with N‐acetyl‐L‐cysteine using BP as a photosensitizer in THF. It was found that the specific angle of rotation of the obtained polymer increases with increasing degree of conversion.