Biologically stimuli-responsive hydrogels, “biomolecule-responsive hydrogels”, undergo changes in volume in response to a target biomolecule such as glucose, a protein, or DNA. Biomolecule-responsive hydrogels have attracted considerable attention as novel smart biomaterials in the biomedical field because target biomolecules such as saccharides and proteins are useful signals for site-specific drug delivery systems or for monitoring physiological changes. There are several strategies for designing biomolecule-responsive hydrogels, which combine the ability to recognize a target molecule with the ability to induce a structural change in the hydrogel network. A standard strategy uses the combination of the molecular recognition events of biomolecules such as enzymes, lectins and antibodies with the responsive behavior of pH- or temperature-responsive polymers. We have proposed another strategy that utilizes biomolecular complexes like lectin-saccharide complexes and antigen-antibody complexes as dynamic crosslinks of hydrogel networks. This article reviews the relevant research of biomolecule-responsive hydrogels that were strategically designed by using the recognition functions of biomolecules such as enzymes, proteins, or DNA.

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Aldehyde-terminated telechelic poly(2-adamantyl vinyl ether)s [poly(2-AdVE)s] were synthesized by water-based end-capping reaction of living poly(2-AdVE) with the bifunctional initiating system 1 [CH₃CH(OCOCH₃)-O(CH₂)₄O-CH(OCOCH₃)CH₃]/Et_1.5AlCl_1.5 in the presence of ethyl acetate in toluene at 0℃. The hydroxy-terminated telechelic poly(2-AdVE)s were synthesized by reduction of the terminal aldehyde groups with NaBH₄. The obtained hydroxy-terminated telechelic polymers possess controlled molecular weights and narrow molecular weight distributions (sample I; M_n = 1,500, M_w/M_n = 1.47, sample II; M_n = 3,200, M_w/M_n = 1.48). ¹H NMR analysis showed that the resulting telechelic poly(2-AdVE)s had quantitative attachment of hydroxy terminals. Subsequent end-group transformation of hydroxy groups into acetate or urethane groups was possible.

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The dominant factor of inhomogeneous molecular mobility (T₂) of acrylonitrile butadiene rubber (NBR), has been studied by pulsed ¹H NMR spectroscopy. We investigated the influence of the number-average molar mass of chain length between crosslinks (M_c) and average monomer sequence length of butadiene (LnBU), which is an inhomogeneity of the first ordered structure. The FID analysis shows that vulcanized samples are composed of 3 components with different molecular mobility, T_2S, T_2M and T_2L. Moreover, we evaluated the M_c dependency of T_2S, T_2M and the ¹H ratio and the change of T_2S, T_2M and the ¹H ratio of before and after vulcanization against LnBU. According to the results, the LnBU showed a more dominant correlation to T₂ and the ¹H ratio than M_c. That implies that the NBR molecular chain with almost the same average monomer sequence length of acrylonitrile mobility at 30℃ originates from the inhomogeneity of the first ordered structure of NBR.

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We studied the thermal decomposition of polyolefins and other similar polymers, generally contained in plastic materials to overcome the problem of flammability. There are different patterns of thermal decomposition of these polymeric compounds such as, random decomposition of the main chain, or the formation of a trimer like compound at the polymer chain end that leads to depolymerization. The relationship between flammability and the type of thermal decomposition for polystyrene and polypropylene components was investigated. We observed that the thermal decomposition occurs through cleavage of a particular part in the polymeric chain as well as simultaneous random cleavage. Also, we found that the thermal decomposition products depend on the molecular weight of the polymers, which affects the flammability significantly. The combustion state of a polymer may vary owing to differences in molecular weight. The molecular weight distribution is different for low and high molecular weight samples and there is no combustion of a particular molecular weight under certain conditions. Finally, we found a specific polyolefin and polystyrene structure that does not burn easily, which is a significant finding to develop nonflammable materials for a safe and secure society.

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