Effect of molecular weight of biscinnamated poly(ethylene glycol) oligomers on the photocycloaddition reaction

Abstract

Poly(ethylene glycol) (PEG) is of great importance in the biomedical applications, owing to their hydrophilicity, nontoxicity, and absence of antigenicity and immunogenicity. Recently, much interest is focused on the utilization of light as a source of stimulus for the applications for biomedical field. In line with this photoreactive PEG has been utilized for photografting onto surface and fabrication of 3D structured hydrogels. In order to allow photoreaction for PEG, mostly conjugation of the photoreactive moiety at the hydroxyl groups in PEG is used. Cinnamoyl group is well known photoreactive group which undergoes [2+2] photocycloaddition reaction when UV is irradiated and photoalignment layer could be obtained by the irradiation of linearly polarized UV (LPUV) onto the coated films of polymer with cinnamoyl groups. Interestingly, it is reported that cinnamoyl group is spontaneously metabolized in the body and thus has been proven to be nontoxic. Additionally, nematic liquid crystal (LC) materials are emerging as promising candidates for a wide range of applications from optoelectronic devices to biosensing. Although there is lack of report on the biscinnamated PEG as a 2D in-plane orientation layer, it can be expected that biscinnamated PEG could provide biocompatible photoaligned substrate for biomedical applications. From the early studies from our group, molecular weight of PEG whether it is attached as a side chain or itself affect on the performance of application field such as ionic conduction behavior, interaction with DNA, and gelatinization of starch. Considering photoalignment layer, we also reported beneficial phenomenon of the utilization of oligomeric cinnamate rather than polymeric cinnamates in some aspects. In this note, we prepared photoalignable oligomers based on the different molecular weight of PEG oligomers and investigated the photoreactivity and the LC aligning property of the prepared oligomers triggered by the linealy polarized UV irradiation.