Synthesis of novel saccharide-pendant vinyl polymer and application to oxygen barrier film

Abstract

Poly(vinylidene chloride) (PVDC) film, which has a high oxygen barrier property, has been widely used as packaging material, however, PVDC creates significant environmental problems. When burned, it forms chloric acid which is liberated into the atmosphere, becoming a component of the acid rain that damages forests. Therefore, many other materials have been substituted for PVDC in packaging applications. Of these alternative packaging materials, cellulose i.e., cellophane is the most environment-friendly material, and also has a high oxygen barrier property in dry conditions. Cellulose, which has been used in various matrix-forming materials, has long been developed. Although cellulose is a sustainable material, it has characteristics of rigidity derived from interand intramolecular hydrogen bonding. Therefore, cellulose shows poor workability due to thermal stability, poor controllability of chemical reactions and low solubility in water and common organic solvents [1, 2]. Cellulose derivatives such as e.g., acylate [3] and xanthate [4], or the cellulose complex with copper such as cupra [5], are required to mold cellulose. In order to overcome the poor characteristics of cellulose, we focused on a functional polymer with a constitutional unit of cellulose, namely cellobiose in the side chain, and developed the novel synthetic monovinylcellobiose. In addition, the synthetic monomer was converted into a polymer by free-radical polymerization in aqueous solution. It is important to determine whether typical cellulose properties (such as functionality, biodegradability [6] and biocompatibility [7] can be advantageously retained in this new synthetic, so in this paper we report the characterization of the synthetic monovinylcellobiose and the obtained polymer, comparing with the characteristics of the corresponding monosaccharide derivative. As a packaging material, the novel saccharidependant vinyl polymer has potential as a coating layer for oxygen barrier film. In this study, we investigated its oxygen barrier property by measuring the change of humidity. The synthesis of monovinylcellobiose monomer was carried out without the use of protecting groups for the cellobiose component, as shown in Scheme 1. As reported by Likhosherstov et al. [8], a high yield of cellobiosylamine could be obtained by reductive amination of cellobiose. Due to the reactivity difference between the amino group and the remaining hydroxyl groups of the cellobiose, the introduction of a variety of functional group to the anomeric position became possible [9]. Due to a lack of by-products, especially acid, salts and fission products, we adopted coupling with 2-(methacryloyloxy)ethy isocyanate (MOI) [10], which reacts mildly. The typical procedure for the synthesis of 2-(methacryloyloxy)ethylureido cellobiose (MOU-Cell) is described below. Cellobiose (15 g, 43.8 mmol) was dissolved in water (100 ml) and solid ammonium hydrogen carbonate (30 g, 379.7 mmol) was added at intervals of 24 h, and was stirred at 37 ◦C for 2 days. Next, the residue was diluted to 200 ml with water and concentrated to 50 ml. This procedure was repeated until the disappearance of the odor of ammonia. The purity of the freeze-dried product was 81% [11]. Cellobiosylamine (8.1 g, 23.7 mmol) was dissolved in 1.0 × 10−3 M KOH aqueous solution (100 ml). MOI (9.20 g, 59.3 mmol) was added and stirred at 3 ◦C for 12 h, producing white precipitation as a by-product. The precipitation was removed by filtration. The filtrate was washed with diethyl ether to remove traces of unreacted MOI and freeze-dried. The raw product was dissolved in water/methanol and recrystallized from acetone/diethyl ether. The yield was 8.78 g (74.5%). m.p.149.4–153.2. The structure of MOUCell is confirmed by its 1H-NMR and IR spectra. 1H-NMR (D2O, ppm): 1.95 (s, 3H, CH2 C(CH3), 3.41–4.02 (m, 12H, from sugar), 3.66 (t, 2H, CH2), 4.26 (t, 2H, CH2), 4.51 (d, 1H, H′-1), 4.85 (d,