Preparation of Phospholipid Polylners and Their Properties as Polymer Hydrogel Membranes

Polymer Journal, Vol. 22, No.5, pp. 355-360 (1990) Preparation of Phospholipid Polymers and Their Properties as Polymer Hydrogel Membranes Kazuhiko ISHIHARA, Tomoko UEDA, and Nobuo NAKABAYASHI Institute for Medical and Dental Engineering, Tokyo Medical and Dental University, 2-3-10, Kanda-Surugadai, Chiyoda-ku, Tokyo 101, Japan (Received October 9, 1989) ABSTRACT: A methacrylate monomer having the phospholipid polar group, 2-methacryloyloxyethyl phosphorylcholine (MPC) was prepared by an improved method with good yield. MPC was copolymerized with n-butyl methacrylate (BMA). The polymer membranes were prepared from the poly(MPC-co-BMA) by a solution casting method. The membrane adsorbed water well and became a hydrogel structure even MPC mole fraction in the copolymer was 0.04. The water content of the hydrogel membrane increased with increase of MPC units and rise of temperature. These properties of the hydrogel membrane were attributed to the highly hydrophilic phospholipid polar group in the copolymer. Water soluble organic compounds and proteins whose molecular weights were below 104 permeated through the hydrogel membrane. However, the protein could not permeate when the molecular weight was higher than 10 5 • KEY WORDS Phospholipid Polymer; 2-Methacryloyloxyethyl Phosphorylcholine ; Membrane; Hydrogel; Water Content; Temperature Response; Permeation; Biomaterials Phospholipids are the main components of the biomembrane and interesting substances in biological and biomedical field. 1,2 Recently, the phospholipid membrane has been used as a drug carrier, sensor, separation membrane. 3 However, these phospholipid membranes were unstable physically and chemically, because the phospholipids constituting membranes do not bond covalently and have high mobility. To improve the mechanical strength of the phospholipid membranes, phospholipid molecules with polymerizable group were synthesized. 4 ,s We have developed new biocompatible materials based on the results that the surface of polymeric material showing good biocompatibility was covered with phospholipid molecules and formed biomembrane-like structure on the material. Therefore, a methacrylate having phosphorylcholine moiety, 2-methacryloyloxyethyl phosphorylcholine Polym. J., Vol. 22, No.5, 1990 (MPC) was synthesized and its copolymerization ability with methyl methacrylate was evaluated. 6 Moreover, the blood compatibility of the poly(MPC-co-MMA)s has been investigated. 7 Since MPC is an extremely hydrophilic monomer, MPC copolymers with hydrophobic monomer are hydro gels. The hydrogels are expected to useful biomaterials. 8 In this article, improvement of the preparation method of MPC and basic properties of MPC copolymers with n-butyl methacrylate as a hydrogel is described. EXPERIMENTAL Materials 2-Chloro-2-oxo-l,3,2-dioxaphospholane (COP) was synthesized according to the method of Edmundson and purified by distillation under reduced pressure, bp 98°Cj 355 K. ISHIHARA, T. VEDA, and N. NAKABAYASHI 1 mmHg (lit.: bp 79°C/0.4mmHg).9 2-Hydroxyethyl methacrylate (HEMA) and n-butyl methacrylate (BMA) were distilled under reduced pressure of argon, and fractions of bp 65°Cj3 mmHg and 60°Cj30 mmHg were used, respectively. 2,2'-Azoisobutyronitrile (A IBN) was recrystallized from methanol. Tetrahydrofuran (THF), acetonitrile, and triethylamine (TEA) were purified by conventional way. Acrylamide (A Am) was recrystallized from benzene. Extra pure grade 2-acrylamide2-methyl propane sulfonic acid (AMPS) was kindly gifted from Nitto Chemical Co., Ltd. Poly(HEMA) was synthesized by a homopolymerization of HEMA in 2-propanol using AIBN as an initiator. Bovine serum albumin, bovine serum y-globulin, insulin, and egg white lysozyme were purchased from Sigma Co. Ltd. Figure 1. The structure of MPC. Into a 200 ml glass pressure bottle were placed 5.0 g of OPEMA and 30 ml of dry acetonitrile. After the bottle was cooled at - 20°C, 2 ml of anhydrous trimethylamine were rapidly added to the solution. The pressure bottIe was closed and allowed to warm up to room temperature. After it was heated at 60°C for 16 h, the bottle was cooled at - 20°C, by which procedure a white precipitate, MPC, began to form from the reaction mixture. The MPC was filtered off under argon atmosphere, washed with cold dry acetnitrile and dried under reduced pressure (yield: 3.2 g). Synthesis of MPC Into a 500 ml three-necked flask equipped The structure of MPC is shown in Figure 1. with a dropping funnel, thermometer, and IH NMR and I3C NMR spectra strongly drying tube, 20 g (0.154 mol) of HEMA, 15.6 g supported the structure of MPC. IH NMR (0.154 mol) of TEA and 200 ml of dry THF (CDC1 3): 6 = 1.90 (--CH 3, 3H), 3.27-3.36 were placed. After the solution was cooled (-N(CH3)' 9H), 3.70--3.80 (-CH2N, 2H), at - 20°C, 21.9 g (0.154 mol) of COP in 100 ml 4.00-4.10 (POCH n 2H), 4.21--4.31 (OCHr of dry THF were added dropwise to the stirred CH 20P, 4H), 5.60 (CH=, 1H), and 6.10 solution over a period of 1 h. The tempera- (CH=, IH). 13C NMR (CDCI 3): 6= 18.59 ture of the reaction mixture was maintained (-CH3)' 54.25 (N(CH 3h), 59.44 (CH 2N), - 30°C for 3 h. Then, the precipitate 63.34 (POCH 2-), 64.41 (-CH 20P), 66.20 - 20 in the reaction mixture which was triethyl- (OCH 2), 126.09 (= CH 2), 136.22 (::C =), and ammonium chloride was filtered off. The 167.36 (CH 3). filtrate was evaporated under reduced pressure. To the residue, 50 ml of dry ethyl ether were Synthesis and Characterization of Poly(MPCco-BMA) added to precipitate a small amount of triethylammonium chloride by filtration. By The desired amounts of MPC, BMA and evaporation of filtrate under reduced pressure, AIBN were dissolved in methanol(MeOH)colorless liquid, 2-(2-oxo-l,3,2-dioxaphospho- THF mixture and the solutions taken into loyloxy)ethyl methacrylate (OPEMA) was polymerization tubes. After oxygen in the tubes obtained (yield: 35.5 g). The IR and I H NMR was eliminated by bubbling of argon into the spectra supported the structure of OPEMA. solution, the tubes were sealed. Then the tubes IR (cm-I): 1720 (C=O), 1640 (C=C), 1300, were shaken at 60°C for 16h. The contents were 1240, 1160 and 1080 (-POCH2-)' IH NMR cooled to stop the reaction and precipitated by (CDCI 3): 6=2.00 (-CH3' 3H), 4.00-4.68 pouring into hexane for copolymers with low (-CH 2-, 8H), 5.60 (-CH =, IH), and 6.20 MPC composition and into diethyl ether for (-CH=,IH). those with high MPC composition. The 356 Polym. 1., Vol. 22, No.5, 1990 Phospholipid Polymer Hydrogel Table I. MPC mole fraction Compolymerization of MPC and BMA [Monomer] Abb. MB-l MB-2 MB-3 MB-4 MB-5 in feed in copolymer" moll- 1 0.05 0.10 0.15 0.20 0.40 0.039 0.116 0.169 0.199 0.268 1.43 1.68 0.92 0.93 1.06 Solvent MeOH/THF 0.13/0.87 0.16/0.84 0.23/0.77 0.23/0.77 0.42/0.58 Time Conv. Mb w TgC Mw/M •b h % 104 23 23 22 24 24 35.7 62.1 50.0 52.4 89.8 2.85 1.40 1.29 1.68 °C 24 27 33 34 38 [AIBN] = I mol% for monomer. " Determined by XPS (...truncated)