Notes Synthesis of Photodegradable Polymers Having Biodegradability and Their Biodegradations and Photolysis Yoichi Hiraguri* and Yutaka Tokiwa National Institute of Bioscience & Human-Technology, 1-1, Higashi, Tuskuba, Ibaraki 305, Japan Received September 9, 1996 Revised Manuscript Received March 4, 1997 Introduction Photodegradable polymers have been used for can carriers, multifilms for agriculture, packing materials, and so on. These photodegradable polymers are de- graded to low molecular weight by light and lose their shapes, but they have little biodegradability after pho- tolysis. 1,2 This is a major problem of photodegradable polymers. We reported polymerization of 2-methylene-1,3,6- trioxocane (MTC) polymerized via ring-opening by a radical initiator to obtain a poly(ester-ether) (eq 1) and found that this poly(ester-ether) was degraded by an enzyme. 3 In addition, we found that MTC copolymer- ized with vinyl monomers such as styrene, methyl methacrylate, and vinyl acetate to produce vinyl poly- mers containing the ester-ether group and that these copolymers were degraded by enzyme. 3 On the other hand, poly(vinyl ketones) are known as photodegradable polymers. 4,5 Photolysis of copolymers of these vinyl ketones and vinyl monomers were studied. 6-9 We carried out radical copolymerization of MTC with methyl vinyl ketone (MVK) in order to impart biode- gradability and photodegradability. We report here the copolymerization of MTC with MVK, enzymatic degra- dation of the copolymers before and after photolysis, and photolysis of the copolymers. Results and Discussion MTC was synthesized according to our previous report. 3 Copolymerization of MTC with MVK. The radical copolymerization of MTC with MVK was carried out in benzene using 2,2′-azobis(isobutyronitrile) (AIBN) as an initiator at 60 °C. All the IR spectra of the obtained copolymers showed the absorption around 1735 cm -1 assigned to the ester group and the absorption around 1710 cm -1 assigned to the ketone group. All the 1 H NMR spectra showed a signal at 4.22 ppm, correspond- ing to the methylene proton (COOCH 2 ). These spectral data show that MTC undergoes a ring-opening reaction during copolymerization with MVK and that ester- ether moieties were incorporated into the backbone of poly-MVK (eq 2). The results of the copolymerizations are summarized in Table 1. There is the tremendous difference in reactivity of MTC and MVK monomers. MVK is very active to the radicals. On the other hand, MTC is less active to radicals than MVK because MTC is a vinyl ether and the R-carbon of MTC is a quaternary carbon. Therefore, even if the feed ratio of MTC is high, much MVK is introduced into the copolymer, and when the feed ratio of MTC increases, the molecular weight of the copolymer decreases. The CdC double bond of MTC is electron sufficient because MTC is a vinyl ether, and the CdC double bond of MVK is electron deficient because the carbonyl group that is electron withdrawing bonds to the CdC double bond. Therefore, MTC and MVK may be bonded alternately in the copolymers. The copolymer with a high degree of introduction of MVK has a high possibility that MVK is next to MTC, and the copolymer that has a high degree of introduction of MTC has a high possibility that MTC is next to MVK. Biodegradability Assay of the Copolymers. The biodegradability of the copolymers was assayed by the rate of solubilization when lipase acted on them. This enzyme assay system did not necessarily involve com- plete degradation into the constituent units. The biodegradability assay of the poly-MTC-MVK copoly- mer was also simultaneously run on polycaprolactone (PCL). The biodegradability of the poly-MTC-MVK copolymer was assayed by a total organic carbon (TOC) analyzer when lipase acted on it. Poly-MTC-MVK was hydrolyzed by Rhyzopus arrhizus lipase. The results are shown in Table 2. The solubilization percentages of poly-MTC-MVK (x:y ) 68:32) were calculated according to eq 3. The value when poly-MTC-MVK (x:y ) 68:32) de- graded completely is 20000 (mg/L) × (12 × 6 × 0.68 + 12 × 4 × 0.32)/(130 × 0.68 + 70 × 0.32) ) 11610 (ppm) (3a) The molecular weight of MTC is 130, and the molecular weight of MVK is 70. Experimental data are 3545 - 119 - 41 ) 3385 (ppm) (3b) The solubilization percentage of poly-MTC-MVK (x:y (1) (2) 3691 Macromolecules 1997, 30, 3691-3693 S0024-9297(96)01327-7 CCC: $14.00 © 1997 American Chemical Society