We synthesized the alternating copolymers of 1,3-diene monomers with sulfur dioxide (SO 2 ) as a new class of thermally stable polymers by the radical copolymerization process and the subsequent hydrogenation. The copolymerizations of 2,4-hexadiene (HD), 1,3-butadiene (BD), and isoprene (IP) with SO 2 were carried out at -78 to 0 °C in toluene in the presence of tert-butyl hydroperoxide, which acts as one component in the redox initiating system in combination with SO 2 . The resulting poly(diene-alt-SO 2 )s were found to consist of highly controlled repeating units, that is, an alternating and 1,4-regiospecific repeating structure. Poly(HD-alt-SO 2 ) was soluble in several organic solvents, such as chloroform, nitromethane, tetrahydrofuran, acetone, and dimethyl sulfoxide. In contrast, poly(IP-alt-SO 2 ) was soluble only in dimethyl sulfoxide, whereas poly(BD-alt-SO 2 ) was insoluble in all of the solvents. The poly(diene-alt-SO 2 )s readily degraded upon heating because of the expected fast depolymerization. We have demonstrated that the thermal stability of the poly(diene-alt-SO 2 )s is modified by the hydrogenation of the double bond in the polymer main chain. The hydrogenation of poly(HD-alt-SO 2 ) resulted in a drastic increase in the 5% weightloss temperature from 135 to 317 °C.

We have fabricated degradable polyperoxides (PP) consisting of well-controlled 5,4-repeating units using various sorbic acid derivatives and molecular oxygen by an alternating radical copolymerization process. The PP obtained from the sorbic esters decompose via a radical chain reaction mechanism, leading to the formation of controlled low-molecular-weight products. In contrast, PP from some amide derivatives include an irregular chain structure, resulting in a more complicated degradation behavior. The theoretical calculations account for the selectivity in the two-step regiospecific propagation depending on the monomer structure. We have demonstrated the synthesis of functional PP based on two methods: one is the copolymerization of functional diene monomers with oxygen, and the other is the polymer reaction of PP including an azide group with a functional alcohol.

We have demonstrated a facile method for the synthesis of a new kind of degradable gel, which is prepared by the introduction of a dienyl group into the side chains or the chain ends of conventional polymers such as poly(acrylic acid), poly(ethylene oxide), poly(2-hydroxyethyl methacrylate), and poly(vinyl alcohol) and the subsequent radical copolymerization of the diene with oxygen in the presence of a radical initiator. The obtained gels contain the polyperoxy units as the cross-linking points and readily degrade upon heating. Sorbic derivatives including epoxy and anhydride functional groups are used as reagents for the dienyl functionalization of the precursor polymers with a high efficiency. The heat of degradation of the polymer gels synthesized in this study is much smaller than that of the previously reported polyperoxides as degradable polymers and gels. This method is applied to the preparation of various kinds of polymer networks programmed for degradation after temporary use.

Polyperoxide, as a new kind of thermally degradable polymer, is synthesized by the radical alternating copolymerization of a 1,3-diene monomer with oxygen. The introduction of polyperoxide units into any other polymer is useful for the fragmentation of polymers and a change in the physical properties of polymeric materials. In the present study, we demonstrate the synthesis and fragmentation of poly(l-lactic acid) (PLLA) modified with thermally degradable branching and cross-linking points, which consist of a repeating polyperoxide structure as the degradable junctions. We prepared several PLLA with a dienyl group at the α- and/or ω-chain ends by the anionic and metal-catalyzed polymerizations of l-lactide. Radical alternating copolymerization of the mono- and difunctional PLLA with oxygen was carried out to obtain branched polymers and gels. These branched and cross-linked PLLA materials readily degraded upon heating to yield linear PLLA chains.

A branched copolymer containing a degradable polyperoxide linkage at a branching point was synthesized by the radical copolymerization of dienyl‐functionalized polystyrene and polyisoprene macromonomers with molecular oxygen. The ternary mixture of the branched copolymer and the macromonomers showed phase‐separated structure after annealing at 45 and 90 °C. The adjacent spacing of the phase‐separated structure was in the order of submicron to micrometer, which is larger than that of general microphase separated structures, due to the presence of homopolymers (macromonomers). Annealing at 110 °C induced thermal decomposition of the polyperoxide followed by in‐situ collapse and a drastic morphology change in the phase‐separated structure.magnified image