Soo-Chang Yu

Degradable polyurethanes containing poly(butylene succinate) and poly(ethylene glycol)

Abstract Biodegradable polyurethanes may be used in the fabrication of plastic films which can replace common films prepared from nondegradable polymers such as polyethylene and polypropylene. Prepolymers were synthesized from poly(butylene succinate) polyol (PBS, M n 1650), poly(ethylene glycol) (PEG, M n 1000), and 4,4′-dicyclohexylmethane diisocyanate, and reacted with 1,4-butanediol chain extender to obtain polyurethanes. Their number-average molecular weights and melting temperatures are in the range of 30,000–38,000 and 99–101°C, respectively. The tensile strengths (2.0–2.4 kg/mm 2 ) of the polymers were somewhat greater than the reported value (1.6 kg/mm 2 ) of PBS with a comparable molecular weight ( M n 20,000). However, their elongations at break (230–330%) were significantly greater than that of the PBS (42%). They were hydrolytically degradaded very rapidly in 3% NaOH solutions at 37°C such that their weight loss was approximately 30–60% within 2 days, depending on the content of PEG and hard segment. On the other hand, polyurethanes containing only PBS as soft segments showed a much slower degradation rate under the identical conditions.

A new polymer containing confined phenylenevinylene segments: synthesis and photoluminescence

Abstract Poly[bis(4,6-di- tert -butyl-1,2-phenylene-1,2-ethenylene)-1,4-phenylene-4,4′-ethylenebis(11-oxyundecanylphenyl urethane)] (PV-PU) consisting of alternating a confined phenylenevinylene segment and a nonconjugated urethane segment in the main chain was synthesized. Photoluminescence (PL) of PV-PU is emitted in the blue region with a maximum intensity at about 440 nm. PV-PU blended with 2-(4-biphenylyl)-5-(4- tert -butylphenyl)-1,3,4-oxadiazole (PBD)–polystyrene (1:2, wt/wt) in weight ratio of 1:10 and 1:15 also show PL spectra similar to that of pure PV-PU but with enhanced intensity, suggesting that the photo-excited PBD donor transfers its energy to PV-PU in the ground state and subsequently the excited PV-PU acceptor emits the blue light.

The electronic states in Ca-doped BaTiO3 ceramics

Abstract We investigated the electronic structures for the ceramic compositions given by Ba 1−x Ca x TiO 3 and BaTi 1−y Ca y O 3 . The measured XPS shapes for the O1s molecular orbitals were changed a lot due to the addition of Ca into BaTiO 3 . The O1s spectra of Ti site doped samples show strongly split energy peaks. On the other hands, there was little change to the spectra for the Ba site doped samples. Through DV-Xα calculations we observe that the replacement of Ca 2+ ion for Ti 4+ sites in Ba 8 Ti 7 O 6 cluster model introduces the strong splitting of the O1s molecular orbital energies. From the O1s pDOS for Ba 8 Ti 7 O 6 , Ba 6 Ca 2 Ti 7 O 6 and Ba 8 Ti 5 Ca 2 O 6 cluster models the O1s energy splitting for the BaTi 1−y Ca y O 3 composition was proven to be caused by the aliovalent ion (Ca 2+ ) substitution for Ti 4+ ion sites.