Volume 48 Issue 11, November 2016

Various conjugated polymers self-assemble to form well-defined microspheres that act as optical resonators. Upon focused laser irradiation, the single isolated microspheres exhibit whispering gallery mode photoluminescence (PL), where sharp and periodic emission lines appear in the PL spectra. Efficient and long-range intersphere light energy transfer is demonstrated using coupled microspheres. Conjugated polymer microspheres are advantageous as optical resonators in terms of their high refractive index, photoabsorptivity, and PL efficiency, as well as simple and low-energy fabrication processes, beneficial for the practical application.

This review focuses on the factors that determine the molecular weight of polyhydroxyalkanoate (PHA), an aliphatic polyester synthesized by bacteria for carbon and energy storage. Because the mechanical strength of PHA increases with its molecular weight, high-molecular weight PHA polymers are preferred. The synthesis of high-molecular weight PHA should consider the following factors: the concentration of PHA synthase, occurrence of chain transfer reaction, catalytic activity of PHA synthase and simultaneous degradation of PHA during biosynthesis. These factors have a direct impact on the molecular weight of PHA.

Novel zinc bis(allyldithiocarbamate) (Zn(ADTC)₂) complexes, prepared from allylamines, carbon disulfide and zinc nitrate, were applied to the synthesis of highly refractive materials. Transparent and flexible films could be prepared by the thiol-ene reaction of Zn(ADTC)₂ derivatives with a tetrathiol in the presence of a diacrylate and Irgacure 651. Refractive indices of the films increased with the feed ratios of the Zn(ADTC)₂ derivatives. The calculated n_D values of the components originating from the two Zn(ADTC)₂ were 1.71 and 1.67.

Poly(N-methylethylene imine) (PMEI) has a wide solubility similar to poly(ethylene oxide) and a high protonation capacity similar to poly(ethylene imine). In addition, PMEI forms aggregates with negatively charged macromolecules, such as polystyrene latex particles, and acts as either a flocculant or a dispersant depending on the environment. An aqueous solution containing the as-synthesized PMEI (weight-average molecular weight: 26 kDa) exhibited an LCST of 116 °C, and a toluene solution exhibited a UCST of 36 °C. Therefore, PMEI is expected to be used as a highly hydrophilic polycation for various applications.

Intrinsic birefringence, Δn₀, is a material constant for the orientational birefringence of polymers, and has been measured by many researchers with various methods. However, the reported values of the same polymer sometimes disagree among the researchers because determination of the orientation degree is somehow complicated. Alternatively, a new method using the modified stress-optical rule (MSOR) was proposed for Δn₀ measurement. In this study, literature data of the Δn₀ for various polymers are assessed and the reliability of Δn₀ estimated via the MSOR is discussed.

The rheological properties of the suspensions of thermo-responsive poly(N-isopropylacrylamide) microgels are investigated in the swollen and collapsed states using creep and oscillatory measurements. The results from the long-time creep tests reveal that in the collapsed state with attractive interparticle interactions, the suspensions with a particle volume fraction of approximately 0.5 become viscoelastic liquids with high viscosities due to the formation of a network-like aggregation of particles. However, the suspensions with the same volume fraction in the swollen state exhibit a Newtonian fluid behavior with low viscosities.

The crystalline species and crystallization behavior of four-armed stereo diblock poly(lactide) (4-LD) polymers and poly(L-lactide) polymers varied depending on crystallization method (precipitation, heating or slow cooling) and L-lactyl unit content. With the deviation of L-lactyl unit content from 50%, the crystalline species of 4-LD polymers changed from only SC-crystallites to amorphous and then to only homo-crystallites (heating and cooling) or from only SC-crystallites to only homo-crystallites (precipitation). Branching architecture rather than stereo diblock architecture interrupted the concurrent crystallization of SC-crystallites and homo-crystallites.