Biodegradable polymer blends consisting of poly(L‐lactic acid) (PLLA) and poly(butylene succinate) (PBS) were prepared in the presence of dicumyl peroxide (DCP). The effects of DCP content on the mechanical properties, thermal and rheological behavior, phase morphology as well as the toughening mechanism of the blends were investigated. The notched Izod impact strength of PLLA/PBS (80/20) blend significantly increased after the addition of 0.05–0.2 phr DCP, but the strength and modulus monotonically decreased with increasing DCP content. PBS acted as a nucleating agent at the environmental temperature below its melting temperature and accelerated the crystallization rate of PLLA but had little effect on its final degree of crystallinity. The degree of crystallinity of PBS and the cold crystallization ability of PLLA gradually reduced with increasing DCP content. The addition of DCP induced an increase in viscosity of the blends at low frequencies as well as finer dispersion of PBS particles and better interfacial adhesion between PLLA and PBS, indicating the in situ compatibilization occurred between the two components. The optical clarity of PLLA/PBS blends was significantly improved after the addition of DCP, which was in accordance with the crystallization behavior and phase structure of the blends. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

This article describes the design and development of squaraine-based semiconducting polymer dots (Pdots) that show large Stokes shifts and narrow-band emissions in the near-infrared (NIR) region. Fluorescent copolymers containing fluorene and squaraine units were synthesized and used as precursors for preparing the Pdots, where exciton diffusion and likely through-bond energy transfer led to highly bright and narrow-band NIR emissions. The resulting Pdots exhibit the emission full width at half-maximum of ∼36 nm, which is ∼2 times narrower than those of inorganic quantum dots in the same wavelength region (∼66 nm for Qdot705). The squaraine-based Pdots show a high fluorescence quantum yield (QY) of 0.30 and a large Stokes shift of ∼340 nm. Single-particle analysis indicates that the average per-particle brightness of the Pdots is ∼6 times higher than that of Qdot705. We demonstrate bioconjugation of the squaraine Pdots and employ the Pdot bioconjugates in flow cytometry and cellular imaging applications. Our results suggest that the narrow bandwidth, high QY, and large Stokes shift are promising for multiplexed biological detections.

One of the most challenging tasks in fabricating multilayer polymer light-emitting diodes (PLEDs) by solution processes is to avoid the interfacial mixing between different layers because most of the commercially available emissive and charge-transporting materials are soluble in common organic solvents. To overcome this difficulty, extensive efforts have been invested in developing novel crosslinkable hole-transporting materials (HTMs). After thermo-or photo-crosslinking, all these crosslinked HTMs possess very good solvent resistance which greatly facilitates the subsequent processing of the emitting layer. By taking advantage of these HTMs, high efficiency red-green-blue (RGB)-emitting PLEDs, as well as white-and quantum dot based PLEDs, have been realized. This article provides a brief overview of the recent development of crosslinkable HTMs and their unique advantages in enhancing the performance of LEDs.

We report the design and synthesis of three alcohol‐soluble neutral conjugated polymers, poly[9,9‐bis(2‐(2‐(2‐diethanolaminoethoxy) ethoxy)ethyl)fluorene] (PF‐OH), poly[9,9‐bis(2‐(2‐(2‐diethanol‐aminoethoxy)ethoxy)ethyl)fluorene‐alt‐4,4′‐phenylether] (PFPE‐OH) and poly[9,9‐bis(2‐(2‐(2‐diethanolaminoethoxy) ethoxy)ethyl)fluorene‐alt‐benzothiadizole] (PFBT‐OH) with different conjugation length and electron affinity as highly efficient electron injecting and transporting materials for polymer light‐emitting diodes (PLEDs). The unique solubility of these polymers in polar solvents renders them as good candidates for multilayer solution processed PLEDs. Both the fluorescent and phosphorescent PLEDs based on these polymers as electron injecting/transporting layer (ETL) were fabricated. It is interesting to find that electron‐deficient polymer (PFBT‐OH) shows very poor electron‐injecting ability compared to polymers with electron‐rich main chain (PF‐OH and PFPE‐OH). This phenomenon is quite different from that obtained from conventional electron‐injecting materials. Moreover, when these polymers were used in the phosphorescent PLEDs, the performance of the devices is highly dependent on the processing conditions of these polymers. The devices with ETL processed from water/methanol mixed solvent showed much better device performance than the devices processed with methanol as solvent. It was found that the erosion of the phosphorescent emission layer could be greatly suppressed by using water/methanol mixed solvent for processing the polymer ETL. The electronic properties of the ETL could also be influenced by the processing conditions. This offers a new avenue to improve the performance of phosphorescent PLEDs through manipulating the processing conditions of these conjugated polymer ETLs.

Partially biobased thermoplastic vulcanizates (TPV) with novel morphology, superior properties and partial degradability were prepared by dynamic cross-link of saturated poly­(lactide) and ethylene-co-vinyl acetate (PLA/EVA) blends using 2,5-dimethyl-2,5-di­(tert-butylperoxy)­hexane (AD) as a free radical initiator. EVA showed higher reactivity with free radicals in comparison with PLA, leading to much higher gel content of the EVA phase (G f‑EVA) than that of the PLA phase (G f‑PLA). However, the G f‑PLA increased more steeply at AD content larger than 1 wt % where the reaction of EVA approached to a saturation point. The competing reaction changed the viscosity ratio of the two components (ηPLA/ηEVA) that resulted in a novel morphology evolution of the TPV, i.e., from sea–island-type morphology to phase inversion via a dual-continuous network-like transition and finally cocontinuity again with increasing the AD content. The cross-link and phase inversion considerably enhanced the melt viscosity (η*), elasticity (G′) and the solid-like behavior of the PLA/EVA-based TPV. Meanwhile, superior tensile strength (σt = 21 MPa), low tensile set (T s = 30%), moderate elongation (εb = 200%) and suitable stiffness (E′ = 350 MPa, 25 °C) were successfully achieved by tailoring the cross-link structure and phase morphology. In addition, the TPV are partially degradable in aqueous alkali. A degradation rate of approximately 5 wt % was achieved within 10 weeks at 25 °C and the degradation mechanism was investigated from both molecular and macroscopic levels. Therefore, this work provides a new type of partially biobased and degradable materials for substitution of traditional TPV.

Double‐grafted cylindrical brushes with poly(lauryl methacrylate) (PLMA) as the side chains were synthesized using the grafting‐from strategy via atom transfer radical polymerization (ATRP). The polyinitiator poly[2‐(2‐bromoisobutyryloxy)ethyl methacrylate] (PBIEM) with $\overline {DP} _{\rm n}$ = 240 and 1 500 served as the backbone. The PLMA side chains of the brushes carry long alkyl chains. GPC and 1H NMR measurements confirmed the successful formation of the PLMA cylindrical brushes. The side chains were cleaved from the cylindrical brushes by transesterification. GPC and 1H NMR results indicate that the initiating efficiency of the bromoester groups on the backbone for the bulky monomer was in the range of 0.34 ≤ f ≤ 0.67. Static and dynamic light scattering show that the ratio of the radius of gyration to the hydrodynamic radius, Rg/Rh, is in the range of 1.2–1.3, indicating that the LMA cylindrical brushes are semiflexible in solution. Atomic force microscopy (AFM) measurements show that short PLMA brushes exhibit a spherical morphology while the long brushes exhibit a worm‐like structure. DSC displayed melting peaks at around −30 °C, indicating the alkyl side chains of the PLMA chains in the double‐grafted cylindrical brushes are crystallizable.magnified image

Luminescent semiconductor quantum dots (QDs) have ideal optical properties and have been used to tag biomolecules for bio-detection and bio-imaging. Some efforts have been made to incorporate QDs into polymer microbeads in order to render them water soluble, chemically stable, and biocompatible in physiological media. While these microbeads are generally very useful for multiplexed immunoassays, they are not suitable for the staining or labelling of subcellular components or intracellular measurements as they are relatively large in size. In this paper, we present a novel and easy way to encapsulate QDs into chitosan nanoparticles. The nanoparticles formed are very monodisperse, spherical in shape, and about 102 nm in size with embedded QDs dispersed within chitosan nanoparticles. The fluorescence quantum yield of the QDs in chitosan is found to be 11.8% higher than that of free QDs. In addition, as chitosan is present on the outermost layer of the nanoparticles, biomolecules can be further attached to the amine and hydroxyl groups on chitosan through chemical bonding. The QD based chitosan nanoparticles will be very useful for either multiplexed bioassays or intracellular study due to their very small sizes. Use of this approach can be extended to the encapsulation of multiple-colour QDs and other colloidal nanocrystals.

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