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Chiral conjugated polymer has promoted the development of the efficient circularly polarized electroluminescence (CPEL) device, nevertheless, it remains a challenge to develop chiral polymers with high electroluminescence performance. Herein, by the acceptor copolymerization of axially chiral biphenyl emitting skeleton and benzophenone, a pair of axially chiral conjugated polymers namely R‐PAC and S‐PAC are synthesized. The target polymers exhibit obvious thermally activated delayed fluorescence (TADF) activities with high photoluminescence quantum yields of 81%. Moreover, the chiral polymers display significant circularly polarized luminescence features, with luminescence dissymmetry factor (|glum|) of nearly 3 × 10−3. By using the chiral polymers as emitters, the corresponding circularly polarized organic light‐emitting diodes (CP‐OLEDs) exhibit efficient CPEL signals with electroluminescence dissymmetry factor |gEL| of 3.4 × 10−3 and high maximum external quantum efficiency (EQEmax) of 17.8%. Notably, considering both EQEmax and |gEL| comprehensively, the device performance of R‐PAC and S‐PAC is the best among all the reported CP‐OLEDs with chiral conjugated polymers as emitters. This work provides a facile approach to constructing chiral conjugated TADF polymers and discloses the potential of axially chiral conjugated luminescent skeletons in architecting high‐performance CP‐OLEDs. [ABSTRACT FROM AUTHOR]

Shape-memory polymers (SMPs), as an important class of smart materials, have been attracting interests from both academia and industries. Over the past two decades, the fundamental principles of SMPs have been well established, facilitating research to design different types of SMPs at the molecular structure level. Meanwhile, in recent years, increasing attention has been paid to design SMPs with unique shape-memory behavior and manufacture SMP articles with sophisticated shape towards practical applications. Notably, photo-cross-linking strategy has actively established a powerful platform to develop SMPs from basic molecular structure design to advanced design and manufacturing. This review emphasizes the view that there is a close connection between photo-cross-linking strategy and SMPs. Following a brief introduction on the important general aspects of SMPs, progress in research on various photo-cross-linking approaches used for molecular structure design of SMPs is reviewed. To depict the significance of photo-cross-linking strategy for SMPs beyond conventional molecular structure design, achievements at unconventional aspects of advanced design and 4D printing are highlighted. [ABSTRACT FROM AUTHOR]

Abstract: As poly(p-dioxanone) (PPDO) with a high molecular weight (viscosity-average molecular weight (M ν)>100,000g/mol) is not easy to be obtained in a short time, a new approach has been developed to produce high molecular weight poly(p-dioxanone) (HPPDO-T) by chain-extending reaction of hydroxyl-terminated PPDO (HPPDO) prepolymers using toluene-2,4-diisocyanate (TDI) as chain extender. Here HPPDO prepolymers were synthesized via ring-opening polymerization of p-dioxanone (PDO) monomer initiated by 1,4-butanediol (BD) with Stannous octoate (SnOct2) as catalyst. The resulting polymers, having a highest M ν of 250,000g/mol, were characterized by 1H NMR, TG, DSC and WXRD. HPPDO prepolymers can react with TDI more effectively than the PPDO prepolymers initiated by mono-functional initiators, and the molecular weights of resulting chain-extended products increase several decade times in an hour comparing to the prepolymers. The chain extended products HPPDO-T have better thermal stability, and higher glass transition temperatures and lower crystallization rates than PPDO homopolymer. [Copyright &y& Elsevier]

Abstract: Poly(1,4-dioxan-2-one) (PPDO)/starch blend is a novel biodegradable polymer system, and it has potential applications in preparing various low-cost environmentally friendly materials. In order to understand the relationship between their structure and properties, the thermal transition, crystallization and spherulitic morphology of PPDO/starch blends have been studied by means of differential scanning calorimetry (DSC) and polarized optical microscopy. It was found that when 5 wt% starch was added to PPDO, a clear nucleating effect was observed. When the blends were crystallized from the melt, they formed banded spherulites that exhibited a well-defined Maltese cross depending on the crystallization temperature. Avrami exponents and crystallization rate constants of the blends with 5 wt% starch were higher than those of PPDO and those of the blends with 10 wt% starch. Both the dynamic DSC results and isothermal crystallization data indicated that the starch, with a content of 5 wt% in the blends, acted as the nucleating agent for PPDO. [Copyright &y& Elsevier]

Starch, one of the most inexpensive and most readily available of all natural polymers, can be processed into thermoplastic materials only in the presence of plasticizers and under the action of heat and shear. Poor water resistance and low strength are limiting factors for the use of materials manufactured only from starch, and hence the modification of starch is often achieved by blending aliphatic polyesters. In this review, the literatures concerning the properties of various blends of starch and aliphatic polyesters have been summarized. The biodegradable rates of blends can be controlled to a certain extent depending on the constitutions of blends, and the mechanical properties of blends are close to those of traditional plastics such as polyethylene and polystyrene. The reduction of their sensitivity to humidity makes these materials suitable for the production of biodegradable films, injection-molded items, and foams. [ABSTRACT FROM AUTHOR]

This paper reviews the synthesis, properties, and applications of biodegradable polymer, poly(p-dioxanone) (PPDO), and its copolymers. Recent progress in ring-opening polymerization of p-dioxanone employing several effective catalysts is described. Properties of PPDO are given. The copolymers based on PPDO are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: A method for enhancing the molecular weight of poly(p-dioxanone) (PPDO) has been provided in this investigation. Higher molecular weight biodegradable polymers have been prepared by chain-extending method from lower molecular weight PPDO using toluene-2,4-diisocyanate (TDI) as a chain extender. The prepolymers and the resulting polymers were characterized by 1H NMR, DSC, WAXD, and TG. The results show that TDI is an effective chain extender for PPDO. Comparing the chain-extended polymers with PPDO prepolymers, no obvious change in melting temperatures and crystal structures has been observed except that glass transition temperatures increase. The studies of the thermal-oxidative degradation of PPDO show that the thermal stability of chain-extended PPDO is higher than that of PPDO prepolymers. [Copyright &y& Elsevier]

Abstract: A new biodegradable polymer system, poly(p-dioxanone) (PPDO)/poly(ethylene glycol) (PEG) blend was prepared by a solvent casting method using chloroform as a co-solvent. The PPDO/PEG blends have different weight ratios of 95/5, 90/10, 80/20 and 70/30. Crystallization of homopolymers and blends were investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). When 5% of PEG was blended, the crystallization exothermal peaks (T c) of PPDO increased sharply and the crystallization exothermal peaks (T c) of PEG decreased slightly compared with the homopolymers. The crystallization rates of both components increased, and caused greater relative crystallization degree (X t%). But when the content of PEG was more than 5%, the crystalline behaviors of blends had no more significant changes accordingly. The melting points of each sample varied little over the entire composition range in this study. The nonisothermal crystallization of PPDO homopolymer and blend (PPDO/PEG=70/30) were also studied by DSC. The crystallization began at a higher temperature when the cooling rates were slower. The nonisothermal crystallization kinetics of blends was analyzed by Ozawa equation. The results showed that the Ozawa equation failed to describe the whole crystallization of the blend, but Mo equation could depict the nonisothermal crystallization perfectly. [Copyright &y& Elsevier]

To obtain a biodegradable polymer material with satisfactory thermal properties, higher elongation and modulus of elasticity, a new copolyester, poly(butylene succinate-co-ethylene succinate-co-ethylene terephthalate) (PBEST), was synthesized via direct polycondensation from three prepolymers of butylenes succinate, ethylene succinate and ethylene terephthalate (ET). The resulting copolyesters, PBEST, were characterized by 1H-NMR, DSC, TG and WAXRD, and their melting temperature (Tm), melting heat of fusion (ΔHm), glass-transition temperature (Tg), and thermal decomposition temperature (Td) (1.5 wt%) were obtained. Compared to poly(butylene succinate-co-ethylene succinate) (PBES), PBEST has improved thermal properties such as higher Tm and Td due to the incorporation of poly(ethylene terephthalate) unit into the main chains of copolyesters, but very low crystallization speeds. The degradation test of copolyesters in a compost condition shows that the degradability of PBEST is as a function of content of ET. [Copyright &y& Elsevier]

Abstract Although increasing efforts have been made to design shape-memory devices, the development of actuators with dual-sensitive capacities and cyclic actuations is still faced with many challenges. In this work, a kind of shape-memory composite (cEVA/G) based on poly(ethylene- co -vinyl acetate) and graphene was prepared. The cyclic actuation is enabled by the cEVA matrix, which possesses an excellent two-way shape-memory effect (2W-SME) featuring crystallization-induced elongation (CIE) and melting-induced contraction (MIC). Moreover, this composite has a suitable crystallization temperature (T c) greater than 40 °C, which allows effective CIE during cooling to room temperature wherein the proposed actuator maintains its normal state. In addition, the incorporated graphene provides a near-infrared (NIR)-response, and thus the actuator exhibits a thermal/light dual-sensitive capacity. The theoretical aspects of 2W-SME were systematically investigated by varying the temperature ranges and heating/cooling rates, and the results indicate that CIE and MIC are sufficiently effective even under the most severe conditions. More importantly, a shape-memory cEVA/G specimen and an indicating circuit, which uses a lamp as an alarm, was assembled to form a conceptual actuator for sensing applications. This actuator can effectively raise an alarm (i.e., the lamp is turned on) when responding to direct heating and NIR irradiation, which reveals its thermal/light dual-sensitive capacity. After removing heating resources, the alarm is disengaged (i.e., the lamp is turned off) because of the automatic elongation of the shape-memory component during natural cooling to room temperature. Moreover, the performance of the proposed actuator in successive cycles of either direct heating or NIR irradiation further demonstrates the excellent cyclic dual-sensitive capacity of the proposed actuator. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract: The crystallization kinetics, morphology and crystal structure of biodegradable double crystalline poly(butylene succinate)-poly(ethylene glycol) (PBS-PEG) multiblock copolymers (PBSEGs) were studied with different composition and segment chain length by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). The isothermal crystallization kinetics results show that the overall crystallization rate and the equilibrium melting point of PBS increase with the increasing PBS fraction and the segment chain length (L PBS); on the other hand, the higher content or longer PEG segment within PBSEGs possesses larger crystallization rate of PEG chains. The nucleation mechanisms are demonstrated to be instantaneous 3D and 2D aggregates for PBS and PEG segments within PBSEGs, respectively (except for PBSEG2K − 50, 2D and 3D aggregates for PBS and PEG segments, respectively). POM observations indicate that the PBS within PBSEG multiblock copolymers presents banded spherulites in the investigated temperature range. After quenched to lower temperature, PBS templates the morphology for PEG crystallization, and PEG crystallization just changes the magnitude of birefringence (lighting the spherulites) but not influences the superstructure. Finally, WAXD measurements determine that the crystal structure is not changed with the compositions. [Copyright &y& Elsevier]

Abstract: A new biodegradable copolymer of starch-graft-poly(1,4-dioxan-2-one) (starch-g-PPDO) was synthesized by solution polymerization in dimethyl sulfoxide using 2,4-tolylene diisocyanate (TDI) as a coupling agent. The length of PPDO graft chains can be controlled easily by using the prepolymers of PPDO with different molecular weights. The copolymers were prepared by two-step reactions. First, the isocyanate–terminated intermediate (PPDO–NCO) was prepared by introducing one NCO group of TDI onto the hydroxyl end-group of PPDO; second, PPDO–NCO was grafted onto corn starch chains by the reaction between the unreacted NCO group and the hydroxyls of starch, and then, starch-graft-PPDO was obtained. The chemical structure of PPDO–NCO and graft copolymers was confirmed by using FT-IR and 1H NMR, and the thermal properties of the copolymers were investigated by DSC and TG. [Copyright &y& Elsevier]

Abstract: Prepolymers of both poly(p-dioxanone) (PPDO) and poly(butylene succinate) (PBS) reacted in the presence of toluene-2,4-di-iso-cyanate(TDI) as a chain extender to produce higher-molecular-weight chain-extended products (PPDOBS) in suitable reaction conditions. The novel biodegradable polymers were characterized by NMR, DSC, TG and WAXD. The results of thermal oxidative degradation show that chain-extended products have better thermal stability than PPDO. The thermal degradation of PPDOBS shows two stages, the first due to the degradation of PPDO segment of PPDOBS, and the second to the degradation of PBS segment. DSC measurement shows that the PPDOBS has only one Tg, which means that PPDO has good compatibility with PBS. PPDOBS has two crystalline peaks during the cooling scan, but no crystalline peak during the heating scan. The diffraction peaks of PPDOBS appear at the same 2θ angles as that of homopolymers, suggesting that the PPDO and PBS of the chain-extended products preserve their own crystal form. This kind of novel biodegradable polymer is expected to have potential applications in environmentally friendly materials. [Copyright &y& Elsevier]