Synthesis and characterization of copolymers with the same proportions of polystyrene and poly(ethylene oxide) compositions but different connection sequence by the efficient Williamson reaction

A Powerful Strategy for Synthesizing Block Copolymers via Bimetallic Synergistic Catalysis

Block copolymers, comprising polyether and polyolefin segments, are an important and promising category of functional materials. However, the lack of efficient strategies for the construction of polyether-b-polyolefin block copolymers have hindered the development of these materials. Herein, we propose a simple and efficient method to obtain various block copolymers through the copolymerization of epoxides and acrylates via bimetallic synergistic catalysis. The copolymerization of epoxides and acrylates proceeds in a sequence-controlled manner, where the epoxides-involved homo- or copolymerization occurs first, followed by the homopolymerization of acrylates initiated by the alkoxide species from the propagating polymer chain, thus yielding copolymers with a block structure. Notably, the high monomer compatibility of this powerful strategy provides a platform for synthesizing various polyacrylate-based block copolymers comprising polyether, polycarbonate, polythiocarbonate, polyester, and polyurethane segments, respectively.

MeNPF4.5 Improves Cassava Nitrogen Use Efficiency and Yield by Regulating Nitrogen Uptake and Allocation

Improving nitrogen use efficiency (NUE) is a very important goal of crop breeding throughout the world. Cassava is an important food and energy crop in tropical and subtropical regions, and it mainly use nitrate as an N source. To evaluate the effect of the nitrate transporter gene MeNPF4.5 on the uptake and utilization of N in cassava, two MeNPF4.5 overexpression lines (MeNPF4.5 OE-22 and MeNPF4.5 OE-34) and one MeNPF4.5 RNA interference (RNAi) line (MeNPF4.5 Ri-1) were used for a tissue culture experiment, combining with a field trial. The results indicated that MeNPF4.5 is a plasma membrane transporter mainly expressed in roots. The gene is induced by NO₃ ^-. Compared with the wild type, MeNPF4.5 OE-22 exhibited improved growth, yield, and NUE under both low N and normal N levels, especially in the normal N treatment. However, the growth and N uptake of RNAi plants were significantly reduced, indicating poor N uptake and utilization capacity. In addition, photosynthesis and the activities of N metabolism-related enzymes (glutamine synthetase, glutamine oxoglutarate aminotransferase, and glutamate dehydrogenase) of leaves in overexpression lines were significantly higher than those in wild type. Interestingly, the RNAi line increased enzymatic activity but decreased photosynthesis. IAA content of roots in overexpressed lines were lower than that in wild type under low N level, but higher than that of wild type under normal N level. The RNAi line increased IAA content of roots under both N levels. The IAA content of leaves in the overexpression lines was significantly higher than that of the wild type, but showed negative effects on that of the RNAi lines. Thus, our results demonstrated that the MeNPF4.5 nitrate transporter is involved in regulating the uptake and utilization of N in cassava, which leads to the increase of N metabolizing enzyme activity and photosynthesis, along with the change of endogenous hormones, thereby improving the NUE and yield of cassava. These findings shed light that MeNPF4.5 is involved in N use efficiency use in cassava.

Synthesis, Hydrophilicity and Micellization of Coil-Brush Polystyrene-b-(polyglycidol-g-polyglycidol) Copolymer-Comparison with Linear Polystyrene-b-polyglycidol

In this paper, an original method of synthesis of Coil-Brush amphiphilic polystyrene-b-(polyglycidol-g-polyglycidol) (PS-b-(PGL-g-PGL)) block copolymers was developed. The hypothesis that their hydrophilicity and micellization can be controlled by polyglycidol blocks architecture was verified. The research enabled comparison of behavior in water of PS-b-PGL copolymers and block-brush copolymers PS-b-(PGL-g-PGL) with similar composition. The Coil-Brush copolymers were composed of PS-b-PGL linear core with average DPn of polystyrene 29 and 13 of polyglycidol blocks. The DPn of polyglycidol side blocks of coil-b-brush copolymers were 2, 7, and 11, respectively. The copolymers were characterized by 1H and 13C NMR, GPC, and FTIR methods. The hydrophilicity of films from the linear and Coil-Brush copolymers was determined by water contact angle measurements in static conditions. The behavior of Coil-Brush copolymers in water and their critical micellization concentration (CMC) were determined by UV-VIS using 1,6-diphenylhexa-1,3,5-trien (DPH) as marker and by DLS. The CMC values for brush copolymers were much higher than for linear species with similar PGL content. The results of the copolymer film wettability and the copolymer self-assembly studies were related to fraction of hydrophilic polyglycidol. The CMC for both types of polymers increased exponentially with increasing content of polyglycidol.

Micellization of Polystyrene-b-Polyglycidol in Dioxane and Water/Dioxane Solutions

In this work, the self-assembly of a series of amphiphilic polystyrene-b-polyglycidol (PS-b-PGL) diblock copolymers in dioxane and dioxane/water mixtures is presented. The PS-b-PGL have an average degree of polymerization (DP) of PS block equal to 29 units and varied degrees of polymerization for the glycidol segments with DPs of 13, 42, 69 and 117. In dioxane, amphiphilic diblock copolymers form micelles with the hydrophilic PGL placed in the core. Critical micelle concentration (CMC) was determined based on the intensity of scattered light vs. concentration. The micelle size was measured by dynamic light scattering and transmission electron microscopy. Also, the behaviour of the copolymer was studied in water/dioxane solutions by following the changes of scattered light intensity with the addition of water to the system. Critical water content (CWC) of the studied systems decreased as the initial PS-b-PGL concentration in dioxane increased. This process was accompanied by a decrease in the size of aggregate formed. For a given initial copolymer concentration, the size of copolymer aggregates decreased linearly with increasing the length of the PGL block