Synthesis of aromatic diamine-based benzoxazines and effect of their backbone structure on thermal and flammability properties of polymers

Three kinds of novel aromatic diamine-based benzoxazines containing naphthalene, propane-2,2-diyldibenzene and neopentyl groups in the backbone, respectively (designated as BAPNCP, BAPBACP and BAPNPGCP, respectively), were synthesized and characterized. In addition, the effects of backbone structures on curing behaviors of the monomers and thermal and flammability properties of the resulting polymers were systematically studied. The results indicated that BAPNPGCP displayed the highest enthalpy of the curing reaction associated with the ring-opening of benzoxazine, which was due to the effect of benzoxazine ring content per unit mass. Interestingly, the 5 wt% weight loss temperature and char residue after thermogravimetric test for poly(BAPNPGCP) were 8 °C and 7% higher than those of poly(BAPBACP). Meanwhile, the total heat release of poly(BAPNPGCP) was less than half of that for poly(BAPBACP), indicating the substantial effect of benzoxazine ring content on flammability and char formation. Furthermore, it was found that poly(BAPNCP) gave the best thermal stability and flame retardancy, which was due to the synergistic effect between naphthalene group and benzoxazine ring content. This study provides new insight into the curing behavior of benzoxazine and further understanding on the high performance of polybenzoxazine.     

Solution Crystallization Behavior of Linear and Star-shaped Poly(ethylene glycol)-b-Poly(ε-caprolactone) Block Copolymers简

Lamellar crystals of diblock, triblock and four-arm poly（ethylene glycol）-b-poly（ε-caprolactone） （PEG-b-PCL） crystalline-crystalline copolymers were successfully obtained from their solution. Morphology and structure of lamellar crystals of crystalline-crystalline copotymers were investigated using tapping-mode atomic force microscopy （AFM） and selected area electron diffraction （SAED）. All of these samples showed the truncated-lozenge multilayer basal shapes with central screw dislocation or central stack, which were all obtained simultaneously from the oil bath. The diffraction pattern of PEG block lamellar crystal is attributed to the （120） diffracting planes and the pattern of PCL block lamellar crystal is attributed to the （1 I0） diffracting planes and （200） diffracting planes according to the SAED results. Four （110） crystal growth planes and two （200） crystal growth planes are discovered for the PCL blocks, but the （120） crystal growth planes of PEG blocks are hided in the figure of AFM. The crystalline structure of the four-arm copolymers （FA） is more disorder and confused than that of the diblock （DI） copolymer and the striated fold surface structures of lamellar crystals of four-arm copolymers （FA） are smoother than these of linear analogues, owing to the confused crystallization of blocks caused by the mutual restriction of blocks and the hindrance of the dendritic cores. In addition, the aspect ratio of FA is greater than that of the others. It is hypothesized that there are two reasons for the change of aspect ratios. First, the （200） diffracting planes of PCL crystals grew slowly compared to their （110） diffracting planes because of difference in the energy barrier. Secondly, edge dislocations on the （200） diffracting planes are also responsible for the variation of the aspect ratio. Consequently, the crystalline defects are augmented by the competing blocks crystallized simultaneously and the hindrance of the dendritic cores.     

A real-time AFM study on crystal nucleation and growth in nanodroplets of isotactic polypropylene

Isotactic polypropylene (iPP) nanodroplets were prepared by using the classical droplet method in this study. The formation of nanodroplets allowed the controlled observation of polymer nucleation as well as access to crystal growth at exceptionally high supercooling in iPP. Three cases including the heterogeneous nucleation and fast crystallization in iPP droplets, the formation of multiple independent homogeneous nuclei within a single droplet and a single nucleus within a single droplet were detected by using atomic force microscopy (AFM) during gradually cooling after remelting the nanodroplets. Moreover, it is found that when the volume of droplet is larger than the value of ca. 130000 nm3, the first case was observed. Otherwise, the latter two cases appeared. The temperature at which the onset of nucleation was observed in individual droplets was found to be mainly dependent on height of the droplets when the size scale of the droplet is comparable to the size of the critical nucleus in at least one dimension, which indicates the nucleation behavior under confinement.     

Synthesis and Crystal Structure of a B-H Activated Compound Containing a Furan Ring and an ortho-Carborane Cage

A new compound [CpCo（Se2C2BIoH9）CH2C（O）C4H30] has been synthesized and characterized by elemental analysis, IR spectroscopy, NMR, MS and single-crystal X-ray diffraction. The complex crystallizes in the monoclinic system, space group P21/c with a = 10.9481（10）, b = 24.6600（12）, c = 25.7430（14） A, β = 100.863（3）°, C42H57B30Co306Se6＂CH2C12＂0.25H20, Mr = 1722.16, V = 6825.6（8） A3, Dc= 1.676 g/cm3, Z = 1 and F（000） = 3346. The molecular structure shows a 1：1 ratio product of the two reactants of 16e half-sandwich complex CpCo（Se2C2B10H10） and alkyne 1-（2-furyl）-2-propyn-l-one. The hydrogen atom in the B（3） position of CpCo（Se2C2B10HIo） has been activated and migrated to the terminal carbon of 1-（2-furyl）- 2-propyn-l-one to form the B-CH2 unit. The title compound molecules are linked and extended further into a one-dimensional chain through atypical hydrogen bonds.     

Synthesis,Characterization, and Crystal Structure of One Novel Indolo[3,2-b]carbazole Derivative

Indolocarbazole derivatives have been reported to be promising organic semicon- ductor candidates and electroluminescent （EL） materials. One novel indolocarbazole derivative, 2,8-acetyl-5,11-dihexyl-6,12-（di-p-tolyl）-5,11-indolo[3,2-b]carbazole （YK4）, has been synthesized, and its crystal structure has also been carefully studied. YK4 is triclinic, space groups Pi with a = 9.409（5）, b = 13.974（5）, c = 15.488（5） A, α = 90.281（5）, β = 105.456（5）, Z= 93.728（5）°, M,. = 688.94, V= 1958.1（14） A3, Z = 2, Dc.= 1.168 g/cm-3,μ = 0.070 mm-1, F（000） = 740, Rint = 0.0475, R （I〉 20（/）） = 0.1146, wR （I〉 20（/）） = 0.2186, R（all data） = 0.2192 and wR （all data） = 0.2701. Like other indolo[3, 2-b]carbazole derivatives which were introduced in the 5- and 11-positions, the intermolecular short contacts are localized between the pendant groups and acetyl groups of the neighboring indolocarbazole molecules. The molecule of YK4 possesses poor face-to-face π-π stacking between two adjacent molecules in the crystal. The calculated bond lengths and bond angles of YK4 also proved the result of crystallography.     

A transflective and viewing angle controllable blue-phase liquid crystal display

A polymer-stabilised blue-phase liquid crystal display (PSBP-LCD) with double-side in-plane switching (DS-IPS) electrode structure is proposed. This structure shows the transflective characteristics because the bottom electrodes are made by aluminium material. For transflective displays, it exhibits a well-matched voltage-dependent transmission and reflection curves through designing the width and gap of the top electrodes. When a bias voltage is applied on the top electrodes, it exhibits as a good viewing angle controllable display.     

The optimal cell gap determination of a liquid crystal wavefront corrector from a single photoelectric measurement

It has been a crucial technique to improve the dynamic response characteristics of a liquid crystal wavefront corrector (LCWFC) with optimal cell gap since the LCWFC needs at least 2π (or π) phase modulation in adaptive optics systems (AOSs). We have given a complete process for obtaining the optimal cell gap accurately from a single photoelectric measurement, which can be conducted with a liquid crystal (LC) cell of any known thickness. This method has been analysed theoretically and confirmed experimentally by using a wedge-shaped cell; the experimental results match very well with the theoretical analysis. The response time of an optimal gap cell can be a novel evaluation method of response performance of LC materials.     

Alignment of liquid crystals induced by a photopolymerized self‐assembled film

An alignment film derived from a photopolymerized self‐assembled film may be used to orient nematic liquid crystals after irradiating the film with linearly polarized UV (LPUV). A photosensitive cationic amphiphile was first synthesized containing two double bonds and which could be polymerized by UV. A layer‐by‐layer self‐assembled multilayer film was next prepared in an aqueous solution of the cationic amphiphile and poly(sodium 4‐styrenesulphonate); the UV‐Vis spectra showed that each layer of the LBL multilayer film was uniform. When the film was irradiated by LPUV, the photosensitive double bonds underwent [2+2] cycloaddition along the vector direction of LPUV. The polarized UV‐Vis absorption spectra also provided evidence that the film was anisotropic, i.e. the photopolymerization was along a certain direction. The anisotropic film was used as an alignment layer for nematic liquid crystals, and observations under a polarizing microscope indicated that the alignment of the liquid crystals was good, as expected, and that the orientation direction of the liquid crystals was always perpendicular to the electric vector of the irradiating LPUV.     

Surface Performance and Cytocompatibility Evaluation of Acrylic Acid-Mediated Carboxymethyl Chitosan Coating on Poly(tetrafluoroethylene-co-hexafluoropropylene)

To improve the biocompatibility of poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film, a technique based on Ar plasma pretreatment and UV-induced grafting polymerization was used to immobilize carboxymethyl chitosan (CMCS) on the FEP film surfaces. Initially Ar plasma was used to treat FEP film. Then, plasma treated FEP film was modified via UV-induced grafting polymerization with hydrophilic acrylic acid (AAc) monomer. The following immobilization of CMCS on the FEP-pAAc surface was carried out via an amidation reaction. The change of chemical composition and surface morphology of FEP film were characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM) and atomic force microscopy (AFM). Results of water contact angles measurement showed that the hydrophilicity of the surface has improved significantly after surface modification. Furthermore, methyl thiazolyl tetrazolium (MTT) assay and cell morphology analysis confirmed that mouse fibroblasts (L929 cells) attachment and proliferation were improved remarkably on the modified FEP surface. These results suggest that CMCS were successfully employed to surface engineering FEP film, and enhanced its cell biocompatibility. The approach presented here may be exploited for surface modification of biomaterials.     

The Effect of Albumin Fusion Patterns on the Production and Bioactivity of the Somatostatin-14 Fusion Protein in Pichia pastoris

Somatostatin is a natural inhibitor of growth hormone, and its analogues are clinically used for the therapy of acromegaly, gigantism, thyrotropinoma, and other carcinoid syndrome. However, natural somatostatin is limited for clinical usage because of its short half-life in vivo. Albumin fusion technology was used to construct long-acting fusion proteins, and Pichia pastoris was used as an expression system. Three fusion proteins, (somatostatin (SS)14)₂-human serum albumin (HSA), (SS14)₃-HSA, and HSA-(SS14)₃, were constructed with different fusion copies of somatostatin-14 and fusion orientations. The expression level of (SS14)₃-HSA and HSA-(SS14)₃ was much lower than (SS14)₂-HSA due to the additional fusion of the somatostatin-14 molecule. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry revealed that severe degradation occurred in the fermentation process. Similar to the standard of somatostatin-14, all three fusion proteins were able to inhibit growth hormone secretion in the blood, with (SS14)₂-HSA being the most effective one. On the whole, (SS14)₂-HSA was the most effective protein in both production level and bioactivity, and increasing the number of small protein copies fused to HSA may not be a suitable method to improve the protein bioactivity.