Convenient Method for the Reduction of the Double-Bond of Cyclic Vinylphosphine Oxides Using Borane

The electronpoor double-bond of cyclic vinylphosphine oxides (1, 3 and 4) is easily reduced by borane in a selective manner to give the corresponding saturated derivatives (2, 4 and 5, respectively) Under forcing conditions, change of the functionality may also take place.     

Solvent‐dependent formation of inclusion complexes between methylated cyclodextrins and biodegradable polymers

The inclusion complexes (ICs) of unmodified natural and methylated α‐cyclodextrins (CDs) with biodegradable polymers, polyethylene glycol and poly(ε‐caprolactone), were prepared by two methods, that is, the one using water and the other using chloroform as the solvent for the respective CDs. The ICs obtained were characterized by IR, WAXD, DSC, and ¹³C CP/MAS NMR. It was found that the possibility and the phenomena of IC formation could be varied with the degree of methyl substitution of CD as well as the type of solvents used. Methylated α‐CDs showed the prominent characteristics of IC formation with polymers in the case where chloroform was used than in the case where water was used as the solvent for CDs, while vice versa in the case of native α‐CD. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 879–891, 2008     

Adiabatic representation for a hydrogen atom photoionization in a uniform magnetic field

A new effective method of calculating wave functions of discrete and continuous spectra of a hydrogen atom in a strong magnetic field is developed on the basis of the adiabatic approach to parametric eigenvalue problems in spherical coordinates. The two-dimensional spectral problem for the Schrödinger equation at a fixed magnetic quantum number and parity is reduced to a spectral parametric problem for a one-dimensional angular equation and a finite set of ordinary second-order radial differential equations. The results are in good agreement with the photoionization calculations by other authors and have a true threshold behavior.     

Competitive [4 + 2] cycloadditions in equimolar mixtures of 1‐arylphosphole oxides

Four different [4 + 2] cycloadditions were observed to take place in the equimolar mixtures of two different arylphosphole oxides 2a + 2b or 2b + 2c . In addition to the phosphole oxide dimers 3a‐a and 3b‐b , or 3b‐b and 3c‐c , the crossed cycloadducts 3a‐b and 3b‐a , or 3b‐c and 3c‐b were also formed in considerable portions. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:633–635, 2001     

Fabrication of Compositional‐Gradient Biodegradable Polymeric Films Showing Self‐Bending Deformation

A compositional graded film of poly(ε‐caprolactone) (PCL) with 4,4′‐thiodiphenol (TDP), in the film thickness direction, was fabricated by self‐diffusing of TDP in the PCL melt. We found out the self‐bending deformation of the gradient film, which bent into a rolled‐up shape by itself. The initial shape of the film was flat when the sample was quenched from the melt. Upon the fast crystallization of PCL, the gradient film bent to the side with low TDP content. Then, after PCL crystallized the film bent to the opposite direction, that is, to the side with high TDP content. This bending to the TDP rich region was induced by not only the crystallization of PCL but also mass transfer due to the diffusion of TDP from TDP rich region to poor region.

     

Effect of Comonomer‐Unit Compositional Distribution on Thermal and Crystallization Behavior of Bacterial Poly[(3‐hydroxybutyrate)‐co‐(3‐mercaptopropionate)]

The physical properties of novel sulfur‐containing biopolymers, poly[(3‐hydroxybutyrate)‐co‐(3‐mercaptopropionate)]s [P(3HB‐co‐3MP)s], have been investigated in detail by¹H and ¹³C NMR spectroscopy, wide‐angle X‐ray diffraction (WAXD) analysis, DSC, and FT‐IR spectroscopy. Based on a solvent/non‐solvent (chloroform/heptane) fractionation method, an original P(3HB‐co‐3MP) sample with 3MP unit content of 16.3 mol‐% was fractionated into eight fractions with 3MP unit content ranging from 10.3 to 37.2 mol‐% and number‐average molecular weight from 0.4 × 10⁵ to 2.9 × 10⁵. The thermal and crystallization behavior were found to be greatly affected by the comonomer‐unit composition and its distribution. Furthermore, the 3MP comonomer unit was found to be included in the crystalline phase in some fractions.

     

Quantum Transparency of Barriers and Reflection from Wells for Clusters of Identical Particles

A method for solving the problem of quantum transmission through potential barriers or potential wells for a compound system consisting of several identical particles coupled via pair oscillator-type potentials in the oscillator representation of the symmetrized coordinates is considered. The efficiency of the proposed approach, algorithms and programs is demonstrated by the examples of calculation of complex energy values and analysis of metastable states of compound systems of two, three, and four identical particles on a straight line, which lead to the effect of quantum transparency of the potential barriers or quantum reflection from the wells.     

Fast Crystallization and Toughening of Poly(<Emphasis Type="Italic">L</Emphasis>-lactic acid) by Incorporating with Poly(ethylene glycol) as a Middle Block Chain

High molecular weight poly(L-lactic acid)-poly(ethylene glycol)-poly(L-lactic acid) (PLLA–PEG–PLLA; PLGL) triblock copolymers with various lengths of the PLLA blocks were synthesized by ringopening polymerization of L-lactide. The amorphous and crystalline PLLA and PLGL films were prepared by hot pressing with different temperature treatments. PLLA and PEG blocks exhibited good miscibility in the amorphous PLGL samples, while phase separation occurred in the crystalline ones. The flexible PEG blocks not only accelerated the crystallization rate of PLLA but also greatly improve its flexibility. The crystallization time of PLGL copolymers shorten to less than 5 min and copolymers showed much better flexibility than neat PLLA, the maximum fracture strain reached about 600% for amorphous sample. The processing time of PLLA was greatly shortened and the brittleness of material was improved.     

Temperature‐dependent polymorphic crystalline structure and melting behavior of poly(butylene adipate) investigated by time‐resolved FTIR spectroscopy

The polymorphic crystalline structure and melting behavior of biodegradable poly(butylene adipate) (PBA) samples melt‐crystallized at different crystallization temperatures were studied by differential scanning calorimetry (DSC) and fourier transform infrared (FTIR) spectroscopy. The crystalline structure and melting behavior of PBA were found to be greatly dependent on the crystallization temperature. By comparison of the FTIR spectra and the corresponding second derivatives between the α‐ and β‐crystal of PBA, the spectral differences were identified for the IR bands appeared at 1485, 1271, 1183, and 930 cm^?1 and the possible reasons were presented. Especially, the 930 cm^?1 band was found to be a characteristic band for the β‐crystal. Combining the DSC data with the analysis of normalized intensity changes of several main IR bands during the melting process, the melting behaviors of the α‐ and β‐crystal were clarified in detail. It is demonstrated by the in situ IR measurement that the β‐crystalline phase would transform into the α‐crystalline phase during the melting process, and the solid–solid phase transition from the β‐ to α‐crystal was well elucidated by comparing the intensity changes of the 1170 and 930 cm^?1 bands. The dependence of the β‐ to α‐crystal phase transition on the heating rate was revealed by monitoring the intensity ratio of the 909 and 930 cm^?1 band. It was suggested that at the heating rate of 0.5 or 1 °C/min, the percent amount of the transformed α‐crystal from the β‐crystal was much higher than that at the higher heating rate. The β‐crystal transforms into the α‐crystal incompletely at the higher heating rate because of the less time available for the phase transition. In addition, the β‐ to α‐crystal phase transition was further confirmed by the IR band shifts during the melting process. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1997–2007, 2009