Xiayu Wang

Synthesis of Star‐Shaped Poly(ϵ‐caprolactone)‐b‐Poly(styrene) Block Copolymer by Combining Ring‐Opening Polymerization and Atom Transfer Radical Polymerization

Newly designed star‐shaped block copolymers made of poly(ϵ‐caprolactone) (PCL) and polystyrene (PS) were synthesized by combining ring‐opening polymerization (ROP) of ϵ‐caprolactone (CL) and atom transfer radical polymerization (ATRP) of styrene (St). The switch from the first to the second mechanism was obtained by selective transformation of “living” radical sites. First, tri‐ and tetrafunctional initiators were used as an initiator for the “living” ring opening polymerization (ROP) of ϵ‐caprolactone producing a hydroxyl terminated three or four arm star‐shaped polymer. Next, the OH end groups of PCL star branches were derivatized into 2‐bromoisobutyrate groups which gave rise to the corresponding tri‐ and tetrabromoester ended‐PCL stars; the latter served as macroinitiators for the ATRP of styrene at 110°C in the presence of CuBr/2,2‐bipyridine (Bipy) catalyst system affording star‐shaped block copolymers PCLn‐b‐PSn (n=3 or 4). The samples obtained were characterizated by 1H‐NMR spectroscopy and GPC (gel permeation chromatograph). These copolymers exhibited the expected structure. The crystallization of star‐shaped block copolymers was studied by DSC (differential scanning calorimetry). The results show that when the content of the PS block increased, the Tm of the star‐shaped block copolymer decreased.

Morphological features and orientational relaxation of films obtained from a liquid crystalline polyester

Abstract Oriented films of an aromatic liquid crystalline polyester obtained from the melt in the mesomorphic state were studied by wide-angle X-ray diffraction, WAXD, polarized light microscopy and infra-red dichroism. The mat structure of the resolidified polymer was found to be in a supercooled liquid crystalline state, not in the crystalline state as in the case of cast films of lyotropic aromatic polyamides. A general picture describing the morphological features of the oriented films at different size levels is depicted. The relaxation of molecular orientation in the mesomorphic state was very slow, and rapid relaxation was only observed near the clearing point.

Studies on the Properties of a New Hybrid Materials Containing Hyperbranched Polymer and SiO2‐TiO2 Networks

EP/SiO2‐TiO2 hybrid materials, which contained hyperbranched polymers (HBPs) chain‐extended urea, were prepared through a sol‐gel process of triethoxylsilyl functionalized HBPs, i.e., chain‐extended urea—H20‐Si(OC2H5), Tetraethoxysilane (TEOS) and tetrabutyltitanate (TBT) using HCl as catalyst. The H20‐Si(OC2H5)3 was obtained by endcapped H20 with tolylene 2,4‐diisocyanate (TDI), followed by a reaction with 3‐aminopropyltriethoxylsilane (WD‐50). The chemical structure of the products was confirmed by IR spectroscopy. The mechanical properties of composites such as, impact strength, tensile strength, dynamic mechanical thermal properties were investigated. The results showed that the glass transition temperatures and the modulus of the modified systems were higher than that of the unmodified system, and the impact strength was enhanced by two times or that compared with the neat epoxy. The morphological structure of the impact fracture surface and the surface of the hybrid were observed by scanning electron microscope (SEM) and atomic force microscopy (AFM), respectively.

Study on Synthesis of Star‐Shaped Poly(ethylene oxide) by Atom Transfer Radical Polymerization

Star‐shaped poly(ethylene oxide) (PEO) was prepared by atom transfer radical polymerization (ATRP) with a 2‐bromoisobutyryl PEO ester as a macroinitiator. Divinylbenzene (DVB) and ethylene glycol dimethacrylate were employed as the coupling reagents. Several factors pertinent to star polymer formation are: type of coupling reagents and solvents, feed ratio of DVB to the macroinitiator, and reaction time. These were studied and used to optimize the star formation process. The optimum yield of star polymer was ca. 90–98%.