Synthesis,kinetic study,and application of Ti[O(CH2)4OCHCH2]4 in ring‐opening polymerization of ε‐caprolactone and radical polymerization

Ti[O(CH₂)₄OCH?CH₂]₄, used for the ring‐opening polymerization (ROP) of ε‐caprolactone, was synthesized through the ester‐exchange reaction of titanium n‐propoxide and 1,4‐butanediol vinyl ether, and its chemical structure was confirmed by nuclear magnetic resonance (¹H NMR) and thermogravimetric analysis (TGA). The mechanism and kinetics of Ti[O(CH₂)₄OCH?CH₂]₄‐initiated bulk polymerization of ε‐caprolactone were investigated. The results demonstrate that Ti[O (CH₂)₄OCH?CH₂]₄‐initiated polymerization of ε‐caprolactone proceeds through the coordination‐insertion mechanism, and all the four alkoxide arms in Ti[O (CH₂)₄OCH?CH₂]₄ share a similar activity in initiating ROP of ε‐caprolactone. The polymerization process can be well predicted by the obtained kinetic parameters, and the activation energy is 106 KJ/mol. Then, the rheological method was employed to investigate the feasibility of producing the crosslinked poly(ε‐caprolactone)‐poly (n‐butyl acrylate) network by using Ti[O(CH₂)₄OCH?CH₂]₄ as the ROP initiator. The tensile test demonstrates that the in situ generated crosslinked PCL‐PBA network in PMMA matrix provides the possibility of ameliorating the tensile properties of PMMA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7773–7784, 2008     

The dynamics of transition layers in solids with discontinuous chemical potentials

We derive a two‐phase segregation model in solids under isothermal conditions where due to plastic effects the number of vacancies changes when crossing a transition layer, i.e. a reconstitutive phase transition. We show the thermodynamic correctness of the model and review the existence of weak solutions in suitable spaces. By a formal asymptotic analysis we study the dynamics of the interface and its dependence on the unsymmetric vacancy distribution. Copyright © 2006 John Wiley & Sons, Ltd.     

Heavy ion induced cluster formation and fragmentation phenomena in amorphous graphite

A study has been conducted into the mechanisms of evolution of clusters and their subsequent fragmentation under energetic heavy ion bombardment of amorphous graphite. The evolving clusters and their subsequent fragmentation under continuing ion bombardment are revealed by detecting various clusters in the energy spectra of the Direct Recoils (DRs) emitted as a result of collisions between ions and surface constituents. The successive DR spectra reveal that the energetics of bond formation as well as any subsequent fragmentation can be related to the processes of energy dissipation in a cylindrical volume of a few ? surrounding the ion path. The dependence of formation or fragmentation is seen to be a function of the ionic stopping powers in this cylindrical volume. Received: 2 January 1998 / Accepted: 5 March 1998     

Rheological behavior of polypropylene/octavinyl polyhedral oligomeric silsesquioxane composites

The reactive blending composites of isotactic polypropylene (PP)/octavinyl polyhedral oligomeric silsesquioxane (POSS) were prepared in the presence of dicumyl peroxide. Comparison of the rheological behavior of physical and reactive blending composites was made by oscillatory rheological measurements. It was found that the viscosity of physical blending composites drops at lower POSS content (0.5–1 wt %) and thereafter increases with increasing POSS content; that of reactive blending composites increases with increasing POSS content and displays a solid‐like rheological behavior at low frequency region when POSS content is higher than 1 wt %. The deviation of reactive blending composites from the scaling log G′–log G″ of linear polymer in Han plot, upturning at high viscosity in Cole–Cole plot, and from van Gurp–Palmen plot are related to the gelation behavior reactively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 526–533, 2008     

Polypropylene/polystyrene blends: In situ compatibilization by Friedel‐Crafts alkylation reaction

The application of Friedel‐Crafts alkylation reaction to the compatibilization of polypropylene (PP)/polystyrene (PS) blends was assessed. A PP macrocarbocation is chemically bonded to the PS benzene ring by aromatic electrophilic substitution. The graft copolymer formed at the interphase (PP‐g‐PS) showed relatively high emulsification strength, suggesting an effective behavior as in situ compatibilizer. The critical micelle concentration (CMC) was related to Friedel‐Crafts catalyst concentration. The amount of PS grafting and possible appearance of crosslinking and chain scission side reactions were also analyzed. The reaction products were characterized by a combination of size exclusion chromatography and Fourier transform infrared techniques applied after a careful solvent extraction separation. It was found, from the emulsification curve, that CMC was achieved when 0.7 wt % AlCl₃ was added. This value was confirmed by scanning electron microscopy observation of phase adhesion on fractured sample surfaces. Mass balances of extracted PS showed that at least 15 wt % of the initial PS resulted grafted at the CMC condition. Chain scission reactions, in parallel with grafting, were verified to occur for PP as well as for PS. Instead, crosslinking reactions were not detected. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 452–462, 2004     

Supertoughness and critical interparticle distance dependence in poly(butylene terephthalate) and poly(ethylene‐co‐glycidyl methacrylate) blends

Supertough poly(butylene terephthalate) (PBT)‐based blends were obtained by the melt blending of PBT with 0–30 wt % poly(ethylene‐co‐glycidyl methacrylate) (EGMA). The reaction between PBT and EGMA was detected by torque measurements. The particle size was almost constant with increasing EGMA content, and this indicated that compatibilization occurred. The minimum EGMA content for achieving supertoughness (i.e., an impact strength 16 times greater than that of PBT) was 20 wt %. The interparticle distance was the parameter controlling toughness in these PBT/EGMA blends. The dependence of the critical interparticle distance (τ_c) on the modulus of the dispersed phase appeared only at low τ_c values, and the primary dependence of τ_c on the ratio of the modulus of the matrix to the modulus of the rubbery dispersed phase was proposed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2236–2247, 2003