Polymerization of Norbornene with CoCl2 and Pyridine Bisimine Cobalt(II) Complexes Activated with MAO

Addition polymerization of norbornene was performed with several pyridine bis(imine) cobalt dichloride complexes activated with methylaluminoxane (MAO), first described for ethylene polymerization. For the first time, norbornene was also polymerized with CoCl₂ associated to MAO. The influence of several reaction parameters has been investigated. Quite different behavior was observed compared with ethylene polymerization. Moreover, the copolymerization of ethylene and norbornene with these complexes was not possible but led to a mixture of both homopolymers.

The pyridine bis(imine) cobalt dichloride complexes used in this study.     

Protection and Labelling of Thymidine by a Fluorescent Photolabile Group

A fluorescent photolabile group including coumarin and MeNPOC moieties was synthesized to protect 5′‐OH terminal function of thymidine (T). Its photochemical and photophysical properties were studied, in particular the photocleavage (photodeprotection under a 365‐nm irradiation) is only lowered by a factor of two by addition of the fluorophore. Fluorescence properties of the coumarin probe are not changed upon irradiation, which is satisfactory for the application required, i.e., in situ synthesis of DNA microarrays.     

A calorimetric comparative study of hydrogenated and deuterated diacetylene 2,4 hexadiynylene bis(p-toluenesulfonate): Phase diagrams and polymerization

Microcalorimetry was used to study the thermal polymerization and the structural instabilities in hydrogenated (pTS-H) and deuterated (pTS-D) diacetylene 2,4-hexadiynylene bis(p-toluenesulfonate). In the induction period, the polymerization reaction proceeds about seven times faster in pTS-D than in pTS-H. Whereas the phase transitions of pure pTS-H and pTS-D monomer crystals and of pure pTS-H and pTS-D polymer crystals are very similar, the situation is completely different for mixed monomer-polymer crystals of pTS-H and pTS-D. The results are interpreted by studying comparative influence of the chain lengths for pTS-H and pTS-D oligomers. A comparison is made between these results and previous experimental results obtained from dielectric measurements, UV-spectroscopy, X-ray, and elastic neutron scattering. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 789–798, 1997     

Generation of Helical States – Breaking of Symmetries,Curie's Principle,and Excited States**

Herein, we deeply detail for the very first time mathematical concepts behind the generation of helical molecular orbitals (MOs) for linear chains of atoms. We first give a definition of helical MOs and we provide an index measuring how far a given helical states is from a perfect helical distribution. Structural properties of helical distribution for twisted -cumulene and cumulene version of Möbius systems are given. We then give some simple structural assumptions as well as symmetry requirements ensuring the existence of helical MOs. Considering molecules which do not admit helical MOs, we provide a first way to induce helical states by the breaking of symmetries. We also explore an alternative way using excited conformations of given molecules as well as different electronic multiplicities.     

Polymerization of norbornene with Co(II) complexes

The norbornene polymerization was studied in the presence of 6 pyridine bis(imine) cobalt(II) complexes activated with methylaluminoxane (MAO). Norbornene was also polymerized with CoCl₂ associated to MAO. All these catalytic systems generate an addition polymerization of norbornene, yielding fully saturated polymers. It was shown that the polymerization yield and the molar masses are highly dependant on several reaction parameters (monomer concentration, [Al]/[Co] ratio, polymerization temperature and time) and the frame of the ligand.     

New Star‐Shaped Metallo‐Polymeric Chromophores

The synthesis of new star‐shaped polymers, prepared by atom transfer radical polymerization of methyl methacrylate with tris(dialkylaminostyryl‐2,2′‐bipyridine) zinc(II) and iron(II) metalloinitiators, is reported. Their thermal and optical (absorption and emission) properties are discussed.

Structure of the star‐shaped polymers.