Under special crystallization conditions from the melt, both ␣-and ␤-forms of isotactic polypropylene were produced simultaneously. The ␣-and ␤-spherulites of polypropylene were differentiated under optical microscope, allowing the nanoindentation of individual spherulites of each crystallographic form. Elastic modulus and hardness of ␤-spherulites were found to be 10 and 15% respectively lower than in ␣-spherulites. The higher stiffness of ␣ may be related to the particular interlocked structure with cross-hatched lamellae, and to a lower molecular mobility in the crystallites.

International audienceIn order to improve the fire behavior of unsatd. polyester resins (UPR) a phosphorus contg. monomer, dimethyl-vinylbenzyl phosphonate (or S1), was used to replace a part of the reactive diluent (styrene). UPR with various phosphorus contents were prepd. Thermal degrdn. was studied using thermogravimetric anal. (TGA) and pyrolysis combustion flow microcalorimeter (PCFC), while fire behavior was investigated by cone calorimeter. The phosphorus yield in the residue was detd. using energy-dispersive X-ray (EDX).TGA pointed out a decrease in thermal stability with increasing S1 content but also an important increase in char formation. Cone calorimetry highlighted pHRR decrease, and from 50% of styrene substitution a barrier effect was evidenced. Residue anal. enabled to det. the partition of phosphorus between vapor and condensed phase. It was shown that this partition depends on the degree of styrene substitution. At high S1 content, interactions between phosphonate groups enable a very efficient condensed phase action by creation of a charred protective barrier. This strategy was also successfully transposed to a vinyl ester resin (VER)

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