Experimental evidence for trapped chain entanglements: their influence on macroscopic behaviour of networks

The swelling and elastic properties of poly(dimethyl siloxane) networks prepared by end-linking and subsequently swollen in heptane and toluene have been investigated as a function of the volume fraction, v_c, at which networks are generated. Increases in both swelling degree and shear modulus with v_c demonstrate the increase in number of trapped entanglements with v_c. The results may be described by a simple scaling law approach.     

Dynamisch-mechanische Analyse naturfaserverstärkter Kunststoffe

Dynamic-mechanical analysis of natural fiber reinforced plastics Recently natural fibers are increasingly used as reinforcement in plastics. These materials are distinguished by their high tensile strength and stiffness as well as their low density at the same time. For technical applications the material behaviour in addiction of temperature is very interesting. Useing the example of flax fiber reinforced polypropylen it is shown, that the dynamic-mechanical analysis can be a meaningful test to describe the behaviour of natural fiber composites by different temperatures.     

3-Trifloxypropene iminium and propyne iminium salts derived fromN-Allyl-,N-Homoallyl-, and N-benzyl-substituted semicyclic enaminones

The novel semicyclic enaminoketones 3a-n , featuring N-allyl, N-homoallyl, N-benzyl, and N-4-chlorobenzyl substitution, have been prepared. Their reaction with triflic anhydride leads to 3-trifloxypropene iminium triflates 4 which are transformed into semicyclic propyne iminium triflates 5 by thermal β-elimination of triflic acid (HOTf). If a 4-chlorophenyl group is attached to the TfO-substituted carbon atom, salts 4 can be isolated ( 4a,d,g,h,k,m ) and converted into propyne iminium triflates 5 at 120 °C. The presence of a 2-thienyl or 3-thienyl group adjacent to the trifloxy group prevents the isolation of 4 since HOTf elimination occurs already below room temperature. Thus, salts 5b,c,e,f,i,j,l,m,n are obtained directly from enaminoketones 3 and triflic anhydride     

Sex Pheromone of the Pine Sawfly, Gilpinia pallida: Chemical Identification, Synthesis, and Biological Activity

We present the identification of the sex pheromone in the pine sawfly, Gilpinia pallida, including analysis of the female pheromone content, male antennal response and attraction in the field, and synthesis of the most active pheromone component. Several 3,7-dimethyl-2-alkanols were identified from female whole-body extracts, including some compounds with a 2R configuration. This is the first observation of such compounds in a pine sawfly species. Antennae of male G. pallida responded strongly in electroantennograph (EAG) recordings to the (2S,3R,7R)-isomers of the propionates of 3,7-dimethyl-2-tridecanol, 3,7-dimethyl-2-tetradecanol, and 3,7-dimethyl-2-pentadecanol, as well as to the acetates of the tri- and pentadecanols (the acetate of the tetradecanol was not tested). The propionate of (2S,3R,7R)-3,7-dimethyl-2-tetradecanol caught more males in the field than the corresponding isomer of tri- or pentadecanol. We suggest that the (2S,3R,7R)-isomer of 3,7-dimethyl-2-tetradecanol is likely the main sex pheromone precursor in G. pallida, with a subsidiary role for the (2S,3R,7R)-isomer of the tridecanol. Preparation of highly pure (2R,3R,7R)- and (2S,3R,7R)-stereoisomers of 3,7-dimethyl-2-tetradecanol, including the biological active esters, was performed via chemoenzymatic methods and is described in detail.