The term “C₂-C₁₀ alkenyl” as used herein refers to an unsaturated straight or branched hydrocarbon group with 2 to 10 carbon atoms having one free valence. Unsaturated means that the alkenyl group contains at least one C—C double bond. C₂-C₁₀ alkenyl includes for example ethenyl, 1-propenyl, 2-propenyl, 1-n-butenyl, 2-n-butenyl, iso-butenyl, 1-pentenyl, 1-hexenyl, and the like. Preferred are C₂-C₆ alkenyl groups, more preferred are C₂-C₄ alkenyl groups, most preferred are ethenyl and propenyl, in particular 1-propen-3-yl, also called allyl.

The term “C₂ to C₁₀ alkynyl” as used herein refers to an unsaturated straight or branched hydrocarbon group with 2 to 10 carbon atoms having one free valence, wherein the hydrocarbon group contains at least one C—C triple bond. C₂-C₁₀ alkynyl includes for example ethynyl, propynyl, 1-n-butinyl, 2-n-butynyl, iso-butinyl, 1-pentynyl, 1-hexynyl, and the like. Preferred are C₂-C₆ alkynyl, more preferred are C₂-C₄ alkynyl, e.g ethynyl, 1-propyn-3-yl (CCCH₃, also called propargyl) and but-2-yn-1-yl (CH₂CCCH₃).

According to one embodiment at least one R is selected from C₁ to C₁₀ alkyl, preferably C₁ to C₆ alkyl, and more preferred C₁ to C₄ alkyl wherein the alkyl may be substituted by one or more additional substituents selected from F and CN, preferably the alkyl is substituted by F. Examples are from methyl, ethyl, n-propyl, i-propyl, n-butyl, 2-methyl propyl, and t-butyl, which may be substituted by one or more additional substituents selected from F and CN like trifluoromethyl, CF₃CH₂, and CF₃CF₂.