V. Van Speybroeck

The relative importance of head-to-head versus head-to-tail addi-tions during the free-radical polymerization of vinyl chloride isdetermined by ab initio methods for different chain lengths ofthe polymer. First, a level of theory study is performed to deter-mine cost-effective methods for the ab initio description of thepropagation kinetics of vinyl chloride. The study includes the fol-lowing DFT-based methods: B3LYP, B3PW91, BHandH, BHandH-LYP, BLYP, BP86, MPW1K and MPW1PW91, in combination withdouble or triple zeta basis sets 6-31G(d) and 6-311GACHTUNGTRENNUNG(d,p). Also,the more recently developed BMK and MPW1K functionals are in-cluded. The influence of diffuse functions is tested by comparisonwith the basis sets 6-31+G(d) and 6-311++GACHTUNGTRENNUNG(3df,2p). The best-performing methods are B3LYP, B3PW91 and MPW1K combinedwith the 6-31+G(d) basis set. The converged probability of head-to-head propagation (2 per 1000 monomer units) is put into rela-tion with the experimental concentrations of defect structures. Acomparison is made with the head-to-head (HH) content of fluo-rine-substituted polymers and poly(vinyl acetate). The ab initiocalculations correctly predict the relative sequence of HH contentamong the various polymers.

An efficient conversion of biorenewable ferulic acid into bio‐catechol has been developed. The transformation comprises two consecutive defunctionalizations of the substrate, that is, C−O (demethylation) and C−C (de‐2‐carboxyvinylation) bond cleavage, occurring in one step. The process only requires heating of ferulic acid with HCl (or H2SO4) as catalyst in pressurized hot water (250 °C, 50 bar N2). The versatility is shown on a variety of other (biorenewable) substrates yielding up to 84 % di‐ (catechol, resorcinol, hydroquinone) and trihydroxybenzenes (pyrogallol, hydroxyquinol), in most cases just requiring simple extraction as work‐up.

A systematic molecular level and spectroscopic investigation is presented to show the cooperative role of Brønsted acid and Lewis acid sites in zeolites for the conversion of methanol. Extra-framework alkaline-earth metal containing species and aluminum species decrease the number of Brønsted acid sites, as protonated metal clusters are formed. A combined experimental and theoretical effort shows that postsynthetically modified ZSM-5 zeolites, by incorporation of extra-framework alkaline-earth metals or by demetalation with dealuminating agents, contain both mononuclear [MOH]+ and double protonated binuclear metal clusters [M(μ-OH)2M]2+ (M = Mg, Ca, Sr, Ba, and HOAl). The metal in the extra-framework clusters has a Lewis acid character, which is confirmed experimentally and theoretically by IR spectra of adsorbed pyridine. The strength of the Lewis acid sites (Mg > Ca > Sr > Ba) was characterized by a blue shift of characteristic IR peaks, thus offering a tool to sample Lewis acidity experimentally. The incorporation of extra-framework Lewis acid sites has a substantial influence on the reactivity of propene and benzene methylations. Alkaline-earth Lewis acid sites yield increased benzene methylation barriers and destabilization of typical aromatic intermediates, whereas propene methylation routes are less affected. The effect on the catalytic function is especially induced by the double protonated binuclear species. Overall, the extra-framework metal clusters have a dual effect on the catalytic function. By reducing the number of Brønsted acid sites and suppressing typical catalytic reactions in which aromatics are involved, an optimal propene selectivity and increased lifetime for methanol conversion over zeolites is obtained. The combined experimental and theoretical approach gives a unique insight into the nature of the supramolecular zeolite catalyst for methanol conversion which can be meticulously tuned by subtle interplay of Brønsted and Lewis acid sites.