Rob Duchateau

Semi-aromatic polyesters by alternating ring-opening copolymerisation of styrene oxide and anhydrides

Ring-opening copolymerisation of styrene oxide with alicyclic anhydrides containing different ring strains (succinic anhydride, maleic anhydride, citraconic anhydride, cyclopropane-1,2-dicarboxylic acid anhydride, cyclopentane-1,2-dicarboxylic acid anhydride and phthalic anhydride) was performed applying metal salen and tetraphenyl porphyrin complexes where for (salen)MX, M = Cr, X = Cl (1), M = Al, X = Cl (2), M = Mn, X = Cl (3), M = Co, X = OAc (4) and salen = N,N-bis(3,5-di-tert-butylsalicylidene)-diimine and for porphyrin complex, M = Cr, X = Cl (5), M = Mn, X = Cl (6), M = Co, X = OAc (7). The chromium catalysts performed best and therefore 1 was chosen as the selected catalyst for further studies. Investigation of the effect of different cocatalysts on the copolymerisation of styrene oxide and phthalic anhydride revealed that phosphines and onium salt showed quite similar activities whereas N-heterocyclic based amines showed somewhat lower activity. 1H NMR and MALDI-ToF-MS spectra of the copolymers formed confirmed the alternating microstructures. Increasing the monomer to catalyst ratio resulted in the isomerisation of styrene oxide to phenyl ethanal. The aldehyde functions as a chain transfer agent influencing the molecular weight of the polymers. Copolymerisation of styrene oxide with anhydrides bearing a double bond in their structure, such as maleic anhydride and citraconic anhydride, was shown to be highly dependent on temperature, time, type of cocatalyst and solvent used in the copolymerisation reaction.

Polyethylene end functionalization using thia-Michael addition chemistry

Thiol end functionalized polyethylenes (PE-SH, Mn around 1000 g mol−1, Đ < 1.3) were used as nucleophiles in thia-Michael additions with different acrylic molecules. It was found that under commonly used practical conditions the addition to methacrylates was very difficult, whereas addition to acrylates was very efficient. First, block copolymers based on PE and poly(methyl methacrylate) (PMMA) were targeted by reaction of PE-SH with PMMA obtained by catalytic chain transfer polymerization (CCTP). The reaction however failed and detailed model experiments using butanethiol and a dimer of MMA showed that the solubilization temperature of PE-SH was an impediment to the success of the reaction. The lack of reactivity towards PMMA obtained by CCTP and methacrylate functions was advantageously used to react molecules containing both an acrylate and a methacrylate group in the presence of tributyl phosphine (PBu3) to produce methacrylate-type PE macromonomers. The presence of a hydroxyl function on 3-(acryloyloxy)-2-hydroxypropyl methacrylate induced side trans-esterification reactions catalyzed by PBu3. This was overcome by using the hydroxyl free 2-(acryloyloxy) ethyl methacrylate. With the latter, the desired PE macromonomer exhibited a functionality as high as 85%. Alternatively, 2-isocyanatoethyl methacrylate could also be reacted with PE-SH to produce a highly functionalized methacrylate type PE macromonomer (functionality 89%). Eventually, the efficiency of the thia-Michael addition of PE-SH onto poly(ethylene glycol) acrylate (PEG-acrylate) was used to synthesize the PE-b-PEG block copolymer.

Catalyst behaviour for 1-pentene and 4-methyl-1-pentene polymerisation for C2-, Cs- and C1-symmetric zirconocenes

1-Pentene and 4-methyl-1-pentene (4M1P) have been polymerised using several C2-symmetric ansa-zirconocene catalysts rac-X(2-R1,4-R2-Ind)2ZrCl2 [X = C2H4, R1 = R2 = H (1); X = SiMe2, R1 = R2 = H (2); X = SiMe2, R1 = Me, R2 = H (3); X = SiMe2, R1 = H, R2 = Ph (4); X = SiMe2, R1 = Me, R2 = Ph (5)] with MAO as cocatalyst. The effects of polymerisation conditions as well as substituents on the indenyl ligand were studied. Except for the poly-1-pentenes synthesized with 3 and 5 at low temperatures, low molecular weight isotactic polymers were generally obtained. Compared to their behaviour in propylene polymerisation, the relative activity and selectivity of catalysts 1–5 are considerably different for 1-pentene and 4M1P polymerisation. Of the five catalysts, 1 and 4 showed the highest activities for both 1-pentene and 4M1P polymerisation, while 5 resulted in the lowest activities, especially for 4M1P polymerisation. Subsequently, a Cs- and several C1-symmetric zirconocenes, (R1)2C(3-R2-Cp)(2,7,-R3-Flu)ZrCl2 (R1 = Me, R2 = R3 = H (6); R1 = R2 = Me, R3 = H (7); R1 = Me, R2 = t-Bu, R3 = H (8); R1 = Me, R2 = R3 = t-Bu (9); R1 = Ph, R2 = t-Bu, R3 = H (10); R1 = Ph, R2 = R3 = t-Bu (11), were tested in 1-pentene and 4M1P polymerisation with MAO as cocatalyst. The effect of substituents on the bridge, the cyclopentadienyl (Cp) and fluorenyl (Flu) ligand, was studied relative to the polymerisation temperature and type of monomer. The molecular weights of the polymers were considerably higher than those of the poly-1-pentenes and P4M1Ps obtained with C2-symmetric zirconocenes (1–5). The catalytic activities and polymer molecular weights strongly depend on the fluorenyl substituent and the bridge, while the type of substituent on the Cp ligand has a strong influence on the tacticity of the polymers.