Lieven Van Renterghem

Design and Use of Organic Nanoparticles Prepared from Star-Shaped Polymers with Reactive End Groups

Star-shaped poly(isobornyl acrylate) (PiBA) was prepared by atom transfer radical polymerization (ATRP) using multifunctional initiators. The optimal ATRP conditions were determined to minimize star-star coupling and to preserve high end group functionality (>90%). Star-shaped PiBA with a narrow polydispersity index was synthesized with 4, 6, and 12 arms and of varying molecular weight (10,000 to 100,000 g x mol(-1)) using 4 equiv of a Cu(I)Br/PMDETA catalyst system in acetone. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis, NMR spectroscopy, and size exclusion chromatography (SEC) confirmed their controlled synthesis. The bromine end group of each arm was then transformed to a reactive end group by a nucleophilic substitution with methacrylic acid or cinnamic acid (conversion >90%). These reactive star polymers were used to prepare PiBA nanoparticles by intramolecular polymerization of the end groups. The successful preparation of this new type of organic nanoparticles on a multigram scale was proven by NMR spectroscopy and SEC. Subsequently, they have been used as additives for linear, rubbery poly(n-butyl acrylate). Rheology measurements indicated that the viscoelastic properties of the resulting materials can be fine-tuned by changing the amount of incorporated nanoparticles (1-20 wt %), as a result of the entanglements between the nanoparticles and the linear polymers.

Preparation of star block co-polymers by combination of cationic ring opening polymerization and atom transfer radical polymerization

The synthesis of star block co-polymers with polytetrahydrofuran (PTHF) core and poly(tert-butyl acrylate) (PtBA) shell was performed using a dual initiator, 4-hydroxy butyl bromoisobutyrate, by combination of cationic ring-opening polymerization (CROP) and atom transfer radical polymerization (ATRP). The in situ reaction of the hydroxyl groups originating from the dual initiator with trifluoromethane sulfonic anhydride provides a triflate ester initiating group for the CROP of THF. PTHF star polymers having three arms with tertiary bromide end groups (PTHF)3 have been prepared by reaction of living PTHF chains with tris(2-aminoethyl)amine (TAEA) in the presence of 2,2,6,6-tetramethylpiperidine (TMP) as a proton trap. Subsequently, the star polymers were used as macroinitiators for the ATRP of tBA using the CuBr/N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) catalyst system to obtain the tri-armed star block co-polymers (PTHF-b-PtBA)3. The polymers were characterized with gel-permeation chromatography (GPC) and1H-NMR. Both techniques demonstrated the formation of tri-armed star block co-polymers.

From Novel Block-Like Copolymers to Reactive Nanoparticles: ATRP and “Click” Chemistry as Synthetic Tools

In this chapter, we report on the synthesis and characterization of well-defined amphiphilic block copolymers, ‘block-like’ copolymers and star copolymers composed of poly(isobornyl acrylate) (PiBA) and poly(acrylic acid) (PAA) by ATRP. As PiBA polymers exhibit interesting physical characteristics, we report first a detailed study of the homopolymerization of iBA. The precursor monomers 1-ethoxyethyl acrylate as well as tert-butyl acrylate have been used to synthesize the precursor polymers for the PiBA-co-PAA block copolymers. Furthermore, a combination of ATRP and ‘click’ chemistry was used to prepare block and graft copolymers using a modular approach. The PiBA-PAA block and ‘block-like’ copolymers were investigated as pigment stabilizers for aqueous pigment dispersions. In the second part of the research, well-defined PiBA star copolymers were prepared, and reactive nanoparticles were obtained by end group modification of the PiBA star polymers with reactive moieties. Finally, the control of the visco-elastic properties by the incorporation of these nanoparticles in an acrylate polymer matrix was investigated.