Project

Valorisation of SET-LRP for the synthesis of amphiphilic and functional copolymers

Duration
01 January 2013 → 31 December 2016
Funding
Regional and community funding: IWT/VLAIO
Research disciplines
  • Natural sciences
    • Organic chemistry
Keywords
copolymers adhesives dispersants viscosity modifiers
 
Project description

The aim of this work was the synthesis of complex polymer architectures for their use as dispersants, viscosity modifiers or adhesives. The interest in synthesizing these structures arose from a, earlier PhD-project in collaboration with Dow Chemical and previous PhD-studies, during which better results were obtained with these materials as stabilizer for pigments or compatabilizer for polymer blends compared to their linear counterparts. Furthermore, a combination of a Cu(0)-mediated polymerization system and thiolactone and triazolinedione (TAD) chemistry as two efficient linking methodologies were used. On the other hand, the use of a Cu(0)-mediated polymerization system as controlled radical polymerization (RDRP) technique enabled the synthesis of polymeric structures with precise control over molecular weight, end group functionality, chain architecture and dispersity.1-9 Furthermore and industrially most relevant, this technique offers the possibility to obtain polymers with a high end group fidelity at high conversion in comparison to classical methods10-12 such as Nitroxide Mediated Polymerization (NMP), Reversible Addition Fragmentation Transfer (RAFT) polymerization or Atom Transfer Radical Polymerization (ATRP).13-15 Additional to the use of RDRP-methods, efficient linking methodologies or “lick”reactions enable polymer chemists to facilitate the synthesis of complex polymeric structures by simplifying complicated procedures and tedious work-ups.16-18 In this context, two in-house developed “lick”chemistries were depicted for the synthesis of complex polymeric structures; thiolactone and triazolinedione (TAD) chemistry.19, 20 Thiolactone units can be implemented as protected thiol functionalities, which can be liberated  upon reaction with an amine and subsequently reacted in a one-pot approach with the acrylate moiety present in the same reaction medium.21 Triazolinedione moieties can be obtained by oxidation of the corresponding urazole unit and react rapidly with (di)enes via a Diels-Alder or Alder-ene reaction.22

In chapter II, a theoretical description on controlled polymerization methods is provided, with a major focus on copper mediated polymerization systems. An overview was presented on the evolution of classical ATRP to the recently developed Cu(0)-mediated polymerization. Furthermore, a critical comparison was given between Single Electron Transfer Living Radical Polymerization (SET-LRP) and Supplemental Activator and Reducing Agent Atom Transfer Radical Polymerization (SARA-ATRP), two resembling but mechanistically argued to be different methods. Next, the different aspects of “lick”chemistry were elaborated in more detail and the different criteria to be considered “lick”were discussed. Additionally, two different inhouse developed methods, which were implemented in this thesis were described in more detail, thiolactone and triazolinedione chemistry. The theoretical part of this thesis was finished with the description of different methodologies that can be utilized for the synthesis of complex polymer architectures while their use as dispersants was explained. In order to moderately increase the level of complexity of the polymer synthesis during this thesis, chapter III started with the double modification of polymer end groups via thiolactone chemistry. First, the synthesis of four different polymers containing a thiolactone end group was performed. Polystyrene (TL-PS) and polybutyl acrylate (TL-PBA) were synthesized via Cu(0)-mediated polymerization of a thiolactone-containing initiator. The thiolactone functionality on polyethylene oxide (PEO-OH) and bifunctional polycaprolacton (HO-PCL-OH) was introduced by end group modification with a thiolactone containing isocyanate. Next, a model study was performed regarding the double modification reaction, benzyl amine and benzyl acrylate were added in a one-pot approach in which the amine opens the thiolactone ring, releasing the thiol which on its turn reacted with the acrylate moiety. The success of the modification reaction was confirmed by SEC, 1H-NMR and MALDI-TOF analysis. Next, a library was created by varying the amine and acrylate structure. In this way, a series of double end-functionalized polymers was generated in which aromatic, furan, tetrahydrofurfuryl, double bond, halogen and hydroxylmoieties were easily introduced. Finally, amphiphilic block copolymers were obtained by linking of PEO-NH2 as hydrophilic amine with TL-PBA while the full conversion to the amphiphilic block copolymer was confirmed by Liquid Chromatography x Size Exclusion Chromatography (LCxSEC), a technique that separates polymers both on polarity and molecular weight. In chapter IV, the complexity of the polymer synthesis was further increased by the synthesis of precision multisegmented macromolecular line-ups, which are multisegmented copolymers containing chemical functionalities well-located along the polymer backbone between each segment connection. First, a hetero-telechelic polymer was synthesized containing a thiolactone and acrylate functionality via Cu(0)-mediated polymerization of a thiolactone-containing initiator and end group modification reactions to transform the bromine end group into an acrylate unit. The success of these modification reactions was confirmed by SEC, 1H-NMR and MALDI-TOF analysis. In a following step, the multisegmented macromolecular line-up was obtained by nucleophilic ring-opening of the thiolactone unit by a functionalized amine and consecutive thiol-Michael addition. Next, a library of macromolecular structures with chemical functionalities precisely positioned onto the polymer backbone was obtained by selective variation of the amine structure introducing aromatic, PEGylated, double bonds and furan moieties at each segment connection. The library of functionalities was extended by postpolymerization modification reactions via thiol-ene or furan-maleimide modification reaction of the respective double bond and furan-containing multisegmented line-up. In this way glycosylated polymers were synthesized by thiol-ene reaction with the corresponding sugar-thiol. Subsequently, amphiphilic precision multisegmented graft copolymers were synthesized by the use PEO-NH2 and the successful synthesis was confirmed by LCxSEC analysis. Finally, chiral benzene-1,3,5-tricarboxamides (BTAs) were introduced via the corresponding amine as hydrogen-bonding units and their self-assembly behavior for the synthesis of single chain polymeric nanoparticles (SCPNs) was investigated. To increase the level of complexity to a final level, Chapter V described the synthesis of two interesting complex architectures via a Cu(0)-mediated polymerization system and thiolactone chemistry, namely amphiphilic graft and toothbrush copolymers. Regarding the synthesis of the graft copolymers, a series of copolymers of butyl acrylate and a varying amount of a thiolactonecontaining acrylate were synthesized. Next, the graft copolymer was obtained by linking the thiolactone-functionalized backbone with PEO-acrylate. For the synthesis of the toothbrush structures, a series of different block-copolymers of tert-butyl acrylate as protected hydrophilic first segment and a copolymer of butyl acrylate and thiolactone acrylate as second segment were prepared in a one-pot procedure. Next, the hydrophobic side-arms, consisting of poly(butyl acrylate), were synthesized separately, introducing the acrylate as end group via a post polymerization modification step. The final toothbrush structure was obtained by linking the block copolymer with the hydrophobic side-arms and deprotection of the hydrophilic segment via methyl sulphonic acid. Finally, the material properties were investigated by dynamic light scattering (DLS) and dispersion tests. It was observed that toothbrush structures exhibited increased stabilizing features compared to the corresponding graft copolymers. The last experimental part, chapter VI, described the use of TAD-chemistry for the synthesis of block, graft and toothbrush structures. The synthesis of the block copolymers was started by the synthesis of polymers containing TAD and ene end groups. For the synthesis of the ene end group, polystyrene was synthesized and the bromine was transformed into a cyclopentadiene. Polymers containing TAD end groups were obtained via Cu(0)-mediated polymerization of butyl acrylate via a urazole-containing initiator. Finally, the urazole was oxidized, the polymers were coupled and the successful outcome was analyzed via LCxSEC analysis. For the synthesis of the graft copolymers, a series of hydrophobic copolymers containing a varying amount of citronellyl acrylate and butyl acrylate were synthesized. In parallel, the hydrophilic poly(N,Ndimethylacrylamide) (PDMA) was synthesized via RAFT polymerization of a urazole-containing RAFT agent, since it was observed that a Cu(0)-mediated polymerization was not able to control the polymerization due to side-reactions of the urazole moiety with the copper catalyst. Finally, the graft copolymer was obtained by oxidizing the urazole moiety and linking the polymers. Regarding the synthesis of the toothbrush structures, a series of different block copolymers were synthesized containing 1-ethoxy ethylacrylate and a copolymer of butyl acrylate and citronellyl acrylate as second block in a one-pot procedure via a Cu(0)-mediated polymerization. Furthermore, hydrophobic side-arms were obtained via RAFT polymerization of butyl acrylate via a urazole-containing RAFT agent. Afterwards, the amphiphilic toothbrush copolymer was obtained by oxidation of the urazole moiety, linking the polybutyl acrylate side-arms to the block copolymer and deprotection of the 1-ethoxyethyl acrylate units by heating. Finally, the material properties were again investigated by DLS and dispersion tests. It was observed confirmed that toothbrush structures exhibit increased stabilizing features compared to the corresponding graft copolymers. In comparison to thiolactone chemistry, it has to be noted that triazolinedione chemistry has very interesting advantages, such as the color switch after reaction and the increased grafting efficiencies, but also drawback such as the stability and synthetic difficulty to obtain these structures in some cases.

Perspectives

In general, it can be expected that the presented results of this work will have an impact on the implementation of Cu(0)-based polymerization systems in industry for the design of complex polymer architectures. First of all, Cu(0)-mediated polymerization provides the possibility of polymerizing monomers to high conversion retaining high end group fidelities. This enables the synthesis of block copolymers in a one-pot approach and facilitates purification at the end of the polymerization, two important aspects for the synthesis of polymers under industrially relevant conditions. In this PhD thesis, the grafting-onto strategy was applied for the synthesis of complex polymer structures, a technique which is strongly competing with the grafting-through method on an industrial level. However, nowadays the grafting-through method is still preferred due to the straightforward synthesis of the reactive macromonomers and corresponding complex structures. However, the grafting-onto method is attracting more attention, as a result of the increased grafting efficiencies that can be obtained by the use of more efficient chemistries. However, the additional cost by implementing new chemistries and related patent issues will still be a big hurdle for implementing this strategy on an industrial level. Furthermore, this manuscript focused on the use of complex structures for the dispersion of pigment particles in water. By simple varying monomer structures and resulting complex architectures, these materials can be implemented as compatabilizers, viscosity modificiers or adhesives. Moreover, the research on sequence-controlled polymer via thiolactone chemistry described in chapter IV is still ongoing. Different strategies, applying both solid- and liquidphase starting materials are investigated for the design of these highly interesting structures. On the other hand, the research area on the synthesis of complex copolymer structures via TADchemistry as efficient linking methodology is still ongoing, and will be explored for the synthesis of cyclic and multisegmented structures. Finally, the implementation of bio-based monomers for the synthesis of thermoplastic elastomers via controlled radical polymerization techniques, derived from terpene-based structures is a research project that was recently started within the own research group.