HyperMacs – long chain hyperbranched polymers: A dramatically improved synthesis and qualitative rheological analysis

Abstract

. (2008) 'HyperMacs long chain hyperbranched polymers : a dramatically improved synthesis and qualitative rheological analysis.', European polymer journal., 44 (3). pp. 665-676. Further information on publisher's website:http://dx.doi.org/10. 1016/j.eurpolymj.2007.12.022 Publisher's copyright statement: NOTICE: this is the author's version of a work that was accepted for publication in European Polymer Journal. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be re ected in this document. Changes may have been made to this work since it was submitted for publication. A de nitive version was subsequently published in European Polymer Journal, 44, 3, March 2008, 10.1016/j.eurpolymj.2007 Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract.We have previously reported a novel (albeit modestly successful) strategy for the synthesis of polystyrene HyperMacs -long chain branched analogues of hyperbranched polymers.The building blocks for HyperMacs, AB 2 macromonomers are synthesized by living anionic polymerization and as such are well-defined in terms of molecular weight and polydispersity but the nature of the coupling reaction used to generate the highly branched HyperMacs results in branched polymers with a distribution of molecular weights and architectures. In our previously reported studies the extent of the coupling reaction was significantly hampered by side reactions, however, we report here dramatic improvements to the coupling chemistry which overcome the previously experienced limitations resulting in a four fold increase in the extent of the coupling reactions.Furthermore we report the effect of the addition of varying amounts of a B 3 core molecule to the coupling reaction and the resultant 'control' of the final molecular weight of the HyperMac. Melt rheology showed polystyrene HyperMacs to be thermorheologically simple, obeying WilliamLandel-Ferry (WLF) behaviour. HyperMacs showed little evidence for relaxation by reptation and when the molecular weight of the macromonomer was ≤ M e for polystyrene, HyperMacs resemble unentangled polymers below the gel point, despite being well above the entanglement molecular weight for linear polystyrene. Increasing the molecular weight of the macromonomer to substantially above Me seems to introduce some entangled nature to the HyperMac as evidenced by the emergence of a near horizontal plateau in G'' -the loss modulus.

Synthesis and temperature gradient interaction chromatography of model asymmetric star polymers by the “macromonomer” approach

“…Each of these coupling reactions requires different chain-end functionality on the 'long' arm. In the case of a Williamson coupling reaction an alkyl halide is required and previous work [56] has shown that a bromide group is particularly effective. The experimental detail for the synthesis of PS90-Br is described above and follows a previous reported methodology [33,56].…”

“…In the case of a Williamson coupling reaction an alkyl halide is required and previous work [56] has shown that a bromide group is particularly effective. The experimental detail for the synthesis of PS90-Br is described above and follows a previous reported methodology [33,56]. In brief the polymerization of styrene is initiated by 3-tert-butyldimethylsiloxy-1-propyllithium (in the presence of TMEDA) which carries a protected primary alcohol functionality.…”

“…The synthesis of stars by Williamson coupling reaction consists of a nucleophilic substitution reaction between an alkyl bromide (the bromide being the leaving group) and a phenol (the nucleophile) that results in an ether linkage -scheme 1 The substitution reaction is carried out in DMF in the presence of cesium carbonate (Cs 2 CO 3 ) [56] with an excess of the long arm. The molar ratios of the reagents are 1 : 2.5 : 10 respectively for 'short' arm, 'long' arm and Cs 2 CO 3 -a slight molar excess of the 'long' arm being used to drive the reaction towards completion.…”

“…However, experience tells us that it is likely that such an intermediate product may be present -see later discussion on TGIC analysis of stars. The reaction conditions chosen for the initial attempt at star synthesis by Williamson coupling reaction ( fig 5) were based on a previously reported procedure for the synthesis of polystyrene HyperMacs [56]. Although it is clear from the SEC data in figure 5 that the reaction proceeds with reasonable efficiency, appearing to be almost complete after 3 hours, the overall extent of coupling was a little disappointing and attempts were made to improve the ultimate extent of reaction.…”

“…Even the most careful use of anionic polymerisation results in some batch to batch variation in molecular weight. The 'macromonomer' approach, first reported by our group for the synthesis of complex dendritically branched polymers such as DendriMacs [33,38], HyperMacs [54][55][56] and more recently HyperBlocks [57], has become widely adopted as a useful route to make a variety of complex dendritic branched architectures with polymer segments between branch points [58][59][60][61][62][63][64][65][66][67]. In essence the 'macromonomer' approach involves the synthesis of the linear segments of a branched polymer by a living/controlled polymerisation mechanism such that the linear segments contain chain-end functionalities which allow the subsequent construction of branched polymers via coupling reactions between macromonomers.…”