Control of End Groups in Anionic Polymerizations Using Phosphazene Bases and Protic Precursors As Initiating System (XH-Bu^<i>t</i>P₄ Approach): Application to the Ring-Opening Polymerization of Cyclopropane-1,1-Dicarboxylates

A synthetic method involving the in situ generation of an anionic initiator X− obtained by reaction of its conjugate acid precursor XH with ButP4 phosphazene base was tested as a possible way to easily and better control the end groups of polymers derived from the anionic ring-opening polymerization of cyclopropane-1,1-dicarboxylates. Several types of precursors were investigated, including thiols, alcohols, a carbazole, and a malonate. In all but one cases, a living polymerization mechanism could be observed, which was exploited to control the nature of the terminal end groups by reaction of the propagating malonate carbanion R−C(COOPr)2− with alkylating agents. It was also demonstrated that toluene was a much better solvent than the traditional one used in these reactions (THF) as a larger range of available temperatures was available despite an almost identical solvent influence on the polymerization. Exploitation of this feature provided access to higher degrees of polymerization than previously possible

Chain Stopper-Assisted Characterization of Supramolecular Polymers

Supramolecular polymers are dynamic materials; consequently, their molar mass is concentration dependent. However, the present experimental results show that an efficient chain stopper (i.e., a monofunctional monomer) can be used to block the concentration dependence of the molar mass of a hydrogen-bonded supramolecular polymer, over a realistic concentration range. This fact was used to derive the molecular weight and radius of gyration of the stopped supramolecular chains (by light scattering) as well as the intrinsic viscosity. In a second step, the molecular weight of the bis-urea-based supramolecular polymer (EHUT) was determined in the absence of a chain stopper

Self-Assembly of Amphiphilic Liquid Crystal Polymers Obtained from a Cyclopropane-1,1-Dicarboxylate Bearing a Cholesteryl Mesogen

We study the self-assembly of a new family of amphiphilic liquid crystal (LC) copolymers synthesized by the anionic ring-opening polymerization of a new cholesterol-based LC monomer, 4-(cholesteryl)­butyl ethyl cyclopropane-1,1-dicarboxylate. Using the t-BuP4 phosphazene base and thiophenol or a poly­(ethylene glycol) (PEG) functionalized with thiol group to generate in situ the initiator during the polymerization, LC homopolymer and amphiphilic copolymers with narrow molecular weight distributions were obtained. The self-assemblies of the LC monomer, homopolymer, and block copolymers in bulk and in solution were studied by small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and transmission electron microscopy (TEM). All polymers exhibit in bulk an interdigitated smectic A (SmAd) phase with a lamellar period of 4.6 nm. The amphiphilic copolymers self-organize in solution into vesicles with wavy membrane and nanoribbons with twisted and folded structures, depending on concentration and size of LC hydrophobic block. These new morphologies will help the comprehension of the fascinating organization of thermotropic mesophase in lyotropic structures

Synthesis and Solid-State Properties of PolyC₃ (Co)polymers Containing (CH₂–CH₂–C(COOR)₂) Repeat Units with Densely Packed Fluorocarbon Lateral Chains

The synthesis and structural characterization of linear PolyC3 polymers containing trimethylene-1,1-dicarboxylate structural repeat units with C6F13 and C8F17 fluorinated side chains is described for the first time, and their properties were compared with the traditional polyvinyl structures that display the fluorinated chain on every second rather than on every third carbon alongside the backbone. Homopolymers as well as statistical and block copolymers with n-propyl and/or allyl trimethylene-1,1-dicarboxylate blocks have been obtained from PolyC3 precursors containing diallyl trimethylene-1,1-dicarboxylate units, by reacting C6F13–C2H4–SH and C8F17–C2H4–SH thiols with the allyl groups using a thiol–ene post-polymerization modification reaction. Solid-state properties have been investigated by differential scanning calorimetry for all of the (co)­polymers and by small-angle X-ray scattering/wide-angle X-ray scattering for the C8F17 homopolymer at several temperatures. The structure of the homopolymer consistently shows a coexistence of two smectic phases at room temperature, which can be identified as SmB and SmC. This coexistence is assumed to arise from the fact that the distances between carboxylic oxygens bonded to the same carbon are very close to the ones between the neighboring carboxylic oxygens alongside the backbone, resulting in two possible ways of packing the pendent fluoroalkyl chains arranged in a hexatic order