Bernard Gallot

Block copolymers with a polyvinyl and a polypeptide block: factors governing the folding of the polypeptide chains

Abstract AB block copolymers polystyrene-poly(γ-benzyl- l -glutamate) (SG) of various molecular weights and compositions were synthesized and studied by X-ray diffraction and infra-red spectroscopy. They exhibit lamellar mesophases in the solid state and in dioxane concentrated solution. Each sheet of the lamellar structure results from the superposition of two layers: one formed by the polyvinyl chains in a disordered conformation, the other formed by the polypeptide chains in an α-helix conformation arranged in a hexagonal array and generally folded. The comparison of the lamellar structure of copolymers polystyrene-poly(γ-benzyl- l -glutamate) (SG), polybutadiene-poly(γ-benzyl- l -glutamate) (BG) and polystyrene-poly(e-carbobenzoxy- l -lysine) (SCK) showed that: (1) for the three types of copolymers (copolymers SG or BG or SCK) the number of folds of the polypeptide chains increases with the molecular weight of both the polyvinyl and the polypeptide blocks; (2) for copolymers of fixed molecular weight of the polyvinyl block and fixed degree of polymerization of the polypeptide block the number of folds of the polypeptide chains depends upon the nature of both the polyvinyl and the polypeptide blocks: a polypeptide chain is more folded when it is linked to a polystyrene chain than to a polybutadiene chain but a poly(e-carbobenzoxy- l -lysine) chain is more rigid than a poly(γ-benzyl- l -glutamate) chain.

Amphipathic block copolymers with two polypeptide blocks: synthesis and structural study of poly(Nε-trifluoroacetyl-L-lysine)-polysarcosine copolymers

Abstract AB block copolymers of poly (N e - trifluoroacetyl- l -lysine)-polysarcosine (KtSa) were synthesized and studied by X-ray diffraction. In order to obtain copolymers with a polydispersity small enough to allow the formation of mesophases, the first block of poly (N e - trifluoroacetyl- l -lysine ) was fractionated before using it as a macromolecular initiator of the polymerization of the second block of polysarcosine. Block copolymers of KtSa exhibit lamellar mesophases in the solid state and in concentrated aqueous solution. Each sheet of the lamellar structure results from the superposition of two layers: one formed by the hydrophilic polysarcosine chains in a disordered conformation, the other formed by the hydrophobic poly (N e - trifluoroacetyl- l -lysine ) chains in an α-helix type conformation arranged in a hexagonal array and tilted. The influence of the water content of the mesophase and of the composition of the copolymers on the structural parameters of the lamellar structure was analysed and it was shown that the angle of tilt of the poly (N e - trifluoroacetyl- l -lysine ) helices increases with both the water content of the mesophases and the length of the polysarcosine chains.

Structural study of polybutadiene‐poly(ethylene oxide) block copolymers. Influence of the nature of the amorphous block on the refolding of the poly(ethylene oxide) chains

Our earlier studies on block copolymers polystyrene-poly(ethylene oxide) has allowed to state the influence of the molecular weight of the copolymer and of its composition on the refolding of the crystallized poly(ethylene oxide) chains. To precise the effect of the nature of the amorphous block, we have studied by X-ray diffraction and differential scanning calorimetry, the lamellar crystalline structures exhibited by block copolymers polybutadiene-poly(ethylene oxide) (BEO) in the presence of a preferential solvent of one block: xylene for polybutadiene (PB), acetic acid or acrylic acid for poly(ethylene oxide) (PEO). In systems BEO copolymer/preferential solvent of PEO, the lamellar structure with crystallized PEO chains (LCC) exists at temperatures below about 45°C and for solvent concentrations ranging from 0 to a value characteristic of the copolymer. In the LCC structure, the chains of PEO crystallize in two layers; the solvent forms a third layer located between the PEO layers. We have studied the influence of the nature of the amorphous block on the variation of the structural parameters with the solvent concentration. In systems BEO copolymer/preferential solvent of PB, the lamellar structure with crystallized PEO chains (LC) appears at temperatures below about 50°C and for all solvent concentrations where the mesophase exists. In the LC structure, the chains of PEO crystallize folding in two superposed layers. We have established the influence of the solvent concentration and the nature of the amorphous block on the number of folds and the crystallinity of the PEO chains.

Structure of Liquid Crystalline Phases from Amorphous Block Copolymers

Abstract We have studied the structure of liquid crystalline phases of A-B block copolymers by small-angle X-ray scattering. We have found three types of structure: lamellar, hexagonal and cubic. We have also shown the influence on the structural type and structural parameters of the following factors: concentration and nature of the solvent, molecular weight and composition of the copolymer.

Use of freeze-fracture electron microscopy to study the refolding of crystallized chains in block copolymers

Abstract Block copolymers with an amorphous block or polystyrene (PS) of polybutadiene (PB) and a crystallizable block of poly(ethylene oxide) (PEO) or poly(ϵ-caprolactone) (PCL) exhibit lamellar crystalline structures. In these structures the elementary sheet results from the superposition of two layers: the first contains the amorphous blocks and the second contains the crystallized and refolded PEO or PCL chains. Study of the lamellar structure by freeze-fracture and electron microscopy provides micrographs that show crystallization of the PEO and PCL chains in two superposed layers and confirm the model proposed to explain the results of earlier X-ray diffraction and differential scanning calorimetry studies.

Poly(L-lysine) containing azobenzene units in the side chains: influence of the degree of substitution on liquid crystalline structure and thermotropic behaviour

The structure of poly(L-lysine)s containing between 20% and 100% of azobenzene units in the side chains has been studied by X-ray diffraction, between room temperature and 250 C. Except for samples having very low contents of azobenzene, the polymers are found to exhibit mesomorphic structures of the smectic A1 type deriving from the beta -structure of polypeptides. For polymers in which all lysine residues were substituted, the polypeptide main chains are arranged in layers corresponding to the sheets of a polypeptide ‘antiparallel’ beta -structure, and the side chains are perpendicular to the smectic layers. For polymers containing both substituted and free lysine side chains, each smectic layer results from the superposition of two layers: one layer contains the free lysine side chains; the other contains the azobenzenemodified lysine side chains and the polypeptide main chains that are arranged in ‘antiparallel’ beta -structures. All polymers exhibit only one smectic A mesophase as a function of tempe...

Methacrylic polymers containing permanent dipole azobenzene chromophores spaced from the main chain: synthesis and characterization

Three photochromic monomers containing a permanent dipole photochromic azobenzene group separated from the methacryloyl moiety by a polymethylene spacer, namely 4-(4-oxy-4′-cyanoazobenzene)but-1-yl methacrylate, 6-(4-oxy-4′-cyanoazobenzene)hex-1-yl methacrylate, and 8-(4-oxy-4′-cyanoazobenzene)oct-1-yl methacrylate, were synthesized in three steps starting from 4-cyanoaniline. These monomers were homopolymerized and copolymerized with an optically active monomer, (−)-menthyl methacrylate, in the presence of AIBN as a radical initiator. The polymeric materials, having a molar content of photochromic units comprised between 5 and 100% and molecular weights of about 15000, were characterized by an almost random distribution of monomeric units and a glass transition temperature ranging from 35 to 131°C. Polymer samples having a content of aromatic units larger than 75% were characterized by a thermotropic liquid crystalline structure, as evidenced by optical microscopy, X-ray diffraction and DSC measurements. Two-dimensional correlations spectroscopy (COSY) allowed an appreciable contribution by intramolecular charge transfer mesomers to the electronic distribution of the azobenzene chromophore to be highlighted.

ORGANIZED STRUCTURES IN BLOCK COPOLYMERS: STABILITY DOMAIN AND STRUCTURAL STUDY

In this paper we describe a safe method for the determination of the structure of block copolymers in concentrated solution and in the dry state. This method involves the use of both low angle x-ray diffraction and electron microscopy. Using these two techniques, we have established the existence of five types of structures for block copolymers and shown that when the composition of the copolymer in the insoluble blocks increases one observes successively: a centred cubic structure, an hexagonal structure, a lamellar structure, an inverted hexagonal structure and an inverted centred cubic structure. We also describe the effect of the concentration of the solvent, the temperature and the polymerization of the solvent.

Homopolymers and copolymers of Nε-4-phenylbenzamido-L-lysine and Nε-trifluoroacetyl-L-lysine: Synthesis and liquid-crystalline properties

In order to obtain comb-like poly-L-lysines bearing a biphenyl mesogen at the end of every repeating unit we have synthesised N e- 4-phenylbenzamido-L-lysine (Kφφ) and the corresponding N-carboxy anydride (Kφφ-NCA). We have homopolymerised the Kφφ-NCA and block-copolymerised it with the NCA of N e -trifluoroacetyl-L-lysine (Kt). The structural study of homopolymers pKt and pKφφ and block copolymers pKt/pKφφ was performed by infrared spectroscopy and X-ray diffraction. Two main types of structures were established: a bidimensional hexagonal one (Hα) where the polypeptide chains adopt an α-helix conformation and a lamellar smectic one (S A ) deriving from the β-pleated- sheet structure of polypeptides. Homopolymers pKt and block copolymers pKt/pKφφ rich in pKt exhibit the Hα structure, whereas the homopolymers pKφφ exhibit an S A2 structure, and block copolymers rich in pKφφ exhibit an S Ad structure. All the liquid-crystalline structures were stable until the beginning of decomposition of the polymers, Hydrolysis of the pKt block of copolymers pKt/pKφφ provided amphiphilic block copolymers pK/pKφφ without modification of the structure of the mesophases.

Polyacetylenes Bearing Mesogenic Side Groups: Synthesis and Properties, 1. Mesogenic Substituents with a Short Flexible Spacer

We report on the synthesis and polymerization of novel acetylenic monomers derived from 3-butyn-1-ol and bearing different potentially mesogenic substitutuents. Polymerization is carried out in solution with typical metathesis catalysts based on Mo and W and yields polyacetylenes with fairly high molecular weight and soluble in common organic solvents. Polymers are fully characterized by the point of view of the molecular structure, by GPC, FT-IR, NMR and UV/VIS techniques, and of the thermal and morphological behavior, by TGA, DSC, POM and X-ray diffraction experiments. Polymers with different amounts of cis and trans units are obtained, depending upon polymerization conditions. Although the monomers do not show any liquid crystalline behavior, polymers P2 and P3, containing in the side-chain respectively biphenyl and benzoyloxy benzoate as mesogenic cores, exhibit an enantiotropic smectic phase.