Side chain mesomorphic polymers : studies of labelled backbones by neutron scattering

2014 Side chain liquid crystal polymers are studied in the isotropic, nematic and smectic phases. The samples are made from a mixture of liquid crystal polymethacrylate with deuterated or protonated backbones. The samples are studied with neutron diffraction and small angle neutron scattering. The results show in particular that in the aligned smectic phase the backbone is highly anisotropic and confined within a smectic layer. The backbone labelling shows local bilayered order. J. Physique Lett. 46 (1985) L-1065 L-1071 15 NOVEMBRE 1985, Classification Physics Abstracts 61.30 61.40K The liquid crystalline polymers studied here are comb like polymers, i.e. each monomer of the backbone is connected with a mesogenic molecule. The bulk properties of these polymers show the existence of phases (isotropic, nematic and smectic) characteristic of liquid crystals. Thus the mesogenic molecules impose their order on the system and the main problem [ 1 ] is how this order influences the conformation and the organization of the chains. From X-ray measurements [2], it is assumed that in the aligned smectic phase the backbone is strongly confined between the mesogenic layers. Such an assumption has to be confirmed by the determination of the anisotropy of a chain conformation. This can be achieved with a labelling method. Deuteration of the backbone associated with neutron diffraction (ND) and small angle neutron scattering (SANS) is the main tool for resolving such problems because this labelling method allows to determine the system organization (from ND [3]) and the chain conformation (from SANS [4]). A first experiment [5] performed with SANS has shown an anisotropy of about 25 % of the radius of gyration in the nematic phase; experimental difficulties prevented the authors from performing similar experiments in the aligned smectic phase. (*) Permanent address : Center for Polymer Studies, Boston University, MA 02215, USA. (**) Laboratoire Commun CEA-CNRS. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyslet:0198500460220106500 L-1066 JOURNAL DE PHYSIQUE LETTRES The results discussed here are obtained with four samples, each with a different value of the concentration 0 (~ = 0 ; 0.25 ; 0.50 and 1) of chains with deuterated backbone. It should be noted that between the sample ~ = 0 and ~ = 1 the number of protons replaced by deuterium varies only 15 %. The experimental part is discussed in section 1, the results concerning the chain conformation in section 2 and that for the chain organization in section 3. 1. Samples and experimental. Liquid crystalline polymethacrylate PMH and PMD were obtained by free radical polymerization of corresponding methacrylate monomers in solution. The synthesis of these monomers was adapted from published method [6-8]. The molecular weight is about 3 x 105.