Structure of Fluorinated Side-Chain Smectic Copolymers: Role of the Copolymerization Statistics G. de Crevoisier, †,§ P. Fabre, †,⊥ L. Leibler, † S. Tence ´ -Girault,* ,† and J. M. Corpart ‡ UMR 167 CNRS-ATOFINA-ESPCI, 10, rue Vauquelin 75031 Paris Cedex 05, France, and CAL-ATOFINA, 95 Rue Danton, 92303 Levallois-Perret, France Received March 15, 2001; Revised Manuscript Received January 14, 2002 ABSTRACT: Side-chain fluorinated copolymers present very specific wetting and tacking properties that are strongly related to their organization. We have studied the structure of these systems by X-ray scattering in the liquid crystalline regime, as a function of the ratio of fluorinated groups on one hand and of the copolymerization statistics on the other. The structures obtained are always highly ordered and exhibit a smectic B type organization, where the two types of pendant groups are able to crystallize independently. However, packing differences appear for copolymers with different chain statistics due to the existence of microphase separation between the side groups. The roles of these parameters on phase transitions, periodicity, and degree of crystallinity of the polymers are discussed. Their behavior with temperature, important for applications, is also studied. Introduction Side-chain liquid crystalline polymers have been the subject of much interest, for both fundamental and applied reasons. Since they present an original archi- tecture, they can potentially display interesting new structures on one hand, while on the other, they are expected to exhibit properties that can lead to new applications such as long-term memory devices or nonlinear optics. In fact, other unexpected applications were found for that type of system: when enough fluorine is present in one of the pendant groups, side- chain copolymers organize in such a way that very hydrophobic and oleophobic properties appear. As a consequence, these types of copolymers are used as antistain coatings. More recently, other specific proper- ties have been reported 1 for these systems, such as a nonsticky to sticky transition related to a structure change with temperature. For both these reasons, it was tempting to study the organization of fluorinated co- polymers, when varying their composition, as a first step to relating their structure to their properties. Moreover, another recent study 2 has led to the original result that it was possible, in these systems, to vary the copolym- erization statistics from statistical to rather blocky, by changing the type of synthesis from solution to emul- sion. With this system, it is thus possible to study how both the composition and the copolymerization statistics of the chain influence the structure, leading to results that will a priori be valid for a whole class of side-chain copolymers. The copolymers studied bear two types of pendant moieties: one fluorinated group and one alkyl group. As explained, their ratio as well as their distribution along the chain was varied, and the two homopolymers were also studied for comparison. To understand the copolymer structure, a knowledge of the monomer’s miscibility is also relevant: for this reason, we deter- mined their phase diagram. The impact of temperature on their structure and in particular the phase transi- tions of the copolymers are also studied in this paper, since they represent very important information as far as their surface (wetting) or volume (stickiness) proper- ties are concerned. The study was realized with both small-angle (SAXS) and wide-angle (WAXS) X-ray scat- tering experiments and with DSC for the phase transi- tions. In the first part, we describe the experimental results for the two homopolymers as well as the phase diagram of the mixture of the two monomers. We then discuss what can be expected for copolymers and describe the experimental results when varying the fluorine ratio and the polymerization statistics. We then present a possible organization of the systems as a function of these two main parameters. Experimental Section Materials. Two main monomers were used in this study, the structures of which are given in Figure 1. The alkyl monomer is an equimolar mixture of stearyl (m ) 17) and palmityl (m ) 15) methacrylate; for simplicity, we will hereafter call this MAS. The fluorinated acrylic monomer, which we call AC8n, is a mixture of acrylates with fluorinated side chains of different lengths: n ) 6 (1%), n ) 8 (65%), n ) 10 (25%), and n ) 12 (9%). We will sometimes refer to the pure n ) 8 fluorinated compound, which we call AC8. Hy- droxyethyl methacrylate (HEMA) was also used as a hydro- philic monomer. All these monomers were provided by ATO- FINA and used without further purification. The polymerization initiators used were 2,2′-azobis(2-amidinopropane) hydrochlo- ride and 2,2′-azobis(isobutyronitrile). These were provided by ATOFINA. The solvents used were acetone and butyl acetate provided by Aldrich. All these compounds were used without further purification. Preparation and Characterization of the Polymers. All syntheses were carried out in a 1 L reactor fitted with an anchor agitator, a double thermoregulated jacket, and a sweep of nitrogen. In the case of synthesis in solution, 425 g of butyl acetate and 75 g of AC8n and MAS monomers were introduced into the reactor in varying proportions, corresponding to the composition of the copolymer that was targeted. For a par- † UMR CNRS-ATOFINA-ESPCI. ‡ CAL-ATOFINA. § Present address: ATOFINA Japan, Kyoto Technical Center SCB#3, Kyoto Research Park,1 Awatacho, Chudoji, Shimigyo-ku Kyoto 600-8815 Japan. ⊥ Present address: CRPP, Av. Dr Schweitzer, 33600 Pessac, France. * To whom correspondence should be addressed. 3880 Macromolecules 2002, 35, 3880-3888 10.1021/ma010459t CCC: $22.00 © 2002 American Chemical Society Published on Web 04/04/2002