Thin film polymerization

The solution coating technique was used in the preparation of the cellulose triacetate membrane discussed above. A solution of cellulose triacetate in chloroform was deposited on the porous support and the solvent was then evaporated leaving a thin film on the porous support. Thin film polymerization was used to prepare a polyfuran membrane barrier layer on polysulfone. In this case, the monomer furfuryl alcohol is polymerized in situ by adjustment of pH and temperature. This membrane proved to be highly susceptible to oxidizing agents and is of limited value. By far the most valuable technique in the formation of membrane barrier layers is interfacial polycondensation. In this method, a polymer is formed on the porous support surface at the interface of organic and aqueous phases by reaction of specific molecules dissolved in each phase. It is by this method that a number of polyamides and polyurea membrane barrier layers have been formed on polysulfone. Elements containing these membranes are available commercially. 

Chung Tai-Shrmg, Cheng Si-Xue. (2000). Effect of Catalysts on Thin-Film Polymerization of Thermotropic Liquid Crystalline Copolyester. J. Polym. Sci. A, 38(8), 1257-1269. 

Chung TS, editor. Thermotropic liquid crystal polymers thin-film polymerization, characterization, blends, and applications. Lancaster, PA TechnomicPub. Co. 2001. ISBN 1566769434. 

Batch-melt (ester-interchanged, direct esterification), continuous polymerized, solid-phase polymerized and thin-film polymerized polymers samples where all analysed. 

Investigation and Synthesis of Liquid Crystalline Polymers by Thin Film Polymerization... 

The thin film polymerization technique provides a powerful tool to answer these questions by experimental approach because the polymerization reactions for LCPs can be in situ investigated on the heating stage of the polarizing microscope. In addition, thin film polymerization consumes an extremely small... 

EFFECTS OF REACTION TEMPERATURE ON THE THIN FILM POLYMERIZATION... 

Figure 2.10 shows the morphologies of the late stage of thin film polymerization at relatively high reaction temperatures. After banded texture fully develops, the sample surface quickly turns into a non-smooth texture. Compared to the final product obtained at a low temperature, the morphology of high temperature product is coarser and fuzzier. 

TABLE 2.3. The Reaction Rate Constants for Uncatalyzed and Catalyzed Thin Film Polymerization Systems at Different Temperatures. Monomer Composition Is 73/27 ABA/ANA. 

Most monomers for LCP synthesis do not have liquid crystallinity. During the polymerization, LC phase forms and evolves with the progress of the polymerization, further annealing or curing reaction. Thin film polymerization technique is a very convenient way to investigate the formation of liquid crystallinity, because the LC phase can be clearly observed during the polymerization once the liquid crystallinity forms, and the reaction temperature, which is a critical parameter to form liquid crystallinity, can be accurately controlled. 

Figure 2.17 Arrhenius plots for the thin film polymerization of P(OBA/ONA). Monomer composition is 73/27 ABA/ANA.

Figure 2.27 The thin film polymerization under a-c electric field. 

Although the importance of surface tension and/or interfacial tension is obvious, most publications on LCPs are focused on the synthesis, phase transition, morphology, rheology, and mechanical property, etc., while comparatively few are reporting surface tension. Therefore this chapter will discuss surface tension of some main-chain TLCP, such as Hoechst Celanese s Vectra A950 and B950, and Amoco s Xydar , etc. Moreover, the surface tension evolution during thin film polymerization will be discussed. 

In addition, the current data re-confirm our conclusions in the previous papers [65,66] that Vectra A950 has a monopolar Lewis base surface because its -y+ values are negligible, which is consistent with Good and van Oss s conclusion that ester has Lewis-base character. This conclusion can also be extended to ABA/ANA copolymers obtained by thin-film polymerization with 73/27,50/50, and 27/73 mole ratios with different polymerization times. 

---