Polymerization epitaxial

The two-step process of epitaxial polymerization has been applied to symmetrically substituted diacetylenes First, the monomers have been crystallized epitaxially on alkali halides substrates from solution and the vapor phase. The oriented monomer crystals are then polymerized under the substrate s influence by gamma-irradiation. The diacetylenes in this study are 2,4-hexadiyn-l,6-diol (HD) and the bis-phenylurethane of 5,7-dodecadiyn-l,12-diol (TCDU). The polydiacetylene crystal structures and morphologies have been examined with the electron microscope. Reactivity and polymorphism are found to be controlled by the substrate. 

The urethane-substituted polydiacetylenes exhibit thermo-chromic transition with low and high temperature crystal phases favoring acetylenic and butatriene backbone, respectively (4-6). Our interest in the application of epitaxial polymerization to diacetylenes has been the possibility of substrate control over orientation, structure, and the single crystal nature of thin films. 

Two diacetylenes have been epitaxially polymerized as thin films in contact with alkali halide substrates. These films in contact with alkali halide substrates. These films consisted of highly oriented single crystals aligned along both <110> directions of the substrate. The structures of both poly(TCDU) and poly(DMDA) were modified by this technique and, in all cases, highly crystalline near-perfect films were achieved. 

Woemer et al. 373) produced polyacetylene with locally oriented regions and an optical anisotropy of 2 x by polymerization on crystals of biphenyl. Yamashita and co-workers 374,375) have recently reported epitaxial polymerization of acetylene on crystals of anthracene, naphthalene and biphenyl where fibrils of cis- or trans-polymer formed, crystallographically aligned with the substrate. Fincher et al. 376) produced a 3 x extension which gave a 4 x optical anisotropy. 

The application of this method to the epitaxial polymerization of diacetylenes will also be discussed. 

It should be noted that none of the (SN) produced by direct epitaxial polymerization was fibrous in nature as is the conventional material in the normal a form.(7-10) jjot only is the a form produced on KCl not fibrous, it contains none of the extensive crystal twinning observed in the conventional polymerization. Thus greater crystal perfection is obtained by epitaxial pol3oneri-zation. The conventional fibrous a(SN) can be produced if a second deposition of S N is made on produced by... 

Epitaxial polymerization may allow complete topochemical control of a variety of solid state reactions to produce single crystals. This technique should continue to prove to be a powerful tool in the molecular engineering of thin polymer films. 

Figure 13.18 Electrochemical epitaxial polymerization STM images of the samples prepared by applying an increasing number of voltage pulses (1.4 V, 150 ms), (a) 5, (b) 13 and (c) 15, to a solution of 24 (10 mM), iodine (0.1 mM) and NBu4 PTe (0.1 M) in DCM. Reprinted with permission from H. Sakaguchi, H. Matsumura, H. Cong, Nature Materials, 3, 551 (2004). Copyright (2004) Nature Publishing Croup...

This situation is common to an epitaxial polymerization, where acetylene polymerization is carried out on the substrate crystal with a homologous isomorphic compound such as naphthalene, anthracene, biphenyl, or terphenyl. The fibril orientation is strongly dependent on the lattice matching between PA and the substrate crystals. 

Hyperbranched poly(acrylic acid) films have been grown on SAMs of alkanoic acid [137]. These films, rich in carboxylic acid groups could be utilized to selectively bind metal ions or serve as sites for further derivatization. Wurm et al. have studied electrochemically induced epitaxial polymerization [135] of iV-alkylpyrrole in solution onto a SAM composed of ((A -pyrrolyl)-n-undecyl)disulfide. These optically smooth films of long chain poly(iV-alkylpyrrole) have excellent stability in air. The Collard group [142] has studied the kinetics of electro-oxidatively polymerized polyaniline and polypyrrole on surfaces modified with SAMs formation of conducting films is initially blocked by the monolayer but nucleation at SAM defect sites leads to eventual deposition of rough polymer films. 

The first Involves a technique we have termed epitaxial polymerization. Monomers are crystallized on crystalline substrates. Lattice matching allows the variation of monomer structure and morphology, yielding different polymer structures and morphologies... 

It should be noted that none of the (SN) produced by direct epitaxial polymerization was fibrous in natu jg is the conventional material in the normal a form. Not only is the... 

It should be noted that epitaxial polymerization can be a general method of obtaining new polymer structures and morphologies. Other systems are currently under investigation. 

Table I. Crystal Forms of (SN) Produced by Epitaxial Polymerization. ...

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