Layer-by-Layer Polycondensation of Nylon-66 with Normal Molecular

Chapter 17

Downloaded by UNIV MASSACHUSETTS AMHERST on September 6, 2012 | http://pubs.acs.org Publication Date: January 28, 1999 | doi: 10.1021/bk-1998-0713.ch017

Layer-by-Layer Polycondensation of Nylon-66 with Normal Molecular Orientation by Alternating Vapor Deposition Polymerization Huili Shao and Norimasa Okui Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Ookayama, Meguroku, Tokyo 152, Japan

Nylon-66 thin films were prepared by alternating vapor deposition polymerization(AVDP) method by the layer-by-layer polycondensation. In the AVDP process, two kinds of bi-functional monomers, such as Adipyl chloride monomer (AC) and Hexamethylene diamine monomer (HMDA) are deposited alternatively onto a substrate. At first, A C is deposited onto the amino covered substrate. A C can react with the amino groups on the substrate and the substrate surface is covered with the chain ends of AC. Next, H M D A is deposited onto the monomolecular layer of the A C yielding the film surface to be covered with the chain ends of HMDA. The resultant nylon films showed the highly ordered structure with the molecular orientation tilting to the substrate. The thickness and the molecular weight for the nylon film increased linearly with the number of deposition reaction cycles. The molecular weight of the film is proportional to the film thickness.

Vapor deposition polymerization (VDP) is a useful and promising method for fabrication of functional polymeric thin films with thermal stability such as polyimide thin films [1,2]. VDP can also be used to fabricate polyurea films having piezoelectricity and pyroelectricity [3]. Compared with the Langmuir-Blodgett (LB) method and other preparation methods of polymeric thin films, V D P has a great advantage since the method is a simple dry process [1]. In addition, molecular orientation in a VDP film can be controlled. For example, the VDP method can produce polyamide [4-7] and polyimide [8,9] films with high molecular orientation perpendicular to the substrate surface. The present paper deals with a basic idea of the alternating VDP (AVDP), in which, two kinds of afunctional monomers, such as a dicarboxylic chloride monomer and a diamine monomer, which can react easily at their chain ends, are deposited

© 1 9 9 8 American Chemical Society In Solvent-Free Polymerizations and Processes; Long, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1999.

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alternatively onto a substrate. The mechanism o f adsorption/desorption of monomers onto the substrate is studied and the feasibility o f A V D P method for preparation of an ultra-high molecular weight nylon-66 thin film with a layer-by-layer structure is investigated.


Expérimentas Hexamethylene diamine ( H M D A , Tm=42°C) and Adipyl chloride ( A C , liquid state at room temperature and atmospheric pressure) were provided by Tokyo Kasei Co. Ltd. and used without further purification. P-type silicon wafers with a (100) plane (Mitsubishi Materials Silicon Co.) were used as substrates. Before the A V D P process, the substrates were treated by a silane-coupling agent ( y -aminoethyl-aminopropyltrimethoxy silane) to form an activated sublayer surface covered with the amino end group [7], which could react with the chain ends of the dicarboxylic chloride monomer. Figure 1 shows the scheme of the experimental apparatus. First, the system was evacuated to remove air by means of opening the valve C for a certain period of time. A C monomer kept at 65°C was introduced into the system by closing valve C and opening valve A for a certain period of time in order to deposit the monomer onto the activated substrate. Next, valve A was closed and valve C was opened to evacuate the residual monomers from the system for a certain period of time. After closing valve C, valve Β was opened to introduce the vapor of H M D A monomer kept at 55°C for a certain period of time in order to deposit the monomer onto the substrate. Valve C was opened again after closing valve Β in order to eliminate the excess monomers and by products from the system. This reaction cycle was repeated to get a film with the desired thickness.

Figure 1 Schematic illustration of the experimental apparatus for A V D P process

In Solvent-Free Polymerizations and Processes; Long, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1999.


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The adsorption/desorption behaviors of monomers onto the substrate were investigated by monitoring the change in the amount of adsorbate on the surface o f Au-coated quartz crystal substrate ( Q C M ) . The substrate surface had been covered with the amino end groups of the si lane-coupling agent by a surface treatment process prior to the deposition of monomers. IR spectra were obtained with transmission and R A S methods using a Fourier transform IR system (Jasco FT-IR 7000) at room temperature in a dry nitrogen atmosphere. X-ray diffraction patterns were recorded in a θ -2 θ reflection mode by a Rigaku R A D - B diffractometer using N i filtered C u K a X-rays. The film thickness was measured by an ellipsometer (EL-8, Optec Co. Ltd.) with an incident angle of 70° of the light from a He-Ne laser (632.8nm). The films on the substrate were scraped off from the substrates for determination of the molecular weight by viscometry in 90% formic acid at 25°C [10]. Differential scanning calorimetric (DSC) measurements were carried out using a Shimazu D S C - 5 0 equipment in the nitrogen atmosphere at a heating rate of 10°C min" . 1

Results and Discussion Deposition behavior of A C monomer. Figure 2 shows the change in the amount of A C monomer adsorbed on the amino-covered quartz crystal substrate kept at 70°C as a function of the time for monomer supply and for evacuation after stopping the monomer supply. When A C monomer is introduced into the system for 10 seconds, the amount of the adsorbed A C monomer on the substrate increases to the stage a in figure 2. Then, the monomer supply is stopped and the residual monomer and by-product HC1 are evacuated from the system for 1 minute. During the above process, the amount of adsorbate remains almost constant, indicating that no admolecules are re-evaporated from the substrate. In other words, A C molecules are adsorbed on the substrate by chemical bonding (chemisorption), which are attributed to the condensation reaction between the carboxylic acid chloride groups in A C and the amino groups on the substrate surface. When A C monomer is introduced into the system for another 10 seconds, the amount of the adsorbed A C monomer is slightly increased and is saturated to the stage b. Then, it keeps at the constant value even i f the subsequent evacuation and the monomer supply are proceeded (stage c to stage d). The saturated value l.OxlO^kg/m at b is coincident with the areal density of A C monomolecular layer with the normal orientation to the substrate. These results indicate that during the first 10s deposition, the amount of the A C monomer is not enough to form the complete monomolecular layer o f A C monomer as shown in figure 3. However, during the next 10s deposition, the non-adsorbed sites on the substrate are occupied by the A C monomer yielding the complete monomolecular layer. 2

Deposition behavior of H M D A monomer. Figure 4 shows the change in the amount of H M D A monomer adsorbed on the quartz crystal surface, which has been covered previously with the A C monomolecular layer, as a function of the time for monomer supply and evacuation after stopping the monomer supply. When H M D A is introduced into the system for 10s, the amount of adsorbate of H M D A monomer on the substrate surface increases rapidly and tends to the stage a in figure 4. After

In Solvent-Free Polymerizations and Processes; Long, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1999.

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2 AC

AC Ν


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Layer-by-Layer Polycondensation of Nylon-66 with Normal Molecular

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