Production of thin films

Thin films are produced by a process in which organic polymers having long-chain side groups are dissolved in an organic solvent, the solution is spread at the water/air interface by the Langmuir-Blodgett technique and the film is transferred onto a solid base material after evaporation of the organic solvent, and the organic polymers used are those which contain long-chain n-alkyl side groups bonded to the main chain of the polymer via polar groups, and some of these long-chain n-alkyl side groups are replaced by shorter-chain n-alkyl side groups, by branched alkyl side groups having the same or a smaller number of carbon atoms or by equally long or shorter side groups having one or more C-C multiple bonds. This process can be used to produce film elements, for example for optical filters.

The present invention relates to a process for the production of thin films 
of organic polymers having long-chain side groups on a solid base material 
by the Langmuir-Blodgett technique, and film elements produced by this 
process. 
The production of monolayers of organic polymers having long-chain side 
groups by the Langmuir-Blodgett technique is known. For example, C. S. 
Winter et al. (Thin Solid Films 134 (1985), 49 et seq) investigated 
Langmuir-Blodgett films of derivatives of octadec-1-ene/maleic anhydride 
copolymers, polyoctadecyl acrylate and polyoctadecyl methacrylate. 
Furthermore, S. J. Mumby et al. (Macromolecules 19 (1986), 1054 et seq) 
studied Langmuir-Blodgett films of the two last-mentioned polymers. A 
maximum of 6 Z layers with a constant transfer ratio are mentioned here. 
H. Nakahara et al. (Thin Solid Films 133 (1985), 29 et seq) investigated 
the effect of side chain length and main chain rigidity on transfer in the 
case of cellulose ester, octadecene/maleic anhydride copolymers and their 
derivatives. 
Monomers of poly-.gamma.-benzyl L-glutamate and poly-.beta.-benzyl 
L-aspartate (S. Ikeda and T. Isemura, Bull. Chem. Soc. Jpn. 34 (1961), 416 
et seq) and monolayers of poly-.gamma.-methyl L-glutamate (F. Takeda et 
al., J. Coll. Int. Sci. 87 (1981), 220 et seq) have also been 
investigated. 
It is an object of the present invention to provide a process for the 
production of thin films of organic polymers having long-chain side groups 
by the Langmuir-Blodgett technique, the said process to constitute an 
improvement with respect to the transferability of the monolayers and to 
have a constant transfer ratio so that better reproducibility is ensured. 
We have found that this object is achieved, surprisingly, by the use of 
organic polymers which contain long-chain n-alkyl side groups bonded to 
the main chain of the polymer exclusively via polar groups, some of these 
long-chain n-alkyl side groups being replaced by shorter-chain n-alkyl 
side groups, by branched carbon radicals or by carbon radicals containing 
C--C multiple bonds. They are therefore comb polymers having different 
side groups in the same molecule. 
The present invention relates to a process for the production of thin films 
of organic polymers having long-chain side groups on a solid base 
material, the organic polymer being dissolved in an organic solvent, the 
solution being spread at the water/air interface by the Langmuir-Blodgett 
technique and the film being transferred to a solid base material after 
evaporation of the organic solvent, wherein organic polymers which contain 
long-chain n-alkyl side groups bonded to the main chain of the polymer 
exclusively via polar groups are used as the organic polymers having 
long-chain side groups, with the proviso that some of these long-chain 
n-alkyl side groups are replaced by shorter-chain n-alkyl side groups, by 
branched alkyl side groups having the same or a smaller number of carbon 
atoms and/or by equally long or shorter side groups having one or more 
C--C multiple bonds. 
Preferred polar groups are --O--, 
##STR1## 
in particular 
##STR2## 
Both copolymers and polycondensates can be used as organic polymers having 
long-chain side groups. 
The novel process is distinguished both by improved transferability of the 
monolayers and a constant deposition ratio and better reproducibility. 
The present invention also relates to film elements which have been 
produced by the novel process. 
The process according to the invention is suitable, for example, for the 
production of filters for optical purposes, for improving the frictional 
properties of materials, for the production of protective layers and other 
relevant uses. 
The base material to be used for the novel process can, if required, be 
rendered hydrophobic before the application of the copolymer monolayers. 
Where corresponding copolycondensate monolayers are applied, it is 
advantageous to render the base material hydrophobic. 
Regarding the novel process and the components of the polymers, the 
following may be stated specifically. 
Examples of copolymers are: 
polyvinyl alkyl ethers where the n-alkyl chain is of 12 to 36 carbon atoms, 
such as polyvinyl octadecyl ether, some of whose straight-chain octadecyl 
groups may be replaced by, for example, hexadecyl, dodecyl, decyl, nonyl, 
octyl, hexyl, n-butyl or isobutyl groups; corresponding copolymers of 
polyvinyl alkyl ketones of different chain lengths; 
poly-N-alkylacrylamides or poly-N-alkylmethacrylamides, where the 
long-chain n-alkyl groups may contain 12 to 36 carbon atoms and are 
partially replaced by n-alkyl radicals having a smaller chain length or 
branched alkyl radicals; 
polymeric esters of acrylic acid, methacrylic acid or other copolymerizable 
.alpha.,.beta.-ethylenically unsaturated monocarboxylic acids having 
straight-chain alkyl groups of not less than 12, preferably 16 to 36, 
carbon atoms, some of these long-chain n-alkyl groups being replaced by 
n-alkyl groups having an alkyl radical which is shorter by one or more, 
preferably 2 to 8, carbon atoms, or being replaced by branched alkyl 
groups having the same or a smaller number of carbon atoms in the alkyl 
radical or by hydrocarbon radicals having the same or a smaller number of 
carbon atoms, these hydrocarbon radicals containing one or more C--C 
multiple bonds, for example --HC.dbd.CH-- or --C.tbd.C-- groups; C--C 
multiple bonds can advantageously be introduced by polymer-analogous 
reaction. 
Examples of long-chain n-alkyl (meth)acrylates (a) are docosyl 
(meth)acrylate, eicosyl (meth)acrylate, octadecyl (meth)acrylate, 
hexadecyl (meth)acrylate, tetradecyl (meth)acrylate and dodecyl 
(meth)acrylate. 
In the copolymers to be used according to the invention, some of the 
long-chain n-alkyl (meth)acrylates of this type are replaced by n-alkyl 
(meth)acrylates having shorter n-alkyl radicals, by those having branched 
alkyl radicals or by those having C--C multiple bonds. 
The proportion of the components (a) and (b) as copolymerized units of the 
copolymer can vary within wide limits and is in general 50 to 99.5 mol % 
for component (a) and from 0.5 to 50 mol % for component (b). 
Preferred copolymers are those which contain from 80 to 99.5, in particular 
from 85 to 99, mol % of component (a) and from 0.5 to 20, in particular 
from 1 to 15, mol % of component (b). 
Copolymers of octadecyl (meth)acrylate with hexadecyl (meth)acrylate, 
dodecyl (meth)acrylate, decyl (meth)acrylate, nonyl (meth)acrylate, octyl 
or isooctyl (meth)acrylate, hexyl (meth)acrylate, butyl (meth)acrylate or 
methyl (meth)acrylate are particularly suitable. 
Thus, these are copolymers in which the amount of the modifying comonomer 
(b) may vary depending on its chain length. 
(Meth)acrylate copolymers are preferred. 
The copolymers to be used according to the invention generally have degrees 
of polymerization of from 10 to 200. Isotactic copolymers are preferred. 
Examples of suitable polycondensates having different side chains are 
polyesters and, in particular, polyamides. Regarding the choice and 
combination of the side chains, the statements made in connection with the 
copolymers are essentially applicable. Among the polyamides, the 
polyglutamates which contain different ester groups in the 
.gamma.-position should be mentioned in particular. Poly(.gamma.-octadecyl 
L-glutamates) where some, e.g. 2-20 mol %, of the octadecyl groups are 
replaced by n-alkyl groups of less than 18, preferably 1 to 16, carbon 
atoms or corresponding branched alkyl radicals or hydrocarbon radicals 
having C--C multiple bonds are preferred. 
Examples of such polycondensates are 
poly(.gamma.-methyl-L-glutamate-co-.gamma.-octadecyl-L-glutamate). Such 
cocondensates can be prepared by polymer-analogous reaction of the 
polymeric homocondensates, for example by partial transesterification of 
the poly-.gamma.-methyl L-glutamate with stearyl alcohol (cf. J. Watanabe, 
Y. Fukuda, R. Gehani and I. Nematyn, Macromolecules 17 (1984), 1004 et 
seq). 
The Langmuir-Blodgett technique, the apparatuses which are suitable for 
this purpose and the preconditions for carrying out this method are known 
and are described in, for example, G. L. Gaines, Insoluble Monolayers at 
Liquid-Gas Interfaces, Interscience Publishers, 1966; in particular, 
reference may be made to pages 44-68, 336-340 and 326-330 of this 
monograph. 
The transfer of monolayers is generally effected in the liquid-analogous 
state. 
The organic polymers are advantageously dissolved in readily volatile 
organic solvents, such as methylene chloride, chloroform, benzene, hexane 
or ethyl acetate, in concentrations of about 0.01-1% by weight, the 
solvent is evaporated off from the polymer solution applied to the water 
surface, and the monolayer is precompressed in a conventional manner 
before transfer onto solid base materials. 
In general, temperatures of 5.degree. to 35.degree. C., preferably from 
10.degree. to 30.degree. C., are employed. 
Suitable base materials for the novel film elements, on which the thin, 
ordered films of well defined structure consisting of organic polymers are 
applied, are any solid, preferably dimensionally stable substrates of a 
very wide range of materials. The substrates serving as the base material 
may be, for example, transparent or translucent, electrically conductive 
or insulating. The surface of the substrate on which the thin film of the 
organic polymers is applied may be rendered hydrophobic. The substrate may 
consist of a hydrophobic material or the surface of the substrate can be 
rendered hydrophobic before application of the thin film of the organic 
polymer in a conventional manner by a suitable pretreatment. The 
hydrophobic substrate surface to be coated should be very clean so that 
the formation of a thin, ordered film, in particular a monomolecular or 
multimolecular layer structure, is not disturbed. For example, the 
presence of surfactants on the substrate surface to be coated can 
adversely affect formation of a good monomolecular or multimolecular film. 
However, it is possible for the substrates serving as the base material to 
be provided, on the surface to be coated, initially with an intermediate 
film prior to application of the thin films of the organic polymer, for 
example in order to achieve good adhesion between the solid, thin film of 
the organic polymer and the substrate. 
Examples of suitable materials for the substrates serving as the base 
material are metals, such as gold, platinum, nickel, palladium, aluminum, 
chromium, niobium, tantalum, titanium, steel and the like. Other suitable 
materials for the substrates included plastics, such as polyesters, e.g. 
polyethylene terephthalate or polybutylene terephthalate, polyvinyl 
chloride, polyvinylidene chloride, polytetrafluoroethylene, etc. 
Examples of other suitable materials for the substrates are silicon, glass, 
silica, ceramic materials and cellulose products. The surface of glass 
substrates can, if required, be rendered hydrophobic in a known manner, 
for example by reaction with alkylsilanes. The choice of the substrate 
materials depends mainly on the intended use of the novel film element. 
For optical elements, as a rule transparent or translucent substrates are 
used as the base material. If the novel film elements are used, for 
example, in the electrical industry or in electrochemical processes, in 
particular electrically conductive materials, such as metals, or materials 
having electrically conductive, in particular metallic, surface layers, 
for example metallized plastic films, serve as substrates. 
The substrates serving as the base material for the novel film elements may 
have any shape, depending on the intended use. For example, they may be 
film-like, foil-like, sheet-like, band-like or cylindrical or may be 
selected from any other shapes. In general, the base materials are flat, 
even substrates, such as film, foils, sheets, bands, metal sheets and the 
like. The substrate surface to be coated is preferably smooth, as is usual 
for the production of thin ordered films having a well defined structure, 
in particular monomolecular films or multimolecular films. In the case of 
the flat even substrates, such as films, foils, bands, etc., the novel 
thin ordered films of well defined structure and consisting of the organic 
polymers may be applied to one or both surfaces of the substrate. 
It may be advantageous to heat the resulting novel film element at elevated 
temperatures, in general from 50.degree. to 200.degree. C., preferably 
about 100.degree.-150.degree. C., directly after transfer of the 
monomolecular films from the water surface onto the substrate. The heating 
process as such may last, for example, for from a few minutes to a few 
hours, depending on the type and thickness of the novel film element. As a 
result of the heating step following the production of the novel film 
elements, the properties of the said elements can be stabilized or varied 
in a specific manner. 
The Examples which follow illustrate the invention. In the Examples, parts 
and percentages are by weight, unless stated otherwise. 
Synthesis of the polymethacrylates 
Atactic polyoctadecyl methacrylate, homopolymer and copolymers, were 
prepared in a conventional manner by free radical polymerization in 
toluene at from 60.degree. to 80.degree. C. using azobisisobutyronitrile 
as a free radical initiator. After the polymerization, the polymer was 
worked up by precipitation in methanol and purified by repeated 
reprecipitation from toluene in methanol. The polymer was finally dried at 
room temperature under reduced pressure. 
Isotactic polyoctadecyl methacrylate, homopolymer and copolymers, was 
obtained by anionic polymerization using phenylmagnesium bromide as an 
initiator (by the process due to W. E. Goode et al., J. Pol. Sc. 46 
(1960), 317 and 47 (1960), 75. Working up was similar to that for the 
atactic polymer. 
Synthesis of the polypeptides 
1. Copolycondensate of .gamma.-methyl L-glutamate and .gamma.-stearyl 
L-glutamate 
Poly-.gamma.-methyl L-glutamate was prepared from the N-carboxyanhydride 
compound of the .omega.-methyl ester of L-glutamic acid by polymerization 
with triethylamine in dioxane as an initiator at room temperature. The 
N-carboxyanhydride compound was prepared by phosgenation of the 
.omega.-methyl ester of L-glutamic acid in dioxane (J. L. Houben, A. 
Fissi, D. Baccrola, N. Rosato, O. Pieroni and F. Ciardelli, Int. J. Biol. 
Macromol. 5 (1983), 94). The degree of stearyl substitution (35% of 
stearyl radicals) was determined by elemental analysis. 
The copolycondensate was prepared from poly-.gamma.-methyl L-glutamate by 
reaction with stearyl alcohol at 60.degree. C. The catalyst used was 
p-toluenesulfonic acid (J. Watanabe, Y. Fukuda, R. Gehani and I. Nematyu, 
Macromolecules 17 (1984), 1004). The molecular weight (12,000) was 
determined by GPC using polystyrene as a standard. 
2. Poly(.gamma.-stearyl L-glutamate) 
The homopolymer was prepared in the same way as poly-.gamma.-methyl 
L-glutamate. The .omega.-stearyl ester of L-glutamic acid was prepared 
from L-glutamic acid and stearyl alcohol in tert-butanol at 80.degree. C. 
using concentrated sulfuric acid as the catalyst (Neth. Appl. 6, 500, 089, 
July 7, 1965; CA 64, 2,159 g (1966)). 
______________________________________ 
Molecular weights 
of the polymers: 
-- Mn .times. 10.sup.3 
______________________________________ 
Atactic polyoctadecyl 
7.2 
methacrylate 
Atactic copolymer of 
8 (13 primary mol 
octadecyl methacrylate % of dodecyl 
and dodecyl methacrylate methacrylate) 
Isotactic copolymer of 
8 (5 primary mol 
octadecyl methacrylate % of hexadecyl 
and hexadecyl methacrylate methacrylate) 
Isotactic polyoctadecyl 
7 
methacrylate 
Isotactic polyoctadecyl 
15 
methacrylate 
Poly(-.UPSILON.-octadecyl L- 
3* 
glutamate) 
Copolycondensate of .gamma.- 
.perspectiveto.12* 
(35% of octa- 
octadecyl L-glutamate and decyl groups) 
.gamma.-methyl L-glutamate 
______________________________________ 
*From GPC, based on polystyrene

EXAMPLE 1 
100 .mu.l of a 0.1% solution of the isotactic copolymer of 95 primary mol % 
of octadecyl methacrylate and 5 primary mol % of hexadecyl methacrylate in 
chloroform (Uvasol quality) were spread on the water surface of a Lauda 
Langmuir film balance by the conventional method at 28.degree. C. After 
the solvent had been evaporated, the film was compressed until the surface 
pressure was 15 mN/m. The film was stabilized under this pressure (about 1 
hour). When the surface area occupied was constant, a small quartz plate 
which had been rendered hydrophobic with hexamethyldisilazane was immersed 
vertically by the Langmuir-Blodgett method and pulled up at a speed of 50 
mm/min. The first film was transferred while the plate was being pulled up 
but the next film was transferred as early as during immersion (Y 
transfer). Transfer in the next cycles was monitored by means of a chart 
recorder. The pauses set were as follows: immersion in 34 seconds, out of 
water in 68 seconds. In this way, it was possible to apply not less than 
49 films with a constant transfer ratio. 
COMATIVE EXAMPLE 1 
The procedure described in Example 1 was followed, except that the polymer 
was an isotactic poly(octadecyl methacrylate) which had virtually no side 
chain nonuniformity and had the same molecular weight. This resulted in a 
rapidly decreasing Z-type transfer. 
COMATIVE EXAMPLE 2 
The procedure described in Comparative Example 1 was followed, except that 
the temperature was 32.degree. C. and the pressure 30 mN/m. The result was 
a Z-type decreasing transfer. 
EXAMPLE 2 
The procedure described in Example 1 was followed, except that the polymer 
used was atactic poly(octadecyl-co-dodecyl methacrylate) (13 primary mol % 
of dodecyl units). The temperature was 25.degree. C. and the pressure 11 
mN/m. The result was initially a Z-type transfer which became a Y transfer 
with constant transfer ratio. 
EXAMPLE 3 
The procedure described in Example 1 was followed, except that the 
substrate used was a gold film applied to glass by vapor deposition, and 
the pressure was 10 mN/m. Y transfer resulted. It was possible to transfer 
not less than 49 films with constant transfer ratio. 
COMATIVE EXAMPLE 3 
The procedure described in Example 1 was followed, except that the polymer 
used was an atactic poly(octadecyl methacrylate) and the pressure was 10 
mN/m. The result was virtually no transfer. 
EXAMPLE 4 
The procedure described in Example 1 was followed, except that the polymer 
used was a copolycondensate of .gamma.-methyl L-glutamate and 
.gamma.-octadecyl L-glutamate, the temperature was 20.degree. C. and the 
pressure was 25 mN/m. The result was 100% transfer of up to 200 films or 
more. 
COMATIVE EXAMPLE 4 
The procedure described in Example 4 was followed, except that the polymer 
used was the homopolymer poly(.gamma.-octadecyl L-glutamate). The result 
was a rapidly decreasing Y transfer. 
COMATIVE EXAMPLE 5 
The procedure described in Comparative Example 4 was followed, except that 
the temperature was 30.degree. C. A decreasing transfer from about the 
15th film onward resulted.