In a family of side-chain homopolymers of the polyacrylate type derived from 1-(phenyl)-2-(4-cyanophenyl)-ethane and exhibiting one or a number of mesophases, the polymer in accordance with the invention corresponds to the following general chemicals formula: ##STR1## where x indicates the degree of polymerization and 2.ltoreq.n.ltoreq.15.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a family of side-chain homopolymers of the 
polyacrylate type derived from 1-(phenyl)-2-(4-cyanophenyl)-ethane and 
exhibiting one or a number of mesophases. 
2. Description of the Prior Art 
Increasing consideration is being given at the present time to the 
possibility of utilizing polymeric materials in devices relating to the 
field of nonlinear optics or to the display field. The use of these 
polymers in display devices is subject to two conditions: they must have 
high dielectric anisotropy and also a nematic mesophase. There also exist, 
however, experimental display systems in which a smectic-A polymer is 
employed. Polymers having both these characteristics are in steadily 
increasing demand. A polymer of this type which possesses in addition a 
glass transition temperature of higher value than room temperature can 
advantageously be employed in the field of nonlinear optics. 
In order to satisfy these requirements, the invention proposes a family of 
homopolymers which exhibits high dielectric anisotropy due to the presence 
of a cyano group which produces at least one nematic mesophase at a high 
dipole moment and also, in the case of certain members of this family, 
gives rise to a glass transition temperature which is higher than room 
temperature. 
SUMMARY OF THE INVENTION 
The object of the invention is accordingly to provide a side-chain 
mesomorphic polymer which essentially corresponds to the following general 
chemical formula: 
##STR2## 
where x indicates the degree of polymerization and 2.ltoreq.n.ltoreq.15. 
The invention also relates to the method of manufacture of polymers of this 
family. 
The polymers obtained are designated by the following names: 
poly[1-(4-acryloyloxyethyloybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxypropyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxybutyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxypentyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-4-acryloyloxyhexyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxyheptyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxyoctyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxynonyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxydecyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxyundecyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxydodecyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane] 
poly[1-(4-acryloyloxytridecyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane 
] 
poly[1-(4-acryloyloxytetradecyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-etha 
ne] 
poly[1-(4-acryloyloxytetradecyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-etha 
ne

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The description which now follows will be concerned with the general 
process of synthesis of polymers in accordance with the invention as well 
as their physical characteristics. 
General synthesis process 
The polymers in accordance with the invention are usually obtained in ten 
steps from the following commercial products .omega.-bromoalkanoic acid, 
4-hydroxybenzoic acid, acrylic acid, 4-bromophenylacetic acid and anisol. 
Reaction 1: Production of 4-bromophenylacetyl chloride. This acid chloride 
is obtained by action of thionyl chloride on 4-bromophenylacetic acid. 
##STR3## 
Reaction 2: Synthesis of 4-(4-bromophenylacetyl)-4'-methoxyphenyl. 
4-(4-bromophenylacetyl)-4'-methoxyphenyl is obtained by action of 
4-bromophenylacetyl chloride on methoxybenzene in the presence of aluminum 
chloride and methylene chloride at a temperature of 4.degree. C. 
(Friedel-Crafts reaction). 
##STR4## 
The reaction yield is 75%. The melting point of the product obtained is 
139.degree. C. 
Reaction 3: Production of 1-(4-bromophenyl)-2-(4'-hydroxyphenyl)-ethane. 
4-(4-bromophenylacetyl)-4'-methoxyphenyl is reduced to 
1-(4-bromophenyl)-2-(4'-hydroxyphenyl)-ethane in accordance with the 
Wolf-Kishner reaction modified by Huang-Minlon by action of hydrazine (in 
an 85 wt % aqueous solution) in a basic medium and in the presence of 
diethyleneglycol. The basic medium is obtained by means of potassium. This 
reaction is accompanied by total interruption of the methyl ether 
function. 
##STR5## 
The phenol is separated from the 
1-(4-bromophenyl)-2-(4'-methoxyphenyl)-ethane by cold-state dissolution in 
methanol. The phenol is then recrystallized in benzene. 
The reaction yield is 85%. The melting point of the product obtained is 
125.degree. C. 
Reaction 4: Synthesis of 1-(4-cyanophenyl)-2-(4'-hydroxyphenyl)-ethane. 
1-(4-cyanophenyl)-2-(4'-hydroxyphenyl)-ethane is obtained by cyanidation of 
1-(4-bromophenyl)-2-(4'-hydroxyphenyl)-ethane by means of cupric cyanide 
by using N-methylpyrrolidone as solvent. 
##STR6## 
The reaction yield is 84%. The melting point of the product obtained is 
152.degree. C. 
Reaction 5 : Production of .omega.-bromoalkanol. 
This alcohol is obtained by reduction of the corresponding 
.omega.-bromoalkanoic acid by means of lithium hydride and aluminum in 
ether. 
##STR7## 
In the case in which n=6, the boiling point of the liquid obtained is 
101.degree. C. under a pressure of 4 mm of mercury and the reaction yield 
is 70%. The alcohols corresponding to n=2, 3 and 11 are available 
commercially. 
Reaction 6: Synthesis of 4(.omega.-hydroxyalkyloxy)-benzoic acid. 
This acid results from the action of .omega.-bromoalkanol obtained on 
completion of Reaction 5 on 4-hydroxybenzoic acid in a water-alcohol 
potassium medium. 
##STR8## 
In the case of n=6, the reaction yield is 66.5% and the thermal behavior is 
as follows: 
EQU C 137.2 (N) 114.2 L 
wherein the temperatures are expressed in degrees Celsius and C designates 
the crystal phase, (N) designates a monotropic nematic phase and L 
designates the liquid phase. 
Reaction 7: Production of 4-(acryloyloxyalkyloxy)benzoic acid. 
Esterification of the 4-(.omega.-hydroxyalkyloxy)benzoic acid obtained on 
completion of Reaction 6 by means of acrylic acid results in 
4-(acryloyloxyalkyloxy)benzoic acid. This esterification is carried out by 
using benzene as solvent and sulfonic paratoluene acid (SPTA) as catalyst. 
During the reaction, hydroquinone is used as polymerization inhibitor. 
##STR9## 
In the case of n=6, the reaction yield is 5% and the phase diagram is as 
follows: 
EQU C 83 S.sub.c 102 N 112 L 
wherein the temperatures are again expressed in degrees Celsius, and 
S.sub.c designates a smectic-C phase and N designates a nematic phase. 
Reaction 8: Synthesis of 4-(acryloyloxyalkyloxy)benzoyl chloride. 
Transition from the acid obtained on completion of Reaction 7 to the acid 
chloride is carried out in the cold state by means of oxalyl chloride by 
using dimethylformamide (DMF) as catalyst. 
##STR10## 
The use of oxalyl chloride instead of thionyl chloride for preparing the 
desired acid chloride makes it possible to retain the acrylate function. 
Reaction 9: Synthesis of 
1'-(4-acryloyloxyalkyloxybenzoyloxyphenyl)-2-(4'-cyanophenyl)-ethane. 
This ester is synthesized by action of the 4-(acryloyloxyalkyloxy)-benzoyl 
chloride obtained on completion of Reaction 8 on 
1-(4-cyanophenyl)-2-(4'-hydroxyphenyl)-ethane obtained on completion of 
Reaction 4 in tetrahydrofuran (THF) in the presence of triethylamine. 
##STR11## 
In the case of n=6, the reaction yield is 55%. 
Reaction 10: Polymerization of the monomers. 
Polymerization may be carried out in vacuo by employing 
.alpha..alpha.'azobisisobutyronitrile as free-radical initiator and by 
using chlorobenzene as solvent. 
By way of example, a few conditions of polymerization are grouped together 
in Table 1 to be found at the end of this specification. There are 
indicated in this table, in respect of a few values of n, the ratio M/A (M 
being the number of moles of the monomer and A being the number of moles 
of free-radical initiator), the temperature T in degrees Celsius and the 
time t in hours. Table 1 also mentions the average molecular weights Mp in 
grams and the index of polydispersity I. The average molecular weights 
have been determined by GPC (gel permeation chromatography) by adopting 
polystyrene as a standard. This table also indicates the efficiency of the 
polymerization operation. 
Reactions 7 and 8 are described in German patent No. DE 3,211,400 to 
Etzbach, Ringsdorf, Portugal and Schmidt. The other chemical reactions are 
conventional. 
A point to be noted is that Reaction 6 is not possible when n=4. In fact, 
in a basic medium, 4-bromol-1-butanol is cyclized in accordance with the 
following reaction: 
##STR12## 
In order to obtain 4-[-4'-acryloyloxybutyloxy]-benzoic acid (that is to say 
the final product coresponding to Reaction 7 in the general synthesis 
process), it is necessary to adopt the reaction diagram given hereunder. 
Shielding of the acid function of 4-hydroxybenzoic acid. 
##STR13## 
Etherification by means of 1,4-dibromobutane 
##STR14## 
Deshielding of the acid function. 
This reaction takes place first in an alcohol potassium medium and then in 
an acid medium. 
##STR15## 
Esterification with lithium acrylate in hexamethylphosphoramide (HMPA). 
##STR16## 
It is therefore apparent that, in the case of n=4, Reactions 5 to 7 of the 
general synthesis process are replaced by the four reactions given above. 
Physical Properties of the Polymers 
In order to determine their mesomorphic properties with accuracy, the 
polymers have been studied by differential enthalpic analysis, optical 
microscope and X-ray diffraction. 
By way of non-limitative example, Table 2 at the end of this specification 
records the results obtained in respect of different values of n. In this 
table, the letters G, N, N.sub.re, S, S.sub.A and L designate respectively 
the glassy, nematic, reentrant nematic, smectic, smectic-A and liquid 
phases. The transition temperatures indicated in this table are expressed 
in degrees Celsius. 
The polymers in accordance with the invention thus exhibit a nematic phase 
(n=2 or 6, for example), have a glass transition temperature which is 
higher than room temperature, are amorphous and carry a permanent dipole 
(cyano group) in their side chain, which permits alignment in an electric 
field). Accordingly, these polymers find a potential application in 
nonlinear optics and more particularly in the generation of second 
harmonics. They can in fact serve as an orientation matrix for small 
molecules having high second-order hyperpolarizability and can lead to 
non-centrosymmetric systems after orientation in an electric field. 
TABLE 1 
______________________________________ 
Conditions of 
polymerization GPC Efficiency 
n M/A T t Mp I (%) 
______________________________________ 
2 37 70 72 10 300 1.4 43 
6 33 70 72 7 900 1.4 77 
11 29 70 96 7 200 1.4 45 
______________________________________ 
TABLE 2 
______________________________________ 
n Mesomorphic properties 
______________________________________ 
2 G 75 N 220 L 
6 G 37 N.sub.re 
110 S.sub.A 
170 N 190 L 
11 G 42 S 210 L 
______________________________________