Poly(benxoic acid), method for the preparation thereof and method for the preparation of poly(p-phenylene) from poly(benzoic acid)

Disclosed is a novel polymeric compound poly(benzoic acid) which is a linear polymer consisting of the 1,4-phenylene linkages, each phenylene group having a carboxyl group. Poly(benzoic acid) can be prepared by hydrolyzing a poly(alkyl benzoate) in the presence of an acid or alkali. The thus obtained poly(benzoic acid) can be converted into a poly(p-phenylene) by the decarbonation reaction thereof in an organic solvent such as quinoline in the presence of metallic copper dust or a copper (II) compound such as copper (II) oxide and copper (II) carbonate hydroxide.

BACKGROUND OF THE INVENTION 
The present invention relates to a poly(benzoic acid), which is a novel 
compound not known in the prior art nor described in any literatures, a 
method for the preparation of a poly(benzoic acid) and a method for the 
preparation of a poly(p-phenylene) having electroconductivity, 
oxidation-reduction characteristic and excellent heat resistance and 
suitable as a polymeric electroconductive material and material of a 
heat-resistant polymer from the poly(benzoic acid). 
Poly(p-phenylene) is a known polymeric material having good 
electroconductivity and excellent heat resistance. Despite these unique 
properties as an organic polymer, the industrial application field of 
poly(p-phenylene) is still not so wide because of the difficult problems 
that poly(p-phenylene) is an insoluble and infusible polymer so that no 
conventional method is applicable to the molding work of the polymer and 
that the molecular weight thereof cannot be high enough with a relatively 
irregular molecular structure not to give a reproducible quality. 
A method for the preparation of a poly(p-phenylene) is disclosed in Journal 
of the American Chemical Society, volume 85, pages 454-458 (1963), 
according to which benzene is subjected to oxidative polymerization in the 
presence of aluminum chloride and copper (II) chloride. An alternative 
method is proposed in Synthetic Metals, volume 44, pages 107-110 (1992), 
in which benzene is electrolytically polymerized in fuming sulfuric acid 
to give a poly(p-phenylene). These methods, however, are practically 
defective since, in the former method, the poly(p-phenylene) is obtained 
in the form of a powder which is not susceptible to molding and, in the 
latter method, the polymer obtained has only a quit low degree of 
polymerization with consequently poor electric and mechanical properties 
although the polymer is obtained in the form of a film deposited on the 
surface of the electrode. 
Besides, a method is proposed in Macromolecules, volume 21, pages 294-304 
(1988), in which a poly(p-phenylene) is obtained in the form of a film 
through an intermediate having moldability. The polymer obtained by this 
method, however, does not consist of the 1,4-phenylene units alone but 
contains about 15% of the 1,2-phenylene units so that the electric 
properties thereof are not as desired. 
SUMMARY OF THE INVENTION 
The present invention accordingly has a primary object to provide a 
poly(benzoic acid) which is a novel polymeric compound having moldability 
and can be an intermediate for the preparation of a poly(p-phenylene) 
consisting substantially of the 1,4-phenylene units only as a secondary 
object of the invention. 
Namely, the present invention provides a poly(benzoic acid) which is a 
linear polymer consisting of the recurring monomeric units expressed by 
the chemical formula 
##STR1## 
In particular, a poly(benzoic acid) having a number-average degree of 
polymerization in the range from 30 to 20,000 can be readily prepared by 
the method described hereinbelow. 
Further, the method of the invention for the preparation of a 
poly(p-phenylene) comprises subjecting the above mentioned poly(benzoic 
acid) to a decarbonation reaction in the presence of a copper dust or a 
copper (II) compound.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The poly(benzoic acid) of the present invention, which is a novel compound 
not known in the prior art, Can be prepared by the hydrolysis of a 
poly(alkyl benzoate) represented by the general formula 
##STR2## 
in which R is a lower alkyl group having 1 to 4 carbon atoms, such as 
methyl, ethyl, propyl and butyl groups, and the subscript n is a positive 
number giving the number-average degree of polymerization, in particular, 
in the range from 30 to 2000. The hydrolysis reaction of a poly(alkyl 
benzoate) can be performed by using an acid or alkali as the catalyst. The 
poly(alkyl benzoate), e.g., poly(methyl benzoate), poly(ethyl benzoate), 
poly(propyl benzoate) or poly(butyl benzoate), as the starting material 
for the preparation of a poly(benzoic acid) can be prepared, for example, 
by the polycondensation reaction of an alkyl 2,5-dichlorobenzoate, e.g., 
methyl 2,5-dichlorobenzoate, in the presence of nickel bromide, triphenyl 
phosphine and metallic zinc according to the procedure disclosed in 
Macromolecules, volume 25, page 1816 (1992). 
The poly(benzoic acid) of the present invention can readily be converted 
into a poly(p-phenylene) when it is heated in an organic solvent in the 
presence of a catalyst to effect decarbonation reaction. Suitable 
catalysts for the decarbonation reaction include metallic copper dust and 
compounds of divalent copper such as copper (II) oxide, copper (II) 
carbonate and the like. Namely, the poly(benzoic acid) is dissolved in an 
organic solvent such as quinoline, N,N-dimethyl aniline and the like and 
the solution, in which the above mentioned copper catalyst is suspended, 
is heated at a temperature in the range from 130.degree. to 300.degree. C. 
or, preferably, from 170.degree. to 260.degree. C. so that the 
poly(p-phenylene) as formed is precipitated in the solution. The thus 
produced poly(p-phenylene) is insoluble in any organic solvents so that no 
known methods are applicable to the determination of the degree of 
polymerization thereof. It would be a fair assumption, however, that the 
above described reactions of the hydrolysis of the poly(alkyl benzoate) 
and decarbonation of the poly(benzoic acid) do not affect the degree of 
polymerization of the polymer so that the average degree of polymerization 
of the thus obtained poly(p-phenylene) be identical with that of the 
starting poly(alkyl benzoate). 
The present invention provides a means to easily obtain a poly(benzoic 
acid) which is soluble in many organic solvents and capable of being 
shaped into any desired forms such as a film. Accordingly, the present 
invention provides a possibility for the preparation of a shaped body, 
e.g., films and sheets, of a poly(p-phenylene), which is considered in the 
prior art to be insusceptible to molding or shaping due to the 
insolubility thereof in organic solvents, by first shaping a poly(benzoic 
acid) into a film or sheet followed by a decarbonation treatment thereof 
in a suitable organic solvent while keeping the shape of the Polymer as 
such. 
In the following, examples are given to illustrate the poly(benzoic acid) 
and the inventive method for the preparation thereof as well as the method 
for the preparation of a poly(p-phenylene) from the poly(benzoic acid) in 
more detail. The Reference Example given below preceding the Examples 
describes a method for the preparation of a poly(methyl benzoate). 
Reference Example 
Into a three-necked flask were introduced 1.30 g of nickel (II) bromide, 
11.9 g of triphenyl phosphine and 12.1 g of metallic zinc dust together 
with 90 ml of N,N-dimethyl formamide to form a reaction mixture which was 
heated at a temperature of 40.degree. to 45 .degree. C. under an 
atmosphere of argon with agitation. When the color of the reaction mixture 
turned reddish, a solution of 12.3 g of methyl 2,5-dichlorobenzoate in 60 
ml of N,N-dimethyl formamide was added dropwise into the reaction mixture 
which was heated at 80.degree. C. for 48 hours thereafter. After the end 
of this reaction time, the reaction mixture cooled to room temperature was 
admixed with an excess volume of acetone and agitated for 30 minutes 
followed by filtration to remove the unreacted methyl 2,5-dichlorobenzoate 
and triphenyl phosphine. The cake of the precipitates obtained by 
filtration was dispersed in an excess volume of diluted hydrochloric acid 
to dissolve the zinc dust followed by filtration of the mixture to collect 
the undissolved precipitates which were successively washed with water, 
methyl alcohol and acetone followed by drying in a vacuum desiccator at 
60.degree. C. for 5 hours. The thus obtained product could be identified 
to be a poly(methyl benzoate) having a number-average degree of 
polymerization of 106. The yield of this product was 85% of the 
theoretical value. 
EXAMPLE 1 
A reaction mixture consisting of 5 g of the poly(methyl benzoate) prepared 
in Reference Example described above and 50 ml of a 20% methyl alcohol 
solution of sodium hydroxide was heated for 1.5 hours under reflux. The 
reaction mixture was added to a dilute hydrochloric acid and heated 
therein for 10 minutes. The precipitates in the reaction mixture were 
collected by filtration, washed with water and dried under reduced 
pressure to give a white powder which could be identified to be a 
poly(benzoic acid) having a number-average degree of polymerization of 
106. The yield of the product was approximately quantitative according to 
the stoichiometry. This poly(benzoic acid) was soluble in quinoline, 
pyridine and an aqueous solution of sodium hydroxide. FIG. 1 of the 
accompanying drawing shows an infrared absorption spectrum of the 
poly(benzoic acid). The characteristic peaks in the spectrum at wave 
numbers of 1710 cm.sup.-1 and 1230 cm.sup.-1 could be assigned to the 
stretching vibration of the C.dbd.O bond and stretching vibration of the 
C--O bond, respectively. 
EXAMPLE 2 
A reaction mixture formed by adding 3.5 g of the poly(benzoic acid) 
prepared in Example 1 and 0.32 g of copper (II) oxide to 50 ml of 
quinoline was heated under reflux for 5 hours in an atmosphere of argon. 
After the end of the reaction time, the reaction mixture was admixed under 
agitation with acetone to remove quinoline and the precipitates separated 
from the reaction mixture were agitated in a dilute hydrochloric acid to 
remove the inorganic matter. The precipitates collected by filtration was 
successively washed with water and methyl alcohol followed by drying in a 
vacuum desiccator at 60.degree. C. for 5 hours. The thus obtained product 
in a powdery form could be identified to be a poly(p-phenylene) from the 
infrared absorption spectrum shown in FIG. 2 of the accompanying drawing, 
in which the strong and sharp peak at about 800 cm.sup.-1 could be 
assigned to the 1,4-phenylene linkage. The yield of the product was 
approximately quantitative assuming the stoichiometry of the decarbonation 
reaction. This poly(p-phenylene) was insoluble in any organic solvents as 
well as in an aqueous alkali or acid solution. 
EXAMPLE 3 
A reaction mixture formed by adding 3.0 g of the poly(benzoic acid) 
prepared in Example 1 and 0.14 g of copper (II) carbonate hydroxide to 48 
ml of quinoline was heated under reflux for 5 hours in an atmosphere of 
argon. The reaction mixture was treated subsequently in the same manner as 
in Example 2 to give a product in a powder form. This product could be 
identified to be poly(p-phenylene) from the infrared absorption spectrum 
which was substantially identical with that of the product obtained in 
Example 2. This poly(p-phenylene) product was also insoluble in any 
organic solvents as well as in an aqueous alkali or acid solution.