Rigid Rod Aromatic Benzthiazole Heterocyclic Polymer

The invention relates to high molecular weight benzobisazole polymers containing pendent benzthiazole groups.

In general, the class of aromatic heterocyclic extended chain polymers are well known for their outstanding thermal, physical and chemical properties. These polymers generally exhibit excellent modulus and tenacity properties, but lack good properties when in compression, which limits their use as reinforcing structural fibers.

It is an object of the present invention to provide aromatic heterocyclic polymers which exhibit improved compressive properties.

Other objects, aspects and advantages of the present invention will be apparent to those skilled in the art from a reading of the following detailed disclosure of the invention.

In accordance with the present invention there are provided polymers having repeating units of the formula ##STR7## wherein R.sub.1 is --H or ##STR8## R.sub.2 is ##STR9## R.sub.3 is ##STR10## and R.sub.4 is R.sub.2 or ##STR11## and B is ##STR12## wherein X is --S--, --O-- or --NH--.

The polymers of this invention are prepared by the polycondensation of 4,6-diaminoresorcinol dihydrochloride, 2,5-diaminohydroquinone dihydrochloride, 4,6-diamino-1,3-benzenedithiol dihydrochloride, 2,5-diamino-1,4-benzenedithiol dihydrochloride or 1,2,4,5-tetraaminobenzene tetrahydrochloride and a phenylbenzthiazole-substituted p-terphenylene dicarboxylic acid of the formula ##STR13## wherein R.sub.1 is --H or ##STR14## R.sub.2 is ##STR15## R.sub.3 is ##STR16## and R.sub.4 is R.sub.2 or ##STR17##

Preparation of the phenylbenzthiazole-substituted p-terphenylene dicarboxylic acid is described in our co-pending application Ser. No. 227,978, filed of even date herewith.

In conducting the process, the amino hydrochloride monomer may be mixed with polyphosphoric acid (PPA), then heated, under vacuum or an inert gas atmosphere to about 70.degree. to 130.degree. C. over a period of about 3 to 24 hours, do dehydrochlorinate the amino monomer. At the end of this period, the dicarboxylic acid is added. An additional amount of phosphorous pentoxide and/or PPA may be added as required to provide a stirrable mixture. Alternatively, the amino hydrochloride and dicarboxylic acid monomers may be mixed with polyphosphoric acid, then heated, under vacuum or an inert gas atmosphere to about 70.degree. to 130.degree. C. over a period of about 3 to 24 hours, to dehydrochlorinate the amino monomer. Equimolar amounts of the amino and dicarboxylic acid monomers are generally used. The amount of PPA used is that which is sufficient to provide a stirrable mixture. In general, the concentration of monomers in the acid ranges from about 0.5 to 12.0 percent.

Following dehydrochlorination, the reaction mixture is heated at a temperature in the range of about 75.degree. to 225.degree. C. for a period ranging from 24 to 96 hours. Preferably, the polymerization is carried out in stages, i.e., a step-wise heating schedule is employed. Step-wise heating is preferred because immediately exposing the reaction mixture to relatively high polymerization temperatures may cause decomposition of the monomers. The selection of a particular step-wise heating schedule is obvious to one of ordinary skill in the art. At the end of the reaction period, the polymer solution is in a very viscous or semi-solid state. After cooling, the product is washed repeatedly with water while stirring, after which it is dried under a high vacuum at an elevated temperature.

The molecular weight of these polymers is commonly indicated by the inherent viscosity of the polymer. The inherent viscosity is commonly determined at a concentration of 0.2 weight/volume percent in methanesulfonic acid at 30.degree. C.

The polymers produced in accordance with the process of the present invention may be used to produce fibers and sheets. In order to form these polymers into fibers or sheets, dopes are prepared containing about 5 to 15 weight percent of the polymer in a strong acid, such a sulfuric acid, methanesulfonic acid, chlorosulfuric acid, and the like, including mixtures thereof. Such dopes may be spun or extruded into a coagulation bath comprising water or a water/methanesulfonic acid mixture.

The following examples illustrate the invention:

The monomers 4,4'-dicarboxy-2'5'-diphenyl-3',6'-[2-(4-phenylbenzthiazole)]-p-terphenyl (0.8892 g, 1.0 mmol) and 2,5-diamino-1,4-benzenedithiol dihydrochloride (0.2452 g, 1.0 mmol) were placed in 97 g PPA (84% P.sub.2 O.sub.5). Under a nitrogen atmosphere, the mixture was heated slowly to 90.degree. C. to effect dehydrochlorination and then heated as follows: 105.degree. C. for 2 h; 150.degree. C. for 19 H; and 190.degree. C. for 24 h. The polymer was precipitated into water, washed with ammonium hydroxide, methanol, and hexane. The air-dried polymer was further dried under reduced pressure (0.02 mm) at 100.degree. C. for 16 h. An intrinsic viscosity of 12 dL/g was measured in methanesulfonic acid at 30.degree. C.

Analysis Calcd. for C.sub.64 H.sub.36 N.sub.4 S.sub.4 : C, 77.70; H, 3.67; N, 5.66. Found: C, 75.88; H, 3.75; N, 5.52.

The monomers 4,4"-dicarboxy-2'-phenyl-3',6'-[2-(4-phenoxyphenyl)benzthiazole]-p-terphen yl (0.4524 g, 0.5 mmol) and 2.5-diamino-1,4-benzenedithiol dihydrochloride (0.1225 g, 0.5 mmol) were placed in 198 g PPA (84% P.sub.2 O.sub.5). Under a nitrogen atmosphere, the mixture was heated slowly to 65.degree. C. to effect dehydrochlorination and then heated as follows: 70.degree. C. for 4 h, 150.degree. C. for 24 h, and 175.degree. C. for 1 h. The polymer was precipitated into water, washed with concentrated ammonium hydroxide, washed with water, methanol, methanol/benzene mixtures, and finally with benzene. The swollen polymer was then frozen and dried under reduced (0.02 mm) pressure to give 0.37 g (93.5%) of polymer: [.eta.]=11.7 dL/g in methanesulfonic acid at 30.degree. C.

Analysis Calcd. for C.sub.64 H.sub.36 N.sub.2 S.sub.4 O: C, 76.46; H, 3.61; N, 5.57. Found: C, 74.52; H, 3.54; N, 5.00.

A mixture of 4,4"-dicarboxy-2'-phenyl-3',6'-[2-(4-phenylbenzthiazole)]-p-terphenyl (3.2517 g, 4.0 mmol), 2,5-diamino-1,4-benzenedithio dihydrochloride (0.9802 g, 4.0 mmol), and 24.98 g, PPA (77 percent P.sub.2 O.sub.5) was placed in a resin flask equipped with a high torque mechanical stirrer, nitrogen/outlet, and a pressure regulator. Under a nitrogen flow, the flask was evacuated by means of a water aspirator pump. The monomers were incorporated into the PPA by stirring, and the resulting mixture was then dehydrochlorinated under reduced pressure (600 mm) by heating as follows: 25.degree. C./4 hours; 60.degree. C./h: 85.degree. C./2 hours. To this mixture was added, under a nitrogen atmosphere 10.45 g of P.sub.2 O.sub.5. The mixture was heated as additional 56 hours/85.degree. C. The polymer was precipitated into water, washed repeatedly with water, methanol and dried under reduced pressure (0.02 mm) at 138.degree. C. An intrinsic viscosity of 23.0 dL/g was measured in methanesulfonic acid at 30.degree. C.

Analysis Calcd. for C.sub.58 H.sub.32 N.sub.4 S.sub.4 : C, 76.28; H, 3.53; N, 6.14. Found: C, 75.30; H, 3.15; N, 5.40.

The monomers 4,4"-dicarboxy-2',5'-diphenyl-3',6'-[2-(4-phenylbenzthiazole)]-p-terphenyl (0.4445 g, k0.5 mmol) and 4,5-diamino-1,3-benzenediol dihydrochloride (0.1065 g, 0.5 mmol) were placed in 100 g PPA (84% P.sub.2 O.sub.5). Under a nitrogen atmosphere, the mixture was heated to 60.degree. C. to effect dehydrochlorination (16 h) and then heated as follows: 100.degree. C. for 5 h, 150.degree. C. for 16 h, 175.degree. C. for 8 h, 180.degree. C. for 16 h, and 190.degree. C. for 2 h. The polymer was precipitated into water, washed with ammonium hydroxide, water, and methanol. The air-dried polymer was further dried under reduced pressure (0.02 mm) at 100.degree. C. for 16 h. An instrinsic viscosity of 7.7 dL/g was measured in methanesulfonic acid at 30.degree. C.

Analysis Calcd. for C.sub.64 H.sub.36 N.sub.4 S.sub.2 O.sub.2 : C, 80.31; H, 3.79; N, 5.85. Found: C, 74.99; H, 3.76; N, 5.67.

The monomers 4,4"-dicarboxy-2'-phenyl-3',6'-[2-4-phenoxyphenyl)benzthiazole]-p-terpheny l (0.4528 g, 0.5 mmol) and 4,6-diamino-1,3-benzenediol dihydrochloride (0.1066 g, 0.5 mmol) were placed in 198 g PPA (84% P.sub.2 O.sub.5). The temperature was raised to 75.degree. C. under a nitrogen atmosphere to effect dehydrochlorination of the amino monomer and then heated as follows: 150.degree. C./18 h; 180.degree. C./6.5 h. The polymer was precipitated into water, washed with concentrated ammonium hydroxide, water, and methanol. The air-dried polymer was further dried under reduced pressure (0.02 mm) at 100.degree. C. for 16 h. An intrinsic viscosity of 8.44 dL/g was measured in methanesulfonic acid at 30.degree. C.

Analysis Calcd. for C.sub.64 H.sub.36 N.sub.4 S.sub.2 O.sub.3 : C, 78.99; H, 3.73; N, 5.76. Found: C, 75.75; H, 3.79; N, 5.36

Various modifications of the present invention can be made in view of the foregoing disclosure without departing from the spirit and scope of the invention.