High refractive index polymers

Ethylenically unsaturated polymerizable acrylic (or methacrylic) monomers having pendant halogenated carbazole moieties, useful for the production of high refractive index polymers, are disclosed. The monomers are useful for the bonding of optical elements in the fabrication of optical devices.

BACKGROUND OF THE INVENTION 
This invention relates to novel polymerizable monomers for the production 
of polymers having application in the production of optical devices. More 
particularly, it relates to certain polymerizable monomers for use in the 
production of polymers exhibiting high refractive indices. 
In the production of optical devices, such as those fabricated from glass 
or plastic materials or components, design considerations will oftentimes 
dictate the use of polymeric materials having particular optical 
properties. In U.S. Pat. No. 4,426,505 (issued Jan. 17, 1984 to R. A. 
Minns) there is described, for example, the production of certain 
polyvinyl polymers which combine a relatively high index of refraction 
with a relatively high Abbe number, so as to provide optical properties 
which exceed those of the polymers which are used conventionally in the 
manufacture of plastic lenses. 
In the production of optical elements, components and devices, particular 
performance requirements may dictate the need for polymeric materials 
which have a high index of refraction. In addition, practical 
considerations will require that the monomeric precursor materials of such 
polymers, or the polymers, have melting, softening or other physical 
properties which permit the polymers to be incorporated into an optical 
element, component or device. For example, a polymeric material exhibiting 
a desirably high index of refraction may exhibit softening point or glass 
transition temperatures which are higher than can be accommodated in the 
manufacture of an optical element, component or device. Similarly, 
polymeric materials which can be readily formed or fabricated will 
oftentimes fail to exhibit the high index of refraction desired for a 
particular application. It will be appreciated, therefore, that there will 
be considerable interest in monomers which can be readily polymerized in 
place to provide high refractive index polymers. 
SUMMARY OF THE INVENTION 
It has been found that polymers having high refractive indices can be 
prepared from certain polymerizable monomers of the acrylic (or 
methacrylic) ester type having pendant halogenated carbazole moieties 
spaced from the reactive (polymerizable) acrylic or methacrylic ester 
group by a spacer or linking group. In one of its composition aspects, the 
present invention provides a polymerizable monomer having the formula: 
##STR1## 
wherein each of X.sup.1, X.sup.2 and X.sup.3 is chlorine, bromine or 
iodine; each of Y.sup.1, Y.sup.2, Y.sup.3, Y.sup.4 and Y.sup.5 is 
hydrogen, chlorine, bromine or iodine; R is hydrogen or methyl; and Z is a 
linking group 
EQU --CH.sub.2).sub.k [O--CH.sub.2).sub. m ].sub.n 
wherein k is an integer of from 1 to 12, m is an integer of from 2 to 4, 
and n is zero or the integer one or two. 
In another of its compositional aspects, the invention provides a polymer 
comprising repeating units of the formula: 
##STR2## 
wherein R, Z, X.sup.1, X.sup.2, X.sup.3, Y.sup.1, Y.sup.2, Y.sup.3, 
Y.sup.4 and Y.sup.5 have the aforedescribed meanings.

DETAILED DESCRIPTION OF THE INVENTION 
As mentioned previously, the polymerizable monomers of the invention, 
represented by Formula (A-1), are useful for the production of polymers 
which have the repeating units represented by Formula (A-2) and which 
exhibit high indices of refraction. The refractive indices of 
homopolymers, for example, are generally in the range of from 1.67 to 
1.77. It can be seen from inspection of Formula (A-1) and the meanings set 
forth in connection therewith, that the polymerizable monomer of the 
invention comprises an ethylenically unsaturated polymerizable acrylic (or 
methacrylic) ester group and a pendant halogen-substituted carbazole 
moiety which is linked to the polymerizable group by a spacer or linking 
group, Z. The halogen-substituted carbazole moieties include certain 
halogen groups (X.sup.1, X.sup.2 and X.sup.3) which independently can 
comprise chlorine, bromine or iodine. It will be seen, thus, that the 
pendant carbazole nucleus contains at least three halogen substituents. In 
general, each of X.sup.1, X.sup.2 and X.sup.3 will be the same halogen, 
for ease in synthetic preparation. These substituent groups need not, 
however, be the same. Since refractive index will normally vary in the 
order Cl&lt;Br&lt;I, it will be preferred that the X.sup.1, X.sup.2 and X.sup.3 
substituents be bromine or iodine. 
Additional positions on the pendant carbazole moiety, represented by 
Y.sup.1, Y.sup.2, Y.sup.3, Y.sup.4 and Y.sup.5, can also be halogen, i.e., 
chlorine, bromine or iodine; or each of Y.sup.1, Y.sup.2, Y.sup.3, Y.sup.4 
and Y.sup.5 can be hydrogen. In general, good results, from the standpoint 
of providing polymers of high index of refraction, can be obtained where 
each of X.sup.1, X.sup.2 and X.sup.3 is chlorine, bromine or iodine 
(preferably, bromine or iodine) and each of the Y groups is hydrogen. Good 
results are also obtained where each of X.sup.1, X.sup.2 and X.sup.3 is 
chlorine, bromine or iodine (preferably, bromine or iodine), Y.sup.1 is 
chlorine, bromine or iodine (preferably, bromine or iodine) and each of 
Y.sup.2, Y.sup.3, Y.sup.4 and Y.sup.5 is hydrogen. Refractive indices can 
be varied with the number and type of halogen substituent and be 
controlled to meet particular requirements. 
Spacer or linking group Z provides an important function in control of the 
melting temperature of the monomeric compound and of physical, e.g., glass 
transition, properties of corresponding polymers. Linking group Z, 
represented by the formula, 
EQU --CH.sub.2).sub.k [ O--CH.sub.2).sub.m ].sub.n 
can be an alkylene linking group (where n is zero) or can be an oxygen 
ether-containing group (where n is an integer one or two). Preferably, for 
ease in preparation, n will be zero, and k will an integer of from 1 to 12 
(e.g., 2 to 6). Alkylene linking groups of from 2 to 6 carbon atoms serve 
to effectively link the halogenated carbazole moiety to the reactive 
(polymerizable) ester group of the monomer. 
If desired, linking group Z can include oxygen ether atoms, i.e., where n 
is one or two. Such linking groups can be incorporated into the monomers 
of the invention by an alkylation procedure, using an 
.alpha.,.omega.-dibromomonoether or diether. Preferably, m will be 
1,2-ethylene and n will be one or two in the case of such ether linking 
groups, Z. 
The nature of linking group Z can influence important properties of 
polymers prepared from the polymerizable monomers of the invention. In 
general, a lengthening of the Z linking group will tend to decrease 
indices of refraction while tending also to lower melting points and glass 
transition temperatures. It will be appreciated that it will be preferred 
that spacer group Z comprise a group which allows the monomer to be 
applied or processed readily in a manufacturing operation and that, 
therefore, a flexible linking group having, for example, 4 to 6 carbon 
atoms will be preferred. The index-lowering effect associated with 
increasing length of the spacer (for desired processability) can be 
compensated for, in part, by the presence of the halogen substituents on 
the carbazole moiety. For example, the refractive index of 
polyvinylcarbazole (no halogen substituents and no spacer) and of 
poly[4-(1,3,6,8-tetrabromo-9-carbazolyl)-1-butyl methacrylate] is in each 
case 1.68. 
Good results from the standpoints of providing low monomer melting points 
(for improved processing, particularly in the application of monomer to 
optical components or devices for processing in place) and high indices of 
refraction of the resulting polymers can be obtained by using a mixture of 
monomer compounds having different spacer groups. The mixtures melt at 
lower temperatures than the individual compounds. In the case of 
heptabromocarbazole methacrylates, a preferred mixture is a ternary 
mixture composed of equal weights of such compounds having butylene, 
pentylene and hexylene linking groups. Although the melting temperature of 
this composition is very broad (and the composition is a soft and 
taffy-like solid at room temperature), it converts completely to an 
isotropic liquid at 50.degree. C., provides a high index of refraction 
(1.72) and can be used as an adhesive for the bonding of optical elements 
or components. 
The polymerizable monomer of Formula (A-1) can be an acrylic or methacrylic 
ester depending upon whether R is hydrogen or methyl. In general, the 
acrylates will provide polymers of lower glass transition temperature than 
the corresponding methacrylates. 
The polymerizable monomers of Formula (A-1) can be prepared by resort to 
known organic preparative routes. The monomers can be prepared from 
carbazole using conventional halogenation, alkylation and esterification 
steps. The synthesis of unsubstituted carbazole acrylates is known and 
details of the preparation thereof are reported by Chau-Jin Hu, et al., J. 
Polym. Sci., Polym. Lett., 26, 441 (1988) and by C. I. Simionescu, et al., 
in Makromol., Chem., 190, 1537 (1989). In the production of the 
substituted carbazolecontaining monomers of the invention, the inexpensive 
and readily available compound, carbazole, can be halogenated (preferably, 
brominated or iodinated) and then alkylated at the nitrogen atom thereof 
by reaction with a difunctional compound of the formula 
EQU Hal-Z-Hal 
where Hal represents halogen (e.g., bromine). The resulting alkylated 
compound can then be esterified by reaction, in known manner, with a 
tetraalkyl ammonium acrylate (or methacrylate). 
In FIG. 1 is shown a reaction scheme for the production of certain 
preferred acrylate (and methacrylate) monomers of the invention having 
pendant bromine-substituted carbazole moieties. The reaction scheme of 
FIG. 1 is intended as being illustrative and is not intended to be limited 
to the particulars illustrated therein. In FIG. 1, is shown the reaction 
of carbazole with bromine in acetic acid (at 90.degree. C. for 8 hours) 
for production of the tetrabrominated carbazole, I. Alternatively, 
iodination can be conducted similarly under mild conditions with 
isolation, for example, of the triiodo compound, VI, shown in FIG. 2. 
The tetrabromo compound (I) shown in FIG. 1 can be alkylated, as previously 
mentioned, for attachment of linking (spacer) group Z, using known 
methodology. As shown in FIG. 1, this can be accomplished by reaction with 
a large excess of, for example, .alpha.,.omega.-dibromoalkane and 
potassium carbonate in refluxing acetonitrile. This straightforward 
reaction provides a high yield of the desired alkylated product, II, shown 
in FIG. 1. In like manner, the alkylated iodine-substituted carbazole 
compound, VII, can be prepared, as in shown in FIG. 2. 
If desired, higher levels of bromination of the brominated rings of 
compound II can be achieved by reaction with equal volumes of bromine and 
tetrachloromethane under reflux, to yield the highly brominated compound 
shown as compound IV in FIG. 1. In the case of bromination of compound II, 
only one of the aromatic rings of carbazole could be perbrominated. 
Bromine could be added to the second ring only at the C-7 position; the 
C-5 position was completely unreactive as the likely result of steric 
hindrance by the bromine atom on the C-4 position of the first ring. In 
like manner, and as shown in FIG. 2, further iodination of an 
iodine-substituted carbazole (VII) can be effected. Iodination of the ring 
of compound VII can be accomplished with iodine and 
[bis(trifluoroacetoxy)iodo]benzene for several days at room temperature to 
yield compound VIII, shown in FIG. 2. Attempts at higher iodination by 
this route were not successful, probably because of steric effects. 
The desired polymerizable monomer of the invention can be provided in high 
yield via an esterification reaction, whereby the N-(.omega.-bromoalkyl) 
halogenated carbazole (e.g., compound II or VII in FIGS. 1 or 2, 
respectively) is reacted with the tetrabutylammonium salt of the desired 
acid anion. In the bromocarbazole series, the yields of III and V ranged 
from 66-91%; for the two iodinated methacrylates, IX and X, the yields 
were 90 and 91%. 
The polymerizable monomers of Formula (A-1) can be polymerized, for 
example, by thermal, bulk polymerization or by conventional free-radical 
solution polymerization methods based upon free-radical initiators such as 
azobisisobutyronitrile and azobis-.alpha.,.gamma.-dimethylvaleronitrile. 
Such methods are known in the art and the desired polymers can be isolated 
by evaporation of the polymerization solvent or, by precipitation into a 
non-solvent for the polymer. 
Polymerization of the monomer can be performed readily by melting the 
monomer (or a mixture thereof) between glass circles on a Fisher-Johns 
melting point apparatus and maintaining the liquid at a temperature above 
its melting point for several minutes. The glass circles adhere together 
as the polymer is formed, resulting in an optically clear and colorless 
sandwich. For example, the compound IIIb shown in Table 1 hereinafter, 
when maintained for several minutes at 170.degree. C. in such an 
apparatus, yields the corresponding homopolymer which softens at 
approximately 200.degree. C. and can be made to flow at 250.degree. C. 
without discoloration. Upon cooling, the glass elements can be pried apart 
(with a razor blade) or dissolved in hydrofluoric acid to separated the 
brittle polymer. Similarly, a low-melting blend (mp&lt;50.degree. C.) of 
three heptabromo monomers V (with n=4,5 and 6) was prepared by dissolving 
20 mg each of Vb, Vc and Vd (described in Table 1) in dichloromethane, 
filtering the solution and evaporating the solvent in a stream of 
nitrogen. Application of a vacuum to remove final traces of solvent 
yielded a taffy-like foam. A sample thereof placed between two glass 
circles on a Fisher-Johns melting point apparatus melted below 50.degree. 
C. to a clear liquid and polymerized at approximately 100.degree. C. to a 
clear film. 
The polymerizable monomers of the invention can be used in the production 
of optical elements, components and devices particularly by polymerization 
in place. For example, in U.S. Pat. No. 4,446,305 (issued May 1, 1984 to 
H. G. Rogers, et al.) there are described optical devices based upon 
highly birefringent rod-like polymers, including an optical beam splitter 
having a film of birefringent polymer between a pair of prismatic 
elements. A mixture of polymerizable monomers of the invention can be 
utilized as an adhesive for the elements of such an optical device and can 
be polymerized in place. The mixture can be liquified and polymerized 
between the elements thereof to provide a colorless, non-birefringent, 
amorphous optical binding agent exhibiting a high refractive index, e.g., 
in the range of 1.67 to 1.77. 
The polymerizable monomers of the invention are characterized by properties 
especially suited for optical applications where a high index polymer is 
required. Typically, a material suited for such applications (1) should be 
a liquid or a low-melting solid near room temperature; (2) must not 
dissolve or swell the polymer film or other element or component of the 
fabricated device; and (3) must polymerize rapidly by thermal or 
photochemical initiation. 
Polymers produced from the monomers must (1) bond polymer films to glass or 
other polymer films; (2) be optically transparent, i.e., colorless and 
nonscattering; (3) not be too brittle; and (4) have a high index of 
refraction, e.g., &gt;1.67. 
Monomers and polymers which provide the aforementioned advantages and meet 
the aforementioned requirements are provided by the present invention. 
Further illustration of the invention is set forth in the following 
examples which are intended as illustrative and not limitative of the 
invention. All parts and proportions, except where otherwise noted, are by 
weight. Molecular structure was confirmed in each Example by NMR and mass 
spectral analyses. 
EXAMPLE 1 
Part A--Preparation of 1,2,6,8-Tetrabromocarbazole (FIG. 1. Compound I) 
Into a 250-ml, three-necked, round-bottomed flask equipped with an oil 
bath, a magnetic stirrer, a thermometer, an addition funnel, and a 
condenser topped by a calcium chloride drying tub=leading to a water trap 
for evolved HBr were placed 3.4 g (0.02 mole) carbazole and 50 ml glacial 
acetic acid. With stirring at room temperature, a solution of 4.5 ml 
bromine in 50 ml acetic acid was run in, then the oil bath was heated to 
90.degree. and the mixture was stirred for 8 hours. After standing 
overnight at room temperature, the product was collected by filtration and 
recrystallized from toluene/acetic acid to yield 7.6 g (79%) of light 
yellow crystals, mp 228.degree.-231.degree. C. (mp 233.degree.-5.degree. 
C. from literature, J. Pielichowski and J. Kyziol, Monarshefte Chemie, 
105, 1306 (1974). 
Part B--Preparation of 9-(4-bromobutyl)-1,3,6,8-tetrabromocarbazole (FIG. 
1, Compound II. n=4) 
Into a 100-ml, three-necked, round-bottomed flask equipped with an oil 
bath, a magnetic stirrer, a thermometer, and a condenser connected to a 
nitrogen bubbler were placed 1.0 g I, 5 ml (20 equiv) 1,4-dibromobutane, 3 
g (10 equiv) powdered anhydrous potassium carbonate, and 20 ml anhydrous 
acetonitrile. The mixture was stirred under reflux with the oil bath at 
100.degree. C. for 18 hours. Most of the acetonitrile was then distilled, 
water and dichloromethane were added, and the two phases were separated. 
The aqueous phase was extracted twice with dichloromethane, and the 
combined organic phase was dried over anhydrous sodium sulfate and 
filtered through a pad of Celite.RTM. to give a light-yellow clear 
solution. Dichloromethane and most of the excess 1,4-dibromobutane were 
evaporated on a steam bath in a stream of nitrogen. The resulting oil was 
dissolved in 100 ml boiling dichloromethane, and methanol was added until 
crystals appeared. After cooling in an ice-water bath, the light yellow 
crystals were filtered and dried to yield 1.02 g (80%); mp 
142.degree.-4.degree. C. 
The following homologues of the compound of Part B of this Example were 
similarly prepared: 
n=2, 92% yield, mp 191.degree.-4.degree. C. 
n=3, 93% yield, mp 157.degree.-9.degree. C. 
n=5, 93% yield, mp 136.degree.-8.degree. C. 
n=6, 90% yield, mp 122.degree.-3.degree. C. 
Part C--Preparation of Compound IIIb, 
4-(1,3,6,8-tetrabromo-9-carbazolyl)-1-butyl methacrylate (FIG. 1, Compound 
III, n=4) 
A solution of tetrabutylammonium methacrylate was prepared in a 50-ml 
round-bottomed flask by titrating 0.1 ml methacrylic acid in 10 ml 
methanol with approximately 1.2 ml of a 1M solution of tetrabutylammonium 
hydroxide in methanol until the solution was just basic to wet pH paper. 
The solution was acidified with several drops of methacrylic acid, and the 
solvents were removed on a rotary evaporator at 30.degree. C. Acetonitrile 
was then added and evaporated to remove remaining water and methanol. The 
resulting oil was dissolved in 10 ml acetonitrile, and 682 mg 
9-(4-bromobutyl)-1,3,6,8-tetrabromocarbazole along with 10 ml benzene were 
added. The mixture was warmed briefly to effect solution, and the 
resulting solution was stirred overnight at room temperature under 
nitrogen. Solvents were then evaporated with the temperature maintained 
below 40.degree. C., water was added, and the mixture was extracted with 
benzene. The organic phase was dried and evaporated, and the crude product 
was purified by flash chromatography on silica gel with 1:1 
dichloromethane/hexanes to yield 594 mg (86%) white crystals; mp 
155.degree.-156.5.degree. C. 
The following homologues of the compound (IIIb) of Part C of this Example 
were similarly prepared: 
IIIa, n=3, mp 177.degree.-8.degree. C. 
IIIc, n=5, 72% yield, mp 146.degree.-8.degree. C. 
IIId, n=6, 94% yield, mp 124.degree.-6.degree. C. 
EXAMPLE 2 
Part A--Preparation of 9-(6-bromohexyl)-1,2,3,4,6,7,8-Heptabromocarbazole 
(FIG. 1, Compound IV, n=6) 
Into a 250-ml round-bottomed flask equipped with an oil bath, a magnetic 
stirrer, and a condenser topped by a calcium chloride drying tube leading 
to a water trap for evolved HBr were placed 5.0 g (7.74 mmol) 
9-(6-bromohexyl)-1,3,6,8-tetrabromocarbazole, 50 ml bromine, and 50 ml 
tetrachloromethane. The solution was stirred overnight under reflux. 
Excess bromine and tetrachloromethane were then recovered by distillation 
for use in another run, and the solid was blown dry in a stream of 
nitrogen. Recrystallization from carbon disulfide/ethanol yielded 6.23 g 
(91%) of a white solid; mp 161.degree.-2.degree. C. The following 
homologues of the compound of Part A of this Example were similarly 
prepared: 
n=4, mp 189.degree.-91.degree. C. 
n=5, 84% yield, mp 165.degree.-7.degree. C. 
Part B--Preparation of 
.gamma.-(1,2,3,4,6.7,8-heptabromo-9-carbazolyl)-.alpha.-alkyl 
(meth)acrylates (FIG. 1, Compound V) 
These monomers (Compounds Va, Vb, Vc and Vd) were prepared from the alkyl 
bromides by a procedure analogous to that described in EXAMPLE 1, Part C, 
for the preparation of 4-(1,3,6,8-tetrabromo-9-carbazolyl)-1-butyl 
methacrylate above. The structures (V) were confirmed by NMR and mass 
spectral analyses. 
Va, n=4, R=H, 66% yield, mp 164.degree.-6.degree. C. 
Vb, n=4 R=Me, 77% yield, mp 170.degree.-2.degree. C. 
Vc, n=5, R=Me, 91% yield, mp 145.degree.-6.degree. C. 
Vd, n=6, R=Me, 88% yield, mp 120.degree.-1.degree. C. 
EXAMPLE 3 
Part A--Preparation of 1,3,6-Triiodocarbazole (FIG. 2, Compound VI) 
The above-named compound was prepared by the following procedure, a 
modification of the preparation described by S. H. Tucker, in J. Chem. 
Soc., 1926, 546. 
Into a 250-ml, three-necked, round-bottomed flask equipped with a heating 
mantle, a magnetic stirrer, and a condenser were placed 8.35 g (0.05 mole) 
carbazole, 11 g (0.066 mole) potassium iodide, and 125 ml glacial acetic 
acid. The mixture was heated to reflux with stirring, the resulting 
solution was cooled slightly, and 16 g (0.075 mole) potassium iodate was 
cautiously added with stirring. After stirring under reflux for 15 
minutes, the iodine color faded. 5 g (0.02 mole) iodine was added and the 
reaction mixture was stirred under reflux for one hour. It was then poured 
into an aqueous solution of sodium bisulfite, and the precipitated solid 
was collected by filtration and extracted with acetone in a Sohlet 
extractor. Fractional crystallization from acetone yielded two products 
with R.sub.f values of 0.33 and 0.64 as determined by thin layer 
chromatographic analysis on silica gel with 20% dichloromethane in 
hexanes. The lower R.sub.f product was an off-white solid, 7.0 g (26%); mp 
228.degree.- 238.degree. C. 
A sample that was purified by flash chromatography on silica gel with 
carbon disulfide followed by recrystallization from carbon 
disulfide/hexanes had a melting point of 237.degree.-8.degree. C. 
Part B--Preparation of 9-(4-bromobutyl)-1,3,6-triiodocarbazole (FIG. 2, 
Compound VII) 
This compound was prepared from Compound VI of Part A of this Example by an 
alkylation procedure analogous to that described for the preparation of 
II. Off-white crystals were obtained in 82% yield; mp 
143.degree.-5.degree. C. 
Part C--Preparation of 4-(1,3,6-triiodo-9-carbazolyl)-1-butyl methacrylate 
(FIG. 2, Compound IX) 
The above-named compound was prepared from the alkyl bromide using a 
procedure analogous to that described in EXAMPLE 1, Part C for the 
production of Compound III, with the following results. 
IX, 90% yield, mp 157.degree.-9.degree. C. 
EXAMPLE 4 
Part A--Preparation of 9-(4-bromobutyl)-1,3,6,8-tetraiodocarbazole (FIG. 2, 
Compound VIII) 
Into a 100 ml round-bottomed flask equipped with a magnetic stirrer were 
added 1.0 g (1.47 mmol) VII, 200 mg (0.79 mmol) iodine, 350 mg (0.81 mmol) 
[bis(trifluoroacetoxy)iodo]-benzene, and 50 ml dichloromethane. After 
stirring the dark purple solution at room temperature for five hours, a 
white solid began to precipitate. Stirring was continued at room 
temperature for two days, then the mixture was allowed to stand at room 
temperature for an additional four days. The white solid was collected by 
filtration and washed with a small volume of dichloromethane to yield 930 
mg (78%) of product; mp 211.degree.-4.degree. C. 
Part B--Preparation of 4-(1,3,6,8-tetraiodo-9-carbazolyl)-1-butyl 
methacrylate (FIG. 2, Compound X) 
The above-named compound was prepared from the alkyl bromide using a 
procedure analogous to that described in EXAMPLE 1, Part C for the 
production of Compound III, with the following results. 
X, 91% yield, mp 157.degree.-9.degree. C. 
EXAMPLE 5 
This Example illustrates the thermal, bulk polymerization of 
4-(1,3,6,8-tetrabromo-9-carbazolyl)-1-butyl methacrylate, i.e., the 
Compound (IIIb) of EXAMPLE 1, Part C. 
Into a 10-ml, round-bottomed flask was placed 280 mg of Compound IIIb. The 
flask was evacuated continuously with a mechanical vacuum pump and heated 
at 160.degree. C. for two hours. The resulting polymer was dissolved in 3 
ml 1-chloronaphthalene with stirring at 150.degree. C., then the viscous 
solution was filtered. The polymer was precipitated into 70 ml 
dichloromethane, filtered, washed thrice with dichloromethane and dried to 
yield 207 mg (74%) white polymer; .eta..sub.inh =0.68 dl/g 
(1-chloronaphthalene), Tg=160.degree. C. as determined by differential 
scanning calorimetry, n.sub.d =1.68 as determined by microscopy using 
Becke line analysis. 
Monomers of the invention can also be polymerized by melting them between 
two glass circles on a Fisher-Johns melting point apparatus and holding 
the liquid at a temperature above its melting point for several minutes. 
The glass circles lock together as the polymer is formed, resulting in an 
optically clear and colorless sandwich. For example, maintaining Compound 
IIIb at 170.degree. C. for several minutes yields the polymer which 
softens at approximately 200.degree. C., and can be made to flow at 
250.degree. C. without discoloration. Upon cooling, the glass can be pried 
apart with a razor blade or dissolved in hydrofluoric acid to separate the 
brittle polymer. 
EXAMPLE 6 
A low-melting blend (mp&lt;50.degree. C.) of the three heptabromo monomers V 
with n=4, 5, and 6 was prepared by dissolving 20 mg each of compounds Vb, 
Vc and Vd in 2 ml dichloromethane, filtering the solution, and evaporating 
the solvent in a stream of nitrogen. Application of a vacuum to remove 
final traces of solvent yielded a taffy-like foam. A sample that was 
placed between two circles on a Fisher-Johns melting point apparatus 
melted below 50.degree. C. to a clear liquid and polymerized at 
approximately 100.degree. C. to a clear film. 
Thermal and optical properties of monomers and polymers described in 
EXAMPLES 1 to 5 and conforming to the following formula are set forth in 
the following TABLE 1. 
__________________________________________________________________________ 
##STR3## 
monomer 
polymer 
X.sup.1, X.sup.2, X.sup.3 
Y.sup.1 
Y.sup.3 
Y.sup.2, Y.sup.4, Y.sup.5 
n R No. 
mp .eta..sub.inh 
T.sub.g 
T.sub.dec 
n.sub.D 
__________________________________________________________________________ 
Br Br 
H H 3 Me IIIa 
177-8.degree. 
-- -- -- -- 
Br Br 
H H 4 Me IIIb 
155-7.degree. 
0.68 
160.degree. 
335.degree. 
1.68 
Br Br 
H H 5 Me IIIc 
146- 8.degree. 
0.27 
132.degree. 
387.degree. 
-- 
Br Br 
H H 6 Me IIId 
124-6.degree. 
0.28 
112.degree. 
400.degree. 
1.67 
Br Br 
H Br 4 H Va 164-6.degree. 
0.07 
176.degree. 
-- -- 
Br Br 
H Br 4 Me Vb 170-2.degree. 
0.17 
198.degree. 
382.degree. 
1.74 
Br Br 
H Br 5 Me Vc 145-6.degree. 
0.21 
185.degree. 
385.degree. 
-- 
Br Br 
H Br 6 Me Vd 120-1.degree. 
0.10 
163.degree. 
377.degree. 
1.72 
Br Br 
H Br 4, 5, 6 
Me Ve &lt;50.degree. 
0.19 
175.degree. 
390.degree. 
1.72 
I H H H 4 Me IX 157-9.degree. 
0.10 
-- -- 1.74 
I I H H 4 Me X -210.degree. 
-- -- -- 1.77 
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