Hyperbranched polyester and polyamide polymers are prepared by a one-step process of polymerizing a monomer of the formula A--R--B.sub.2 so that high molecular weight globular polymers having a multiplicity of a particular functional group on the outside surface are obtained.

BACKGROUND OF THE INVENTION
 The present invention is directed to the preparation of high molecular
 weight hyperbranched polyester and polyamide polymers. The polymers are
 produced by a one-step process which entails polymerizing specific
 monomers of the formula A--R--B.sub.2 in such a manner that
 side-reactions, i.e. reverse reactions, isomerization, crosslinking, and
 the like are substantially avoided.
 P. J. Flory, J. Am. Chem. Soc., 74, 2718 (1952) and Principles of Polymer
 Chemistry, Cornell University Press, 1953, pp. 361-70, discusses the
 theory of condensation polymerization of so-called AB.sub.n -type monomers
 wherein A and B functions condense together to form branched polymers.
 While theoretically such polymers should be of high molecular weight, such
 has not been the case in actual practice. The only specific disclosures of
 such polymers are obtained by (i) the Friedel-Crafts condensation of
 benzyl halides in the presence of a MX.sub.3 catalyst wherein X is a
 halogen, (ii) the elimination metal halides from alkali metal salts of
 trihalophenols, and (iii) intermolecular etherification of D-glucose in
 the presence of dilute acids to form a soluble polyglucose. Hyperbranched
 polyester and polyamide polymers are not disclosed. Also, only low
 molecular weight polymers, i.e. less than about 1,000 daltons, were
 obtained.
 A recent attempt at producing a poly(arylene)polymer by following Flory's
 theory has also resulted in a polymer having a number average molecular
 weight below 10,000. Kim et al., J. Am. Chem. Soc., 1990, 112, 4592-3, and
 Kim U.S. Pat. No. 4,857,630 disclose wholly aromatic poly(arylene)
 polymers prepared by the homocoupling of (3,5-dibromophenyl) boronic acid
 in a mixture of an organic solvent and aqueous sodium carbonate along with
 a palladium-containing catalyst. The molecular weight of the polymer was
 found to depend on the organic solvent and temperature employed during
 polymerization and addition of additional monomer at the end of the
 polymerization neither increased the molecular weight nor gave a bimodal
 distribution. Kim et al. could not explain what causes the molecular
 growth of the system to stop. Only low molecular weight polymers, i.e.
 about 5,000 daltons, were produced. During the polymerization, only single
 bonds between arylene groups are formed and no polyester or polyamide
 polymers are disclosed or suggested.
 Baker et al. U.S. Pat. No. 3,669,939 discloses condensation polymerizing
 other ARB.sub.2 monomers, i.e. polyhydroxymonocarboxylic acid aliphatic
 compounds, but only succeeds in generating polymers with molecular weights
 below 4,000 daltons. While the molecular weights obtained in Baker et al.
 are not provided, the acid values which are provided permit the
 calculation thereof.
 In view of the previous inability to directly prepare high molecular weight
 hyperbranched polymers in accordance with Flory's theory, the art is
 replete with multi-step procedures attempting to accomplish a similar
 result. For instance, Tomalia et al. U.S. Pat. Nos. 4,507,466, 4,558,120,
 4,568,737, 4,587,329, and 4,737,558 disclose dense "starburst" polymers
 produced by allowing a polyfunctional amide core molecule to react with
 excess methyl acrylate in a Michel-type addition. Each arm of the
 resulting star-branched molecule is then reactivated to an
 amine-terminated moiety by exhaustive amidation using excess
 1,2-diaminoethane to afford a chain extended product in which each primary
 amino group becomes a new branch point in the next series of Michael
 additions. The polymers are thus built up, layer after layer, from a core
 substance by selective condensation of functional groups with each
 successive layer becoming a core for the subsequent layer. Only aliphatic
 polyamides and polyethers are exemplified and the monomers used are of the
 A-B type.
 Similarly, Denkewalter et al. U.S. Pat. Nos. 4,289,872, 4,360,646 and
 4,410,688 disclose highly branched polyamide polymers produced from
 lysine--an A--R--B.sub.2 monomer having one carboxy group, two amino
 groups, and an aliphatic body--but utilizes a multi-step process of
 blocking the functional groups and then unblocking them. only relatively
 low molecular weight polymers were produced due to the inherent difficulty
 in obtaining complete reaction for each of the multiple of blocking,
 unblocking, and reacting steps.
 Copending application U.S. Ser. No. 07/369,270, filed Jun. 21, 1989, now
 U.S. Pat. No. 5,041,516, issued Aug. 20, 1991, of Frechet et al. discloses
 a convergent pathway for preparing dendritic molecules in which accurate
 placement of one or more functional groups on the outer surface of the
 macromolecules is accomplished. The convergent approach entails building
 the final molecule by beginning at its periphery, rather than at its core
 as in divergent procedures, but still requires a blocking-unblocking
 multi-step operation, albeit of only a single reactive group at a single
 focal point which avoids the prior art problem of dealing with a
 multiplicity of reactive groups as the molecule grows.
 Extensive prior art exists on the preparation of linear aromatic polyesters
 derived from, for example, 4-hydroquinone and phthalic acid or derivatives
 thereof. Also, Kricheldorf et al., Polymer Bulletin 1, 383-388 (1979)
 discloses preparing linear aromatic polyesters by heating
 trimethylsilyloxybenzoyl chloride to greater than 150.degree. C.
 Kricheldorf et al., Polymer, 23, 1821-29 (1982) discloses forming
 predominantly aromatic polyesters from 3-trimethylsilyloxybenzoyl chloride
 and incorporating small amounts, i.e. 0.6 to 16.6 mole %, of
 3,5-bis(trimethylsilyloxy)benzoyl chloride to produce a few branch points.
 The polyesters so formed behave as predominantly linear polymers since
 they contain only a few potential branches while the present high
 molecular weight hyperbranched polyesters behave much more like individual
 particles.
 Accordingly, the art has failed to teach a method which succeeds in
 producing high molecular weight hyperbranched aromatic polyester and
 polyamide polymers and it is an object of the present invention to produce
 such polymers to take advantage of their unique properties, i.e. of high
 polarity, low crystallinity, and lower than usual viscosity.
 SUMMARY OF THE INVENTION
 The present invention provides soluble hyperbranched aromatic polyester or
 aromatic polyamide polymers having at least 40% branching and a molecular
 weight of at least 10,000 and 1,00 daltons respectively, as determined by
 gel permeation chromatography with polystyrene calibration.
 DESCRIPTION OF THE PREFERRED EMBODIMENT
 The soluble hyperbranched polymers of the present invention are derived
 from monomers of the formula A--R--B.sub.2 in which R is or contains an
 aromatic moiety and A and B are reactive groups that (i) can take part in
 either an esterification reaction or an amidation reaction and (ii) yield
 a by-product which is gaseous at the conditions of the reaction.
 Suitable aromatic moieties R for use herein include phenyl, napthyl,
 bi-phenyl, diphenyl ether, diphenyl sulfone, benzophenone, and the like.
 Suitable A and B groups for use in preparing the hyperbranched polyesters
 include trialkylsilyloxy and acid halide wherein the alkyl groups contain
 about 1 to 4 carbon atoms and the halide is chloride, bromide, or
 fluoride. Specific such monomers include 3,5-bis(trimethylsilyloxy)benzoyl
 chloride, 5-trimethylsilyloxy-isophthaloyl dichloride,
 3,5-bis(triethylsilyloxy)benzoyl chloride,
 3,4-bis(trimethylsilyloxy)benzoyl fluoride,
 2,4-bis(triethylsilyloxy)benzoyl bromide, and the like in which the
 benzoyl group is replaced with other aromatic moieties such as those
 above.
 Suitable A and B groups for use in preparing the hyperbranched polyamides
 include trialkylsilylamino and acid halide wherein the alkyl groups
 contain about 1 to 4 carbon atoms and the halide is chloride, bromide, or
 fluoride. Specific such monomers include
 3,5-bis(trimethylsilylamino)benzoyl chloride,
 5-trimethylsilylamino-isophthalamino dichloride,
 3,5-bis(triethylsilylamino)benzoyl chloride,
 3,4-bis(trimethylsilylamino)benzoyl fluoride,
 2,4-bis(triethylsilylamino)benzoyl bromide, and the like in which the
 benzoyl group is replaced with other aromatic moieties such as those
 above.
 The condensation polymerization of the A--R--B.sub.2 monomer is preferably
 performed neat, i.e. in the absence of any solvent, since the presence of
 a solvent has been found to substantially reduce the molecular weight of
 the resulting hyperbranched polymer. The polymerization rapidly occurs by
 heating the monomer to an elevated temperature at which reaction between A
 and B will occur. The temperature must not be so high as to cause either
 monomer or polymer decomposition or degradation. Generally a temperature
 of about 150 to 300.degree. C. will be suitable with the lower
 temperatures currently preferred for producing higher molecular weight
 polymers.
 The hyperbranched polymers produced herein contain only four different
 structural units. The first unit is a "focal unit" in which the A group is
 unreacted and both B groups have reacted. Only a single "focal unit" is
 present in a polymer molecule. The second unit is a "dendritic repeating
 unit" in which the A group and both B groups have reacted to form ester or
 amide linkages. The third unit is a "half-reacted repeating unit" in which
 the A group and only one of the B groups have reacted while the other B
 group is unreacted and results in a termination point. The "half-reacting
 repeating units" reduce the overall degree of branching of the
 hyperbranched polymer while also contributing to overall growth and the
 unusual properties of the hyperbranched polymer. The fourth unit is the
 "terminal unit" in which the A group has reacted but neither of the B
 groups has reacted.
 In the final polymer, it will be quite common for the work-up thereof to
 hydrolyze or otherwise change the unreacted groups to such as --OH, simple
 alkoxy groups, or carbamate. Alternatively, after polymerization is
 complete and before work-up, the hyperbranched polymer may be reacted with
 a monosubstituted polymer chain terminating compound of the formula
 Y--R.sup.1 --A, wherein Y is hydrogen or any functional group which is
 unreactive under the conditions of the polymerization, R.sup.1 is any
 aliphatic or aromatic moiety, and A is as defined above. Examples of
 suitable Y groups include such as ester, cyano, ketone, halide, nitro,
 amide, thioether, sulphonic ester, alkoxy, and the like. Thus, the outer
 surface of the globular polymer has a multiplicity of a single functional
 group.
 The degree of branching (DB) of the hyperbranched polymers may be
 determined by the following formula:
 ##EQU1##
 wherein the 1 is for the single focal unit since it also contributes to
 overall branching. As such, the DB must be equal to or less than 1. The %
 branching is merely DB.times.100.
 The hyperbranched polymers of this invention have a % branching of at least
 40%, preferably at least 50%. The % branching for a particular polymer may
 be controlled. To increase it, for example, a polyfunctional core molecule
 containing more than two B groups can be used to initiate growth and
 control subsequent growth; the monomer unit can be added slowly to the
 reaction mixture rather than all present initially; different reaction
 conditions can be used; fluoride ion activation with such as CsF, KF, or
 (n-butyl).sub.4 NF as sources of fluoride ion; or the like. To decrease
 the % branching, small amounts of an A--R--B monomer or a chain
 terminating compound as described above may be added before or during the
 polymerization. Generally, however, as high a % branching as possible will
 be preferred with the theoretical maximum being 100%.
 The molecular weight of the hyperbranched polyester polymers is at least
 10,000 daltons and the molecular weight of the hyperbranched polyamide
 polymers is at least 10,000 daltons, both as determined by gel permeation
 chromatography with polystyrene calibration. The molecular weight of the
 polyester polymers is preferably at least 20,000 daltons; more preferably
 at least about 40,000; and still more preferably from about 40,000 to
 about 200,000 daltons. The molecular weight of the polyamide polymers is
 preferably from about 1,000 to about 50,000 daltons. In view of the
 reporting of polystyrene equivalent weights, the actual molecular weight
 of the polymers may in fact be substantially different from these values.
 The hyperbranched polyester or polyamide polymers have a generally globular
 shape with a substantial number of hydroxyl, amino, carboxylic acid or
 ester groups located at the outer surface of the globules. The presence of
 the multiplicity of a single type functional group contributes to the
 usefulness of the hyperbranched polymers. For instance, when the groups
 are polar hydroxyl groups, the polymers are particularly useful in
 coatings since their adhesion to polar surfaces is enhanced over less
 functional materials. And when the groups are carboxylic acid, they can be
 transformed to ionic carboxylate units in basic medium to form a dendritic
 ionomer which will be useful in aqueous medium in coatings, additives,
 high resistance waxes, rheology control additives, and the like. In
 addition, the hyperbranched polymers exhibit very low crystallinity, very
 low compressibility, and a lack of shrinking.
 The hyperbranched polymers also exhibit a substantially lower than usual
 viscosity for such high molecular weight polymers. This is in sharp
 contrast to the higher viscosity observed with conventional linear and
 normal lightly branched polyesters and polyamides of lower molecular
 weight. Accordingly, the hyperbranched polymers are particularly useful in
 both high solids-contents and dry coatings. Also, due to the fully
 aromatic structures, the polymers possess high thermal stability.
 In addition, the hyperbranched polyester and polyamide polymers are
 expected to be useful in blends, as rheological modifiers, as stiffening
 agents, and the like, either alone or in combination with linear and/or
 lightly branched polyesters, polyamides, polycarbonates, polyphenylene
 oxides, and the like.

In the following non-limiting examples, all parts and percents are by
 weight unless otherwise specified.
 EXAMPLE I
 Preparation of Trimethylsilyl 3,5-bis(trimethylsilyloxy)benzoate
 To a solution of 3,5-dihydroxybenzoic acid (50.0 g, 0.32 mol) and
 trimethylsilyl chloride (113 g, 1.04 mol) in dry toluene (500 ml) was
 added dropwise triethylamine (108 g, 1.07 mol). The mixture was then
 heated at refluxed for 3 hours under nitrogen, cooled, filtered and
 evaporated to dryness. The crude product was purified by distillation and
 the fraction boiling at 179-190.degree. C. (0.3 mm was collected. The
 trimethyl silyl ester was obtained as a colorless oil (111 g, 90%).
 Preparation of 3,5-bis(trimethylsilyloxy)benzoyl chloride
 To a solution of trimethylsilyl ester (42.0 g, 114 mmol) in dry
 dichloromethane (60 ml) containing trimethylammonium chloride (190 mg, 1.2
 mmol) was added freshly distilled thionyl chloride (16.2 g, 136 mmol)
 dropwise under nitrogen. After the addition was complete, the solution was
 heated at reflux for three hours, cooled, and evaporated to dryness at
 room temperature. The crude product was purified by short path
 distillation at 175.degree. C. (0.3 mm) to give the acid chloride as a
 pale yellow oil (20.6 g, 65%).
 Polymerization of 3,5-bis(trimethylsilyloxy)benzoyl chloride
 The purified acid chloride (6.0 g, 19.0 mmol) was heated with stirring
 under nitrogen in an oil bath at 200.degree. C. for one hour. Vigorous
 effervescence was observed initially and the reaction mixture solidified
 after about 30 minutes. After cooling, the residue was dissolved in the
 minimum amount of pyridine/benzene (1:1, ca. 10 ml) at 50.degree. C. and
 precipitated into methanol (ca 1000 ml). The precipitated polymer was
 collected by filtration and dried at 80.degree. C. under high vacuum for 3
 days and was obtained as a light brown solid (91% yield). Gel permeation
 chromatology (with polystyrene calibration) showed that the polymer thus
 obtained had a weight-average molecular weight M.sub.w of approximately
 150,000 and a polydispersity of 3.0. The % branching was 55%.
 EXAMPLE II
 The procedure of Example I was repeated except that the polymerization was
 conducted at 250.degree. C. Vigorous effervescence was observed initially
 and the reaction mixture solidified after ca. 15 minutes. After cooling
 the residue was dissolved in the minimum amount of pyridine/benzene (1:1,
 ca. 10 ml) at 50.degree. C. and precipitated into methanol (ca 1000 ml).
 The precipitated polymer was collected by filtration and dried at
 80.degree. C. under high vacuum for 3 days and was obtained as a light
 brown solid (80% yield). The polymer thus obtained had a M.sub.w of ca.
 50,000 (by GPC with polystyrene standards) and a polydispersity of 2.0).
 The % branching was 55%.
 Comparative Example A
 The procedure of Example I was repeated except that (i) the purified acid
 chloride (5.0 g) was dissolved in 1,2-dichlorobenzene solvent (15 ml)
 prior to commencing the polymerization and (ii) the polymerization was
 conducted at the reflux temperature of the solvent, 180.degree. C. The
 resultant polymer was found to have a molecular weight of only about 3,000
 (by GPC with polystyrene standards) with about 50% branching.
 Comparative Example B
 The procedure of Example I was repeated except that the acid chloride was
 not purified by the short path distillation before polymerization was
 attempted. The subsequent polymerized material was insoluble and thus no
 data could be obtained. It was discarded.
 Comparative Example C
 The purified acid chloride (6.0 g, 19.0 mmol) of Example I was dissolved in
 dry tetrahydrofuran (THF) solvent (10 ml) and added dropwise to a solution
 of tetra-n-butylammonium fluoride (1 M sol in THF, 39.0 ml, 39.0 mmol).
 After stirring at room temperature for 30 minutes, the reaction mixture,
 which contained a heavy precipitate, was evaporated to dryness and
 redissolved in methanol (20 ml). The polymer was then precipitated from
 the methanol solution into a 1:1 mixture of conc. HCl and water. The
 precipitated polymer was collected by filtration and dried at 80.degree.
 C. under high vacuum for 3 days. It was obtained as alight brown solid
 (91% yield). Gel permeation chromatography (with polystyrene calibration)
 showed the polymer to have a weight-average molecular weight of about
 7,000 and a polydispersity of 1.35. The % branching was 50%.