Dense star polymers having core, core branches, terminal groups

Dense star polymers having terminal group densities greater than conventional star polymers exhibit greater and more uniform reactivity than their corresponding conventional star polymers. For example, a third generation, amine-terminated polyamidoamine dense star polymer prepared from ammonia, methyl acrylate and ethylenediamine has 1.24.times.10.sup.-4 amine moieties per unit volume (cubic Angstrom units) in contrast to the 1.58.times.10.sup.-6 amine moieties per unit volume contained by a conventional star polymer. Such dense star polymers are useful as demulsifiers for oil/water emulsions, wet strength agents in the manufacture of paper, and agents for modifying viscosity in aqueous formulations such as paints.

BACKGROUND OF THE INVENTION 
This invention relates to a novel class of branched polymers containing 
dendritic branches having functional groups uniformly distributed on the 
periphery of such branches. This invention also relates to processes for 
preparing such polymers as well as applications therefore. 
Organic polymers are generally classified in a structural sense as either 
linear or branched. In the case of linear polymers, the repeating units 
(often called mers) are divalent and are connected one to another in a 
linear sequence. In the case of branched polymers, at least some of the 
mers possess a valency greater than 2 such that the mers are connected to 
a nonlinear sequence. The term "branching" usually implies that the 
individual molecular units of the branches are discrete from the polymer 
backbone, yet have the same chemical constitution as the polymer backbone. 
Thus, regularly repeating side groups which are inherent in the monomer 
structure and/or are of different chemical constitution than the polymer 
backbone are not considered as branches, e.g., dependent methyl groups of 
linear polypropylene. To produce a branched polymer, it is necessary to 
employ an initiator, a monomer, or both that possess at least three 
moieties that function in the polymerization reaction. Such monomer or 
initiators are often called polyfunctional. The simplest branched polymers 
are the chain branched polymers wherein a linear backbone bears one or 
more essentially linear pendant groups. This simple form of branching, 
often called comb branching, may be regular wherein the branches are 
uniformly and regularly distributed on the polymer backbone or irregular 
wherein the branches are distributed in nonuniform or random fashion on 
the polymer backbone. See T. A. Orofino, Polymer, 2, 295-314 (1961). An 
example of regular comb branching is a comb branched polystyrene as 
described by T. Altores et al. in J. Polymer Sci., Part A, Vol. 3, 
4131-4151 (1965) and an example of irregular comb branching is illustrated 
by graft copolymers as described by Sorenson et al. in "Preparative 
Methods of Polymer Chemistry", 2nd Ed., Interscience Publishers, 213-214 
(1968). 
Another type of branching is exemplified by cross-linked or network 
polymers wherein the polymer chains are connected via tetravalent 
compounds, e.g., polystyrene molecules bridged or cross-linked with 
divinylbenzene. In this type of branching, many of the individual branches 
are not linear in that each branch may itself contain groups pendant from 
a linear chain. More importantly in network branching, each polymer 
macromolecule (backbone) is cross-linked at two or more sites to two other 
polymer macromolecules. Also the chemical constitution of the 
cross-linkages may vary from that of the polymer macromolecules. In this 
so-called cross-linked or network branched polymer, the various branches 
or cross-linkages may be structurally similar (called regular 
cross-linked) or they may be structurally dissimilar (called irregularly 
cross-linked). An example of regular cross-linked polymers is a 
ladder-type poly(phenylsilsesquinone) as described by Sorenson et al., 
supra, at page 390. The foregoing and other types of branched polymers are 
described by H. G. Elias in Macromolecules, Vol. I, Plenum Press, New York 
(1977). 
More recently, there have been developed polymers having so-called star 
structured branching wherein the individual branches radiate out from a 
nucleus and there are at least 3 branches per nucleus. Such star branched 
polymers are illustrated by the polyquaternary compositions described in 
U.S. Pat. Nos. 4,036,808 and 4,102,827. Star branched polymers prepared 
from olefins and unsaturated acids are described in U.S. Pat. No. 
4,141,847. The star branched polymers offer several advantages over 
polymers having other types of branching. For example, it is found that 
the star branched polymers may exhibit higher concentrations of functional 
groups thus making them more active for their intended purpose. In 
addition, such star branched polymers are often less sensitive to 
degradation by shearing which is a very useful property in formulations 
such as paints, in enhanced oil recovery and other viscosity applications. 
Additionally, the star branched polymers have relatively low intrinsic 
viscosities even at high molecular weight. 
While the star branched polymers offer many of the aforementioned 
advantages over polymers having more conventional branching, it is highly 
desirable to provide polymers which exhibit even greater concentrations of 
functional groups per unit volume of the polymer macromolecule as well as 
a more uniform distribution of such functional groups in the exterior 
regions of the macromolecule. In addition, it is often desirable to 
provide polymers having macromolecular configurations that are more 
spheroidal and compact than are the star branched polymers. 
SUMMARY OF THE INVENTION 
In its broadest aspect, this invention is a dense star polymer having at 
least one branch (hereinafter called a core branch) emanating from a core, 
said branch having at least one terminal group provided that (1) the ratio 
of terminal groups to the core branches is two or greater, (2) the density 
of terminal groups per unit volume in the polymer is at least 1.5 times 
that of a conventional star polymer having a comparable molecular weight 
and number of core branches, each of such branches of the conventional 
star polymer bearing only one terminal group, and (3) a molecular volume 
that is equal to or less than about 60 percent of the molecular volume of 
said conventional star polymer as determined by dimensional studies using 
scaled Corey-Pauling molecular models. 
In a somewhat more limited and preferred aspect, this invention is a 
polymer having a novel ordered star branched structure (herein called 
starburst structure). Hereinafter this polymer having a starburst 
structure in called a dendrimer. Thus, a "dendrimer" is a polymer having a 
polyvalent core that is covalently bonded to at least two ordered 
dendritic (tree-like) branches which extend through at least two 
generations. As an illustration, an ordered second generation dendritic 
branch is depicted by the following configuration: 
##STR1## 
wherein "a" represents the first generation and "b" represents the second 
generation. An ordered, third generation dendritic branch is depicted by 
the following configuration. 
##STR2## 
wherein "a" and "b" represent the first and second generation, 
respectively, and "c" represents the third generation. A primary 
characteristic of the ordered dendritic branch which distinguishes it from 
conventional branches of conventional polymers is the uniform or 
essentially symmetrical character of the branches as is shown in the 
foregoing illustrations. In addition, with each new generation, the number 
of terminal groups on the dendritic branch is an exact multiple of the 
number of terminal groups in the previous generation. 
Another aspect of this invention is a process for producing the dense star 
polymer comprising the steps of 
(A) contacting 
(1) a core compound having at least one nucleophilic or one electrophilic 
moiety (hereinafter referred to in the alternative as N/E moieties) with 
(2) an excess of a first organic coreactant having (a) one moiety 
(hereinafter called a core reactive moiety) which is reactive with the N/E 
moieties of the core compound and (b) an N/E moiety which does not react 
with the N/E moiety of the core under conditions sufficient to form a core 
adduct wherein each N/E moiety of the core compound has reacted with the 
core reactive moiety of a different molecule of the first coreactant; 
(B) contacting 
(1) the core adduct having at least twice the number of N/E moieties as the 
core compound with 
(2) an excess of a second organic coreactant having (a) one moiety 
(hereinafter called an adduct reactive moiety) which will react with the 
N/E moieties of the core adduct and (b) an N/E moiety which does not react 
with the N/E moiety of the core adduct under conditions sufficient to form 
a first generation adduct having a number of N/E moieties that are at 
least twice the number of N/E moieties in the core adduct; and 
(C) contacting the first generation adduct with an excess of a third 
organic coreactant having one moiety that is reactive with the N/E 
moieties of the first generation adduct and an N/E moiety that does not 
react with the N/E moieties of the first generation adduct under 
conditions sufficient to form a second generation dendrimer. In the 
foregoing process, the first coreactant differs from the second 
coreactant, and the second coreactant differs from the third coreactant, 
but the first and third coreactants may be the same or different 
compounds. The third and higher generation dendrimers are formed by 
repeating steps (B) and (C) of the aforementioned process. 
Other aspects of this invention are methods for using the dendrimers in 
such applications as demulsifiers for oil/water emulsions, wet strength 
agents in the manufacture of paper, agents for modifying viscosity in 
aqueous formulations such as paints and the like. 
The dense star polymers of the present invention exhibit the following 
properties which are unique or are superior to similar properties of 
conventional star branched polymers and other branched polymers having 
similar molecular weight and terminal groups: 
(a) greater branch density; 
(b) greater terminal group density; 
(c) greater accessibility of terminal groups to chemically reactive 
species; and 
(d) lower viscosity. 
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
In the dense star polymers of the present invention, the core is covalently 
bonded to at least one core branch, preferably at least two, most 
preferably at least three, core branches with each core branch having a 
calculated length of at least 3 Angstrom units (A), preferably at least 4 
A, most preferably at least 6 A. These polymers preferably have an average 
of at least 2, more preferably at least 3 and most preferably at least 4 
terminal groups per polymer molecule. Preferably, the core branches have a 
dendritic character, most preferably an ordered dendritic character as 
defined hereinafter. In preferred dense star polymers, the terminal groups 
are functional groups that are sufficiently reactive to undergo addition 
or substitution reactions. Examples of such functional groups include 
amino, hydroxy, mercapto, carboxy, alkenyl, allyl, vinyl, amido, halo, 
urea, oxiranyl, aziridinyl, oxazolinyl, imidazolinyl, sulfonato, 
phosphonato, isocyanato and isothiocyanato. The dense star polymers differ 
from conventional star or star-branched polymers in that the dense star 
polymers have a greater concentration of terminal groups per unit of 
molecular volume than do conventional star polymers having an equivalent 
number of core branches and an equivalent core branch length. Thus, the 
density of terminal groups per unit volume in the dense star polymer is at 
least about 1.5 times the density of terminal groups in the conventional 
star polymer, preferably at least 5 times, more preferably at least 10 
times, most preferably from about 15 to about 50 times. The ratio of 
terminal groups per core branch in the dense polymer is at least 2, 
preferably at least 3, most preferably from about 4 to about 1024. 
Preferably, for a given polymer molecular weight, the molecular volume of 
the dense star polymer is less than 50 volume percent, more preferably 
from about 16 to about 50, most preferably from about 7 to about 40 volume 
percent of the molecular volume of the conventional star polymer. 
In the preferred polyamidoamine dense star polymers, the density of 
terminal (primary) amine moieties in the polymer is readily expressed as 
the molar ratio of primary amine moieties to the total of secondary and 
tertiary amine moieties. In such polymers this 1.degree. amine: (2.degree. 
amino+3.degree. amine) is preferably from about 0.37:1 to about 1:33:1, 
more preferably from about 0.69:1 to about 1.2:1, most preferably from 
about 1.1:1 to about 1.2:1. 
The preferred dendrimers of the present invention are characterized as 
having a polyvalent core that is covalently bonded to at least two ordered 
dendritic branches which extend through at least two generations. Such 
ordered branching can be illustrated by the following sequence wherein G 
indicates the number of generations: 
##STR3## 
Mathematically, the relationship between the number of terminal groups on a 
dendritic branch and the number of generations of the branch can be 
represented as follows: 
EQU # of terminal groups per dendritic branch=N.sub.r.sup.G /2 
wherein G is the number of generations and N.sub.r is the repeating unit 
multiplicity which is at least 2 as in the case of amines. The total 
number of terminal groups in the dendrimer is determined by the following: 
EQU # of terminal groups per dendrimer=N.sub.c N.sub.r.sup.G /2 
wherein G and N.sub.r are as defined before and N.sub.c represents the 
valency (often called core functionality) of the core compound. 
Accordingly, the dendrimers of the present invention can be represented in 
its component parts as follows: 
##EQU1## 
wherein the Core, Terminal Moiety, G and N.sub.c are as defined before and 
the Repeat Unit has a valency or functionality of N.sub.r +1 wherein 
N.sub.4 is as defined before. 
An illustration of a functionally active dendrimer of a ternary or 
trivalent core which has three ordered, second generation dendritic 
branches is depicted by the following configuration: 
##STR4## 
wherein I is a trivalent core atom or molecule having a covalent bond with 
each of the three dendritic branches, Z is a terminal moiety and "a" and 
"b" are as defined hereinbefore. An example of such a ternary dendrimer is 
polyamidoamine represented by the following structural formula: 
##STR5## 
wherein Y represents a divalent amide moiety such as 
##STR6## 
and "a" and "b" indicate first and second generations, respectively. In 
these two illustrations, N.sub.c is 3 and N.sub.r is 2. In the latter of 
the two illustrations, the Repeat Unit is YN. While the foregoing 
configuration and formula illustrate a trivalent core, the core atom or 
molecule may be any monovalent or monofunctional moiety or any polyvalent 
or polyfunctional moiety, preferably a polyvalent or polyfunctional moiety 
having from 2 to about 2300 valence bonds of functional sites available 
for bonding with the dendritic branches, most preferably from about 2 to 
about 200 valence bonds or functional sites. In cases wherein the core is 
a monovalent or monofunctional moiety, the dense star has only one core 
branch and must be compared with a linear polymer in order to determine 
appropriate terminal group density and molecular volume. Accordingly, this 
dense star must have at least 2 generations in order to exhibit the 
desired density of terminal groups. Also, Y may be any other divalent 
organic moiety such as alkylene, alkylene oxide, alkyleneamine, and the 
like, with the depicted amide moiety being the most preferred. In addition 
to amine, the terminal groups of the dendrimer may be any functionally 
active moiety that can be used to propagate the dendritic branch to the 
next generation. Examples of such other moieties include carboxy, 
aziridinyl, oxazolinyl, haloalkyl, oxiranyl, hydroxy and isocyanato, with 
amine or carboxylic ester moieties being preferred. While the dendrimers 
preferably have dendritic branches having 2 to 6 generations, dendrimers 
having dendritic branches up to 12 generations are suitably made and 
employed in the practice of this invention. 
The dendrimers of this invention are readily prepared by reacting a 
compound capable of generating a polyvalent core with a compound or 
compounds which causes propagation of dendritic branches from the core. In 
the preparation of these dendrimers, it is essential to maintain an excess 
of coreactant to reactive moieties in the terminal groups in the core, 
core adduct or subsequent adducts and dendrimers in order to prevent 
cross-linking and to maintain the ordered character of the dendritic 
branches. In general, this excess of coreactant to reactive moities in the 
terminal groups is from about 2:1 to about 120:1, preferably from about 
3:1 to about 20:1 on a molar basis. 
For example in the formation of the aforementioned ternary dendritic 
polyamidoamine, ammonia, a nucleophilic core compound, is first reacted 
with methyl acrylate under conditions sufficient to cause the Michael 
addition of one molecule of the ammonia to three molecules of the methyl 
acrylate to form the following core adduct: 
##STR7## 
Following removal of unreacted methyl acrylate, this compound is then 
reacted with excess ethylenediamine under conditions such that one amine 
group of the ethylenediamine molecule reacts with the methyl carboxylate 
groups of the core adduct to form a first generation adduct having three 
amidoamine moieties represented by the formula: 
##STR8## 
The molar excess of ethylene diamine to methyl acrylate moieties is 
preferably from 4:1 to 50:1. Following removal of unreacted 
ethylenediamine, this first generation adduct is then reacted with excess 
methyl acrylate under Michael's addition conditions to form a second 
generation adduct having terminal methyl ester moieties: 
##STR9## 
which is then reacted with excess ethylenediamine under amide forming 
conditions to produce the desired polyamidoamine dendrimer having ordered, 
second generation dendritic branches with terminal amine moieties. The 
molar excess of coreactant to reactive moieties in each case is preferably 
from 1.1:1 to about 40:1, most preferably from about 3:1 to about 10:1. 
Similar dendrimers containing amidoamine moieties can be made by using 
organic amines as the core compound, e.g., ethylenediamine which produces 
a tetra-branched dendrimer or diethylenetriamine which produces a 
penta-branched dendrimer. 
Alternatively, water or hydrogen sulfide may be employed as nucleophilic 
cores for the production of binary dendrimers. Examples of other 
nucleophilic core compounds include phosphine, polyalkylene polyamines 
such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine 
and both linear and branched polyethylenimine; primary amines such as 
methylamine, hydroxyethylamine, octadecylamine and polymethylenediamines 
such as hexamethylenediamine; polyaminoalkylarenes such as 
1,3,5-tris(aminomethyl)benzene; tris(aminoalkyl)amines such as 
tris(aminoethyl)amine; heterocyclic amines such as imidazolines and 
piperidines; and various other amines such as hydroxyethylaminoethylamine, 
mercaptoethylamine, morpholine, piperzine, amino derivatives of 
polyvinylbenzyl chloride and other benzylic polyamines such as 
tris(1,3,5-aminomethyl)benzene. Other suitable nucleophilic cores include 
ethylene glycol and polyalkylene polyols such as polyethylene glycol and 
polypropylene glycol; 1,2-dimercaptoethylene and polyalkylene 
polymercaptans; thiophenols, and phenols. Of the core compounds, ammonia 
and the polyalkylene polyamines are preferred. 
Examples of coreactant materials used to react with the nucleophilic core 
compounds include .alpha.,.beta.-ethylenically unsaturated carboxylic 
esters and amides such as methyl acrylate, ethyl acrylate, acrylonitrile, 
methyl itaconate, dimethyl fumarates, maleic anhydride, acrylamide, as 
well as esters, acids and nitriles containing an acrylyl moiety, with 
methyl acrylate being the preferred coreactant material. In general other 
preferred unsaturated reactants are volatile or otherwise readily removed 
from the core/coreactant reaction products without deleteriously affecting 
the reaction product. 
Examples of the second coreactant materials used to react with the adduct 
of the nucleophilic core and the first coreactant include various 
polyamines such as alkylene polyamines and polyalkylene polyamines such as 
ethylenediamine and diethylenetriamine; benzylic polyamines such as 
tris(1,3,5-aminomethyl)benzene; alkanolamines such as ethanolamine; and 
aziridine and derivatives thereof such as N-aminoethyl aziridine. Of these 
second coreactant materials, the volatile polyamines such as 
ethylenediamine and diethylenetriamine are preferred, with ethylenediamine 
being especially preferred. 
Alternatively, the dendrimers can be prepared by reacting an electrophilic 
core such as a polyester with a coreactant such as a polyamine to form a 
core adduct which is then reacted with a suitable second coreactant such 
as an unsaturated ester to form the first generation product. Thereafter, 
this first generation product is reacted with a suitable third coreactant 
such as polyamine and then with the second coreactant such as unsaturated 
ester to form the desired second generation dendrimer. Examples of 
suitable electrophilic cores include the C.sub.1 -C.sub.4 alkyl esters of 
various polycarboxylic acids such as benzene tricarboxylic acid, oxalic 
acid, terphthalic acid and various other carboxylic acids represented by 
the formula: 
##STR10## 
wherein Y is hydrocarbyl or a hydrocarbon polyl wherein the hydrocarbon 
radical is alkyl, aryl, cycloalkyl, alkylene, arylene, cycloalkylene, and 
corresponding trivalent, tetravalent, pentavalent and hexavalent radicals 
of such hydrocarbons; and Z is a whole number from 1 to 6. Preferred 
electrophilic cores include poly(methyl acrylates), poly(acryloyl 
chloride), poly(methacryloyl chloride), alkyl acrylate/alkyl methacrylate 
copolymers, polymers of alkyl fumarates, and polymers of alkyl itaconates. 
Of the electrophilic cores, alkyl acrylate/alkyl methacrylate copolymers 
and alkyl acrylate/alkyl itaconate copolymers are most preferred. 
Suitable first coreactants for reaction with the electrophilic core include 
polyalkylene polyamines such as ethylenediamine, diethylenetriamine, 
triethylenetetraamine and other polyamines represented by the formula: 
##STR11## 
wherein R.sup.1 and R.sup.2 independently represent hydrogen or an alkyl, 
preferably C.sub.1 -C.sub.4 alkyl, hydroxyalkyl, cyanoalkyl, or amido; n 
is at least 2 and preferably 2 to 6 and m is 2 to 100, preferably 2 to 5. 
Examples of suitable second coreactants to be used in preparing dendrimers 
from electrophilic cores include alkyl esters of ethylenically unsaturated 
carboxylic acids such as methyl acrylate, methyl methacrylate, ethyl 
acrylate and the like. Examples of suitable third coreactants are those 
illustrated for the first coreactant. 
Thus prepared, the dendrimers can be reacted with a wide variety of 
compounds to produce the polyfunctional compounds having the unique 
characteristics that are attributable to the structure of the dendrimer. 
For example, a dendrimer having terminal amine moieties, as in the 
polyamidoamine dendrimer, may be reacted with an unsaturated nitrile to 
yield a polynitrile (nitrile-terminated) dendrimer. Alternatively, the 
polyamidoamine dendrimer may be reacted with (1) an 
.alpha.,.beta.-ethylenically unsaturated amide to form a polyamide 
(amide-terminated) dendrimer, (2) an .alpha.,.beta.-ethylenically 
unsaturated ester to form a polyester (ester-terminated) dendrimer, (3) an 
oxirane to yield a polyol (hydroxy-terminated) dendrimer, or (4) an 
ethylenically unsaturated sulfide to yield a polymercapto 
(thiol-terminated) dendrimer. In addition, the dendrimer may be reacted 
with an appropriate difunctional or trifunctional compound such as an 
alkyl dihalide or an aromatic diisocyanate to form a poly(dendrimer) 
having a plurality of dendrimers linked together through the residues of 
the polyhalide or polyisocyanate. In all instances, such derivatives of 
the dendrimers are prepared using procedures and conditions conventional 
for carrying out reactions of organic compounds bearing the particular 
functional group with the particular organic reactant.

Such reactions are further exemplified by the following working examples. 
In such working examples, all parts and percentages are by weight unless 
otherwise indicated. 
EXAMPLE 1 
A. Preparation of Core Adduct 
To a one-liter, 3-neck flask equipped with stirrer, condenser and 
thermowell, and containing methyl acrylate (296.5 g, 3.45 moles) is added 
at room temperature with stirring over a 6-hour period ammonia (8.7 g, 
0.58 mole) dissolved in 102.2 g of methanol. The mixture is allowed to 
stand at room temperature for 48 hours at which point excess methyl 
acrylate is removed by vacuum distillation (1 mm Hg at 22.degree. C.) 
yielding 156 g of residue. This residue is analyzed by size exclusion 
chromatography (C.sub.13 NMR) and liquid chromatography. This analysis 
indicates the coreactant adduct to be the Michael's addition product of 1 
mole of ammonia and 3 moles of methyl acrylate at a 97.8 percent yield. 
B. Preparation of First Generation Adduct 
To ethylenediamine (505.8 g, 8.43 moles) dissolved in 215.4 g of methanol 
in a 3-liter reaction flask equipped with stirrer, condenser and 
thermowell, is added the aforementioned ammonia/methyl acrylate adduct 
(28.1 g, 0.1022 mole), and the reaction mixture is allowed to stand at 
room temperature for 55 hours. The resulting mixture (747.6 g) is 
subjected to vacuum distillation to remove excess ethylenediamine and 
methanol at 2 mm Hg and 72.degree. C. The residue (35.4 g) is analyzed by 
size exclusion chromatography and other suitable analytical techniques. 
The analyses indicate that essentially all of the ester moieties of the 
ammonia/methyl acrylate adduct had been converted to amides in the form of 
a compound represented by the following structural formula: 
##STR12## 
thus indicating a yield of 98.6 percent. 
C. Preparation of Second Generation Polyester Dendrimer 
To methyl acrylate (93.2 g, 1.084 moles) in a one-liter flask equipped with 
condenser, stirrer and thermowell, and heated to 32.degree. C. is added 
the aforementioned first generation adduct (18 g, 0.0501 mole) dissolved 
in 58.1 g of methanol over 1.5 hours. The resulting mixture is maintained 
at 32.degree. C. for an additional 5 hours and allowed to stand an 
additional 18 hours at room temperature. The reaction mixture (165.7 g) is 
stripped of methanol and excess methyl acrylate by vacuum distillation (2 
mm Hg and 50.degree. C.) to produce 43.1 g of residue. Analysis by 
suitable techniques indicates the product to be a second generation 
polyester dendrimer represented by the following formula: 
##STR13## 
in 98.4 percent yield. 
D. Preparation of Second Generation Polyamine Dendrimer 
To ethylenediamine (328.8 g, 5.48 moles) dissolved in 210.2 g of methanol 
at room temperature in the aforementioned flask is added with stirring the 
second generation polyester dendrimer (34.9 g, 0.0398 mole) dissolved in 
45.3 g of methanol. The resulting mixture is allowed to stand for 66 hours 
at room temperature at which time excess ethylenediamine and methanol is 
stripped from the product by vacuum distillation (2 mm Hg at 72.degree. 
C.) to yield 41.1 g (99.0 percent yield) of product. This product is 
determined by size exclusion chromatography to be the second generation 
polyamine of the aforementioned polyester dendrimer. 
E. Preparation of Third Generation Polyester Dendrimer 
To methyl acrylate (65.1 g, 0.757 mole) is added the aforementioned second 
generation polyamine dendrimer (28.4 g, 0.0272 mole) dissolved in 84.6 g 
of methanol over a period of 1 hour and 15 minutes. The resulting mixture 
is allowed to stand for 18 hours at 25.degree. C. after which time excess 
methyl acrylate and methanol are removed by vacuum distillation (2 mm Hg 
at 50.degree. C.) to yield 56.3 g (100.0 percent yield) of product 
residue. Analysis of this residue by suitable analytical techniques 
indicate that it is a third generation polyester dendrimer having 3 core 
branches with 4 terminal ester moieties per core branch thereby providing 
12 terminal ester moieties per dendrimer molecule. 
F. Preparation of Third Generation Polyamine Dendrimer 
To ethylenediamine (437.6 g, 7.29 moles) dissolved in 192 g of methanol is 
added the aforementioned third generation polyester dendrimer (44.9 g, 
0.0216 mole) dissolved in 69.7 g of methanol. The addition occurs over a 
period of 48 hours at 25.degree. C. with stirring. The resulting reaction 
mixture is then allowed to stand for 19 hours at 25.degree. C. after which 
time excess methanol and ethylenediamine are removed by vacuum 
distillation (2 mm Hg at 72.degree. C.) to yield 51.2 g of residual 
product. Analysis of this residue indicates a yield of 85.3 percent of a 
third generation polyamine dendrimer having 3 core branches with 4 
terminal primary amine moieties per core branch, thereby providing 12 
terminal primary amine moieties per molecule of dendrimer. This dendrimer 
is calculated to have a molecular volume of 50,000 to 97,000 cubic .ANG. 
and a density of a terminal amine moiety of 1 to 3(.times.10.sup.-4) 
moieties/cubic .ANG.. 
EXAMPLE 2 
Following the procedure of Example 1, except that a molar equivalent amount 
of ethylenediamine is substituted for ammonia as the core compound, a 
third generation polyamine dendrimer is prepared. Upon analysis, it is 
determined that this dendrimer has four core branches with 4 terminal 
primary amine moieties per core branch, thereby providing 16 terminal 
primary amine moieties per molecule of dendrimer. This dendrimer has a 
molecular volume of 60,000 to 120,000 cubic .ANG. and a terminal amine 
density of 2 to 6(.times.10.sup.-4) amines/cubic .ANG.. 
Similar dendrimers are obtained when equimolar amounts of 
1,2-diaminopropane, 1,3-diaminopropane and 1,6-diaminohexane 
(hexamethylenediamine) are substituted for the ethylenediamine as the core 
compound in the foregoing procedure. When an equimolar amount of 
dodecylamine or benzylamine is substituted for the ethylenediamine as the 
core compound, the resulting dense star polymers have 2 core branches per 
molecule with 4 terminal primary amine groups per branch, thereby 
providing a total of 8 primary amine groups per polymer molecule. 
Substitution of triaminoethylamine for ethylenediamine as the core 
compound yields a dendrimer having 6 core branches with 4 terminal primary 
amine moieties per core branch, thereby providing 24 terminal primary 
amine moieties per molecule of dendrimer. 
EXAMPLE 3 
A. First Amidation 
Following the procedure of Example 1, 5 g (0.0198 mole) of 
trimethyl-1,3,5-benzenetricarboxylate is mixed with 6.3 g (0.0368 mole) of 
aminoethylethanolamine (NH.sub.2 CH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 OH) 
to form a white paste. This mixture is heated at 120.degree. C. for 3 
hours to form 9.48 g of a light yellow syrup which infrared and nuclear 
magnetic resonance spectral analysis indicate is an amidoamine represented 
by the structural formula: 
##STR14## 
B. First Alkylation 
A 9.48 g (0.0202 mole) of this amidoamine is combined with a stoichiometric 
excess (11.0 g, 0.127 mole) of methyl acrylate and heated for 24 hours at 
80.degree. C. which, after devolatilization, is a light yellow syrup 
weighing 14.66 g. Nuclear magnetic resonance (H.sup.1) and infrared 
spectral analysis of the syrup indicates that it is a triester represented 
by the structural formula: 
##STR15## 
C. Second Amidation 
Following the procedure of part A of this example, the triester (4.57 g, 
6.3.times.10.sup.-3 mole) produced in part B is mixed with 1.96 g 
(1.89.times.10.sup.-2 mole) of aminoethylethanolamine and heated at 
90.degree. C. for 48 hours to form 5.8 g of a light yellow, highly viscous 
syrup. Analysis of this product by nuclear magnetic resonance (H.sup.1) 
(DMSO-d.sub.6) and infrared spectroscopy indicates that it is a 
triamidoamine represented by the structural formula: 
##STR16## 
wherein each A is individually 
##STR17## 
EXAMPLE 4 
A. First Amidation 
A 27.3-g portion (0.1 mole) of a triester represented by the formula: 
##STR18## 
is mixed with 30 g (0.405 mole) of N-methyl ethylenediamine (MEDA) and 
16.6 g of methanol and then heated at 63.degree. C. for 11 hours. The 
product is then stripped of unreacted MEDA and methanol to yield 36.1 g of 
a triamide represented by the formula: 
##STR19## 
B. First Alkylation 
To the aforementioned triamide (36.1 g, 0.09 mole) is added 38.5 g of 
methanol to yield a clear solution to which is added 50.5 g (0.59 mole) of 
methyl acrylate dropwise over a period of 2 hours at 38.degree. C. The 
temperature of the resulting mixture is increased to 53.degree. C. for 5 
additional hours after which unreacted methyl acrylate and methanol are 
removed under vacuum to yield 61 g of a light yellow syrup. Analysis of 
this product by nuclear magnetic resonance (H.sup.1) spectroscopy 
indicates that it is represented by the formula: 
##STR20## 
C. Second Amidation 
To 60.8 g of the aforementioned first alkylation product are added with 
stirring 42.7 g of methanol and 26.6 g (0.359 mole) of MEDA followed by 
heating the resulting mixture at 65.degree. C. for 6 hours. Vacuum 
stripping of the mixture yields 72.7 g of a light yellow syrup. Analysis 
of this product (syrup) indicates that it is a mixture of isomers having 
the following structures: 
##STR21## 
D. Second Alkylation and Third Amidation 
Alkylation of the aforementioned second amidation product with methyl 
acrylate and then amidation of the resulting alkylated product with MEDA 
in accordance with aforementioned procedures yield a mixture of isomers 
having core branches with dendritic characteristics.