Synthesis of hyperbranched aromatic poly(amide-imide): Copolymerization of B′B2 monomer with A2 monomer

Article abstract of DOI:10.1021/ma021499f

A hyperbranched aromatic poly(amide-imide) was prepared by the copolymerization of 4-(3,5-dicarboxyphenoxy)phthalic anhydride, a B′B₂type monomer, and 1,4-phenylenediamine, an A₂ type monomer. The rapid reaction between the anhydride and amino group led to the formation of the dominant imide intermediate which can be regarded as a new AB₂ type of monomer. The intermediate, without isolation, was subjected to further polymerization in the presence of TPP/pyridine, as condensing agents, to give the hyperbranched poly(amide-imide), containing carboxylic acid chain ends. In comparison, the AB₂ monomer was prepared separately, and the conventional self-polymerization of this monomer was also studied. The structures of the obtained polymers were characterized by FTIR and ¹H NMR spectroscopy. The spectral data showed that these two polymers, prepared from two different synthetic approaches, have nearly identical structures. The degree of branching of the hyperbranched poly(amide - imide)s was estimated to be 60-61%. The terminal carboxylic acid groups were modified by reaction with a variety of aromatic amines to give the corresponding amide derivatives. The nature of the chain ends was shown to have a significant effect on the solubility and T_g of the hyperbranched poly(amide-imide)s.

Full text of DOI:10.1021/ma021499f

Macromolecules 2003, 36, 661-666
661
Synthesis of Hyperbranched Aromatic Poly(amide-imide):
Copolymerization of B′B2 Monomer with A2 Monomer
Ya o-Te Ch a n g a n d Ch in g-F on g Sh u *
Department of Applied Chemistry, National Chiao Tung University, Hsin-Chu,
Taiwan 30035, Republic of China
ABSTRACT: A hyperbranched aromatic poly(amide-imide) was prepared by the copolymerization of
4-(3,5-dicarboxyphenoxy)phthalic anhydride, a B′B2 type monomer, and 1,4-phenylenediamine, an A2 type
monomer. The rapid reaction between the anhydride and amino group led to the formation of the dominant
imide intermediate which can be regarded as a new AB2 type of monomer. The intermediate, without
isolation, was subjected to further polymerization in the presence of TPP/pyridine, as condensing agents,
to give the hyperbranched poly(amide-imide), containing carboxylic acid chain ends. In comparison, the
AB2 monomer was prepared separately, and the conventional self-polymerization of this monomer was
also studied. The structures of the obtained polymers were characterized by FTIR and 1H NMR
spectroscopy. The spectral data showed that these two polymers, prepared from two different synthetic
approaches, have nearly identical structures. The degree of branching of the hyperbranched poly(amide-
imide)s was estimated to be 60-61%. The terminal carboxylic acid groups were modified by reaction
with a variety of aromatic amines to give the corresponding amide derivatives. The nature of the chain
ends was shown to have a significant effect on the solubility and Tg of the hyperbranched poly(amide-
imide)s.
In tr od u ction
preparation of hyperbranched aromatic poly(amide-
imide)s. In this paper, we report the synthesis of a new
hyperbranched poly(amide-imide) by copolymerization
of an unsymmetrical B′B2 type monomer with an A2 type
monomer. In the B′B2 monomer, there are one anhy-
dride and two carboxylic groups, while in the A2
monomer, there are two amino functionalities. The
anhydride (B′) is much more reactive than the carboxylic
group (B) toward the amino group in the A2 monomer.
At the initial stage of the polycondensation, the rapid
reaction between B′ and A groups results in the forma-
tion of the dominant imide intermediate. The interme-
diate can be regarded as a new AB2 type of monomer,
which contains one aminophenyl and two carboxyl
functionalities. Without isolation, the AB2 intermediate
was subjected to further polymerization in the presence
of TPP/pyridine, as condensing agents, to give the
hyperbranched poly(amide-imide).28,29 For comparison,
the AB2 intermediate was prepared separately and
characterized; the conventional one-step self-polymer-
ization of this AB2 monomer was also studied.
Hyperbranched macromolecules have received con-
siderable attention since their unique, highly branched
structure is expected to exhibit some unusual physical
and chemical properties.1-4 These polymers can be
conveniently synthesized in a single step via a one-pot
polymerization,5 yet they maintain many of the archi-
tectural features and properties found in their well-
defined dendrimer counterparts,6-8 which are built up
by tedious stepwise synthetic sequences.9-12 The one-
step synthesis allows hyperbranched polymers to be
more readily available and prepared on a large scale
for potential applications. These attractive features have
led to the development of novel synthetic routes for the
preparation of such polymers. Most hyperbranched
polymers that have been developed were synthesized
by the one-step self-polycondensation of ABn type mono-
mers. Only a few studies have concerned the prepara-
tion of hyperbranched polymers through the copolym-
erization method, even if that route has more flexibility
in generating diverse, hyperbranched materials. Fre´chet
et al. have reported the synthesis of hyperbranched
aliphatic polyethers by the copolymerization of A2 and
B3 type monomers.13 Using this A2 + B3 strategy,
hyperbranched aromatic polyamides and polyimdes
have been prepared by Kakimoto’s and Okamoto’s
groups.14-16 Recently, Yan et al. have reported a new
A2 + BB′2 approach for the synthesis of hyperbranched
copoly(sulfone-amine)s.17
Exp er im en ta l Section
Gen er a l Dir ection s. N-Methyl-2-pyrrolidinone (NMP) and
N,N-dimethylformamide (DMF) were distilled over CaH2
under reduced pressure. Pyridine was dried by distillation
after being refluxed with KOH. 1,4-Phenylenediamine was
recrystallized from MeOH. Triphenyl phosphite (TPP) was
purified by distillation under reduced pressure. (2,3-Dihydro-
2-thioxo-3-benzoxazolyl)phosphonic acid diphenyl ester (DBOP)
was used as received. All other reagents and solvents were
used as received from commercial sources unless otherwise
stated. 1H and 13C NMR spectra were recorded on a Varian
Unity 300 MHz or a Bruker-DRX 300 MHz spectrometer. IR
spectra were obtained on a Nicolet 360 FT-IR spectrometer.
Mass spectra were obtained on a J EOL J MS-SX 102A mass
spectrometer. Size exclusion chromatography (SEC) was car-
ried out on a Waters chromatography unit, interfaced with a
Waters 410 differential refractometer. Three 5 µm Waters
styragel columns (300 × 7.8 mm), connected in series of
decreasing order of pore size (105, 104, and 103 Å), were used
with DMF as the eluent. Standard samples of PMMA were
Linear polyamides and polyimides are well-known as
high-performance polymeric materials.18,19 Their hyper-
branched analogues have been prepared by the self-
polymerization of AB2 type monomers20-25 or more
recently by copolymerization methods.14-16 Aromatic
poly(amide-imide)s are a class of high-performance
polymers which may combine the advantages of poly-
amides and polyimides; the resulting polymers should
possess high thermal stabilities, coupled with good
mechanical and chemical properties.26,27 To the best of
our knowledge, there has been no report regarding the
10.1021/ma021499f CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/07/2003

662 Chang and Shu
Macromolecules, Vol. 36, No. 3, 2003
used for calibration. Differential scanning calorimetry (DSC)
was performed using a Du Pont TA 2000 instrument, with a
heating/cooling rate of 20 °C min-1. Samples were scanned
from 30 to 400 °C and then cooled to 30 °C and scanned a
second time from 30 to 400 °C. The glass transition temper-
ature (Tg) was determined from the second heating scan.
Thermogravimetric analyses (TGA) were made on a Du Pont
TGA 2950 instrument. The thermal stability of the samples
was determined in nitrogen by measuring weight loss while
solution was then added dropwise to water (200 mL). The
precipitated product was collected by filtration and purified
by recrystallization from acetic acid to afford 6 (1.01 g, 82.2%).
1H NMR (DMSO-d6): δ 7.38-7.58 (m, 7H), 7.82 (d, 2H, J )
1.2 Hz), 8.01 (d, 1H, J ) 8.1 Hz), 8.32 (t, 1H, J ) 1.2 Hz),
13.51 (br, 2H). 13C NMR (DMSO-d6): δ 113.3, 124.0, 124.3,
126.0, 126.2, 126.7, 127.4, 128.2, 129.0, 132.0, 133.7, 134.4,
155.9, 161.6, 165.9, 166.2, 166.4. HRMS [M+]: 403.0694. Calcd
403.0692 for C22H13NO7.
heating at a rate of 20 °C min-1
.
Syn th esis of Mod el Com p ou n d s 7 a n d 8. A solution of 5
(531 mg, 2.24 mmol), 6 (600 mg, 1.49 mmol), DBOP (570 mg,
1.49 mmol), and 3 drops of triethylamine in NMP (6.0 mL)
was stirred at 25 °C under nitrogen for 12 h. The resulting
solution was added dropwise to a mixture of methanol (50 mL)
and water (50 mL). The precipitated product was collected by
filtration and purified by column chromatography, eluting with
CHCl3/ethyl acetate (4:1) to give 8 (0.44 g, 35%). Further
elution with CHCl3/CH3OH (3:1) and recrystallization from
acetic acid afforded 7 (0.31 g, 33%). Compound 7: 1H NMR
(DMSO-d6): δ 7.37-7.61 (m, 9H), 7.80 (br, 1H), 7.88-8.10 (m,
8H), 8.47 (br, 1H), 10.69 (s, 1H), 12.68 (br, 1H). 13C NMR
(DMSO-d6): δ 113.1, 120.9, 122.8, 123.3, 123.4, 124.1, 124.9,
126.0, 126.6, 127.4, 127.5, 127.7, 128.1, 128.9, 131.6, 131.9,
133.5, 134.5, 134.7, 137.3, 138.5, 155.6, 161.7, 163.8, 166.1,
166.2, 166.4, 167.1. HRMS [M+ + H]: 624.1415. Calcd
624.1407 for C36H22N3O8. Compound 8: 1H NMR (DMSO-d6):
δ 7.40-7.63 (m, 9H), 7.82-8.10 (m, 9H), 8.55 (br, 1H), 10.59
(s, 2H). 13C NMR (DMSO-d6): δ 113.4, 121.5, 122.7, 124.1,
124.4, 124.6, 126.7, 127.1, 127.9, 128.3, 128.7, 129.5, 132.3,
132.7, 135.1, 135.4, 138.1, 139.2, 156.0, 162.7, 164.8, 166.8,
166.9, 167.7. HRMS [M+ + H]: 844.2046. Calcd 844.2044 for
Dim eth yl 5-(3,4-Dicya n op h en oxy)isop h th a la te (1). A
mixture of dimethyl 5-hydroxyisophthalate (5.00 g, 26.9 mmol),
4-nitrophthalonitrile (4.65 g, 26.9 mmol), K2CO3 (5.00 g, 36.2
mmol), and DMF (20 mL) was heated at 130 °C for 4 h. After
this period, the reaction mixture was cooled and poured into
200 mL of water. The precipitated crude product was collected
by filtration, dried under vacuum, and purified by recrystal-
lization from ethyl acetate to afford 1 (8.20 g, 91.4%). 1H NMR
(DMSO-d6): δ 3.89 (s, 6H), 7.53 (dd, 1H, J ) 8.7, 2.7 Hz), 7.89
(d, 1H, J ) 2.7 Hz), 7.93 (d, 2H, J ) 1.5 Hz), 8.14 (d, 1H, J )
8.7 Hz), 8.36 (t, 1H, J ) 1.5 Hz). 13C NMR (DMSO-d6): δ 52.7,
109.2, 115.2, 115.7, 116.9, 122.8, 123.1, 125.2, 126.4, 132.5,
136.3, 154.4, 160.2, 164.5. HRMS [M+]: 336.0745. Calcd
336.0746 for C18H12N2O5.
4-(3,5-Dica r boxyp h en oxy)p h th a lic Acid (2). To a solu-
tion of KOH (14.0 g, 0.25 mol) in a mixture of water-ethanol
(100 mL/80 mL) was added compound 1 (7.00 g, 28.3 mmol).
The mixture was then refluxed for 24 h. The resulting solution
was diluted with water (250 mL) and acidified with 6 N HCl-
(aq) to pH ∼1. The precipitated product was filtered, washed
thoroughly with water, and dried to give 2 (7.00 g, 97.1%). 1H
NMR (DMSO-d6): δ 7.24 (dd, 1H, J ) 8.7, 2.7 Hz), 7.71 (d,
1H, J ) 2.7 Hz), 7.73 (d, 2H, J ) 1.5 Hz), 8.23 (d, 1H, J ) 8.7
Hz), 8.28 (t, 1H, J ) 1.5 Hz). 13C NMR (DMSO-d6): δ 120.6,
121.5, 123.4, 125.6, 130.1, 133.9, 135.4, 137.8, 156.4, 157.8,
166.2, 167.4. HRMS [M+ - H]: 345.0236. Calcd 345.0247 for
C
50H30 N5O9.
P r ep a r a tion of P olym er P AI-1. (A) Direct polymerization
of monomer 3 with 1,4-phenylenediamine: The monomer 3 (200
mg, 610 µmol) was added in one portion to a stirred solution
of 1,4-phenylenediamine (65.9 mg, 610 µmol) in NMP (2.0 mL)
under nitrogen at 25 °C. Stirring was continued at 25 °C for
2 h and at 150 °C for 12 h. The solution was cooled, added
pyridine (0.50 mL) and TPP (0.32 mL, 1.22 mmol), and then
heated at 120 °C for 12 h. After cooling, the resulting polymer
was precipitated into methanol. The polymer was collected,
washed with hot water, purified by reprecipitation from DMF
into methanol twice, and dried under vacuum to give P AI-1
(202 mg, 83.2%). (B) Self-polycondensation of monomer 4: A
solution of compound 4 (800 mg, 1.61 mmol), TPP (1.0 mL,
3.2 mmol), and LiCl (160 mg, 3.77 mmol) in NMP/pyridine
(10.0 mL, 4:1 v/v) was heated at 120 °C under nitrogen for 12
h. After cooling, the resulting polymer was precipitated into
methanol. The polymer was collected, washed with hot water,
purified by reprecipitation from DMF into methanol twice, and
C
16H9O9.
4-(3,5-Dica r boxyp h en oxy)p h th a lic An h yd r id e (3). A
mixture of compound 2 (6.00 g, 17.3 mmol), acetic anhydride
(6.0 mL), and acetic acid (6.0 mL) was stirred under reflux for
12 h. After cooling, the precipitate was collected by filtration,
washed with a small amount of glacial acetic acid, and then
dried under vacuum at 140 °C for 12 h to yield 3 (4.85 g, 85.
%). 1H NMR (DMSO-d6): δ 7.63 (dd, 1H, J ) 8.1, 2.1 Hz), 7.68
(d, 1H, J ) 2.1 Hz), 7.84 (d, 2H, J ) 1.2 Hz), 8.10 (d, 1H, J )
8.1 Hz), 8.34 (t, 1H, J ) 1.5 Hz), 13.55 (br, 2H). 13C NMR
(DMSO-d6): δ 114.2, 124.2, 125.7, 126.0, 126.6, 127.9, 134.1,
134.3, 155.2, 162.5, 162.6, 162.9, 165.9. HRMS [M+]: 328.0209.
Calcd 328.0219 for C16H8O8.
N-(4-Am in op h en yl)-4-(3,5-d ica r boxyp h en oxy)p h t h a l-
im id e (4). To a solution of compound 3 (400 mg, 1.22 mmol)
in NMP (4.0 mL) was added 1,4-phenylenediamine (132 mg,
1.22 mmol). The mixture was stirred at 25 °C under nitrogen
for 2 h and then heated at 150 °C for 12 h. The resulting
solution was cooled and then poured into dilute HCl(aq) (60
mL). The precipitated product was filtered, washed with water,
1
dried under vacuum to give P AI-1 (732 mg, 95.6%). H NMR
(DMSO-d6): δ 7.30-7.68 (m, 4H), 7.75-8.08 (m, 5H), 8.28-
8.56 (m, 1H), 10.69 (s, 1H), 13.51 (br, 1H). IR (KBr): 2500-
3500 (broad, O-H and N-H), 1772, 1716 (CdO, imide ring),
1665 (CdO, amide), 1373 cm-1 (C-N, imide).
P r ep a r a tion of P olym er P AI-2. A solution of P AI-1 (100
mg, 250 µmol), aniline (85 mg, 0.91 mmol), DBOP (383 mg,
1.00 mmol), and 3 drops of triethylamine in NMP (2.0 mL)
was stirred at 25 °C under nitrogen for 12 h. The resulting
solution was added dropwise to methanol (100 mL) with
agitation. The polymer was collected by filtration, washed with
warm water, and purified by reprecipitation from DMF into
methanol twice to give P AI-2 (114 mg, 96.0%). 1H NMR
(DMSO-d6): δ 6.80-7.65 (m, 8H), 7.70-8.10 (m, 6H), 8.42-
8.58 (m, 1H), 10.48 (br, 1H), 10.68 (br, 1H). IR (KBr): 1772,
1716 (CdO, imide ring), 1665 (CdO, amide), 1373 cm-1 (C-
N, imide).
P r ep a r a tion of P olym er P AI-3. P AI-3 was prepared from
P AI-1 (100 mg, 250 µmol) and 4-n-decylaniline (233 mg, 1.00
mmol) following the same procedure as described for the
preparation of P AI-2. Yield: 138 mg, 89.8%. 1H NMR (DMSO-
d6): δ 0.55-1.62 (m, 21H), 6.80-7.80 (m, 9H), 7.82-8.20 (m,
4H), 8.40-8.56 (m, 1H), 10.39 (br, 1H), 10.69 (br, 1H). IR
(KBr): 1772, 1716 (CdO, imide ring), 1665 (CdO, amide), 1373
cm-1 (C-N, imide).
1
and dried to give 4 (421 mg, 82.6%). H NMR (DMSO-d6): δ
6.67 (d, 2H, J ) 8.4 Hz), 7.03 (d, 2H, J ) 8.4 Hz), 7.40-7.54
(m, 2H), 7.81 (d, 2H, J ) 1.2 Hz), 7.96 (d, 1H, J ) 8.9 Hz),
8.31 (s, 1H). 13C NMR (DMSO-d6): δ 113.2, 114.3, 120.5, 123.9,
124.2, 125.8, 126.1, 126.8, 128.3, 133.6, 134.5, 147.7, 156.0,
161.4, 165.8, 166.7, 166.9. HRMS [M+]: 418.0785. Calcd
418.0801 for C22H14N2O7.
N-(4-Am in op h en yl)p h th a lim id e (5). A solution of 1,4-
phenylenediamine (3.00 g, 27.8 mmol) and phthalic anhydride
(4.11 g, 27.8 mmol) in DMF (6.0 mL) was heated at 150 °C for
4 h. The solution was poured into water (200 mL). The
precipitated product was filtered and dried to give 5 (5.95 g,
1
90.0%). H NMR (DMSO-d6): δ 5.33 (s, 2H), 6.62 (d, 2H, J )
8.4 Hz), 7.00 (d, 2H, J ) 8.4 Hz), 7.81-7.95 (m, 4H). 13C NMR
(DMSO-d6): δ 113.6, 119.6, 123.2, 128.2, 131.6, 134.5, 148.8,
167.6. HRMS [M+]: 238.0737. Calcd 238.0742 for C14H10N2O2.
Syn th esis of Mod el Com p ou n d 6. A solution of compound
3 (1.00 g, 3.05 mmol) and aniline (284 mg, 3.05 mmol) in NMP
(6.0 mL) was heated at 150 °C under nitrogen for 12 h. The

Macromolecules, Vol. 36, No. 3, 2003
Hyperbranched Aromatic Poly(amide-imide) 663
Sch em e 1
Sch em e 2
mixture of the monomer 3 and 1,4-phenylenediamine
was reacted in NMP to form the amic acid, which was
then thermally cyclized to give the AB2-type intermedi-
ate in situ, with an imide linkage. It should be noted
that the amino group in the AB2 molecule is deactivated
in comparison with the original amino groups in the A2
monomer, due to the formation of the imide (amide)
group in the para position of the benzene ring system.14
Therefore, the possibility of reaction of the former with
the phthalic anhydride (B′) of a second B′B2 molecule
is diminished and can be neglected under the reaction
conditions; the formation of the AB2 intermediate is the
predominate reaction at the initial stage of the copo-
lymerization. This is supported by the fact that the AB2
intermediate, which is identical to the AB2 type mono-
mer 4, can be isolated with an almost quantitative yield
in the first stage of the polymerization. Without isola-
tion, the AB2 type intermediate was polymerized at 120
°C for 12 h in the presence of TPP/pyridine, as condens-
ing agents, to yield P AI-1. No gelation occurred during
this polymerization. This polymer could also be synthe-
sized by the self-polycondensation of the AB2 type
monomer 4. The one-step polymerization of 4 was
carried out in NMP at 120 °C for 12 h using TPP/
pyridine as condensing agents. The structure of P AI-1
P r ep a r a tion of P olym er P AI-4. P AI-4 was prepared from
P AI-1 (100 mg, 250 µmol) and compound 5 (238 mg, 1.00
mmol) following the same procedure as described for the
preparation of P AI-2. Yield: 146 mg, 94.2%. 1H NMR (DMSO-
d6): δ 7.30-7.68 (m, 6H), 7.80-8.08 (m, 11H), 8.54 (br, 1H),
10.69 (br, 2H). IR (KBr): 1772, 1716 (CdO, imide ring), 1665
(CdO, amide), 1378 cm-1 (C-N, imide).
Resu lts a n d Discu ssion
Mon om er Syn th esis. Two kinds of monomers, 3 and
4, were prepared as shown in Scheme 1. Nucleophilic
substitution of the nitro function of 4-nitropthalonitrile
with the phenoxide of dimethyl 5-hydroxyisophthalate
in a K2CO3/DMF medium yielded dimethyl 5-(3,4-
dicyanophenoxy)isophthalate (1). Alkaline hydrolysis of
compound 1 in KOH(aq)/ethanol gave 4-(3,5-dicarboxy-
phenoxy)phthalic acid (2), which was subsequently
dehydrated with acetic anhydride to form the B′B2 type
monomer 3. The condensation of 3 with 1,4-phenylene-
diamine followed by cyclodehydration afforded the AB2
type monomer 4. Monomer 3 has one phthalic anhydride
and two carboxylic acid groups, while monomer 4
contains one aminophenyl and two carboxyl function-
alities joined with an ether-imide linkage. The struc-
tures of the synthesized compounds were verified by 1H
NMR and 13C NMR spectroscopy as well as by mass
spectroscopy. Figure 1 shows the 1H NMR spectra of
monomers 3 and 4, which are consistent with the
assigned structures.
1
was characterized by FTIR and H NMR spectroscopy.
It was found that the two different synthetic approaches
led to hyperbranched poly(amide-imide)s with almost
identical structures. In the IR spectra, the polymers
exhibit characteristic carbonyl absorptions correspond-
ing to an imide ring at 1772 (CdO asymmetric stretch-
ing) and 1716 cm-1 (CdO symmetric stretching), in
addition to the typical aromatic-imide C-N stretching
at 1373 cm-1. The carbonyl absorptions of the cyclic
anhydride unit at 1849 and 1783 cm-1 in monomer 3
have disappeared. In addition, the CdO stretching of
the amide group appears at 1665 cm-1. The carbonyl
stretching of the terminal carboxylic acid group at
∼1700 cm-1 is obscured by the absorption of the imide
ring. The broad bands between 2500 and 3500 cm-1 are
attributed to amide N-H and acid O-H stretches. In
P olym er Syn th esis. As shown in Scheme 2, the
hyperbranched poly(amide-imide) P AI-1 was prepared
by the direct polymerization of the B′B2 monomer 3 with
the A2 monomer 1,4-phenylenediamine. An equimolar
1
the H NMR spectrum of P AI-1s, the resonance of the
proton of the amide group appears at 10.69 ppm, and a
broad peak at 13.51 ppm from the proton of the terminal
carboxylic acid group is also observed.
The hyperbranched poly(amide-imide), P AI-1, which
has a high number of terminal carboxyl groups, could
not be analyzed directly by gel permeation chromatog-
raphy (GPC) because the polymer adsorbed to the
column, resulting in incomplete elution.30 This problem
was overcome by the transformation of the carboxylic
acids groups into amide groups. By reacting with excess
aniline, P AI-1 was readily converted to the amide-
terminated polymer P AI-2 (vide post). GPC analyses
showed that the weight-average molecular weights (Mw)
and polydispersities (Mw/Mn) were approximately 4.4 ×
F igu r e 1. 1H NMR spectra of compounds (a) 3 and (b) 4 in
DMSO-d6.

664 Chang and Shu
Macromolecules, Vol. 36, No. 3, 2003
Sch em e 3
F igu r e 2. 1H NMR spectra in DMSO-d6 of model compounds
(a) 6, (b) 7, and (c) 8 compared with the hyperbranched poly-
(amide-imide)s P AI-1s prepared by either the (d) self-polym-
erization of monomer 4 or (e) the copolymerization method.
104 g/mol and 2.7, respectively, for the amide-terminated
polymer of P AI-1 prepared from the direct polymeriza-
tion of the B′B2 with the A2 monomers,. The amide
derivative of P AI-1, prepared by the self-polyconden-
sation of the AB2 type monomer 4 under the same
conditions, has similar Mw and Mw/Mn values: 4.1 ×
104 g/mol and 2.5. These values, however, are only
indicative, since the highly branched nature of P AI-1
deviates strongly from that of linear, coillike poly-
(methyl methacrylate) standards. The solution viscosity
of P AI-1s was also evaluated in DMAc at a concentra-
1H NMR spectra are depicted in Figure 2. A distinct
resonance for the terminal model compound, 6, appears
at 8.32 ppm (Ht), whereas resonances of the correspond-
ing protons for the linear and dendritic model com-
pounds, 7 (Hl), and 8 (Hd), are observed at 8.47 and 8.55
ppm, respectively. Figure 2 also shows the 1H NMR
spectra of the hyperbranched poly(amide-imide)s. In
1
comparing the H NMR spectra of P AI-1s with those of
the model compounds, one can clearly assign the
resonances at 8.32, 8.47, and 8.55 ppm to the proton of
the terminal, linear, and dendritic subunits in the
hyperbranched polymer, respectively. On the basis of
the integration of these well-resolved resonances, the
relative percentages of each subunit in P AI-1s can be
determined. It was noted that the percentage estimated
for the terminal subunit is approximately equal to that
for the dendritic subunit. This result is consistent with
the theoretical prediction that the number of dendritic
units is equal to the number of terminal units for an
AB2 type hyperbranched polymer possessing high mo-
lecular weight.5 With these formulas, the DB of the poly-
(amide-imide) P AI-1, prepared by the direct polymer-
ization of monomer 3 with 1,4-phenylenediamine, is
estimated to be 61%. This value is nearly the same as
the DB calculated for the P AI-1 synthesized by the self-
polycondensation of the AB2 type monomer 4, which is
60%.
Ch em ica l Mod ifica tion . As predicted theoretically
by Flory,5 the direct polymerization of ABn type mono-
mers is expected to produce a highly branched, irregular
structure that contains a large number of end groups.
In this study, the end groups in the resulting hyper-
branched poly(amide-imide) P AI-1 are carboxylic acids,
which could be readily functionalized to yield hyper-
branched polymers with a variety of functional chain
ends. As shown in Scheme 4, the modification of the
carboxylic end groups of P AI-1 was carried out with
different kinds of aromatic amines, in the presence of
DBOP as the condensation agent, to give the corre-
sponding amide derivatives. We chose DBOP as the
activator33 and ran the condensation reaction at room
temperature to prevent transamination, which is a side
reaction occurring at high temperatures. In the modi-
tion of 0.5 g/dL at 30 °C. The inherent viscosity (ηinh
)
was 0.29 and 0.28 g/dL respectively for the hyper-
branched polymers P AI-1s prepared by the copolymer-
ization method and by the self-polymerization of mono-
mer 4. The comparison of the solution viscosity reveals
that there is no cross-linking taken place in the direct
copolymerization. This is consistent with the observa-
tion that no gelation occurred during the copolymeri-
zation.
Degr ee of Br a n ch in g. Hyperbranched polymers,
which were formed by a sequence of condensation of AB2
monomers, have an irregular dendritic structure in
which three different types of subunits may be present.
In this work, the hyperbranched poly(amide-imide)
P AI-1 is composed of three kinds of repeating units: the
terminal units, which have two carboxylic acid groups,
the linear units, which have one amide group and one
carboxylic acid group, and the dendritic units, which
have two amide groups and no free carboxylic acid
group. The degree of branching (DB), a typical property
often used to evaluate the structural irregularity of
hyperbranched polymers, was defined as the sum of
dendritic and terminal units vs the total number of
units.31,32 A combination of NMR spectroscopy and
comparative studies on a model compound was used to
quantify the different subunits present in the hyper-
branched polymer and, subsequently, to determine its
DB.31
The preparation of the model compounds useful for
NMR characterization is illustrated in Scheme 3. Model
compounds 6, 7, and 8 resemble the terminal unit, the
linear unit, and the dendritic unit, respectively. Their

Macromolecules, Vol. 36, No. 3, 2003
Hyperbranched Aromatic Poly(amide-imide) 665
Ta ble 1. Th er m a l a n d Solu bility P r op er ties of
Sch em e 4
Hyp er br a n ch ed P oly(a m id e-im id e)s
solubilityc in
polymer Tg (°C) THF DMF DMAc DMSO pyridine
P AI-1a
P AI-1b
P AI-2
P AI-3
P AI-4
262
263
248
223
283
-
-
-
+
-
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+ -
+
a
Prepared by the copolymerization approach. b Prepared by self-
polymerization of monomer 4. c Solubility: +, soluble; -, insoluble;
+ -, soluble on heating.
intermolecular interactions in the polymeric mol-
ecules.35 The Tg of P AI-1, which has polar carboxylic
terminal groups, is 262 °C, while the Tg value of P AI-
2, which has less polar amide terminal groups, is 248
°C. A further decrease in Tg to 223 °C was observed for
P AI-3, due to the introduction of long, flexible n-decyl
chain ends. P AI-4, which has rigid, imide chain ends,
has a Tg of 283 °C. Because of their highly branched
structures, these poly(amide-imide)s have enhanced
solubility in organic solvents and are highly soluble in
polar solvents such as DMAc, NMP, and pyridine (Table
1). However, the different chain ends led to solubility
differences in very polar and in relatively nonpolar
solvents. P AI-1-2 and P AI-4 are soluble in DMSO and
insoluble in THF, whereas P AI-3, which possesses long
n-decyl chain ends, is soluble in hot DMSO as well as
in THF.
fication reaction, the use of excess amino reagents
resulted in almost complete (>95%) functionalization,
1
as confirmed by the H NMR spectra of the derivative.
After end-capping, the broad peak at 13.51 ppm, as-
sociated with the proton of the terminal carboxylic acid
group, disappeared. For P AI-2-3, an additional reso-
nance due to the proton of the terminal amide group
appears in the region of 10.4-10.5 ppm. It is interesting
to note that for P AI-4 the signals corresponding to the
proton of the terminal (Ht), linear (Hl), and dendritic
(Hd) subunits shown in Figure 2 coalesce at 8.54 ppm.
This is attributed to the similarity of the chemical
environments for the three different subunits in P AI-
4. This result is consistent with the observation that,
in P AI-4, the chemical shift of the proton of the terminal
amide group is the same as that of the interior amide
group. Thus, there is only one resonance with an
integration of 2 H for the protons of the two different
Su m m a r y
We have synthesized a hyperbranched poly(amide-
imide) via the A2 + B′B2 approach. The copolymerization
of 4-(3,5-dicarboxyphenoxy)phthalic anhydride (3), a
B′B2 type monomer, and 1,4-phenylenediamine, an A2
type monomer, resulted in a hyperbranched poly-
(amide-imide) containing terminal carboxylic acid
groups. No gelation occurred during the polymerization.
For comparison, we also carried out the synthesis of this
hyperbranched polymer via the conventional self-
polymerization of N-(4-aminophenyl)-4-(3,5-dicarboxy-
phenoxy)phthalimide (4), an AB2 monomer. Both ap-
proaches led to hyperbranched poly(amide-imide)s with
almost identical structures. The degree of branching of
the polymers was approximately 60%, as determined by
1
kinds of amides. The integration analyses of H NMR
spectra of the derivatives indicate that the modification
reactions proceeded almost quantitatively.
The nature of the end groups influences the physical
and chemical properties of hyperbranched polymers.34
The glass transition temperatures (Tg’s) of poly(amide-
imide)s P AI-1-4 were investigated by differential scan-
ning calorimetry (DSC), and the results are presented
in Figure 3 and Table 1. As reported, the transition from
the polar function to nonpolar end groups results in a
decrease in Tg due to the reduction in the extent of
1
a combination of model compound studies and H NMR
integration data. End-capping of the terminal carboxylic
acid groups was accomplished by reacting with different
kinds of aromatic amines. Thermal and solubility prop-
erties of the resulting polymers depend on the nature
of the chain-end groups.
Ack n ow led gm en t. We thank the National Science
Council of the Republic of China for financial support.
Refer en ces a n d Notes
(1) Malmstro¨m, E.; Hult, A. J . Macromol. Sci., Rev. Macromol.
Chem. Phys. 1997, C37, 555.
(2) Kim, Y. H. J . Polym. Sci., Part A: Polym. Chem. 1998, 36,
1685.
(3) Voit, B. J . Polym. Sci., Part A: Polym. Chem. 2000, 38, 2505.
(4) J ikei, M.; Kakimoto, M. Prog. Polym. Sci. 2001, 26, 1233 and
references cited in the reviews.
(5) Flory, P. J . J . Am. Chem. Soc. 1952, 74, 2718.
(6) Fre´chet, J . M. J . Science 1994, 263, 1710.
(7) Newkome, G. R.; Moorefield, C. N.; Vo¨gtle, F. Dendritic
Molecules: Concepts, Syntheses, Perspectives; VCH: Wein-
heim, FRG, 1996.
F igu r e 3. DSC thermograms of hyperbranched poly(amide-
imide)s (a) P AI-1 prepared by self-polymerization of monomer
4, (b) P AI-1 prepared by the copolymeriztion method, (c) P AI-
2, (d) P AI-3, and (e) P AI-4.

666 Chang and Shu
Macromolecules, Vol. 36, No. 3, 2003
(8) Hecht, S.; Fre´chet, J . M. J . Angew. Chem., Int. Ed. 2001, 40,
74.
(9) Tomalia, D. A.; Baker, H.; Dewald, J .; Hall, M.; Kallos, G.;
Martin, S.; Roeck, J .; Ryder, J .; Smith, P. Polym. J . 1985,
17, 117.
(10) Newkome, G. R.; Yao, Z.-Q.; Baker, G. R.; Gupta, V. K. J .
Org. Chem. 1985, 50, 2003.
(11) Hawker, C. J .; Fre´chet, J . M. J . J . Am. Chem. Soc. 1990, 112,
7638.
Fujii, K.; Yang, G.; Kakimoto, M. J . Polym. Sci., Part A:
Polym. Chem. 2001, 39, 3304.
(22) Monticilli, O.; Mendichi, R.; Bisbano, S.; Mariani, A.; Russo,
S. Macromol. Chem. Phys. 2000, 201, 2123.
(23) Yamanaka, K.; J ikei, M.; Kakimoto, M. Macromolecules 2000,
33, 1111. (b) Yamanaka, K.; J ikei, M.; Kakimoto, M. Macro-
molecules 2000, 33, 6937. (c) Yamanaka, K.; J ikei, M.;
Kakimoto, M. Macromolecules 2001, 34, 3910.
(24) Thompson, D. S.; Markoski, L. J .; Moore, J . S. Macromolecules
1999, 32, 4764. (b) Markoski, L. J .; Thompson, J . L.; Moore,
J . S. Macromolecules 2000, 33, 5315.
(12) Xu, Z. F.; Moore, J . S. Angew. Chem., Int. Ed. Engl. 1993,
32, 1354.
(13) Emrick, T.; Chang, H.-T.; Fre´chet, J . M. J . Macromolecules
1999, 32, 6380.
(14) J ikei, M.; Chon, S.-H.; Kakimoto, M.; Kawauchi, S.; Imase,
T.; Watanebe, J . Macromolecules 1999, 32, 2061.
(15) Fang, J .; Kita, H.; Okamoto, K. Macromolecules 2000, 33,
4639.
(25) Wu, F.-I.; Shu, C.-F. J . Polym. Sci., Part A: Polym. Chem.
2001, 39, 2536.
(26) Liaw, D.-J .; Hsu, P.-N.; Chen, W.-H.; Liaw, B.-Y. J . Polym.
Sci., Part A: Polym. Chem. 2001, 39, 3498.
(27) Yang, C.-P.; Chen, R.-S.; Wang, M.-J . J . Polym. Sci., Part A:
Polym. Chem. 2002, 40, 1092.
(16) Hao, J .; J ikei, M.; Kakimoto, M. Macromolecules 2002, 35,
5372.
(28) Yamazaki, N.; Matsumoto, M.; Higashi, F. J . Polym. Sci.,
Polym. Chem. Ed. 1975, 13, 1373.
(29) Tullos, G. L.; Mathias, L. J .; Langsam, M. J . Polym. Sci., Part
A: Polym. Chem. 1999, 37, 1183.
(30) Shu, C.-F.; Leu, C.-M. Macromolecules 1999, 32, 100.
(31) Hawker, C. J .; Lee, R.; Fre´chet, J . M. J . J . Am. Chem. Soc.
1991, 113, 4583.
(32) Ho¨lter, D.; Burgath, A.; Frey, H. Acta Polym. 1997, 48, 30.
(33) Ueda, M.; Maneyama, A.; Hashimoto, K. Macromolecules
1988, 21, 18.
(17) (a) Yan, D.; Gao, C. Macromolecules 2000, 33, 7693. (b) Gao,
C.; Yan, D. Macromolecules 2001, 34, 156. (c) Gao, C.; Yan,
D. Chem. Commun. 2001, 107. (d) Gao, C.; Yan, D.; Zhu, X.;
Huang, W. Polymer 2001, 42, 7603. (e) Gao, C.; Yan, D.; Tang,
W. Macromol. Chem. Phys. 2001, 202, 3035.
(18) Cassidy, P. E. Thermally Stable Polymer; Marcel Dekker:
New York, 1980.
(19) Polymides; Wilson, D., Stenzenberger, H. D., Hergenrother,
P. M., Eds.; Blackie: New York, 1990.
(20) Kim, Y. H. J . Am. Chem. Soc. 1992, 114, 4947.
(21) (a) Yang, G.; J ikei, M.; Kakimoto, M. Macromolecules 1998,
31, 5964. (b) Yang, G.; J ikei, M.; Kakimoto, M. Macromol-
ecules 1999, 32, 2215. (c) J ikei, M.; Fujii, K.; Yang, G.;
Kakimoto, M. Macromolecules 2000, 33, 6228. (d) J ikei, M.;
(34) Hawker, C. J .; Chu, F. Macromolecules 1996, 29, 4370.
(35) Schmaljohann, D.; Ha¨ussler, L.; Po¨tschke, P.; Voit, B. I.;
Loontjens, T. J . A. Macromol. Chem. Phys. 2000, 201, 49.
MA021499F