Synthesis and ring-opening polymerization of 5-Azepane-2-one ethylene ketal: A new route to functional aliphatic polyamides

Article abstract of DOI:10.1021/ma902233k

A functional derivative of e-caprolactam, 5-azepane-2-one ethylene ketal or y-ethylene ketal e-caprolactam, has been synthesized by a very straightforward and highly efficient Beckmann rearrangement reaction. Homopolymers of this new monomer and its copol

Full text of DOI:10.1021/ma902233k

9
68 Macromolecules 2010, 43, 968–974
DOI: 10.1021/ma902233k
Synthesis and Ring-Opening Polymerization of 5-Azepane-2-one Ethylene
Ketal: A New Route to Functional Aliphatic Polyamides
Eylem Tarkin-Tas and Lon J. Mathias*
School of Polymers and High Performance Materials, University of Southern Mississippi, 118 College Drive,
Hattiesburg, Mississippi 39406-0076
Received October 7, 2009; Revised Manuscript Received December 11, 2009
ABSTRACT: A functional derivative of ε-caprolactam, 5-azepane-2-one ethylene ketal or γ-ethylene ketal
ε-caprolactam, has been synthesized by a very straightforward and highly efficient Beckmann rearrangement
reaction. Homopolymers of this new monomer and its copolymers with ε-caprolactam have been synthesized
by anionic ring-opening polymerization using N-acetyl-ε-caprolactam and NaH. The ketone groups can be
easily released by deacetalyzation, and subsequent reaction leads to complete reduction to hydroxyl pendant
groups. The ketone-containing (co)polymers respond sensitively to both thermal and photo-cross-linking in
this novel class of materials. These new aliphatic polyamides bearing either ketone or hydroxyl pendant
groups provide entries into a large number of application areas.
Introduction
synthesized by a sequence of reactions starting from 4-benzoloxy-
methylcyclohexanol. The yields of racemic and optically active
Polyamides or nylons are extremely versatile engineering ther-
moplastics that encompass a broad range of applicability in
industries. One of the most common types of polyamide is poly-
polymer from the anionic ring-opening polymerization of γ-tert-
butoxymethylcaprolactam ranged from 10 to 56% with a num-
ber-average molecular weight of 3000 g/mol. Obtained polymers
were treated to remove the tert-butyl protective group to yield
polyamide with hydroxymethyl pendant groups. Although the
hydroxymethyl-substituted polyamides were soluble in polar
solvents such as methanol, ethanol, and 2,2,2-trifluoroethanol,
they were not soluble in water.
(
ε-caprolactam), PCL, which is also known as nylon-6. The
industrial production of PCL involves either water initiated
hydrolytic) or strong base initiated (anionic) ring-opening poly-
(
merization of ε-caprolactam. While the hydrolytic polymerization
of ε-caprolactam is the most important for commercial production
of PCL, high molecular weight polymer with defined end groups
1
A modified poly(ε-caprolactam) containing sulfonate pendant
can be produced very rapidly via anionic polymerization.
4
groups has been reported by Nijenhuis et al. γ-Phenylsulfonate
PCL prepared from ring-opening polymerization of ε-capro-
lactam possess excellent tensile, flexural, and compressive
strengths as well as resistance to abrasion and chemicals due to
caprolactam was synthesized starting from 4-phenylcyclohexa-
none. Beckmann rearrangement of 4-phenylcyclohexanone oxime
to yield lactam and sulfonization of the phenyl ring were accom-
plished in one step using concentrated sulfuric acid. Finally, the
alkali salt of γ-phenylsulfonate caprolactam was prepared by
addition of alkali hydroxide. The polymers were synthesized
under hydrolytic ring-opening polymerization conditions. While
the phenyl sulfonate pendant group did not affect the thermal
properties of the polymer, it did lead to a higher zero shear melt
viscosity.
1
a high degree of crystallinity. Nevertheless, it is desirable to have
aliphaticpolyamides having functional groupsalongthe chains in
order to tune properties such as hydrophilicity, crystallinity,
solubility, and elasticity; to promote (bio)adhesion, biocompat-
ibility, and/or biodegradability; or to label the polymer by
attaching other compounds pendant to the backbone. However,
the shortage of polyamides bearing functional groups is a severe
limitation to further progress in this field.
To date, there are only a few reports on polyamides that are
formed from the ring-opening polymerization of ε-caprolactam
derivatives with functional groups. Reimschuessel et al. reported
the synthesis and polymerization of β-carboxymethylcaprolac-
tam. The synthesis of this monomer was accomplished in four
steps starting from R-bromocaprolactam. The product of the
thermal polymerization of β-carboxymethylcaprolactam gave
poly[(2,2-dioxo-1,4-piperidinediyl)trimethylene] as a hard crys-
talline polymer with melting temperature of 280 °C. In other
words, instead of polyamide with carboxylic acid pendant
groups, a novel linear polyimide was obtained fromisomerization
polymerization.
γ-Carboxyethylcaprolactam and γ-aminoethylcaprolactam
were used for the synthesis of hyperbranched aliphatic poly-
amides. Carboxy- and amino-functionalized caprolactams were
prepared by a multistep synthesis starting from methyl 3-(4-
hydroxyphenyl)propanoate. Carboxy- and amino-terminated
hyperbranched polyamides were obtained by using acidolytic
formation of poly(ε-caprolactam). Cross-linked fractions were
observed on heating for 48 h for the carboxy system and 4 h for
2
5
the amino system.
As shown by these examples, the typical pathway to functional
polymers is based on functional monomers which are capable
of polymerization. The functional groups must be selected or
protected in such a way that they do not interfere with the
polymerization mechanism. The shortage of examples is gene-
rally due to difficulties in synthesis of new monomers which
are generally obtained by rather complex and time-consuming
procedures. The aim of this paper is to report an efficient route to
a new monomer as a precursor for a novel class of (co)polyamides
Racemic and optically active γ-tert-butoxymethylcaprolactam
was polymerized by Overberger et al. The monomer was
3
*
Corresponding author: Tel þ1 601 266 4871; Fax þ1 601 266 5504;
e-mail lon.mathias@usm.edu.
pubs.acs.org/Macromolecules
Published on Web 12/31/2009
r 2009 American Chemical Society

Article
Macromolecules, Vol. 43, No. 2, 2010 969
bearing ketone and/or hydroxyl groups on the polymer back-
bone.
Scheme 1
Experimental Section
Materials. 1,4-Cyclohexanedione monoethylene ketal
>97%) and 2,2,2-trifluoroethanol (TFE) were purchased from
(
Fluka. Hydroxylamine hydrochloride (99%), ε-caprolactam,
and sodium borohydride (>98%) were purchased from
Aldrich. p-Toluenesulfonyl chloride (p-TSCl) was purchased
from Acros (>98%). Sodium acetate, sodium bicarbonate,
sodium sulfate (anhydrous), sodium hydroxide, and all solvents
were purchased from Fisher Scientific and used as received.
ε-Caprolactam was recrystallized from acetone prior to use.
Synthesis of 4-Oximinocyclohexanone Ethylene Ketal (1).
Hydroxylamine hydrochloride (85.3 mmol) and sodium acetate
unreacted monomers. The polymers were dissolved in TFE and
precipitated into diethyl ether.
General Procedure for the Deprotection of Ketone Groups. A
sample of 0.2 g of (co)polymer was dissolved in 10 mL of
aqueous HCl (4 wt %) solution. The mixture was maintained
under stirring at room temperature overnight, during which
the deprotected polymer precipitated from the solution. After
(
85.3 mmol) were dissolved in 35 mL of H O in a 250 mL round-
2
bottomed reaction flask. 1,4-Cyclohexanedione monoethylene
ketal (77.5 mmol) in 145 mL of methanol was added. The
temperature was then raised to 85 °C, and the reaction mixture
was allowed to reflux for 2 h. After evaporation of methanol,
10 mL of H O was added, and the aqueous solution was
2
transferred to an extraction funnel. The aqueous phase was
3
neutralization with NaHCO , the polymer was filtered and
washed with water several times. The white polymer powder
was dried under vacuum at 50 °C. For the copolymers with high
ε-caprolactam content (i.e., 75 mol %), deprotection of the
ketone groups was performed using moist trifluoroacetic acid
at room temperature. The deprotected polymer was then pre-
cipitated into water, filtered, and dried at 50 °C under vacuum.
General Procedure for the Reduction of Ketone Groups. A 1.0 g
portion of (co)polymer was dissolved in 35 mL of a 5:2 v:v
extracted with ethyl acetate (3 ꢀ 100 mL). The combined organic
3
phase was neutralized with aqueous NaHCO (10 wt %) solution
(
3 ꢀ 50 mL), separated, dried over anhydrous Na
2 4
SO , filtered,
and evaporated. The product was further dried under vacuum at
room temperature overnight. 4-Oximinocyclohexanone ethylene
ketal (13.0 g, 98%) was obtained in the form of white crystals, mp
CHCl
had been dried and purged with N
3
:TFE mixture in a 50 mL round-bottomed flask which
. NaBH (0.1 g) was added
2
4
into the reaction vessel quickly. The mixture was maintained
under stirring at room temperature for 30 min. After filtration,
the solvent mixture was evaporated. The polymer was dissolved
in TFE and precipitated into diethyl ether. The white powder
(co)polymers were filtered and dried under vacuum at 50 °C
overnight.
6
9.7 °C. Anal. Calcd for C
Found: C: 55.98 H: 7.59 N: 8.05. H NMR (300 MHz, CDCl
ppm) = 9.7 (s, 1H), 3.9 (t, 4H), 2.6 (t, 2H), 2.3 (t, 2H), 1.7 (t, 4H).
8
H
13NO
3
; C: 56.13 H: 7.65 N: 8.18.
1
3
): δ
(
1
3
C NMR (75 MHz, CDCl
2.9, 28.7, 21.0.
Synthesis of 5-Azepane-2-one Ethylene Ketal (2). Oxime 1
60 mmol) was dissolved in 170 mL of acetone in a 500 mL
3
): δ (ppm) = 158.3, 107.9, 64.3, 34.2,
3
UV Irradiation. Thin films of a ketone-containing homopo-
lymer, P(KCL), were cast using TFE as a solvent. The films were
dried under vacuum for 24 h and then placed into a quartz box
which was purged with argon for 24 h prior to UV irradiation.
The box was then placed under a medium-pressure mercury
(
round-bottomed flask charged with a magnetic stirrer. Addition
of 60 mL of 4 N aqueous NaOH solution was followed by slow
addition of p-toluenesulfonoyl chloride (108 mmol) dissolved in
2
1
70 mL of acetone. The reaction mixture was allowed to mix 2 h
at room temperature. After the evaporation of acetone 40 mL of
O was added. The reaction mixture was then neutralized by
lamp with light intensity 40 mW/cm . The quartz box was
continuously purged with argon during irradiation with UV
light. The inside temperature of the quartz box was around 30 °C
after 5 h of irradiation so thermal reaction did not occur.
H
2
dropwise addition of 4 N aqueous HCl solution. The reaction
was allowed to proceed overnight at room temperature. The
reaction mixture was transferred into an extraction funnel,
and the product was separated by extraction with CH Cl (5 ꢀ
1
13
Characterization. H and C NMR spectra were obtained in
TFE:CDCl (70:30 v:v mixture) using Varian Gemini 300 and
3
UNITY
INOVA 500 spectrometersoperating at 300 or 500 MHz for
proton and 75 or 125 MHz forcarbon. Solution C NMRspectra
2
2
1
3
2
00 mL). Combined organic phases were dried over anhydrous
UNITY
Na
2
SO
4
and filtered, and the solvent was evaporated. 5-Aze-
pane-2-one ethylene ketal, KLCL (9.6 g, 93%), was recrsytal-
for the end-group analysis were collected on
INOVA
500 MHz NMR operating at 125 MHz spectral frequency.
NMR samples were prepared by dissolving polymers in a solvent
mixture consisting of a 7:3 ratio of TFE to CDCl to give low-
3
lized twice from acetone, mp 104 °C. Anal. Calcd for C H NO ;
8
13
3
1
C: 56.13 H: 7.65 N: 8.18. Found: C: 56.26 H: 7.71 N: 8.09. H
NMR (300 MHz, CDCl
(
3
): δ (ppm) = 7.7 (s, 1H), 3.7 (s, 4H), 3.0
viscosity solutions. To maximize signal-to-noise ratios, the sam-
ples were prepared at high concentrations (∼25 wt %), and the
number of scans was kept as high as 20 000 scans (∼18 h). The
number-average molecular weights of the polymers were calcu-
lated from the peak intensities of main-chain carbonyl and end-
1
t, 2H), 2.3 (t, 2H), 1.6 (m, 4H). C NMR (75 MHz, CDCl ):
3
3
δ (ppm) = 178.3, 108.6, 64.0, 38.7, 37.0, 32.5, 30.3. IR (KBr):
ν 3214 (s), 2967 (w), 2896 (w), 1664 (s), 1448 (m), 1114 (s), 896
-
1
(
m) 507 (w) cm
General Procedure for the Anionic (Co)polymerization. In
.
group carbonyl.
Solid-state NMR spectroscopy was performed on a
UNITY
a typical experiment, monomer or combined monomers (20
mmol) were weighed and added to a flame-dried polymerization
tube. The system was purged with nitrogen for 30 min. After the
addition of N-acetylcaprolactam (0.2 mmol) through a syringe,
the polymerization tube was placed into an oil bath adjusted at
INOVA
400 spectrometer using a standard Chemagnetics 7.5 mm PENCIL-
style probe. Samples were loaded into zirconia rotor sleeves, sealed
with Teflon caps, and spun at 4.0 kHz. The standard cross-polariza-
tion/magic angle spinning (CP/MAS) technique was used with
6
1
40 °C. The reaction mixture was maintained under stirring
for 15 min at this temperature before the addition of NaH
0.2 mmol, 50 wt % dispersion in mineral oil). The polymeriza-
tion was allowed to proceed for 3 h under N atmosphere. After
proton decoupling implemented during data acquisition. In addi-
tion, the TOSS technique was implemented to remove/minimize
7
spinning side bands. The acquisition parameters were as follows:
(
1
H 90° pulse width was 5.5 μs, cross-polarization contact time was
2
cooling down to room temperature, the homopolymer was
ground to a powder and dispersed in methanol, stirred for
1.5 ms, dead time delay was 6.4 μs, acquisition time was 45 ms, and
recycle delay between scans was 3 s.
24 h, and filtered. The copolymers were ground and dispersed
in CH Cl , stirred for 24 h, and filtered in order to remove
FTIR spectra were recorded on an ATI-Mattson Galaxy 5000
FTIR spectrometer. Thermal analyses were performed on a TA
2
2

9
70 Macromolecules, Vol. 43, No. 2, 2010
Table 1. Homopolymerization of KLCL Initiated by N-AcCL in Bulk at 140 °C
Tarkin-Tas and Mathias
a
-3
b
-3
entry
[KLCL]/[N-AcCL]
[NaH]/[N-AcCL]
M
ntheo (g/mol) (ꢀ10
)
polym time (h)
conv (%)
M
nexp (g/mol) (ꢀ10
)
1
2
3
4
a
90
75
100
100
2.0
2.5
1.5
1.5
15.4
12.9
17.3
0.5
1
3
61
67
68
98
15.0
11.1
16.6
13.0
13.3
3
b
M
n,theo: molecular weight calculated from monomer-to-initiator ratio.
M
n,exp: molecular weight determined from NMR end-group analysis.
1
3
1
Figure 2. C NMR spectra of KLCL (top) and P(KLCL) (bottom).
Figure 1. H NMR spectra of KLCL (top) and P(KLCL) (bottom).
conversion under the same conditions. In general, the equilibrium
monomer concentration appears to increase with the bulk of
Instruments SDT 2960 TGA-DTA at 10 °C/min under nitrogen
from ambient temperature to 600 °C and on a DSC 2920 at
9
,10
substituent on the seven-membered ring lactams.
Thus, the
1
0°C/minunder nitrogenfromambientto250°C. AnUbbelohde
viscometer was used for the dilute solution viscosity measure-
bulky ethylene ketal group might be limiting the conversion of
KLCL.
ments in TFE at 25 °C at low concentrations (in the range of
The unreacted monomer was removed by extraction with
methanol for 24 h. The complete removal of monomer was
0
.05-0.2 g/dL). The viscosity-average molecular weights were
calculated using previously reported Mark-Houwink constants
determined for poly(ε-caprolactam). Elemental analyses were
performed by Quantitative Technologies, Inc.
1
13
confirmed by H and C NMR spectra of the polymer after
8
1
13
extraction. The H and C NMR spectra also showed that the
ketal groups were stable toward the initiating and propagating
species under these experimental conditions (Figures 1 and 2).
Results and Discussion
13
C NMR end-group analysis for molecular weight determina-
Synthesis of 5-azepane-2-one ethylene ketal (alternatively
named as ethylene ketal substituted ε-caprolactam or KLCL)
was accomplished through a modified Beckmann rearrange-
ment reaction. The classic Beckmann rearrangement conditions
require high temperatures and very strong protic acids such as
concentrated or fuming sulfuric acid, trichloroacetic acid, or
poly(phosphoric acid). In this study, traditional Beckmann
rearrangement conditions led to undesired products. However,
the synthesis of KLCL was successful in the presence of p-TSCl
and sufficient NaOH(aq) to maintain neutrality. A 93% yield was
obtained. This procedure is not only very efficient but also very
mild because the reaction takes place at room temperature in a
neutral medium. The schematic representation of the reaction
pathway starting from the commercially available 1,4-cyclohex-
anedione monoethylene ketal is shown in Scheme 1.
tion is a useful technique which has been used for many different
11,12
nylons in our research group previously.
The molecular
1
3
weights were calculated from C NMR data using the relative
intensity of the carbonyl peak (at 173.3 ppm, peak 4) of the
N-acetyl end group resulting from N-AcCL co-initiator and the
amide carbonyl peak (at 174.9 ppm, peak 3) of the monomer
repeat units in Figure 3. Values obtained are in good agreement
with values calculated from the monomer-to-initiator ratios
(Table 1).
KLCL and CL were copolymerized using the same polymer-
ization conditions, i.e., at 140 °C under N atmosphere. The
2
copolymer compositions as well as copolymer sequences were
1
3
determined by C NMR analysis. The carbonyl region and the
1
3
aliphatic region of the C NMR spectra of both homopolymers
and their copolymers are given in Figure 4. There are four
different amide carbonyl groups for the copolymers which is
consistent with random copolymer composition; i.e., the peak at
174.9 ppm corresponds to KLCL units next to each other, the
peak at 176.0 ppm corresponds to CL units next to each other,
and the two peaks in the middle (at 175.2 and 175.2 ppm) belong
to alternating units. In addition, the copolymer composition
determined from the relative peak intensities of each monomer
unit is in close agreement with the monomer feed amounts used
(Table 2).
The polymerization of KLCL was achieved by anionic ring-
opening polymerization. The polymerization reaction was car-
ried out in bulk at 140 °C using N-acetylcaprolactam (N-AcCL)
and NaH, the ratios of which are given in Table 1. The
polymerization was allowed to proceed under a N atmosphere.
2
Although the polymerization mixture became very viscous and
solidified within 5 min, only 68% conversion after 3 h of
1
3
polymerization was calculated from the C NMR spectrum of
the crude product. In contrast, ε-caprolactam (CL) shows 98%

Article
The experimental molecular weights of P(KLCL) were calcu-
lated from C NMR data as mentioned earlier. The molecular
weight of PCL was calculated from the relative intensity of the
carbonyl peak (at 173.5 ppm) of the N-acetyl end group (coming
from N-AcCL initiator) in ratio to the amide carbonyl peak
Macromolecules, Vol. 43, No. 2, 2010 971
The synthesis of aliphatic polyamides bearing functional
pendant groups is shown in Scheme 2. The first step is the
synthesis of polymer bearing ketal pendant groups. Deprotection
of the ketone groups was carried out with either aqueous HCl
solution or moist trifluoroacetic acid. The ketone groups were
then completely reduced to hydroxyl groups using sodium
13
(
at 176.0 ppm) of the monomer units. Similarly, the molecular
1
13
weights of the copolymers were calculated from the relative peak
intensities of N-acetyl end groups and combined main-chain
carbonyl groups corresponding to each monomer unit.
borohydride. Both H and C NMR analysis of homopolymers
provide clear evidence for the completeness of each reaction step
(Figures 5 and 6).
The thermal properties of the polymers and copolymers with
ketal, ketone, and hydroxyl pendant groups were analyzed by
differential scanning calorimetry (DSC), and the data are sum-
marized in Table 3. On the basis of these results, this new family
of polyamides appears to show typical semicrystalline polymer
1
3
Figure 3. C NMR spectrum (carbonyl region only) of P(KLCL) in
TFE:CDCl solvent mixture.
3
1
Figure 5. H NMR spectra of P(KLCL), P(KCL), and P(HOCL) in
3
TFE:CDCl solvent mixture.
Scheme 2
1
3
Figure 4. C NMR spectra (carbonyl and aliphatic regions) of homo-
and copolymers in TFE:CDCl
3
solvent mixture.
Table 2. Copolymerization of KLCL with CL at Various Molar Compositions ( fKLCL
)
a
b
c
-3
d
-3
e
f
v
-3
sample
f
KLCL (mol %) conv (%)
F
KLCL (mol %)
M
n,theo (g/mol) (ꢀ10
)
M
n,exp (g/mol) (ꢀ10
)
[η] (g/dL)
M
(g/mol) (ꢀ10
)
P(KLCL)
100
75
50
25
0
68
70
88
94
99
100
74
48
24
17.3
15.9
14.4
12.9
16.6
15.7
14.2
12.4
13.0
0.55
0.62
0.71
0.91
1.09
18.2
20.5
22.9
30.2
36.1
P(KLCLcoCL)
P(KLCLcoCL)
P(KLCLcoCL)
PCL
a
100
13.3
c
b
f
KLCL: mol % of KLCL in feed.
F
KLCL: mol % of KLCL in copolymer.
M
n,theo: molecular weight calculated from monomer-to-initiator ratio.
d
e
f
Mn,exp: molecular weight determined from NMR end-group analysis. [η]: intrinsic viscosity measured in TFE at 25 °C. M : molecular weight
v
8 -4 0.75
calculated from Mark-Houwink equation [η] = 5.36 ꢀ 10
M
.

9
72 Macromolecules, Vol. 43, No. 2, 2010
Tarkin-Tas and Mathias
1
3
Figure 6. C NMR spectra of P(KLCL), P(KCL), and P(HOCL) in
TFE:CDCl solvent mixture.
3
Table 3. DSC Data for Homopolymers and Copolymers
comonomer
(mol %)
a
b
m
c
g
sample
T
(°C)
ΔH
m
(J/g)
T
(°C)
P(KLCL)
100:0
143
64
60
55
51
47
49
158
127
81
51
65
57
56
P(KLCLcoCL)
P(KLCLcoCL)
P(KLCLcoCL)
PCL
75:25
50:50
25:75
0:100
100:0
75:25
50:50
25:75
100:0
75:25
50:50
25:75
123
177
222
218
203
182
180
21
69
83
202
135
239
78
P(KCL)
P(KCLcoCL)
P(KCLcoCL)
P(KCLcoCL)
P(HOCL)
P(HOCLcoCL)
P(HOCLcoCL)
P(HOCLcoCL)
Figure 7. (a and b) TGA and (c and d) DSC thermograms of P(KCL).
d
28
thermal cross-linking reaction was taking place. In addition, the
high values of melting enthalpies might be explained by assuming
that the cross-linking reaction is endothermic. In order to shed
more light on this unexpected thermal behavior, a series of
experiments were carried out.
133
162
196
31
51
55
a
b
c
mol % of KLCL in feed. DSC first heating scan. DSC second
d
heating scan. DSC scan after annealing 18 h at 100 °C.
First, the melting behavior of the ketone-containing homo-
polymer, P(KCL), was observed visually using a capillary melting
apparatus. As soon as polymer started to melt, the color turned
paleyellow and extensive bubble formation took place, consistent
with some form of reaction occurring. Second, the films of
homopolymer and copolymers were prepared by melt pressing.
The pressed films were yellow in color and contained trapped
bubbles inside. More importantly, they totally lost solubility in
the solvents which can dissolve the polymers before melt pressing.
This behavior was observed even at very low comonomer con-
tent, i.e., 5 mol %.
behavior. The glass transition (T ) values reported here are
measured from the second heating scans because in the first scans,
very broad transitions were observed which might be caused by
g
the evaporation of residual solvent. T values of P(KLCL) as well
g
as its copolymers are higher than the PCL homopolymer. On the
other hand, the melting temperatures (T ) and the melting
m
enthalpies (ΔH ) of the copolymers are lower compared to those
m
of PCL. This indicates that the rigid ketal groups increase the
glass transition temperature while inhibiting close packing and
decreasing the melting temperature and crystallinity. T values of
m
ketal-containing copolymers also support random copolymer
sequences. The melting endotherms of P(KLCL) are only
observed in the first DSC scans, and no melting endotherms are
observed for the 75 mol % KLCL containing copolymer in the
first scan even after annealing at 100 °C for 24 h.
Further analysis by TGA revealed a two-stage thermal decom-
position process (Figure 7a). The temperature at which the
greatest weight loss was observed in the first stage before
decomposition (derivative temperature curve, Figure 7b) is very
close to the melting temperatureobservedin the DSC first heating
scan (Figure 7d). This clearly indicates that a reaction liberating a
volatile compound is taking place soon after melting starts. In
addition, the residual wt % at 600 °C is above 30%, consistent
with cross-linking which facilitates char formation. The TGA
curves of ketone-containing copolymers (data not shown) also
show two-stage thermal decomposition, and the percentage of
residue at 600 °C increased with ketone comonomer content.
The change in the chemical structure upon heating above the
melting temperature of the polymer could not be investigated by
solution NMR analysis because the polymers became insoluble.
Quite interestingly, after the deprotectionof ketonegroups, the
(
co)polymers showed very broad melting endotherms with very
high enthalpy values. In fact, the melting enthalpy of the P(KCL)
is significantly higher than that of PCL. Even more interesting,
while T values of the ketal containing (co)polymers are in the
g
range of the values for typical aliphatic polyamides, significantly
higher Tg values were observed with increasing comonomer
content for the ketone-containing (co)polymers (Table 3). This
unexpected increase in the glass transition temperatures of
the ketone-containing (co)polymers seemed to indicate that a

Article
Macromolecules, Vol. 43, No. 2, 2010 973
1
3
Figure 8. C TOSS spectra of (a) P(KLCL), (b) P(KCL), and (c) P(KCL)
after melting.
Figure 9. FTIR spectra of P(KCL) (a) before UV irradiation and (b)
after 5 h UV irradiation.
Scheme 3
the actual value determined from TGA (Figure 7a) is in close
agreement at 11.8%.
The ketone-containing polymers are sensitive to not only
thermal cross-linking but also photo-cross-linking. The thin films
of P(KCL) were irradiated as described in the Experimental
Section. The FT-IR spectra of a polymer film before and after 5 h
irradiation are given in Figure 9. The most distinguishable
changes are due to reduction in the peak intensity for both ketone
-
1
-1
groups (1700 cm ) and amide groups (1645 and 1555 cm ),
-
1
especially the NH stretching at 3300 cm . However, the reduc-
tion in the peak intensities was not as significant as in the melt-
pressed films. The FT-IR photodegradation studies of previously
investigated ketone-containing AA-BB type nylons showed
Fortunately, solid-state NMR experiments enabled monitor-
ing of the change in chemical composition. As it can be seen in
Figure 8b,c, the ketone group at 205 ppm completely disappeared
upon heating the polymer above its meltingtemperature, and new
peaks formed at ca. 142 and 97 ppm. There is also an obvious
change in the aliphatic region, consistent with the number of
methylene groups decreasing from four to three after cross-
linking. In addition to NMR, FT-IR analysis of the melt-pressed
films (data not shown) showed significant reduction of amide and
ketone group absorptions, indicative of reaction between ketone
and amide groups after heating and two new peaks appeared at
15
similar results. In addition to FT-IR analysis, we observed that
the films became insoluble after photolysis, consistent with a
photo-cross-linking mechanism that involves reaction of both
ketone and amide groups.
Reductive conversion of the ketone groups to hydroxyls results
in decreases in Tm and melting enthalpies compared to ketal
containing homo- and copolymers and PCL homopolymer
(
Table 3). In fact, a melting endotherm of P(HOCL) which was
previously precipitated from TFE solution into diethyl ether was
not observed for either first or second scans. In addition, the
copolymers containing 75 mol % HOCL did not show any
melting endotherm in the second scan, and virtually no change
in Tg was observed. The hydroxyl-containing homopolymer
was also soluble in water and methanol at room temperature.
These results are consistent with the hydroxyl groups disrupting
packing and reducing overall crystallinity in the homo- and
copolymers.
-
1
1
332 and 1204 cm
.
Thermal properties of polyamides bearing ketone groups were
1
3
analyzed previously by Pearce et al. The carbonyl groups were
introduced into the backbone by the interfacial polymerization of
ketone containing diacid chlorides and diamines. Similar to our
results, they obtained insoluble materials when the polymer
samples were heated above 300 °C. FT-IR analysis of their
heated samples showed reduction of the peak intensities of both
ketone and amide groups. According to our visual observations
and spectroscopic analysis, as well as this support from the
Conclusions
13
literature, the most reasonable cross-linking mechanism sug-
gested involves the attack of amide nitrogen at the ketone
carbonyl with subsequent loss of water and formation of enamide
linkages between chains (Scheme 3). Although solid-state NMR
data for enamides could not be found in the literature, the peaks
at 142 and 97 ppm in the TOSS spectrum of P(KCL) after cross-
linking (Figure 8c) are in close agreement with chemical shifts in
solution NMR spectra of enamides. Furthermore, assuming
water is the product of this reaction and all or most of the ketone
groups are consumed, the calculated weight loss is 13.8% while
The synthesis of 5-azepane-2-one ethylene ketal from 1,4-
cyclohexandione monoethylene ketal was accomplished using
an efficient and high yielding procedure under very mild condi-
tions. It homo- and copolymerized efficiently using anionic ring-
opening methods. The deprotection of the polymer chains
quantitatively released ketone groups which then could be
reduced to hydroxyl pendant groups. The ketone-containing
polymers respond sensitively to both thermal and photo-cross-
linking conditions for this novel class of materials. Indeed,
after cross-linking, solubility in organic solvents is lost, and
1
4

9
74 Macromolecules, Vol. 43, No. 2, 2010
Tarkin-Tas and Mathias
increasingly high glass transition temperatures are obtained with
increasing KCL content. The sensitivity to thermal and photo-
cross-linking is a special feature of the ketone-containing poly-
mers. In other words, the ketal- and hydroxyl-containing poly-
mers do not undergo cross-linking upon heating or UV
irradiation. Thus, aliphatic polyamides bearing ketone and
hydroxyl pendant groups can be easily prepared and provide
pathways to new applications in a broad variety of uses.
(e) Reimschuessel, H. K.; Roldan-Gonzalez, L.; Sibilia, J. P. J. Polym.
Sci., Polym. Phys. Ed. 1968, 6, 559–574.
3) Overberger, C. G.; Kozlowski, J. H.; Radlmann, E. J. Polym. Sci.,
(
Part A-1 1972, 10, 2265–2289.
(
(
4) Nijenhuis, A. J. World Patent WO02/44246A1, 2002.
5) Chikh, L.; Arnaud, X.; Guillermain, C.; Tessier, M.; Fradet, A.
Macromol. Symp. 2003, 199, 209–221.
(6) Schaefer, J.; Stejskal, E. O.; Buchdahl, R. Macromolecules 1977, 10,
384–405.
7) Dixon, W. T. J. Chem. Phys. 1982, 77, 1800–1809.
8) Mattiussi, A.; Gechele, G. B.; Francesconi, R. J. Polym. Sci., Part
A: Polym. Chem. 1969, 7, 411–422.
(
(
Acknowledgment. The authors thank Christopher A. Lange
13
for recording solid-state C NMR spectra of the polymers and
Dr. Charles E. Hoyle (deceased) for help in UV photolysis
studies.
(
9) Wolinski, L. E.; Mighton, H. R. J. Polym. Sci. 1961, 49, 217–223.
(10) Cubron, R. C. P. Makromol. Chem. 1964, 80, 44–53.
(11) Davis, R. D.; Steadman, S. J.; Jarrett, W. L.; Mathias, L. J.
Macromolecules 2000, 33, 7088–7092.
(
(
12) Davis,R.D.;Jarrett,W.L.;Mathias,L.J.Polymer 2001,42,2621–2626.
13) Do, C. H.; Pearce, E. M.; Bulkin, B. J.; Reimschuessel, H. K.
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References and Notes
(
(
1) Kohan, M. I. Nylon Plastics Handbook; Hanser: New York, 1995.
2) (a) Reimschuessel, H. K. Macromol. Synth. 1982, 8, 37–40.
(14) Meth-Cohn, O.; Westwood, K. T. J. Chem. Soc., Perkin Trans. 1
1984, 1173–1182.
(15) Do, C. H.; Pearce, E. M.; Bulkin, B. J.; Reimschuessel, H. K.
J. Polym. Sci., Part A: Polym. Chem. 1987, 25, 2301–2321.
(b) Reimschuessel, H. K.; Pascale, J. V. US Patent US3542744, 1970.
(c) Reimschuessel, H. K.; Pascale, J. V. US Patent US3422093, 1969.
(d) Reimschuessel, H. K. Adv. Chem. Ser. 1969, 91, 717–733.