Polyamide-6,6-based blocky copolyamides obtained by solid-state modification

Article abstract of DOI:10.1002/pola.26944

Copolyamides based on polyamide-6,6 (PA-6,6) were prepared by solid-state modification (SSM). Para- and meta-xylylenediamine were successfully incorporated into the aliphatic PA-6,6 backbone at 200 and 230 °C under an inert gas flow. In the initial stage of the SSM below the melting temperature of PA-6,6, a decrease of the molecular weight was observed due to chain scission, followed by a built up of the molecular weight and incorporation of the comonomer by postcondensation during the next stage. When the solid-state copolymerization was continued for a sufficiently long time, the starting PA-6,6 molecular weight was regained. The incorporation of the comonomer into the PA-6,6 main chain was confirmed by size exclusion chromatography (SEC) with ultraviolet detection, which showed the presence of aromatic moieties in the final high-molecular weight SSM product. The occurrence of the transamidation reaction was also proven by ¹H nuclear magnetic resonance (NMR) spectroscopy. As the transamidation was limited to the amorphous phase, this SSM resulted in a nonrandom overall structure of the PA copolymer as shown by the degree of randomness determined using ¹³C NMR spectroscopy. The thermal properties of the SSM products were compared with melt-synthesized copolyamides of similar chemical composition. The higher melting and higher crystallization temperatures of the solid state-modified copolyamides confirmed their nonrandom, block-like chemical microstructure, whereas the melt-synthesized copolyamides were random. Copyright

Full text of DOI:10.1002/pola.26944

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Polyamide-6,6-Based Blocky Copolyamides Obtained by Solid-State
Modification
Albert Jeyakumar,1 Han Goossens,1 Bart Noordover,1* Manoranjan Prusty,2
Matthias Scheibitz,2 Cor Koning1
1Faculty of Chemical Engineering and Chemistry, Laboratory of Polymer Materials,
Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
2BASF Aktiengesellschaft, GKT/U - B001, 67056 Ludwigshafen, Germany
Correspondence to: H. Goossens (E-mail: J.G.P.Goossens@tue.nl) or B. Noordover (E-mail: B.A.J.Noordover@tue.nl)
Received 3 September 2013; accepted 9 September 2013; published online 25 September 2013
DOI: 10.1002/pola.26944
ABSTRACT: Copolyamides based on polyamide-6,6 (PA-6,6)
were prepared by solid-state modification (SSM). Para- and
meta-xylylenediamine were successfully incorporated into the
aliphatic PA-6,6 backbone at 200 and 230 ꢀC under an inert gas
flow. In the initial stage of the SSM below the melting temper-
1H nuclear magnetic resonance (NMR) spectroscopy. As the
transamidation was limited to the amorphous phase, this SSM
resulted in a nonrandom overall structure of the PA copolymer
as shown by the degree of randomness determined using 13C
NMR spectroscopy. The thermal properties of the SSM prod-
ucts were compared with melt-synthesized copolyamides of
similar chemical composition. The higher melting and higher
crystallization temperatures of the solid state-modified copo-
lyamides confirmed their nonrandom, block-like chemical
ature of PA-6,6,
a decrease of the molecular weight was
observed due to chain scission, followed by a built up of the
molecular weight and incorporation of the comonomer by
postcondensation during the next stage. When the solid-state
copolymerization was continued for a sufficiently long time,
the starting PA-6,6 molecular weight was regained. The incor-
poration of the comonomer into the PA-6,6 main chain was
confirmed by size exclusion chromatography (SEC) with ultra-
violet detection, which showed the presence of aromatic moi-
eties in the final high-molecular weight SSM product. The
occurrence of the transamidation reaction was also proven by
microstructure, whereas the melt-synthesized copolyamides
C
V
were random. 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part
A: Polym. Chem. 2013, 51, 5118–5129
KEYWORDS: poly(amide-6,6); size exclusion chromatography
(SEC); solid-state (co)polymerization; transamidation
INTRODUCTION Since their invention by Carothers,1 polya-
mides are well known and used in many applications
because of the high dimensional stability under dry condi-
tions, good mechanical and thermal properties, and excellent
solvent resistance. Also, polyamide copolymers have gained
attention, as additional features can be introduced while
retaining the original advantageous properties of the
homopolyamides.
mides and water or a diol in the case of polyesters, are
removed from the system by an inert gas stream or by
applying vacuum. A number of studies were reported in lit-
erature on SSP methods,2–6 SSP reactor-design, and SSP
kinetics7–10 for both polyesters2 and polyamides.6,7,11,12 In
most cases, these studies focused on solid-state postconden-
sation. Only a few studies reported on copolymerization or
modification reactions using SSP, which in this study is called
solid-state modification (SSM).
Solid-state polymerization (SSP), in which the polymerization
is performed below the melting temperature but well above
the glass transition temperature of semicrystalline polymers,
was specially developed to increase the molecular weight
and viscosity of condensation polymers, such as (co)polyest-
ers and (co)polyamides, after an initial melt polymerization.
During the SSP process between Tg and Tm, the residual
reactive end groups of polyamides and polyesters present in
the amorphous phase have enough mobility to react and the
condensation products, normally water in the case of polya-
Copolymers of polyamides can be obtained by either copoly-
condensation or ring-opening copolymerization in the melt,
in solution or using phase transfer methods, but these syn-
thesis routes usually yield random copolymers. Groeninckx
and coworkers13–18 studied the modification of polyamides
by transamidation reactions in the melt. When these reac-
tions were carried out in a single-phase system, fully random
copolyamides were obtained and it was very difficult to con-
trol the chemical microstructure and/or limit randomization.
C
V
2013 Wiley Periodicals, Inc.
5118
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
Especially for higher comonomer contents, random copoly-
mers usually lose their ability to crystallize, which is a major
disadvantage of such copolymers.
To the best of our knowledge, Jansen et al.19–24 applied for
the first time the SSP process for the chemical modification
of a condensation polymer, viz. poly(butylene terephthalate)
(PBT). The solid-state modification (SSM) resulted in a
nonrandom incorporation of significant amounts of comono-
mer (e.g., 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, bis(2-
hydroxyethyl)terephthalate, and 2,20-biphenyldimethanol)
into PBT without completely losing the crystallinity of the
resulting block-like copolyester.23 This is due to the fact that
the reaction was constrained only to the mobile fraction of
the amorphous phase, leaving intact long crystallizable
sequences of pure PBT along the main chain.
To our knowledge, SSP copolymerization or SSM has not yet
been applied for polyamides of the PA-x.y type, obtained by
polymerizing a diamine and a dicarboxylic acid, although the
concept has been proven for PA-6 by Cakir et al.25 A differ-
ence with the mentioned PBT SSM is that commercial poly-
amides usually do not contain a polymerization catalyst.
Titanates are used as catalyst in the preparation of polyest-
ers (viz. poly(ethylene terephthalate) (PET), PBT) and they
are not removed. So, mostly commercial PBT may contain
some active titanate catalyst residues. Conversely, the PA-6,6
used in our study contains no such catalyst. In this article,
we describe the incorporation of semiaromatic “nylon salts”
from p- or m-xylylene diamine and adipic acid (PxAd resp.
MxAd) into the amorphous phase of polyamide-6,6 (PA-6,6)
in the solid state using a process very similar to the one
described above for the PBT SSM. The main objective of this
article is to demonstrate that this SSM indeed results in a
less random chemical microstructure than a modification in
the melt with a similar comonomer composition, and that
the SSM product exhibits better thermal properties than
those of the corresponding melt copolymerization product.
In addition, for a fixed amount of salt, the kinetics of the
incorporation of the “nylon salt” at different temperatures
was studied for a constant SSM reaction time. The aromatic
comonomer incorporation was monitored using ultraviolet
(UV) detection coupled to size exclusion chromatography
FIGURE 1
Laboratory-scale SSM reactor. [Color figure can be
viewed in the online issue, which is available at
wileyonlinelibrary.com.]
fluoro-2-propanol (HFIP, 99%), obtained from Biosolve (Val-
kenswaard, the Netherlands), was used for solution mixing
of PA-6,6 with the diamine/AA salt. For NMR measurements,
deuterated trifluoroacetic acid (TFA-d, 99.5% deuterated)
was obtained from Cambridge Isotope Laboratories.
Solution Preparation of the SSM Reaction Mixture
PA-6,6 pellets were ground into powder by a Retsch type ZM
100 mill in a cryogenic way. This powder was dried in a vac-
uum oven at 70 ꢀC for 48 h. Then, 80 mol % of PA-6,6 and
20 mol % of comonomer salt (either PxAd or MxAd) were
dissolved in 10–15 mL of HFIP at a temperature of approxi-
mately 50 ꢀC. All the reaction mixtures were prepared in
this way unless otherwise mentioned and no transamidation
catalyst was present in or added to the starting material.
After complete dissolution, the temperature was raised to 65
ꢀC and HFIP was removed by drying under vacuum. The
solid mixture lump was dried in an oven for 24 h and was
then cooled in liquid nitrogen and ground into powder using
an analytical laboratory mill (Waring, type 32BL80), after
which the powder was filtered using a sieve to get a more
or less uniform particle size of 100 mm or smaller. This pow-
der was subsequently dried in a vacuum oven for a period of
48 h prior to the SSM reaction.
1
(SEC) and using H nuclear magnetic resonance (NMR) spec-
troscopy. In a subsequent article, a more detailed analysis of
the crystalline nature of the blocky reaction products
obtained after SSM versus the more random copolyamides
obtained from the melt route will be presented.
SSM and Melt Polymerization
The experimental setup for SSM consisted of a glass reactor,
equipped with a fluidizing purge gas tube. A salt mixture of
KNO3 (53 wt %), NaNO2 (40 wt %), and NaNO3 (7 wt %)
was used as the heating medium for the reactor.26 The reac-
tor consisted of a glass tube (inner diameter ꢁ2.4 cm) and a
sintered glass-filter plate at the bottom. A small heat
exchange glass coil (inner diameter ꢁ5 mm) surrounded the
reactor (Fig. 1). An argon gas flow was heated by passing
through this heated coil before entering the inner glass tube
at the bottom just below the glass filter plate. The gas flow
EXPERIMENTAL
Materials
R
PA-6,6 (UltramidV A-27) pellets (Mn 5 38 kg/mol, Mw 5 72
kg/mol) were supplied by BASF SE, Ludwigshafen, Germany.
Adipic acid (AA) as well as para- and meta-xylylenediamine
(PXDA, MXDA, resp.) were purchased from Sigma Aldrich.
Ethanol (99%) required for the preparation of the diamine/
diacid salt was also purchased from Aldrich. 1,1,1,3,3,3-Hexa-
was controlled by
a flow meter. The SSM reaction
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129
5119

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 1
Synthesis of the aromatic comonomer salt.
temperature was measured with a thermocouple inserted
into the PA-6,6/nylon salt mixture.
400 MHz) were recorded overnight at room temperature
with an acquisition time of about 1.5 s and a delay time (d1)
of about 10 s in the nuclear overhauser effect (NOE)-
decoupling mode.
For the melt copolymerization, performed at 280 ˚C, 80 mol
% of PA-6,6 salt and 20 mol % of MXDA/adipic acid salt
(MxAd) were mixed and reacted for 3 h in the melt under
nitrogen atmosphere.
Differential Scanning Calorimetry (DSC)
The melting (Tm) and crystallization (Tc) temperatures and
enthalpies were measured by a TA Instruments Q100 Differen-
tial Scanning Calorimeter (DSC) equipped with an autosam-
pler and a refrigerated cooling system. The DSC cell was
purged with a nitrogen flow of 50 mL/min. The temperature
was calibrated using the onset of melting for indium. The
enthalpy was calibrated with the heat of fusion of indium. For
the copolyamides prepared via SSM or melt polymerization
(MP), samples having a weight of 4–6 mg were prepared in
crimped hermetic pans. All samples were measured in the
temperature range from 240 to 290 ꢀC using heating and
cooling rates of 10 ꢀC/min (unless specified), respectively, and
isothermal periods of 5 min at, respectively, 0 and 290 ꢀC.
Preparation of Comonomer Salt
The preparation of “comonomer salts” involved mixing the
diamine (p-xylylene diamine or m-xylylene diamine) with AA
in equimolar proportions, by mixing equivalent amounts of
ethanol solutions of both components (see Scheme 1, where
Ar 5 CH2-phenyl-CH2). The nylon salts, viz., m-xylylene adipic
acid salt (MxAd), p-xylylene adipic acid salt (PxAd), precipi-
tated out of ethanol in an equimolar composition once they
were formed. The salts were fꢀiltered, vacuum dried at a tem-
perature of approximately 50 C for 4 h and their equimolar-
1
ity was checked and confirmed by H NMR spectroscopy.
Characterization
Size Exclusion Chromatography
RESULTS AND DISCUSSION
SEC was used to determine the average molecular weight
and molecular weight distribution (Mw/Mn) of the polymer
samples. For the PA-6,6 and SSM reaction samples, SEC in
1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) was performed on a
system equipped with a Waters 1515 Isocratic HPLC pump,
a Waters 2414 refractive index detector (35 ꢀC), and UV
detectors operating at a wavelength of 275 nm (these detec-
tors were in series, respectively), a Waters 2707 auto sam-
pler, and a polymer standards service (PSS) polar fluoro gel
(PFG) guard column followed by 2 PFG-linear-XL (7 mm, 8 3
300 mm) columns in series at 40 ꢀC. HFIP with potassium
trifluoroacetate (3 g/L) was used as eluent at a flow rate of
0.8 mL/min. The molecular weights were calculated using a
calibration performed with poly(methyl methacrylate) stand-
ards (Polymer Laboratories, Mp 5 580 Da up to Mp 5 7.1 3
106 Da). Before the SEC analysis was performed, the samples
were filtered through a 0.2-mm poly(tetrafluoroethylene)
(PTFE) filter (13 mm, PP housing, Alltech). It has to be men-
tioned that some of the reaction samples that are branched/
cross-linked might contain some gel particles. As the gel par-
ticles were filtered out before the SEC measurements, the
data obtained may not be a true representation of the sam-
ple, and for these specific samples, the Mn and Mw values as
well as the polydispersity index (PDI) may be
underestimated.
SSM Recipe
For the reactions, 80 mol % of PA-6,6 and 20 mol % of the
PxAd or MxAd salt was dissolved in HFIP without any cata-
lyst and the reaction mixture was prepared as explained in
the experimental section on Solution preparation of the SSM
reaction mixture. The molar percentage is calculated as the
number of moles of the salt with respect to the total number
of moles of the repeating groups in PA-6,6 plus the total
number of moles of salt, either PxAd or MxAd, present in the
mixture. This solution mixing is done prior to the SSM reac-
tion to ensure optimum homogenization of the mixture and
to maximize the chance that the salt is dissolved into the
amorphous phase of PA-6,6. It is unlikely that the salt is
incorporated into the PA-6,6 crystals, which are formed dur-
ing the slow evaporation of the solvent. The SSM reaction is
expected to occur exclusively in the amorphous phase at the
chosen reaction temperature, leaving the crystalline phase
unaffected. This also limits the maximum amount of comono-
mer incorporation into the backbone by SSM.
SSM of PA-6,6 with p-xylylenediamine
The reaction of PA-6,6 (80 mol %) with the equimolar nylon
salt based on PXDA and AA (20 mol %) (denoted as
(PA66)80(PxAd)20) was performed in the solid state at 200
ꢀC for 24 h under 1 L/min argon gas purge. Samples were
taken at different intervals of the reaction and were analyzed
with SEC (refractive index (RI) and UV detection). The SEC
chromatograms of the starting materials, viz. PA-6,6 and
PxAd salt as well as those of pure PXDA and pure AA, are
presented in Figure 2. With the RI detector, the PA-6,6 poly-
mer (elution time ca. 21 min) and the salt components (viz.
PXDA or protonated PXDA at ca. 26.8 min and AA or depro-
tonated AA at ca. 28.6 min) are clearly observed [Fig. 2(a)].
NMR Spectroscopy
NMR spectra were recorded on a Varian Mercury Vx (400
MHz) spectrometer at 25 ꢀC. The solvent used was TFA-d
and 1H NMR spectra were referenced internally using the
signal of residual solvent protons. Sequential analysis of the
copolyamides was probed in 13C NMR using HFIP:CDCl3 in a
3:1 vol %/vol % ratio. The 13C NMR spectra (5-mm probe,
5120
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
FIGURE 2
SEC chromatograms of SSM reaction starting materials, that is, mixtures of PA-6,6 and PxAd salt, and pure PA-6,6
and salt components PXDA and AA: (a) RI detection and (b) UV detection. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
Aliphatic PA-6,6 does not give a strong UV signal [see Fig.
2(b)], so only the PxAd components (PXDA or its protonated
form at ca. 25.6 min, respectively, 26.2 min, and AA or its
deprotonated form at ca. 27.4 min) give a signal in the UV
detection chromatogram [Fig. 2(b)].
The broad PA-6,6 peak, recorded for the nonmodified Ultra-
R
midV A-27 starting material, is found around 18 min with a
peak maximum around an elution time of 20–21 min. The
molecular weight reduced initially, which is visible from the
slight shift of the peak maximum from about 20–21 min for
the initial, nonmodified PA-6,6 (left peak of bottom chromat-
ogram) to a slightly higher elution time for the sample taken
after 2 h of SSM reaction time. The shift, which is extremely
small, is attributed to transamidation reactions occurring
between the PA-6,6 main chain and the nylon salt compo-
nents, causing chain scission resulting in an increase of the
number of free carboxylic acid and amine end groups. These
newly formed end groups can at a later stage be postcon-
densed to form a higher molecular weight copolyamide,
which is illustrated by the slight shift of the peak maximum
recorded after 2 h back to a lower elution time recorded
ꢀ
The SSM reaction at 200 C monitored by the SEC RI detec-
tor, as shown in Figure 3(a), reveals that the peak of the
PXDA comonomer around 26 min slowly starts to disappear
as the reaction proceeds. After 2 h of SSM reaction time the
intensity of this peak has clearly decreased and after ꢁ8 h,
the peak is no longer visible. However, the diacid signal is
only reduced after 4 h. It seems as if first the diamine is
incorporated, leading to a decrease in molecular weight, and
a corresponding mismatch in stoichiometry. Subsequently,
the diacid is incorporated, leading to an increase in molecu-
lar weight.
FIGURE 3
and (b) UV detection. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
SEC chromatograms of SSM reaction products obtained by modification of (PA66)80(PxAd)20 at 200 ꢀC: (a) RI detection
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129
5121

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
form (PXDA ca. 25.6 min, AA ca. 27.4 min). Please note that
in the physical mixture of PA-6,6 and the PxAd salt, so before
any reaction took place, no UV absorption is visible in the
low elution region corresponding to the polymer. This is as
expected, as the fully aliphatic PA chain has no or a negligi-
ble UV absorption. With increasing SSM reaction time the
intensity of the PXDA peak is decreasing, but the polymer,
eluting around 17–23 min, starts to become UV active
(around ꢁ275 nm), confirming the incorporation of the aro-
matic and UV-active PXDA monomer. As the original PA-6,6
curve is not visible in the chromatograms with UV detection,
no shift of the high-molecular weight peak to higher resi-
dence times is visible, but for longer SSM times the shift to
lower retention times can be seen. The observation that the
initial molecular weight can be regained after a first break-
down of the chains is a strong indication that not only the
PXDA, but also the AA residues become incorporated into
the PA-6,6 main chain, which agrees with the disappearance
of the peak of the deprotonated AA peak around 27.4 min. If
this would not be the case, the nonequivalence of functional
groups would prevent the restoration of the initial molecular
weight. The observed trend in the number-average molecular
weight (Mn) development as a function of SSM reaction time,
viz. an initial decrease due to chain scission followed by an
increase due to postcondensation (see Fig. 4), is typical for
an SSP process involving transreactions between polymers
and low-molecular weight compounds.19 It has to be men-
FIGURE 4
Number-average molecular weight (Mn) and PDI
(from SEC) for the SSM product (PA66)80(PxAd)20 as a function
of SSM reaction time at 200 ꢀC. [Color figure can be viewed in
the online issue, which is available at wileyonlinelibrary.com.]
after 8 and 24 h of SSM. During this postcondensation, the
condensation product (water) is removed from the reaction
mixture by the continuous inert gas stream passing through
the reactor.
ꢀ
The UV detection chromatogram, shown in Figure 3(b),
shows a similar trend for the disappearance of PXDA como-
nomer or its protonated form and AA or its deprotonated
tioned that the decrease in Mn during SSM at 200 C is very
limited and that the transreactions proceed in a slow way.
The PDI of this reaction system overall shows an increasing
FIGURE 5
(a) RI detection and (b) UV detection. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
SEC chromatograms of SSM reaction products obtained from the sample (PA66)80(PxAd)20 upon reaction at 230 ꢀC:
SCHEME 2
Origin of cross-linking of PA-6,6 by amine end group reaction, causing higher molecular weight branched PA or
even insoluble gels. The secondary amine can react with a carboxylic acid-terminated PA chain.
5122
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
[Fig. 3(b)]. Since the nonsoluble part of the SSM product is
filtered out before performing SEC, the reported molecular
weights and PDIs are underestimated. It also has to be men-
tioned that after 2 h of SSM the postcondensation reaction
dominates the chain scission reaction.
ꢀ
The same SSM reaction was done at 230 C for 24 h under a
1 L/min inert gas stream (see Fig. 5 for SEC results). At this
higher temperature, the reaction rate of the chain scission of
the PA-6,6 main chain by the PxAd salt was significantly
faster than at 200 ꢀC, and a significantly lower number-
average molecular weight (Mn) was obtained during the first
part of the transreaction processes (see Fig. 4 compared to
Fig. 6). Also, during the second part of the SSM process, a
much higher molecular weight was obtained due to a more
efficient postcondensation at this higher temperature.
Whereas at 200 ꢀC chain scission appears to be the domi-
nant process until an SSM reaction time of 2 h, at 230 ꢀC,
the postcondensation already dominates after 1 h.
FIGURE 6
Molecular weight (Mn) and PDI as a function of
SSM reaction time at 230 ꢀC for (PA66)80(PxAd)20. [Color figure
can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
The development of the PDI as a function of time points to a
significant deꢀgree of branching for longer SSM times, espe-
cially at 230 C. Branching and even some cross-linking was
evidenced by the presence of some HFIP-insoluble polymer
material. These gel particles are filtered out before the sam-
ple is examined by SEC, which may explain the remarkable
development of PDI with increasing SSM time. The reaction
trend, as seen in Figure 4, as during postcondensation some
chains gain a lot in weight, whereas some low-molecular
weight chains remain present. It should be mentioned that
in view of the exclusion of the crystalline part of the PA-6,6
from the transreactions, one cannot expect the theoretical
PDI value of 2, as in this case after SSM no Flory27 distribu-
tion is obtained. In addition, at this reaction temperature
after the occurrence of transamidation reactions, some gel-
formation is observed, most probably initiated by the reac-
tion between two amine end groups with release of ammo-
nia.28 The resulting secondary amine group, still able to
react with carboxylic acid groups, causes branching or even
cross-linking (see Scheme 2), which is also confirmed by the
development of a tail at lower elution times of about 14–16
min in the UV detection chromatogram of the SSM product
ꢀ
kinetics of tꢀhe trans-amidation at 230 C is much faster than
that at 200 C (compare Figs. 4 and 6).
SSM of PA-6,6 with m-xylylenediamine
The PA-6,6-based copolyamide resulting from the incorpora-
tion of PxAd might have a crystal structure in which both
the 6,6 and PXDA,6 repeat units could fit in view of their
similar distances (1.72 nm) between the hydrogen bonding
motifs (c-axis of the unit cell of the crystal). So, after melting
cocrystallization might be possible in the corresponding SSM
products given the rather similar distance between the
FIGURE 7
and (b) UV detection. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
SEC chromatograms of SSM reaction products obtained from the sample (PA66)80(MxAd)20 at 200 ꢀC: (a) RI detection
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129
5123

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 8
SEC chromatograms of SSM reaction products obtained for the sample (PA66)80(MxAd)20 at 230 ꢀC: (a) RI detection
and (b) UV detection. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
nitrogens in PXDA and 1,6-hexamethylenediamine, the major
difference being the presence of the phenyl group in PXDA.
Therefore, it is interesting to investigate the modification of
PA-6,6 with both MxAd and PxAd, as MXDA,6 units are not a
priori expected to fit into the crystal lattice of PA-6,6. The
possible cocrystallization studies will be presented in a sub-
sequent article. Here, a similar modification of PA-6,6 was
done with the equimolar nylon salt of m-xylylenediamine
and adipic acid (MxAd), also at 200 ꢀC (see Fig. 7) and
230 ꢀC (Fig. 8) for 24 h under 1 L/min inert gas stream.
Samples taken at different time intervals were analyzed by
SEC (RI and UV detection). The molecular weight trend (Mn)
is similar to that of the PA-6,6 SSM modification with the
equimolar PxAd salt, although the reactivity of the MxAd salt
was found to be lower. This is obvious if one compares Fig-
ures 6 and 9(b) at one and the same temperature. The
higher the rate of transamidation, the faster is the chain scis-
sion resulting in a lower molecular weight.
The incorporation of the aromatic MXDA comonomer into
the high molecular weight PA-6,6 was confirmed by SEC,
both by RI detection, showing the disappearance of the
MXDA peak around 25–28 min, and by UV detection, show-
ing both the disappearance of the MXDA peak and the incor-
poration of a UV-active moiety in the high molecular weight
fully aliphatic polyamide, which in itself is not or only mod-
erately UV active. The initiation of the transamidation reac-
tion of the SSP with MxAd comonomer salt is faster both at
200 and 230 ꢀC. Hence, the comonomer salt disappears as
soon as it is incorporated into the PA-6,6 backbone. This is
supported by the development of intense UV peaks in the
chromatograms.
1
The H NMR spectra of the neat PA-6,6, the starting material,
FIGURE 9
(PA66)80(MxAd)20: Molecular weight (Mn) and PDI
and the comonomer along with the solid state-modified
product are given in Figure 10. The benzyl proton (G) of the
comonomer is shifted from ꢁ3.5–4.0 to ꢁ4.5–5.0 ppm after
incorporation into the aliphatic PA-6,6 backbone. The
as a function of SSM reaction time at reaction temperatures of
(a) 200 ꢀC and (b) 230 ꢀC. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
5124
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
FIGURE 10
1H NMR spectra of the starting materials and the SSM reaction product of (PA66)80(MxAd)20 (top to bottom): (a) PA-
6,6, (b) m-xylylenediamine, and (c) solid state-modified PA-6,6 with aromatic diamine MXDA. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
amount of comonomer incorporation was calculated, both
for the SSM and the corresponding melt copolymerization
(PA66)80(MxAd)20 product, from the ratio of the intensity of
the comonomer signal to that of both PA-6,6 and comonomer
in nature. The microstructures, more specifically the copolya-
mide sequences, of the copolyamides with comparable molar
ratio either prepared via the melt route (MP) or by SSM were
investigated using 13C NMR spectroscopy. Hereto, 10 wt % of
the product was dissolved in HFIP and then CDCl3 was added
to obtain a 3:1 vol/vol ratio of HFIP:CDCl3. The solvent mix-
ture results in a low viscosity and enables an accurate struc-
tural characterization of 13C NMR spectra (Fig. 11) of
polyamides as reported by Novitsky and Mathias.29
1
in the H NMR spectra (NMR spectrum of melt route product
not shown here). The MxAd content in the copolyamides
was 17 mol % for the SSM product and 17.6 mol % for the
melt route product, whereas 20 mol % of equimolar MxAd
salt was present in the reaction feed in both cases (Note: In
the remaining part of this article the copolyamide will still
be identified as (PA66)80(MxAd)20).
Different dyads present in the copolyamides can be identified
by analyzing the different carbonyl carbon peaks occurring
in the 13C NMR spectra. The carbonyl carbons positioned
between two aliphatic main chain parts (an AA and a hexam-
ethylene diamine) have different chemical shifts compared to
the carbonyl carbons in between both an aromatic MXDA or
PXDA residue and an aliphatic residue. The influence of an
aromatic residue on the shift of carbonyl carbons may be felt
even at a position separated from this moiety by six methyl-
ene groups in the chain, as illustrated in Figure 12, and for
the PA-6,6/MxAd copolyamide at least four different carbonyl
carbons can be expected. The carbonyl group in the copolya-
mides surrounded by a high concentration of moieties based
on methylene-based diamines is shifted to higher ppm values
Chemical Microstructure and its Effect on Thermal
Transitions
The reaction products obtained after the SSM and melt copoly-
merization reactions were analyzed by NMR spectroscopy and
DSC in order to determine the relation between the degree of
randomness of the copolyamides and the crystallization and
melting behavior. For the SSM product one might expect a
block-like copolymer structure, as transreactions are expected
to occur only in the amorphous phase leaving the crystalline,
pure PA-6,6 phase intact. Conversely, the copolyamide pre-
pared via the melt route (MP) is expected to be more random
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129
5125

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
FIGURE 11
13C NMR spectra of (PA66)80(MxAd)20 copolyamide with 20 mol % of MxAd salt in the feed: (a) SSM reaction product
and (b) analogous product by melt route. The structure given in Figure 10(c) was used for the peak identification. [Color figure can
be viewed in the online issue, which is available at wileyonlinelibrary.com.]
compared to carbonyl carbons surrounded by lower num-
bers of methylene diamine residues.30–32
The degree of randomness (R) of the copolyamides can be cal-
culated using eqs 1–4, by incorporating the integral values
listed under the deconvoluted peaks shown in Figure 13. These
integral values of the four sequences are normalized to one.
F
HAØ;total 5FHAØ;HAØ-side 1FHAØ;ØAH-side
(1)
(2)
À
Á
F
HAH ;total 5 FHA
=2 1FHAH
ØX;total
À
Á
F
ØAØ;total 5 FHAØ;total =2 1FØAØ
(3)
(4)
À
Á
Rtotal 5 FHAØ;total =2 FHA-H ;total 3FØ
A-Ø;total
Fi denotes the molar fraction of each sequence, as shown in
Figure 13. FHAH,total, FHAØ,total denote the total molar fractions
of the aliphatic and aromatic (MXD) side, respectively.
FIGURE 12
Four possible sequences (A–D) of dyads in the
PA-6,6/MxAd copolyamides represented by their chemical
structure. H 5 hexamethylene diamine, A 5 adipic acid, and
Ø 5 m-xylylene diamine. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
From Table 1, it is evident that the microstructure of the
solid state-modified product is arranged in a more blocky
way than that of the melt-route product having the same
5126
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
FIGURE 13
dyads in the 176.5–176.0 ppm region with A–D sequences of (a) melt-route product (MP) and (b) solid state-modified product.
13C NMR spectra of (PA66)80(MxAd)20. As-recorded spectra above and deconvoluted spectra below of the carbonyl
overall chemical composition, as the degree of randomness
(R) of the SSM product is far below 1, which is the theoreti-
cal R value for a completely random copolymer. The degree
of randomness of the melt-polymerized copolyamide is, as
expected, very close to unity.
modified PA-6,6 is increased by ꢁ11 ꢀC [from ca. 55 to 63
ꢀC, see Fig. 14(a)], by the incorporation of 17.0 mol % of
MxAd salt. The crystallization temperature as well as the
melting temperature determined during the second heating
run of the solid state-modified material are significantly
higher than the corresponding temperatures of the melt-
modified material containing 17.6 mol % MxAd, and are in
fact very close to the Tc and Tm values of pure PA-6,6 (see
Table 2). This is due to the block-like structure of the SSM
copolyamide, which affords relatively long pure PA-6,6
sequences and concomitantly thicker lamellae than the ran-
dom copolyamide prepared by the melt route. As such, the
approximate retention of the second heating melting temper-
Now, we have identified pronounced differences in the chem-
ical microstructure, although the overall composition of the
SSM and MP copolyamide is very similar, it is very interest-
ing to compare possible differences in their crystallization
and melting behavior as analyzed by DSC. From the second
cooling run shown in Figure 14(b), it is apparent that the
onset of the crystallization peak after the SSM is not changed
with respect to the pure PA-6,6, which strongly indicates
that the modification with the MxAd salt happened only in
the amorphous phase, leaving long pure PA-6,6 blocks with a
good crystallization behavior. The Tg of the solid state-
ature of (PA6680MxAd20 SSM,Feed copolyamide is symptomatic
)
of a lack of cocrystallization of MXDA-based units with PA-
6,6 repeat units. On the contrary, the SSM copolyamides
modified by similar amounts of PxAd comonomer exhibited
TABLE 1 Molar Fractions of the Aliphatic–Aliphatic (HAH), Aromatic–Aromatic (ØAØ), Aromatic-Aliphatic (ØAH), and Aliphatic-
Aromatic (HAØ) Sequences and the Calculated Degrees of Randomness (R) for Solid State-Modified and Melt-Polymerized Copo-
lyamides as Derived from 13C NMR Spectra using eqs 2–5
(PA66)80(MxAd)20 Copolyamide
No.
Synthesized by
FHAØ,total
FHAH,total
FØAØ,total
Rtotal
1.
2.
Melt route
0.326
0.085
0.779
0.844
0.221
0.113
0.95
0.43
Solid-state modification
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129
5127

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
tals was expected to enhance the melting temperature due
to the enhanced chain stiffness. The unexpected lowering of
Tm with respect to PA-6,6 is possibly due to a somewhat dis-
turbed packing of the chains in the a- and b-direction of the
unit cell of the crystal structure, also resulting in a reduced
crystallinity (see corresponding melting enthalpies in Table
2). The (PA6680PxAd20 SSM,Feed
)
also resulted a higher crystal-
ꢀ
lization temperature (Tc ca. 233 C) compared to neat PA-6,6
at a 10 ꢀC/min cooling rate. A detailed analysis of the crys-
tallization behavior as a function of the incorporated mol %
of comonomer salt will be presented in a subsequent article.
CONCLUSIONS
For the first time for polyamides of the PA-x.y type, a SSM of
the amorphous phase of a polyamide was performed below
the melting temperature. Semi-aromatic para- and meta-
xylylene diamine/AA “nylon salts” were incorporated into
the main chain of PA-6,6. In a first step, these salts were
mixed into the amorphous PA-6,6 phase by a solution-
evaporation process using the cosolvent HFIP. SEC in combi-
nation with a UV detector confirmed the presence of the aro-
matic moiety in the aliphatic PA-6,6 main chain. As the PA-
6,6 chain segments present in the crystals during the SSM
process do not participate in the transamidation reactions,
the SSM reaction results in relatively long blocks of pure PA-
6,6 segments and blocks of copolyamide segments. As
expected, the kinetics of the transamidation is much faster at
ꢀ
230 C than at 200 ꢀC and the solid state-modified copolya-
mide initially shows a significant molecular weight reduction
by chain scission by transamidation with the incorporated
salt, followed by a restoration of the molecular weight to a
value close to the starting value after 8–12 h of reaction
time. At higher reaction temperatures branching and cross-
linking reactions, resulting in gel formation, are observed
after 8 h of reaction. The degree of randomness (R) of the
SSM reaction products proved to be around 0.4, whereas for
a melt-polymerized copolymer with a similar composition an
R value of about 0.95 was obtained, which is very close to
the theoretical value of 1 for a fully random copolymer. The
more blocky microstructure of the SSM product, exhibiting
longer PA-6,6 sequences, is also reflected in a more favorable
crystallization behavior of this copolyamide from the melt,
showing higher melting and crystallization temperatures in
comparison to a melt-synthesized copolyamide with similar
composition. In fact, the melting and the crystallization tem-
peratures of the SSM product containing 17 mol % of MxAd
salt are very close to the corresponding values of pure PA-
6,6, whereas a melt-polymerized copolyamide containing
17.6 mol % MxAd exhibits significantly lower values for both
transitions. Moreover, the Tg was raised by the incorporation
of the semiaromatic salt into the PA-6,6.
FIGURE 14
The DSC thermograms of unmodified PA-6,6 and
PA-6,6 modified with 20 mol % MxAd, PxAd salt: (a) second
melting run and (b) second cooling run. [Color figure can be
viewed in the online issue, which is available at
wileyonlinelibrary.com.]
a lower melting temperature than that of PA-6,6 (Tm ca.
254.5 ꢀC, see Table 2), pointing to cocrystallization of the
repeat units based on the aromatic diamine (PXDA) with six
carbon atoms between the amine groups, being exactly the
number of C-atoms as in hexamethylenediamine. The intro-
duction of the rigid PxAd residues into the copolyamide crys-
TABLE 2 Results of DSC Analysis of (PA66)80(MxAd)20 Copo-
lyamide by Melt- and SSM-Route from Second Heating Cycles
(10 ꢀC/min)
No. Sample
Tg (ꢀC) Tm (ꢀC) DHm (J/g) Tc (ꢀC)
1.
2.
3.
PA-6,6 unmodified
ꢁ55
262.6
260.5
244.4
70.8
57.9
43.3
221.0
220.5
198.6
SSM (17 mol % MxAd) 62.5
ACKNOWLEDGMENTS
Melt route (17.6
mol % MxAd)
66.3
The authors thank BASF SE, Ludwigshafen, Germany, for the
financial support. Also Dr. Arnold Schneller, BASF SE, is
4.
SSM (18 mol % PxAd) 62.5
254.5
65.3
233.1
5128
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
18 K. L. L. Eersels, G. Groeninckx, Y. Mengerink, S. VanderWal,
Macromolecules 1996, 29, 6744–6749.
acknowledged for his support and his lab is thanked for provid-
ing the melt-copolymerized samples.
19 M. A. G. Jansen, J. G. P. Goossens, G. de Wit, C. Bailly, C.
E. Koning, Macromolecules 2005, 38, 2659–2664.
REFERENCES AND NOTES
20 M. A. G. Jansen, J. G. P. Goossens, G. de Wit, C. Bailly, C.
Schick, C. E. Koning, Macromolecules 2005, 38, 10658–10666.
1 W. H. Carothers, U.S. Patent 2,149,273, 1939.
21 M. A. G. Jansen, J.G.P. Goossens, G. de Wit, C. Bailly, C. E.
Koning, Anal. Chem. Acta 2006, 557, 19–30.
2 S. N. Vouyiouka, C. D. Papaspyrides, Solid-State Polymeriza-
tion, Wiley, New York, 2002.
3 Z. Yao, W. H. Ray, AIChE J. 2001, 47, 401–412.
22 M. A. G. Jansen, L. H. Wu, J. G. P. Goossens, G. De Wit, C.
Bailly, C. E., Koning, J. Polym. Sci. Part A: Polym. Chem. 2007,
45, 882–899.
4 A. C. Boussia, C. C. Damianou, S. N. Vouyiouka, C. D.
Papaspyrides, J. Appl. Polym. Sci. 2010, 116, 3291–3302.
5 C. D. Papaspyrides, S. N. Vouyiouka, I. V. Bletsos, J. Appl.
Polym. Sci. 2003, 88, 1252–1257.
23 M. A. G. Jansen, L. H. Wu, J. G. P. Goossens, G. De Wit, C.
Bailly, C. E. Koning, J. Polym. Sci. Part A: Polym. Chem. 2008,
46, 1203–1217.
6 C. D. Papaspyrides, S. N. Vouyiouka, I. V. Bletsos, J. Appl.
Polym. Sci. 2004, 92, 301–306.
24 M. Ziari, O. van Asselen, M. A. G. Jansen, J. G. P.
Goossens, P. Schoenmakers, Macromol. Symp. 2008, 265, 290–
296.
7 S. N. Vouyiouka, G. E. Koumantarakis, C. D. Papaspyrides,
J. Appl. Polym. Sci. 2007, 104, 1609–1619.
8 S. N. Vouyiouka, C. D. Papaspyrides, R. Pfaendner, Macro-
mol. Mater. Eng. 2006, 291,1503–1512.
25 S. Cakir, M. M. L. Nieuwenhuizen, P. G. A. Janssen, R.
Rulkens, C. E. Koning, Polymer 2012, 53, 5242–5250.
9 S. N. Vouyiouka, C. D. Papaspyrides, J. Weber, D. Marks,
J. Appl. Polym. Sci. 2005, 97, 671–681.
26 R. E. Kirk, , D. F. Othmer, In Kirk-Othmer Encyclopedia of
Chemical Technology, 4th ed.; J. I. Kroschwitz, M. Howe-Grant,
Eds.; Wiley-Interscience: New York, 1997; Vol. 22, p 400.
10 S. N. Vouyiouka, C. D. Papaspyrides, J. N. Weber, D. N.
Marks, Polymer 2007, 48, 4982–4989.
27 P. J. Flory, In Principles of Polymer Chemistry; Cornell Uni-
versity Press: London, 1953; Chapter 8, p 317.
11 C. D. Papaspyrides, S. N. Vouyiouka, I. V. Bletsos, Polymer
2006, 47, 1020–1027.
28 R. Rulkens, C.E. Koning, In Polymer Science: A Comprehen-
12 S. N. Vouyiouka, E. K. Karakatsani, C. D. Papaspyrides,
Prog. Polym. Sci. 2005, 30, 10–37.
€
sive Reference; K. Matyjaszewski, M. Moller, Eds.; Elsevier B.V.,
Amsterdam, 2012.
13 A. M. Aerdts, K. L. L. Eersels, G. Groeninckx, Macromole-
cules 1996, 29, 1041–1045.
29 T. F. Novitsky, L. J. Mathias, J. Polym. Sci. Part A: Polym.
Chem. 2000, 38, 4154–4164.
14 K. L. L. Eersels, A. M. Aerdts, G. Groeninckx, Macromole-
cules 1996, 29, 1046–1050.
30 H. R. Kricheldorf, W. E. Hull, J. Macromol. Sci. Chem. 1977,
A11, 2281–2292.
15 K. L. L. Eersels, G. Groeninckx, Polymer 1996, 37, 983–989.
€
31 H. R. Kricheldorf, R. Muhlhaupt, Angew. Makromol. Chem.
1977, 65, 169–182.
16 K. L. L. Eersels, G. Groeninckx, J. Appl. Polym. Sci. 1997, 63,
573–580.
17 K. L. L. Eersels, G. Groeninckx, M. H. J. Koch, H. Reynaers,
Polymer 1998, 39, 3893–3900.
32 H. R. Kricheldorf, G. Schilling, Makromol. Chem. -Macromol.
Chem. Phys. 1976, 177, 607–619.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 5118–5129
5129