Mechanically linked poly(ethylene terephthalate)

Article abstract of DOI:10.1021/ma048575u

The synthesis, by solid-state copolymerization, and properties of poly(ethylene terephthalate) (PET) copolymers containing various amounts of [2]catenane mechanical linkages are described. Polymers end-capped by the corresponding noninterlocked macrocycle as well as a copolymer with a rigid fluorene monomer unit were also prepared as reference systems. Size exclusion chromatography and ¹H NMR indicate that the catenane is quantitatively incorporated during synthesis but that a small fraction ring-opens to form noninterlocked macrocycles, incorporated as either chain ends or branching points. Catenanes induce a smaller increase in the glass transition temperature than the macrocycle at the same weight content. This is probably due to the suppression of interchain hydrogen bonds upon interlocking and points to a specific effect of the mechanical linkage on properties. The crystallization and melting temperatures of catenane copolymers are only slightly depressed compared to those of PET homopolymer, further demonstrating significant flexibility of the catenane rings. SAXS results show that the amorphous interlayer between lamellae increases with increasing catenane content at constant lamellar thickness, confirming that the uncrystallizable catenane units concentrate in the amorphous phase during solid-state polymerization.

Full text of DOI:10.1021/ma048575u

7884
Macromolecules 2004, 37, 7884-7892
Mechanically Linked Poly(ethylene terephthalate)
C. A. F u stin ,†, G. J . Cla r k son ,‡ D. A. Leigh ,*,§ F . Va n Hoof,† A. M. J on a s,† a n d
C. Ba illy*,†
Unite´ de Physique et de Chimie des Hauts Polyme`res, Universite´ catholique de Louvain,
Place Croix du Sud 1, B-1348 Louvain-la-Neuve, Belgium; Centre for Supramolecular and
Macromolecular Chemistry, Department of Chemistry, University of Warwick, Gibbert Hill Road,
Coventry CV4 7AL, United Kingdom; and School of Chemistry, University of Edinburgh,
The King’s Buildings, West Mains Road, Edinburgh EH9 3J J , United Kingdom
Received J uly 14, 2004; Revised Manuscript Received August 13, 2004
ABSTRACT: The synthesis, by solid-state copolymerization, and properties of poly(ethylene terephthalate)
(PET) copolymers containing various amounts of [2]catenane mechanical linkages are described. Polymers
end-capped by the corresponding noninterlocked macrocycle as well as a copolymer with a rigid fluorene
monomer unit were also prepared as reference systems. Size exclusion chromatography and 1H NMR
indicate that the catenane is quantitatively incorporated during synthesis but that a small fraction ring-
opens to form noninterlocked macrocycles, incorporated as either chain ends or branching points.
Catenanes induce a smaller increase in the glass transition temperature than the macrocycle at the same
weight content. This is probably due to the suppression of interchain hydrogen bonds upon interlocking
and points to a specific effect of the mechanical linkage on properties. The crystallization and melting
temperatures of catenane copolymers are only slightly depressed compared to those of PET homopolymer,
further demonstrating significant flexibility of the catenane rings. SAXS results show that the amorphous
interlayer between lamellae increases with increasing catenane content at constant lamellar thickness,
confirming that the uncrystallizable catenane units concentrate in the amorphous phase during solid-
state polymerization.
In tr od u ction
mobility within a polymer chain. Furthermore, because
of the very slow crystallization of PC, it was not possible
to assess the influence of the mechanical links on
crystallization rate, a key property dependent upon
chain flexibility. Here we describe the effects of incor-
porating mechanical linkages into a complementary
commercial polymer, poly(ethylene terephthalate) (PET).
PET has been commercially available since the 1950s
and is arguably the most important engineering polymer
in the world today, finding applications in fields as
diverse as textile fibers, soft-drink bottles, food contain-
ers, and support film for magnetic recordings or pho-
tography, etc. The enhanced flexibility of PET over PC
is demonstrated by its lower glass transition tempera-
ture (∼75 °C) and relatively fast crystallization rate.
Although PET can be quenched from the melt, it readily
recrystallizes upon heating.
The incorporation of mechanically interlocked rings,
i.e., catenanes, into a covalently bonded polymer is in
principle an attractive strategy for the modification of
conventional polymer properties.1-14 If flexible (or swit-
chable) catenane linkages are incorporated, the polymer
chains should gain new degrees of freedom, significantly
affecting the dynamics and conformation of the polymer
backbone. This could, in turn, influence various solid-
state, rheological, and solution properties. However,
thus far very few examples of well-defined systems have
been prepared in sufficient quantities for these issues
to be experimentally addressed. We recently described15
the synthesis of bisphenol A polycarbonate (PC) copoly-
mers containing various amounts of a flexible benzylic
amide [2]catenane incorporated by solid-state polymer-
ization. This mechanically linked analogue of an im-
portant commercial polymer allowed for the detailed
characterization of a well-understood system which
unambiguously showed the influence of mechanical
linkages on several important solution and solid-state
properties. Catenane flexibility and mobility within the
polymer chain were demonstrated by the limited effects
of catenane incorporation on the glass transition tem-
perature and the presence of a new mechanical transi-
tion below room temperature. However, PC is a some-
what rigid polymer, and it could be argued that these
results do not constitute a severe test of catenane
The objective of this work was to assess the influence
of catenane incorporation on the solid-state and melt
properties of PET. We used a copolymerization method
to introduce a [2]catenane similar to that used previ-
ously for PC.15 In this way we were able to incorporate
[2]catenane linkages into PET as 5-20 wt % (0.8-3 mol
%) of repeat units. To build up our understanding of
the role played by the mechanical bond, PET copolymers
incorporating a rigid bulky comonomer 4,4′-(9-fluore-
nylidene)bis(2-phenoxyethanol) (10 wt %) as well as
PET end-capped by the corresponding noninterlocked
macrocycle (5-10 wt %) were prepared for property
comparisons. The bis-functional [2]catenane16-18 1 used
in this study was synthesized on a multigram scale
without the need of chromatography. Catenane 1 con-
tains two hydroxyethyloxyl groups and is thus suitable
as a comonomer for the synthesis of PET copolymers.
The rings can interact via intramolecular hydrogen
bonds, and hence their mobility is partly restricted. In
† Universite´ catholique de Louvain.
‡ University of Warwick.
§ University of Edinburgh.
Present address: Unite´ CMAT, Universite´ catholique de
Louvain, Place L. Pasteur 1, B-1348 Louvain-la-Neuve, Belgium.
* To whom correspondence may be addressed: bailly@poly.
ucl.ac.be (fax +32-10-451593) or David.Leigh@ed.ac.uk (fax +44-
131-6679085).
10.1021/ma048575u CCC: $27.50 © 2004 American Chemical Society
Published on Web 09/23/2004

Macromolecules, Vol. 37, No. 21, 2004
Mechanically Linked PET 7885
Sch em e 1. Syn th esis of Ca ten a n e 1 a n d of Ma cr ocycle 2a
a
(i) NMO, OsO4, THF (catenane) or DMAc (macrocycle), 72% catenane; (ii) NaIO4, NaBH4, DMF/THF, 63% catenane.
Sch em e 2. Syn th esis of P ET P r ep olym er
this respect, the PET catenane comonomer used in this
Catenane 5 was then converted into the bishydroxyca-
tenane 1 (63% yield) by reaction with sodium periodate
followed by sodium borohydride. Macrocycle 415 was
converted into macrocycle 2 following a similar proce-
dure. Details of the synthesis are provided in the
Experimental Section.
study is significantly different from the one used for the
polycarbonate copolymers reported previously.15 In the
latter case, the amide groups were methylated, which
suppressed hydrogen bonding and enhanced rotational
mobility. The comparison between these two examples
should bring about new insights concerning the influ-
ence of ring mobility on copolymer properties. Here we
focus on proving that the catenanes have been quanti-
tatively incorporated into the polymer and on the
discussion of some solid-state properties, especially
crystallization.
P olym er Syn th esis. PET prepolymer was obtained
in two steps as described in Scheme 2. Bis(2-hydroxy-
ethyl) terephthalate (BHET) 7 was first synthesized
from dimethyl terephthalate (DMT) and ethylene glycol
with manganese acetate as catalyst following a modi-
fication of a reported procedure.19 BHET was then
polymerized by melt polycondensation with antimony
trioxide as catalyst to yield low molecular weight PET.
Size exclusion chromatography (SEC) was used to
characterize the molecular weight distribution of the
prepolymer (Mw ) 13 kg/mol, Mn ) 7.4 kg/mol). Dif-
ferential scanning calorimetry (DSC) was performed on
the amorphous prepolymer to yield a glass transition
temperature of 72 °C and a melting point of 259 °C.
Resu lts a n d Discu ssion
Ca ten a n e Mon om er Syn th esis. The benzylic amide
[2]catenane 1 and macrocycle 2 were prepared according
to Scheme 1. Catenane 3, the synthesis of which has
already been described elsewhere,15 was reacted with
N-methylmorpholine-N-oxide (NMO) and osmium tetrox-
ide to give the tertahydroxycatenane 5 in 72% yield.

7886 Fustin et al.
Macromolecules, Vol. 37, No. 21, 2004
Sch em e 3. Syn th esis of P ET Cop olym er s w ith (i) Ca ten a n e 1 a n d (iii) F lu or en e 8 a n d of En d -Ca p p ed P olym er
w ith Ma cr ocycle 2 (ii)
A 5, 10, or 20 wt % amount of catenane 1 or 5 or 10
wt % of macrocycle 2 (Scheme 3) and PET prepolymer
were copolymerized by solid-state polymerization (SSP)
after solution blending. The reaction was performed
under vacuum (approximately 6 × 10-2 mbar) by
applying an increasing temperature program from 160
to 215 °C for approximately 25 h total (details in
Experimental Section). We confirmed that this program
does not lead to loss of catenane monomer from the
mixture by evaporation/sublimation. Since solid-state
polymerization requires crystalline precursors,20,21 the
first step of the temperature program (160 °C) was
dedicated to crystallize the blend. In this case, crystal-
linity of the blends offers an important advantage: upon
crystallization, most defectssincluding catenane and
chain endssare rejected in the amorphous phase. Ca-
F igu r e 1. SEC traces in CHCl3/HFIP of the blend of PET
oligomers and catenane 1 (full line) and of the copolymer
containing 20 wt % catenane 1 (dashed line).
tenanes and chain ends are therefore in close proximity
and can react together more easily. Furthermore, the
reaction conditions are much milder than melt polycon-
densation, thus minimizing the chance of catenane
However, the formation of branched chains certainly
degradation.
contributes to this shoulder since it was observed that
a prolonged heating above Tm induces cross-linking.
Catenane copolymers heated at 285 °C for 15 min are
more difficult to solubilize and even form a gel for 20%
catenane concentration. Moreover, an attempt to copo-
lymerize catenane 1 and PET in the melt at 280 °C
Qu a n tita tive Mon om er In cor p or a tion . SEC was
used to determine whether catenanes have been quan-
titatively incorporated into PET. Samples coming out
of SSP are highly crystalline and are often difficult to
solubilize. Therefore, crystallinity was first eliminated
by a quick heating-cooling cycle before dissolution in
under vacuum, starting from the same blend as for SSP,
1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and dilution
yielded insoluble, highly cross-linked, polymer. Branch-
with chloroform. Figure 1 shows SEC chromatograms
ing points can be produced by exchange reactions
of the PET prepolymer blend containing 20 wt %
between catenane amide groups and PET ester func-
catenane 1 before and after SSP. The peak attributed
to catenane monomer (around 21 min) has completely
disappeared after polymerization. Since catenane could
tions. These reactions are indeed well-known in the case
of melt blending of polyesters and polyamides.22 The
exchange reactions will open one macrocycle of the
catenane to yield a branching point with three arms and
a chain end-capped by the other macrocycle. During SSP
those reactions are slower due to the lower temperature
but can still occur. These results show that, despite the
occurrence of some side reactions, the SSP copolymer-
ization is a much milder and more efficient route than
melt copolymerization. The small peak at the right-hand
side of both chromatograms (and also present for PET
not escape from the reacting mixture by evaporation and
since the total dissolved sample was injected in the SEC
columns, all catenanes must have been incorporated
into PET, and no free catenanes remain after SSP. A
small shoulder is visible on the tail of the chromatogram
at the low retention time side. This shoulder, observed
for all three compositions, evidences some degree of
heterogeneity in the copolymers. The exact origin of the
observed shoulder is difficult to ascribe at this point.

Macromolecules, Vol. 37, No. 21, 2004
Mechanically Linked PET 7887
F igu r e 2. Aliphatic region of the 1H NMR spectra of the
copolymer containing 20 wt % catenane, of catenane 1, and of
macrocycle 2 recorded in CDCl3/HFIP.
F igu r e 3. Aromatic region of the 1H NMR spectra of the
copolymer containing 20 wt % catenane and of catenane 1
recorded in CDCl3/HFIP.
Ta ble 1. P ET Equ iva len t Molecu la r Weigh ts of
Cop olym er s Con ta in in g Va r iou s Am ou n t of Ca ten a n e 1,
Ma cr ocycle 2, or F lu or en e 8 Obta in ed by SEC in
CHCl3/HF IP
by the first mechanism can then react with PET to yield
macrocycle end-capped chains. The existence of these
side reactions was already hypothesized on the basis of
the SEC results (see above). The amount of byproducts
is, however, very small: 16% of 0.8 to 3 mol % starting
catenane, making between 0.13 and 0.48 mol % of
byproducts. This amounts, on average, to less than one
branching point or macrocycle chain-end per chain,
except in the case of the 20% copolymer. The percentage
of catenane degraded into macrocycle is slightly higher
for PET copolymers than for polycarbonate copoly-
mers.15 This could come from the fact that catenane 1
contains secondary amides instead of tertiary amides
as is the case for the catenane incorporated into PC.
Secondary amides are generally more reactive than
tertiary amides due to less steric hindrance. The aro-
matic proton regions of the copolymer and catenane 1
NMR spectra are presented in Figure 3. The changes
occurring in this region upon incorporation are much
more pronounced than for the aliphatic region. The
peaks situated on the catenane spectrum around 6.8 and
6.9 ppm, associated with protons of the para-substituted
rings, do not change, but the three other peaks around
7.5, 7.6, and 7.9 ppm, linked to protons of the isoph-
thaloyl rings and of the amide groups, are shifted to
totally different positions. It is difficult to assign pre-
cisely the peaks in their new position because of their
broad and unresolved features. However, the integration
of this whole group of peaks compared to the integration
of the two peaks at 6.8 and 6.9 ppm yields the correct
intensity ratio considering the catenane structure. The
changes occurring in the aromatic region of the NMR
spectrum upon incorporation can be explained as fol-
lows. The catenane coconformation when incorporated
into the PET is certainly different from the coconfor-
mation of a free catenane in solution, and hence the
intramolecular hydrogen bond pattern may be some-
what different as well.24,25 The isophthaloyl rings bear
the functional tail by which the catenane is attached to
PET and thus interact rather strongly with the polymer
chain. This interaction, affecting the local environment
of the isophthaloyl rings, could explain the different
chemical shift observed for the protons of these rings
compared to the catenane monomer. The peaks above
7.8 ppm on the copolymer spectrum are not linked to
catenanes but are associated with the PET aromatic
groups and chain ends. The NMR spectra of the other
copolymers (not shown) are very similar to those shown
Mn (kg/mol)
Mw (kg/mol)
PDI
PET
31
25
21
17
19
13
29
72
67
61
52
51
40
68
2.3
2.7
2.9
3.0
2.7
3.1
2.3
PET-Cat. 5%
PET-Cat. 10%
PET-Cat. 20%
PET-Mac 5%
PET-Mac 10%
PET-fluorene 10%
homopolymer) is associated with PET cyclic trimers.23
Table 1 summarizes the molecular weight results,
expressed in PET equivalents, for different copolymers.
Compared to a PET homopolymer prepared under the
same conditions, molecular weight decreases and poly-
dispersity increases with increasing comonomer con-
centration. This is probably due to the side reactions
mentioned above as well as to partial decomposition of
the catenane into macrocycle (see below). This is not
observed for the fluorene copolymer since in this case
such side reactions cannot occur. As one could expect,
the molecular weight of the macrocycle copolymers are
lower than the PET homopolymer since the macrocycle
is monofunctional and acts as chain stopper.
1
Solution H NMR in CDCl3/HFIP has been performed
on the copolymers. The aliphatic proton region of the
NMR spectrum of the copolymer containing 20 wt %
catenane 1 is presented in Figure 2 together with the
spectra of monomer catenane 1 and macrocycle 2. This
region’s features are associated with protons of the alkyl
chains of the catenane or of the macrocycle. The other
aliphatic protons, i.e., the benzylic methylene groups
and ethoxy groups, are situated at higher ppm but are
hidden by the HFIP and PET ethoxy group peaks. The
copolymer spectrum appears to be a superposition of the
catenane and macrocycle spectra indicating that part
of the catenane, 16% as determined by integration of
the NMR peaks, has been decomposed into macrocycle
during SSP. These macrocycles are not free since there
is no corresponding peak on the chromatogram (Figure
1). Macrocycles can be produced by two parallel mech-
anisms: a thermal ring opening-ring closure mecha-
nism, since it has been observed that a small amount
of macrocycle is produced when catenane 1 is heated
for a few hours at 215 °C under vacuum, and/or an
amide-ester exchange reaction22 between amides of the
catenane and PET ester moieties. Macrocycles produced

7888 Fustin et al.
Macromolecules, Vol. 37, No. 21, 2004
F igu r e 6. Tcc variation with respect to pure PET of same
molecular weight according to comonomer concentration (wt
%).
F igu r e 4. Dependence for pure PET of Tg (circle), Tcc (square),
and Tm (triangle) according to molecular weight. The full line
represents the Flory-Fox law determined on the basis of
experimental data.
certainly comes from the formation of hydrogen bonds
between the macrocycles and PET ester moieties or
between macrocycles from different polymer chains. One
macrocycle bears indeed four amide groups, and they
cannot form intramolecular hydrogen bonds considering
the macrocycle structure. The N-H moiety of the
amides could thus form hydrogen bonds between poly-
mer chains, and this will increase interchain interac-
tions, decreasing overall chain mobility and thus in-
creasing Tg. In the catenane, on the other hand,
macrocycles are interlocked, and most of the amides are
involved in intra-catenane hydrogen bonds, which partly
restrict ring mobility,24 but form fewer or no interchain
hydrogen bonds. This induces a weaker Tg increase,
resulting mainly from added in-chain rigidity. However,
the Tg increase for the catenane copolymer is much
smaller than is the case of a bulky, very rigid, comono-
mer such as fluorene 8. At the same weight concentra-
tion, the molecular weight corrected Tg increase for the
fluorene copolymer is twice as large as for the catenane,
similar to the increase observed for the macrocycle end-
capped polymers. This strongly suggests that, despite
the intra-catenane hydrogen bonds, the catenane rings
have still some degree of mobility since a completely
rigid comonomer of comparable bulkiness induces a
much larger Tg increase. The Tg behavior points there-
fore to a specific effect of the mechanical linkage on the
solid-state properties. In a previous study on polycar-
bonate-catenane copolymers, it was observed that the
macrocycle-containing polymers have a lower Tg than
the catenane-containing copolymers at same level of
incorporation. In the PC case, the dominant influence
on Tg is the free volume increase associated with
macrocycle chain ends, since hydrogen bonds are sup-
pressed. The interlocking of the macrocycle rings to form
catenanes compensates the free volume increase and
thus raises Tg. In the present case, the dominant
influence is hydrogen bonding. The interlocking of the
catenane rings suppresses interchain hydrogen bonds
and thus lowers Tg.
F igu r e 5. Tg variation with respect to pure PET of same
molecular weight according to comonomer concentration (wt
%).
in Figures 2 and 3, differing only by the intensity of the
catenane peaks.
Solid -Sta te P r op er ties. It is known that the glass
transition temperature (Tg), temperature of crystalliza-
tion on cooling (Tcc), and melting temperatures (Tm) of
PET vary with molar mass.26 Since the molar masses
of the different copolymers span a rather broad range,
the evolution of Tg, Tcc, and Tm vs molecular weight has
first been measured for PET homopolymers synthesized
by the same method. The corresponding evolutions are
presented in Figure 4. From the evolution of Tg vs
molecular weight, the parameters of the Flory-Fox
equation have been determined for the studied range
of Mw:
Tg ) 83 - 2.6 × 102/Mw
for pure PET, with Tg in °C and Mw in kg/mol.
The data for the copolymers have then been compared
to those predicted for pure PET at same molecular
weight, and the differences have been plotted versus
comonomer concentration. In this way, a clean depen-
dence of the properties with respect to composition can
be obtained. Figure 5 presents such a dependence for
Tg, measured on amorphous quenched samples. The Tg
of catenane copolymers and macrocycle end-capped
polymers increases gradually with comonomer concen-
tration, but the increase is higher for macrocycle end-
capped polymers than for catenane copolymers. This
Evolution of the crystallization temperature on cool-
ing (Tcc) vs comonomer concentration is presented in
Figure 6. There is almost no change for 5% catenane or
macrocycle, only a very small one for 10%, but a large
decrease of about 30 °C for 20% catenane. These
observations are confirmed by the evolution of the
crystallization temperature on heating (Tch). However,
because of the difficulty in obtaining a reliable evolution
of Tch vs molecular weight in the case of pure PET, no

Macromolecules, Vol. 37, No. 21, 2004
Mechanically Linked PET 7889
Ta ble 2. En th a lp y of F u sion a n d Cr ysta llin ity Obta in ed
on th e F ir st Hea tin g DSC Tr a ce Sta r tin g fr om Sa m p les
Com in g Dir ectly fr om th e SSP a n d fr om Am or p h ou s
Sa m p les P r ep a r ed by Qu en ch in g
SSP
quenched
∆Hm crystallinity ∆Hm crystallinity
(J /g)
(%)
(J /g)
(%)
PET
60
61
61
53
62
72
58
44
45
45
39
46
53
43
36
32
32
27
45
44
24
26
24
24
20
33
32
18
PET-Cat. 5%
PET-Cat. 10%
PET-Cat. 20%
PET-Mac 5%
PET-Mac 10%
PET-fluorene 10%
tion kinetics, Tch (167 °C) being indeed rather close to
Tm (239 °C) for this copolymer. It is again interesting
to compare the behavior of PET copolymers to the PC
copolymers previously reported. In the latter case, we
have observed a decrease of the absolute crystallinity
after SSP with comonomer concentration but a constant
“corrected” crystallinity, in the sense that the crystal-
linity of the crystallizable fraction remains constant.30
These observations were consistent with the SSP pro-
cess.20,31 The resulting copolymers indeed consist of PC
homopolymer blocks, the crystallizable fraction, and of
random PC-catenane copolymer blocks, which are
unable to crystallize. When the catenane concentration
increases, the global amount of amorphous phase and
the local catenane concentration in the amorphous
phase increase, but the quality of the crystalline phase
is unaffected. In the case of PET copolymers, although
there is an indication that the absolute crystallinity is
constant up to 10% comonomer, the differences with
respect to constant “corrected” crystallinity are rather
small (order of 6 J /g) and of the order of the experimen-
tal error. Therefore, the hypothesis of a constant “cor-
rected” crystallinity remains consistent with the data.
The results of the 20% catenane copolymer will not be
discussed for the same reasons as discussed above
(branching). Crystallinity of macrocycle end-capped
polymers is higher than for the catenane copolymers and
even higher than for the PET homopolymer. This is due
to the much lower molecular weight of these polymers
which tends to increase the crystallinity.
F igu r e 7. Tm variation with respect to pure PET of same
molecular weight according to comonomer concentration (wt
%).
values of ∆Tch are given. The melting temperature
follows the same evolution as Tcc: only a small decrease
of Tm at low catenane concentration and a more impor-
tant change for a concentration of 20 wt % (Figure 7).
Surprisingly, the crystallization rate of the copolymers
decreases only slightly when catenane concentration
increases up to 10 wt %. It is important to notice that
for a given concentration the decrease in Tcc is much
larger for the copolymer containing the fluorene 8. The
catenane has thus little effect on chain mobility and on
the crystallization of PET compared to very rigid
comonomer, showing once again a certain degree of
flexibility of the catenane rings. It is more difficult to
interpret the changes observed for Tm and Tcc for the
20% catenane copolymer because of their uncertain
origin. SEC results (see above) indeed suggest that this
copolymer contains branched and/or cross-linked chains.
Therefore, these results will not be further discussed.
A comparison with results from the literature further
confirms the surprisingly small influence of catenanes
on the crystallization properties of PET. Usually, the
incorporation of small amount (up to 10 mol %) of
comonomers such as 1,4-cyclohexanedimethanol, isoph-
thalic acid, 2,2-butyl-ethyl-1,3-propanediol, etc., de-
creases Tcc and Tm by several degrees.27 For example,
the incorporation in PET of 2.5 mol % phthalate, 1,8-
naphthalenedicarboxylate, or 1,8-anthracenedicarboxy-
late induces a decrease of Tm between 4 and 9 deg and
a decrease of Tcc between 18 and 24 deg, depending on
the comonomer, much more than what we have ob-
served for catenanes.28
The enthalpy of fusion (∆Hm) of the copolymers has
been measured by DSC during the first heating. Highly
crystalline samples coming directly from SSP, and
amorphous samples prepared by quenching in cold
water have both been measured and compared to a PET
homopolymer prepared also by SSP with the same
temperature program. The crystallinity of the samples
has been calculated on the basis of an enthalpy of fusion
of 135.8 J /g for 100% crystalline PET homopolymer.29
The results are reported in Table 2. The measured
crystallinity of SSP samples is of course higher than the
crystallinity measured on quenched/crystallized samples.
SSP samples have indeed been annealed much longer
at high temperature. Table 2 indicates that crystallinity
of catenane and fluorene copolymers, up to 10% comono-
mer, is roughly equal to that of PET homopolymer. For
the quenched copolymer containing 10% fluorene 8,
crystallinity is lower because of the slower crystalliza-
SAXS measurements were performed on the copoly-
mers after isothermal crystallization from the amor-
phous state at 160 °C for 15 min and then at 200 °C for
60 min to erase previous thermal history. Since it is
known for PET that the long period and the thickness
of amorphous interlamellar regions depend on the molar
mass,32 a PET homopolymer with a molecular weight
(Mw ) 63 kg/mol) close to the one of the 10% catenane
copolymer was chosen as reference. Figure 8 presents
the Lorentz-corrected scattering data vs momentum
transfer q for the melted and recrystallized samples,
together with their normalized Fourier transform (cor-
relation function) and the opposite of the second deriva-
tive of the Fourier transforms (interface distribution
functions). The Fourier transforms and their second
derivatives allow us to estimate with precision the
lamellar thickness and the long period of PET samples,
as detailed elsewhere.33 The incorporation of the cat-
enane in the PET chain after SSP is clearly demon-
strated by the SAXS data recorded after isothermal
crystallization. Such conditions should lead to crystals
of identical thickness Lc, according to standard crystal-
lization theory, since the melting temperatures of the

7890 Fustin et al.
Macromolecules, Vol. 37, No. 21, 2004
solid-state process. The glass transition temperature of
the PET-catenane copolymers increases with comono-
mer concentration but less than for macrocycle end-
capped polymers. This difference is attributed to a
specific effect of the catenane mechanical linkage (prob-
ably intra- vs intermolecular hydrogen bonding). The
effect is opposite to that observed for PC-non-hydrogen-
bonding catenane copolymers described previously,
where free volume effects dominate and therefore mac-
rocycles tend to reduce Tg. Moreover, for the same
comonomer concentration, the Tg of a catenane-contain-
ing PET copolymer is well below the Tg of a copolymer
containing a bulky and rigid comonomer at the same
weight content. This observation suggests a significant
relative internal mobility/flexibility of the catenane
rings. Up to 10 wt % incorporation, the catenane has
only a small influence on the crystallization properties
of the PET copolymers, indicating once more the relative
flexibility of the catenane rings. SAXS results indicate
that the amorphous interlayer between crystalline
lamellae grows thicker with increasing catenane comono-
mer content while the lamellar thickness remains
constant. This in turn is consistent with a model
previously observed for PC-catenane copolymers15 where
the uncrystallizable catenane units concentrate in the
interlamellar amorphous phase during the solid-state
process.
F igu r e 8. (top) Lorentz-corrected small-angle X-ray scattering
of the samples of this study. (bottom) Normalized correlation
function and interface distribution function computed from the
SAXS. Dotted lines: PET homopolymer; continuous lines:
PET-Cat. 10%. The samples were crystallized from the amor-
phous state at 160 °C for 15 min and then at 200 °C for 60
min to erase previous thermal history. The morphological
parameters (estimates for the crystal thickness Lc and for
thickness of amorphous interlamellar regions La) are indicated
in the lower figure.33
Exp er im en ta l Section
Mea su r em en ts. Size exclusion chromatography experi-
ments were carried out on a Gilson system equipped with a
Waters 484 UV tunable absorbance detector and two mixed
bed HFIPgel columns from Polymer Laboratories. Universal
calibration using polystyrene standards was performed. The
chloroform/1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) 98/2 mix-
ture was used as solvent, and the flow rate was set to 0.8 mL/
min. Mark-Houwink coefficients of pure poly(ethylene tereph-
thalate)23 were used for all copolymers, thus giving PET
equivalent molecular weights. Before solubilization all SSP
samples were dried under vacuum at 50 °C for 24 h and then
heated to 280 °C for 1 min under dry nitrogen and quickly
cooled to room temperature. Thermal analyses were performed
on a Perkin-Elmer DSC 7, working with a heating rate of 10
°C/min. Before measurements, samples were dried under
vacuum at 50 °C for 12 h. When amorphous samples were
needed, the following procedure was applied to erase previous
thermal history. Samples were dried in a vacuum at 50 °C for
24 h, then heated in a DSC pan to 280 °C for 2 min under a
nitrogen atmosphere, and then quickly cooled by dipping the
DSC pan in cold water to obtain amorphous samples. Samples
were dried again under vacuum at 50 °C for 12 h just before
two samples are close (255 °C for the PET homopolymer
and 253 °C for the copolymer containing 10 wt %
catenane).34 This is confirmed by the examination of the
locations of the first maximum of the interface distribu-
tion functions, which are a good estimates for Lc.33
Values of 3.4 and 3.5 nm are found for PET homopoly-
mer and the copolymer containing 10 wt % catenane,
respectively. In contrast, the long period, which is
properly estimated by the location of the first broad
maximum in the correlation functions,33 is significantly
different for the two samples, since it increases from
9.7 to 10.5 nm upon incorporation of the catenane
moieties. This may only be due to thicker interlamellar
amorphous regions in the copolymers (La), correspond-
ing to the accumulation of catenane-rich segments of
the chains in these regions. These results are consistent
with a constant “corrected” crystallinity as discussed
above and are in complete agreement with a model of
chain architecture consisting of catenane links inter-
spersed among regular PET sequences.
1
the analysis. H NMR spectra were recorded at room temper-
ature on a Bruker Advance 500 MHz spectrometer, using
deuterated chloroform/HFIP 85/15 mixture as solvent and as
internal standard or on a Bruker Avance 400 MHz spectrom-
eter using other solvents. Before solubilization all samples
were dried under vacuum at 50 °C for 24 h. SAXS measure-
ments were conducted in a Kratky camera (Anton-Paar KKK)
using a Braun OED 50M proportional position-sensitive detec-
tor and Ni-filtered Cu KR radiation form a copper anode
generator operated at 40 kV/300 mA. They were performed
on polymer powders encapsulated in glass capillaries of 2 mm
diameter at room temperature and under primary vacuum.
Acquisition data were spline-smoothed, corrected for parasitic
scattering, desmeared, background-subtracted, and Lorentz-
corrected, as described elsewhere.35
Con clu sion
The synthesis of PET copolymers containing various
amounts of a benzylic amide [2]catenane and of poly-
mers end-capped with the corresponding macrocycle has
been achieved by solid-state copolymerization. During
this process, catenane incorporation into the polymer
is quantitative, but a small fraction of the catenane
decomposes, yielding macrocycles, incorporated into
PET as chain ends and/or branching points. If melt
copolymerization is used, an insoluble polymer is ob-
tained, confirming the versatility and usefulness of the
Solven ts a n d Rea gen ts. All solvents used were com-
mercial HPLC grade. All other chemicals were purchased from
Aldrich or Acros and used as received.
Syn th esis. Catenane 1. The bis-allyloxycatenane 3 (0.5 g,
0.4 mmol), the synthesis of which has already been described

Macromolecules, Vol. 37, No. 21, 2004
Mechanically Linked PET 7891
elsewhere,15 was dissolved in the minimum of dimethylforma-
mide (5 mL) and diluted with THF (20 mL). To the rapidly
stirred solution was added a solution of N-methylmorpholine-
N-oxide (50% in water, 0.5 mL, 0.6 g, 2 mmol). Osmium
tetroxide in tert-butanol (0.5 mL, 2.5 wt %, catalytic) was added
and the solution stirred until thin-layer chromatography (CH2-
Cl2/DMAc/MeOH (8:1:1), product rf 0.1) showed total consump-
tion of starting material. The reaction mixture was then
poured into an excess of rapidly stirred diethyl ether. The
precipitate was filtered off and then recrystallized from
2-propanol/water to give tiny white cubes of tetrahydroxyca-
tenane 5 (0.38 g, 72%); mp 216-219 °C, m/z 1261 (M + H)+.
1H NMR (400 MHz, d6-DMSO) δ: 9.67 (4H, br s, NH), 8.40
(4H, br t, J ) 5.5 Hz, NH), 7.70 (2H, s, ArH), 7.45 (4H, br s,
ArH), 7.32 (8H, d, J ) 8.0 Hz, ArH), 6.94 (8H, d, J ) 8.0 Hz,
ArH), 5.03 (2H, d, J ) 5.5 Hz, OH), 4.72(2H, t, J ) 5.5 Hz,
OH), 4.10 (8H, br m, ArCH2N) and CH2CHOHCH2), 3.80 (4H,
br m, CH2OH), 3.48 (4H, m, CH2OAr), 2.13 (8H, br s, COCH2),
1.30 (8H, br s, COCH2CH2) and 0.77 (16H, br s, CH2).
COCH2CH2), and 1.24 (8H, br s, CH2). 13C NMR (100 MHz,
d6-DMSO) δ: 171.5, 166.1, 160.0,138.6, 136.7, 133.9, 128.8,
119.3, 118.2, 116.3, 70.3, 59.8, 43.1, 36.3, 29.4, 28.4, and 25.5.
PET Prepolymer. A three-necked round-bottom flask was
charged with dimethyl terephthalate (194 g, 1 mol) and
ethylene glycol (620 g, 10 mol), and manganese acetate (122.5
mg, 5 × 10-4 mol) was added as transesterification catalyst.
A light nitrogen flux was applied, and the mixture was
progressively heated to 200 °C. Stirring was switched on upon
melting of dimethyl terephthalate (140 °C). The methanol
produced by the transesterification was distilled off. Reaction
was stopped when the production of methanol stopped. The
mixture of prepolymer and ethylene glycol was poured in a
crystallizing dish and allowed to cool. One liter of cold water
was added in the crystallizing dish, and the mixture was
filtered to separate the prepolymer from water and ethylene
glycol. The prepolymer was dissolved in boiling water and
filtered to separate BHET 7, which is soluble in boiling water,
from higher PET oligomers. The solution of BHET was then
placed at 4 °C overnight to allow its recrystallization. The
purification step was repeated twice.
A glass reactor was charged with BHET 7 (60 g, 0.24 mol),
and antimony trioxide (18 mg, 6.2 × 10-5 mol) was added as
transesterification catalyst. Vacuum (0.2 mbar) was applied,
and the temperature was slowly (in 20 min) raised to 285 °C.
Stirring was switched on when the temperature reached 200
°C, and the speed was set to 60 rpm. Reaction was stopped
after 45 min. The system was then returned to atmospheric
pressure, and the glass reactor was quickly removed from the
oven and immersed in water to quickly cool PET.
Copolymer. Copolymerization was performed on batches of
300 mg. PET and catenane 1 (5, 10, and 20 wt %) or macrocycle
2 (5 and 10 wt %) or 4,4′-(9-fluorenylidene)bis(2-phenoxyetha-
nol) 8 (10 wt %) were dissolved in 5 mL of HFIP. Solvent was
evaporated under vacuum while stirring the solution, and the
resulting powder was dried under vacuum for 12 h at 50 °C.
After this step, the sample is already partially crystallized.
The blend was ground to obtain a finely divided powder. Solid-
state polymerization was performed under vacuum (6 × 10-2
mbar) applying the following temperature program: (i) room
temperature for 30 min; (ii) 160 °C for 1 h; (iii) 190 °C for 1 h;
(iv) 200 °C for 2 h; (v) 205 °C for 1 h; (vi) 210 °C for 18 h; (vii)
215 °C for 2 h. Heating was ensured by a salt bath enabling a
temperature control within 2 °C.
The tetrahydroxycatenane 5 (0.5 g, 0.4 mmol) was dissolved
in a mixture of dimethylformamide (5 mL) and THF (20 mL).
To this stirred mixture was added an aqueous solution of
sodium periodate (0.2 g, 0.9 mmol in 2 mL of water). The
reaction was monitored by thin-layer chromatography (CH2-
Cl2/MeOH/DMAc: 7:1.5:1.5) until the starting material was
consumed, and then sodium borohydride (50 mg) was added
in small portions. The mixture was stirred for an hour and
then filtered through a small pad of Celite, and the solvent
was removed by evaporation under reduced pressure. The
thick oil was purified twice by recrystallization from dimeth-
ylformamide/water to give the bis-hydroxycatenane 1 as tiny
white needles (0.3 g, 63%); mp 248-250 °C, m/z 1201 (M +
H)+. C68H80O12N8 requires C, 67.98; H, 6.71; N, 9.33%. Found:
C, 67.4; H, 6.8; N, 9.4%. 1H NMR (400 MHz, d6-DMSO) δ: 9.70
(4H, br s, NH), 8.37 (4H, br t, J ) 5.5 Hz, NH), 7.72 (2H, br s,
ArH), 7.45 (4H, br s, ArH), 7.34 (8H, d, J ) 8.0 Hz, ArH), 6.94
(8H, d, J ) 8.0 Hz, ArH), 4.93 (2H, t, J ) 5.5 Hz, OH), 4.11
(8H, br s, ArCH2), 3.94 (4H, br m, ArOCH2CH2OH), 3.73 (4H,
br q, J ) 5.5 Hz, ArOCH2CH2OH), 2.14 (8H, br s, COCH2),
1.30 (8H, br s, COCH2CH2) and 0.81 (16H, br s, CH2). 13C NMR
(100 MHz, d6-DMSO) δ: 175.5, 170.0, 162.6, 142.2, 140.3,
136.6, 132.3, 122.8, 121.8, 120.1, 73.9, 63.5, 47.2, 40.1, 33.2,
32.1, and 29.3. FT-IR (KBr): 3320, 2935, 1645, 1607, 1540,
1520, 1415, 1310, and 1255 cm-1
.
Macrocycle 2. To a stirred solution of macrocycle 4 (1.5 g,
2.5 mmol), the synthesis of which has already been described
elsewhere,15 in dimethylacetamide (20 mL) at room temper-
ature was added N-methylmorpholine-N-oxide monohydrate
(95%, 0.37 g, 2.7 mmol) dissolved in dimethylacetamide (10
mL). OsO4 (2.5 wt % solution in tert-butanol, 0.1 mL, catalytic)
was added, and the solution stirred until thin-layer chroma-
tography (CH2Cl2/MeOH/DMF (10:1:1), product rf 0.15) showed
total consumption of starting material. The reaction mixture
was then poured into an excess of rapidly stirred diethyl ether.
The precipitate was filtered off and used without further
purification. The tetrahydroxy macrocycle 6 was then dissolve
in dimethylformamide (15 mL) and diluted with THF (10 mL).
Sodium periodate (0.53 g, 2.5 mmol) was added in one portion
to the stirred mixture. The reaction was monitored by thin-
layer chromatography (CH2Cl2/DMAc/MeOH (10:1:1), product
rf 0.6) until the material was consumed, and then sodium
borohydride (100 mg, excess) was added in small portions and
the mixture stirred for an hour. The mixture was then filtered
through a small pad of Celite, and the solvent was removed
to a small volume. This was then added to a rapidly stirred
excess of water. The precipitate was filtered and recrystallized
from DMF/water as small white cubes of macrocycle 2; mp >
310 °C, m/z 601 (M + H)+. C34H40O6N4 requires C, 67.98; H,
6.71; N, 9.33%. Found: C, 67.6; H, 6.8; N, 9.5%. 1H NMR (400
MHz, d6-DMSO) δ: 9.81 (2H, s, NH), 8.76 (2H, br t, J ) 5.4
Hz, NH), 7.69 (1H, s, ArH), 7.51 (4H, d, J ) 8.4 Hz, ArH),
7.48 (2H, br s, ArH), 7.24 (4H, d, J ) 8.4 Hz, ArH), 4.94 (1H,
t, J ) 5.5 Hz, OH), 4.38 (4H, d, J ) 5.4 Hz, ArCH2), 4.11 (2H,
t, J ) 5.0 Hz, CH2CH2OH), 3.77 (2H, br q, J ) 5.0 Hz, CH2CH2-
OH), 2.29 (4H, br t, J ) 6.4 Hz, COCH2CH2), 1.57 (4H, br m,
Ack n ow led gm en t. This work has been supported
by the European Community, TMR Contract No. HPRN-
CT-2000-00024 (MIPA Network). D.A.L. is an EPSRC
Advanced Research Fellow (Grant AF/982324). C.A.F.
gratefully acknowledges support from UCL through an
FSR grant.
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