Carbon monoxide-ethene copolymerization catalyzed by [PdCl2(dppb)] in H2O-H(CH2)nCOOH (dppb = 1,4-bis(diphenyphosphino)butane; N = 0, 1, 2)

Article abstract of DOI:10.1016/j.molcata.2015.09.026

[PdCl₂(dppb)] is highly active in the catalytic CO-ethene copolymerization in H₂O-H(CH₂)_nCOOH (n = 0, 1 or 2). The influence on the productivity, the limiting viscosity number and the average viscosity molecular weight MWˉv of the following reaction conditions is investigated: (i) solvent composition; (ii) temperature; (iii) CO and ethene partial pressure at a given pressure of one monomer; (iv) monomers ratio at a given total pressure; (v) total pressure at CO/ethene = 1/1; (vi) reaction time. The productivity passes through a maximum with a H₂O molar fraction of 0.55-0.70 (14,800 gPK(g Pd h)^-1 in H₂O-HCOOH, H₂O molar fraction = 0.58, 45 bar, CO/ethene = 1/1, 90°C; LVN = 0.48 dLg^-1, MWˉv = 21,194 Da). The productivity is in the order of the strength of the acid n = 0 > n = 1 > n = 2, whereas the activation energy is in the opposite order. These findings suggest that the protonation of the resting states β- and γ-chelate rings destabilizes them, thus favoring the chain-growing process. Proposed power rate laws fit the productivity data obtained at different monomer pressures. The productivity lowers with time, but in the first hour the rate remains almost constant. The morphology and crystallinity of selected PKs determined by solid state NMR is also discussed.

Full text of DOI:10.1016/j.molcata.2015.09.026

Journal of Molecular Catalysis A: Chemical 410 (2015) 202–208
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Carbon monoxide-ethene copolymerization catalyzed by
[PdCl2(dppb)] in H2O–H(CH2)nCOOH
(dppb = 1,4-bis(diphenyphosphino)butane; n = 0, 1, 2)
Matteo Pagota, Luigi Tonioloa,∗, Claudia Antonettib, Claudia Fortec,
Anna Maria Raspolli Gallettib
a Department of Molecular Sciences and Nanosystems, University Ca’ Foscari of Venice, Dorsoduro 2137, 30123 Venice, Italy
b Department of Chemistry and Industrial Chemistry, University of Pisa, Via G. Moruzzi 13, 56124 Pisa, Italy
c ICCOM CNR via G. Moruzzi 1, 56124 Pisa, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
[PdCl2(dppb)] is highly active in the catalytic CO-ethene copolymerization in H2O–H(CH2)nCOOH (n = 0, 1
or 2). The influence on the productivity, the limiting viscosity number and the average viscosity molecular
weight MWv of the following reaction conditions is investigated: (i) solvent composition; (ii) temper-
ature; (iii) CO and ethene partial pressure at a given pressure of one monomer; (iv) monomers ratio at
a given total pressure; (v) total pressure at CO/ethene = 1/1; (vi) reaction time. The productivity passes
through a maximum with a H2O molar fraction of 0.55–0.70 (14,800 gPK(g Pd h)−1 in H2O–HCOOH, H2O
molar fraction = 0.58, 45 bar, CO/ethene = 1/1, 90 ◦C; LVN = 0.48 dLg−1, MWv = 21,194 Da). The productiv-
ity is in the order of the strength of the acid n = 0 > n = 1 > n = 2, whereas the activation energy is in the
opposite order. These findings suggest that the protonation of the resting states ␤- and γ-chelate rings
destabilizes them, thus favoring the chain-growing process. Proposed power rate laws fit the productivity
data obtained at different monomer pressures. The productivity lowers with time, but in the first hour
the rate remains almost constant. The morphology and crystallinity of selected PKs determined by solid
Received 16 July 2015
Received in revised form
28 September 2015
Accepted 29 September 2015
Available online 9 October 2015
Keywords:
Palladium catalyst
Water-organic acid
CO/ethene
Polyketone
state NMR is also discussed.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
is weakly coordinated [9]. The corresponding neutral acetate or
chloride complexes, inactive in MeOH [9], turn to be highly active
The palladium catalyzed copolymerization of CO with olefins
continues to be of great interest as demonstrated by recent pub-
lications in this field, which includes also the application of
polyketones (PKs) in the area of heterogeneous catalysis [1–8].
Normally, the copolymerization is carried out in MeOH using
“cationic” Pd(II)-diphosphine complexes in which the cationic
charge of the central metal is balanced by weakly coordinating
anions [9–11]. The need to replace volatile toxic organic solvents
prompted the research to avoid the use of any solvent [1,5,12]
or to check benign solvents, such as H2O. In order to make the
catalyst soluble in this solvent, sulfonate analogues of the diphos-
phine were used [13–17]. The key aspect for the success of the
copolymerization is the availability of “free” coordination sites on
the metal centre, which is guaranteed when the counter anion
in H2O–AcOH. Since the first report [18] several other investiga-
tions appeared [19–24], including the employment of H2O–HCOOH
with [PdCl2(dppf)] (dppf = 1,1ꢀ-bis(diphenylphosphino) ferrocene)
[25–27]. Generally, the use of H2O-organic acid as copolymer-
ization medium allows the achievement of PKs both in higher
yields and molecular weights than those obtained using the corre-
sponding “cationic” complexes in MeOH. Thus, for instance, when
the tosylate complex [Pd(TsO)2(dppf)] is employed in MeOH, low
molecular weight PKs are formed together with lower oxygenates
such as methyl propanoate, methyl 4-oxohexanoate, dimethyl
succinate and dimethyl 4-oxoheptanedioate [28]. However, the
molecular weight of the PK obtained in MeOH is not always lower
than that of the PK achieved in H2O–AcOH, as reported in the paper
of Bianchini C. [21]. When the copolymerization is catalyzed by the
corresponding tosylate complex [Pd(TsO)2(dppb)] in MeOH, PKs
of moderate molecular weight are produced together with lower
amounts of methyl propanoate, diethyl ketone and co-oligomers
[29]. Therefore, on the basis of these considerations, we decided
∗
Corresponding author. Fax: +39 412348517.
E-mail address: toniolo@unive.it (L. Toniolo).
http://dx.doi.org/10.1016/j.molcata.2015.09.026
1381-1169/© 2015 Elsevier B.V. All rights reserved.

M. Pagot et al. / Journal of Molecular Catalysis A: Chemical 410 (2015) 202–208
203
Scheme 1. Catalytic cycle for the formation of the PK.
The 1H, 13C and 31P NMR spectra were recorded on a Bruker
Avance 300 spectrometer. The PK spectra were recorded in
1,1,1,3,3,3-hexafluoroisopropanol/CDCl3 (10/1, vol/vol) using the
inverse 1H-gated decoupling technique. The 31P NMR spectrum
of the complex [PdCl2(dppb)] complex was recorded in CDCl3,
external 85 % H3PO4. Solid state NMR spectra were carried out
on a Bruker AMX300WB spectrometer working at 300.13 MHz
for proton and 75.47 MHz for carbon-13 using 4 mm CP/MAS
probe head. All experiments were performed at 25 ◦C. The selected
investigated samples were obtained under standard conditions
(CO/ethene = 1/1, 45 bar at 90 ◦C, 1 h): three polymers with simi-
lar H2O fraction (0.55–0.6), but different acid (H2O fraction 0.55 for
sample I in HCOOH; 0.6 for sample II in AcOH and 0.55 for sample III
in EtCOOH), and one with EtCOOH but higher H2O fraction (0.68)
(sample IV). On-resonance 1H FIDs were recorded on static sam-
ples using a solid echo pulse sequence with an echo delay of 16 ␮s,
accumulating 400 transients with a recycle delay of 10 s. [32]. The
experiments were performed at room temperature. The FIDs were
fitted using a home-made non-linear least-squares fitting program.
to investigate the catalytic activity of [PdCl2(dppb)] (dppb = 1,4-
bis(diphenyphosphino) butane) in H2O-organic medium. The cat-
alyst activity and product characteristics are here presented and
discussed, also highlighting the morphology and crystallinity of
some PKs by means of solid state NMR. In particular, the analysis of
the Free Induction Decay (FID) in wideline 1H NMR was employed
to detect motionally different domains, this method providing easy
access to the number and relative proportions of motionally distinct
regions [30].
2. Experimental
2.1. Reagents
Carbon monoxide and ethene were purchased from SIAD Com-
pany (‘research grade’, purity >99.9%). PdCl2 was purchased from
Chimet S.p.A.. Dppb, formic acid, acetic acid, propanoic acid,
acetonitrile, 1,1,1,3,3,3-hexafluoropropanol (99%), m-cresol, EtOH,
CH2Cl2 and CDCl3 were Aldrich products and were used as received.
The complex [PdCl2(PhCN)2] was prepared as reported in the lit-
erature [31]. [PdCl2(dppp)] was prepared from [PdCl2(PhCN)2]
dissolved in CH2Cl2 and dppb (10% excess) dissolved in EtOH. 31P
NMR in CDCl3 ␦ 29.858 ppm.
2.3. Carbon monoxide-ethene copolymerization
The copolymerization reactions were carried out by using a
Hastelloy C autoclave of ca. 250 mL provided with a four-blade self-
aspirating turbine. In order to avoid contamination by metallic
species because of corrosion of the internal surface of the auto-
clave, solvent and catalyst were contained in a ca. 150 mL Pyrex
bottle, placed inside the autoclave. The monomers were supplied
to the autoclave in the ratio 1/1 from a gas reservoir connected
to the autoclave through a constant pressure regulator. In a typ-
ical experiment, 0.50 mg of [PdCl2(dppb)] (8.3 × 10−4 mmol) was
added to 80 mL of solvent (H2O-organic acid) contained in the bottle
placed in the autoclave. The autoclave was washed by pressurising
with a 1/1 mixture of CO/C2H4 (ca. 0.5 MPa) and then depressuris-
ing to atmospheric pressure (this cycle was repeated 5 times, at
room temperature with stirring). The autoclave was then pres-
surised with 0.5 MPa of the gas mixture and then heated to 90 ◦C
in 10 min without stirring. The pressure was then adjusted to the
2.2. Equipment
The catalyst precursor was weighed on a Sartorious Micro bal-
ance (precision 0.001 mg). Gas-chromatographic analysis of the liq-
uid phase was performed on a Hewlett Packard Model 5890, Series
II chromatograph fitted with a HP 1, 30 m × 0.35 ␮m × 0.53 ␮m col-
umn (detector: FID; carrier gas: N2, 0.2 mL/min; oven: 50 ◦C (2 min)
to 200 ◦C at 15 ◦C/min). Gas-phase analysis was performed on the
same cromatograph fitted with a 18 ft × 1/8 SS Silica Gel 60/80
packed column (detector: TDC; carrier gas: He, 30 mL/min; oven:
40 ◦C (2 min) to 100 ◦C at 15 ◦C/min). NMR spectra were recorded
on a Bruker Avance 300 spectrometer.
Linearization of the proposed power law equations was carried
out using OriginPro8 as program.

204
M. Pagot et al. / Journal of Molecular Catalysis A: Chemical 410 (2015) 202–208
desired value (typically 4.5 MPa total pressure) and, while stirring,
maintained constant throughout the experiment (1 h, rate stirring
700 rpm) by continuously supplying the monomers from a reser-
voir. At the end of the experiment the autoclave was quickly cooled
and carefully depressurised. The PK slurry was filtered, washed
with water and acetone and dried under vacuum at 70 ◦C. The
dried polymer was weighed and the productivity was calculated
as gPK·(gPd × h)−1. The kinetic in the first hour of the reaction was
followed by monitoring the reservoir weight drop with time. In
the liquid phase, analysed by GC, no propanoic acid or other low
MW products were present. The CO2 evolution during the copoly-
merization was monitored by GC analysis of the gas phase of the
autoclave.
2.4. Limiting viscosity number measurement and average
viscosity molecular weight calculation
Fig. 1. Influence of the solvent composition on the productivity and the MWv.
Run conditions: [PdCl2(dppb)] 8.3 × 10−4 mmol; Ptot 45 bar at the reaction tempera-
ture 90 ◦C; CO/ethene = 1/1; reaction time 1 h; solvent 80 mL: (a) H2O + HCOOH; (b)
H2O + AcOH; (c) H2O + EtCOOH.
The limiting viscosity number (LVN) of a dilute solution of a PK
sample in m-cresol was measured by using the Huggins relation-
ship between the viscosity number and the PK concentration by
extrapolation to zero concentration [33]. The viscosity was mea-
sured by using a Cannon–Fenske type capillary viscosimeter at
25 ◦C. The average viscosity molecular weight (MWv) of the PK was
calculated from the LVN using the Mark–Houwink equation [34]:
pKEtCOOH = 4.88). When the catalyst precursor [PdCl2(dppf)] was
employed, the productivity and the LVN were also higher in
H2O–HCOOH [27] than in H2O–AcOH [20]. The solubility of the
monomers in these media does not differ significantly, though
it is lower in the first medium than in the other ones [27].
Therefore, the strength of the acid plays a significant role on the
benign effect of the acid (see below and in 3.3.). The trends of
Fig. 1 are close to those found for the copolymerization catalyzed
by [PdX2(P-P)] in H2O–AcOH (P–P = 1,3-bis(diphenylphosphino)
propane, X = AcO, Cl) [18,19]; (P–P = 1,1ꢀ-bis(diphenylphosphino)
ferrocene, X = Cl) [20]; (P–P = 1,3-bis-(di(2-methoxyphenyl) phos-
phino) propane, X = Cl) [22,24] or in H2O–HCOOH (P–P = 1,1ꢀ-
bis(diphenylphosphino) ferrocene, X = Cl) [27]. The fact that the
productivity passes through a maximum was explained as the
result of a compromise between contrasting influences of H2O
and the acid. On one hand, H2O may stabilize the coordinatively
unsaturated three-coordinate Pd(II) species, which would tend to
achieve the preferred four-coordination, with formation of less
active dimeric species. In addition, H2O may re-form the Pd-H ini-
tiator from a Pd-[OCOR] species which may arise by the action of
the acid on the Pd-OH species which is formed in the termina-
tion step “t” (see Scheme 1). On the other hand, upon increasing
the H2O concentration, the solubility of the monomers decreases,
which disfavors the copolymerization process. The acid may sta-
bilize the Pd-H initiator and destabilize the ␤- and γ-chelate rings
through protonation of the oxygen atoms of the rings, which are
resting states in the chain growing process [35]. By contrast, LVN
decreases regularly with the increasing of the H2O content, which
suggests that the protonolysis termination step occurs through H2O
not the acid. At the same time, the acid concentration as well as the
effect of the destabilization of the ␤- and γ-chelate rings and the
solubility of the monomers [18] decrease, both contributing to the
lowering of the LVN.
0.85
[␩]m − cresol,25
◦
C = 1.01 × 10−4MWv
(1)
3. Results and discussion
The influence on the productivity, the LVN and MWv of the fol-
lowing reaction parameters was investigated: (i) composition of
the solvent; (ii) temperature; (iii) CO and ethene partial pressure at
a given pressure of one monomer; (iv) monomers ratio at a given
total pressure; (v) total pressure at CO/ethene = 1/1; (vi) reaction
time. Points (i) and (ii) were studied using H2O in mixture with each
one of the three acids, whereas points (iii)–(vi) were studied using
H2O–HCOOH and H2O–AcOH, only. In addition, the crystallinity of
selected copolymer samples was determined by solid state NMR.
3.1. On the catalytic cycle
As in the cases of other catalytic CO-ethene copolymerizations
catalyzed by diphosphine Pd(II) complexes carried out in H2O-acid,
the PK chains of the present study consist of perfectly alternat-
ing monomers with keto-ending groups and the formation of the
PK occurs with concomitant evolution of CO2 [18–27]. With the
purpose of making the understanding of the rest of the discussion
easier, a catalytic cycle, already discussed in previous articles, is
shown in Scheme 1.
3.2. Influence of the solvent composition on the productivity, the
LVN and the MWv
With each acid in mixture with H2O, the formation of PKs was
not accompanied by low molecular weight products. Thus, the ter-
mination step is much slower than the steps of the insertion of the
monomers in the chain-growing process. The productivity of the
PK passes through a maximum upon increasing the H2O content in
the solvent, whereas the LVN and MWv decrease regularly (Fig. 1).
In this figure and in the following, only MWv is reported since LVN
and MWv are related by equation (1).
The highest productivity was achieved in H2O–HCOOH (14,800
gPK(gPd × h)−1 at 0.58H2O molar fraction, moles of H2O/(moles
of H2O + moles of acid)). The MWv depends also on the nature
of H(CH2)nCOOH in the order n = 0 > n = 1 > n = 2, which is also the
order of the strength of the acid (pKHCOOH = 3.75, pKAcOH = 4.76,
Here and below, the influence on the LVN does not deserve any
special comment because they are related by Eq. (1).
3.3. Influence of the temperature on the productivity and the
MWv
The influence of the temperature on the productivity and the
MWv is shown in Fig. 2 for the acid/H2O compositions in which
the productivity reaches the maximum. The productivity increases
and the LVN decreases upon increasing the temperature, suggesting
that the chain growing process has an activation energy lower than
that of the termination step, which is in line with the fact the this

M. Pagot et al. / Journal of Molecular Catalysis A: Chemical 410 (2015) 202–208
205
Fig. 2. Influence of the temperature on the productivity and the MWv.
Run conditions: [PdCl2(dppb)] 8.3 × 10−4 mmol; Ptot 45 bar; CO/ethene = 1/1; reac-
tion time 1 h; solvent 80 mL: (a) H2O–HCOOH, H2O molar fraction = 0.58 (b)
H2O–AcOH, H2O molar fraction = 0.55, (c) H2O–EtCOOH, H2O molar fraction = 0.70.
step occurs only after a relatively high number of monomer inser-
tion steps. From the Arrhenius plot, the activation energy is 10.3,
18.1 and 18.6 kcalmol−1 for the copolymerization carried out in the
presence of HCOOH, AcOH or EtCOOH, respectively (see Supple-
mentary information). The activation energy is significantly lower
with HCOOH, the strongest of the three acids. This is in line with
the view that the acid may destabilize the ␤- and γ-chelate rings.
The strongest acid has the strongest destabilization capacity.
3.4. Influence of the pressure of the monomers on the
productivity and the MWv
Fig. 3. Influence of the partial pressure of a monomer, keeping constant the pressure
of the other monomer (10 bar), on the productivity and the MWv.
Run conditions: [PdCl2(dppb)] 8.3 × 10−4 mmol; temperature 90 ◦C; reaction time
1 h; solvent 80 mL: (a) H2O–HCOOH, H2O molar fraction = 0.58, (b) H2O–AcOH, H2O
mole fraction = 0.40.
The influence of the pressure of the monomers was studied
under conditions of compromise assuring values of both produc-
tivity and MWv relatively high, i.e. at 90 ◦C and 0.58 and 0.40H2O
molar fraction for the copolymerization carried out in H2O–HCOOH
or H2O–AcOH, respectively.
In H2O–AcOH the pressure of one monomer was varied from 10
to 60 bar, keeping constant the pressure of the other monomer at
10 bar. The productivity and the MWv vary as shown in Fig. 3, (1)
b and (2) b. Equations of the type (2) and (3) are proposed, whose
parameters are reported in Table 1. In each case, the calculated
productivities (continuous lines) fit well the experimental data.
3.4.1. Influence of the pressure of one monomer at constant
partial pressure of the other monomer
In H2O–HCOOH, the pressure of ethene was varied between
10 and 40 bar, at constant partial pressure of CO of 10 bar. The
other conditions are reported under Fig. 3. Both productivity and
MWv increase with increasing the pressure of ethane (Fig. 3, 1),
a). The productivity does not increase linearly with the pressure of
ethene. Linearization of the proposed power law Eq. (2) affords the
parameters k1 and ␣ reported in Table 1 (see the Supplementary
information).
3.4.2. Influence of the pressure of the monomers at a constant
total pressure
Fig. 4(a) shows how the productivity and the MWv vary upon
varying the pressure of the monomers under a total pressure of
50 bar in H2O–HCOOH. The highest productivity is achieved at a
CO/ethene ratio slightly >1. The “bell” shape behaviour suggests
that the monomers compete for coordination to the metal centre.
The combination of Eqs. (2) and (3) gives Eq. (4), in which
kobs is related to k1 and k2 by the relations (5). From k1 and
k2 is kobs = 139.40 and 156.98, respectively. The average value is
reported in Table 1. Analogously from k1 and k2 for the copolymer-
ization in H2O–AcOH, it is possible to calculate kobs = 368.79 and
372.33, respectively. The average value is reported in Table 1.
Productivity = k1·pE␣
(2)
Analogously, the pressure of CO was varied from 10 to 40 bar,
keeping the pressure of ethene constant at 10 bar. The productivity
is almost proportional to the pressure of CO (Fig. 3, 2), a). Lin-
earization of the proposed power law (3) allows us to achieve the
parameters k2 and ␤ reported in Table 1.
␤
Productivity = k2·pCO
(3)
␣
␤
Productivity = kobs·pE ·pCO
(4)
Table 1
Parameters of Eqs. (2)–(4) in H2O–HCOOH and H2O–AcOH.
␤
␣
k1 = kobs·pCO = k1 = kobs·10 bar1.028andk2 = kobs·pE
Acid
˛
k1
␤
k2
kobs
= kobs·10 bar0.55
(5)
HCOOH
AcOH
0.55
0.45
1192.2
905.3
0.93
0.39
557.1
1049.3
148.2
370.6

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M. Pagot et al. / Journal of Molecular Catalysis A: Chemical 410 (2015) 202–208
Fig. 4. Influence of the CO/ethene ratio at constant total pressure on the productiv-
ity and the MWv.
Fig. 5. Influence of the total pressure on the productivity and the MWv.
Run conditions: [PdCl2(dppb)] 8.3 × 10−4 mmol; CO/ethene = 1/1; reaction tem-
perature 90 ◦C; reaction time 1 h; solvent 80 mL: (a) H2O–HCOOH, H2O molar
fraction = 0.58, (b) H2O–AcOH, H2O molar fraction = 0.40.
Run conditions: [PdCl2(dppb)] 8.3 × 10−4 mmol; reaction temperature 90 ◦C; reac-
tion time 1 h; solvent 80 mL: (a) H2O–HCOOH, H2O molar fraction = 0.58, (b)
H2O–AcOH, H2O molar fraction = 0.40; Ptot: (a) 50 bar, (b) 70 bar.
Also in H2O–AcOH, the productivity and the LVN present a “bell”
shape behaviour (Fig. 4(b)). The highest productivity is achieved
for a CO/ethene slightly <1. The continuous line, drawn by intro-
ducing the parameters reported in Table 1 into an equation of type
(4), fits well the experimental data. In conclusion the parameters
reported in Table 1 represent a set of consistent kinetic constants
and exponential coefficients.
alyst precursor [PdCl2(P–P)] (P–P = 1,3-bis-(di(2-methoxyphenyl)
phosphino) propane) in H2O–AcOH [24]. The effects of the time
were rationalized as follows. The productivity is related to the rate
of the chain-growing and on their concentration, which in turn
depends on the concentration of the Pd-H+ initiator. The MWv
depends on the relative rates of the chain-growing and of the termi-
nation. After the termination process the re-formation of the active
Pd-hydride species becomes less efficient and/or that the copoly-
mer lowers the rate of the monomer insertion more than the rate
of the termination step. In addition, as the amount of polyketone
increases with time, the stirring may become less efficient [24].
The lowering of the productivity is evident in 3–5 h, particu-
larly at 90 ◦C. However, in the first hour, the copolymerization rate
remains almost constant, as it was found for the copolymerization
catalyzed by [PdCl2(dppf)] in H2O–HCOOH [27] and by the cata-
lyst formed in situ from Pd(AcO)2-dppp-acid or with preformed
[Pd(TsO)2(dppp)] in MeOH-toluene [36,37].
3.4.3. Influence of the total pressure with the monomers in the
ratio 1/1
Both the productivity and the LVN increase upon increasing the
total pressure as shown in Fig. 5. LVN increases regularly with the
increase of the total pressure. The productivity increases in agree-
ment with what found in 3.4.1. and 3.4.2..
3.5. Influence of the copolymerization time on the productivity
and the MWv
Fig. 6 shows how the productivity and the MWv vary with time.
In H2O–HCOOH, the productivity lowers of about 12.5 or 23% after
3 h and of 40 or 30% after 5 h at 90 ◦C or 65 ◦C, respectively. The MWv
is little affected at 90 ◦C, whereas it increases of about 26% after 5 h
at 65 ◦C. In H2O–AcOH the trends are similar. The productivity low-
ers of 27 and 53% after 5 h at 65 or 90 ◦C, respectively, under 45 bar
in both cases, and 57% under 70 bar at 90 ◦C after 5 h. The lowering of
the productivity and the increasing of the MWv with time has been
observed also for the copolymerization carried out using the cat-
3.6. Solid state NMR
The 13C NMR spectra of the different samples analysed are all
quite similar; as an example, the spectrum of sample I is shown in
the Supporting Information (Fig. S8). The spectra show signals at
35.7 and 209.3 ppm (referred to TMS, using adamantane as exter-
nal standard) for methylene and carbonyl carbons, respectively,
approximately in the ratio 2/1, and a weak signal at 6.5 ppm for the
terminal methyl carbon (there are also signals due to spinning side

M. Pagot et al. / Journal of Molecular Catalysis A: Chemical 410 (2015) 202–208
207
being in sample IV (on the nature of samples I–IV samples, see
Experimental). These results suggest that the solvent composition
exerts some influence on the morphology of the polymer, affecting
both the crystallinity as well as the mobility of the crystalline and
amorphous phases.
4. Conclusions
The CO-ethene copolymerization catalyzed by [PdCl2(dppb)]
in H2O-H(CH2)nCOOH (n = 0, 1 or 2) yields an alternating polyke-
tone in high yield and of relatively high molecular weight without
the formation of lower products. The influence of the reaction
conditions on the productivity and the MWv is investigated. The
reaction is strongly influenced by the composition of the solvent
and the strength of the acid. The highest productivity is achieved
with the strongest of the acid, HCOOH [14,800 gPK(g Pd h)−1, H2O
molar fraction = 0.58, 45 bar, CO/ethene = 1/1, 90 ◦C; LVN = 0.48;
MWv = 21,194 Da]. It is remarkable that the obtained productivi-
ties were generally higher than those reported in the literature for
the corresponding cationic [Pd(TsO)2(dppb)] systems in MeOH as
solvent [29]. The productivity remains almost constant in the first
hour of the reaction, then it lowers to some extent. The kinetic
parameters of power rate laws, which fit the experimental data
at different monomer pressures, are calculated.The ascertained
effects of the main reaction parameters on the productivity and
polymer characteristics are explained on the basis of the copoly-
merization mechanism. Solid state NMR results suggest that the
solvent composition exerts some influence on the morphology of
the polymer, affecting both the crystallinity as well as the mobility
of the crystalline and amorphous phases.
Acknowledgement
The authors thank MIUR for financial support.
Appendix A. Supplementary data
Fig. 6. Influence of the reaction time on the productivity and the MWv.
Run conditions: [PdCl2(dppb)] 8.3 × 10−4 mmol; (a), CO/ethene = 1/1; 80 mL sol-
vent: (a) H2O–HCOOH, H2O molar fraction = 0.58, (b) H2O–AcOH, H2O molar
fraction = 0.40.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molcata.2015.09.
026.
bands at ca. 330, 155 and 90 ppm). In order to obtain the degree
of crystallinity, 1H FIDs were recorded and analysed. A fitting of
the experimental FIDs was performed using a linear combination
of suitable analytical functions, each characterized by a spin–spin
relaxation time T2. A good fitting of the decays was obtained in
all cases assuming the superposition of a Pake type [38,39] and an
exponential function, the former ascribable to the crystalline phase,
the latter to armorphous domains. An example of the fitting curves
is shown in Fig. S10, and the best fitting parameters are given in
Table S11. The results of the fitting procedure indicated that all
polymers are highly crystalline, with the fraction of Pake function,
which can be considered corresponding to the crystallinity degree,
ranging from 78 to 88%, the less crystalline sample being sample IV,
i.e. the one with higher water fraction in the solvent. The other three
samples, differing in the acid used for the synthesis, showed sim-
ilar crystallinity (85–88%), with sample I, obtained using HCCOH,
displaying the highest crystallinity degree. It must also be pointed
out that whereas the crystalline phase in samples II and III resulted
to have a similar Pake ␤ parameter (inversely proportional to T2),
the more crystalline sample I resulted to have a higher ␤ value
(and hence a smaller T2 value) indicating higher rigidity, whereas
the less crystalline sample IV had the lowest ␤ value (and hence
highest T2) indicating a less rigid crystalline phase. As far as the
amorphous component is concerned, samples I and II showed sim-
ilar higher T2 values (92–97 ␮s), sample III showed an intermediate
value (76 ␮s), and sample IV the smallest value (69 ␮s), indicating
that the samples differ also in the mobility of the amorphous phase,
the more mobile ones being in samples I and II, the less mobile
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