Synthesis and characterization of polycarbonates by melt phase interchange reactions of alkylene and arylene diacetates with alkylene and arylene diphenyl dicarbonates

Article abstract of DOI:10.3390/molecules15053661

This work presents a new synthetic approach to aromatic and aliphatic polycarbonates by melt polycondensation of bisphenol A diacetates with alkylene- and arylenediphenyl dicarbonates. The diphenyl dicarbonates were prepared from phenyl chloroformate and

Full text of DOI:10.3390/molecules15053661

Molecules 2010, 15, 3661-3682; doi:10.3390/molecules15053661
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Characterization of Polycarbonates by Melt
Phase Interchange Reactions of Alkylene and Arylene Diacetates
with Alkylene and Arylene Diphenyl Dicarbonates
Bassam A. Sweileh 1,*, Yusuf M. Al-Hiari 2, Mohammad H. Kailani 1 and Hani A. Mohammad 3
1
Department of Chemistry, Faculty of Science, The University of Jordan, Amman 11942, Jordan;
E-Mail: kailani@ju.edu.jo (M.H.K.)
2
Department of Pharmaceutical Sciences, Faculty of Pharmacy, The University of Jordan, Amman
11942, Jordan; E-Mail: hiary@ju.edu.jo (Y.M.A.-H.)
3
Department of Chemistry, Faculty of Arts and Sciences, University of Petra, P.O. Box 961343,
Amman 11196, Jordan; E-Mail: hanimohammad@uop.edu.jo (H.A.M.)
* Author to whom correspondence should be addressed; E-Mail: sweilehb@ju.edu.jo;
Tel.: +96-26 5355000 (Ext. 22134); Fax: +96-26 5300253.
Received: 4 March 2010; in revised form: 17 May 2010 / Accepted: 18 May 2010 /
Published: 18 May 2010
Abstract: This work presents a new synthetic approach to aromatic and aliphatic
polycarbonates by melt polycondensation of bisphenol A diacetates with alkylene- and
arylenediphenyl dicarbonates. The diphenyl dicarbonates were prepared from phenyl
chloroformate and the corresponding dihydroxy compounds. The process involved a
precondensation step under a slow stream of dry argon with the elimination of phenyl
acetate, followed by melt polycondensation at high temperature and under vacuum. The
potential of this reaction is demonstrated by the successful synthesis of a series of
aromatic-aromatic and aromatic-aliphatic polycarbonates having inherent viscosities from
0.19 to 0.43 dL/g. Thus low to intermediate molecular mass polymers were obtained. The
13C-NMR spectra of the carbon of the carbonate group showed that the formed
polycarbonates contain partial random sequence distribution of monomer residues in their
1
chains. The polycarbonates were characterized by inherent viscosity, FTIR, H-NMR and
13C-NMR spectroscopy. The glass transition temperatures, measured by DSC, of the
polycarbonates were in the range 13–108 ºC. The thermogravimetric curves of showed that
these polymers have good thermal stability up to 250 ºC. The present approach may open
the door for novel polycarbonates containing other organic functional groups.

Molecules 2010, 15
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Keywords: diphenyl dicarbonate; diacetates; polycondensation; polycarbonates; synthesis;
interchange reactions
1. Introduction
Polycarbonates are high heat engineered thermoplastic polymers having unique properties. They are
characterized by outstanding mechanical, optical and thermal properties and have a wide range of
applications [1–8]. Aromatic polycarbonates derived from bisphenol A have been extensively studied
and found to be interesting because of their useful properties; such as rigid molecular structure,
exceptional impact resistance, chemical and dimensional stability, toughness, optical clarity, and
thermal stability [6–8,9–11]. They also offer excellent moldability and extrudability, good fire
resistance, dimensional stability, and high optical transparency opening the door for a wide range of
industrial applications [1,12]. Other properties such as modulus, dielectric strength and tensile strength
are comparable to other amorphous thermoplastics at similar temperatures below their respective glass
transition temperatures (Tgs). However, while most amorphous polymers are stiff and brittle below
their Tg values, polycarbonates retain their ductility and impact resistance below their Tg values [1].
Polycarbonates are prepared industrially by two different processes: 1) Schotten-Baumann reaction
of phosgene with an aromatic dihydroxy compound in an amine-catalyzed interfacial polycondensation
reaction and 2), base-catalyzed transesterification of a bisphenol with diphenyl carbonate [1,3,4,13].
The first process uses phosgene, which is known for its high toxicity and lethality, whereas
dichloromethane is suspected to be a carcinogen and a source of chlorine in producing dioxin [14]. The
method also produces sodium chloride wastes contaminated with organic substances [15]. Since there
is an increasing pressure to avoid using chlorinated organic solvents in the chemical industry, the
search for environmentally benign synthetic routes to polycarbonates that don’t involve phosgene and
chlorinated solvents is still required [2,4,14,16]. The second process utilizes diphenyl carbonate (DPC),
now prepared by a variety of nonphosgene methods [1,17,18] in a melt phase polycondensation
reaction. The high temperatures of the reaction melt, the low pressures, the high viscosity of the
polymer melt, the difficulty to regulate the molecular weight and the side reactions that give a slightly
yellowish color to the product are major drawbacks of this process [1,3,4].
Numerous polycarbonates based on bisphenol A (BPA) and other diphenols and aliphatic diols have
been prepared to improve the physical properties of homopolycarbonates. Among the main variations
carried on polycarbonates was the synthesis of liquid crystalline polycarbonate as poly(alkylene
carbonate)s. Aliphatic polycarbonates have attracted lesser attention as structural materials compared
to aromatic polycarbonates due to their poor mechanical properties. Nevertheless, they show potential
as biodegradable and biocompatible materials for drug delivery systems [5,19–21]. Aromatic–aliphatic
polycarbonates are a combination of aliphatic and aromatic components to improve the flexibility and
elasticity of aromatic polycarbonates and enhancing the poor physical properties of aliphatic
polycarbonates [22].
Alkylene- and arylenediphenyl dicarbonates were used as monomers reacting with aliphatic and
aromatic dihydroxy compounds by melt polycondensation for the synthesis of polycarbonates. Several

Molecules 2010, 15
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studies used this reaction for the synthesis and investigation of thermotropic liquid crystalline
properties of homo-, co-, and terpolycarbonates prepared by this method [23–32]. Liaw and coworkers
[9,33,34] used selected arylene- and alkylenediphenyl dicarbonats (e.g., bisphenol AF diphenyl
dicarbonate) to prepare copolycarbonates via melt polycondensation with bisphenols (e.g., bisphenol
S) and studied their thermal properties.
Many literature methods have been reported for the preparation of polycarbonates utilizing
bisphenol A diaceatate as a starting monomer. The methods comprise reactions with dicarboxylic acid
dimethyl esters and diol dicarbonates [35] dialkyl carbonates in the melt [2] or with dialkyl or diaryl
carbonate in presence of an inert high boiling solvent [36–39].
We have recently been interested in the melt-phase interchange process for the preparation of
polycarbonates from alkylene- and arylenediphenyl dicarbonates and dihydroxy compounds in an
effort to direct the technology to environmentally friendly processes [22,40]. In this context, the
reported literature utilizing BPA diacetate (BPAAc2) involves reaction with dimethyl carbonate
(DMC) [2]. In the course of our program of work involving the study of preparation of polycarbonate,
we investigated the synthesis of polycarbonates by a different reaction. Thus the synthesis of
polycarbonates from alkylene- or arylenediacetate reacting with alkylene- or arylenediphenyl
dicarbonates instead of DMC was examined. This approach is completely novel and has no precedent
in the literature. Therefore, the objective of this work was to study a new synthetic method to
polycarbonates by melt-phase polycondensation of alkylene- and arylenediacetate with alkylene- and
arylenediphenyl dicarbonates. The advantage of this reaction is that it permits varying the structures of
the alkylene and arylene units in both monomers which would lead to polymers with widely varying
structures and properties (e.g., thermal properties, i.e. Tg). This article presents the results of this study.
2. Results and Discussion
2.1. Synthesis and characterization of monomers
The synthetic approach used in this work was based on interchange reaction of alkylene- or arylene-
diacetates with alkylene- or arylenediphenyl dicarbonates. Bisphenol A diacetate (BPAAc2) used was
a commercial sample. 1,4-Cyclohexanedimethylene diacetate (CHDMAc2) was prepared from
1,4-cyclohexanedimethanol (CHDM) and acetyl chloride in the presence of excess pyridine in
chloroform solution. The alkylene- and arylenediphenyl dicarbonates were prepared in THF solution
by the reaction of the various dihydroxy compounds with phenyl chloroformate (PCF) in the presence
of excess pyridine [33] as shown in Scheme 1. The structures of 1,4-cyclohexanedimethylene diacetate
and the diphenyl dicarbonate monomers, which were obtained in high yields as white solids or slightly
1
viscous liquids, were confirmed by melting point, IR spectroscopy, H-NMR and 13C-NMR
spectroscopy. The yields and the physical properties of the diacetate and the alkylene- and arylene-
diphenyl dicarbonate monomers are presented in Table 1.

Molecules 2010, 15
Scheme 1. Synthesis of alkylene- and arylenediphenyl dicarbonate monomers.
3664
O
,
O
O
0-5 C
N
2
+
HO
X
OH
X
DMAP, THF
Cl
O
O
O
O
O
X
,
,
,
,
R
(CH2)2
(CH2)3
(CH2)4
(CH2)5
H2C
CH2
X
,
,
,
,
Ar
Table 1. The yield and physical properties of alkylene- and arylenediphenyl dicarbonate
and diacetate monomers.
Yield (%) Tm (°C)
C-O-C (cm-1)
C=O (cm-1)
Diphenyl dicarbonates
1,2- Ethanediol
1,3-Propanediol
1,4-Butanediol
92.7
87.5
89.8
94.4
90.2
83.3
85.1
87.1
94
52
82
52
1209, 1257
1210, 1242
1205, 1260
1210, 1252
1757
1761
1754
1760
1755
1787
1775
1769
1768
1775
1,5-Pentanediol
1,4-Cyclohexanedimethanol
Catechol
145–150 1208, 1260
100–103 1197, 1245
126
Resorcinol
1128, 1163, 1234
Hydroquinone
124
1271
4,4'-Bis(hydroxyphenyl)methane 91.6
97–100
90
1158, 1184, 1253
1170, 1189, 1235
Bisphenol A
84.4
Diacetates
Bisphenol A diacetate
1,4-Cyclohexanedimethanol
diacetate
—
87
89–91
70
1170, 1210
1239
1755
1741
The diacetate and diphenyl dicarbonate monomers were obtained in high yields. The melting points
of the alkylene- and arylenediphenyl dicarbonates were in the range 52–150 °C. 1,3-Propanediol
diphenyl dicarbonate (PrD DPDC) and 1,5-pentanediol diphenyl dicarbonate (PeD DPDC), which have
odd-carbon numbers in the alkane chain, showed the lowest melting points of all of the synthesized
diphenyl dicarbonates. Even-carbon number alkylenes diphenyl dicarbonates fit better in their crystal
lattices than odd ones probably due to their structural symmetry and thus exhibited slightly higher
melting points. On the other hand, 1,4-cyclohexanedimethylene diphenyl dicarbonate (CHDM DPDC)
showed unexpectedly the highest melting point among the diphenyl dicarbonates prepared. This fact
may have been due to that the molecule contains a number molecular sections (i.e., the chair
cyclohexane ring, the carbonate group and the phenyl group) which can fit very well to the

Molecules 2010, 15
3665
corresponding planes is another molecule, so they can stack easily in their crystal lattice. It seems that
the chair conformation of the cyclohexylene ring although not planar it permits good packing. It has
been reported that the incorporation of trans-1,4-cyclohexylene units in the backbone of glassy
poly(ester carbonate)s improves chain packing due to ring inversion and the shape of the trans
1,4-cyclohexylene rings [41] (Figure 1).
Figure 1. The structure of CHDM DPDC showing the various planar molecular sections.
O
O
O
O
O
O
O
O
O
O
O
O
2.1.1. Infrared spectroscopy
The FTIR spectra of BPA diacetate and CHDM diacetate (Figure 2 and Table 1) showed strong
absorption bands due to the C=O stretching vibration of the ester group at 1,755 and at 1,741 cm-1,
respectively.
Figure 2. FTIR spectra of (a) BPA diacetate (b) CHDM diacetate (c) BPA DPDC (d)
CHDM DPDC (e) BPA-PeD polycarbonate (f) CHDM-BHPM polycarbonate.

Molecules 2010, 15
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The absorption bands of the C-O-C stretching vibrations of BPA diacetate were observed at 1,170
and 1,210 and that of CHDM diacetate at 1,239 cm-1. The IR spectra of diphenyl dicarbonate
monomers (Figure 2 and Table 1) showed strong absorption bands due to the C=O stretching vibration
of the carbonate group from 1,768 to 1,787 cm-1 for arylene diphenyl dicarbonates, and from 1,754 to
1,761 cm-1 for alkylene diphenyl dicarbonates. The absorption bands of the C-O-C stretching
vibrations for both alkylene and arylene diphenyl dicarbonates were observed in the 1,158 to
1,271 cm-1 range. These IR data are typical for the carbonate group [22,23,32,33,40] and thus suggest
the formation of the proposed diacetate and diphenyl dicarbonate monomers in this work.
2.1.2. NMR spectroscopy of monomers
1
1H-NMR Spectra: The H-NMR data for selected alkylene- and arylenediphenyl dicarbonates and
diacetates are listed in Table 2. The 1H-NMR spectrum of BPA diacetate showed the aromatic protons
of the BPA unit as an AB splitting system ranging from δ = 7.0 to 7.2. The methyl protons of the BPA
unit were observed in the spectrum as a singlet at δ = 1.65, whereas the methyl protons of the acetate
1
group were observed as a singlet at δ = 2.27. In the H-NMR spectrum of CHDM diacetate, the
terminal methylene protons of attached to the ester group were observed as a doublet centered at
δ = 3.81. The cyclohexylene ring tertiary CH protons were observed at δ = 1.74 whereas the CH2 ring
protons were observed at δ = 1.0–1.7. The methyl protons of the acetate group were observed as a
1
singlet at δ = 1.98. Regarding the diphenyl dicarbonate monomers, the H-NMR spectra of the
following diphenyl dicarbonates: 1,2-ethanediol (EG DPDC), 1,3-propanediol (PrD DPDC),
1,4-butanediol (BuD DPDC), 1,5-pentanediol (PeD DPDC), resorcinol (RESOL DPDC), and hydro-
quinone (HQ DPDC) were fully described in our previous publications [22,40]. The monomers:
catechol diphenyl dicarbonates (CAT DPDC), and bis(4-hydroxyphenyl)methane diphenyl
dicarbonates (BHPM DPDC), were introduced in this work. Here the spectra of the new diphenyl
dicarbonate monomers utilized are only described. The 1H-NMR spectrum of CHDM DPDC showed a
doublet peak for the protons of the terminal methylene group attached to the carbonate group at
δ = 4.08.
O
H2C
CH2
CH
CH2
CH2
CH
OCO
H2C
Table 2. 1H and 13C-NMR data for selected alkylene- and arylenediphenyl dicarbonates and diacetates.
Chemical shift δ (ppm)
1
2
3
4
5
6
7
8
9
10
11
Dicarbonate
3
5
9
1H
4.08
1.91
1.0-
1.0-
1.91
4.08
—
—
a
a
a
4
1
6
O
7
O
8
10
11
2
1.7
1.7
13C
73.5
37.0
28.6
28.6
37.0
73.5
—
153.9 151.2 121.1 129.6
126
a
O
O
1
1H
—
a
a
a
a
—
—
a
a
9
O
O
6
7
8
2
3
10
11
13C
142.2
123
126.6 126.6
123
142.2 151.3
151
121
129.7 127.3
O
5
4
1H
4.0
—
a
a
—
—
—
a
a
a
4
8
7
5
6
O
O
3
9
2
13C
40.6
138.8 129.6
121
149.5 152.2
151
121
130
126.4
1
O
10

Molecules 2010, 15
3667
Table 2. Cont.
Diacetate
1
1H
13C
1H
1.65
—
—
7.20
6.97
—
—
2.27
4
3
5
6
O
2
O
7
31.0 42.5 147.9 127.9 121 148.6 169.6 21.2
8
8
O
O
O
5
3
3.81 1.74
69.4 37
1.0-
1.7
23.76 23.76
1.0-
1.7
1.74
37
3.81
—
1.98
21
4
1
6
O
7
2
13C
69.4 171.2
O
O
a The aromatic proton signals appear in the range δ = 7.1-7.5 as multiplets.
The peak for the tertiary CH ring proton was observed at δ = 1.91, whereas the CH2 ring protons
were observed in the 1.0–1.7 range. The proton peaks of all arylenediphenyl dicarbonates were
collectively observed as asymmetric multiplets interfering with the symmetrical signals of the various
arylene units at δ = 7.1–7.5. In the spectrum of BHPM DPDC the aliphatic methylene protons of the
BHPM unit (–C6H5–CH2–C6H5–) were observed as a singlet at δ = 4.0. The signals for the aromatic
protons of the phenyl rings of the diphenyl dicarbonates were observed at δ = 7.1–7.4.
13C-NMR Spectra: The carbon signals of the BPA unit in BPA diacetate were observed in the
spectra at the correct chemical shifts for this unit. The signal of the aliphatic quaternary carbon atom
bearing the methyl groups appeared at δ = 42.5, while that of the methyl carbon atoms appeared at
δ = 31.0. The signal of the aromatic quaternary carbon atoms of the rings next to the aliphatic
quaternary carbon appeared at δ = 147.9. The signals of the quaternary carbon atoms of the aromatic
rings attached to the ester group appeared at δ = 148.6. The signals of the carbon atoms of the ring in
ortho and meta positions to the quaternary carbon atoms attached to the ester group appeared at
δ = 121 and at 127.9. The signal of the methyl carbon atom of the acetate group appeared at δ = 21.2.
The signal of the carbonyl carbon of the ester function was observed at δ = 169.6, which is the correct
position for this type of carbonyl carbon.
In the 13C-NMR spectrum of CHDM diacetate, the peak of the terminal methylene carbon attached
to the ester group appeared at δ = 69.4 ppm. The peak of the tertiary CH carbon atom of the
cyclohexylene ring appeared at δ = 37.0. The peak of the methylene ring carbon atoms appeared at
δ = 28.8. The signal of the methyl carbon atom of the acetate group appeared at δ = 21.0 ppm. The
signal of the carbonyl carbon of the ester function appeared at δ = 171.2 ppm.
The 13C-NMR spectra of EG DPDC, PrD DPDC, BuD DPDC, PeD DPDC, RESOL DPDC, and HQ
DPDC were fully described in our previous works [22,40]. The 13C-NMR spectrum of CHDM
diphenyl dicarbonate showed peaks due to the terminal methylene carbon atoms (–OCOOCH2–)
attached to the carbonate group at δ = 73.5. The peak of the tertiary CH carbon atom was observed at
δ = 37.0 and that of the ring methylene carbon atoms at δ = 28.6, respectively. The aromatic catechol
ring carbon atoms of catechol diphenyl dicarbonate attached to the carbonate group appeared at
δ = 142.2 and those ortho to them at 123 whereas those meta to them at δ = 126.6. The peak of the
aliphatic methylene carbon atom of BHPM diphenyl dicarbonate was observed at δ = 40.6. The peak of
the quaternary aromatic carbon atoms attached to the aliphatic methylene carbon atoms was observed
at δ = 138.8 while that of the quaternary aromatic carbon atoms attached to the carbonate group was
observed at δ = 149.5. The peak of the carbonyl carbon of catechol and that of BHPM were observed
at δ = 151.3 and 152.2, respectively.

Molecules 2010, 15
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2.2. Synthesis and characterization of polycarbonates
The various polycarbonates (Scheme 2) were synthesized from alkylene or arylene diacetates and
alkylene- or arylenediphenyl dicarbonates. The polymerization reaction proceeded by the catalyzed
nucleophilic reaction of the acetate group of the diacetate with the phenyl carbonate group of the
diphenyl dicarbonate molecule using Ti(OBu)4 as the transesterification catalyst. The reaction afforded
aromatic-aromatic, aromatic-aliphatic as well as aliphatic-aliphatic polymers. This assertion follows
1
13
from the spectroscopic analysis of the formed polycarbonates especially the H-NMR and C-NMR
spectra of the alkylene and arylene groups attached to the carbonate group and from the analysis of the
carbonyl carbon peak of the carbonate group. It was found that conducting the polycondensation
reaction at and above 240 °C did not afford any polymers, whereas at 220 °C it led to the formation of
methanol insoluble polycarbonates.
Scheme 2. Synthesis of polycarbonate by melt polycondensation of alkylene and arylene
diacetates with alkylene and arylene diphenyl dicarbonates (Series A and B).
O
_
O
O
O
O
O
O
O
X'
X'
X
+
,
X
O
O
Ti(OBu)4
O
O
O
O
O
O
O
O
X' =
1A
4A
2A
3A
,
,
(CH2)2
(CH2)3
(CH2)4
(CH2)5
X
X
5A
7A
8A
6A
,
,
,
CH2
CH2
X' =
1B
2B
3B
4B
,
,
,
CH2
CH2
(CH2)4
X
2.2.1. Solution viscosity measurements
The inherent viscosities of the polycarbonates were calculated from viscosity measurements of
dilute polymer solutions (0.5 g/dL) in chloroform at 25 °C. The polycarbonates had inherent viscosities
(Table 3) in the range from 0.19 to 0.43 dL/g. The synthesized polycarbonates had low to intermediate
inherent viscosities, which implies that polymers with low to moderate molecular masses were

Molecules 2010, 15
3669
obtained. The differences in the observed inherent viscosities (i.e., molecular mass) may be attributed
to the adverse effect of some factors.
An important factor that would limit the attainment of high molecular mass polycarbonates is the
fact that the diphenyl dicarbonate and BPA diacetate compounds have unequal volatility at the
polymerization conditions. This difference in volatility would slightly disturb the stoichiometric
balance of the monomers in the reaction melt and would lead to polycarbonates with lower viscosities.
The occurrence of other interchange reactions during polymerization is also another factor. The major
and most reactive interchange reaction taking place for polymer chain buildup was the nucleophilic
attack of the acetate group of BPA diacetate upon the phenyl carbonate group of the diphenyl
dicarbonate monomer. This reaction yields linear polycarbonate chains in which the two monomer
units are connected alternately along the entire length of the polymer chain. In addition to this reaction,
another possible reaction was the self-condensation of the diphenyl dicarbonate monomer. Another
possible competing reaction that could also occur was the partial elimination of cyclic aliphatic
carbonates from the alkylene diphenyl dicarbonates or from already formed polymer chains. In fact, in
this study, it was observed that EG DPDC or CAT DPDC reacting with bisphenol A diacetate, did not
afford the postulated polycarbonate. In the synthesis of BPA-CAT polycarbonate, the formation of
catechol cyclic carbonate was found to be the exclusive reaction occurring in the reaction melt. In
addition to these reactions and under our experimental conditions, the formed polymer chains may
undergo polymer-polymer, or polymer-monomer interchange reactions which would lead to viscosity
alterations. In fact, these side reactions are essentially similar to the polycondensation reaction and
would also occur under the same reaction conditions.
Table 3. Physical properties of polycarbonates as a function of the structure of the monomers.
Inherent viscosity
Sample Polycarbonate Polym code IR [v (cm-1)] C=O C-O
Tg (°C)
(ηinh) (dL/g)
Series A
1
2
BPA-EGa)
BPA-PrD
1A
2A
—
—
—
—
1,764
1,164, 1,194, 0.19
1,231
68.1
3
BPA-BuD
3A
1,761
1,164, 1,195, 0.23
1,245
56.5
4
5
6
7
BPA-PeD
4A
5A
6A
7A
1,761
—
1,218, 1,250 0.24
49.5
—
BPA-CAT a)
BPA-RESOL
BPA-HQ
—
—
1,777
1,772
1,164, 1,203 0.24
1,163, 1,193, 0.26
1,228
83.1
97.0
8
BPA-BHPM
8A
1,772
1,161, 1,188, 0.27
1,231
107.8

Molecules 2010, 15
3670
Table 3. Cont.
Series B
9
CHDM-BuD
1B
1,743
1,743
1,761
1,760
1,254
1,252
0.43
0.36
13.0
38.7
90.4
56.9
10
11
12
CHDM-CHDM 2B
CHDM-BPA
3B
1,216, 1,249 0.29
1,185, 1,220, 0.24
1,251
CHDM-BHPM 4B
a) Polycarbonate soluble in methanol.
2.2.2. Infrared spectroscopy
The FTIR spectra of the polycarbonates showed strong absorption bands due to the C=O stretching
vibration of the carbonate group from 1,772 to 1,777 cm-1 for aromatic-aromatic polycarbonates and
from 1,761 to 1,764 cm-1 for aromatic-aliphatic polycarbonates and at 1,743 cm-1 for aliphatic-aliphatic
polycarbonates. Strong absorption bands due to the C–O–C stretching frequency for all polycarbonates
were observed in the range from 1,161 to 1,254 cm-1 (Figure 2 and Table 3). These IR data are in
accordance with the literature [22,23,32,33,42–44] and, therefore, confirm the formation of the various
polycarbonates in this work. It was, however, observed that the C=O stretching vibration of aliphatic-
aliphatic polycarbonate (1,743 cm-1) was very close to that of CHDM diacetate (1,741 cm-1). This
confusion was resolved by the disappearance of the 1H-NMR signal of the methyl group and 13C NMR
peak of the C=O of the ester group of the diacetate monomer in the NMR spectra of the final
polycarbonates.
2.2.3. NMR spectra of polycarbonates
1H-NMR spectra: The polymers synthesized in series A exhibit a similarity in the core structure,
derived from BPA diacetate, but differ in the alkylene or the arylene parts of the various diphenyl
dicarbonates. Therefore, the change in the pattern of the spectra could be correlated with the alkylene
1
or arylene parts of the DPDC monomers in both aliphatic and aromatic polymers. The H-NMR
spectra for the BPA unit were similar in terms of position and pattern of proton signals to those of the
BPA diacetate for all polycarbonates. With regard to the aliphatic chains, the signal for the protons of
the terminal methylene groups (–OOCOCH2–) attached to the carbonate group was observed in the
range δ = 4.23–4.35 for all of the polycarbonates. The protons of the aliphatic methylene group next to
the terminal methylene groups (–OOCOCH2CH2–) in the polycarbonates of BPA with Pr-1,3-D, Bu-
1,3-D, and Pe-1,5-D were observed in the range δ = 1.77–2.14 with the correct pattern of splitting in
1
each polycarbonate. In all H-NMR spectra of the polycarbonates, the peak of the protons of the
methyl group of the acetate group, which was observed as singlet peak at δ = 2.27 in BPA diacetate
was completely absent. The 1H-NMR spectra of the aromatic–aromatic polycarbonates were generally
not indicative in confirming the chemical structures of these polycarbonates. The signals of the protons
of the aromatic rings were collectively observed at δ values in the range δ = 7.1–7.3. The peak of the
protons of the benzylic methylene group (–C6H5–CH2–C6H5–) of BHPM unit in BPA-BHPM

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1
polycarbonate was observed at δ = 3.92. These data, deduced from the H-NMR spectra, confirm the
formation of aromatic aliphatic polycarbonates.
Parallel to series A polycarbonates, the chemical structure of the polycarbonates synthesized in
series B consisted of a cyclohexanedimethylene unit bonded to different alkylene or arylene units
through a carbonate group. The 1H-NMR spectra for the CHDM unit showed slightly shifted positions
1
of proton signals of the CHDM diacetate monomer. The H-NMR spectrum of CHDM unit showed a
doublet peak for the protons of the terminal methylene group attached to the carbonate group in the
range from δ = 3.91–4.00. The peak for the tertiary CH ring proton was observed in the range from
δ = 1.80–1.85 whereas the CH2 ring protons was observed in the same range at δ = 1.0–1.7. With
regard to the aliphatic chains, the signals for the protons of the terminal methylene group
(–OOCOCH2–) of BuD moieties attached to the carbonate group were observed at δ = 4.12. The
protons of the aliphatic methylene group next to the terminal methylene groups (–OOCOCH2CH2–)
was observed at δ = 1.73.
O
H2C
CH2
2
2
C
H2
CH
1
CH
OCO
1
H2C
CH2
The proton signals of BPA and BHPM units in the polymers of series B were observed at
1
approximately the same positions as those in series A. In all H-NMR spectra of the polycarbonates,
the peak of the protons of the methyl of the acetate group, which was observed as singlet peak at
δ = 1.98 in CHDM diacetate monomer, was completely absent. These data, deduced from the 1H-NMR
spectra, confirm the formation of the various polycarbonates.
The disappearance of the proton singlet peaks of the methyl groups of the acetate function of both
BPA diacetate (observed at δ = 2.27) and CHDM diacetate (observed at δ = 1.98) monomers from the
1H-NMR spectra of the various polycarbonates, indicates that the polycondensation reaction has
occurred via these groups. Furthermore, the attachment of the terminal methylene group to the
carbonate oxygen atom led to a downfield shift in the position of the signal in the spectrum to
δ = 4.23–4.35. These facts were highly indicative and represent a spectral evidence of the formation of
the various polycarbonates in this work.
13C-NMR spectra: The 13C-NMR spectra of the polycarbonates were quite informative and showed
signals due to all aliphatic carbon atom types. Again the polymers synthesized exhibit a similar core
structure derived from BPA diacetate, but differs in the alkylene or the arylene parts of the various
diphenyl dicarbonates. The change in the pattern of the spectra could also be correlated with the
13
alkylene or arylene parts in both aliphatic and aromatic polymers. The C-NMR spectra for the BPA
unit were similar to those reported above for the BPA unit in BPA diacetate monomer for all
polycarbonates.
With regard to the aliphatic chains of the polycarbonates in series A, the carbon atoms of the
terminal methylene groups (–OOCOCH2–) attached to the carbonate group showed downfield effects
1
similar to those observed in the H-NMR spectra and their signals appeared in the spectra of the
polycarbonates of BPA with Pr-1,3-D, Bu-1,4-D, and Pe-1,5-D in the range δ = 65.1–68.5. The signals
of the aliphatic methylene carbon atoms next to the terminal methylene carbons (–OOCOCH2CH2–)
appeared in the range δ = 25.2–28.3.

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The 13C-NMR spectra of the aromatic-aromatic polycarbonates, also confirmed the chemical
structures of these polycarbonates. The signal of the quaternary carbon atoms of the aromatic rings of
the dihydroxy compounds attached to the carbonate group appeared at δ = 148.3–151.4. The signal of
the quaternary carbon atoms of the aromatic rings linked to the aliphatic quaternary carbon atom in
BPA and in BHPM units, appeared in the range δ = 139–149. The signals of the carbon atoms of the
aromatic rings of all aromatic dihydroxy compounds in ortho and meta positions to the quaternary
carbon atom appeared in the range δ = 114–130. The peak of the carbon atom of the aliphatic
methylene group (–C6H5–CH2–C6H5–) of BHPM unit in BPA-BHPM polycarbonate was observed at
δ = 40.6. The characteristic signal of the carbonyl carbon of the carbonate group in all polycarbonates
appeared in the range δ = 152.2–153.9. In all 13C-NMR spectra, the signals of the methyl carbon atom
of the methyl acetate group and the carbonyl carbon of the ester group of BPA diacetate were
completely absent.
13
13
Regarding the C-NMR spectra of series B polycarbonates, the C-NMR spectra for the CHDM
unit showed slightly shifted positions for the carbons peaks of the CHDM diacetate monomer.
O
2
2
C
H2
1
1
OCO
The signal of the terminal methylene carbon atoms of cyclohexanedimethylene unit attached to the
carbonate group appeared in the range δ = 72.8–73.1. The signal of the tertiary CH carbon atom and
the methylene carbon atoms CH2 of the cyclohexylene ring, labeled 1 and 2 appeared at δ = 37.0 and
δ = 28.6, respectively. With regard to CHDM-BuD polycarbonate, the terminal methylene carbon
atoms of the BuD moiety (–OOCOCH2–) attached to the carbonate group and those next to them
(–OOCOCH2CH2CH2–) showed their peaks at δ = 67.3 and δ = 25.2, respectively. The signals of the
aromatic and aliphatic carbon atoms of BPA in CHDM-BPA polycarbonate and those of BHPM in
CHDM-BHPM polycarbonate as well as their quaternary carbon atoms appeared approximately at the
same positions as those observed in series A polycarbonates. The signal of the carbonyl carbon of the
carbonate group in the polycarbonates of series B appeared in the range δ = 153.9–155.5. In all
13C-NMR spectra of the polycarbonates synthesized, the signal of the methyl carbon atom of the
methyl acetate group of CHDM diacetate and the carbonyl carbon of the ester group, which appeared
13
at δ = 21 and 171.2 ppm, were completely absent. The C-NMR spectra of CHDM diacetate, BuD
DPDC and CHDM-BuD polycarbonate (Series B) are compared in Figure 3.
The disappearance of peaks 7 and 8 of CHDM diacetate (Figure 3, spectrum 1) and peaks 7, 8 and 9
13
of BuD diphenyl dicarbonate (Figure 3, spectrum 2) from the C-NMR spectrum of the CHDM-BuD
polycarbonate (Figure 3, spectrum 3), indicates that the polycondensation reaction has occurred via the
methyl acetate and the phenyl carbonate groups of the monomers. This fact also represents a spectral
evidence of the formation of the various polycarbonates in this work.
2.2.4. 13C-NMR spectral evidence of unit sequence randomization
In addition to the above findings, a spectral evidence for the existence of structural variations within
the polymer backbone of the polycarbonates was also observed. An interesting pattern of peaks
observed in the 13C-NMR spectra of almost all polycarbonates synthesized was the appearance of three

Molecules 2010, 15
3673
peaks for the carbon atom of the carbonate group (C=O) in the range δ = 151–156 ppm instead of a
13
single peak for the perfectly alternating sequence of monomer residues. For example, the C-NMR
spectrum of CHDM-BuD polycarbonate:
O
O
O
O
O
O
displayed three peaks for the carbonyl carbon (C=O) of the carbonate function, as illustrated in Figure
4. In order to interpret the peaks, poly(1,4-tetramethylene carbonate) homopolymer was synthesized
13
13
from BuAc2 and Bu DPDC and its C-NMR spectrum was recorded. When the C-NMR spectra of
poly(1,4-tetramethylene carbonate) homopolymer was compared to that of poly(CHDM carbonate)
homopolymer (polycarbonate 2B in Scheme 2 series B), the C=O carbon peak positions of the
carbonate groups were observed at 155.20 and at 155.52 ppm, respectively. The observed pattern was,
therefore, accounted for as in the Figure 4.
Figure 3. 13C-NMR spectra of: (1) CHDMAc2 (2) BuD DPDC (3) CHDM-BuD
polycarbonate (Series B).

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3674
This pattern proves that the backbone of the polycarbonates synthesized by interchange reactions
possessed a partial random sequence of units in which all of these sequences coexisted. Peak B in the
spectrum represents the alternate sequence of monomer residues in the polymer backbone. This peak
should be due to the sequence resulting from the direct reaction of the diacetate with the diphenyl
dicarbonate monomers. The occurrence of the random sequences A and C may have been due to other
interchange reactions such as self-condensation of DPDC monomers, elimination of cyclic aliphatic
carbonates from polymer chains, polymer-polymer and polymer-monomer reactions.
Figure 4. 13C-NMR peaks of C=O observed in the spectrum of CHDM–BuD polycarbonate.
In order to expand the discussion of the subject matter of the present method, it may be
advantageous to compare the results of the present method to those of interchange reactions of
dihydroxy compounds with alkylene- and arylenediphenyl dicarbonates. The results of the diacetate-
diphenyl dicarbonate reaction indicated that this reaction generally afforded lower reaction yields and
lower polymer inherent viscosities (i.e., lower molecular mass) than the diol-diphenyl carbonate
reaction. The diacetate and the diphenyl dicarbonate monomers vary in their volatility so it is difficult
to maintain a good stoichiometric balance of monomers throughout the reaction. Furthermore the
reaction is accompanied by a yellow discoloration which is more intense than in the case of diol-
diphenyl dicarbonate reaction. This discoloration becomes more intense with increasing the
temperature and heating time. Finally, polycarbonates were not obtained from diacetates and diphenyl
dicarbonates at temperatures in excess of 240 °C. This disadvantage precludes achieving high
molecular mass polycarbonates.
2.3. Thermal properties
The thermal properties of polycarbonates synthesized were investigated with DSC and TGA. The
glass transition temperature (Tg) values of the aromatic-aromatic polycarbonates were generally higher
than those of aromatic-aliphatic polycarbonates (Figure 5 and Figure 6). The Tg values of the
polycarbonates (Table 3) were in the range 13–107.8 °C. The aromatic-aromatic polycarbonates
showed Tg values in the range 83.1–107.8 °C, aromatic-aliphatic polycarbonates in the range
49.5–90.4 °C, and aliphatic-aliphatic polycarbonates showed values at 13 and at 38.7 °C. The high Tg

Molecules 2010, 15
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values of aromatic-aromatic polycarbonates may have been due to the stiffening effect of aromatic
groups which restricted the movement of the polymer chains and thus increased Tg. The presence of
aliphatic segments in the polymer backbone imparted flexibility to move under the effect of
temperature. This ease of motion was reflected in the lower Tg values of aromatic-aliphatic
polycarbonates.
Figure 5. DSC Thermograms of polycarbonates (Series A).
Figure 6. DSC Thermograms of polycarbonates (Series B).
As shown in the TGA thermograms (Figure 7 and Figure 8), the thermal decomposition
temperatures (Td) of aromatic-aromatic polycarbonates were considerably higher than those of
aromatic-aliphatic or aliphatic-aliphatic polymers. They also have higher residual mass percentages at
500 °C. The TGA curves of the polycarbonates displayed a slow mass loss starting between
250–400 °C and a relatively fast mass loss occurring between 350–500 °C. In particular, the
thermogravimetric curves of aromatic-aromatic polycarbonates showed that these polymers have good
thermal stabilities and displayed typical one-stage characteristics with a relatively fast mass loss
occurring at temperatures higher than those of the aromatic-aliphatic or aliphatic-aliphatic
polycarbonates.

Molecules 2010, 15
Figure 7. TGA thermograms of polycarbonates (Series A). TG % is the mass percentage of
3676
the polymer sample remaining after heating the polymer to a high temperature.
Figure 8. TGA thermograms of polycarbonates (Series B). TG % is the mass percentage of
the polymer sample remaining after heating the polymer to a certain temperature.
3. Experimental
3.1. Materials
Reagents and chemicals are all commercially available and were used without any further
purification. The following chemicals were purchased from the corresponding companies: ethylene
glycol, 1,4-butanediol, hydroquinone, and phenyl chloroformate from Merck (Schuchardt, Germany);
1,3-propanediol, titanium(IV) n-butoxide, 4,4'-isopropylidenediphenol, 1,4-cyclohexanedimethanol,
4-dimethylaminopyridine, and 4,4'-isopropylidenediphenol diacetate from Acros Organics (New
Jersey, USA); bis(4-hydroxyphenyl)methane from Aldrich (Milwaukee, WI, USA); resorcinol from

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Riedel-de Haën (Seelze, Germany); and 1,5-pentanediol from Lancaster (Morecambe, England).
1,4-Cyclohexanedimethylene diacetate was prepared and characterized in our laboratories as described
in the experimental part. Chloroform was dried over diphosphorus pentoxide. Tetrahydrofuran was
purified by refluxing and distillation over sodium wire and benzophenone. Zinc acetate dihydrate was
dried at 100 °C under vacuum overnight.
3.2. Monomer synthesis
1,4-Cyclohexanedimethylene diacetate: The diacetate was prepared from 1,4-cyclohexane
dimethanol and acetyl chloride according to the following procedure: acetyl chloride (7.85 g, 0.10 mol)
in chloroform solution (30 mL) was added dropwise to a stirred solution of 1,4-cyclohexanedimethanol
(7.21 g, 0.050 mol), pyridine (17.40 g, 0.22 mol) and a catalytic amount of 4-dimethylaminopyridine
(4-DMAP) in chloroform (60 mL) below 5 °C. The reaction mixture was stirred for 1 h at 0–5 °C and
overnight at room temperature, and then washed with 5% HCl solution and 2 × 100 mL of water. The
chloroform layer was poured onto distilled water (600 mL) yielding the 1,4-cyclohexanedimethylene
diacetate as solid crystals, which were collected by filtration, washed with 2 × 60 mL of distilled water
and dried at 30 °C under reduced pressure to yield white crystals (8.71 g, 87% yield, Tm = 70 °C).
Alkylene and arylene diphenyl dicarbonates: The diphenyl dicarbonate monomers were prepared by
the reaction of the corresponding dihydroxy compounds with phenyl chloroformate as shown in
Scheme 1, following previously published procedures [33]. A brief general synthetic procedure for the
preparation of 1,5-pentanediol diphenyl dicarbonate (PeD DPDC) follows:
Phenyl chloroformate (15.66 g, 0.10 mol) in dry THF (20 mL) was added dropwise to a stirred
solution of 1,5-pentanediol (5.21 g, 0.050 mol), pyridine (9.50 g, 0.12 mol) and a catalytic amount of
4-dimethylaminopyridine (4-DMAP) in THF (350 mL) at 0–5 °C. The reaction mixture was stirred for
1 h at 0–5 °C and overnight at room temperature, and then poured into distilled water (600 mL). The
precipitate formed was collected by filtration, washed several times with 10% aqueous sodium
carbonate solution; the product was purified by recrystallization from ethyl acetate and dried at 50 °C
under vacuum overnight to give white crystals (14.98 g, 87 % yield, Tm = 52 °C).
The following diphenyl dicarbonates of the other dihydroxy compounds were prepared by the same
procedure: ethylene glycol diphenyl dicarbonate (EG DPDC), 1,3-propanediol diphenyl dicarbonate
(PrD DPDC), 1,4-butanediol diphenyl dicarbonate (BuD DPDC), 1,4-cyclohexanedimethanol diphenyl
dicarbonate (CHDM DPDC), catechol diphenyl dicarbonate (CAT DPDC), resorcinol diphenyl
dicarbonate
(RESOL
DPDC),
hydroquinone
diphenyl
dicarbonate
(HQ
DPDC),
bis(4-hydroxyphenyl)methane diphenyl dicarbonate (BHPM DPDC), and bisphenol A diphenyl
dicarbonate (BPA DPDC). The yields and physical properties of these compounds are listed in Table 1.
3.3. Polycarbonate synthesis
The polycarbonates were synthesized from BPA diacetate and the various diphenyl dicarbonates
(Scheme 2) according to the following general procedure: a glass reaction tube (150 × 30 mm outside
diameter) equipped with a gas inlet and outlet and stop cocks, was filled with a homogeneous solid
mixture composed of 10 mmol BPA diacetate, 10 mmol diphenyl dicarbonate and Ti(OBu)4 (2% mol
of the dicarbonate). The reaction mixture was heated in a silicone oil bath at 160 °C under a slow

Molecules 2010, 15
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stream of argon gas for 30 min. The temperature of the bath was then heated at 170 °C, at 190 °C and
then at 200 °C for 1 h for each temperature. The reaction mixture was further heated to 220 ºC and
kept at this temperature for 1 h. While maintaining the temperature at 220 °C the gas inside the tube
was gradually evacuated over a period of 1 h, and heating was maintained for 1 h. Finally, the reaction
tube was cooled, the formed polymer was dissolved in chloroform, the solution was filtered and the
polymer precipitated by drop wise addition to methanol. The polymer was filtered and dried in vacuo
in a drying pistol at 60 °C over night.
The same procedure was followed for the preparation of the following polycarbonates: BPA–PrD
polycarbonate, BPA–BuD polycarbonate, BPA–PeD polycarbonate, BPA–RESOL polycarbonate,
BPA–HQ polycarbonate, and BPA–BHPM polycarbonate
Two series of polycarbonates were prepared as demonstrated in Scheme 2:
1) Series A: was prepared from the reaction of BPA diacetate with alkylene and arylene diphenyl
dicarbonates.
2) Series B: was prepared from the reaction of 1,4-cyclohexanedimethylene diacetate with alkylene
and arylene diphenyl dicarbonates.
3.4. Monomer and polymer characterization
Inherent viscosity measurements: The inherent viscosity of polymer solutions in chloroform were
measured with a dilution Ubbelohde glass capillary viscometer (Rheotek, Poulten Selfe & Lee Ltd.,
Essex, England) in a thermostated water bath temperature at 25 °C. The solutions were temperature
equilibrated for approximately 10 min before viscosity was measured.
Molecular characterization: The Fourier transform infrared (FTIR) spectra (Spectral resolution:
4 cm-1) of the monomers and polymers were recorded as neat films with Thermo Nicolet Nexus 670
FT-IR spectrophotometer (Madison, WI, USA). The films were prepared by cast solution of purified
1
monomer or polymer in chloroform over NaCl plates. The H-NMR and 13C-NMR spectra of the
monomers and polymers were recorded with a Bruker Avance DPX 300 FT-NMR Spectrometer at
1
300 MHz (Wissembourg Cedex, France) in deuterated chloroform. Chemical shifts (δ) for H and of
75 MHz for 13C are given in ppm with respect to tetramethylsilane (TMS) as the standard.
3.5. Thermal properties
The glass transition temperature (Tg) values of polymer samples were studied with a Netzsch DSC
204 F1 Differential Scanning Calorimeter (Selb Bavaria, Germany). The Tg measurements were
conducted on 10 ± 2 mg samples under dry nitrogen. The samples were first heated to 150 °C and
maintained for 2 minutes before rapid cooling with liquid nitrogen to ambient or sub-ambient start
temperature. The thermal behaviors of the samples were probed by heating to the molten state at a
heating rate of 20 °C/min for aromatic-aromatic polycarbonates and 10 °C/min for aromatic-aliphatic
polycarbonates. The Tg values were taken as the mid point of the step transition. The thermal stabilities
of the polymer samples were studied by thermogravimetric analysis (TGA) with a Netzsch STA 409
PG/PC thermal analyzer (Selb Bavaria, Germany). Measurements were conducted at a heating rate of
20 °C/min under dry nitrogen atmosphere purging at a flow rate of 50 mL/min.

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4. Conclusions
In the present study, a new method of synthesis of polycarbonates, useful as engineering plastics,
based on reaction of alkylene and arylene diacetate with alkylene- and arylenediphenyl dicarbonates in
the molten state was presented. The inherent viscosity range obtained utilizing the present method was
0.19–0.43 dL/g, which implies that the polycarbonates with low to intermediate molecular mass were
formed. The potential of this method was demonstrated by the successful synthesis of several
polycarbonates prepared in this study. The 13C-NMR spectra of the carbon of the carbonate group
showed that the formed polycarbonates contain a partial random sequence distribution of monomer
residues in their chains. With this approach, it was possible to provide a flexible method of synthesis of
polycarbonates whose properties could be varied by varying the structure of the diacetate or the
dicarbonate monomers. Compared to polycarbonates obtained by diol-diphenyl dicarbonate
interchange reaction, the method practically afforded polymers with lower yields and smaller
molecular mass.
Acknowledgements
The authors thank the Deanship of Academic Research (DAR) of The University of Jordan for
providing the facilities and chemicals. The authors also thank Jalal Zahra and Ms Fatima Mustafa, for
NMR analyses, and to Ruba Zalloum for FTIR, DSC, and TGA, analyses.
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Sample Availability: Samples of the compounds are available from the authors.
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