Synthesis and polymerization reactions of cyclic imino ethers. VI. Polymers with biphenyl structure

Article abstract of DOI:10.1002/pola.26199

A monomer of the AB-type and a bifunctional comonomer of the AA-type containing two 2-oxazoline rings and a biphenyl structural unit were prepared from the corresponding carboxylic acids via their esterification and subsequent amidation with an aminoalcohol. The cyclization of an amide to 2-oxazoline structure was achieved by treatment with thionyl chloride followed by liberation of the free base with sodium hydrocarbonate in an aqueous solution. The prepared monomers were used for the polyaddition polymerization of the AB-type monomer having a 2-oxazoline and phenol group bound on adjacent rings of the biphenyl structure in solution. The monomer of the AA-type was used for AA+BB-type polyaddition reactions with aliphatic dicarboxylic acids. Both types of polymerizations have been performed in melt and in solution. The structures of the polymers were determined, and the thermal properties of the polymers were evaluated. Liquid-crystalline (LC) structures of the prepared polymers were observed by DSC measurements and optical microscopy. The polyaddition reactions of the monomers containing a 2-oxazoline ring and a biphenyl unit represent a new efficient way for the preparation of a biphenyl unit containing poly(ether amide)s and poly(ester amide)s.

Full text of DOI:10.1002/pola.26199

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Synthesis and Polymerization Reactions of Cyclic Imino Ethers. VI.
Polymers with Biphenyl Structure
1
1
1
1
ꢀ
ꢀ
Jozef Lustonˇ , Juraj Kronek, Angela Kleinova, Ivica Janigova,
2
2
ꢀ
Helena Valentova, Jan Nedbal
1Polymer Institute, Slovak Academy of Sciences, Center of Excellence GLYCOMED, Dubravska cesta 9, 84541 Bratislava, Slovakia
2
ꢀ
Charles University, Faculty of Mathematics and Physics, Na Holesˇovicˇkach 2, 18000 Prague 8, Czech Republic
Correspondence to: J. Kronek (E-mail: upolkron@savba.sk)
Received 21 December 2011; accepted 15 May 2012; published online
DOI: 10.1002/pola.26199
ABSTRACT: A monomer of the AB-type and
a
bifunctional
melt and in solution. The structures of the polymers were
determined, and the thermal properties of the polymers were
evaluated. Liquid-crystalline (LC) structures of the prepared
polymers were observed by DSC measurements and optical
microscopy. The polyaddition reactions of the monomers con-
taining a 2-oxazoline ring and a biphenyl unit represent a new
comonomer of the AA-type containing two 2-oxazoline rings
and a biphenyl structural unit were prepared from the corre-
sponding carboxylic acids via their esterification and subse-
quent amidation with an aminoalcohol. The cyclization of an
amide to 2-oxazoline structure was achieved by treatment
with thionyl chloride followed by liberation of the free base
with sodium hydrocarbonate in an aqueous solution. The pre-
pared monomers were used for the polyaddition polymeriza-
efficient way for the preparation of a biphenyl unit containing
C
V
poly(ether amide)s and poly(ester amide)s.
2012 Wiley Peri-
odicals, Inc. J Polym Sci Part A: Polym Chem 000: 000–000,
2012
tion of the AB-type monomer having
a 2-oxazoline and
phenol group bound on adjacent rings of the biphenyl struc-
ture in solution. The monomer of the AA-type was used for
AAþBB-type polyaddition reactions with aliphatic dicarboxylic
acids. Both types of polymerizations have been performed in
KEYWORDS: 2-oxazolines; addition polymerization; biphenyl;
high-temperature materials; liquid-crystalline polymers (LCP);
poly (ester amide)s; step-growth polymerization
INTRODUCTION Cyclic imino ethers, mainly 2-oxazolines, are
versatile compounds with broad utilization in organic and
polymer chemistry.1 2-Oxazolines react with carboxylic
acids,2 phenols,3 and thiols.3 They also take part in cationic
ring opening polymerizations and enzymatic ring-opening
polyaddition reactions.4,5 It is noteworthy to mention that
the 2-oxazoline ring behaves as a bifunctional group in cati-
onic polymerizations and as a monofunctional moiety in
addition reactions.
monomer with various length aliphatic linkers between acid
groups.9 However, there exists another way to enhance the
possibilities of the exploitation of such systems, for instance,
changing the basic skeleton of the monomer with groups
bearing a specific characteristic and/or special property.
Recently, we presented the preparation of poly(ether amide)s
containing a naphthalene group.11
Another example of such a group is a biphenyl structure
considered as a mesogen that is typically used for the prepa-
ration of liquid crystalline (LC) compounds and LC poly-
mers.12–18 LC polymers can contain the biphenyl structure
incorporated into the main chain or into the side chain.
Recently, poly(ester amide)s containing a biphenyl moiety in
the main chain were prepared from butyrolactone, different
aliphatic or aromatic diamines, and dichlorides of dicarbox-
ylic acids.19
In previous articles,6–11 we have shown broad perspectives
of the polymerization of 2-oxazoline containing compounds
either in the AAþBB, or in the AB and AB2 modes, as well as
in cationic (co)polymerization, where a number of different
polymers of the poly(ether amide), poly(ester amide), poly
(amino amide), or poly(imino ether) types were formed.4
These reactions proceed due to the presence and reactions
of different functional groups on the basic skeleton of the
molecule of the monomer. In such a way, poly(ester amide)s
with a broad range of melting temperatures have been syn-
thesized in AAþBB mode from the same bis-2-oxazoline as
the AA compounds and with dicarboxylic acids as the BB
In our studies on the synthesis and polymerization of 2-oxa-
zolines, we prepared polymers containing a mesogen group
in the molecule where the biphenyl unit was chosen as the
mesogen. Two different compounds, 4-hydroxy-40-(2-oxazo-
lin-2-yl)biphenyl (HBiOX) and 4,40-bis (2-oxazolin-2-yl)
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TABLE 1 Conditions and Results of Polyadditions of 4,40-Bis(2-oxazolin-2-yl)biphenyl (BiBOX) with Different Dicarboxylic Acids
Amount
(mmol)
Solvent
(mL)
Temp.
(ꢀC)
Time
(h)
Yield
(%)
Mn
Tm
(ꢀC)
No.
1
Diacid
(VPO)
Note
Sebacic
0.5
–
155
5
90
–
270–273
Acid did not
dissolved BiBOX
2
3
4
5
6
7
8
Sebacic
0.5
0.5
0.5
0.5
0.5
0.5
0.5
DMF/0.3
TMS/0.5
DMSO/0.5
TMS/1
170
180
180
180
180
180
155
5
5
5
5
5
5
8
95
–
–
Phase separation
Sebacic
97
Sebacic
100
95
Suberic
8,330
275–292
303–306
258–265
300–307
Adipic
TMS/1
100
95
22,000
Dodecanedioic
Succinic
TMS/1
TMS/0.5
91
biphenyl (BiBOX), were prepared as monomers of AB- and
AA–BB-types for polyaddition reactions.
Synthesis of 4,40-Bis(2-oxazolin-2-yl)biphenyl (BiBOX)
4,40-Biphenyldicarboxylic acid (BiDAc, 4.84 g, 0.02 mol) and
thionyl chloride (7.3 mL, 0.1 mol) were heated under reflux
for 3 hours. The excess SOCl2 was removed and colorless
crystals of biphenyl-4,40-dicarbonylchloride (BiDCl) were
obtained. Yield: ꢁ100%. mp ¼ 186–188ꢀC.
BiDCl (5.6 g, 0.02 mol) and 2-chloroethylamine hydrochlor-
ide (4.64 g, 0.04 mol) were dispersed in a mixture of aque-
ous NaOH (4.5 g, 0.08 mol) and dichloromethane (70 mL). A
white precipitate was formed immediately. The solid was
then separated, washed with water, and dried. A white pow-
der of N, N0-Bis(2-chloroethyl)biphenyl-4,40-dicarboxamide
(BiDAm) was obtained. Yield: 99.5%. mp >300ꢀC.
EXPERIMENTAL
Materials
The starting materials including 40-hydroxy-4-biphenylcar-
boxylic acid (HBiAc) and 4,40-biphenyldicarboxylic acid
(BiDAc) were purchased from Aldrich. All other available
reagents (Aldrich) were used as received. All solvents used
for polymerizations and subsequent measurements were dis-
tilled and dried over molecular sieves before the use.
Synthesis of 40-Hydroxy-4-(2-oxazolin-2-yl)
biphenyl (HBiOX)
BiDAm (5.48 g, 0.015 mol) was dissolved in methanolic KOH
(0.03 mol), and the solution was heated under reflux for 3
hours. After cooling, the precipitate was separated and the
residue was concentrated. A white solid of BiBOX was
The ester (HBiEs) was prepared from 40-hydroxy-4-biphenyl-
carboxylic acid (HBiAc) (5 g, 0.023 mol) by heating under
reflux in methanol (50 mL) in the presence of a catalytic
amount of sulfuric acid (0.11 mL, 0.002 mol) for 5 hours.
The reaction yield was 97%. mp 226–229ꢀC. 1H NMR
(DMSO-d6): 3,86 (s, OCH3, 3H), 6,88 (d, ar, 2H), 7,59 (d, ar,
2H), 7,74 (d, ar, 2H), 7,98 (d, ar, 2H), 9,74 (s, Ar-OH, 1H).
1
obtained. Yield: 87%. mp ¼ 320ꢀC, sublimation at 250ꢀC. H
NMR (DMSO-d6): 3.99 (t, CH2N, 4H), 4.43 (t, CH2O, 4H), 7.83
(d, ar, 4H), 7.97 (d, ar, 4H).
Polymerization in Melt
The hydroxyamide HBiAm was prepared by the reaction of
HBiEs (2.97 g, 0.013 mol) with 2-aminoethanol (6.35 g,
0.104 mol) at 150ꢀC for 3 hours. The excess of 2-aminoetha-
nol was removed with suction and the residue was poured
into water. A white crystalline compound was obtained. The
yield: 98%. mp 240–242ꢀC. 1H NMR (DMSO-d6): 3,35 (q,
CH2N, 2H), 3,52 (d, CH2O, 2H), 4,75 (s, RAOH, 1H), 6,86 (d,
ar, 2H), 7,57 (d, ar, 2H), 7,67 (d, ar, 2H), 7,91 (d, ar, 2H),
8,44 (t, NH, 1H), 9,57 (broad s, ArAOH, 1H).
Calculated amounts of comonomers were weighed in a dry
ampoule, which was evacuated and filled with argon several
times before sealing. The tube was then immersed in a pre-
heated oil bath. After finishing polymerization, the ampoule
was opened; the polymer was dissolved in hot DMF, precipi-
tated in nonsolvent, separated, washed, and dried under
vacuum. Detailed polymerization conditions and results are
listed in Table 1.
HBiOX was prepared by cyclization of HBiAm (3.01 g, 0.012
mol) in dichloromethane (70 mL). Thionyl chloride (4.4 mL,
0.06 mol) was added dropwise in an ice bath, and the reac-
tion mixture was stirred for 20 hours at an ambient temper-
ature. The white solid of hydrochloride was isolated, dried,
and neutralized with saturated aqueous NaHCO3. A white
precipitate was isolated and recrystallized from ethanol.
Yield: 79%. mp 238–240ꢀC. 1H NMR (DMSO-d6): 3,97 (t,
CH2N, 2H), 4,41 (t, CH2O, 2H), 6,89 (d, ar, 2H), 7,58 (d, ar,
2H), 7,79 (d, ar, 2H), 7,91 (d, ar, 2H), 9,67 (broad s, ArAOH,
1H), UV (CH3OH): 220 nm (log e ¼ 4,17), 297 (log e ¼ 4,38).
Polymerization in Solution
Calculated amounts of comonomers were weighed in a dry
ampoule, solvent was added, and the mixture was bubbled
with argon for 5 min and then sealed. The ampoule was
immersed in an oil bath preheated to the desired tempera-
ture and withdrawn after the desired time. The liquid or vis-
cous product was precipitated in a nonsolvent (methanol,
water). The solid product was dissolved in the solvent used
during polymerization and precipitated in nonsolvent.
Detailed polymerization conditions and results are listed in
Table 1.
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Analytical Measurements
1H and 13C NMR spectra were measured on an AMX-300
spectrometer (Bruker) operating at 300.13 MHz for 1H and
75.47 MHz for 13C and on a DRX-500 NMR spectrometer
(Bruker) operating at 500.13 MHz for 1H and 125.77 MHz
for 13C. The samples were measured in DMSO-d6 at room
temperature. The solvent was used as a lock and internal
standard (d (1H) ¼ 2.50 ppm, d (13C) ¼ 39.6 ppm). FTIR
spectra were recorded with IR spectrophotometer NICOLET
8700TM (Nicolet, USA) with 64 scans and steps of 4 cmꢂ1 in
KBr pellets. UV spectra were taken with Shimadzu UV
C1650. Melting points were measured on a Koffler melting
point apparatus (VEB Analytik, Germany) and are
uncorrected.
1
FIGURE 1 H NMR spectrum of the 4-hydroxy-40-(2-oxazolin-2-
yl)biphenyl (HBiOX) in DMSO-d6.
HPLC measurements were done on a HPLC Agilent 1200 se-
ries system equipped with an isocratic pump and UV detec-
tion. Measurements were done in a mixture of methanol–
water (8/2), at a flow rate of 0.5 mL/min, a C-18 column
(Zorbax), and UV-detection at 254 nm.
obtained in the hydrochloride form as a white powder. The
liberated base was obtained after treatment with potassium
hydrogen carbonate in high yield. H NMR spectrum (Fig. 1)
1
confirmed the expected structure of the monomer. The reac-
tivity of the hydroxyl group, expressed by the chemical shift
d, equals to 9.67 ppm and is similar to the 2-(4-hydroxy-
phenyl)-2-oxazoline with d of the hydroxyl group proton
equal to 10.08 ppm described in the first part of this series.5
The slightly lower value is due to the donor character of the
biphenyl structure. However, this value is more than 1 ppm
higher than the value of OH groups in hydroquinone, which
supports the push-pull effect of phenolic and 2-oxazoline
groups connected by a conjugated system. This implies that
monomers of the AB-type containing a 2-oxazoline ring and
a phenolic group in one molecule will be more reactive com-
pared with the case of the reaction between the appropriate
bis(2-oxazoline) and hydroquinone (Scheme 1).
A number of average molecular weights were measured by
vapor pressure osmometry (Knauer, DMSO, 90ꢀC). Thermal
analysis was done with a Mettler Toledo DSC instrument at a
heating rate of 10 K/min.
The texture of the sample and phase transition temperatures
of polymers were determined by a polarizing optical micro-
scope (Nikon Eclipse 80i, cross polarizers) equipped with a
heating stage Linkam LTS350) at a heating rate of 10 K/min.
RESULTS AND DISCUSSION
Monomer Synthesis
Two different monomers containing at least one 2-oxazoline
structural unit and a biphenyl structure, namely 4-hydroxy-
40-(2-oxazolin-2-yl)biphenyl (HBiOX) and 4,40-bis(2-oxazolin-
2-yl)biphenyl (BiBOX), were prepared as monomers of the
AB- and AAþBB types for polyaddition reactions.
The second monomer, containing two 2-oxazoline groups on
the biphenyl unit, 4,40-bis(2-oxazolin-2-yl)biphenyl (BiBOX),
was prepared from biphenyl-4,40-(dicarboxylic acid) accord-
ing to Scheme 2.
In the first step dichloride of dicarboxylic acid (BiDCl) was
prepared by heating the acid (BiDAc) in excess thionyl chlo-
ride. The acid chloride provides a bis-chloroethylamide after
reacting it with 2-chloroethylamide which, after boiling in
KOH/MeOH, provided BiBOX. It is noteworthy to mention
that a very high reaction yield was obtained in all steps.
The synthetic approach to the HBiOX is shown in Scheme 1.
The starting point was an aromatic hydroxy acid HBiAc,
which was esterified under acid catalysis to an ester HBiEs.
The treatment of HBiEs with ethanolamine for 3 hours at
150ꢀC yielded a hydroxyamide intermediate HBiAm which
was isolated in high yield (nearly 100%). The cyclization of
HBiAm with an excess of thionyl chloride was performed by
the addition of the reagent to the substrate under cooling
with ice bath and then by the agitation of the reaction mix-
ture at room temperature overnight. The desired HBiOX was
AB-Type Polyadditions
The prepared HBiOX was used in thermally initiated poly-
merization in bulk and in a solution. The treatment of
HBiOX at a temperature of 245ꢀC, which is slightly higher
SCHEME 1 Synthesis of 40-hydroxy-4-(2-oxazolin-2-yl)biphenyl
SCHEME 2 Synthesis of 4,40-bis (2-oxazolin-2-yl)biphenyl
(HBiOX).
(BiBOX).
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different alkylene chain lengths (from succinic to dodecane-
dioic acids) (Scheme 4). In contrast with the AB polymeriza-
tions, phenolic groups as B groups have been replaced by
carboxylic groups. This is mainly attributed to the aliphatic
OH groups not being reactive enough to provide an addition
reaction with the 2-oxazoline ring. Moreover, the push-pull
system of the electron-donor phenolic group and the elec-
tron-acceptor 2-oxazoline ring of AB-type monomer is neces-
sary for enhancing the reactivity of both groups in the addi-
tion reactions. The thermally induced polyaddition of
biphenyldicarboxylic acid with 1,3- and 1,4-phenylenebis (2-
oxazoline) is an example of a polymerization of aromatic
comonomers and has been published previously.10 All poly-
merizations were thermally initiated and were attempted to
be prepared in a melt or in a solution of high boiling sol-
vents. Conditions and results of all polymerizations are sum-
marized in Table 1. The influence of polymerization condi-
tions during the course of polymerization was studied in the
polyaddition of BiBOX with sebacic acid. The melt polyaddi-
tion of these two comonomers was limited by the very low
solubility of BiBOX in the melt of sebacic acid. Therefore, po-
lymerization proceeded in a heterogeneous polymerization
mixture. For solution polymerization, two high boiling sol-
vents were used: N, N-dimethylformamide (DMF) and tetra-
methylene sulfone (TMS). During polymerization of BiBOX
with sebacic acid in DMS, phase separation was observed.
Therefore, TMS was used in all solution polymerizations. All
polyadditions proceeded in high yields (90–100%). The mea-
surement of molecular characteristics of the resultant poly-
mers was complicated by limited solubility in common sol-
vents. As seen in Table 1, only polymers prepared from
adipic and suberic acids were soluble in DMSO, and their
number average molar masses (Mn) were measured by vapor
phase osmometry (VPO). Values of Mn were equal to 22,000
g/mol and 8330 g/mol, which represent 50 and 18 biphenyl
units, respectively.
SCHEME 3 Polyaddition reaction of 40-hydroxy-4-(2-oxazolin-2-
yl)biphenyl (HBiOX).
than the melting point of the monomer, ensured the homoge-
neity of the system during polymerization. The duration of
the polymerization was 1 hour. Under these conditions, the
poly(HBiOX) was obtained in 88% yield.
For polymerization in solution, N-methylcaprolactam was
used as a solvent. However, despite having a very high sol-
vent power, a stepwise precipitation of the polymer from the
solution during polymerization was observed. Therefore,
short chains were obtained with the degree of polymeriza-
tion equal to 4, as estimated from NMR. This implies that
the melt polyaddition is the only effective way for HBiOX
polymerization.
As expected from previous results,6,20 in the case of poly-
merization of an AB-type monomer with 2-oxazoline and
phenolic functional groups, poly(ether-amide) was formed in
the absence of side reactions (Scheme 3). Also in this case,
the molar ratio of both the 2-oxazoline and phenol remains
the same and is equal to one.
We can see in Figure 2 that the structure of the polymer
poly(HBiOX) confirmed the following changes in the spec-
trum. The protons of the oxazoline structure with d 3.97 and
4.41 ppm are substituted with protons of the opened struc-
ture with the chemical shift 4.25 and 4.56 ppm, respectively.
The spectrum also shows protons of the 2-oxazoline end
groups at d 5.15 and 4.65 ppm. The ratio of integrals of the
chemical shift hydrogen atoms of the linear and end hydro-
gen atoms determined the average degree of polymerization
(DP). In this case, the value is 15. Also, it is evident that the
phenolic proton completely disappeared. The values of the
chemical shift of aromatic protons and ring protons are
slightly shifted to a lower field, which may also be due to
the solvent.
The structure of all polymers prepared by the AAþBB-type
1
polyaddition was confirmed by H NMR spectra measured in
DMSO-d6 (Fig. 3). In all spectra, signals of the symmetrical
biphenyl unit, amidic proton, and ethylene groups take place
at almost the same chemical shift. Two doublets at 7.79 and
8.02 ppm can be assigned to protons of the biphenyl unit,
while broad peaks at 8.43 ppm represent the proton of the
AA1BB-Type Polyadditions
The bifunctional monomer BiBOX was used in the polymer-
ization of AAþBB-type with aliphatic dicarboxylic acids of
SCHEME 4 Polyaddition reactions of 4,40-bis (2-oxazolin-2-yl)
biphenyl (BiBOX) with various aliphatic dicarboxylic acids.
FIGURE 2 1H NMR spectrum of poly(HBiOX) in D2SO4.
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at 3300–3400 cmꢂ1 can be assigned to NAH stretching.
These signals are in all cases accompanied with a shoulder
at wave numbers higher than 3500 cmꢂ1. All spectra contain
signals from an ester group: C¼¼O stretching at 1735 cmꢂ1
and signal of CAO stretching at 1287 cmꢂ1. Ring bonds rep-
resent signals at 1610, 1491, 845, and 756 cmꢂ1. The last
two bands are in the fingerprint region and are characteris-
tic for p-disubstituted benzene rings (Fig. 4).
While the area from 500 to 2000 cmꢂ1 is almost the same,
the area from 2800 to 3500 cmꢂ1 depends on the length of
aliphatic spacer in the aliphatic part of structural unit. Three
small and broad peaks take place in the spectra of the poly
(BiBOX-succinic acid) at 2963, 2938, and 2875 cmꢂ1. The
intensity of all of the peaks increases with increasing the
aliphatic chain length; in addition, a shift of all three bands
is observed (Fig. 5).
FIGURE 3 1H NMHR spectra of polymers prepared by polyaddi-
tion of BiBOX with various dicarboxylic acids measured in
DMSO-d6.
Thermal Properties
Thermal properties of the poly(HBiOX) are shown in the Fig-
ure 6 where first and second heating scans in thermal inter-
vals between 0 and 300ꢀC are presented. In the first scan,
several endotherms are visible at 100, 180, 235, and 293ꢀC.
These peaks do not appear in the second scan and probably
belong to unstable crystalline areas formed during cooling of
the amide bonds formed in the polymerization process.
amidic NH group. Peaks at 4.20 and 3.60 ppm can be
assigned to the protons of CH2O and CH2N, respectively. The
others represent signals from alkyl chains. The 2-oxazoline
end-groups are present at 4.50 and 4.05 ppm for CH2O and
CH2N, respectively. The ratio of integrals of ethylene amide
protons signals to signals of the end-groups can give infor-
mation about the degree of polymerization. Although it was
not possible to calculate the degree of polymerization (DP)
from NMR spectra, it is clearly seen in Figure 3 that the
higher DP have polymers prepared from adipic, suberic, and
sebacic acids.
Another interpretation is based on the phase transitions of
the liquid crystalline (LC) phase in the polymer.11–17 It
seems that there is a coincidence between the third endo-
therm at 235ꢀC and the polymerization temperature at
245ꢀC in bulk polymerization (mp ¼ 238–240ꢀC). A clear
movement of the heated monomer was observed at this tem-
perature by means of a microscope during melting point
measurements. In fact, the appearance of an LC phase was
expected on the basis of previous results, and it was a rea-
son for the synthesis and polymerization of this compound.
IR spectra supported the formation of the ester-amide struc-
ture of all polymers (Fig. 4). The C¼¼N bond stretch in an
oxazoline unit at 1648 cmꢂ1 was substituted in all cases by
signals from the C¼¼O stretch of the amidic group at 1641
cmꢂ1. The peaks at 1536 cmꢂ1 are characteristic of the
CANH stretch of a secondary amide group, and the signals
FIGURE 4 IR spectra of polymers prepared in AAþBB mode
FIGURE 5 Detail of IR spectra of AAþBB polymers of the area
from 2500 to 3100 cmꢂ1
.
measured in KBr pellets.
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a biphenyl group increases the stiffness of the polymer chain
which causes an increase of Tg of the biphenyl unit contain-
ing polymer. In previous articles dedicated to the preparation
of naphthalene ring containing poly(ether amides) and poly
(ester amides), the glass-transition temperature of poly[2-(6-
hydroxy-2-naphthalene-2-yl)-2-oxazoline] prepared by AB-
type polyaddition is 182ꢀC, which is higher than the value of
AAþBB-type polymers.11 This corresponds to the larger con-
tent of hard aromatic segments in latter type of polymers.
The presence of an aliphatic chain should decrease the Tg of
the AAþBB-type poly(ester amides). However, the values of
Tg in DSC records of all AAþBB were not measurable [Fig.
7(b)]. This may be due to decomposition at higher tempera-
tures during the first heating [broad exotherms, Fig. 7(a)].
Figure 7(a) shows that DSC records of poly(BiBOX-succinic
acid) and poly(BiBOX-adipic acid) contain one endothermic
peak assigned to the isotropization process while DSC
records of polymers with longer alkyl chain contain two
FIGURE 6 Record of first and second heating of poly(HBiOX).
A glassy transition temperature (Tg) of the poly(HBiOX) was
observed as high as 169ꢀC. This value is higher than Tg of
analogous polymers of AB-type containing a phenyl ring,
namely poly[2-(4-hydroxyphenyl)-2-oxazoline] with Tg equal
to 150ꢀC. As expected, the substitution of the phenyl ring by
FIGURE 7 Records of the first (a) and second (b) heating of
DSC in the temperature range between 25 to 350ꢀC for poly-
mers prepared in AAþBB mode. Used diacid (1) succinic acid
(2) adipic acid (3) suberic acid (4) sebacic acid (5) dodecanoic
acid.
FIGURE 8 Optical microphotographs of BiBOX at 250ꢀC (a) and
poly(BiBOX-dodecanedioic acid) at 260ꢀC (b). Width of pictures
is 400 mm, and the magnification of an objective is ꢃ20.
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mation of the monomer starts at the temperature of 250ꢀC.
The sublimation is visible in the microscope as disappearing
of the sample. The melting temperature of the BiBOX is
330ꢀC and no LC phase was observed.
As follows from the observation under a polarizing micro-
scope, melting temperature from the mesophase to an iso-
tropic liquid is 260ꢀC for the poly(BiBOX-dodecanedioic
acid) [sample 5 in Fig. 7(a, b)] and 270ꢀC for the poly(Bi-
BOX-sebacic acid) [sample 4 in Fig. 7(a, b)], respectively.
This is in accordance with DSC results [Fig. 7(a, b)]. The
presence of the LC phase (probably nematic) was observed
in AAþBB polymers at the isotropization temperatures. Fig-
ure 8(b) shows the melting of the mesophase of sample 5 at
260ꢀC with nematic droplets in the back field indicating the
isotropic phase. Figure 9 presents the microphotographs of
the characteristic textures for poly(BiBOX-sebacic acid)
(sample 4): (a) crystalline phase at 30ꢀC and (b) nematic
phase with the some crystalline parts (yellow rod-like
spots).
CONCLUSIONS
Two different types of compounds containing a biphenyl
unit, 2-oxazoline units and another functionality in the same
molecule were synthesized. The first monomer of AB-type
contained, beside the biphenyl as mesogen, a hydroxyl group
and the 2-oxazoline, while the second type contains two 2-
oxazoline groups and represents a monomer of the AA-type.
Both monomers were used in thermally induced polyaddi-
tion reactions. The structure of all polymers was determined
by NMR and IR spectroscopy. The rod-like structure of the
biphenyl unit containing polymers influenced thermal prop-
erties and thermal stability. Thermal properties of AAþBB-
type polymers are strongly influenced with the length of an
alkyl linker. Microphotographs of polymers proved the exis-
tence of the mesophase with nematic texture in the related
temperature range below the isotropization temperature.
FIGURE 9 Optical microphotographs of poly(BiBOX-sebacic
acid) at 30ꢀC (a) and 250ꢀC (b). Width of pictures is 400 mm;
magnification of the objective is ꢃ20.
ACKNOWLEDGMENTS
endothermic signals. The isotropization temperatures
decrease with the increasing length of the aliphatic chain in
the backbone. The area between these two signals should
represent a mesophase (approximately 250–300ꢀC) as con-
firmed by microscopy measurements. Thermal properties of
poly(BiBOX-succinic acid) and poly(BiBOX-adipic acid) are
influenced by the fact that the signals of isotropization and
degradation processes above 300ꢀC are overlapped. There-
fore, the signals of isotropization were missing in the records
of second heating [Fig. 7(b)]. The overlapping of isotropiza-
tion and degradation was confirmed in DSC measurements,
where the temperature range of first heating was from 25 to
300ꢀC.
This work was supported by Project no. 2/0157/09 from the
Slovak Scientific Grant Agency and by Ministry of Education,
Youths and Sports of the Czech Republic (grant MSM
0021620835). The authors are also thankful to N. Pronayova
for measurements of NMR spectra in the frame of Slovak
national program for the research and development No.
2003SP200280203. This publication is the result of the project
implementation: Centre for materials, layers and systems for
applications and chemical processes under extreme conditions
supported by the Research & Development Operational Pro-
gram funded by the ERDF.
REFERENCES AND NOTES
The texture of crystalline and LC phases and phase transition
temperatures of monomers and polymers were determined
by a polarizing optical microscope equipped with a heating
stage. Figure 8(a) shows a crystalline structure of the BiBOX
below 250ꢀC. This structure is stable up to 250ꢀC and subli-
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