Synthesis and liquid crystal behavior of main-chain aliphatic carbonate copolymers derived from diosgenin

Article abstract of DOI:10.1080/15421406.2019.1606398

To synthesize new main-chain aliphatic carbonate liquid crystal (LC) copolymers Dios-(CH₂)₆-(TMC)_x-(DLLA)_y, a compound of diosgenyl derivative Dios-(CH₂)₆-OH was used as an initiator and re

Full text of DOI:10.1080/15421406.2019.1606398

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Synthesis and liquid crystal behavior of main-
chain aliphatic carbonate copolymers derived
from diosgenin
Qifan Chen, Chaoxian Chen, Zhihao Guo, Xiaoxu Xu & Yanhua Lu
To cite this article: Qifan Chen, Chaoxian Chen, Zhihao Guo, Xiaoxu Xu & Yanhua Lu
(
2018) Synthesis and liquid crystal behavior of main-chain aliphatic carbonate copolymers
derived from diosgenin, Molecular Crystals and Liquid Crystals, 675:1, 19-28, DOI:
0.1080/15421406.2019.1606398
1
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
018, VOL. 675, NO. 1, 19–28
2
https://doi.org/10.1080/15421406.2019.1606398
Synthesis and liquid crystal behavior of main-chain
aliphatic carbonate copolymers derived from diosgenin
a
b
b
a
a,c
Qifan Chen , Chaoxian Chen , Zhihao Guo , Xiaoxu Xu , and Yanhua Lu
a
b
School of Chemical Engineering, Eastern Liaoning University, Dandong, 118001, P. R.China; Center for
Molecular Science and Engineering, College of Science, Northeastern University, Shenyang 110819, P. R.
c
China; Key Laboratory of Functional Textile Materials, Liaoning Province, Dandong, 118001, P. R. China
ABSTRACT
KEYWORDS
liquid crystal; aliphatic
polycarbonate; diosgenin;
synthesis; copolymer
To synthesize new main-chain aliphatic carbonate liquid crystal (LC)
2 6 x y
copolymers Dios-(CH ) -(TMC) -(DLLA) , a compound of diosgenyl
derivative Dios-(CH ) -OH was used as an initiator and reactant
2
6
through the ring-opening polymerization of 1,3-trimethylene carbon-
ate and d,l-lactide without other catalyst. The chemical structures of
the copolymers obtained in this study were characterized by Fourier
transform infrared spectrum and proton nuclear magnetic resonance
spectrum. Their LC properties were investigated by polarizing optical
microscopy, differential scanning calorimetry, and X-ray diffraction
measurement. The effect of the diosgenyl derivative content on mes-
ophase and phase transition temperature of the copolymers was dis-
cussed. It was found that three copolymers all displayed fan-shaped
texture of a smectic A phase. The results seemed to show an
increased tendency toward the isotropic temperature for the LC
copolymers with increasing the content of the diosgenyl derivative.
1. Introduction
It is well established that the field of liquid crystal (LC) is multi-disciplinary, requiring
concepts and techniques from chemistry, physics, mathematics, biology and some types
of engineering [1]. At present, more and more LC materials may be applied in bio-
logical related fields such as living systems owing to their self-organising structures
through non-covalent specific interactions [2, 3].
In recent years, aliphatic polycarbonates have been considered as the promising bio-
materials because of their good biocompatibility and well-defined degradation mecha-
nisms [4–6], and no acidic degradation products [7]. A certain application progress has
been made [8–17]. Meanwhile, it has excellent physical properties and surface erosion
degradation mechanism [18], which enable them to proper for applications in the fields
of medicine and life science, such as drug delivery, tissue engineering and organ repair
[19–24]. Until now, many modification methods have been used to gain better proper-
ties. Among them, the incorporation of the bioactive or self-assembly functional com-
pounds to the polymer chain has become one of the most important modification
strategies [25–33]. Copolymerization is an effective method that monomer unit is intro-
duced into the polymers chain to improve the properties [34–36].
CONTACT Xiaoxu Xu
3x.931@163.com
ß 2019 Taylor & Francis Group, LLC

2
0
Q. CHEN ET AL.
Diosgenin, an important kind of steroidal compounds extracted from dioscorea zingi-
berensis [37–40], and it has been traditionally used to hypercholesterolemia [41], and
gastrointestinal ailments [42]. In addition, diosgenin and its derivatives exhibit anti-pro-
liferative and pro-apoptotic activities on cancer cells in vitro [43, 44], including breast
cancer [45], colorectal cancer [46], osteosarcoma [47]. To the best of our knowledge,
however, little research is reported on the biodegradable main-chain aliphatic polycar-
bonate end-capped with diosgenyl groups. Hence, it is necessary to synthesize new
copolymers based on diosgenin, and to study their structure-properties relationships
and explore potential applications in drug delivery.
In this study, new main-chain aliphatic polycarbonates based on diosgenin were syn-
thesized using a diosgenyl derivative as an initiator through the ring-opening polymer-
1
ization of TMC and DLLA. The chemical structure was identified by FT-IR and H
NMR. The LC properties of the copolymers were characterized by polarizing optical
microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction
measurement (XRD). The effect of the diosgenyl derivative content on the phase transi-
tion temperature of the copolymers was discussed.
2. Experimental method
2.1 Materials
All chemicals were obtained from the indicated sources. Tosyl chloride was purchased
from Sinopharm Chemical Reagent Co., Ltd. (Shenyang, China). Diosgenin was pur-
chased from Wuhan Chemical Industry Co., Ltd. (Wuhan, China). 1,6-Hexanediol was
purchased from Qingdao Lilai Fine Chemical Industry Co., Ltd. (Qingdao, China). 1,3-
Trimethylene carbonate (TMC) and d, l-lactide (DLLA) were purchased from Jinan
Biological Engineering Co., Ltd. (Jinan, China). All other solvents and reagents used
were purified by standard methods.
2.2 Measurements
FT-IR spectra were recorded as a KBr disk on a PerkinElmer spectrum One (B) spectrom-
1
eter (PerkinElmer, Foster City, CA, USA). H NMR spectra were obtained using a Bruker
ARX 600 (Bruker, F €a llanden, Swiss) high resolution NMR spectrometer, and chemical
shifts were reported in ppm with tetramethylsilane (TMS) as an internal standard. The
thermal properties was determined with a Netzsch 204 (Netzsch, Hanau, Germany) DSC
ꢀ
equipped with a cooling system at a heating and cooling rate of 10 C/min in a nitrogen
atmosphere. The optical texture was observed with a Leica DMRX POM (Leica, Wetzlar,
Germany) equipped with a Linkam THMSE-600 (Linkam, London, UK) cool and hot
stage. XRD measurements were performed with a nickel-filtered Cu-K radiation with a
a
Bruker D8 Advance (Bruker, Germany) powder diffractometer.
2
.3 Synthesis of Dios-(CH ) -OH
2 6
The synthetic route of the diosgenyl derivative is shown in Scheme 1. 6-
Diosgenoxyhexane-1-ol (Dios-(CH ) -OH) was synthesized according to the method
2
6

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
21
Scheme 1. Synthetic route of diosgenyl derivative
ꢀ
ꢁ1
reported by Hu et al. [33] Yield: 73%, mp: 109.8 C. IR (KBr, cm ): 3333 (–OH); 2929,
2
1
3 2 3
850 (CH –, –CH –); 1241, 1097 (C–O–C). H NMR (d, CDCl , 600 MHz): 5.34 (t, 1H,
J ¼ 2.4Hz, H–6), 4.41(q, 1H, J ¼ 7.8Hz, H–16), 3.64 (t, 2H, J ¼ 6.6Hz, H–1), 3.49–3.43
(
(
m, 3H, H–2 and H–26eq), 3.38 (t, 1H, J ¼ 10.8Hz, H–26ax), 3.12 (m, 1H, H–3), 2.37
m, 1H, H–4eq), 2.18 (m, 1H, H–4ax), 1.02 (s, 3H, H–19), 0.98 (d, 3H, J ¼ 7.2Hz,
H–21) , 0.80 (m, 6H, H–18, H–27), 2.03–1.05 (m, 31H, others).
2
.4 Synthesis of Dios-(CH ) -(TMC) -(DLLA)
2 6 x y
The synthetic route of three copolymers is shown in Scheme 2. They were synthesized
through the ring-opening polymerization of TMC and DLLA using Dios-(CH ) -OH as
2
6
an initiator under argon atmosphere. According to feed ratio, three copolymers were
named as P : Dios-(CH ) -OH/TMC/DLLA ¼ 0.2/1/1, P : Dios-(CH ) -OH/TMC/
1
2 6
2
2 6
DLLA ¼ 0.25/1/1, and P : Dios-(CH ) -OH/TMC/DLLA ¼ 1/1/1.
3
2 6
The general synthetic procedure for the copolymers was described as follows:
Dios-(CH ) -OH, TMC and DLLA with different feed ratio were placed into a poly-
2
6
merization glass tube, which was degassed in vacuum by several vacuum-purge
cycles, and then sealed under argon atmosphere. The sealed tube was placed into the
ꢀ
oil bath for 8 h at 150 C. After completion of the reaction, the polymerization tube
was chopped, the obtained crude product was purified by dissolving it in dichloro-
methane and precipitated in methanol. The resulting product was placed in a vac-
uum oven overnight to obtain the final product Dios-(CH ) -(TMC) -(DLLA) . As
2
6
x
y
an example, the structure characterization of the copolymer P was supplied. Yield:
2
ꢁ
1
1
4
2%; IR (KBr, cm ): 2930, 2901 (–CH , –CH –); 1744 (C ¼ O); 1249 (C–O–C). H
3
2
1
NMR (d, ppm from TMS in CDCl ): H NMR (d, CDCl , 600 MHz): d ¼ 5.34 (H–1),
3
3
5
2
1
.17 (H–2), 4.23 (H–3), 3.46 (H–4), 3.38 (H–5), 3.11 (H–6), 2.36 (H–7), 2.19 (H–8),
.01 (H–9), 1.38(H–10), 1.03 (H–11), 0.95 (H–12), 0.79 (H–13, H–14),
.93–1.05 (others)。

2
2
Q. CHEN ET AL.
Scheme 2. Synthetic route of the copolymers P -P3
1
3. Results and discussion
3.1 Synthesis and characterization
To obtain main-chain aliphatic carbonate LC copolymers, a diosgenyl derivative with
six methylene segments, shown in Scheme 1, was synthesized according to the reported
literature [33]. Then three copolymers were obtained through the ring-opening poly-
merization of TMC and DLLA using Dios-(CH ) -OH as macroinitiator under argon
2
6
1
atmosphere, the corresponding synthetic route is shown in Scheme 2. FT-IR and H
NMR spectra were used to identify chemical structure of the aliphatic carbonate
LC copolymers.
Figure 1 shows FT-IR spectra of three LC copolymers. Due to similar structure,
P was analyzed as an example. FT-IR spectrum of P showed typical stretching
2
2
ꢁ
1
vibration bands at 2930-2901, 1744, and 1249 cm , which were assigned to C–H,
1
C ¼ O, and C–O–C, respectively. Figure 2 shows H NMR spectrum of P . After the
2
polymerization, the typical signal of the diosgenyl group could be observed, but the
signal peaks of HOCH – at 3.64 ppm for Dios-(CH ) -OH shifted to 3.46 ppm for
2
2 6
P2. In addition, DLLA and TMC repeating units also appeared at 5.17 and 4.23 ppm,
respectively. The spectra were agreed well with the proposed molecular structure
of P2.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
23
Figure 1. FT-IR spectra of P -P3
1
1
Figure 2. H NMR spectrum of P2
3.2 POM analysis
To observe the optical textures and phase transition temperatures of three copolymers
obtained in this study, a POM with hot stage was used. The diosgenyl derivative Dios-
(
CH ) -OH exhibited enantiotropic fan-shaped texture of smectic A (S ) phase [33].
2
6
A
Three copolymers P -P derived from Dios-(CH ) -OH also showed fan-shaped texture
1
3
2 6
of a S phase during the heating and cooling cycles. As a representative, P was dis-
A
2
ꢀ
cussed. When P was heated to about 45 C, the color texture appeared and the birefrin-
gence disappeared at 108 C. When the isotropic state was cooled to 106 C, the
mesomorphism appeared, when cooling continued to 80 C, typical fan-shaped texture
2
ꢀ
ꢀ
ꢀ
of a smectic phase appeared, and no crystallization behavior could be observed with fur-
ther cooling. Similar textures were found for P and P . The optical textures of P are
1
3
2
shown in Figure 3.

2
4
Q. CHEN ET AL.
ꢀ
Figure 3. Optical textures of P (200ꢂ). (a) color texture on heating to 45 C; (b) fan-shaped texture
2
ꢀ
on cooling to 80 C.
3.3 DSC analysis
DSC was used to study the thermal behavior of the copolymers. The corresponding
phase transition temperatures and enthalpy changes were obtained during first cooling
and second heating scans. All phase transitions were reversible and do not change on
repeated heating and cooling cycles. The phase transition temperatures determined by
DSC were consistent with POM results. DSC curves of the copolymers P -P are shown
1
3
Figure 4.
According to the literature reported by Hu et al. [33], the DSC curves of the dio-
ꢀ
sgenyl derivative Dios-(CH ) -OH revealed a melting transition at 106.1 C and a S to
2
6
A
ꢀ
isotropic phase transition at 126.9 C. For three copolymers, as could be clearly seen in
Figure 4, they only showed a S to isotropic phase transition on heating cycle and iso-
A
tropic to a S phase transition on cooling cycle, which can be confirmed by POM and
A
XRD. However, the glass transition or melting transition peaks were not found on heat-
ing cycle. In addition, with increasing the content of the diosgenyl derivative Dios-
(
CH ) -OH, the isotropic temperature (T ) of the corresponding copolymers P -P
2 6 i 1 3
showed an increased tendency. Similarly, their isotropic to LC phase transition tempera-
ture (T ) also increased. For example, when the content of the diosgenyl derivative was
ai
ꢀ
ꢀ
increased from 9.1% to 33.3%, the T increased from 91.4 C of P to 107.7 C of P ,
i
1
3

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
25
Figure 4. DSC curves of P -P . (a) heating cycle; (b) cooling cycle
1
3
ꢀ
ꢀ
and the T increased from 86.9 C to 103.1 C. These phenomena can be explained as
ai
follows: when the more rigid mesogenic core with diosgenyl unit is introduced into the
polymer molecular chain, intermolecular force is enhanced, this causes an increase in
the T or T .
i
ai
3
.4 XRD analysis
To further identify the LC structure of the copolymers, XRD measurement with variable
temperature was carried out. In general, a sharp and strong peak corresponding to the
periodic distance with short-range order within the layers at small-angle region and a
broad and weak peak associated with lateral packing at wide-angle region can be

2
6
Q. CHEN ET AL.
Figure 5. XRD pattern of P2
observed for smectic structure. For nematic or cholesteric structure, no peak at small-
angle angle appears and only a broad peak at wide-angle region can be observed.
ꢀ
The XRD pattern of the diosgenyl derivative Dios-(CH ) -OH at 118 C showed a
2
6
ꢀ
ꢀ
sharp and intense peak at 2h ¼ 4.4 , and a weak and diffuse peak at 2h ¼ 15.7 , respect-
ively. The corresponding d-spacing of the first-order reflection was 20.1 Å [48]. The
XRD patterns of three copolymers were similar. As a representative, the XRD pattern of
ꢀ
P is shown in Figure 5, which showed a strong peak at 2h ¼ 2.3 , which represented
2
that the molecules arranged in layers with short range, and the calculated first-order
layer d-spacing was 38.5 Å, indicating the formation of a smectic phase, this was in
agreement with the result observed with POM.
4. Conclusions
In the study, three novel aliphatic carbonate liquid crystal copolymers were prepared by
the ring-opening polymerization of TMC and DLLA using diosgenyl derivative as an
initiator under argon atmosphere. They all exhibited fan-shaped texture of a S phase,
A
and only showed a S to isotropic phase transition, while the glass transition or melting
A
transition peaks were not found. Moreover, the corresponding T and T showed an
i
ai
increased tendency with increasing the content of the diosgenyl derivative.
Acknowledgements
This work was supported by Foundation of Eastern Liaoning University (2017ZD004),
Department of Education of Liaoning Province (ldxy2017002), Science and Technology
Committee of Liaoning Province (201602342), and National Nature Science Foundation of
China (51873084).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
27
Declaration of interest statement
No potential conflict of interest was reported by the authors.
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