Synthesis and characterization of side-chain cholesterol derivatives based on double bond

Article abstract of DOI:10.1016/j.molstruc.2012.03.034

After steps of esterification, epoxidation and ring-opening, a series of novel monomers of 5-hydroxyl-6-methacryloyloxy-3-alkylate, C_nCOOCh (n = 1, 2, 3, 4, 5) were synthesized. After that, the corresponding polymers (P_nCOOCh, n = 1, 2, 3, 4, 5) were obtained by free radical polymerization. The molecular structure, composition and thermal behaviors of monomers and polymers were confirmed by ¹H NMR, FTIR, single crystal diffractometer, GPC, DSC and TGA. The results indicate that although their molecular weights are not high, all the polymers have high glass transition (T_g) and degradation temperature. In addition, T_g gradually decreases with increasing of alkyl chain lengths, and the degradation temperature increases with the increase of carbon number.

Full text of DOI:10.1016/j.molstruc.2012.03.034

Journal of Molecular Structure 1019 (2012) 1–6
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis and characterization of side-chain cholesterol derivatives based
on double bond
⇑
Yun-Long Yu, Jun-Wei Bai, Jun-Hua Zhang
State Key Laboratory of Polymer Materials Engineering of China, Sichuan University, Chengdu 610065, China
a r t i c l e i n f o
a b s t r a c t
Article history:
After steps of esterification, epoxidation and ring-opening, a series of novel monomers of 5-hydroxyl-6-
methacryloyloxy-3-alkylate, CnCOOCh (n = 1, 2, 3, 4, 5) were synthesized. After that, the corresponding
polymers (PnCOOCh, n = 1, 2, 3, 4, 5) were obtained by free radical polymerization. The molecular struc-
ture, composition and thermal behaviors of monomers and polymers were confirmed by 1H NMR, FTIR,
single crystal diffractometer, GPC, DSC and TGA. The results indicate that although their molecular
weights are not high, all the polymers have high glass transition (Tg) and degradation temperature. In
addition, Tg gradually decreases with increasing of alkyl chain lengths, and the degradation temperature
increases with the increase of carbon number.
Received 10 January 2012
Received in revised form 14 March 2012
Accepted 14 March 2012
Available online 2 April 2012
Keywords:
Cholesterol
Synthesis
Ó 2012 Elsevier B.V. All rights reserved.
Polymers
Crystal structure
Thermal analysis
1. Introduction
have been paid on the synthesis and characterization of MJLCPs
[17–21]. As known to all [6], cholesterol is a good mesogen unit
Cholesterol is a kind of cyclopentane phenanthrene derivatives
(Scheme 1), belonging to the family of steroid compound. Seen
from the structural formula, there are two functional groups in
cholesterol skeleton, hydroxyl on C3 position and double bond
on C5AC6 position. In the past years, side chain [1–5] and liquid
crystal [6–12] polymers based on cholesterol have been docu-
mented, mainly because of their particular optical properties, such
as selective reflection and transmission of light, thermochromism
and circular dichroism [13]. The research work mentioned above
were all done based on hydroxyl of the cholesterol, because
C3AOH has good reactivity than the double bond. However, be-
sides C3AOH, C5@C6 can be used to fabricate novel cholesterol
derivatives having unique functions, which will be interesting
and attractive. In our previous research work [14,15], a series of
new type of monomers and corresponding polymers modified on
C6 position have been reported, the difference is that the hydroxyl
groups was protected by etherification method with different
length. In this paper, the hydroxyl group was protected by esterifi-
cation method with different alkyl length.
with fairly rigidity. We want to know if these kinds of monomers
and their corresponding polymers synthesized based on double
bond of cholesterol will have the properties like MJLCPs. Wang
et al. [15] in our group have synthesized novel cholesterol deriva-
tives starting from the double-bond of cholesterol. All the poly-
mers display apparent glass transition (Tg) and excellent
degradation temperature though no liquid crystalline properties
have been found. In their work, C3AOH was firstly protected by
etherification, however, to our knowledge; the ether bond is not ri-
gid enough to induce the generation of liquid crystalline. So, in this
paper, we reported our new molecular design of novel cholesterol
derivatives. C3AOH of cholesterol was firstly protected by esterifi-
cation, and then C5@C6 was modified by oxidizing and ring-open-
ing reaction to synthesize novel polymerizable monomers and
corresponding polymers.
2. Experimental
2.1. Materials
Since Zhou et al. [16] firstly proposed the concept of mesogen-
jacketed liquid crystalline polymers (MJLCPs), in which the
mesogenic groups are laterally attached to the polymer backbones
without or with only short linkages. Then considerable attentions
Cholesterol, acetic anhydride, propionic acid, butyric acid,
pentanoic acid, hexanoic acid, dicyclohexylcarbodiimide (DCC),
4-dimethylaminopyridine (DMAP), pyridine, 3-chloroperoxyben-
zoic acid (m-CPBA),
a-methacrylic acid, hydroquinone, etc., all
⇑
were purchased from GuangHua Chemical Co. of China, and used
as received. Tetrahydrofuran (THF, analytical reagent; GuangHua
Corresponding author. Fax: +86 28 85402465.
E-mail address: zhangjh@scu.edu.cn (J.-H. Zhang).
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.03.034

2
Y.-L. Yu et al. / Journal of Molecular Structure 1019 (2012) 1–6
2.3. Synthesis process
The final cholesteryl derivatives were synthesized starting from
cholesterol. The detailed synthetic route is shown in Scheme 2.
2.3.1. Synthesis of cholesteryl acetate
Cholesterol (30 g, 0.08 mol), acetic anhydride (15 ml), DCC (8 g,
0.04 mol), and a few drops of pyridine were added to fleshly dis-
tilled THF (100 ml) and the reaction mixture was refluxed for
72 h under N2 atmosphere. Then the white precipitate was re-
moved by filtration and the filtrate was evaporated, the crude
product was recrystallized twice from ethanol. Yield: 90.2%. 1H
NMR (400 MHz, CDCl3, ppm) d = 5.37 (s, 1H, 6-H), 4.62 (m, 1H,
3-H), 2.26 (m, 2H, ACH2A), 2.01 (m, 3H, ACH3), 0.67–1.96 (m,
Scheme 1. The chemical structure of cholesterol.
Chemical Reagents) was refluxed over sodium and distilled before
use. Benzoyl peroxide (BPO) was purified by recrystallization twice
from ethanol. Chlorobenzene was washed with H2SO4, NaHCO3,
distilled water and then distilled from anhydrous magnesium sul-
fate. Other solvents were used directly without any purification.
41H). IR (KBr pellet, cmÀ1):
m = 2942.9–2867.2 (stretching of
ACH3 and ACH2A), 1735.7 (stretching of AC@O), 1667.6 (stretch-
ing of AC@C), 1244.7, 1032.0 (stretching of CAOAC).
2.3.2. Cholesteryl propionate
Cholesterol (5 g, 0.01 mol), DCC (2.67 g, 0.01 mol), DMAP
(0.12 g, 1 mmol), propionic acid (1.9 g, 0.02 mol), and dried THF
(100 ml) were mixed in a 250 ml round-bottom flask and stirred
for 36 h at room temperature. The floating solid was filtrated off
and the solvent was concentrated. After that, the concentrated
mixture was poured into 500 ml distilled water with fierce stirring.
After twice washing, the white sediment was collected and recrys-
tallized from ethanol. Yield: 91.3%. 1H NMR (400 MHz, CDCl3, ppm)
d = 5.37 (s, 1H, 6-H), 4.61 (m, 1H, 3-H), 2.25 (m, 2H, ACH2A), 0.67–
2.2. Instruments
FTIR spectra were measured on a FT-IR (Nicolet) spectropho-
tometer. Proton nuclear magnetic resonance (1H NMR) spectra
were recorded on a BrukerARMx-400 operating at 400 MHz in deu-
terated chloroform. Differential scanning calorimetry (DSC) was
carried out on a Thermal analysis (TA) DSC-Q30 with a liquid nitro-
gen cooling system. The rates of heating and cooling rates were
10 °C/min. Thermogravimetric analysis (TGA) was performed from
30 to 500 °C at a heating rate of 10 °C/min on a TA TGA-DSC Q600
thermogravimetric analyser under nitrogen atmosphere. The crys-
tal structure was obtained on CAD4SDP-44 M/H four-circle single
crystal diffractometer made by Enraf–Nonius Company of Holland.
The gel permeation chromatography (GPC) was conducted with a
Breeze Waters system equipped with a Water 515 HPLC pump
using polystyrenes as the standard and tetrahydrofuran (THF) as
the eluent at a flow rate of 1.0 ml/min at 40 °C.
1.94 (m, 46H). IR (KBr pellet, cmÀ1):
m = 2943.8–2866.6 (stretching
of ACH3 and ACH2A), 1737.7 (stretching of AC@O), 1664.7
(stretching of AC@C), 1243.5, 1031.2 (stretching of CAOAC).
Cholesteryl butyrate: Yield: 91.7%. 1H NMR (400 MHz, CDCl3,
ppm) d = 5.38 (s, 1H, 6-H), 4.63 (m, 1H, 3-H), 2.28 (m, 2H, ACH2A),
0.67–1.93 (m, 48H). IR (KBr pellet, cmÀ1):
m = 2945.9–2867.3
(stretching of ACH3 and ACH2A), 1736.9 (stretching of AC@O),
1666.8 (stretching of AC@C), 1243.5, 1032.2 (stretching of
CAOAC).
Cholesteryl valerate: Yield: 92.5%. 1H NMR (400 MHz, CDCl3,
ppm) d = 5.37 (s, 1H, 6-H), 4.60 (m, 1H, 3-H), 2.25 (m, 2H, ACH2A),
0.67–1.86 (m, 50H). IR (KBr pellet, cmÀ1):
m = 2943.7–2866.8
(stretching of ACH3 and ACH2A), 1735.9 (stretching of AC@O),
1667.2 (stretching of AC@C), 1244.9, 1031.9 (stretching of
CAOAC).
Cholesteryl caproate: Yield: 93.4%. 1H NMR (400 MHz, CDCl3,
ppm) d = 5.36 (s, 1H, 6-H), 4.61 (m, 1H, 3-H), 2.22 (m, 2H, ACH2A),
0.67–1.88 (m, 52H). IR (KBr pellet, cmÀ1):
m = 2941.8–2868.9
(stretching of ACH3 and ACH2A), 1736.1 (stretching of AC@O),
1668.1 (stretching of AC@C), 1246.7, 1032.5 (stretching of
CAOAC).
2.3.3. Synthesis of 5,6-epoxy-cholesteryl acetate
5,6-Epoxy-cholesteryl acetate was prepared according to the
method reported elsewhere [22]. Cholesteryl acetate (8.57 g,
0.02 mol), m-CPBA (4.14 g, 0.024 mol), CH2Cl2 (60 ml) were added
to a 150 ml round-bottom flask with flap loosely capped, and then
stirred for 24 h at room temperature. After removing the white
precipitate, the filtrate was washed by saturated sodium bicarbon-
ate and sodium chloride solution several times, sequentially, and
purified from methanol at last. Yield: 89.2%.1H NMR (400 MHz,
CDCl3, ppm) d = 5.02 (s, 1H, 6-H), 4.85 (m, 1H, 3-H), 2.18 (m, 2H,
ACH2A), 2.03 (m, 3H, ACH3), 0.67–1.96 (m, 41H). IR (KBr pellet,
cmÀ1):
m = 2952.4–2868.8 (stretching of ACH3 and ACH2A),
1732.7 (stretching of AC@O), 1240.9, 1039.4 (stretching of
CAOAC).
5,6-Epoxy-cholesteryl propionate: Yield: 91.6%.1H NMR
(400 MHz, CDCl3, ppm) d = 5.01 (s, 1H, 6-H), 4.84 (m, 1H, 3-H),
Scheme 2. The synthetic route of monomers and corresponding polymers.

Y.-L. Yu et al. / Journal of Molecular Structure 1019 (2012) 1–6
3
2.20 (m, 2H, ACH2A), 0.67–1.94 (m, 46H). IR (KBr pellet, cmÀ1):
= 2945.5–2851.6 (stretching of ACH3 and ACH2A), 1732.2
2.4. Synthesis of polymers
m
(stretching of AC@O), 1208.4, 1084.0 (stretching of CAOAC).
5,6-Epoxy-cholesteryl butyrate: Yield: 89.3%. 1H NMR
(400 MHz, CDCl3, ppm) d = 5.03 (s, 1H, 6-H), 4.86 (m, 1H, 3-H),
2.21 (m, 2H, ACH2A), 0.68–1.92 (m, 48H). IR (KBr pellet, cmÀ1):
All the free radical polymerization occurred in chlorobenzene
with BPO as initiator. A representative polymerization was as
follows: typically, 0.3 g CnCOOCh and 2 mg BPO were placed in a
reaction tube with a magnetic stir bar, and then, 1.5 g chloroben-
zene was added. After that, the reaction mixture was purged with
nitrogen and subjected to four freeze–thaw cycles and sealed un-
der vacuum. The tube was placed into an oil bath at 90 °C for
48 h. The tube was broken and the mixture was precipitated into
methanol. White precipitates were filtered and dissolved in THF
again. After another process of precipitation, white solids were
collected and dried under vacuum at 60 °C for 24 h.
m
= 2947.5–2869.6 (stretching of ACH3 and ACH2A), 1732.3
(stretching of AC@O), 1191.8, 1010.5 (stretching of CAOAC).
5,6-Epoxy-cholesteryl valerate: Yield: 86.5%. 1H NMR (400 MHz,
CDCl3, ppm) d = 5.02 (s, 1H, 6-H), 4.84 (m, 1H, 3-H), 2.19 (m, 2H,
ACH2A), 0.66–1.87 (m, 50H). IR (KBr pellet, cmÀ1):
m = 2957.4–
2868.5 (stretching of ACH3 and ACH2A), 1737.5 (stretching of
AC@O), 1186.8, 1029.1 (stretching of CAOAC).
5,6-Epoxy-cholesteryl caproate: Yield: 92.5%. 1H NMR
(400 MHz, CDCl3, ppm) d = 5.04 (s, 1H, 6-H), 4.86 (m, 1H, 3-H),
2.21 (m, 2H, ACH2A), 0.67–1.89 (m, 52H). IR (KBr pellet, cmÀ1):
3. Results and discussion
m
= 2951.8–2868.3 (stretching of ACH3 and ACH2A), 1738.2
3.1. Synthesis and characterization of monomers
(stretching of AC@O), 1174.8, 1028.2 (stretching of CAOAC).
In our previous work [14], the hydroxyl group on C3 position
was firstly protected by etherification method, in this paper, the
hydroxyl group was firstly esterified by acetic anhydride or fatty
acid with different chain length. For the synthesis of cholesteryl
acetate, many methods such as esterified by acylchloride [23,24],
DCC–DMAP [25], acetic anhydride [26], etc. can be adopted. The
method by anhydride was adopted in this experiment due to its
less pollution and relatively mild reaction conditions. The other
cholesteryl esters were synthesized by directly esterification with
different fatty acids under DCC–DMAP catalyst.
2.3.4. Synthesis of 5-hydroxyl-6-methacrylate-cholesteryl acetate
(C1COOCh)
5,6-Epoxy-cholesteryl acetate (3 g, 6.7 mmol) and 1 mg hydro-
quinone were dissolved in 15 ml
a-methacrylic acid without any
catalyst. The reaction was allowed to proceed at 80 °C for 48 h un-
der nitrogen atmosphere. The mixture was dissolved in acetic ether
and then washed by saturated sodium bicarbonate and sodium
chloride solution several times, sequentially. The organic layer
was dried by magnesium sulfate anhydrous for a night, and the
crude product was obtained after evaporation of solvent under re-
duced pressure. And then it was purified by silica gel column chro-
matography with mineral ether and acetic ether (8:1). Yield: 58.8%.
1H NMR (400 MHz, CDCl3, ppm) d = 5.62, 6.13 (s, 2H, @CH2), 5.31
(m, 1H, 6-H), 4.78 (s, 1H, 3-H), 2.22 (m, 2H, ACH2A), 2.01 (m,
After the esterification on C3 position, the double bond between
C5, C6 position was oxidated and with an epoxy-ring-opening reac-
tion with methacrylic acid to obtain a series of new monomers, just
as the method we reported [14].
The structures of all the monomers were confirmed by 1H NMR
and FTIR. Take C2COOCh as an example, the characteristic absorp-
tion peak of CH2@CHA was found at about 1636 cmÀ1 in FTIR spec-
tra. The 1H NMR spectrum of monomer C2COOCh (Fig. 1) showed
the representative resonances of the vinyl group at 6.11 and
5.60 ppm, indicating that ring-opening occurred between epoxide
3H, ACH3), 0.67–1.98 (m, 45H). IR (KBr pellet, cmÀ1):
m = 3474.9
(stretching of AOH), 3101.7 (stretching of AC@CH2), 2941.9–
2869.5 (stretching of ACH3 and ACH2A), 1737.0, 1696.2 (stretch-
ing of AC@O), 1636.1 (stretching of AC@C), 1241.7, 1025.2
(stretching of CAOAC).
5-Hydroxyl-6-methacrylate-cholesteryl propionate (C2COOCh):
Yield: 62.2%. 1H NMR (400 MHz, CDCl3, ppm) d = 5.60, 6.11 (s,
2H, @CH2), 5.19 (m, 1H, 6-H), 4.74 (s, 1H, 3-H), 2.26 (m, 2H,
and a-methacrylic acid. The spectrum also showed the character-
istic resonances of ACOOCHA (c and d) on C6 and C3 position at
5.19 and 4.74 ppm, respectively. All of the above results verified
that the terminal double bond was connected to the cholesterol
side-chain as a pendant group, and the polymerizable monomers
were successfully obtained.
ACH2A), 0.68–2.05 (m, 50H). IR (KBr pellet, cmÀ1):
m = 3478.2
(stretching of AOH), 2945.9–2869.1 (stretching of ACH3 and
ACH2A), 1737.1, 1701.3 (stretching of AC@O), 1636.0 (stretching
of AC@C), 1188.4, 1013.3 (stretching of CAOAC).
In our previous work [15], we have proved that the polymeriz-
able group is connected on C6 position by single crystal. Again, a
single crystal of monomer C1COOCh was cultivated from its acetic
ether solution, and clear pictures were obtained through four-cir-
cle single crystal diffractometer shown in Fig. 2. The picture of
monomer C1COOCh shows that C3 connects with CH3COOA (up),
C5 with AOH (down) and C6 with CH2@C (CH3) COOA (up). The de-
tailed single crystal data are listed in Table 1.
5-Hydroxyl-6-methacrylate-cholesteryl butyrate (C3COOCh):
Yield: 56.7%. 1H NMR (400 MHz, CDCl3, ppm) d = 5.60, 6.12 (s,
2H, @CH2), 5.17 (m, 1H, 6-H), 4.74 (s, 1H, 3-H), 2.25 (m, 2H,
ACH2A), 0.66–2.07 (m, 52H). IR (KBr pellet, cmÀ1):
m = 3486.8
(stretching of AOH), 2943.1–2869.2 (stretching of ACH3 and
ACH2A), 1731.9, 1701.3 (stretching of AC@O), 1636.1 (stretching
of AC@C), 1282.4, 1011.7 (stretching of CAOAC).
5-Hydroxyl-6-methacrylate-cholesteryl valerate (C4COOCh):
Yield: 58.5%. 1H NMR (400 MHz, CDCl3, ppm) d = 5.60, 6.11 (s, 2H,
@CH2), 5.15 (m, 1H, 6-H), 4.73 (s, 1H, 3-H), 2.25 (m, 2H, ACH2A),
3.2. Synthesis and characterization of polymers
0.66–2.06 (m, 54H). IR (KBr pellet, cmÀ1):
m = 3474.9 (stretching of
AOH), 3101.7 (stretching of AC@CH2), 2941.9–2869.5 (stretching
of ACH3 and ACH2A), 1737.0 (stretching of AC@O), 1636.1 (stretch-
ing of AC@C), 1241.7, 1025.2 (stretching of CAOAC).
The free radical polymerizations of monomers were carried out
in chlorobenzene at 90 °C using BPO as the initiator. The polymer-
ization results are summarized in Table 1. All the monomers can be
polymerized to give the corresponding polymers, but the molecu-
lar weights are not high, corresponding to 8–12 repeat units. This
may be due to the fact that the large lateral structure exhibits ste-
ric hindrance, decreasing the accessibility of the double bond for
polymerization. The polymers obtained are white solids that have
good solubility in many common organic solvents, such as THF,
chloroform, dichloromethane, toluene, dimethylsulfoxide (DMSO)
5-Hydroxyl-6-methacrylate-cholesteryl caproate (C5COOCh):
Yield: 62.1%. 1H NMR (400 MHz, CDCl3, ppm) d = 5.59, 6.11 (s,
2H, @CH2), 5.16 (m, 1H, 6-H), 4.73 (s, 1H, 3-H), 2.24 (m, 2H,
ACH2A), 0.66–2.08 (m, 56H). IR (KBr pellet, cmÀ1):
m = 3476.6
(stretching of AOH), 2951.7–2868.5 (stretching of ACH3 and
ACHA), 1717.9, 1702.4 (stretching of AC@O), 1637.4 (stretching
of AC@C), 1159.5, 1017.6 (stretching of CAOAC).

4
Y.-L. Yu et al. / Journal of Molecular Structure 1019 (2012) 1–6
Fig. 1. 1H NMR spectra of monomer C2COOCh and polymer P2COOCh.
Fig. 2. The crystal structure of C1COOCh.
and ethyl acetate. The chemical structures of CnCOOCh and
PnCOOCh were confirmed by a combination of analytical tech-
niques, for example, infrared (IR), 1H NMR (Fig. 1). The characteris-
tic peaks at 5.8–6.4 ppm of vinyl groups in the 1H NMR spectrum of
monomer disappeared after being polymerized and those of the
ACHACH2A, polymer backbone were observed instead, indicating
the formation of the polymers. The results of polymerization are
summarized in Table 2. The sharp characteristic signals of
CnCOOCh became broad after polymerization due to the limited
mobility of protons.
Fig. 3 presents DSC thermograms of the polymers on the second
heating, and the phase transition temperatures are summarized in

Y.-L. Yu et al. / Journal of Molecular Structure 1019 (2012) 1–6
5
Table 1
Crystal data for monomer C1COOCh.
Parameter
C1COOCh
Crystal size (mm3)
Formula
0.36 Â 0.28 Â 0.19
C
33H54O5
Temperature (K)
Formula weight
Crystal system
Space group
296.0
530.76
Monoclinic
C2
a, b, c (Å)
31.9922, 9.9421, 10.3358
a
, b,
c
(°)
90.00, 93.758(3), 90.00
3280.4(2)
4
1.075
1168
Volume (Å3)
Z
qcalc (mg, mm3)
F(000)
Reflections collected
Final R indices (all data)
7423
R1 = 0.0756, wR2 = 0.1692
Table 2
Polymerization, GPC, DSC and TGA results of polymers.
Fig. 4. TGA thermograms of the polymers.
b
b
c
d
Polymers Yielda (%) Mn
Mw
Db
Tg (°C) Td1 (°C) Td2 (°C)
P1COOCh 61
P2COOCh 57
P3COOCh 54
P4COOCh 49
P5COOCh 42
5880 8420 1.43 222.5
3850 5180 1.35 180.1
3380 4660 1.38 178.6
3320 4460 1.34 175.6
3200 4380 1.37 173.3
329.4
330.5
333.3
337.4
342.7
347.3
349.9
353.6
356.1
360.2
a
Yield was calculated after twice molecular weight fractionation through dis-
solution–precipitation.
b
Obtained from a Waters 2410 GPC instrument, linear PS as standards.
c,d
The temperature at which starting weight loss and maximum weight loss of the
sample was reached from TGA under nitrogen atmosphere at 10 °C/min.
Scheme 3. The structure diagram of the corresponding polymers.
Table 3
The length of Ln with different carbon number through
molecular modeling.
Polymers
Length of Ln (Å)
P1COOCh
P2COOCh
P3COOCh
P4COOCh
P5COOCh
5.252
5.959
7.094
8.034
9.249
ble bond on cholesterol. In cholesterol esters, double bond offers
rigidity to the mesogen units, however, the ring-opening reaction
destroyed the rigidity, and then no mesogen units exist to be free
oriention. Compared to polymers with etherification on C3AOH
[15], polymers with esterification have a higher Tg, which shows
us that ester bond has indeed more rigidity than ether bond.
Fig. 4 shows TGA thermograms of the polymers, and the TGA
data is listed in Table 2. It exhibited that the initial weight loss
temperatures were greater than 329 °C for all the polymers, indi-
cating that they behave excellent thermal stability. In addition,
as the length of side chain at C3 position increases gradually, the
degradation temperature presents an increasing trend. Because
with the increase of carbon number, the symmetry of the side
chain increases and the steric hindrance also increases. The linkage
point is gradually moving to the middle of the side chain, more ste-
ric hindrance provides more thermal stabilities of polymers. The fi-
nal decomposition temperature can reach higher than 400 °C,
Fig. 3. DSC thermograms of the polymers.
Table 2. For all the polymers, glass transitions can be observed
clearly. The temperature of glass transition (Tg) of polymers de-
creased slightly from 222.5 to 173.3 °C with increase of carbon
number (n) in alkyl chains on C3 position from 1 to 5. Because
the alkyl chains are flexible, more carbon numbers offer more flex-
ibility for polymer domains. That is to say, the existence of flexible
side group is helpful for the movement of polymer chain. Because
C1COOCh has relatively smaller steric hindrance, after polymeriz-
ing, higher molecular weight with a higher Tg was obtained. There
are not other thermal transitions displayed in the DSC thermo-
grams, which tell us that all the polymers are amorphous rather
than crystalline. Even under POM, we cannot observe any liquid
crystal phase transition, which indicated that all the polymers
did not behave liquid crystal properties due to the damage of dou-

6
Y.-L. Yu et al. / Journal of Molecular Structure 1019 (2012) 1–6
indicating that the polymers have good thermal properties and can
be potentially used as heat-resisting materials.
Acknowledgment
In order to better understand the alkyl length influence on Tg
and thermal properties, simply molecular modeling was used to
describe the molecular structure. We suppose that all the alkyl
chains connected on C3 position are straight line arrangement.
The side chain was divided into two parts from C6 position, as
shown in Scheme 3, the length of left part Ln is changeable with
the alkyl length changes, and the length of right part L is fixed. Here
L is 13.237 Å, while the length of the other side is Ln (n = 1–5) pre-
senting in Table 3. Seen from the structure diagram of molecule
and Table 3, the distance from C6 to the terminal group of alkyl
chain becomes increasingly large with the increase of carbon num-
ber. And the result implies that the side chain gets much better
symmetry. The improvement of side chain symmetry provides
more regular arrangement and high stereo-tacticity in polymers.
This work described in this article was supported by the Na-
tional Nature Science Foundation of China (Grant No. 20804026).
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4. Conclusion
A series of novel cholesteryl monomers with different ester
chain length on C3 position and their corresponding polymers
were prepared. The polymerizable groups are connected in the lat-
eral part of cholesterol skeleton. After polymerization, the struc-
tures of all the monomers and polymers were characterized by
1H NMR, FTIR. And all the polymers were characterized by GPC,
DSC, POM, and TGA. Though all the polymers were not observed
having liquid crystal properties, high temperature of Tg and degra-
dation temperature was detected. In addition, the Tg of the poly-
mers decreases, while the degradation temperature increases
with increase of the chain length. On one hand, the side chain is
flexible, and it is helpful for chain movement. Longer side chain of-
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the other hand, the symmetry of the side chain is helpful for
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