Synthesis and characterization of side chain polymer with helical PLLA segments containing mesogenic end group

Article abstract of DOI:10.1016/j.polymer.2010.11.041

Series of mesogenic biphenol derivatives HO6OPPOn (n = 4,6,8) were prepared by asymmetric reaction and purified. Then HOLAxO6OPPOn were prepared with controlled molecular weights by adjusting the feed ratios of HO6OPPOn, SnOct₂ catalyst and LLA

Full text of DOI:10.1016/j.polymer.2010.11.041

Polymer 52 (2011) 400e408
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesis and characterization of side chain polymer with helical PLLA segments
containing mesogenic end group
*
Hongru Chen, Qingbin Xue , Zhuohua Li, Lingmin Sun, Quanxuan Zhang
Key lab of Colloid and Interface Chemistry, Ministry of Education, Chemistry and Chemical Engineering College, Shandong University, Shanda South Road No. 27, Jinan 250100, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 June 2010
Received in revised form
Series of mesogenic biphenol derivatives HO6OPPOn (n ¼ 4,6,8) were prepared by asymmetric reaction
and purified. Then HOLAxO6OPPOn were prepared with controlled molecular weights by adjusting the
feed ratios of HO6OPPOn, SnOct catalyst and LLA by Ring-Opening Polymerization. P-AOLAxO6OPPOn
2
materials were obtained in high yields by the free radical polymerization of polymerizable macro-
monomers of AOLAxO6OPPOn synthesized by esterization of HOLAxO6OPPOn with acrylic acid in the
presence of DCC/DMAP. Their molecular weights were characterized by 1H NMR and GPC. Differential
Scanning Calorimeter method and Polarized Optical Microscopy method were used to study their
thermal behaviors. Both AOLAxO6OPPOn and P-AOLAxO6OPPOn materials are found to form LCs with
18 October 2010
Accepted 23 November 2010
Available online 1 December 2010
Keywords:
Poly-l-Lactide
Side chain liquid crystals
Ring-opening polymerization
increased T
resulted in the increase of T
g
, T
m
and T
i
with longer O-LLA segment length. Polymerization of AOLAxO6OPPOn also
, T and T . X-ray diffraction measurements revealed the presence of smectic
g
m
i
phase in these materials. The O-LLA segments are in helical structure from CD spectra and this makes the
resulting polymer materials good candidate of optical materials for huge optical rotation power.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Kimura et al. [34] has prepared series of oligo(
L-lactic acid) with
an isopropoxyl end group. The ellipticity of oligo(L-lactic acid) (O-
PolyLactide (PLA) is one of the most important bioactive poly-
mers used as biodegradable and biocompatible materials [1e10]. It
LLA) by Circular Dichroism (CD) increased with the increase of
degree of polymerization and reached a maximal value at n ¼ 8,
indicating the completely built up of the helical structure in O-LLA,
The ellipticity was keep almost constant for O-LLA with more
repeating numbers but the ellipticity is a little lower than the
maximal value. The better processability of O-LLAs than PLLAs is an
advantage for large area flexible thin film optical devices.
is also noticeable that L,
enantiomers of Lactide, can form interesting helical chiral poly-
mers, Poly- -Lactide (PLLA) or PDLA. Compared to those well
L-Lactide or D, D-Lactide, as important two
L
studied racemeric PLAs used as biomaterials, PLLA and PDLA as
optical pure chiral helical polymers are still not well studied
[
11e16].
Samuel I. Stupp et al. [35,36] has reported for the first obser-
vation of Liquid Crystal (LC) behavior of O-LLA with Cholesteryl
groups attached at the end and studied the self-assembling prop-
Until now many papers have focused on the research of helical
polymers [17e27], but extensive study on PLLA helical polymer as
optically active polymers is still rare [28e31]. Helical PLLA poly-
mers were expected to exhibit optical rotation power in solid state
due to the asymmetric arrangement of atoms in helical main chain
structure. Kobayashi [32] has processed and measured the huge
intrinsic optical rotation power of PLLA in the fiber axis direction of
uniaxial crystal,
of
erty of Chol-(L-Lactic Acid)xOH as building blocks for self-assem-
bling materials. Attachment of LC groups to form LC-LLA materials
can be also a very good way of combining the self-organization
property of LC group and the optical rotation power of helical O-LLA
to get self-organized materials with huge optical rotation power.
Considering that these self-assembling materials could be very
good candidates as biomaterials and also good optical materials,
the study of LC-OLLA materials is one of the very interesting areas
of future.
This report presents the preparation, thermal and phase
behaviors of series of side chain polymers with O-LLA as important
helical chain segments, involving the preparation of molecular
weight-controlled LC-OLLA materials HOLAxOmOPPOn, AOLAx-
OmOPPOn and P-AOLAxOmOPPOn (Scheme 2 and Scheme 3).
ꢀ
r
, as large as 7200 /mm, 300 times larger than that
a
-quartz. Also the measured response change in the amplitude of
transmitted light was up to 10 MHz for fast light modulation [33].
This devotes PLLA as potential mateirals for optical elements and
devices.
*
Corresponding author. Tel.: þ86 531 88366096; fax: þ86 531 88564464.
E-mail address: qbxue@sdu.edu.cn (Q. Xue).
0
032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.11.041

H. Chen et al. / Polymer 52 (2011) 400e408
401
BrC H
n
2n+1
KOH, NaI,
HO
OH
HO
OC H
n 2n+1
EtOH-H
2
O
HOPPOH
HOPPOn
n=4,6,8
HO(CH ) Cl, KOH
2
6
HO(CH
2
)
6
O
n 2n+1
OC H
Toluene/H O, Bu NBr, Reflux
2
4
HO6OPPOn
n=4,6,8
Scheme 1. Synthesis routine of the initiators.
2
. Experimental sections
2.2. Synthesis
2
.1. Materials
2.2.1. Synthesis of mono-substituted biphenol compounds
The synthesis procedure of the initiators was presented as
Scheme 1.
L-Lactide (LLA) was purified by recrystallization three times
from toluene dried as following method. The polymerization of LLA
was performed under Argon atmosphere. Toluene used for the
The general operations were as following [38]: After biphenol
(30 g, 0.16 mol) and KOH (40 g, 0.71 mol) forming a clear solution in
ring-opening polymerization of
L-Lactide as best solvent was dried
2
192 mL Ethanol/H O (v/v 2:1) solution at reflux by magnetic stir-
on Sodium/potassium alloy Na/K (Benzophenone) and distilled off
just before use and transferred with syringes.
ring, equimolar BrCnH2n þ 1 (n ¼ 4,6,8) in ethanol were added
dropwisely under stirring and reflux for 12 h by Thin Layer Chro-
matography (TLC) monitor. The filtrates after filtering off nOPPOn
solid were diluted with large amount of diluted sodium hydroxide
water to recover the resultants by filtration as noted HOPPOn
(n ¼ 4,6,8) and recrystallized twice from ethanol.
Acrylic acid was distilled just before use. Azodiisobutyronitrile
(
AIBN) was recrystallized from ethanol and stored in refrigerator
ꢀ
at 0 C. Stannous octoate, SnOct
2
, was redistilled three times first
as reported in reference [37] and used by quantitatively trans-
ferring with syringe as toluene (Na/K dried) solution of known
0
0
concentration. N, N -Dicyclohexylcarbodiimide (DCC), 4-N, N -
dimethylamino- pyridine (DMAP) was vacuum dried before use.
HOPPO4 yield 32.8%, R
HOPPO6 yield 23.3%, R
HOPPO8 yield 32.0%, R
f
f
f
¼ 0.46 (CHCl
3
2 5
:C H OH ¼ 15:1)
2 5
:C H OH ¼ 15:1)
2 5
:C H OH ¼ 15:1)
CH
2
Cl
2
was dried over P
2
O
5
, when necessary. All the other
¼ 0.44 (CHCl
3
3
materials are commercial available and used as received unless
noted elsewhere.
¼ 0.46 (CHCl
O
O
H
O
ROH/Sn(Oct)2
O
HO
O
O
OR
O
anhydrous toluene, Ar
H
intiators:
ROH:
H
O
x-2
O
L-LA
HOC H12O
OC H
HOLAxO6OPPOn (n=4,6,8)
6
n
2n+1
Cl
1
)
)
O
O
O
H
THF, NEt , BHT
3
O
O
O
OR
OH
O
H
H
O
x-2
2
O
AOLAxO6OPPOn (n=4,6,8)
DCC, DMAP, BHT
Scheme 2. Ring-opening polymerization of LLA and the synthesis of the acrylic esters of the PLLA macromonomers.

402
H. Chen et al. / Polymer 52 (2011) 400e408
O
O
H
O
O
O
2 6
O(CH ) O
n 2n+1
OC H
O
H
H
O
x-2
AOLAxO6OPPOn (n=4,6,8)
AIBN
THF
*
O
O
H
O
O
O
2 6
O(CH ) O
n 2n+1
OC H
O
H
H
O
x-2
*
P-AOLAxO6OPPOn (n=4,6,8)
Scheme 3. Radical polymerization of the acrylic ester macromonomers of O-LLAs.
2
.2.2. Initiators HO6OPPOn (n ¼ 4,6,8)
2.2.3. Ring-opening polymerization of L-LA
A general procedure for the Ring-Opening Polymerization (ROP)
of L-LA was shown in Scheme 2. The feed ratios of L-LA to
HOPPOn were reacted with NaOH, NaI, and Cl(CH
2
)
6
OH in
proper amount of solvent for 48 h with refluxing or by phase-
transfer reaction in toluene with catalytic amount of Bu4NBr for
2
HO6OPPOn and SnOct were adjusted in order to get oligomers/
8
h, monitoring by TLC. HO6OPPOn were recovered by Rotary
polymers of different molecular weight. The procedure was briefly
Evaporator and recrystallization from ethanol yielding white solid.
HO6OPPOn were then recrystallized in toluene and dried for ROP
reaction.
as following:
Proper amount of L-LA, HO6OPPOn were vacuum dried at near
ꢀ
50 C for 3 h and then mixed with SnOct
2
(tridistilled) solution in
toluene with typical ratio (x:1:1, x ¼ 5,10,15,20) and toluene. After
ꢀ
HO6OPPO4, yield 83.1%, R
f
¼ 0.35 (CH
2
Cl
2
:C
2
H
5
O
stirring for 10 h at 100 C the viscous mixture was cooled and
C
H
2 5
:CH (CH CH
3
2
)
4
3
¼ 2:1:1)
2 2
evaporated to dryness. Then the residual was dissolved with CH Cl
and washed with 1 M HCl aqueous and water, concentrated. The
concentrated solution was then poured into ethanol or petroleum
ether to precipitate. The final targeted polymer compounds were
collected as white solid by filtration and dried (The H atoms marked
HO6OPPO6, yield 60.6%, R
f
¼ 0.40
(
CH Cl :C OC :CH (CH CH
2
2
2
H
5
2
H
5
3
2
)
4
3
¼ 2:1:1)
1
HO6OPPO8, yield 73.1%, R
f
¼ 0.35 (CHCl :C
3
2
H
5
OH ¼ 15:1)
for H NMR measurement were shown as in Fig. 1).
Fig. 1. A representative 1H NMR spectral of AOLA
O6OPPOn.
x

H. Chen et al. / Polymer 52 (2011) 400e408
403
Table 1
Molecular weight and degree of polymerization and Degree of Polydispersity Index
Table 3
ꢀ
x
Phase transition temperatures ( C) of macromonomers AOLA O6OPPOn.
1
(
DPI) of HOLAxO6OPPOn obtained by H NMR and GPC methods.
Samples
T
g
T
m
T
i
Theo.
n
1H NMR
n
GPC
Mn
AOLA10O6OPPO4
AOLA20O6OPPO4
AOLA30O6OPPO4
AOLA40O6OPPO4
AOLA10O6OPPO6
AOLA20O6OPPO6
AOLA30O6OPPO6
AOLA40O6OPPO6
AOLA10O6OPPO8
AOLA20O6OPPO8
AOLA30O6OPPO8
AOLA40O6OPPO8
22.8
26.4
30.0
35.2
17.0
e
53.0
89.0
102.2
119.6
117.2
62.0
56.8
28.2
75.6
39.4
51.8
87.3
90.6
118.0
125.2
137.2
107.9
125.2
129.6
139.1
107.9
126.9
130.4
136.8
Mn
Mn
Mw
Mw/Mn
HOLA10O6OPPO4
HOLA20O6OPPO4
HOLA30O6OPPO4
HOLA40O6OPPO4
HOLA10O6OPPO8
HOLA20O6OPPO8
HOLA30O6OPPO8
HOLA40O6OPPO8
10
20
30
40
10
20
30
40
1063
1783
2504
3225
1119
1839
2560
3281
10.8
19.9
29.1
39.6
9.9
19.5
29.1
37.6
1119
1777
2436
3196
1110
1802
2497
3111
1944
2880
3633
4328
1924
2827
3681
4932
2425
3952
5018
6213
2390
3917
5100
6352
1.25
1.37
1.38
1.44
1.24
1.39
1.39
1.29
28.2
32.4
e
17.8
21.7
30.4
1
HOLAxO6OPPO4 H NMR (300 MHz, CDCl
3
):
d
(ppm) ¼ 0.986 (t,
1
3
H, a); 1.406e1.706 (m, 3x þ 8, e þ f þ j þ p); 1.739e1.831 (m, 4H,
AOLAxO6OPPO6 H NMR (300 MHz, CDCl3): d(ppm)＝0.913 (t,
d); 2.700 (b, 1H, q); 3.986 (t, 4H, b); 4.155 (t, 2H, c); 4.319e4.389 (m,
3H, a); 1.24e1.70 (m, 3x þ 12H, j þ p þ e þ f); 1.76e1.85 (m, 4H, d);
3.988 (t, 4H, b); 4.154 (m, 2H, c); 4.350 (m, 1H, k); 5.129e5.200 (m,
nH, i þ k); 5.892 (d, 1H, s); 6.180 (t, 1H, t); 6.44 (d, 1H, r);
1
H, k); 5.116e5.230 (m, n ꢁ 1, i); 6.913e7.469 (m, 8H, h).
1
HOLAxO6OPPO6 H NMR (300 MHz, CDCl
3
):
d(ppm) ¼ 0.941 (t,
3
H, a); 1.255e1.703 (m, 3x þ 12, e þ f þ j þ p); 1.749e1.842 (m, 4H,
6.913e7.468 (m, 8H, h).
1
d); 2.700 (b, 1H, q); 3.984 (t, 4H, b); 4.156 (t, 2H, c); 4.323e4.392(m,
1
AOLAxO6OPPO8 H NMR (300 MHz, CDCl ):
d
(ppm) ¼ 0.890 (t,
3
H, k); 5.094e5.235 (m, n ꢁ 1, i); 6.914e7.470 (m, 8H, h).
3H, a); 1.294e1.707 (m, 3x þ 16H, e þ f þ j þ p); 1.754e1.844 (m,
1
HOLAxO6OPPO8 H NMR (300 MHz, CDCl
3
):
d
(ppm) ¼ 0.941 (t,
4H, d); 3.962e4.005(m, 4H, b); 4.125e4.177 (m, 2H, c); 5.129e5.200
3
H, a); 1.255e1.703 (m, 3x þ 16, e þ f þ j þ p); 1.749e1.842 (m, 4H,
(m, nH,
i
þ
k); 5.815e5.913 6.134e6.227 6.385e6.509 (m,
d); 2.700 (b, 1H, q); 3.984 (t, 4H, b); 4.156 (t, 2H, c); 4.323e4.392(m,
1
1H þ 1H þ 1H, r þ s þ t); 6.914e7.470 (m, 8H, h).
H, k); 5.094e5.235 (m, n ꢁ 1, i); 6.914e7.470 (m, 8H, h).
2.2.5. Polymerization of macromonomers
2.2.4. Preparation of macromonomers
Side chain grafted comb-like polymers with biphenyl group and
The preparation of the macromonomers was performed by the
O-LLA segments were prepared by the radical polymerization of the
macromonomers, AOLAxO6OPPOn, prepared above. General
routine was as follows (AOLA10O6OPPO4 as an example):
reactions either with excess amount of acryloyl chloride/triethyl-
amine or acrylic acid/DCC/DMAP using 2,6-Di-tert-butyl-4-meth-
ylphenol (BHT) as inhibitor. Generally, the mixture of LC-OLLA-OH
corresponding to macromonomer with BHT, DCC/DMAP, dissolved
AOLA10O6OPPO4 (0.1069 g, 95.7
and purged with dry Argon gas to remove oxygen before THF 3 mL
and AIBN (46 L AIBN/THF solution, 0.96 mol) were added. The
mmol) was placed in a 10 mL flask,
in CaH
2
-dried CH
2
Cl
2
, was kept magnetic stirring for 60 h at room
m
m
ꢀ
temperature and stopped with small amount of Ethanol/Acetic acid
resulting mixture was kept for 10 h at 70 C under magnetic stirring
under Argon atmosphere. The targeted polymers were collected in
good yield by filtration as white solid after poured the reaction
mixture into petroleum ether to precipitate and then vacuum dry
overnight for further characterization.
mixture. After filtration and concentration the residual was poured
ꢀ
into cooled ethanol (ꢁ18 C) and kept hours in refrigerator. White
powder was collected by the filtration of the cooled ethanol solu-
tion and vacuum dried to get the polymerizable macromonomers
in good yield.
AOLAxO6OPPO4 1H NMR (300 MHz, CDCl
d
(ppm) ¼ 0.986
3
):
(
t, 3H, a); 1.496e1.706 (m, 3x þ 8, e þ f þ j þ p); 1.739e1.827 (m, 4H,
2.3. Measurements and characterization
d); 3.962e4.016(m, 4H, b); 4.113e4.170 (m, 2H, c); 5.129e5.200 (m,
nH, i þ k); 5.878e5.913 6.135e6.227 6.451e6.507(m,1H þ 1H þ 1H,
r þ s þ t); 6.913e7.468 (m, 8H, h).
1
H NMR was recorded on a AVANCE 300M/400M spectrometer
1
(Bruker) in CDCl or DMSO-D6 at room temperature. By H NMR,
3
Table 2
Molecular weight and degree of polymerization and Degree of Polydispersity Index (DPI) of AOLAxO6OPPOn and P-AOLAxO6OPPOn obtained by 1H NMR and GPC method.
Samples
M.W. of AOLAxO6OPPOna
Theo.
M.W. of P-AOLAxO6OPPOn By GPC
1H NMRa
Mn ꢂ 10ꢁ
3
Mw ꢂ 10ꢁ3
Mw/Mn
DP of PAb
x
Mn
O-LLA x/Mn
P-AOLA10O6OPPO4
P-AOLA20O6OPPO4
P-AOLA30O6OPPO4
P-AOLA40O6OPPO4
P-AOLA10O6OPPO6
P-AOLA20O6OPPO6
P-AOLA30O6OPPO6
P-AOLA40O6OPPO6
P-AOLA10O6OPPO8
P-AOLA20O6OPPO8
P-AOLA30O6OPPO8
P-AOLA40O6OPPO8
10
20
30
40
10
20
30
40
10
20
30
40
1117
1837
2558
3279
1144
1864
2588
3303
1171
1893
2614
3335
12/1261
25/2137
33/2774
44/3567
9/1072
23/2070
31/2660
43/3519
15/1531
24/2181
33/2830
42/3479
21.2
24.5
28.7
38.5
11.6
12.5
20.3
21.9
15.9
23.3
33.1
33.6
23.2
26.7
31.7
47.7
14.6
15.2
30.7
28.1
17.5
27.3
37.2
39.5
1.09
1.09
1.11
1.24
1.26
1.22
1.51
1.28
1.1
17
11
10
11
11
7
8
6
10
11
12
10
1.17
1.13
1.18
a
The theoretical molecular weight and degree of polymerization of macromonomers AOLAxO6OPPOn;
The degree of polymerization of P-AOLLA determined based on the Mn of P-AOLLAs by GPC and Mw of macromonomers as repeat units as side chains.
b

404
H. Chen et al. / Polymer 52 (2011) 400e408
Table 4
Phase transition temperatures ( C) and degree of crystallinity of P-AOLAxO6OPPOn.
Differential Scanning Calorimeter (DSC) measurements were
ꢀ
performed on a DSC-SP (Rheometric Scientific Inc., New Jersey,
0
a
(%)b
ꢀ
Samples
T
T
g
T
m
T
i
D
Hm(J/g)
c
c
USA) from ꢁ50e200 C under inert N
2
atmosphere with a scanning
) were deter-
g
ꢀ
rate of 10 C/min. Glass transition temperatures (T
g
P-AOLA10O6OPPO4
P-AOLA20O6OPPO4
P-AOLA30O6OPPO4
P-AOLA40O6OPPO4
P-AOLA10O6OPPO6
P-AOLA20O6OPPO6
P-AOLA30O6OPPO6
P-AOLA40O6OPPO6
P-AOLA10O6OPPO8
P-AOLA20O6OPPO8
P-AOLA30O6OPPO8
P-AOLA40O6OPPO8
ꢁ3.1
ꢁ3.8
ꢁ5.5
ꢁ5.1
ꢁ4.4
ꢁ4.7
ꢁ4.3
ꢁ4.5
ꢁ4.2
ꢁ4.2
ꢁ5.4
ꢁ5.5
24.8
39.8
31.6
41.1
30.1
24.5
45.1
20.1
25.3
44.2
36.8
41.4
43.1
e
e
e
106.4
106.9
106.9
61.0
107.9
105.7
107.2
68.9
120.5
120.6
127.9
e
14.32
23.72
33.08
e
15.28
25.31
35.30
e
mined by the mid point of baseline shift. Polarized Optical Micro-
scope observation was performed on a Olympus BX51p with
ꢀ
a Linkam THMSE600 coldehot stage (ꢁ196e600 C) and photo-
graphed by a Q-imaging Micropublisher 5.0RTV (CCD). The thermal
transition temperatures were determined combining the DSC
measurement and POM observation.
131.9
127.3
132.3
106.0
137.6
139.2
130.3
22.17
10.39
12.65
e
24.36
11.42
13.90
e
The X-ray diffraction measurements were performed on a Rigaku
D/Max-rB X-ray diffractometer equipment (Japan) with CueK
106.0
106.4
106.8
31.70
36.70
40.10
33.80
39.20
42.80
ꢀ
ꢀ
(l
¼ 1.54056 Å), 40 KV* 100 mA and scanned from 0.5 to 5 at a scan
ꢀ
ꢀ
ꢀ
ꢀ
rate of 2 /min and 3 e50 at 4 /min. The samples were spin-coated
a
0
The T s are the glass transition temperatures of the polyacrylate ester main
g
ꢀ
or melt-pressed into pellets and annealed at 80 C for 12 h.
chain parts;
b
the DHm of complete crystal of PLLA is 93.7 J/g.
3. Results and discussions
the DPs of O-LLAs, DP ¼ a þ 1, where the values of a were evaluated
by comparing the proton peak areas of triple peak -CH2ꢁ of active
eO-R at
(ppm) ¼ 4.15 with those of chiral -*CHꢁ of PLLA at
3
.1. Preparation of initiators
a
d
d
The preparation of mono-substituted derivatives, HOPPOn, is
(
ppm) ¼ 5.17 (Fig. 1. where the H peaks were noted).
the most important step, while the resulting mixtures always
contain three possible compounds HOPPOH, HOPPOn and nOPPOn
because of the o-alkylation’s selectivity of homo- and bis- substi-
tutions biphenol, HOPPOH. Recrystallization only is not enough to
separate. The pure HOPPOn were obtained by a two-step operation
according to the different solubility in different solutions: HOPPOH
is completely removed first by dissolving in alkaline solution and
then nOPPOn can be removed as solid by filtration of the hot
Ethanol/water alkaline solution. The HOPPOn could be recovered
by neutralization of the resulting filtrate. Further twice recrystal-
lization is enough to get pure HOPPOn free of HOPPOH and
nOPPOn. Best for initiators could be achieved by phase-transfer
GPC measurements were performed on an HPLC equipped with
15HPLC pump, Waters 2414 Refractive Index Detector and Ultra-
5
vis detector and HR3/HR4/HR6 columns at 1.00 mL/min using THF
ꢀ
as eluent under 40.0 C with Polystyrene standard (Shodex Stan-
dard SL-105，Japan). The samples were prepared by passing the
2 3
THF solution through a short neutral Al O to remove any metal
cations and then pass 0.22 m microfilter film.
m
UV and the Circular Dichroism (CD) spectra were recorded on
J-810-150L Spectropolarimeter (Jasco, Japan) from 190 nm to
5
50 nm at scan rate 0.1 nm using acetonitrile solvent under inert N
2
at 20 L/min, cell length 0.5 mm, pure acetonitrile as blank. The [
q
]
value was only contributed LA part and thus calculated based on
the O-LLA segments.
reaction of HOPPOn with corresponding
chloride for ROP of L-LA.
u-HO-alkane bromide or
ꢀ
ꢀ
Fig. 2. POM textures of P-AOLAxO6OPPOn. a, P-AOLA30O6OPPO4 at heating the original sample to 84 C; b, P-AOLA40O6OPPO6 heated to 104 C; c, P-AOLA20O6OPPO8 cooled to
1
ꢀ ꢀ
11 C; d, P-AOLA40O6OPPO8 heated to 113 C.

H. Chen et al. / Polymer 52 (2011) 400e408
405
1
3
3
.2. Preparation and characterization of AO-LAxO6OPPOn
and the DP of P-AOLLA. The disappearance of the peaks in H NMR
spectra between 5.8 and 6.3, the acrylate part, is also distinct. The
polymerization of AO-LLA can be again confirmed by the appearance
of peaks at higher molecular weight region and the disappearance of
the peak corresponding to a lower molecular weight of AO-LLA by
GPC. The only single peak thus detected from each GPC was corre-
sponding to the Mw/Mn of P-AOLAxO6OPPOn as listed in Table 2.
.2.1. ROP of L-LA
The HO-group of HO6OPPOn was sufficient active for the ROP of
2
L-Lactide if SnOct was used as catalyst but, for best results; need to
be recrystallized with dry toluene just before use to remove any
HO-containing molecules. Better control of the molecular weights
2
of the resulting O-LLAs can be achieved when SnOct was distilled
under vacuum for three times or more just before use. It is also
important that the L-LA solid were recrystallized with toluene
3
.4. Thermal behavior of macromonomers AOLAxO6OPPOn and
Poly-AOLAxO6OPPOn
(
Na/K dry) three times or more and used just before use. Among the
solvents used to recrystallize the L-LA, toluene is easy to purify and
dry for the best results.
The thermal behavior was evaluated by DSC measurements and
transition temperatures were confirmed again with POM observa-
tions. One or two heat scans were performed for macromonomers
ꢀ
The ROP reaction was almost complete around 12 h at 80 C in
ꢀ
toluene but best results were achieved for 10 h at 100 C.
(Table 3) and polymers (Table 4).
2
The SnOct was removed by washing with cold HCl (0.5 M)
By POM observation on a hot stage with crossed polarizer all
these materials showed distinct birefringent texture, characteristic
aqueous solution and water. Generally, the O-LLA samples with
lower feed ratios often have much lower yields due to the more
apparent weight loss caused by water-dissolve of low molecular
weight O-LLAs when washing with water.
DSC curves at 1st heating
3
.2.2. Molecular weight of O-LLA segments
The molecular weights of O-LLAs were determined by H NMR,
1
of AOLAxO6OPPOn
x=10,n=4
GPC and listed inTable 1. The measured molecular weights of O-LLAs
were in good agreement with the theoretical results and found to
be well controlled by the feed molar ratios of the SnOct
2
catalyst,
L-LA to HO6OPPOn (n ¼ 4,8) providing enough SnOct was used.
2
x=20,n=4
x=30,n=4
3.2.3. Preparation of macromonomers AOLAxO6OPPOn (AOLLA)
To form the polymerizable macromonomers, the acrylate esters
of O-LLA segments, acrylic group was attached by reacting with
HO-group of O-LLA. Considering that the HO-group percentages
were very low in each HOLLAxO6OPPOn’s, acrylic acid was used in
excess amount and used in its activated state. The procedure
involving the acrylic chloride, a highly active species, and trie-
thylamine, proton absorbent, was fast but the products color are
slight yellow and difficult to be avoided and removed. It changed
much more when acrylic acid/DCC/DMAP was used instead. White
powder samples were thus obtained from the later. However more
acrylic acid was necessary to achieve better conversion of
HOLAxO6OPPOn to AOLAxO6OPPOn. For example, here 10 times
x=40,n=4
x=10,n=6
x=20,n=6
x=30,n=6
excess of acrylic acid was used in this paper. The appearance of the
1
peaks of CH
2
¼ CHꢁ around 5.8 to 6.3 in H NMR spectra and the
proper amount of protons indicated the successful complete
attachment of the acrylic group to the end of the O-LLA segments
x=40,n=6
(
as may have noted in Fig. 1, for example). Also a slightly increase of
the average DP or the molecular weights of AOLAxO6OPPOn were
observed from 1H NMR, indicating the weight loss of AO-LLA
molecules with lower DPs in the precipitation process due to their
higher solubility in the cold ethanol solution. The weight loss of
lower DPs also lead to the lower yields of AOLAxO6OPPOn, around
x=10,n=8
x=20,n=8
6
0% for x ¼ 10 and above 90% for x ¼ 40. The molecular weights of
the resulting products AOLAxO6OPPOn were then determined by
1
x=30,n=8
x=40,n=8
H NMR and GPC measurements and listed in Table 1.
3.3. Preparation and characterization of Poly-AOLAxO6OPPOn
The macromonomers, as acrylate esters, can polymerize to form
comb-like polymers with polyacrylate as main chain and O-LLA
segments with mesogenic end group at the free end as side chains.
As the DP of AO-LLA may be controlled bychanging the initiator feed
ratios, the resulting P-AOLLA will be formed with a distinct side
0
50
100
150
200
chain length. The molecular weights of the polymers P-AOLLA
o
Temperature ( C)
1
characterized by GPC were listed in Table 2, together with the
H
NMR results listed for the calculation of the DP of AO-LLA segments
x
Fig. 3. DSC curves of AOLA O6OPPOn.

406
H. Chen et al. / Polymer 52 (2011) 400e408
of layered smectic mesopahse, Fig. 2, until T
what had been reported by Samuel I. Stupp, not only the T
i
was reached. Similar to
and T
higher x values as shown in Fig. 4, indicates the melting behavior of
PLLA segments but not a simple glass transition behavior.
m
i
of both the AOLAxO6OPPOn and P-AOLAxO6OPPOn samples
moved to higher temperature end, but also the LC phase ranges of
higher regime liquid crystal phases were decreased with longer O-
For the P-AOLAxO6OPPOns, compared with those correspond-
g
ing macromonomers, AOLAxO6OPPOns, T s moved to higher
0
temperature ranges and another Tg appeared distinctly at lower
ꢀ
LLA segments length. Again, the T
became higher after polymerized to P-AOLAxO6OPPOn. POM
observations also give evidence that between T and T , POM
m
and T
i
of the AOLAxO6OPPOn
temperature range, around ꢁ4 w ꢁ5 C, denoted to those of the
polyacrylate ester main chains, and generally were more apparent
g
m
at second scans. However they are still not distinguished more
0
textures also existed if only treated by proper cut or press to
confirm, however the viscosity was relatively high compared to
samples at higher temperatures. This means that LC phases may
exist at these temperature ranges, as reported by Samuel I. Stupp.
apparent at the second scans than those of T
shifted not large enough compared with the T
g
. The T s baseline-
g
g
s of O-LLA segment
parts. This is apparently corresponding to the relative higher
percentage of O-LLA segments and the lower percentage of acrylate
0
From DSC curves, each macromonomer AOLAxO6OPPOn (Fig. 3)
parts in P-AOLAxO6OPPOn. The almost constant T s are also the
g
ꢀ
showed a distinct T
g
around 30 C and the T
g
increased with the
indication of the similarity DPs of P-AOLAxO6OPPOns, which were
increase of the degree of polymerization, x, of O-LLA segments from
s of AOLAxO6OPPOn and P-AOLAx-
g
listed in Table 2, while those always increase of T s changed much
ꢀ
x ¼ 10 to 40. The fact that T
g
from 20 to 40 C for P-AOLAxO6OPPOns with the apparent increase
of x, from x ¼ 10 to x ¼ 40. Anyway these values are still lower than
O6OPPOn with x ¼ 10, presented as distinct relative apparent
ꢀ
endothermic peaks, not baseline shifts only as those samples with
57 C, the normal Tg of those of high molecular weight PLLA [39].
g
Low T s are good help for the movement of the O-LLA segments
to form layered smectic phase which existed in both AOLAx-
O6OPPOn and P-AOLAxO6OPPOn samples. Generally, both types
of compounds have more than one peak on DSC curves indicating
DSC curves at 1st heating
of P-AOLAxO6OPPOn
the formation of mesophase at higher temperatures above T
listed in Table 4 are the degrees of crystallinity, , of the
P-AOLAxO6OPPOn materials. Apparently the [40] values
g
. Also
c
c
c
c
increased with the increase of LLA chain length, indicating
a stronger crystallization tendency for higher molecular weight
x=10,n=4
x=20,n=4
x=30,n=4
x=40,n=4
x=10,n=6
x=20,n=6
x=30,n=6
x=40,n=6
x=10,n=8
x=20,n=8
x=30,n=8
x=40,n=8
0
50
100
Temperature ( C)
150
200
o
ꢀ ꢀ
Fig. 5. XRD scans of P-AOLA40O6OPPO4 at 80 C and P-AOLA10O6OPPO8 at 80 C.
Fig. 4. DSC scans of P-AOLAxO6OPPOn.

H. Chen et al. / Polymer 52 (2011) 400e408
407
presence of the layered structures for P-AOLAxO6OPPOn polymers
Fig. 5). This is in good agreement with cholesterol initiated O-LLA
materials, which form layered phase reported by Samuel I. Stupp.
(
3.6. CD spectra of P-AOLAxO6OPPOn
All the CD spectra of P-AOLAxO6OPPOn materials showed
typical positive cotton effect, a peak can be observed for each
polymer around 210 nm, the absorption of C]O groups of O-LLA
2
ꢁ1
segments, with [
indicated that stable helical structure has formed for these poly-
mers because the [ ] value is comparative with any high Mw PLLA
q
] ¼ 4000e5000 deg*cm decimol (Fig. 6.). This
q
materials with good helical structure. The CD spectra give clear
evidence that the P-AOLAxO6OPPOn materials may show strong
optical rotation power if they are proper treated to form ordered
films. Considering that LC materials can self-organized easily to
form ordered materials, the study of P-AOLAxO6OPPOn may be
used as optical materials in the future.
4. Conclusions
Series of mesogenic biphenol derivatives with active HO-group
have been used as initiators successively to form Oligomeric L-LA
materials with controlled molecular weight by adjusting the feed
2
ratios by Ring-Opening Polymerization of LLA with SnOct catalyst.
Main Chain polymers P-AOLAxO6OPPOn were finally prepared by
freeradical polymerization of these polymerizable macromonomers
esters thatobtained byattaching acrylic grouptothese Oligomeric L-
LA materials correspondingly. These macromolecules can be
1
prepared with a controlled LLA length confirmed by H NMR and
GPC. All these materials can form good LC smectic phase from
a-crystal. The O-LLA segments are in helical structure and this makes
the resulting polymer materials good candidate of optical materials.
Fig. 6. Typical CD spectra of P-AOLAxO6OPPO4 and P-AOLAxO6OPPO8.
Acknowledgements
PLLA. The
c
c values are important for the preparation of layered
This work was financially supported by the National Natural
Foundation of China (No. 20304006) and Key Technologies R&D
Program of Shandong Province, China (No. 200810002017). The
authors also thank much for the kind help of Prof. Zaijun Lu of
ShandongUniversity for GPC measurements and kind discussions.
The authors thank the Prof. Minghua Liu, Dr. Penglei Chen (Institute
of Chemistry, ChineseAcademy of Sciences (CAS)).
phase, because the crystals of PLLA are often spherulites.
3.5. Phase behaviors of P-AOLAxO6OPPOn
X-Ray diffraction characterizations were performed to confirm
the LC phase structure which may exist in P-AOLAxO6OPPOn and
several were listed in Fig. 5. Peaks in the wide angle region, strong
ꢀ
ꢀ
ꢀ
one at 2
q
¼ 16.86 and those weak peaks at 2
q
¼ 19.05 , 22.46
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(
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