Main-chain functionalization of poly(L -lactide) with pendant unsaturations

Article abstract of DOI:10.1002/pola.26084

Main-chain-functionalized poly(L-lactide) (PLLA) with pendant unsaturations was synthesized through a one-pot postpolymerization procedure with the PLLA homopolymer as the starting material. The material was functionalized through α-hydrogen abstraction by a sterically hindered strong base, lithium diisopropylamide, followed by the addition of an acid chloride. Two different acid chlorides were examined, lauroyl chloride as a concept electrophile and oleoyl chloride to provide the pendant unsaturations. The semisolvated system, together with branching reactions from the alpha position of the acid chloride, yielded a high molar amount of the incorporated reactant in the material. The unsaturations were preserved under the chosen conditions and the material exhibited surfactant-like properties in blends with oleic acid and PLLA.

Full text of DOI:10.1002/pola.26084

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Main-Chain Functionalization of Poly(L-lactide) with Pendant
Unsaturations
ꢀ
Peter Olsen, Karin Odelius, Ann-Christine Albertsson
Department of Fibre and Polymer Technology, Royal Institute of Technology, SE-10044, Stockholm, Sweden
Correspondence to: A.-C. Albertsson (E-mail: aila@polymer.kth.se)
Received 28 February 2012; accepted 30 March 2012; published online
DOI: 10.1002/pola.26084
ABSTRACT: Main-chain-functionalized poly(L-lactide) (PLLA)
with pendant unsaturations was synthesized through
branching reactions from the alpha position of the acid
chloride, yielded a high molar amount of the incorporated
reactant in the material. The unsaturations were preserved
under the chosen conditions and the material exhibited
a
one-pot postpolymerization procedure with the PLLA homo-
polymer as the starting material. The material was func-
tionalized through a-hydrogen abstraction by
a
sterically
surfactant-like properties in blends with oleic acid and
C
V
hindered strong base, lithium diisopropylamide, followed
by the addition of an acid chloride. Two different acid
PLLA.
2012 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 000: 000–000, 2012
chlorides were examined, lauroyl chloride as
a concept
electrophile and oleoyl chloride to provide the pendant
unsaturations. The semisolvated system, together with
KEYWORDS: branched; graft copolymer; LDA; polyester; postpo-
lymerization modification
INTRODUCTION A key step in designing new functional poly-
mers is the choice of raw material, as this will govern the
material’s inherent properties such as degradation character-
istics, mechanical properties, and hydrophilicity. The basic
chemical structure of the polymer will also regulate the pos-
sibility of postpolymerization alterations that permit a tailor-
ing of its inherent properties toward a specific application.
Poly(L-lactide) (PLLA) can be polymerized from renewable
resources, and it is expected to be an alternative to many of
the petroleum-based materials in the near future, although
some properties need to be improved in order for it to be an
equal match.
with L-lactide or as pure homopolymers, with functionalities
including alkynes,4,6,14 alkenes,1,2,5 ethers,15,16 ketones,17
epoxides,3 and so forth. These functional polymers make it
possible to steer the properties of PLLA toward a specific
application. However, the synthetic pathway in terms of raw
material, number of reaction steps and yield, together with
the reagents and solvents necessary for obtaining the func-
tional monomer/polymer are of immense importance for
achieving a wider commercial significance.
Another approach to form a functional PLLA is to use a func-
tional initiator in the ring-opening polymerization. This ini-
tiator can either be molecular7,9,10 or macromolecular.8 Our
group has developed a functional macroinitiator based on
the condensation reaction between malonic acid and 2-
butene-1,4-diol, which gives a PLLA material with superior
mechanical properties, in terms of elongation at break, and a
more rapid degradation profile compared to that of PLLA
homopolymer.8,18
One major drawback of PLLA is it nonfunctionality, that is, in
its pure form, it lacks easily accessible and easily transform-
able sites in the main chain that are susceptible to chemical
alteration. Various strategies for achieving a functional PLLA
have therefore been developed, such as ring-opening copoly-
merization with a functional monomer,1–6 the use of a
functional initiator,7–10 and various post polymerization
modifications.7,11–13
Postpolymerization modification offers a convenient and
easy way to introduce functionality into PLLA. Two synthetic
strategies are generally utilized for postpolymerization modi-
fication, either an end-group modification19 or a reaction on
the polymer backbone.12,13 The postpolymerization modifica-
tion of the polymer backbone opens the possibility of a
greater degree of alteration simply due to the greater abun-
dance of reaction sites. The most active site in the PLLA
repeating unit, besides the ester moiety, is the slightly acidic
A crucial aspect to consider when copolymerizing L-lactide
with a functional lactone is that the functionality must be
retained during polymerization, and that, for example, the
monomer is sufficiently ring-strained to enable ring-opening
polymerization. Over the years, many lactones bearing differ-
ent functional groups have been successfully polymerized by
ring-opening polymerization in a controlled way together
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the polymer chain, mainly through back-biting reactions orig-
inating from the macroanion. From this point of view, the
surface modification procedure is more favorable because
the bulk is shielded from degradation; on the other hand, it
also yields an inhomogeneous material. In light of this, our
synthetic procedure is based on a semisolvated system to
combine the advantages of the two methods.
PLLAs solubility in toluene is very temperature dependent
and this makes it possible to create a system where the solu-
bility of PLLA can be altered during the reaction. PLLA was
ꢀ
therefore dissolved in toluene at 100 C, followed by a rapid
decrease in temperature to ꢁ78 ꢀC. As the polymer started
to precipitate, the LDA was added. The reaction mixture was
subsequently stirred for 5 min and then terminated by the
addition of the electrophile. To form a PLLA-based material
with a pendant functionalizable site in the main chain, two
fatty acid chlorides were chosen, lauroyl chloride (LOC) and
oleoyl chloride (OOC). LOC was used as a concept electro-
phile to access the system and to eliminate reactions origi-
nating from the unsaturation of OOC.
SCHEME 1 The different reaction pathways that arise from the
duality of the reactant lauroyl chloride (LOC). [S1] is believed to
be the major reaction for the covalent attachment of lauroyl
chloride to PLLA main chain and [S2], and [S3] are the major
branching and end-group reactions.
Synthesis and Characterization of
Poly(L-lactide-g-lauroyl)
a-proton. The a-proton of PLLA can be abstracted using a
sterically hindered strong base to form a macroanion. The
major problem is that the ester groups are susceptible to
nucleophilic attack originating from the formed polyanion
and this in turn fragments the polymer chain.12,13 A surface-
assisted modification procedure can to a certain extent
reduce high bulk degradation but does not change the poly-
mers bulk properties.20
LOC was used as a concept electrophile for the covalent
attachment of a fatty acid structure to the main chain of
PLLA. The covalent attachment of lauroyl (LO) to the main
chain can be seen in 1H nuclear magnetic resonance (NMR)
as a change in the chemical shift corresponding to the a-pro-
tons in LOC, and poly(L-lactide-g-lauroyl) (PLLA-g-LO), as
shown in, Figure 1. The a-protons have a very distinctive tri-
plet originating from its two equivalent neighboring protons,
PLLA-g-LO and LOC a-protons have a chemical shift of d
2.33 ppm and d 2.87 ppm, respectively, Figure 2. The 1H
NMR spectra also revealed a reduction in the relative
amount of a-protons (d 2.33 ppm) in relation to the X-pro-
tons (d 0.90 ppm) in the material, which is a consequence of
branching reactions originating from the reactive duality of
LOC. Under the reaction, the polymer is subjected to highly
The aim of this work was to synthesize a main-chain-func-
tionalized PLLA-based material with pendant functionality.
The approach adopted was an a-hydrogen abstraction from
the L-lactide repeating unit, followed by the addition of an
electrophile with a pendant unsaturation. We hypothesize
that by using a semisolvated system together with an elec-
trophile that can offer both monoaddition and different
branching reactions, a material with a high degree of func-
tionality should be obtainable.
RESULTS AND DISCUSSION
Ester structures with accessible a-protons offer the possibil-
ity for direct a-alkylation with an electrophile through ani-
onic activation. This synthetic methodology has been used
both in the monomeric stage and in postpolymerization
modifications of aliphatic polyesters.12,13,21 The postpolyme-
rization modification through anionic activation of PLLA can
roughly be divided into two different approaches, as either
bulk or surface modification. The bulk or surface modifica-
tion is controlled by choosing a solvent or a nonsolvent for
the polymer as the reaction medium. The general procedure
for both approaches is as follows a non-nucleophilic strong
base, that is, lithium diisopropylamide (LDA) abstracts the a-
proton of the ester moiety, forming a polymeric macroanion.
After the polymeric anion is formed, the electrophile is
added and terminates the reaction, Scheme 1.12,13,20 The
major drawback of this reaction is that it strongly fragments
FIGURE 1 1H NMR of the product mixture obtained from
the reaction with peak-designation according to the major
product [S1].
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FIGURE 3 Proportion of fatty-structures in the material deter-
mined from 1H NMR as a function of starting reaction equiva-
lents of LDA to PLLA.
FIGURE 2 The displacement of the chemical shift for lauroyl
chloride (LOC) a-protons as a result of the reaction with anioni-
cally activated PLLA to give the product PLLA-g-LO.
clusions regarding the degrees of attached fatty-structures to
PLLA solely through changes in the molecular weight, Figure
4 and Table 1. The two other elution peaks originate from
the fragmented polymer chains from the surface of the pre-
cipitate that to different degrees are functionalized by the
acid chloride, stemming from a mixture of pathways [S1],
[S2], and [S3], Scheme 1.
basic conditions. This result in that some sites on the poly-
meric backbone can remain anionically activated under the
precipitation step with MeOH and as a consequence gives
rise to the depicted acid base reactions in Scheme 2.
There are three dominating reaction pathways between LDA,
PLLA, and LOC, occurring simultaneously, that lead to the
incorporation of lauoryl (LO) and oleoyl (OO)-structures in
the material. These pathways are shown in Scheme 1 where
[S1] is believed to be the most probable and dominating
path. In addition to [S1], other reactions such as further
branching, [S2], and end-group reactions, [S3], can also occur.
The proportion of LO incorporated into the material is
almost linearly dependent on the increasing proportion of
LDA to PLLA, Figure 3. However, a higher proportion of LDA
to PLLA in the reaction simultaneously leads to more frag-
mentation, Figure 4.
Synthesis of Poly(L-lactide-g-oleoyl)
Poly(L-lactide-g-OOLA) (PLLA-g-OO) was synthesized by
attaching OOC to the PLLA main chain in same manner as
for PLLA-g-LO, which confirmed that the same synthetic
strategy could be applied to both electrophiles, and the 1H
NMR spectra showed that the unsaturation (d 5.42 ppm)
remained intact, Figure 5. The reaction was performed with
a batch size 10 times greater than previously described, and
the material had the same features regarding different elu-
tion peaks for the low molar proportion of LDA to PLLA but
yielded a fully fragmented material with a larger molar pro-
portion of LDA to PLLA, Figure 6 and Table 2. This effect is
due to the larger batch size, for example, more reagent and
longer addition time. This longer addition time meant that
the precipitated structures of PLLA were fully consumed,
that is, degraded, before termination with methanol.
Size exclusion chromatography (SEC) revealed the formation
of three separate fractions, Figure 4, and a bulk decrease in
Mn with increasing ratio of LDA and acid chloride to PLLA.
However, the highest molecular weight fraction had a slight
increase in molecular weight with increasing LDA and LOC
in the reaction. This increase in molecular weight is believed
to originate from the small precipitated assemblies of PLLA
with LO-structures attached on the surface, stemming from
reactions [S1] and [S2], Scheme 1. The hydrodynamic volume
of a polymer chain is greatly influenced by an inherent solu-
bility of its component. The difference in solubility of the
grafted components makes it difficult to draw definite con-
The dual nature, in terms of miscibility for the functionalized
PLLA, was studied by blending of PLLA-g-OO15, PLLA and
oleic acid (OA) in various compositions Table 3. The degra-
dation behavior of PLLA is strongly influenced by its molecu-
lar weight and molecular weight distribution. The heteroge-
neity in molecular weight for PLLA-g-OO15, together with the
SCHEME 2 Acid–base reactions between PLLA chain and methanol in the precipitation step.
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FIGURE 6 SEC elution curves for PLLA-g-OO with different ini-
FIGURE 4 SEC elution curves for PLLA-g-LO with different ini-
tial molar ratios of LDA and oleoyl chloride to PLLA.
tial molar ratios of LDA and lauroyl chloride to PLLA.
carboxylic acid groups from OA, in the blends should further
increase the degradation. This should mean that these
blended materials would show a more rapid degradation
profile in comparison to pure PLLA.
also hinder the mobility of the amorphous phase, and the Tg
therefore is increased.
The mechanical properties further support the antiplasticiz-
ing ability of OA in the different blends, Table 4. Only a small
decrease in the E-modulus was found after further addition
of PLLA-g-OO15 and OA to the blends, Table 4. The strain-at-
break decreased rapidly with increasing amount PLLA-g-
OO15 in the blends, but the E-modulus seemed to be less
affected in three-component blend than the pure PLLA and
OA, Table 4. The smaller effect on the E-modulus in the
blends with PLLA-g-OO15 is in direct relation to the observed
higher relative crystallinity in the blends, Table 4. This indi-
cates that PLLA-g-OO15 acts in some way as a surfactant
encapsulating the OA and allowing the PLLA phase to organ-
ize into more crystalline clusters.
Blends with Poly(L-lactide-g-oleoyl)
The thermal properties of the blends, evaluated by differen-
tial scanning calorimetry (DSC), showed that the Tg for PLLA
increased slightly in the blended material. The relative crys-
tallinity, defined as the melting transition of the PLLA frac-
tion in the blended material, also increased in all of the
blends, Table 4. It is therefore concluded that the fatty acid
phase in the material has an antiplasticizing ability on the
PLLA phase. The fatty acid phase helps the PLLA phase to
order itself into a more crystalline structure by being em-
bedded in the amorphous phase and pushing the PLLA
chains to a more crystalline order. Added PLLA-g-OO15 in the
blends resulted in an even higher relative crystallinity then
in the two-component blends with only PLLA and OA,
Table 4. The more crystalline features of the PLLA phase
As the fraction of PLLA-g-OO15 increased in relation to the
weight fraction of OA, the relative molar melt enthalpy value
(DHf.OA) for OA decreased, see Table 4. The decrease in
DHf.OA also confirms the surfactant-like properties of PLLA-g-
OO15 in the blends, because this property should hinder the
melt transition of OA by the branched OO-structures pro-
truding into the OA phase.
The scanning electron microscope (SEM) images confirm
why there is a drastic decrease in strain-at-break for the
blended material, Table 4. The visual information about the
different blends revealed that they have very porous surfa-
ces, in comparison to the pure PLLA sample that is com-
pletely smooth. A higher fraction of PLLA-g-OO15 to OA
yields a material with more homogeneously distributed and
smaller pores, Figure 7, and this also explain the more main-
tained E-modulus. The porous structures in the material are
believed to originate from the solvent-casting procedure and
are an effect of the immiscible nature of the different compo-
nents.22,23 In summary, the blending system can be
described as a micellar system, where PLLA is the matrix,
PLLA-g-OO15 the surfactant and OA the micelles. The immis-
cible nature of the PLLA and OA make it is possible to tailor
FIGURE 5 1H NMR of the product mixture obtained from the
reaction, with peak-designation for PLLA-g-OO as the major
product [S1].
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TABLE 1 Mn Values of the Different Elution Peaks Obtained by SEC
Mn Last Fraction
Mn Second
Mn First
Polymer Name
n(%LDA)
(g/mol)
Fraction (g/mol)
Fraction (g/mol)
PLLA
0
144,600
151,600
152,900
–
–
a
PLLA-g-LO4
12.5
200
16,400
6,600
2,200
1,500
a
PLLA-g-LO25
a
The number denotes the molar amount of oleoyl-structures in the polymer determined by 1H NMR.
the size and amount of the porous features by using a prede-
termined ratio of surfactant (PLLA-g-OO15) to OA.
Synthesis of Poly(L-lactide-g-lauroyl) and
Poly(L-lactide-g-oleoyl)
PLLA-g-LO and poly(L-lactide-g-oleoyl) (PLLA-g-OO) were syn-
thesized through postpolymerization functionalization of PLLA.
The different electrophiles, laroyl chloride (LOC) and OOC,
were covalently bonded to PLLA main chain according to the
procedure described below. All reaction glassware was silan-
ized and dried at 110 ꢀC over night before use. PLLA (3.55 and
35.5 mmol for the synthesis of PLLA-g-LO and PLLA-g-OO,
EXPERIMENTAL
Materials
The reactants, LDA (1.8 M, Sigma-Aldrich), oxalyl chloride
(99%, Sigma-Aldrich), LOC (98%, Sigma-Aldrich), and OA
(90%, Alfa Aesar) and the solvents, toluene (99, 8%; Sigma-
Aldrich), dichloromethane 99.5%; Sigma-Aldrich), hexane
(general purpose grade, Fischer Scientific, Germany), and
methanol (general purpose grade, Fischer Scientific,
Germany) were used as received.
ꢀ
respectively) was dissolved in dry toluene (0.2 M) at 100 C
ꢀ
followed by rapid cooling to ꢁ78 C. On precipitation of PLLA,
LDA was added. The solution was stirred for ꢂ5 min followed
by the addition of LOC or OOC (twice the equivalent of LDA).
ꢀ
The catalysts, stannous 2-ethylhexanoate, Sn(Oct)2 (Sigma-
Aldrich), and the initiator ethylene glycol (Merck, Germany),
were dried over molecular sieves and placed under an inert
N2 atmosphere before use. The monomer L-lactide (Serva
Feinbiochemica) was recrystallized twice from toluene before
use.
The mixtures were stirred at ꢁ78 C and at ambient tempera-
ture for 30 min, respectively. The mixtures were concentrated
and precipitated at ꢁ18 ꢀC in pure methanol.
Solution Casting of Films
Neat and blended films were made by solution casting in a
10 % (w/w) mixture of PLLA, PLLA-g-OO, and OA in chloro-
form. The mixtures were dissolved in a vial and placed on a
shaker (yellow line os, 10 basic) for 2 h. The solutions were
then poured into Petri dishes and placed in a fume hood.
The solutes were then allowed evaporate, leaving films with
an approximate thickness of 150 lm.
Synthesis of Oleoyl Chloride
OOC was synthesized by reacting OA with oxalyl chloride in
dichloromethane. The general procedure was as follows: OA
(57 mmol) was dissolved in a 250-mL two-headed round-
bottomed flask in dichloromethane (200 mL) at 0 ꢀC fol-
lowed by the slow addition of oxalyl chloride (85.5 mmol)
under an inert atmosphere. After 15 min, the mixture was
Characterization
Nuclear Magnetic Resonance Spectroscopy
ꢀ
placed in an oil bath at 40 C, and the reaction was followed
1H NMR spectra were recorded on a Bruker DMX-500 NMR
spectrometer at 500 MHz and analyzed using Bruker soft-
ware. Samples ꢂ10 mg in weight were dissolved in CDCl3
(Aldrich Chemical) in 5-mm external diameter sample tubes.
Nondeuterated chloroform was used as an internal standard
(d ¼ 7.26 ppm). The total amounts of LO and OO structures
(Xt) in the sample were determined by evaluation of the in-
by 1H NMR. The reaction was complete after 6 h. The prod-
uct was concentrated in vacuum and used without further
purification.
Polymerization of L-lactide
All glassware was silanized before use and stored under a
N2 atmosphere. The polymerization of L-lactide was per-
formed in bulk at 110 ꢀC for 72 h with Sn(Oct)2 (1:10,000
monomer ratio) as a catalyst and ethylene glycol (1:600
monomer ratio) as initiator.24 The polymer was precipitated
three consecutive times in a 95:5 hexane/methanol mixture.
I
Xoyl=3
tegral peaks given by Xt ¼
using the mean of three
IPLLAþIaoyl=2
independent 1H NMR spectra. The X-protons are divided by
the a-protons corresponding to the repeating unit and OO
group.
TABLE 2 Mn Values of the Different Elution Peaks Obtained by SEC
Mn Fraction 1
Mn Second
Mn First Fraction
Polymer Name
n(%LDA)
(g/mol)
Fraction (g/mol)
(g/mol)
Yield (%)
PLLA
0
118,000
91,900
–
–
–
95
71
37
a
PLLA-g-OO5
12.5
100
9,100
12,600
400
–
a
PLLA-g-OO15
a
The number denotes the molar amount of oleoyl-structures in the polymer determined by 1H NMR.
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TABLE 3 Amount of Oleoyl-Structures in the Different Blends Determined by 1H NMR
PLLA
PLLA-g-OO15
Oleic Acid
(% w/w)
Total Amount
of Fatty Acid (% w/w)#
Name (B(xPLLA-PLLA-g-OO15-xOA))
(% w/w)
(% w/w)
PLLA
100
80
80
80
60
80
0
0
0
B(80PLLA-15 PLLA-g-OO155ꢁOA)
15
10
5
5
8.0
B(80PLLA-10 PLLA-g-OO1150ꢁOA)
10
15
20
20
11.8
18.0
23.0
22.0
B(80PLLA-5 PLLA-g-OO15
-
15OA)
20OA)
B(60PLLA-20 PLLA-g-OO15
B(80PLLA-20OA)
-
20
0
aThe number denotes the molar amount of oleoyl-structures deter-
mined from 1H NMR in the material.
xDenotes the added %(w/w) composition in the blend.
Differential Scanning Calorimetry
acceleration voltage of 10 kV. The samples were mounted on
metal stubs and sputter-coated with gold and platinum
(2 nm) using a Denton Vacuum Desk II cold sputter etch
unit operating at 45 mA for 2 s. The films were placed in a
vacuum oven for 24 h before analysis, and the samples were
randomly chosen from a representative piece of the material.
The thermal properties of the materials were investigated
using DSC (Mettler Toledo DSC 820 module) under a nitro-
gen atmosphere. About 2–10 mg of the polymer was incap-
sulated in a 40-lL aluminum container without pin. The
specimens where heated from ꢁ55 to 200 ꢀC and then
ꢀ
ꢀ
cooled to ꢁ55 C and thereafter heated again to 200 C at a
ꢀ
rate of 10 C/min. The Tg and Tm values were recorded after
CONCLUSIONS
the first heating scan. Tg was determined as the midpoint
temperature of the glass transition, and the Tm as the maxi-
mum value of the melting peak.
We have successfully synthesized a highly functionalized
PLLA-based material with pendant unsaturations by abstract-
ing the a-hydrogen of the lactide repeating unit using the
sterically hindered strong base, LDA, followed by the addi-
tion of an electrophile. A semisolvated system together with
branching reactions originating from the electrophile yielded
a high molar amount of reactant incorporated into the mate-
rial. The amount of LOC incorporated into the material was
controlled in the range of 2–63 mol % with increasing LDA
in the reaction. Reaction with the unsaturated electrophile,
OOC, at two different equivalents of LDA yielded 5 and 15
mol % of incorporated OO-structures in the material. 1H
NMR also revealed that the unsaturation remained intact
under these reaction conditions, which is a vital for further
functionalization. The properties of PLLA grafted with 15
mol % (PLLA-g-OO15) were evaluated in blends solvent-cast
together with OA and PLLA. The Tg increased slightly in all
of the blends originating from the antiplasticizing ability of
OA. The E-modulus was almost constant in the three-compo-
nent blend between PLLA, OA, and PLLA-g-OO15, even with
Size Exclusion Chromatography
SEC was used to monitor the changes in molecular weight and
dispersity of the synthesized polymer before and after the
functionalization. The polymers were analyzed with a Verotech
PL-GPC 50 Plus system equipped with a PL-RI Detector and
two PolarGel-M Organic (300 ꢃ 7.5 mm2) columns from Var-
ian. The samples were injected with a PL-AS RT Autosampler
for PL-GPC 50 Plus, and tetrahydrofuran (THF) was used as
mobile phase (1 mL/min, 35 ꢀC). The system was calibrated
using polystyrene standards. Corrections for flow rate fluctua-
tions were made using toluene as an internal standard. Cir-
rusTM gel permeation chromatography (GPC) Software was
used to process the data.
Scanning Electron Microscope
The microstructure of the blends was evaluated on the pro-
duced films by means of a JOEL JSM-5400 SEM using an
TABLE 4 Thermal and Mechanical Properties of the Blends
a
n
DTg
(ꢀC)
Relative
E-Modulus
(MPa)
Strain at
DHf.OA
DHf.OA/bnOA
Name (B(xPLLA-xPLO15-xOA))
Crystallinity (%)
Break (%)
(J/g)
(J/mol.OA)
PLLA
0 6 0.4
49 6 2.4
58 6 2.9
58 6 2.2
64 6 2
11.7 6 1.3
10.6 6 0.9
9.5 6 0.6
10.6 6 0.4
8.8 6 1.4
6.5 6 0.7
8.9 6 3.1
5.4 6 1.4
3.5 6 1.3
5.4 6 1.8
3.7 6 1.0
3.7 6 0.9
–
–
B(80PLLA-15 PLO15-5OA)
B(80PLLA-10 PLO15-10OA)
B(80PLLA-5 PLO15-15OA)
B(60PLLA-20 PLO15-20OA)
B(80PLLA-20OA)
3.5 6 0.8
2.6 6 0.3
2.8 6 0
3.4 6 0.1
8.1 6 0.1
14.1 6 0.2
15.1 6 1.4
23.7 6 0.7
41.8 6 0.9
68.4 6 4.0
61.5 6 1.0
83.8 6 8.1
107.4 6 3.0
3.6 6 0.3
2.9 6 0.1
64 6 1.4
56 6 0.8
b
xThe added % (w/w) composition in the blend.
The value of the peak corresponding to the melt transition of oleic
acid at 7–16 ꢀC obtained from DSC.
The molar amount of oleic acid in the material obtained from 1H NMR.
nThe melting value for 1 mol of oleic acid (OA) in a blend with the par-
ticular composition of PLLA, PLLA-g-OO15 and OA.
a
6
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FIGURE 7 The dark areas represent the porous structures in the material with various compositions of PLLA, PLLA-g-OO15 and OA
in the blend.
9 Finne, A.; Albertsson, A.-C. J. Polym. Sci. Part A: Polym.
Chem. 2004, 42, 444–452.
high molar equivalents of OA and PLLA-g-OO15, but the
strain at break was greatly reduced. SEM images revealed a
larger amount of small porous structures with increasing
proportion of PLLA-g-OO15 to OA in the material. It is pro-
posed that the PLLA-g-OO15 acts as a surfactant and dis-
perses the OA phase in the PLLA matrix, resulting in more
and smaller porous structures in the material blend.
ꢀ
ꢀ
10 Dubois, P.; Ropson, N.; Jeroˆ me, R.; Teyssie, P Macromole-
cules 1996, 29, 1965–1975.
11 Kricheldorf, H. R.; Fechner, B. J. Polym. Sci. Part A: Polym.
Chem. 2002, 40, 1047–1057.
12 Ponsart, S.; Coudane, J.; Morgat, J. L.; Vert, M. J. Labelled
Compd. Radiopharm. 2001, 44, 677–687.
ACKNOWLEDGMENT
13 Ponsart, S.; Coudane, J.; Vert, M. Biomacromolecules 2000,
1, 275–281.
The authors gratefully acknowledge the ERC Advanced Grant,
PARADIGM, (Grant no: 246776) for the financial support for
this work.
14 Cooper, B. M.; Emrick, T. J. Polym. Sci. Part A: Polym.
Chem. 2009, 47, 7054–7065.
15 Mathisen, T.; Masus, K.; Albertsson, A. C. Macromolecules
1989, 22, 3842–3846.
REFERENCES AND NOTES
16 Mathisen, T.; Albertsson, A. C. Macromolecules 1989, 22,
3838–3842.
1 Jing, F.; Hillmyer, M. A. J. Am. Chem. Soc. 2008, 130,
ꢀ
17 Latere, J.-P.; Lecomte, P.; Dubois, P.; Jeroˆ me, R. Macromo-
13826–13827.
lecules 2002, 35, 7857–7859.
2 Mecerreyes, D.; Miller, R. D.; Hedrick, J. L.; Detrembleur, C.;
€
˚
18 Malberg, S.; Hoglund, A.; Albertsson, A.-C. Biomacromole-
ꢀ
Jeroˆ me, R. J. Polym. Sci. Part A: Polym. Chem. 2000, 38,
cules 2011, 12, 2382–2388.
870–875.
19 Ryner, M.; Valdre, A.; Albertsson, A.-C. J. Polym. Sci. Part
A: Polym. Chem. 2002, 40, 2049–2054.
3 Veld, M. A. J.; Palmans, A. R. A.; Meijer, E. W. J. Polym. Sci.
Part A: Polym. Chem. 2007, 45, 5968–5978.
20 El Habnouni, S.; Darcos, V.; Garric, X.; Lavigne, J.-P.; Notte-
let, B.; Coudane, J. Adv. Funct. Mater. 2011, 21, 3321–3330.
4 Parrish, B.; Quansah, J. K.; Emrick, T. J. Polym. Sci. Part A:
Polym. Chem. 2002, 40, 1983–1990.
ꢀ
21 Parrish, B.; Breitenkamp, R. B.; Emrick, T. J. Am. Chem.
Soc. 2005, 127, 7404–7410.
5 Lou, X.; Detrembleur, C.; Lecomte, P.; Jeroˆ me, R. J. Polym.
Sci. Part A: Polym. Chem. 2002, 40, 2286–2297.
22 Kim, J.-K.; Taki, K.; Nagamine, S.; Ohshima, M. J. Appl.
Polym. Sci. 2009, 111, 2518–2526.
6 Jiang, X.; Vogel, E. B.; Smith, M. R.; Baker, G. L. Macromole-
cules 2008, 41, 1937–1944.
23 Kim, J.-K.; Taki, K.; Ohshima, M. Langmuir 2007, 23,
12397–12405.
7 Ryner, M.; Finne, A.; Albertsson, A.-C.; Kricheldorf, H. R. Mac-
romolecules 2001, 34, 7281–7287.
˚
˚
8 Malberg, S.; Plikk, P.; Finne-Wistrand, A.; Albertsson, A.-C.
24 Plikk, P.; Malberg, S.; Albertsson, A.-C. Biomacromolecules
Chem. Mater. 2010, 22, 3009–3014.
2009, 10, 1259–1264.
WWW.MATERIALSVIEWS.COM
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