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Electronic Supplementary Information
PROP: an in situ cascade polymerization method for the facile
synthesis of polyesters
Xiang Zhu,a Jiali Gu,a Xiaohong Li,a Xiaoming Yang,a Lian Wang,b Yongjin Li,b He Li c and Yingfeng Tu,*a
aJiangsu Key Laboratory of Advanced Functional Polymer Design and Application, State and Local Joint Engineering Laboratory for Novel Functional Polymeric Materials, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
bCollege of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036, China
cKey Laboratory of Marine Materials and Related Technologies, Ningbo Institute of Materials Technology & Engineering, CAS, Ningbo 315201, China
Corresponding Author: E-mail: [email protected].
Materials……………………………………………….…………………………………………………………………..……Page.S2
Synthesis of cyclic oligo(alkylene terephthalate)s…………………………..………………….……….Page.S2-S3
Synthesis of bis(hydroxyalkylene) terephthalates (initiators)……………………………….….…Page.S3-S4
Synthesis of PNT by traditional condensation polymerization…………………..…………….….…..Page.S4
Characterization methods…………………………………………………………………………………..………Page.S4-S6
Deduction of equation 1…………………………………………………………………………………...….……Page.S6-S7
Molecular weights calculation by 1H NMR………………………………………….………….………..……..Page.S7
Table S1-S4…………………………………………………………………………………………………...…..……….Page.S8-S9
Fig. S1-S12……………………………………………………...………………………………………..…………….Page.S10-S21
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Electronic Supplementary Material (ESI) for Polymer Chemistry.This journal is © The Royal Society of Chemistry 2017
Experimental Details
Materials
Terephthaloyl chloride (TPC) (Aladdin, 97%) was purified by recrystallization from hexane three
times. 2-Methyl-1,3-propylene glycol (Aladdin, 99%) was purified by vacuum distillation after
stirring with calcium hydride overnight. 1,4-Diazabicyclo[2.2.2]octane (DABCO) (Chem
Greatwall of Wuhan, 99%) was purified by sublimation in vacuum. Triethylamine (Et3N)
(Sinopharm Chemical, AR), dichloromethane (CH2Cl2) (Qiangsheng Chemical of Suzhou, AR), and
tetrahydrofuran (THF) (Qiangsheng Chemical of Suzhou, AR) were purified by stirring with
calcium hydride overnight and then distilled under nitrogen. Neopentylene glycol (9 Ding
Chemistry, 99%), 2-methyl-2-propyl-1,3-propylene glycol (Adamas-beta, 99%), dimethyl
terephthalate (DMT) (Aladdin, 99%), zinc acetate (J&K, 97.5%) and titanium tetrabutoxide (Ti(n-
C4H9O)4) (Alfa Aesar, 98%) were used as received.
Synthesis of cyclic oligo(alkylene terephthalate)s
The cyclic oligoesters were synthesized via a pseudo-high dilution reaction process similar to
previous reports. A general experimental procedure for the synthesis of cyclic oligo(2-methyl-
1,3-propylene terephthalate)s (COMPTs) is given below: A 1000 mL three-necked flask with a
mechanical stirrer, constant pressure funnel, and nitrogen inlet was charged with a solution of
DABCO (1.12 g, 0.01mol) and Et3N (20.24 g, 0.2 mol) in 700 mL of dichloromethane. The mixture
solution was cooled to 0 °C, and a solution of terephthaloyl chloride (21.32 g, 0.105 mol) and 2-
methyl-1,3-propylene glycol (9.01 g, 0.1 mol) in 120 mL of THF was added via the addition
funnel over 180 min. After the reaction was quenched with ammonium hydroxide (20 mL) and
deionized water (50 mL), the solution was filtered, and the aqueous layer was extracted with
dichloromethane (50 mL in 3 times). The organic layer was washed with dilute HCl and
deionized water and then the solvent was removed. Cyclic oligomers were obtained by column
chromatography (eluent: 4% acetone in dichloromethane) The product was precipitated in
peroleum ether, filtered, vacuum dried at 60 °C for 12 h, and obtained as a white powder. Cyclic
S2
oligo(neopentylene terephthalate)s (CONTs) and cyclic oligo(2-methyl-2-propyl-1,3-propylene
terephthalate)s (COMPPTs) were synthesized via a similar procedure. COMPTs: Rf: 0.69; 36%
yield; mp: 191-213 °C; 1H NMR (600 MHz, CDCl3), δ (ppm): 7.62-8.08 (m, 4H, phenyl H), 4.31-
4.50 (m, 4H, CH2O), 2.47-2.66 (m, 1H, CH2CH(CH3)CH2), 1.09-1.18 (m, 3H, CH2CH(CH3)CH2).
CONTs: Rf: 0.73; 31% yield; mp: 262-274 °C; 1H NMR (600 MHz, CDCl3), δ (ppm): 7.67-8.09 (m,
4H, phenyl H), 4.26-4.30 (s, 4H, CH2O), 1.16-1.19 (s, 6H, CH2C(CH3)2CH2). COMPPTs: Rf: 0.76; 42%
yield; mp: 215-224 °C; 1H NMR (600 MHz, CDCl3), δ (ppm): 7.66-8.08 (m, 4H, phenyl H), 4.28-
4.36 (m, 4H, CH2O), 1.39-1.59 (m, 4H, CH2CH2CH3), 1.10-1.12 (m, 3H, CH2C(CH3)CH2, 0.93-1.03
(m, 3H, CH2CH2CH3).
Synthesis of bis(hydroxyalkylene) terephthalates (initiators)
Bis(3-hydroxy-2-methylpropyl) terephthalate (BHMPT), bis(3-hydroxy-neopentyl) terephthalate
(BHNT) and bis(3-hydroxy-2-methyl-2-propylpropyl) terephthalate (BHMPPT) were synthesized
by the transesterification of their corresponding diols with DMT. A typical procedure is
described in the following: DMT with large excess amounts (50 folds of the stoichiometric
quantity) of corresponding diols were charged to a three-necked flask, and zinc acetate (0.05 wt
%) was added. The reaction mixture was heated to 180 °C under a nitrogen atmosphere. The
reaction was stopped after theoretical amount of methanol was collected in a Dean & Stark
trap (typically 90 minutes). Once the reaction mixture was cooled, deionized water was added
and the formed precipitate was collected. The precipitates of BHMPT and BHNT were white
powder and purified by recrystallization from deionized water. Pure crystals were obtained
with narrow melting point range. The crude BHMPPT was purified by silica gel column
chromatography using dichloromethane/acetone (5/1, v/v) as eluent. The product was dried in
a vacuum oven to yield a vicious liquid. BHMPT: 70% yield; mp: 74-75 °C; 1H NMR (600 MHz,
CDCl3), δ (ppm): 8.10 (s, 4H, phenyl H), 4.34-4.42 (m, 4H, COOCH2), 3.59-3.66 (m, 4H, CH2OH),
2.12-2.20 (m, 2H, CH2CH(CH3)CH2), 1.06 (d, 6H, CH2CH(CH3)CH2). BHNT: 74% yield; mp: 120-122
°C; 1H NMR (600 MHz, CDCl3), δ (ppm): 8.11 (s, 4H, phenyl H), 4.22 (s, 4H, COOCH2), 3.41 (s, 4H,
CH2OH), 1.03 (s, 12H, CH2C(CH3)2CH2). BHMPPT: 63% yield; 1H NMR (600 MHz, CDCl3), δ (ppm):
S3
8.11 (s, 4H, phenyl H), 4.22-4.27 (m, 4H, COOCH2), 3.39-3.46 (m, 4H, CH2OH), 1.33-1.41 (m, 8H,
CH2CH2CH3, 0.98 (s, 6H, CH2C(CH3)CH2), 0.94-0.96 (m, 6H, CH2CH2CH3).
Synthesis of PNT by traditional condensation polymerization
PNT was prepared by a traditional two-stage melt polycondensation method in a stainless steel
batch reactor. Terephthalic acid (TPA) (500 g) and neopentylene glycol (NPG) (376 g) in a molar
ratio of TPA/NPG=1/1.2 and catalyst of 125 ppm Sb (antimony acetate) were charged into the
reactor. The reaction mixture was heated at 220 °C under nitrogen atmosphere and stirred at a
constant speed (20 Hz). The first step (esterification) is considered to be completed after the
collection of theoretical amount of liquid, which was removed from the reaction mixture by
distillation and collection in a graduated cylinder. In the second step, the temperature was
raised to 260 °C and a vacuum (~20 Pa) was applied slowly over a period of time about 1 h. The
polycondensation reaction was continued for about 5 h. After the polycondensation reaction
was completed, the PNT product was collected and dried at 50 °C under reduced pressure for
15 h. PNT was characterized by GPC with Mn of 18.1 kDa and PDI of 2.02.
Characterization Methods
1H nuclear magnetic resonance (NMR) spectra were recorded on an Agilent Technologies 600
MHz DD2 spectrometer with PFG 1H/19F/X probe at 25 °C, using deuterated chloroform as the
solvent and tetramethylsilane (TMS) as the internal reference.
Gel permeation chromatography (GPC) analysis was performed on a modular system
comprising a Waters 1515 pump, a 717 plus autosampler, and a 2410 refractive index detector.
Separations were achieved using two PL Mixed-C columns (7.5 × 300 mm, 5 μm bead size, 200 -
2000000 Dalton), calibrated with 9 narrow distribution polystyrene standards with a molecular
weight range from 474 to 177000 Dalton. All samples (2 mg/mL) were passed through 0.45 μm
PTFE filter before analysis and THF was used as mobile phase at a flow rate of 1.0 mL/min at 35
°C.
S4
Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrum was
acquired on a Bruker Ultraflex-Treme TOF/TOF mass spectrometer (Bruker Daltonics, Inc.,
Billerica, MA) equipped with a Nd:YAG laser (355 nm). All spectra were recorded in reflective
mode. Trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB, Aldrich, >
99%) was used as matrix (20 mg/mL in CHCl3) while sodium trifluoroacetate as the cationization
agents (10 mg/mL in ethanol). The matrix and cationization agents were mixed with the ratio of
10/1 (v/v). The sample preparation involved depositing 0.5 μL of matrix and salt mixture on the
wells of a 384-well ground-steel plate, depositing 0.5 μL of the sample (10 mg/mL in CHCl3) on a
spot of dry matrix, and adding another 0.5 μL of matrix and salt mixture on top of the dry
sample. After evaporation of the solvent, the plate was inserted into the MALDI source. The
mass scale was calibrated externally using the peaks obtained from protein standard (700 to
3500 Dalton), and the data were analyzed by Bruker’s flexAnalysis and PolyTool software.
Thermogravimetric analysis (TGA) was carried at a heating rate of 10 °C/min from room
temperature to 600 °C under a continuous nitrogen flow of 50 mL/min with a TA Instrument
SDT-2960TG/DTA. The temperature of thermal degradation (Td) was measured at the point of
5% weight loss relative to the weight at room temperature.
Differential scanning calorimetry (DSC) was performed on a TA Instruments DSC 2010 within
temperature region from -20 °C to 250 °C at a scanning rate of 10 °C/min under nitrogen
atmosphere with the samples sealed in aluminum pans. The second heating curve was used to
estimate the glass transition temperature (Tg).
Dynamic mechanical analysis (DMA) was conducted on a TA Instrument Q800. Rectangular
samples with size of 15 × 5 mm were clamped in multi-frequency-strain mode using tension:
film ramp. The frequency was 1 Hz, while the furnace heated at 3 °C/min from -110 °C to the
temperature above which the storage modulus of the sample was too low to be measured by
the instrument. Tg measurements were recorded using the maximum in tan δ peak. All DMA
test strips were dried overnight at 30 °C under vacuum to remove residual water. The
measurement was replicated up to 5 times for each sample.
S5
Tensile tests were carried out with 6 repeat times using an Instron model 5966 universal
material testing system, which maintained under the same conditions and operated at an
extension rate of 10 mm/min. Dumbbell-shaped tensile-test specimens (central portion, 2.96 ×
0.5 mm thick; gauge length 18mm) were cut from the sheets and conditioned at room
temperature for 24 h.
The oxygen permeability through polyester films was measured by VAC-V2 Oxygen Permeation
Tester (Labthink Instruments Co., Ltd., China). The permeability was expressed as the volume
rate of gas penetrating a unit thickness of film at constant pressure, humidity, and temperature.
The tests were performed at 23 °C, 0.1 MPa and 0% relative humidity using high-purity
(˃99.99%) oxygen gas. Determination of water vapor transmission rate (WVTR) was performed
by i-Hydro 7500 water vapor transmission rate tester (Labthink Instruments Co., Ltd., China) at
38 °C and 90% relative humidity.
Film Preparation
Polyesters were dried at 50 °C under vacuum for 24 h to remove residual water prior to
compression molding. Films (~0.5 mm thick) were pressed between two PTFE sheets at 220 °C
and 10 MPa for 4 min before immediately quenching in a cold press at room temperature under
a pressure of 10 MPa. All films were amorphous as determined by DSC. The obtained sheets
were directly used for characterization.
Deduction of Equation 1
For a typical first-order kinetics ROP process, where the reversible depolymerization of linear
polyesters to cyclic oligoesters is neglected, equation ESI.1 can be obtained:
(ESI.1)]][][[
][ ICatCOEnkdt
COEndp
where [Cat], [I], and [COEn] is the concentration of catalyst, initiator, and cyclic oligoesters with
DO of n, t is the reaction time. This equation leads to the traditional equation ESI.2 related to
conversion:
S6
(ESI.2)ln(1 ) [ ][ ]COEn p appConv k Cat I t K t
in which ConvCOEn is the conversion of the cyclic oligoesters with DO of n, Kapp is the apparent
reaction rate constant related to kp, the concentration of catalyst and initiator.
From equation ESI.2, we have
(ESI.3) 1 appCOEn
K tConv e
Since , we have app(dimer) app(trimer) app(tetramer) app(pentamer)K = K = K = K = ...
(ESI.4)2 3 4 5 ...COE COE COE COEConv Conv Conv Conv
indicating the conversion of each cyclic oligoesters is same at same reaction time, independent
of the ring size. Thus the conversion for each cyclic oligomer is same as the total conversion,
which leads to Equation 1:
(1)- ln(1- ) appConv K t
where Conv is the total conversion of the cyclic oligoesters.
Molecular weights calculation by 1H NMR
The total repeating units (n) can be calculated by integration ratio of chain end groups
corresponding groups of repeating units by 1H NMR spectra. The chain end groups (peak a) and
aromatic hydrogen groups (peak d) are chosen for calculation using the following equations:
(ESI.5)4
4nII
a
d
where Ia and Id are the integration values for the corresponding peak a and d. The number-
average molecular weights (Mn) can thus be calculated by Mn/Da = 220.2 n + 90.1 for PMPT,
Mn/Da = 234.3 n + 104.1 for PNT, and Mn/Da = 262.3 n + 132.2 for PMPPT, and the results are
listed in Table S4.
S7
Tables and Figures
Table S1 Number-average molecular weights and polydispersity indices (PDIs) of PMPT samples
taken at different polymerization time intervals determined by GPC
Time (min)
5 10 15 20 25 30 45 60 90 120 150 180
Mn (kg/mol)
21.6 22.8 23.3 23.8 24.5 25.0 25.8 26.6 27.1 28.3 28.8 30.8
PDI 1.60 1.62 1.62 1.65 1.67 1.67 1.68 1.70 1.71 1.73 1.73 1.73
Table S2 Number-average molecular weights and polydispersity indices (PDIs) of PNT samples
taken at different polymerization time intervals determined by GPC
Time (min)
2 4 6 8 10 15 20 30 60 90 120 150 180
Mn (kg/mol)
23.3 27.0 28.1 29.6 30.1 31.2 31.4 31.8 32.2 32.6 32.9 33.0 33.6
PDI 1.56 1.64 1.65 1.66 1.67 1.68 1.68 1.68 1.69 1.69 1.69 1.70 1.71
S8
Table S3 Number-average molecular weights and polydispersity indices (PDIs) of PMPPT
samples taken at different polymerization time intervals determined by GPC
Time (min)
10 20 30 40 50 60 90 120 150 180 210 240
Mn (kg/mol)
6.8 9.9 13.1 16.4 18.8 21.2 22.9 24.8 26.0 27.0 27.3 28.5
PDI 1.28 1.32 1.36 1.37 1.44 1.50 1.55 1.55 1.59 1.59 1.63 1.64
Table S4 Integration value of peaks by 1H NMR for polyester samples and number-average
molecular weights calculated
Sample peak a integration (δ ppm)
peak d integration (δ ppm)
n Mn NMR (kg/mol)
PMPT-l 4 277 69 15.3PNT-l 4 439 110 25.8
PMPPT-l 4 278 70 18.3
S9
Fig. S1 GPC curves of cyclic oligoesters: COMPTs (a), CONTs (b) and COMPPTs (c), using THF as
the eluent.
S10
Fig. S2 1H NMR spectra of cyclic oligoesters in CDCl3: COMPTs (a), CONTs (b) and COMPPTs (c).
S11
Fig. S3 GPC curves of samples taken at different polymerization time intervals; Polymerization
conditions: CONTs: BHNT = 100:1 (w/w) at 270 °C; Eluent: THF.
S12
Fig. S4 GPC curves of samples taken at different polymerization time intervals; Polymerization
conditions: COMPPTs: BHMPPT = 100:1 (w/w) at 250 °C; Eluent: THF.
S13
Fig. S5 GPC curves of samples taken at different polymerization time intervals; Polymerization
conditions: COMPTs: BHMPTs = 100:1 (w/w) at 240 °C with 0.2 wt % Ti(n-C4H9O)4 as catalyst;
Eluent: THF.
S14
Fig. S6 Semilogarithmic plot of COMPTs’ conversion vs. time; Polymerization condition: COMPTs:
BHMPTs = 100:1(w/w) at 240 °C with 0.2 wt % Ti(n-C4H9O)4 as catalyst.
S15
Fig. S7 Semilogarithmic plot of COMPTs’ conversion vs. time; Polymerization condition: COMPTs:
BHMPTs = 20:1(w/w) at 240 °C with 0.2 wt % Ti(n-C4H9O)4 as catalyst.
S16
Fig. S8 The plot of the PMPT’ molecular weights and PDI vs. conversion of COMPTs.
Polymerization condition: 20:1 weight ratio of COMPTs to BHMPT, with 0.2 wt % Ti(n-C4H9O)4 as
catalyst.
S17
Fig. S9 GPC curves of purified low molecular weight polyester samples: PMPT-l, PNT-l and
PMPPT-l synthesized with cyclic monomer to initiator weight ratio of 50:1(w/w); Eluent: THF.
S18
Fig. S10 1H NMR spectra of purified low molecular weight polyester samples: PMPT-l, PNT-l and
PMPPT-l.
S19
Fig. S11 GPC curves of polyester samples: PMPT-h, PNT-h and PMPPT-h synthesized with cyclic
monomer to initiator weight ratio of 500:1 (w/w). Preparation condition: PMPT-h and PNT-h
were characterized without any purification process, PMPPT-h was precipitated once in
methanol before characterization.
S20
Fig. S12 TGA curves of polyesters and cyclic oligomers with a heating rate of 10 °C/min under
nitrogen.
S21