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: tuyingfeng@suda.edu.cn.

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

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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):

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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.

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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.

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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:

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(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.

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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

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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

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Fig. S1 GPC curves of cyclic oligoesters: COMPTs (a), CONTs (b) and COMPPTs (c), using THF as

the eluent.

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Fig. S2 1H NMR spectra of cyclic oligoesters in CDCl3: COMPTs (a), CONTs (b) and COMPPTs (c).

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Fig. S10 1H NMR spectra of purified low molecular weight polyester samples: PMPT-l, PNT-l and

PMPPT-l.

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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.

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Fig. S12 TGA curves of polyesters and cyclic oligomers with a heating rate of 10 °C/min under

nitrogen.

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