1

Electronic Supplementary Information

Crack healing and reclaiming of vulcanized rubber by triggering rearrangement of inherent sulfur crosslinked networks

Hong Ping Xiang,a Hu Jun Qian,b Zhong Yuan Lu,b Min Zhi Rong*a and Ming Qiu Zhang*a

a Key Laboratory for Polymeric Composite and Functional Materials of Ministry of Education, GD HPPC

Lab, School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, P. R.

China. E-mail: cesrmz@mail.sysu.edu.cn and ceszmq@mail.sysu.edu.cn. b State Key Laboratory of Theoretical and Computational Chemistry, Institute of Theoretical Chemistry,

Jilin University, Changchun 130023, China

Determination of equilibrium constant and kinetic parameter of model disulfide metathesis

For the following disulfide metathesis in equilibrium, A-S-S-A + B-S-S-B A-S-S-B, the

equilibrium constant, Keq, was calculated from:

eqeq

eqeqK

BSSBASSA

BSSA 2

where [A-S-S-A]eq and [B-S-S-B]eq denote equilibrium concentrations of reactants A-S-S-A and

B-S-S-B, while [A-S-S-B]eq denotes equilibrium concentration of product A-S-S-B.

Supposing disulfide metathesis follows the first- or second-order kinetics:

ktx

1

1ln (first order kinetics)

ktx

1

1 (second order kinetics)

where x is conversion, k rate constant and t reaction time. Linear fit of the data offers rate constant

at a given temperature. Finally, activation energy, Ea, can be calculated from Arrhenius equation

based on the relationship between k and T:

/RTaEk Ae

Determination of densities of sulfur crosslinks[S1-S4]

To determine the percentage of sulfur crosslinks in the total number of crosslinks of

vulcanized rubber, selective scission of specific crosslinks in association with crosslinking density

Electronic Supplementary Material (ESI) for Green Chemistry.This journal is © The Royal Society of Chemistry 2015

2

measurement was applied. Firstly, the vulcanizate was treated with 0.4M propanethiol in

piperidine at 25 ºC for 6 h to cleave only the polysulfidic crosslinks. Then, the cosslinking density

of the treated vulcanizate was measured by equilibrium swelling method (see below). Comparison

of the crosslinking densities of the vulcanizate before and after the treatment allowed the

calculation of the contribution of polysulfidic crosslinks to the total degree of crosslinks.

Similarly, the concentration of both polysulfide and disulfide crosslinks was estimated by treating

the vulcanizate with 1M 1-hexanethiol in piperidine at 25 ºC for 48 h to cleave polysulfide and

disulfide crosslinks. As a result, the individual contribution of disulfide crosslinks was obtained

by subtracting the concentration of polysulfidic crosslinks from that of polysulfide and disulfide

crosslinks.

To measure crosslinking density, vulcanized samples (~0.5 g) were immersed in toluene to

swell at 25 ºC for 72 h. The swollen samples were weighed after removal of surface liquid with

filter paper. Then the swollen samples were dried at 80 ºC in vacuum to constant weight and

weighed again. The crosslinking density per unit volume, , was calculated from Flory-Rehner

equation:

)5.0(

)1ln(3/1

2

rrs

rrr

s

rsr

rr

mm

m

where vr is the volume fraction of rubber in the swollen sample, vs is the molar volume of the

solvent, mr is the weight of the rubber network after drying, ms is the weight of solvent absorbed

at equilibrium, r is the density of rubber, s is the density of solvent, is the Flory-Huggins

interaction parameter for polybutadiene rubber-toluene system taken as a constant (0.36). On the

basis of the crosslinking densities, concentration of polysulfide crosslinks, Sx% (x>2), and total

concentration of polysulfide and disulfide crosslinks, Sx1% (x2), can be known by:

%100)2%(

t

x xS

%100)2%( 1

t

x xS

3

where v is the crosslink density of the virgin sample, vt is the crosslink density of the sample

treated by propanethiol, vt1 is the crosslink density of the sample treated by hexanethiol.

0 5 10 15 20 25 300.0

0.2

0.4

0.6

0.8

1.0

1.2

To

rqu

e

[Nm

]

Time [min]

Control 1 Control 2 VR-SH

Fig. S1 Rheographs of the rubbers cured at 150 ºC. The characteristic t90, the optimum vulcanization time required for reaching specific torque value which is the sum of minimum torque and 90 % of the differentials between maximum and minimum torque.

(a) (b)

Fig. S2 (a) Scanning electron microscopic (SEM) micrograph of typical fractured surface of CuCl2/polybutadiene rubber (CuCl2 content = 1 phr), which was compounded under the same conditions as VR-SH. (b) Energy dispersive spectroscopy (EDS) image of typical fractured surface of VR-SH using copper as the indicator element.

4

0 10 20 30 40 50 60 700.0

0.1

0.2

0.3

0.4

0.5

0.6

Mo

lar

fra

cti

on

Reaction time [min]

HEED HEDS DEDS

HEDS-DEDS-RT #409 RT: 10.33 AV: 1 SB: 66 8.17-9.63 , 10.82-12.40 NL: 4.23E5T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bundance

93.88

137.92

65.86

78.87

63.88

58.93 91.90

95.97 139.9475.93 90.94 106.95

136.93108.90 140.76 169.96 186.85

(a) (b) Fig. S3 (a) Time dependences of molar fractions of the disulfides in equimolar mixture of HEDS and DEDS determined from HLPC chromatograms in Fig. 1 (25 ºC, acetonitrile, 0.5 mol% CuCl2). (b) Mass spectrum of the metathesis product HEED. The signal at m/z ≈ 138 is a molecular ion peak, just half of the sum of m/z ≈ 154 (HEDS) and half of m/z ≈ 122 (DEDS). The ion peaks at m/z ≈ 94, 79 and 66 belong to the fragments of -S-S-C2H5, -S-S-CH2, and -S-S-, respectively.

SS

OH

5

0 2 4 6 8 10 12

70 oC

60 oC

50 oC

Retention time [min]

DEDS

EPDS

DPDS

40 oC

0 50 100 150 200 2500.0

0.1

0.2

0.3

0.4

0.5

0.6

Mo

lar

fra

cti

on

Reaction time [min]

EPDS DEDS DPDS

(a) (b)

DEDS-DPDS #792 RT: 8.23 AV: 1 SB: 318 7.28-8.02 , 8.45-9.41 NL: 5.73E6T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bundance

135.80

93.75

65.72

137.8095.7878.7558.80

106.80 138.8480.80 133.74 195.22159.06 176.86

(c)

Fig. S4 (a) HLPC analysis of equimolar mixture of DPDS and DEDS collected at different temperatures (3 h, n-heptane, 0.5 mol% CuCl2). Here, DPDS replaces HEDS used in (Fig. 1) because the latter does not dissolve in n-heptane. (b) Time dependences of molar fractions of the disulfides in equimolar mixture of DPDS and DEDS determined from HLPC chromatograms at 70 ºC. (c) Mass spectrum of the metathesis product ethyl propyl disulfide (EPDS).

0 2 4 6 8 10

DPDS

DEDS

Retention time [min]

25C 100C

Fig. S5 HPLC analysis of equimolar mixture of DEDS and DPDS in acetonitrile at 25 ºC for 5 h and in n-heptane 100 ºC for 1 h.

S

S

6

0 50 100 150 200 2500.0

0.1

0.2

0.3

0.4

0.5

0.6

M

ola

r fr

ac

tio

n

Reaction time [min]

0.05 mol% 0.25 mol% 0.5 mol%

0 20 40 60 80 100 120

0.34

0.38

0.42

0.46

0.50

Mo

lar

frac

tio

n

Reaction time [min]

1:1, 2:1 1:2, 3:1 1:3

(a) (b)

Fig. S6 Time dependences of molar fractions of HEED produced from disulfide metathesis between HEDS and DEDS at 25 ºC in acetonitrile. (a) Effect of CuCl2 dosage on conversion of equimolar HEDS and DEDS. (b) Effect of initial molar ratio of HEDS to DEDS on conversion (CuCl2: 0.5 mol%). Table S1. Effect of initial molar ratio of reactants on Keq in acetonitrile at 25 ºC *

[HEDS]o:[DEDS]o [HEDS]o [DEDS]o [HEDS]eq [DEDS]eq [HEED]eq Keq

1:1 100 100 49.94 50.05 100 4.00 2:1 133.33 66.67 82.37 26.26 91.37 3.86 3:1 150 50 106.66 14.90 78.39 3.87 1:2 66.67 133.33 20.52 94.44 85.05 3.73 1:3 50 150 11.34 117.95 70.73 3.74

*[HEDS]o and [DEDS]o are initial concentrations of HEDS and DEDS. [HEDS]eq, [DEDS]eq and [HEED]eq are equilibrium concentrations of HEDS, DEDS and HEED. Unit of the concentrations: mmol L-1. Content of CuCl2: 0.50 mol%. Table S2. Effect of temperature on Keq in acetonitrile*

T (ºC) [HEDS]o [DEDS]o [HEDS]eq [DEDS]eq [HEED]eq Keq

0 100 100 49.47 50.69 99.96 3.99 -10 100 100 60.52 60.74 78.88 1.69 -15 100 100 63.98 67.64 68.31 1.08 -20 100 100 69.78 70.18 59.87 0.73 -30 100 100 77.94 79.02 43.07 0.30

*Content of CuCl2: 0.50 mol%.

7

Table S3. Effect of dosage of CuCl2 on Keq in acetonitrile at 25 ºC

Dosage (mol %)

[HEDS]o [DEDS]o [HEDS]eq [DEDS]eq [HEED]eq Keq

1.25 100 100 49.41 50.66 99.82 3.98 0.50 100 100 49.94 50.05 100 4.00

Table S4. Effect of temperature on Keq in n-heptane*

T (ºC) [DPDS]o [DEDS]o [DPDS]eq [DEDS]eq [EPDS]eq Keq

50 100 100 88.14 94.04 17.82 0.04 53 100 100 80.36 85.69 34.02 0.17 55 100 100 75.75 76.48 47.80 0.39 60 100 100 50.05 50.07 99.96 3.99

*Content of CuCl2: 0.50 mol%.

0 5 10 15 20 25 30 350.00

0.09

0.18

0.27

0.36

0.45

ln

(1/(

1-x

))

Time [min]

k=2.97x10-3dm

3mol-1s

-1(R2=0.953)k=4.3x10

-3 dm3 mol

-1 s-1 (R

2 =0.977)k=4.57x10-3 dm

3 mol-1 s

-1 (R2 =0.994)

k=5.81x10-3 dm

3 mol-1 s

-1 (R2 =0.994)k=8.18x10

-3 dm3 mol

-1 s-1 (R

2 =0.982) -30oC

-20oC

-15oC

-10oC

0oC

0 5 10 15 20 25 30 351.0

1.1

1.2

1.3

1.4

1.5

k=3.16x10-3dm

3mol-1s

-1 (R2=0.951)

k=4.97x10-3 dm

3 mol-1 s

-1 (R2 =0.983)

k=5.66x10-3 dm

3 mol-1 s

-1 (R2 =0.994)

k=7.02x10-3 dm

3 mol-1 s

-1 (R2 =0.997)

k=1.085x10-2 dm

3 mol-1 s

-1 (R2 =0.991)

1

/(1

-x)

Time [min]

-30C

-20C

-15C

-10C

0C

(a) (b)

3.6 3.7 3.8 3.9 4.0 4.1 4.2-6.0

-5.8

-5.6

-5.4

-5.2

-5.0

-4.8

-4.6

-4.4

1/T [103K-1]

lnk

Ea = 22.3 kJ/mol (R2=0.991)

(c)

Fig. S7 Linear regression of conversion, x, versus time, t, of disulfide metathesis between HEDS and DEDS with 0.5 mol% CuCl2 in acetonitrile according to (a) first-order and (b) second-order kinetics. The higher regression coefficients of the plots in (b) suggest that the second-order kinetics reaction should be more reasonable. Therefore, the activation energy is estimated using k values provided by the second-order kinetics.

8

10 20 30 40 50 600.04

0.06

0.08

0.10

0.12

0.14

k=1.76x10-4dm

3mol-1s

-1 (R2=0.957)k=3.23x10

-4dm3mol

-1s-1 (R

2=0.985)

k=4.79x10-4 dm

3mol-1s

-1 (R2=0.974)

k=1.12x10-3 dm

3 mol-1 s

-1 (R2 =0.958)

ln(1

/(1

-x))

Time [min]

60oC

55oC

53oC

50oC

10 20 30 40 50 601.04

1.07

1.10

1.13

1.16

k=1.856x10-4dm

3mol-1s

-1 (R2=0.957)k=3.404x10

-4dm-mol

-1s-1 (R

2=0.985)

k=5.207x10-4dm

3mol-1s

-1 (R2=0.975)

k=1.24x10-3 dm

3 mol-1 s

-1 (R2 =0.961)

1/(1

-x)

Time [min]

60oC

55oC

53oC

50oC

(a) (b)

3.00 3.02 3.04 3.06 3.08 3.10-9.0

-8.5

-8.0

-7.5

-7.0

-6.5

1/T [103K-1]

lnk

Ea = 172.3 kJ/mol (R2=0.996)

(c)

Fig. S8 Linear regression of conversion, x, versus time, t, of disulfide metathesis between DEDS and DPDS with 0.5 mol% CuCl2 in n-heptane according to (a) first-order and (b) second-order kinetics. The higher regression coefficients of the plots in (b) suggest that the second-order kinetics reaction should be more reasonable. Therefore, the activation energy is estimated using k values provided by the second-order kinetics.

9

RT: 8.77 - 10.55

8.8 9.0 9.2 9.4 9.6 9.8 10.0 10.2 10.4Time (min)

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nd

an

ce

9.74

9.51

9.29

9.819.05 9.90 10.4110.078.82 9.17 10.21

NL:2.60E7TIC F: MS DADS-DPDS

DADS-DPDS #1030 RT: 9.51 AV: 1 SB: 39 9.36-9.45 , 9.56-9.66 NL: 6.41E6T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nd

an

ce

147.82

105.73

63.7372.84

149.8477.75 107.7958.81

78.79 114.87102.78 150.88145.93127.01 180.72 191.97

(a) (b)

Fig. S9 GC-MS analyses of the metathesis between DADS and DPDS with 0.5 mol% CuCl2 in n-heptane at 70 ºC for 3 h. (a) Gas chromatograph of the reaction system, and (b) mass spectrum of the metathesis product. The peak at 9.51 min is assigned to be allyl propyl disulfide, because the molecular ion peak (m/z ≈ 148) is just half of the sum of DPDS (m/z ≈ 150) and DADS (m/z ≈ 146).

DBDS-DMTS #844 RT: 8.51 AV: 1 SB: 332 7.84-8.30 , 9.01-10.32 NL: 1.20E6T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bu

nd

an

ce

135.87

79.81

56.91

78.80

63.76 137.8881.81

92.8377.80 138.9794.90 106.86 133.80 151.87 189.15177.99

DBDS-DMTS #1494 RT: 11.99 AV: 1 SB: 295 9.46-10.70 , 12.14-12.47 NL: 8.41E5T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bu

nd

an

ce

167.84

111.77

56.90

78.79

63.78 169.85

113.78110.7086.8877.82

102.89 170.85119.85 135.87 166.59 188.84

(a) (b) Fig. S10 Mass spectra of the metathesis products between DBDS and DMTS with 0.5 mol% CuCl2 in n-heptane at 70 ºC for 3 h. Because scission of DMTS would offer two species (CH3-S- and CH3-S-S-) to react with DBDS at the same time, two metathesis products appear, i.e. (a) methyl butyl disulfide (m/z ≈ 136) and (b) methyl butyl trisulfide (m/z ≈ 168).

S

S

S

S

S

S

S

10

DMTS-CuCl2 #597 RT: 3.23 AV: 1 SB: 93 3.18 , 3.66-4.15 NL: 2.89E6T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100R

ela

tive

Ab

un

da

nce

93.90

78.88

60.93 95.9463.89

80.9277.8397.0091.97 109.09 136.52 155.21 166.53 199.68190.18

DMTS-CuCl2 #1384 RT: 7.44 AV: 1 SB: 359 6.20-6.88 , 7.78-9.01 NL: 3.64E6T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Re

lativ

e A

bu

nd

an

ce

157.87

78.86

63.88

159.8993.92

110.9179.94

60.94 64.93 95.94 111.9392.92 161.93156.05142.85 194.12185.08

(a) (b)

Fig. S11 Mass spectra of the metathesis products of DMTS with 0.5 mol% CuCl2 in acetonitrile at 25 ºC for 1 h. (a) Dimethyl disulfide (m/z ≈ 94) and (b) dimethyl tetrasulfide (m/z ≈ 158).

RT: 2.98 - 14.16

3 4 5 6 7 8 9 10 11 12 13 14Time (min)

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bundance

8.08

6.52

9.59

6.65 9.808.343.58 10.274.10 12.54 13.604.83 5.58

NL:2.89E7TIC F: MS DEDS-DPDS-DBDS

RT: 3.78 - 16.09

4 6 8 10 12 14 16Time (min)

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bundance

9.67

11.08

8.08

9.57

6.5212.51

8.16 12.856.65 11.3110.45 13.53 14.964.10 4.67 5.71

NL:2.75E7TIC F: MS DEDS-DPDS-DBDS-1

(a) (b)

DEDS-DPDS-DBDS-1 #393 RT: 8.10 AV: 1 SB: 49 6.96-7.59 , 8.40-9.02 NL: 1.09E6T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bundance

94.01

136.03

65.99

79.0359.04 96.01138.0593.02

81.04 107.00 139.12133.83 165.04 195.28188.50

DEDS-DPDS-DBDS-1 #513 RT: 9.67 AV: 1 SB: 50 8.45-9.15 , 9.93-10.53 NL: 5.71E6T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bundance

94.01

150.04

57.12

65.94

96.0278.99 152.07

88.0868.01107.04 153.11121.01 148.03 191.29179.38

(c) (d)

SS

S

S

S

S

S

S

S

S

11

DEDS-DPDS-DBDS-1 #623 RT: 11.10 AV: 1 SB: 48 10.12-10.76 , 11.52-12.12 NL: 2.34E6T: + c Full ms [ 50.00-200.00]

60 80 100 120 140 160 180 200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rela

tive A

bundance

57.12

108.01

164.05

122.0366.01

73.04 79.00110.03 165.1188.06

124.0790.16 167.12162.09150.08 181.55 196.84

(e)

Fig. S12 Dynamic reversibility of disulfide metathesis in acetonitrile catalyzed by 0.5 mol% CuCl2 at 25 ºC. (a) Gas chromatograph of metathesis between DEDS and DPDS in equilibrium. (b) Gas chromatograph of metathesis among DEDS, DPDS and DBDS in equilibrium. Equimolar DBDS was added when the metathesis between DEDS and DPDS had reached the equilibrium. (c) Mass spectrum of the metathesis product (ethyl propyl disulfide (EPDS)) between DEDS and DPDS. (d) Mass spectrum of the metathesis product (ethyl butyl disulfide (EBDS)) between DEDS and DBDS. (e) Mass spectrum of the metathesis product (propyl butyl disulfide (PBDS)) between DPDS and DBDS. The ratios of DEDS:EPDS:DPDS:EBDS:PBDS:DBDS attained from the normalized peak areas are 11:21:12:23:22:12, near the statistical values.

4 6 8 10 12

PPh3

DPDS

EPDS

DEDS

2h

Retention time [min]

12h

Fig. S13 HLPC analysis of disulfide metathesis between equimolar HEDS and DEDS at 100 ºC catalyzed by 1 mol% PPh3. Because of the high evaporation rate of acetonitrile and n-heptane at 100 ºC, the reaction proceeded in the absence of any solvent.

S

S

12

0 2 4 6 8 10 12

with antiager, 15 min

DPDSEPDSDEDS

DEDS

HEEDHEDS

Retention time [min]

with antiager, 2 h

with antioxidant, 2 h

with antioxidant, 15 min

b

a

Fig. S14 HLPC analysis of disulfide metathesis between (a) equimolar DEDS and DPDS in the presence of 5 mol% antioxidant tris(2,4-di-tert-butylphenyl)phosphate, and (b) equimolar HEDS and DEDS in the presence of 5 mol% antiager poly(1,2-dihydro-2,2,4-trimethyl-quinoline). The reactions are carried out in acetonitrile at 25 ºC with 0.5 mol% CuCl2.

0 1 2 3 4 5 6 7

HEEDTEMPO DEDS

HEDS

Retention time [min]

5 min

15 min

30 min

1 h

1.5 h

12 h

24 h

Equimolar mixture of HEDS and DEDS in acetonitrile with 0.5 mol% CuCl

2 and 1 mol% TEMPO

Acetonitrile solution of 0.5 mol% CuCl2 and 1 mol% TEMPO

25 G

(a) (b)

25 G

0 1 2 3 4 5 6 7 8

TEMPO

DEDS

HEDS

Retention time [min]

1 h

3 h

15 h

(c) (d)

Fig. S15 (a) HLPC analysis of disulfide metathesis between equimolar of HEDS and DEDS in acetonitrile with 0.5 mol% CuCl2 and 1 mol% TEMPO at 25 ºC. All the chemicals are mixed at

13

the same time. (b) ESR spectrum of the reaction system in (a) collected at 24 h in comparison with that of a reference system, which has the same compositions as (a) but the disulfide mixtures are replaced by isopycnic acetonitrile. (c) Integration of (b). (d) HLPC analysis of the reaction system having the same components as (a), but CuCl2 and TEMPO are firstly mixed in acetonitrile under stirring for 30 min prior to the addition of acetonitrile solution of HEDS and DEDS.

0 2 4 6 8

Retention time [min]

HEDSHEES

DEDS

Benzoquinone

Benzoquinone

Ethyl acetate

HCl

H2O

Control

0 1 2 3 4 5 6 7 8

DEDS

HEED

HEDS

Retention time [min]

20 mol% CuCl,

60oC, 1 h

2 mol% CuCl,

25oC, 24 h

1 mol% CuCl,

60oC, 24 h

(a) (b)

Fig. S16 (a) Effect of different inhibitors (10 mol %) on disulfide metathesis between equimolar HEDS and DEDS in acetonitrile for 30 min with 0.5 mol% CuCl2 at 25 ºC. (b) HLPC analysis of disulfide metathesis between equimolar HEDS and DEDS in acetonitrile catalyzed by CuCl under different conditions.

0 100 200 300 400 500 600 700 8000

20

40

60

80

100

We

igh

t [

%]

Temperature [oC]

Control 1 Control 2 VR-SH

Fig. S17 Thermal decomposition behaviors of the cured rubbers.

14

0 2 4 6 8

CuO

Cu2O

DEDS

Retention time [min]

HEDS

Cu2S

CuS

Fig. S18 HLPC analysis of disulfide metathesis between equimolar HEDS and DEDS in acetonitrile at 60 ºC for 24 h catalyzed by 5 mol% Cu2S, CuS, Cu2O and CuO, respectively.

Fig. S19 Identification of non-contact regions on the combined fractured surfaces. Firstly, paired tensile fractured specimens were cooled down by liquid nitrogen. Then, one part of the pair was uniformly dyed with red oil paint. Finally, the dyed fragment was brought into contact with its undyed counterpart. When the two halves of the broken specimen were separated again, the unstained portions on the originally undyed fragment (refer to the photos shown above) represent the non-contact regions on the combined fractured surfaces.

Fig. S20 EDS images of the fracture surface of control vulcanized rubber without Si-69 using a) copper and b) sulfur as the indicator elements. Here the vulcanized rubber has the same composition as VR-SH but excludes Si-69. The attached scale bars represent 1 mm in length.

15

Fig.S21 Model experiment showing improved mobility of CuCl2 with the help of Si-69. (a) SEM and (b-f) EDS images of side faces of two pieces of contacted rubbers (left: VR-SH; right: polybutadiene). The VR-SH in (a1-f1) contains Si-69, while that in (a2-f2) does not. The indicator elements of EDS images include (b) copper, (c) chlorine, (d) silicon, (e) oxygen, and (f) sulfur. After treatment at 110 ºC for 48 h, CuCl2 successfully migrates from VR-SH to polybutadiene with the aid of Si-69, and is dispersed in the latter (refer to b1-f1). Comparatively, only a few CuCl2 can migrate from VR-SH to polybutadiene because of lack of Si-69 (refer to b2-f2). The attached scale bars represent 1 mm in length.

16

0 100 200 300 4000

1

2

3

4

5

Str

es

s

[MP

a]

Strain [%]

VR-SH (virgin, with Si-69) VR-SH (healed, with Si-69) VR-SH (virgin, without Si-69) VR-SH (healed, without Si-69)

Fig. S22 Typical tensile stress-strain curves of virgin and healed VR-SH specimens in comparison with those of virgin and healed control vulcanized rubber without Si-69. Healing temperature: 110 ºC; healing time: 12 h.

Notes and references

S1 P. Posadas, A. Fernández, J. Brasero, J. L. Valentín, A. Marcos, A. Rodríguez and L.

González, J. Appl. Polym. Sci., 2007, 106, 3481-3487.

S2 L. González, A. Rodríguez, A. Del Campo and A. Marcos-Fernández, J. Appl. Polym. Sci.,

2002, 85, 491-499.

S3 J. L. Valentín, A. Rodríguez, A. Marcos-Fernández and L. González, J. Appl. Polym. Sci.,

2004, 93, 1756-1761.

S4 R. L. Fan, Y. Zhang, F. Li, Y. X. Zhang, K. Sun and Y. Z. Fan, Polym. Test., 2001, 20,

925-936.