S1

Supporting information for:

Photocontrolled degradation of stimuli-responsive poly(ethyl glyoxylate): Differentiating

features and traceless ambient depolymerization

Bo Fana, John F. Trantb, Rebecca Yardleyb, Andrew Pickeringa, Francois Lagugne-Labarthetb

and Elizabeth R. Gilliesa,b*

aDepartment of Chemical and Biochemical Engineering, bDepartment of Chemistry, The University of Western Ontario, 1151 Richmond St., London, Ontario, Canada, N6A 5B7 Table of contents: 1. 1H NMR and 13C NMR spectra and SEC traces for the PEtGs………………….....S2-S4 2. Control coating erosion of a non-photo-responsive PEtG……………………….…S5 3. 1H NMR spectra of residual coatings………………………………………………S6-S7 4. Proposed cleavage and depolymerization mechanisms……………………………S8-S9 5. Mass loss profile for a 300 µm thick coating………………………………………S10 6. Experimental set-up for the collection of depolymerized ethyl glyoxylate……......S10 7. NMR spectra of collected and repolymerized ethyl glyoxylate………..………..…S11 8. SEC traces of PEtG after repolymerization…………………………..…………….S12 9. References………………………………………………………………………….S13

  S2

Figure S1. 1H NMR spectrum of the PEtG-NVOC used in this study (CDCl3, 600 MHz). Zoom insets show peaks corresponding to the end-cap.

Figure S2. 13C NMR spectrum of PEtG-NVOC used in this study (CDCl3, 150 MHz).

  S3

Figure S3. Size exclusion chromatogram of the PEtG-NVOC used in this study (refractive index detection).

Figure S4. 1H NMR spectrum of PEtG end-capped by benzyl chloroformate used in this study (CDCl3, 600 MHz). Zoom inset shows peaks corresponding to the end-cap.

  S4

Figure S5. 13C NMR spectrum of PEtG end-capped by benzyl chloroformate used in this study (CDCl3, 150 MHz).

Figure S6. Size exclusion chromatogram of the PEtG end-capped by benzyl chloroformate used in this study (refractive index detection).

  S5

Figure S7. Mass loss profiles of coatings prepared PEtG end-capped with a non-photo-responsive benzyl carbonate end-cap either with irradiation or without irradiation in 0.1 M, pH 7.0 phosphate buffer at 20 °C.    

  S6

Figure S8. 1H NMR spectrum (CDCl3, 600 MHz) of residual coating material from a 150 µm-thick coating of irradiated PEtG-NVOC after 3 days of immersion in 0.1 M, pH 7 buffer at 20 °C. The spectrum shows the absence of end-cap peaks, confirming the complete removal of end-cap during the irradiation. In addition, peaks corresponding to ethyl glyoxylate hydrate (EtGH) are observed at 5.41 and 6.79 ppm. Assignment of the EtGH peak was made with reference to the previous depolymerization study in solution.1 The high integration of the peak at 6.79 ppm is believed to result from bound H2O, which can hydrogen bond to the hydrate. This is also consistent with the broadness and downfield shift of the H2O peak at 2.1 ppm.

Figure S9. 1H NMR spectrum (CDCl3, 600 MHz) of residual coating material from a 150 µm coating of irradiated PEtG-NVOC after 6 days of immersion in 0.1 M, pH 7 buffer at 20 °C. The same discussion as for Figure S8 applies.

  S7

Figure S10. 1H NMR spectrum (CDCl3, 600 MHz) of residual coating material from a 150 µm coating of non-irradiated PEtG-NVOC after 8 days of immersion in 0.1 M, pH 7 buffer at 20 °C. Intact end-cap peaks are observed at ~4 ppm and 7-8 ppm and no degradation products are observed.

Figure S11. 1H NMR spectrum (CDCl3, 600 MHz) of residual coating material from a 150 µm coating of non-irradiated PEtG-NVOC after 38 days of immersion in 0.1 M, pH 7 buffer at 20 °C. The same comments as for Figure S10 apply.  

  S8

Scheme S1. Proposed acid-catalyzed cleavage of an acetal linkage in the PEtG backbone. R represents the terminal group. The resulting hemiacetal-terminated polymers/oligomers can subsequently decompose via the mechanisms shown in Scheme S2-S3.

Scheme S2. Proposed PEtG terminal hemiacetal cleavage and ethyl glyoxylate hydrate formation by an acid-catalyzed mechanism (based on reference 2). R represents the terminal group.

O OHO

OEtO

OEtO

R n+ O O

OEtO

OEtO

R O O O

OEtO

OEtO

R Hn

O O

OEtO

OEtO

R

O O O

OEtO

OEtO

R nO O

OEtO

OEtO

R H+

H+ H2O

O O

OEtO

OEtO

RHO

H+

OHO O

OEtO

OEtO

R Hn+

OEtO

OH

O O O

OEtO

OEtO

R Hn H+O O O

OEtO

OEtO

R Hn-1

H+ H2O

H+

OEtO

OHHO

continued depolymerization

  S9

Scheme S3. Proposed PEtG terminal hemiacetal cleavage and ethyl glyoxylate hydrate formation by a base-catalyzed mechanism (based on reference 1). R represents the terminal group. Note that a “water-catalyzed” reaction has been proposed to follow a similar mechanism, where H2O rather than HO- serves as the base.2

Scheme S4. Mechanism proposed for the depolymerization of PEtG in the absence of water. Poly corresponds to the polymer matrix in the solid state.

O O O-

OEtO

OEtO

R n

H

OEtO

O

O O O

OEtO

OEtO

R HnHO- O O O-

OEtO

OEtO

R n-1

HO-

OEtO

OHHO+ H2O

continued depolymerization

O O OH

OEtO

OEtO

R n-1

H

OEtO

O

O O O

OEtO

OEtO

R Hn continued depolymerization

Poly+-H

Poly

  S10

Figure S12. Mass loss profile for UV light irradiated (I) and non-irradiated (N-I) PEtG-NVOC immersed pH 7.0 buffer at 20 °C pH 7.0. The film thickness was 300 µm. Incomplete depolymerization of the irradiated polymer is attributed to incomplete end-cap cleavage.

Figure S13. Experimental set-up for the collection of depolymerized ethyl glyoxylate.

  S11

Figure S14. 1H NMR spectrum (600 MHz, CDCl3) of collected ethyl glyoxylate.

Figure S15. 1H NMR spectrum (600 MHz, CDCl3) of repolymerized PEtG-NVOC.  

  S12

Figure S16. Size exclusion chromatogram of repolymerized PEtG-NVOC after depolymerization, monomer collection and repolymerization.  

  S13

References

1. Fan, B.; Trant, J. F.; Wong, A. D.; Gillies, E. R. Polyglyoxylates: A versatile class of triggerable self-immolative polymers from readily accessible monomers. J. Am. Chem. Soc. 2014, 136, 10116-10123.

2. Funderburk, L. H.; Aldwin, L.; Jencks, W. P. Mechanisms of general acid and base catalysis of the reactions of water and alcohols with formaldehyde. J. Am. Chem. Soc. 1978, 100 , 5444-5459.