Supporting Information Combined effect of Chain Extension and Supramolecular Interactions on Rheological and Adhesive Properties of Acrylic Pressure-Sensitive-Adhesives Xavier Callies a,b*, Olivier Herscher c, Cécile Fonteneau c, Alexis Robert a,b, Sandrine Pensec c, Laurent Bouteiller c, Guylaine Ducouret a,b, Costantino Creton a,b* a Laboratoire Sciences et Ingénierie de la Matière Molle, CNRS, ESPCI Paris, PSL Research University, 0 rue Vauquelin, Paris, France b Laboratoire Sciences et Ingénierie de la Matière Molle, Université Pierre et Marie Curie, Sorbonne- Universités, 0 rue Vauquelin, France c Sorbonne Universités, UPMC Univ Paris 06, CNRS, IPCM, Chimie des Polymères, F-75005 Paris, France xavier.callies@etu.upmc.fr, costantino.creton@espci.fr S
Synthesis n-butylacrylate (Acros, 99%), glycidyl methacrylate (Aldrich, 97%) and pentamethyldiethylenetriamine (PMDETA) (Acros, 99%) were distilled prior to use. Methyl- 2-bromopropionate (Aldrich), Copper chloride CuCl (Aldrich, 99.99%), DMF (Normapur) were used without purification. The procedure for bis-urea ATRP initiator synthesis and bis-urea center-functionalized PnBAX homopolymerization were previously described [Fonteneau, C.; Pensec, S.; Bouteiller, L., Versatile synthesis of reversible comb-shaped supramolecular polymers. Polym. Chem. 204, 5, 2496-2505] General procedure for bis-urea center-functionalized copolymers (E7-PnBAX and E4- PnBAX) Bis-urea ATRP initiator (425 mg, 0.77 mmol, eq.), copper chloride (38 mg, 0.39 mmol, 0.5 eq.), PMDETA (67 mg, 0.39 mmol, 0.5 eq.), n-butylacrylate (6.04 ml, 46.6 mmol, 60 eq.) and DMF ( ml, 0% w/w) were introduced in a schlenck flask equipped with a magnetic stirring bar, sealed with a rubber septum and then degassed by three freeze/pump/thaw cycles. The mixture was stirred in an oil bath at 80 C. Samples were withdrawn periodically from the reaction to determine conversion by NMR. At the same time, a second flask charged with n- butylacrylate (2.62 ml, 20.2 mmol, 26 eq.) and glycidyl methacrylate (0.4 ml, 3. mmol, 4 eq.) was degassed by three freeze/pump/thaw cycles. When the reaction in the first flask reached a conversion of 55%, the mixture of the second flask was transferred into the first flask via a double tipped needle. After 35 minutes, the mixture was cooled, diluted in ethyl acetate and washed with water until the disappearance of the green color. The organic phase was dried on MgSO 4, filtered, evaporated and dried under vacuum at 80 C. H NMR (200 MHz, DMSO) δ (ppm) : 0.89 (t, (CH 3 -CH 2 -) n ),.3 (m, (CH 3 -CH 2 -) n ),.5 (m, (CH 3 -CH 2 -CH 2 ) n ),.77 (br, (CH 2 -CH-COO) n ), 2.06 (s, 3H, Ph-CH 3 ), 2.2 (br, (CH 2 -CH- COO) n ), 2.55 et 2.7 (CH-O-CH 2 epoxy), 3. (CH-O-CH 2 epoxy), (3.99 (br, (CH 2 -O) n ), 6.28 (d, 2H, CH-NH-CO), 6.85 (s, H, Ph-H), 7.5 (s, 2H, CO-NH-Ph), 7.99 (s, H, Ph-H). 3 C NMR (200 MHz, DMSO) δ(ppm) : 0.9 (CH 3 -CH 2 ), 3.77 ((CH 3 -CH 2 ) n ), 8.6 (Ph- CH 3 ), 9.69 ((CH 3 -CH 2 ) n ), 25.8 (CH 3 -CH 2 ), 3.35 ((CH 3 -CH 2 -CH 2 ) n ), 32.5 ((CH 2 -CH- COO) n ), 42.44 ((CH 2 -CH-COO) n ), 50.85 (CH-COO), 52.7 (CH-CH 2 -O epoxy), 53.5 (CH- CH 2 -O epoxy), 55. (CH 3 -CH), 56.6 (CH-NH), 65 ((CH 2 -O) n ), 66.72 (CH 2 -O), 67.4 (O-CH 2 - S2
epoxy), 9.48 (Ph-H), 25.8 (Ph-CH 3 ), 32.49 (Ph-H), 36.3 (Ph-NH), 56.57 (NH-CO- NH), 69.76 (CO-O), 75.3 ((CO-O) n ). For the synthesis of E8-PnBA, the general procedure for E7-PnBAX and E4-PnBAX was used by replacing the bis-urea initiator by 2-methyl-bromopropionate..2 Normalized RI 0.8 0.6 0.4 60' 20' 80' 0.2 0 3.5 4.5 5.5 6.5 Ve (ml) Figure S: Size Exclusion Chromatograms versus time of polymerization for the ATRP of n- butylacrylate/glycidyl methacrylate initiated by 2-methyl-bromopropionate in DMF at 80 C. a water S3
b Figure S2: H NMR spectrum of copolymer E4-PnBAX. (a) in CDCl 3 /d 6 DMSO mixture; (b) in CDCl 3 : Mn = 930 g/mol DPe= 3.5 S4
Analysis of the curing of copolymer by diamine The kinetics of the chemical reaction between diamine and epoxy groups was studied on a poly(butylacrylate -co- glycidyl methacrylate) copolymer by Differential Scanning Calorimetry (DSC). This copolymer, called E8-PnBA, was synthesized from a commercial initiator (methyl-2-bromo-propionate) and it contains 8 epoxy groups per chain (M w 3.8kg/mol). This copolymer is mixed with the diamine in the ratio epoxy for amine (NH 2 ). When this material is heated from -40 C to 250 C, a broad exothermic peak is measured, as expected from the exothermic reaction between amine and epoxy. When the same sample is heated again, no peak is observed. This absence of peak reveals that all amine groups reacted with epoxy groups after the first heating step. The heat of reaction measured for the first temperature ramp was used to estimate the conversion of the cross-linking reaction. Figure S3: 2 successive heating DSC curves at 0 C/min from -40 C to 250 C (Step and 3). Between these two steps, the temperature decreases from 250 to -40 C at -0 C/min (Step 2). In order to minimize the degradation of the urea groups in the supramolecular copolymers, the curing temperature was set at 80 C. E8-PnBA was cured at 80 C for various times and was analyzed by DSC. As shown in Figure S8, the exothermic peak observed during the temperature ramp decreases with the curing time. The area under this peak allows us to S5
estimate the conversion of the epoxy-amine reaction (see Figure S9). While only 40% of cross-linkers reacted with copolymers after hour at 80 C, the cross-linking reaction is over after 2 days at 80 C. Figure S4: DSC heating curves at 0 C/min from -40 C to 250 C after different curing time at 80 C. Figure S5: conversion of the cross-linking reaction estimated by DSC for various curing times at 80 C. S6
Adhesion and Rheology A B Figure S6: Images illustrating the cavitation process during the detachment of the steel probe from PnBAX8 (A) and E4-PnBAX (B) layers for V t =00µm/s and room temperature. 0 5 7 6 5 4 T=80 C E7-PnBAX E7-PnBAX-C E7-PnBAX-C5 E7-PnBAX-C20 G' & G'' (Pa) 0 4 0 3 0 2 T=80 C E7-PnBAX E7-PnBAX-C E7-PnBAX-C5 E7-PnBAX-C20 2 4 6 2 4 6 0 2 4 6 00 Angular Velocity (rad/s) G''/G' 3 2 7 6 5 2 4 6 8 2 4 6 8 0 2 4 6 8 00 Angular Velocity (rad/s) Figure S7: Frequency Sweep G and G (left) and tan δ =G /G (right) in the linear regime at 80 C, for pure bis-urea copolymer (E7-PnBAX) and for the lightly crosslinked materials based on E7- PnBAX (after curing). S7
0 5 G' G' G''/G' E4-PnBAX G''/G' E4-PnBAX-C20 3 2 0 4 0 G'(Pa) 0 3 T=80 C 6 5 4 G''/G' 3 0 2 2 0 0. 2 4 6 2 4 6 2 0 4 6 00 Angular Velocity (rad/s) Figure S8: Frequency Sweep G (filled markers) and tan δ (unfilled markers) in the linear regime at 80 C for pure bis-urea copolymer (E4-PnBAX) and mixtures with cross-linker (after curing). Figure S9: photos of the detachment of the probe from E8-PnBA-C5 (A & B) and E8-PnBA-C20 (C & D) layer. A and C show the cavitation process at the beginning of the probe-tack test while B & D illustrate the state of the adhesive layer at the end of the probe-tack test,, i.e. when the force drops to 0N. These pictures reveal the cohesive failure observed for E8-PnBA-C5 and the adhesive failure observed for E8-PnBA-C20. Cavitation and fingering processes occur during the detachment of the probe for both films. For E8-PnBA-C5, the rupture of fibrils between S8
cavities is clearly observed at the end of the test (see image B) while only white spots are observed on the film of E8-PnBA-C20 (see image D). These spots correspond to local deformation of the adhesive surface due to the nucleation of bubbles. A B C D E Figure S0: Adhesive debonding by propagation of cracks at the probe surface (sample: E7-PnBAX- C20). (A) Before the debonding test, the probe is in contact with the adhesive layer during the compression step (F N =-70N). Appearance (B) and growth (D&E) of crack and cavitation at the beginning of the debonding test, surface of the polymer film after the test (E). A B C D E Figure S: Adhesive debonding with fibrillar structures (sample: E7-PnBAX-C). (A) Before the debonding test, the probe is in contact with the adhesive layer during the compression step (F N =-70N). S9
Cavitation (B&C) at the beginning of the debonding test, uniaxial deformation of the fibrils (D) revealed by the scattering of the light. Image (E) of the surface of the adhesive layer after the adhesion test. S0
Complementary Investigations on the hydrogen bonded interactions between urea and epoxy groups As detailed in the discussion part, the rheological experiments carried out in the melt state on poly(butylacrylate-stat-glycidyl methacrylate) copolymers bearing bis-urea groups suggest that the interactions of bis-urea groups with glycidyl methacrylate monomers are favored over weaker interactions with butylacrylate monomers. In order to confirm that glycidyl methacrylate is a better hydrogen bond acceptor than butyl methacrylate, model experiments were performed at low concentration in non polar solvents. Following the publication of Bouteiller and coworkers (Beilstein J. Org. Chem. 200, 6, 869), we compared the chain-stopper ability of glycidyl methacrylate and butyl methacrylate toward the supramolecular polymer formed by a well-known model bis-urea (EHUT). Three solutions containing EHUT at the same concentration (0.09 mol/l) were prepared in mesitylene. The blank sample only contains EHUT and the solution is viscous due to the selfassembly of the bis-urea into polymer-like aggregates. Solutions, called GMA and BMA in the following figure, also contain 0.33 mol/l of glycidyl methacrylate and butyl methacrylate, respectively. The relative viscosity (η solution /η solvent ) of each solution were measured with a capillary viscometer (Anton-Paar AMVn ) at 25 C. The measurements were performed with an angle of 50 and 70 and similar results were observed for both angles. As shown in figure S2, both monomers are chain-stoppers, since the viscosity of both solutions is lower than that of the blank samples. However the reduced viscosity measured for GMA solution reveals that glycidyl methacrylate is a stronger hydrogen bond competitor for the bis-urea than butyl methacrylate. This effect is probably due to the fact that the glycidyl methacrylate monomer contains two hydrogen bond acceptor groups (carbonyl and epoxy) that may interact cooperatively with the bis-urea moiety. 7 6 rela ve viscosity 5 4 3 2 0 blank GMA BMA Figure S2: Relative viscosity of EHUT (0.09 mol/l) solutions in mesitylene without (blank) or with butyl methacrylate (0.33 mol/l, BMA) and glycidyl methacrylate (0.33 mol/l, GMA). S