Synergetic Binary Organocatalyzed Ring Opening Polymerization for the Precision Synthesis of Polysiloxanes

doi:10.21203/rs.3.rs-3160966/v1

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Synergetic Binary Organocatalyzed Ring Opening Polymerization for the Precision Synthesis of Polysiloxanes

https://doi.org/10.21203/rs.3.rs-3160966/v1

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published 21 Mar, 2024

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Organocatalytic ring opening polymerization (ROP) is a versatlie method for synthesizing well-defined polymers with controlled molecular weight, dispersity, and nonlinear macromolecular architectures. Despite spectacular advances in organocatalytic ROP, precision synthesis of polysiloxanes remains challenging due to the mismatch in polarity between highly polar initiators and nonpolar monomers and polymers and the difficulty in suppressing the formation of scrambling products via transetherification reactions during ROP of cyclic siloxanes. Here, we describe a binary organocatalytic ROP (BOROP) of hexamethylcyclotrisiloxane (D3) employing organic bases as catalysts and (thio)ureas as cocatalysts. The BOROP of D3 using triazabicyclodecene (TBD) and (thio)ureas generates polydimethylsiloxanes (PDMSs) with narrow dispersity (M_w/M_n < 1.1). Despite the similar basicity of TBD and 1,8-bis(tetramethylguanidino)naphthalene (TMGN), which is known as a proton sponge, a unitary organocatalytic system using TMGN was inactive for the ROP of D3. When TMGN was paired with acidic urea, the BOROP of D3 yielded PDMSs with narrow dispersity (M_w/M_n < 1.1). Data suggest that the synergetic use of TMGN and urea is in an unprecedented activation–deactivation equilibrium between dormant and propagating species. The benefits of the present BOROP system are demonstrated based on the formation of PDMS elastomers with more uniform network structures with highly stretchy and excellent mechanical properties.

Physical sciences/Chemistry/Polymer chemistry/Polymer synthesis

Physical sciences/Materials science/Soft materials/Polymers

Ring opening polymerization (ROP) is an important class of methodologies for synthesizing polymers with controlled molecular weights (MWs) and dispersities (Ðs)¹. Encouraged by the first report of organocatalytic ROP utilizing 4-dimethylaminopyridine (DMAP) by Hedrick et al. in 2001², herculean efforts over the years in this area have developed a great number of organocatalysts such as amidine and guanidine bases^3,4, N-heterocyclic carbenes (NHCs)^5,6, phosphazenes^7,8, and urea anions⁹. These catalysts have been shown to exhibit excellent activity, selectivity, and compatibility with various monomers including epoxides, lactones, and carbonates, to mention a few, in addition to low toxicity compared to metal-based catalysts¹⁰.

Polysiloxanes are industrially important materials that cannot be replaced by carbon-based polymers, due to their unique properties such as high thermal stability, low surface energy, and excellent biocompatibility¹¹. Historically, polysiloxanes have been synthesized by equilibrium polymerization using strong acids or catalyst-free ROP of cyclic siloxanes^12,13. As polysiloxanes synthesized by equilibrium polymerization have broad dispersity (M_w/M_n = Ð), synthesizing polysiloxanes by the ROP of cyclic siloxanes is important when expected applications require meticulous care for molecular weight (MW) and Ð¹⁴. In particular, the use of organic catalysts in the ROP of cyclic siloxanes is attractive as reported by Hedrick, Waymouth, and coworkers^15,16. Unlike other organic catalysts, they reported that the ROP of 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane (TMOSC) using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) after full conversion of monomers did not show a broadening in dispersity¹⁵. They have also reported that organocatalytic ROP of cyclic siloxanes initiated from silanols¹⁵ can avoid the inclusion of labile Si-O-C linkages, or silylether to the resulting polysiloxane. Inspired by these prominent studies, we synthesized star-shaped PDMSs with controlled MWs and Ðs upon organocatalytic ROP of hexamethylcyclotrisiloxane (D3) initiated from multifunctional silanols¹⁷. Although a mixture of TBD and multifunctional silanols showed poor solubility in solvents for polymerization due to the mismatch of the highly polar nature of initiating system with nonpolar monomers and polymers, an initiating system using urea anions overcomes this solubility problem. In fact, ROP using urea anions affords polymers with a narrow Ð when the conversion of D3 is low. However, with urea anions, the ROP reaches equilibrium when the conversion of D3 exceeds approximately 50%, and the Ð of the resulting PDMS in the mixture broadens¹⁷. As the most widely used polysiloxane is PDMS, the development of an efficient catalyst system that can solve both the solubility and equilibrium polymerization problems with the ROP of D3 remains a crucial challenge.

Herein, we report the binary organocatalytic ROP (BOROP) of D3 using organic bases as catalysts and (thio)ureas as cocatalysts. The synergetic use of TBD and (thio)urea for the ROP of D3 enables both the solubilization of multifunctional silanols in THF and the production of PDMS with narrow Ð until the monomer conversion reaches approximately 90%. Moreover, we also investigated the applicability of proton sponges to the ROP of D3. While a unitary organocatalytic system using proton sponges was inactive, ROP of D3 proceeded with the synergetic use of 1,8-bis(tetramethylguanidino)naphthalene (TMGN) and urea. In the cocatalytic system with TBD and urea, ROP is accelerated with less acidic urea. Despite the similar basicity of TBD and TMGN, ROP was accelerated with a more acidic urea. This mechanistically suggests that the BOROP system using TMGN is in activation–deactivation equilibrium between dormant and propagating species similar to those reported in living radical polymerization. The advantage of the present BOROP system was finally confirmed by the excellent mechanical properties of highly stretchy elastomeric PDMS formed from three-armed star-shaped PDMSs. The developed BOROP would be highly beneficial for the precision synthesis of polysiloxanes and enables facile access to those with branched macromolecular architectures with narrow Ð.

ROP of D3 with a unitary organocatalytic system

We first surveyed the catalytic activity of a series of organic bases. The pK_a values of the conjugate acids of these bases (pK_BH⁺) in MeCN indicate similar catalytic activities between 4-dimethylaminopyridine (DMAP) (pK_BH⁺ = 17.95)¹⁸ and 1,8-bis(dimethylamino)naphthalene (DMAN) (pK_BH⁺ = 18.18)¹⁹ and between TBD (pK_BH⁺ = 26.03)¹⁸ and 1,8-Bis(tetramethylguanidi-no)naphthalene (TMGN) (pK_BH⁺ = 25.10)¹⁹ (Fig. 1). The ROP of D3 in THF ([D3] = 2.4 M) initiated from trifunctional silanol (I₃) (Fig. 2a) with these organic bases readily revealed that less basic DMAP and DMAN, which is known as a proton sponges, are inactive under the polymerization conditions tested (Table 1, entries 1 and 2). Similar to the pioneering study reported by Waymouth, Hedrick, and coworkers¹⁵, the ROP of D3 with strongly basic TBD proceeded and the conversion reached 92% with a polymerization time of 120 min (Table 1, entry 3). Plots of monomer conversion against time determined using size exclusion chromatography (SEC) showed a monotonic increase in conversion, whereas Ð apparently broadened after 60 min (Fig. 2b). While a previous study on the ROP of TMOSC indicated that TBD could avoid the formation of scrambling products via transetherification reactions¹⁶, in the case of D3, the considerably smaller M_n than that calculated from conversion (M_n,theo) and the broadening of Ð at higher conversions suggest the formation of oligomers and scrambling products (Fig. 2c). Considering that the pK_BH⁺ values of TBD and TMGN are comparable (Fig. 1), in terms of basicity, the ROP of D3 using TMGN as an organocatalyst should proceed. However, no monomer consumption was observed (Table 1, entry 4). This suggests that the basicity of the organocatalyst is not the only factor affecting catalytic activity in the ROP of D3. Compared to TBD, TMGN is more sterically hindered, and thus the difference in the steric configuration of the basic reactive center may be responsible for the polymerizability.

Table 1

ROP of D3 initiated from I3 with a series of organic basesa
Entry	Cat.	Time (min)	Conv. (%)^b	M_n^c	Đ^d
1	DMAP	120	0	N.D.	N.D.
2	DMAN	120	0	N.D.	N.D.
3	TBD	120	92	15900 (27600)	1.90
4	TMGN	120	0	N.D.	N.D.
^aThe polymerizations were performed at 25°C. [I₃]₀ : [Cat.]₀ : [D3]₀ = 1 : 1.5 : 135. [I₃]₀ = 0.018 M, [D3]₀ = 2.14 M. ^bConversion determined by ¹H NMR. ^cNumber average molecular weight, determined by SEC with RI detector. The number in the parenthesis represents molecular weight calculated from conversion. ^dDispersity (Đ = M_w/M_n), determined by SEC. SEC measurements were performed after terminating with benzoic acid.

ROP of D3 with binary organocatalytic system

To examine the effect of cocatalysts on the ROP of D3 and to test the generality, we screened a series of ureas to be paired with TBD (Fig. 3a). We first monitored the interactions between I₃, TBD, and U(Cy) in THF based on a deuterated solvent-free ¹H NMR (80 MHz) spectrometry. While signals that should appear at 1–4 ppm in the ¹H NMR spectrum overlap with THF-derived signals, the signals appearing in the spectrum of I₃ (Supplementary Fig. 1a, marked a, b, and c) corresponded to those appearing in the separately measured ¹H NMR (500 MHz) spectrum (Supplementary ¹H NMR). and U(Cy) (Supplementary Fig. 1b, marked Ph_U) corresponded to their reported ones and that appeared in the spectrum of their mixture remained unchanged (Supplementary Fig. 1c). When TBD was added to the THF mixture of I₃, the resulting mixture became turbid due to the insolubility of silanol-derived ionic species in THF. The ¹H NMR spectrum of the soluble fraction showed the disappearance of the signal derived from silanol, and the signal derived from dimethyl protons at 0.23 ppm broadened and split into two signals (marked b), also indicating its poor solubility in THF. (Supplementary Fig. 1d). Furthermore, the signal derived from benzene ring significantly broadened and its intensity decreased. This decrease in the mobility of protons suggests that the components thought to be dissolved in THF might aggregate. In contrast, while the addition of U(Cy) to the mixture of I₃ and TBD significantly increased the intensity of the signal derived from the benzene ring of I₃ (marked a), that derived from silanol was still absent (Supplementary Fig. 1e). A more noticeable change is that the split and broadened signals derived from dimethyl groups have become one narrowed signal. In addition to the fact that the addition of U(Cy) apparently solubilized the mixture of I₃ and TBD, these results also suggest a rapid and reversible exchange reaction between the silanols and TBD/U(Cy).

Having confirmed the effective formation of hydrogen bonding between silanols of I₃ and TBD/U(Cy), we tested a total of 8 entries of the binary organocatalytic ROP (BOROP) of D3 with different conditions to obtain star-shaped PDMSs with narrow Ð, and the results of the screening are presented in Table 2. Since TBD should extract a proton from urea in the reaction system, the reactivity of BOROP should be of the same order as the reactivity of the urea anion. With that, we started from the use of U(Cy) as a cocatalyst, which has been reported to produce the most reactive urea anion, and readily recognized that the Ð of the product with monomer conversion similar to that of the unitary system (Table 1, entry 3) (M_n = 15900, Đ = 1.90) was remarkably narrowed (Table 2, entry 1) (M_n = 35500, Đ = 1.27). A decrease in the amount of TBD further narrowed Ð (M_n = 23400, Đ = 1.16), and a decrease in the amount of U(Cy) resulted in the broadening of Ð (M_n = 24700, Đ = 1.42). These results directly demonstrate the role of urea in narrowing Ð. Next, the effect of the number of CF₃ groups on BOROP was examined. As expected, the increase in CF₃ groups slowed the polymerization (Table 2, entries 4–6). However, what was more interesting was that Ð became noticeably narrower as CF₃ increased. Remarkably, the Ð of the PDMS in the polymerization mixture was less than 1.1 even when monomer conversion reached 99% (Table 2, entry 6). The use of a more acidic TU also afforded PDMS with a narrow Ð but required significantly longer reaction times (Table 2, entries 7 and 8). From these results, the synergetic use of TBD and U(4CF₃) optimizes the BOROP of D3.

Table 2

BOROP of D3 initiated from I3 catalyzed by TBD with a series of cocatalystsa
Entry	Cocatalyst	[I₃]₀ : [TBD]₀ : [HBA]₀ : [D3]₀	Time (min)	Conv. (%)^b	M_n^c	Đ^d
1	U(Cy)	1 : 1.5 : 3 : 135	90	91	12000	1.31
2	U(Cy)	1 : 0.75 : 3 : 135	90	88	23400	1.16
3	U(Cy)	1 : 0.75 : 1.5 : 135	90	93	24700	1.42
4^e	U(1CF₃)	1 : 0.75 : 3 : 135	135	75	28600	1.17
5^e	U(4CF₃)	1 : 0.75 : 3 : 135	60	57	28200	1.07
6^e	U(4CF₃)	1 : 1.5 :3 : 135	120	> 99	35700	1.09
7	TU	1 : 1.5 : 3 : 135	120	44	12600	1.09
8	TU	1 : 0.75 : 3 : 135	120	26	7300	1.06
^aThe polymerizations were performed at 30°C. [D3]₀ = 2.14 M. Calculated number average molecular weight at the full consumption of D3 was 30000. ^bConversion determined by ¹H NMR. ^cNumber average molecular weight, determined by SEC with RI detector. ^dDispersity (Đ = M_w/M_n), determined by SEC. SEC measurements were performed after terminating with benzoic acid. ^e[D3]₀ = 2.25 M.

BOROP of D3 in activation–deactivation equilibrium between dormant and propagating species

Having optimized the BOROP conditions, we next screened organocatalysts (Fig. 1) to be paired with U(4CF₃). While less basic DMAP and DMAN were again inactive even in the presence of U(4CF₃) (Table 3, entries 1 and 2), interestingly, the BOROP of D3 with the synergetic use of TMGN and U(4CF₃) produced PDMSs with narrow Ð (Table 3, entries 3 and 4). The plots of conversion against time showed exceptional linearity (Fig. 4a), and Ð remained narrow even with a polymerization time of 360 min. In the case of the TBD/urea catalytic system, BOROP of D3 should proceed with neutral and imidate-mediated H-bonding mechanisms as reported previously (Fig. 4c)²⁰. However, taking into account that the unitary catalytic system using TMGN was inactive, activation–deactivation equilibrium, similar to that observed for living radical polymerization such as atom transfer radical polymerization (ATRP)²¹, can be proposed for the present synergetic BOROP system using TMGN and U(4CF₃) (Fig. 4d). Thus, when protons derived from silanols are abstracted by TMGN, the formed complex cannot attack the monomer due to the steric hindrance of the methyl groups surrounding the TMGN, as recognized in the unitary ROP system (Table 1, entry 4). On the other hand, if the abstraction of protons derived from U(4CF₃) is in equilibrium, the growing species would be able to attack the monomer (Fig. 4d). Given that the pKa of I₃ can be approximately between Et₃SiOH (pKa = 13.63) and Ph₃SiOH (pKa = 16.57–16.63)^22,23, and the reported pKa of U(4CF₃) is 13.8²⁴, it is reasonable to assume this equilibrium. With this activation–deactivation equilibrium between dormant and propagating species, BOROP with less acidic U(Cy) (pKa = 22.8 (25.1))²⁵ should not proceed because no proton abstraction could occur. This hypothesis was readily supported by the inactivity of the TMGN/U(Cy) cocatalytic system (Table 3, entry 5). While the urea anion formed from less acidic urea is more active in the conventional ROP (Fig. 4c), following this activation–inactivation process (Fig. 4d) mechanistically reverses the relationship between the acidity of urea and polymerization rate, despite TBD (pK_BH⁺ = 26.03) and TMGN (pK_BH⁺ = 25.10) having similar basicity (Fig. 1). In the present case, the moderate acidity of U(4CF₃) would push the equilibrium to the left hand side (Fig. 4d), and thus result in slower polymerization compared to the TBD/U(4CF₃) cocatalytic system.

Table 3

ROP of D3 initiated from I3 catalyzed by various organic bases with U(4CF3) a
Entry	Cat.	[I₃]₀ : [Cat.]₀ : [HBA]₀ : [M]₀	Time (min)	Conv. (%)^b	M_n^c	Đ^d
1	DMAP	1 : 1.5 : 3 : 135	120	N.D.
2	DMAN	1 : 1.5 : 3 : 135	120	N.D.
3	TMGN	1 : 1.5 : 3 : 135	120	26	6700	1.06
4	TMGN	1 : 1.5 : 3 : 135	360	80	13000	1.10
5^e	TMGN	1 : 1.5 : 3 : 135	360	N.D.
^aThe polymerizations were performed at 30°C. [M]₀ = 2.4 M. Calculated number average molecular weight at the full consumption of D3 was 30000. ^bConversion determined by ¹H NMR. ^cNumber average molecular weight, determined by SEC with RI detector. ^dDispersity (Đ = M_w/M_n), determined by SEC. SEC measurements were performed after terminating with benzoic acid. ^eU(Cy) was used instead of U(4CF₃).

Fabrication of a highly transparent, elastic, and stretchy elastomer enabled by precisely-defined star-shaped PDMS.

The established BOROP would provide unexampled opportunities for various silicone-based materials. To pursue the feasibility of the study, we examined the potential application of our star-shaped PDMSs enabled by BOROP for silicone potting compounds (SPCs). SPCs are an important class of curable liquid polysiloxanes used, for example, in electronics, medical applications, and microfluidics. Silicone elastomers can be formed simply by mixing two liquid polysiloxanes. We synthesized 3-armed star-shaped PDMS with hydrosilane (P_H) and vinyl groups (P_V) based on BOROP of D3 initiated from I₃ using TBD/U(Cy). The synthesized P_H and P_V were subjected to hydrosilylation-based elastomer formation, which is one of the most frequently applied conditions for SPC (Fig. 5a). Time-dependent plots of G’ and G’’ measured immediately after mixing P_H (1.5 g) and the mixture of P_V (1.5 g) and Karstedt’s catalyst (10 µL) showed a dramatic increase in G’ after the induction period of approximately 100 s (Fig. 5b). At 230 s, G’ exceeded G’’ and the mixture became solid (G’ > G’’). After approximately 1000 s, the reaction reached equilibrium, and a highly transparent silicone elastomer (S_E) with a G’ of 220 kPa was formed (Fig. 5b). The elastic nature of S_E is obvious from static mechanical analysis. Thus, the tensile modulus (E), elongation at break (ε_B), tensile strength (σ_T), and fracture energy (Γ) were calculated as 0.41 MPa, 330%, 0.48 MPa, and 1.2× 10⁴ J m^− 2, respectively, from its stress–strain curve (Fig. 5c). It would be meaningful to compare the mechanical properties with existing SPCs. Notably, the measured Γ (1.2× 10⁴ J m^− 2) of our S_E is 10 to 100 times greater than those of widely used SPCs such as Sylgard 184-based elastomers and is comparable to or higher than those of conventional PDMS composites (Γ ~ 10³–10⁴ J m^− 2)²⁶, despite our S_E not containing any filler. Another intriguing property is the highly stretchy nature of our S_E. While several studies indicate that the ε_B of Sylgard 184 would be up to 200%^27,28, S_E showed ε_B of 330%, demonstrating its highly stretchy nature. Hence, the formation of a more uniform network for SPC has been proven to be advantageous for the formation of elastomers with highly stretchy and excellent mechanical properties.

In conclusion, we have established a facile, versatile, and scalable methodology for synthesizing polysiloxanes based on the BOROP of D3. Pairing urea and either TBD or highly basic proton sponge enables the precision synthesis of PDMS with controlled MW and narrow dispersity, even at high monomer conversion. The BOROP developed here is also expected to benefit the development of various silicone-based materials. Furthermore, to the best of our knowledge, proton sponges have never been used as organocatalysts for ROP, and the present binary catalyst system has the potential to be applied to various ring monomers.

Materials

D3 (98%, Aldrich), DMAP, DMAN, TBD (98%, Aldrich), and TMGN were first dissolved in superdehydrated stabilizer-free THF (99.5%, Wako) and then dried over MS4A for 24 h before use. Chlorodimethylsilane (98%, Aldrich), chlorodimethylvinylsilane (98%, Aldrich), platinum(0)-1,3-divinyltetramethyldisiloxane complex solution (Karstedt’s catalyst) (Pt ~ 2% in xylene, Aldrich) and other reagents were used as received. Benzene-1,3,5-triyltris(dimethylsilanol) (I₃)¹⁷ and (thio)ureas⁹ were synthesized according to the reported procedures.

Unitary catalytic ring opening polymerization

A mixture of I₃ (10 mg, 0.10 mmol for OH groups), D3 (1.0 g, 4.5 mmol), and THF (1.8 mL) was prepared in a vial. To this mixture, a THF solution (0.3 mL) of TBD (7 mg, 0.050 mmol) was added to initiate ROP and the resluting solution was stirred at room temperature (25°C). Aliquots were taken from the mixture at given times and subjected to ¹H NMR and SEC analyses to determine monomer conversion, M_n, and Ð.

Binary catalytic ring opening polymerization

A mixture of U(Cy) (22 mg, 0.10 mmol), I₃ (10 mg, 0.10 mmol for OH groups), D3 (1.0 g, 4.5 mmol), and THF (1.8 mL) was prepared in a vial. To this mixture, a THF solution (0.3 mL) of TBD (7 mg, 0.050 mmol) was added to initiate ROP and the resluting solution was stirred at room temperature (25°C). Aliquots were taken from the mixture at given times and subjected to ¹H NMR and SEC analyses to determine monomer conversion, M_n, and Ð. Likewise, other combinations of base (DMAP, DMAN, TBD, and TMGN) and (thio)urea were employed.

Synthesis of P _H and P _V

A mixture of U(Cy) (654 mg, 3.0 mmol), I₃ (300 mg, 3.0 mmol for OH groups), D3 (30.0 g, 135 mmol), and THF (54 mL) was prepared in a flask. To this mixture, a THF solution (9 mL) of TBD (209 mg, 1.5 mmol) was added to initiate ROP, and the resulting solution was stirred at room temperature (25°C). After 1 h, a THF solution (9 mL) of benzoic acid (3.7 g, 30 mmol) was added to terminate the polymerization, and the solution was stirred at room temperature (25°C). After 3 h, the mixture was concentrated to dryness and washed with acetone to afford three-armed star-shaped PDMS with hydroxy end groups. The yield was 25.0 g, which was used for the following end-capping reaction without further purification. Thus, the resulting PDMS (20.0 g) was dissolved in THF (40 mL), pyridine (11.6 mL, 144 mmol), and chlorodimethylsilane (5.23 mL, 48 mmol) were added in this order, and the resulting mixture was stirred at room temperature. After 17 h, the mixture was poured into excess H₂O/hexane, and the aqueous layer was separated and extracted with hexane. The combined hexane phase was washed with water, dried over Na₂SO₄, and concentrated to dryness. The residue was washed successively with MeOH and acetone and dried under reduced pressure to afford three-armed star-shaped PDMS with hydrosilane end groups (P_H) as a colorless oil. The yield was 16.7 g. ¹H NMR (500 MHz, acetone-d₆, δ): 0.07 (–SiO(CH₃)₂–), 4.71 (–Si(CH₃)₂H), 7.76 (s, ArH). Number-averaged molecular weight (M_n) and dispersity (Đ = M_w/M_n) measured by SEC calibrated with polystyrene standards; M_n = 24600, Ð = 1.20.

Likewise, three-armed star-shaped PDMS with vinyl end groups (P_V) was synthesized from three-armed star-shaped PDMS with hydroxy end groups (5.0 g) by using chlorodimethylvinylsilane as an end-capping reagent instead of chlorodimethylsilane. The yield was 4.0 g. ¹H NMR (500 MHz, acetone-d₆, δ): 0.07 (–SiO(CH₃)₂–), 5.72 (dd, –Si(CH₃)₂CH=CH₂), 5.92 (dd, –Si(CH₃)₂CH=CH₂), 6.13 (dd, –Si(CH₃)₂CH=CH₂), 7.76 (s, ArH). M_n and Đ measured by SEC calibrated with polystyrene standards; M_n = 24900, Ð = 1.18.

Elastomer formation

A weighed amount of P_V (1.5 g) and P_H (1.5 g) was first mixed in a vial. To this mixture, Karstedt’s catalyst (10 µL) was added to allow the formation of elastomers, and then the mixture was immediately poured into a polystyrene antistatic weighing dish. After 1 h, the solidified PDMS elastomer (S_E) with a thickness of 1 mm was peeled from the dish and cut with a dumbbell blade (No. 7) to form a dumbbell-shaped tensile test specimen (ISO 527-2:2012, Type 5B).

Data availability

All data supporting the findings of this study are available within the article (and Supplementary Information File(s)) or available from the corresponding author on reasonable request.

Acknowledgements

The authors are grateful to Dr. Minami Oka (The University of Tokyo) for her kind support for the synthesis of PDMSs. This work was supported by JSPS KAKENHI (Grant Numbers 21H01632 and 23K17337 S.H.), Fuji Seal Foundation (S.H.), and UTEC-UTokyo FSI Research Grant Program (S.H.).

Author contributions

S.H. conceived the concept of the project. H.O. and K.F. performed the polymer synthesis and characterization. H.O. and S.H. performed elastomer formation and mechanical tests. S.H. wrote the paper, and S.H. supervised the project. All authors discussed the manuscript.

Corresponding author

Correspondence to Satoshi Honda

Competing interests

The authors declare no competing interests.

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published 21 Mar, 2024

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Synergetic Binary Organocatalyzed Ring Opening Polymerization for the Precision Synthesis of Polysiloxanes

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Abstract

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Main

Results and discussion

ROP of D3 with a unitary organocatalytic system

ROP of D3 with binary organocatalytic system

BOROP of D3 in activation–deactivation equilibrium between dormant and propagating species

Conclusions

Methods

Materials

Unitary catalytic ring opening polymerization

Binary catalytic ring opening polymerization

Elastomer formation

Declarations

References

Additional Declarations

Supplementary Files

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