Organocatalyzed Photoredox Radical Ring-Opening Polymerization of Functionalized Vinylcyclopropanes

Abstract

Organocatalyzed photoredox radical ring-opening polymerization (rROP) of vinylcyclopropanes (VCPs) is employed for the synthesis of polymers with controlled molecular weight (MW), dispersity, and composition. Herein, we report the study on the rROP of a variety of VCP monomers bearing diverse functional groups (such as amide, alkene, ketal, urea, hemiaminal ether, and so on) under organocatalyzed conditions with varying light sources and temperature. Notably, VCP monomers bearing natural product functionality or their derivatives can be polymerized in a controlled manner to produce poly(VCPs) with predictable MW, low dispersity, tunable composition, high thermal stability, and tailored glass transition temperature (T_g), ranging 39 to 107 °C. Lastly, successful “grafting through” synthesis of molecular brush copolymers containing 1.0 or 5.0 kDa polydimethylsiloxane (PDMS) side chains from readily accessible EtVCP-PDMS macromonomers further demonstrates the robustness of this organocatalyzed photoredox rROP.

Graphical Abstract

INTRODUCTION

Radical ring-opening polymerization (rROP) of strained 1,1-disubstituted vinylcyclopropanes (VCPs) is an interesting and useful polymerization methodology that often exhibits low volume shrinkage, or even volume expansion, which has application potential in modeling and restorative materials.^1,2 In early studies, two radical polymerization pathways were proposed after the initial ring-opening event to deliver poly(VCPs) containing distinct unsaturated linear (l) and saturated cyclic (c) repeat units.³ However, control over the molecular weight and dispersity of the resulting polymer remained a challenge. To tailor the molecular weight (MW) and l/c selectivity within the polymer, Cu(I)-catalyzed atom transfer radical polymerization (ATRP) was successfully applied to the polymerization of 1,1-diethoxycarboxyl-2-vinylcyclopropane (EtVCP), producing poly(EtVCP) with 98.7% linear repeat units and low dispersity (Đ) of 1.12.⁴ However, the monomer conversion was low (<50%), presumably due to the Cu(I) catalyst poisoning by coordination of EtVCP or poly(EtVCP).^5,6

Recently, our group demonstrated a photocontrolled rROP of VCP monomers using an organic photocatalyst (PC), N,N′-di-2-naphthyldihydrophenazine,⁷ which allowed high monomer conversion to produce poly(VCPs) with predictable MW and low Đ (Scheme 1A),⁸ while the photoredox controlled polymerization mechanism^9–11 enabled temporal control over the polymerization.^12–26 Moreover, the high Br chain-end group fidelity allowed an unexpected polymer-chain modification of an isolated poly(EtVCP) that converted l repeat units into c repeat units, which inspired de novo regulation on the polymer structure as well as further investigations into the mechanism of c repeat unit formation and structure–property relationships of the thermal/viscoelastic characteristics of the obtained polymers. However, our previous report focused on VCP monomers bearing simple alkyl esters, and the compatibility of functional groups on the cyclopropane ring with this organocatalyzed photoredox polymerization conditions remains unknown. Given the importance of functional polymers,²⁷ we became interested in exploring the polymerization of diversely functionalized VCP monomers to prepare well-defined poly(VCPs) with tailored composition and properties (Scheme 1B).

Scheme 1.

Organocatalyzed Photoredox Radical Ring-Opening Polymerization of VCPs

RESULTS AND DISCUSSION

To gain preliminary insights into the functional group tolerance under our organocatalyzed photoredox polymerization conditions, 20 small molecule additives were selected and introduced in the rROP of EtVCP. Specifically, MeOH and 2,2,2-trifluoroethanol led to slightly lower monomer conversions, while excellent control over polymerizations was retained. Brønsted acids, such as benzoic acid and benzamide, significantly slowed the polymerizations probably due to decreased stability of PC 1 under acidic conditions. Lewis bases, including triethylamine and triphenylphosphine, may interfere with the deactivation step by quenching [PC^•+Br⁻], and their presence resulted in the loss of control over polymerization. The addition of electrophilic propagating carbon radicals to electron-rich heteroarenes (e.g., indole and furan) could be considered as a potential termination pathway. Other additives, such as electron-deficient benzene derivatives, aldehyde, ketone, alkyne, epoxide, alkyl bromide, carbodiimide, and even phenol, were well-tolerated to achieve high monomer conversions, producing poly(EtVCP) with predictable MWs, low dispersities, and high S_L values (also see Scheme S1 for details).

Encouraged by discovering a variety of additive functional groups were tolerated in the rROP of EtVCP, we began our exploration of functionalized VCP monomers with varying the substituents at the C1 position. The three monomers CNVCP, EtVCP-CN, and EtVCP-NHPh were prepared and polymerized under previously optimized conditions ([monomer]: [DBMM]:[PC 1] = [1000]:[10]:[1] with irradiation by white LED at ~28 °C) (Table 1).⁸ Unfortunately, no monomer conversion was observed in the polymerization of CNVCP (Table 1, entries 1 and 2), while the polymerization of EtVCP-CN achieved 90% monomer conversion within 12 h, achieving an initiator efficiency (I* = M_n,theo/M_n,measured × 100%) of 86%, to produce highly linear poly(EtVCP-CN) (S_L = 99%) with a number-average molecular weight (M_n) of 17.6 kDa and low Đ of 1.22 (Table 1, entry 3). Modulation of the monomer feed ratio allowed for synthesis of poly(EtVCP-CN) with predictable MWs (from 11.2 to 25.4 kDa) and low dispersities (Đ < 1.19) (Table 1, entries 4 and 5). Polymerization of EtVCP-NHPh was faster than EtVCP-CN and reached 96% monomer conversion within 6 h, exhibiting excellent control over polymer composition (S_L = 99%), molecular weight (M_n = 25.9 kDa, I* = 97%), and dispersity (Đ = 1.19) (Table 1, entries 6 and 7). It has been demonstrated that increased stability of the C1–C2 bond of vinylcyclopropanes would result in lower monomer conversion in free radical polymerization. Calculated two-center energy suggested that the C1–C2 bond of CNVCP is more stable than that of EtVCP by 0.17 eV (i.e., 3.9 kcal/mol).³ Given the radical polymerization mechanism under these organocatalyzed photoredox conditions, the ring-opening polymerizability approximately increases in the order EtVCP-NHPh ≈ EtVCP > EtVCP-CN ≫ CNVCP. Interestingly, compared to EtVCP, the presence of the cyano and amide groups led to preferential formation of linear polymer composition (S_L = 86% and 60%, respectively) under conditions of 34 W blue LED and 60 °C (entries 6 and 8).

Table 1.

Results of Polymerization of Monomers with Variable C1 Substituents^a

entry	monomer	[M]/[I]/[PC]	time (h)	convb (%)	Mnc (kDa)	Ð (Mw/Mn)c	I*d (%)	SLb (%)
1	CNVCP	1000/10/1	12	0
2	CNVCP	1000/10/1	12	0
3	EtVCP-CN	1000/10/1	12	90	17.6	1.22	86	99
4	EtVCP-CN	500/10/1	12	84	11.2	1.18	64	92
5	EtVCP-CN	2000/10/1	12	70	25.4	1.19	92	95
6e	EtVCP-CN	1000/10/1	12	99	28.0	1.13	60	87
7	EtVCP-NHPh	1000/10/1	6	96	25.9	1.19	97	99
8e	EtVCP-NHPh	1000/10/1	6	99	30.9	1.11	85	60

^aPolymerizations performed using 1.0 mmol of monomer, DBMM as the initiator, 1.0 mL of anhydrous EtOAc, and irradiated by 1.6 W white LEDs at 28 °C.

^bMeasured by crude ¹H NMR. S_L = l/(l + c).

^cMeasured by gel-permeation chromatography (GPC).

^dInitiator efficiency (I*) = M_n,theo/M_n,measured × 100%, where M_n,theo = MW(initiator) + MW(monomer) × conversion × ([monomer]/[initiator]).

^ePolymerizations performed in 5.0 mL of EtOAc and irradiated by 34 W blue LED at 60 °C.

RROP of Natural Product-Derived Vinylcyclopropanes.

Because of the efficient and controlled polymerization of EtVCP, this parent monomer was selected for incorporation of further functional groups. A two-step synthetic route was developed which consisted of (1) selective hydrolysis of EtVCP to provide major cis EtVCP-CO₂H (cis:trans = 10:1) and (2) high yielding coupling reactions of EtVCP-CO₂H with a few natural products or their derivatives (e.g., vitamin E, uridine, dehydroabietic acid, and cholesterol)^28,29 to afford a series of the targeted monomers with diverse functionalities, such as phenyl ether, hemiaminal ether, ketal, urea, and alkene (Scheme 2).

Scheme 2.

Divergent Synthesis of Natural Product Derived VCP Monomers

The investigation into the polymerization of natural product-derived vinycyclopropane monomers was initially performed in EtOAc, with a [500]:[10]:[1] ratio of EtVCP-VE:DBMM:PC 1 and white LED at 28 °C (Table 2, entry 1), which achieved 96% monomer conversion and produced poly(EtVCP-VE) 31.6 kDa, and with good control over the chain growth as indicated by a low Đ of 1.29, a high I* of 91%, and a high S_L of 96%. This success suggested high compatibility of the vitamin E moiety with the organocatalyzed photoredox polymerization protocol, which encouraged further optimization and study of other natural product-derived vinylcyclopropane monomers. The effect of PC (Table 2, entries 1–3), initiator, and solvent (Tables S5 and S6) on the polymerization of EtVCP-VE revealed that 1 was superior to other PCs while the use of chlorobenzene (PhCl) as the solvent resulted in the lowest Đ of 1.23 (Table 2, entry 4). Lower loadings of PC 1 were still able to drive the polymerization and achieved high monomer conversions, however, at the cost of less control over the chain growth as the Đ value increased from 1.23 to 1.65 (Table 2, entries 5 and 6). Importantly, varying the loading of EtVCP-VE or DBMM allowed tuning of the MW of poly(EtVCP-VE) (Table 2, entries 8–10).

Table 2.

Results of Polymerization of Natural Product-Based VCP Monomers at 28 °C Irradiated with a White LED^a

entry	monomer	PC	[M]/[I]/[PC]	time (h)	convb (%)	Mnc (kDa)	Ð (Mw/Mn)c	I*d (%)	SLb (%)
1	EtVCP-VE	1	500/10/1	6	96	31.6	1.29	91	96
2	EtVCP-VE	2	500/10/1	6	98	30.8	1.54	96	96
3	EtVCP-VE	3	500/10/1	6	91	27.2	1.62	101	95
4e	EtVCP-VE	1	500/10/1	6	94	27.6	1.23	103	96
5e	EtVCP-VE	1	500/10/0.5	6	99	31.6	1.35	94	96
6e	EtVCP-VE	1	500/10/0.1	6	95	28.8	1.61	99	96
7e	EtVCP-VE	1	500/10/2	6	91	30.4	1.45	81	95
8e	EtVCP-VE	1	250/10/1	6	73	13.9	1.15	81	92
9e	EtVCP-VE	1	500/20/1	6	84	15.7	1.15	82	92
10e	EtVCP-VE	1	1000/10/1	6	90	42.2	1.59	128	95
11	EtVCP-U	1	500/10/1	6	90	29.4	1.77	84	95
12e	EtVCP-U	1	500/10/1	6	99	33.7	1.67	81	93
13f	EtVCP-U	3	500/10/1	6	99	33.9	1.35	81	95
14	EtVCP-DA	1	500/10/1	6	90	21.6	1.51	94	81
15	EtVCP-DA	2	500/10/1	6	82	12.3	1.57	153	76
16	EtVCP-DA	3	500/10/1	12	61	14.9	1.48	95	75
17e	EtVCP-C1	1	500/10/1	12	96	28.5	1.21	94	94
18e	EtVCP-C2	1	500/10/1	12	90	30.9	1.32	97	78

^aPolymerizations performed using 0.5 mmol of monomer, DBMM as the initiator, 0.5 mL of anhydrous EtOAc, and irradiated by 1.6 W white LED at 28 °C.

^bMeasured by crude ¹H NMR. S_L = l/(l + c).

^cMeasured by GPC.

^dInitiator efficiency (I*) = M_n,theo/M_n,measured × 100%, where M_n,theo = MW(initiator) + MW(monomer) × conversion × ([monomer]/[initiator]).

^ePhCl was used as the solvent.

^f1,2-Dichloroethane (DCE) was used as the solvent.

The polymerization of EtVCP-VE was monitored over time, and first-order kinetics was observed for the monomer consumption (Figure 1A). Analysis of poly(EtVCP-VE) produced at different time points indicated a linear increase of polymer MW with respect to monomer conversion, while low to moderate dispersity (Đ = 1.21–1.34) was achieved during the entire course of polymerization (Figure 1B). Temporal control was also investigated by using a pulsed-irradiation experiment, and the polymerization proceeded only under light irradiation, paused upon removal of light source (as long as 12 h), and could be resumed with continued irradiation (Figure 1C). The temporal control supported a light-driven reversible activation–deactivation polymerization mechanism as well as the presence of the Br chain-end groups, which allowed the synthesis of advanced polymer architecture. As such, chain extension could be used from the synthesized poly(EtVCP-VE) as a macroinitiator for the rROP of cholesterol-derived monomer EtVCP-C2 under photoredox conditions. ¹H NMR characterization (Figure S31) and the observation of shorter retention time of the GPC trace of the chain-extended poly(EtVCP-VE)—although a low molecular weight shoulder was present, which is likely due to the loss of some Br chain-end groups in poly(EtVCP-VE) macroinitiator synthesis or radical termination during chain extension—indicated success in synthesizing a block copolymer poly-(EtVCP-VE)-b-poly(EtVCP-C2) (Figure 1D).

Figure 1.

Organocatalyzed photoredox rROP of EtVCP-VE: (A) plots of the natural log of monomer conversion as a function of time; (B) plots of experimentally measured M_n and dispersity as a function of monomer conversion; (C) plots of experimentally measured M_n and dispersity as a function of time for a pulsed irradiation experiment; (D) chain-extension polymerization from a poly(EtVCP-VE) macroinitiator with EtVCP-C2 and GPC traces before and after the polymerization.

We next explored the polymerization behavior of the other natural product-derived vinylcyclopropane monomers. Under previously optimized conditions ([monomer]:[DBMM]:[1] = 500:10:1 in EtOAc at 28 °C, with white LED),⁸ the polymerization of the uridine-derived monomer EtVCP-U was uncontrolled as indicated by a high Đ of 1.77 (Table 2, entry 11). The use of PhCl as the solvent led to higher monomer conversion (99%) and slightly lower Đ of 1.67 (entry 12). The polymerization of EtVCP-U with 3,7-di(4-biphenyl)-N-naphthylphenoxazine (3)³⁰ as the PC in DCE achieved 99% conversion within 6 h and afforded the best control over the chain growth to product poly(EtVCP-U) of 33.9 kDa, with a lower Đ of 1.35, I* of 81%, and S_L of 95% (entry 13). Screening of PCs for the polymerization of dehydroabietic acid-derived monomer EtVCP-DA (in EtOAc at 28 °C, with white LED) suggested that 1 was superior to 2 and 3 in terms of monomer conversion and the S_L value (entries 14–16). Lastly, polymerizations of cholesterol-derived monomer EtVCP-C1 with PC 1 in PhCl reached 96% monomer conversion to produce poly(EtVCP-C1) of 28.5 kDa, with Đ of 1.21, I* of 94%, and S_L of 94% (entry 17). Polymerization of EtVCP-C2 was a little bit slower than that of EtVCP-C1, reaching 90% monomer conversion within 12 h (entry 18). The presence of an alkyl linker in EtVCP-C2 results in less steric hindrance on the cyclopropane motif, which may lower the ring strain and slow down the ring-opening process for propagation. The overall control over the polymerization of EtVCP-C2 was good (low Đ of 1.32 and high I* of 97%), except that significant amount of cyclic polymer composition was formed (S_L = 77%).

The impact of the monomer functionality on the l/c selectivity under varying conditions was also explored. In general, regardless of the nature of the functional group, poly(VCPs) synthesized at 60 °C and with high power blue LED exhibited a higher degree of cyclic composition than those prepared at 28 °C and with white LED (Table 2 vs Table 3). In the polymerization of EtVCP-VE, the S_L decreased from 96% to 60% while the overall control over the chain growth remained excellent (Đ = 1.06, I* = 77%; Table 3, entry 1). Lower polymerization concentration led to a decreased S_L value (entry 2) while polymerization with increased monomer feed ([EtVCP-VE]:[DBMM]:[1] = 1000:10:1) achieved 72% conversion to give poly(EtVCP-VE) of 29.2 kDa, with Đ = 1.20, I* = 147%, and S_L = 42% (entry 3). When 1.0 mL of solvent was used, polymerizations of EtVCP-U with PC 3 in DCE, EtVCP-DA with PC 1 in EtOAc, and EtVCP-C2 with PC 1 in PhCl all reached high monomer conversion (85–99%) to afford polymers with low to moderate Đ (1.05–1.57), moderate to high I* (72–92%), and moderate S_L (41–60%) (entries 4, 6, and 10). Polymerizations of EtVCP-U, EtVCP-DA, and EtVCP-C2 in 2.5 mL of indicated solvents generally achieved lower monomer conversion (65–90%), while the polymers synthesized exhibited low Đ, with an exception that the Đ of poly(EtVCP-DA) was 1.96, high I*, and further decreased S_L (entries, 5, 7, and 11). It is noteworthy that due to the bulky steric hindrance of the cholesterol motif, polymerization of EtVCP-C1 under conditions of 34 W blue LED and 60 °C still produced major linear polymer composition (S_L = 85–90%; entries 8 and 9).

Table 3.

Results of Polymerization of Natural Product-Based VCP Monomers at 60 °C with Blue LED^a

entry	monomer	PC	solvent	time (h)	convb (%)	Mnc (kDa)	Ð (Mw/Mn)c	I*d (%)	SLb (%)
1	EtVCP-VE	1	EtOAc	6	82	32.0	1.06	77	60
2e	EtVCP-VE	1	EtOAc	6	70	29.6	1.03	72	55
3e,f	EtVCP-VE	1	EtOAc	6	72	29.2	1.20	147	42
4	EtVCP-U	3	DCE	6	99	29.7	1.16	92	41
5e	EtVCP-U	3	DCE	6	90	24.5	1.16	100	35
6	EtVCP-DA	1	EtOAc	6	90	28.6	1.57	72	52
7e	EtVCP-DA	1	EtOAc	6	72	19.8	1.96	82	50
8	EtVCP-C1	1	PhCl	12	87	27.7	1.08	88	90
9e	EtVCP-C1	1	PhCl	12	83	24.9	1.05	93	85
10	EtVCP-C2	1	PhCl	12	85	35.0	1.05	82	60
11e	EtVCP-C2	1	PhCl	12	65	20.4	1.08	107	45

^aPolymerizations performed using 0.5 mmol of monomer, DBMM as the initiator, 1.0 mL of anhydrous solvent, and irradiated by 34 W blue LED at 60 °C.

^bMeasured by crude ¹H NMR. S_L = l/(l + c).

^cMeasured by GPC.

^dInitiator efficiency (I*) = M_n,theo/M_n,measured × 100%, where M_n,theo = MW(DBMM) + MW(monomer) × conversion × ([monomer]/[DBMM]).

^e2.5 mL of solvent was used.

^f[monomer]:[DBMM]:[PC 1] = 1000:10:1.

Thermal Property of Natural Product-Derived Poly(VCPs).

Thermal properties of the synthesized natural product-derived polymers [poly(NPVCPs)] containing either a high degree of linear composition [l-poly(NPVCPs)] or cyclic composition [c-poly(NPVCPs)] were examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Generally, regardless of the polymer composition, poly(EtVCP-VE), poly(EtVCP-U), and poly(EtVCP-DA) exhibited a much higher decomposition temperature (T_d, defined by the temperature at 10% weight loss) than poly(EtVCP-C2) (Figures 2A and 2B), while increased cyclic composition led to higher thermal stability and higher T_d of 339–385 °C (Figure 2A vs 2B). Compared to poly(EtVCP) (glass transition temperature, T_g = 32 °C), higher T_gs were observed for both l-poly(NPVCPs) and c-poly(NPVCPs), indicating that the presence of all four natural products in the side chain reduced the free volume (Figures 2C and 2D). It is worth noting that T_g values of poly(NPVCPs) were drastically influenced by the nature of the natural product installed in the side chains. For example, l-poly(EtVCP-U) and l-poly(EtVCP-DA) exhibited high T_gs (94 and 86 °C), while T_gs of l-poly(EtVCP-VE) and l-poly(EtVCP-C2) decreased to 39 and 44 °C, respectively (Figure 2C). Moreover, the composition of the polymer main chain might also substantially change the T_g values. For instance, T_g of c-poly(EtVCP-U) was 13 °C higher than that of l-poly(EtVCP-U).

Figure 2.

TGA curves of l-poly(NPVCPs) (A) and c-poly(NPVCPs) (B). DSC curves of l-poly(NPVCPs) (C) and c-poly(NPVCPs) (D). l-poly(NPVCPs) were l-poly(EtVCP-VE) (M_n = 27.6 kDa, Đ = 1.23, S_L = 96%), l-poly(EtVCP-U) (M_n = 33.9 kDa, Đ = 1.35, S_L = 95%), l-poly(EtVCP-DA) (M_n = 21.6 kDa, Đ = 1.51, S_L = 81%), and l-poly(EtVCP-C2) (M_n = 30.9 kDa, Đ = 1.32, S_L = 78%). c-poly(NPVCPs) were c-poly(EtVCP-VE) (M_n = 29.2 kDa, Đ = 1.20, S_L = 42%), c-poly(EtVCP-U) (M_n = 29.7 kDa, Đ = 1.16, S_L = 41%), c-poly(EtVCP-DA) (M_n = 28.6 kDa, Đ = 1.57, S_L = 52%), and c-poly(EtVCP-C2) (M_n = 20.4 kDa, Đ = 1.08, S_L = 45%).

Synthesis of Molecular Brush Polymers through RROP.

Given the steric interactions of the side chains tethered to a linear backbone, densely grafted brush polymers often bond with compact conformation/dimension and unique material properties, thus holding a vast potential for applications in catalysis, medical diagnosis, drug delivery, and so on.^31–33 It is noteworthy that the “grafting through” method, i.e., the direct polymerization from macromonomers (MMs), has been one of the simplest ways to synthesize densely grafted brush polymer with well-defined side chains.^34–38 Although tremendous advances have been made, the diversity of the polymer backbone where side chains are covalently bonded to remains limited, which piqued our curiosity about synthesizing a novel type of brush polymers through organocatalyzed photoredox rROP of VCP-derived MMs. Commercially available monocarbinol-terminated polydimethylsiloxanes (PDMS) of 1.0 and 5.0 kDa were chosen for dicyclohexylcarbodiimide-mediated coupling reaction with EtVCP-CO₂H, affording two EtVCP-PDMS macromonomers (i.e., MM-1 of 1.4 kDa and MM-2 of 5.0 kDa; see the Supporting Information). Polymerization with a [500]: [10]:[1] ratio of MM-1:DBMM:PC 1 under optimized conditions and irradiated with a white LED at 28 °C successfully achieved 95% conversion within 12 h, producing molecular brush poly(EtVCP-PDMS) with a M_n 67.4 kDa, a low Đ of 1.09, a high I* of 99%, and a moderate S_L value of 77% (Table 4, entry 1). Increasing the macromonomer feed ratio to [1000]:[10]:[1] of MM-1:DBMM:PC 1 provided brush poly(EtVCP-PDMS) of 111 kDa, while good control over the polymerization was retained (Đ = 1.26, I* = 116%, entry 2). However, when targeting a higher degree of polymerization (200 or 400) in rROP of MM-1, the macromonomer conversions decreased (71–90%) while Đ values increased (1.41–1.47), and it became challenging to predictably tune the MW of the synthesized poly(EtVCP-PDMS) as the experimental MWs appreciably deviated from the theoretical values as indicated by I* > 100% (entries 3–5). The side chain length also influenced the polymerization behavior in that the rROP of MM-2 under optimized conditions with white LED irradiation at 28 °C generally achieved lower conversions and exhibited less control in terms of Đ, I*, and S_L than the rROP of MM-1 (entries 6–7 vs 1–2). Interestingly, rROP of MM-1 and MM-2 with blue LED at 60 °C resulted in polymers possessing lower dispersities (Đ = 1.06–1.10) and major cyclic compositions (S_L = 30–33%), affording brush poly(EtVCP-PDMS) with M_n of up to 308.7 kDa (entries 8–10).

Table 4.

Synthesis of Molecular Brush Poly(EtVCP-PDMS)^a

entry	macromonomer	[M]/[I]/[PC]	time (h)	convb (%)	Mnc (kDa)	Ð (Mw/Mn)c	I*d (%)	SLb (%)
1	MM-1	500/10/1	12	95	67.4	1.09	99	77
2	MM-1	1000/10/1	12	95	111.0	1.26	116	66
3	MM-1	1000/5/1	12	90	102.7	1.47	245	63
4	MM-1	2000/10/1	12	78	141.7	1.41	149	60
5	MM-1	4000/10/1	12	71	208.8	1.41	184	60
6e	MM-2	500/10/1	12	84	84.5	1.14	160	74
7e	MM-2	1000/10/1	12	62	98.2	1.25	316	56
8f,g	MM-1	500/10/1	12	84	121.2	1.08	49	33
9f,g	MM-1	1000/10/1	12	82	165.0	1.10	70	31
10f,h	MM-2	500/10/1	12	75	308.7	1.06	61	30

^aPolymerizations performed using 0.2 mmol of EtVCP-PDMS macromonomer, DBMM as the initiator, 0.5 mL of anhydrous EtOAc, and irradiated by white LED at 28 °C.

^bMeasured by crude ¹H NMR. S_L = l/(l + c).

^cMeasured by GPC.

^dInitiator efficiency (I*) = M_n,theo/M_n,measured × 100%, where M_n,theo = MW(DBMM) + MW(MM) × conversion × ([MM]/[DBMM]).

^e1.0 mL of EtOAc was used.

^fPolymerization was performed at 60 °C and with 34 W blue LED.

^g2.5 mL of anhydrous EtOAc was used.

^h5.0 mL of anhydrous EtOAc was used.

CONCLUSIONS

We have performed a study of the monomer scope for organocatalyzed photoredox radical ring-opening polymerization. The polymerizability of VCP monomers containing varying substituents at the C1 position was first evaluated, identifying that C1-ethoxycarbonyl resulted in the most efficient polymerization, which guided the subsequent incorporation of multiple functional natural products or their derivatives (such as vitamin E, uridine, dehydroabietic acid, and cholesterol) onto one ester group of EtVCP to expand the functional diversity of the monomers. The polymerization behavior of four natural product-derived VCP monomers was investigated by using N,N-diaryldihydrophenzaines or 3,7-di(4-biphenyl)-N-naphthylphenoxazine as the photocatalyst. By varying the light sources (white LED or blue LED) and temperature (28 or 60 °C), natural product-derived poly(VCPs) with predictable MW, low dispersity, tunable linear or cyclic composition, and tailored thermal properties were synthesized. Importantly, this organocatalyzed photoredox protocol was also amenable to “grafting through” brush polymer synthesis through the polymerization of EtVCP-PDMS macromonomers with moderate to excellent control. These findings, demonstrated herein, improve the robustness of radical ring-opening polymerization of vinylcyclopropanes and offer new opportunities for future design and preparation of structurally novel polymeric materials.