Self-Condensing Iodine Transfer Copolymerization for Highly

Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

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Self-Condensing Iodine Transfer Copolymerization for Highly Branched Polymers Using an in Situ Formed Chain Transfer Monomer Hongjun Yang,† He Chang,‡ Yiye Song,‡ Zhongrui Wang,† Wenyan Huang,*,† Qimin Jiang,† Xiaoqiang Xue,† Li Jiang,† and Bibiao Jiang*,†,‡

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Jiangsu Key Laboratory of Environmentally Friendly Polymeric Materials, School of Materials Science and Engineering, Jiangsu Collaborative Innovation Centre of Photovoltaic Science and Engineering, Changzhou University, Changzhou, Jiangsu P. R. China 213164 ‡ Changzhou University Huaidei College, Jingjiang, Jiangsu P. R. China 214500 S Supporting Information *

ABSTRACT: We reported a facile and effective method for the preparation of highly branched polymers by combining the concepts of self-condensing vinyl polymerization (SCVP) and iodine transfer polymerization (ITP). This procedure used a chain transfer monomer synthesized in situ from a commercially available chloride compound, p-chloromethylstyrene (CMS). The efficiencies of the halogen exchange from the alkyl chloride (−CH2Cl) to the alkyl iodide (−CH2I) at room and high temperature were studied using CMS and benzyl chloride as model halogenated compounds. The structures of the resulting polymer and the branching behavior were analyzed by nuclear magnetic resonance (NMR) spectroscopy and size-exclusion chromatography (SEC) equipped with a differential refractive index detector, a multiangle laser light scattering detector, and a viscometer detector. The model study using small molecules revealed that −CH2Cl could efficiently halogen exchange with sodium iodide (NaI) at both room and high temperature. The model linear polymerization in the presence of benzyl chloride and NaI confirmed the controlled nature of the polymerization. The results of the branched polymerization studies suggested that the degree of branching in the resulting polymers increased as the amount of NaI increased, and the majority of the branching occurred during the last stage of the polymerization. The current work should provide a simple procedure for the synthesis of highly branched polymers from commercially available compounds, and this method could be used for the preparation of various highly branched polymers.

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INTRODUCTION Self-condensing vinyl polymerization (SCVP), first reported by Fréchet and co-workers in 1995, is one of the most versatile and powerful synthetic tools for synthesizing well-defined highly branched polymers (HBPs).1,2 This strategy involves a polymerizable AB* monomer containing a double bond (A) and a pendant group (B*) that either initiate polymerization or be converted into a moiety capable of initiation once triggered. The former case is termed an “inimer”, and the latter is termed a “chain transfer monomer”. Because of the operational simplicity and synthetic versatility for forming highly branched structures with the desired functional groups, SCVPs have received significant attention and have been successfully extended to a variety of living polymerization techniques, such as ionic polymerization,3−5 group transfer polymerization (GTP),6 ring-opening polymerization (ROP),7,8 and several controlled radical polymerizations, including nitroxide-mediated radical polymerization (NMP),9−11 atom transfer radical polymerization (ATRP),12−14 and reversible addition−fragmentation chain transfer (RAFT) polymerization.15−20 Despite © XXXX American Chemical Society

receiving much attention, the major drawback of SCVPs is that the majority of reported monomers are not available from common commercial sources and must be synthesized before use. To date, there is only a few polymerizations were reported by using a commercially available or in situ formed AB* monomer.21−24 Iodine transfer polymerization (ITP), discovered by Tatemoto25,26 and substantially developed by Matyjaszewski27,28 and Goto29−34 and co-workers, is a famous family of living radical polymerizations. These reactions follow a controlled process based on an iodo derivative as a degenerative transfer compound (Scheme 1). This technique has many advantages. First, ITP is suitable for a wide range of vinyl monomers, such as acrylates, styrene, and vinyl acetate. Next, the polymerization system for ITP is quite simple because only a radical initiator, an iodinated transfer agent, and Received: November 1, 2018 Revised: January 17, 2019

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DOI: 10.1021/acs.macromol.8b02338 Macromolecules XXXX, XXX, XXX−XXX

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other hand, CMS is commercially available and does not need to be prepared in house. This strategy for highly branched polymer would be quite simple and be suitable for industrial production. The synthesized polymers were fully characterized, and their branching behavior was investigated in detail.

Scheme 1. General Scheme of Iodine Transfer Polymerization (ITP)

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RESULTS AND DISCUSSION

Alkyl iodides (−CH2I) are effective transfer agents for ITP. However, most of them lack long-term stability. One can imagine that an AB* monomer that contains both a reactive double bond and an iodinated transfer group in one molecule would be much less stable than a common vinyl monomer. Herein, we attempted to synthesize AB* monomers in situ for ITP using a halogen exchange reaction. CMS contains two groups in the molecule: the double bond and the chloromethyl group (−CH2Cl). The former could directly take part in the radical polymerization, and the latter might participate in the ITP after a halogen exchanging from −CH2Cl to −CH2I. If both functional groups of CMS reacted, a polymer with a branched structure would be synthesized (Scheme 2a). Moreover, because of the limited amount of NaI present, only a small portion of the −CH2Cl moieties of the CMS could be converted into −CH2I, which would result in most of the CMS reacting as a monomer instead of a chain transfer monomer, this is, unlike the of CMS, and would generally avoid cross-linking.44,45 Efficiency of the Halogen Exchange from Alkyl Chloride to Alkyl Iodide. As reported by Goto42 and Cheng43 et al., the halogen exchange reaction between alkyl bromides (−CH2Br) and NaI is highly effective. However, the

a monomer are necessary. Last, because no catalyst is used, the purification is very simple.35−40 Nevertheless, the iodinated transfer agents for ITP are light and temperature sensitive and are not stable upon long-term storage. For this reason, SCVP is seldom successfully applied to ITP for the preparation of HBPs.41 Recently, Goto42 and Cheng43 et al. found that alkyl iodide could be formed in situ using an alkyl bromide as a precursor. This method for preparing alkyl iodides is inexpensive, nontoxic, and operationally simple. Inspired by this, the current work attempted to develop a simple procedure for the synthesis of highly branched polymers by using commercially available p-chloromethylstyrene (CMS) as the pre-chaintransfer monomer for ITP. On one hand, the double bonds in CMS could participate in the polymerization, and its alkyl chloride group could undergo halogen exchange with sodium iodide (NaI) to produce a chain transfer group in situ. On the

Scheme 2. Proposed Mechanism for the ITP-SCVP by Using CMS as a Pre-Chain-Transfer Monomer

B


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M. The resulting polymers were characterized by size-exclusion chromatography (SEC) equipped with a differential refractive index detector (dRI), a multiangle laser light scattering (MALLS) detector, and a viscometer detector; the corresponding results are listed in Table S1. The SEC curves from the dRI detector (Figure 2a) show a symmetrical signal for each polymer. Moreover, the number-average molecular weights (Mn.dRI values detected by dRI detector, Figure 2b) are close to the theoretical values (Mn.th values) and increase with increasing [St]/[BzCl] molar ratio. These results indicate that this polymerization is controlled to some extent. Figure 3 shows the results of the kinetic analysis of the polymerization with a [St]/[BzCl]/[NaI]/[AIBN] molar ratio of 80/1.0/1.2/0.5. The semilogarithmic plots of the monomer conversion vs time (Figure 3a) are linear, indicating that the polymerization proceeded by a first-order kinetic pathway. However, a higher molecular weight product (4.49 × 103 g/ mol) was obtained at lower monomer conversion (21.7%), which is different from most controlled/“living” radical polymerizations, such as ATRP, but this is frequently observed with ITP.39,46 After a certain monomer conversion, the Mn.dRI increased linearly and finally reached 5.35 × 103 g/mol. During the polymerization, the molecular weight distribution (Đ) decreased from 1.71 to 1.62. Compared with other “living” radical polymerizations, such as ATRP or RAFT, the Đ values here are much broader, which might be due to the large concentration of AIBN that was employed. Hence, a polymerization with a low concentration of AIBN was conducted. The results in Table S1 show that by decreasing the equivalents of AIBN from 0.5 to 0.05, the distribution of the resulting polymer slightly narrowed. However, the monomer conversions significantly decreased. This result suggests that an excess amount of AIBN is necessary for the polymerization. Regardless, the model linear polymerizations indicate that NaI is clearly undergoing halogen exchange with BzCl, making the polymerization controlled to some extent. Confirmation of Branching Structures for the ITPSCVP of CMS. After confirming the high efficiency of the reaction from −CH2Cl to −CH2I, we performed the ITP of CMS at 80 °C with a [CMS]/[NaI]/[AIBN] molar ratio of 80/3.0/1.0. Similar to the linear polymerization, DGDE was employed as the solvent to ensure complete mixing of the reactants; the molar concentration of CMS was 10 M. For comparison, another polymerization was conducted under the same conditions but without NaI. As expected, a white precipitate was observed for the system with NaI as soon as the polymerization started. This white precipitate is due to the formation of NaCl and suggests the success of the halogen exchange from alkyl chloride to alkyl iodide. No precipitate was observed until the end of the polymerization in the control system. After 8 h, the polymerizations were stopped, and the conversions of double bonds were 91.3% and 94.8% for the systems with and without NaI, respectively. For convenience, the polymers prepared using the system with and without NaI were termed h-PCMS-1 and l-PCMS-1,

efficiency of the halogen exchange from alkyl chloride (−CH2Cl) to alkyl iodide has not been reported. Hence, the efficiency of the halogen exchange of CMS was studied first. The reaction was first conducted at room temperature to prevent the undesirable thermally initiated radical polymerization. Diethylene glycol dimethyl ether (DGDE) was employed as the solvent to ensure complete mixing of the reactants. The molar concentration of CMS ([CMS]) was 10 M. A slight excess of NaI ([CMS]/[NaI] = 1.0/1.2) was used to obtain a high halogen exchange efficiency. Figure 1 shows the 1H NMR spectra of CMS and mixtures of CMS, NaI, and DGDE after reacting for 10 and 120 min,

Figure 1. 1H NMR spectra of CMS and the mixture of CMS, NaI, and DGDE at room temperature at different reaction times ([CMS]/ [NaI] = 1.0/1.2, [CMS] = 10 M).

respectively. The signal (a) at 4.58−4.59 ppm is due to the proton of −CH2Cl in CMS, and the signal (a′) was attributed to the proton of −CH2I formed by the reaction between CMS and NaI. The 1H NMR spectra suggested that 80.7% of the −CH2Cl units had been converted into −CH2I within 10 min, and nearly all of the −CH2Cl had been consumed after 120 min. These results confirmed the high efficacy of the halogen exchange reaction from −CH2Cl to −CH2I and further suggested that the synthesis of HBPs by using CMS as a pre-chain-transfer monomer for ITP-SCVP is possible. Linear Polymerization Model. Because most vinyl polymerizations are performed at a high temperature, the efficiency of the transfer from −CH2Cl to −CH2I at 80 °C was also studied using benzyl chloride (BzCl) as a model substrate. As before, DGDE was employed as the solvent to make all reactant mix completely. The [BzCl]/[NaI] molar ratio was 1.0/1.2, and [St] is 10 M. The 1H NMR spectra (Figure S1) showed that in 10 min the −CH2Cl had been completely consumed, which further supports our proposed use of CMS as a pre-chain-transfer monomer for ITP-SCVP. Subsequently, a model linear polymerization using styrene (St) as a monomer and BzCl as a chain transfer agent was performed (Scheme 3). All of the linear polymerizations were conducted in DGDE at 80 °C for 8 h, the [BzCl]/[NaI]/[AIBN] molar ratio was fixed at/1.0/1.2/0.5, and the molar concentration of St was 10 Scheme 3. Polymerization of Styrene in the Presence of NaI

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Figure 2. (a) SEC-dRI curves and (b) molecular weights (Mn.dRI values) of the polymers obtained with different monomer/transfer agent ratios ([BzCl]/[NaI]/[AIBN] = 1.0/1.2/0.5, [St] = 10 M).

Figure 3. (a) Conversions (squares) and ln([M]0/[M]) (circles) of St as a function of the reaction time. (b) Variations in Mn.dRI (squares) and Đ (circles) with ConvSt ([St]/[BzCl]/[NaI]/[AIBN] = 80/1.0/1.2/0.5; [St] = 10 M).

respectively, and were analyzed by SEC. Interestingly, the Mn.dRI of l-PCMS-1 is 1.22 × 104 g/mol, which is slightly higher than that of h-PCMS-1 (1.13 × 104 g/mol). However, the average weight molecular weight of l-PCMS-1 (2.45 × 104 g/mol) is significantly lower than the corresponding value for h-PCMS-1 (7.74 × 104 g/mol). Figure 4 shows the evolution

Figure 5. Dependence of intrinsic viscosity ([η]) on molecular weight (Mw.MALLS) for l-PCMS-1 and h-PCMS-1 (l-PCMS-1: CMS/AIBN = 80/1.0, [CMS] = 10 M; h-PCMS-1: CMS/NaI/AIBN = 80/3.0/1.0, [CMS] = 10 M).

lower than those of l-PCMS-1 with the same molecular weight. Moreover, the Mark−Houwink parameter (α) for h-PCMS-1 was 0.38, which is substantially smaller than that of l-PCMS-1 (0.66) and is also smaller than the value (0.43) reported by Fréchet et al. for the polymer poly(3-(1-chloroethy1)ethenylbenzene), which possesses a similar structure as hPCMS-1.1 All of these suggest that h-PCMS-1 formed a densely packed three-dimensional structure as a result of its highly branched topology. In addition, the gap between the two curves increased with increasing Mw.MALLS, suggesting that the degree of branching in the fractionated samples also increased with increasing molecular weight, which is supported by Figure 4. To facilitate structural assignment using NMR analyses, another polymerization was performed with a high amount of NaI (h-PCMS-2, [CMS]/[NaI]/[AIBN] is 80/10/1.0) under similar conditions. The M n.dRI and Đ values of the

Figure 4. Evolution of the differential molecular weight distributions for h-PCMS-1 (CMS/NaI/AIBN = 80/3.0/1.0, [CMS] = 10 M) and l-PCMS-1 (CMS/AIBN = 80/1.0, [CMS] = 10 M).

of the differential molecular weight distributions. The curve for l-PCMS-1 shows only a narrow monomodal peak, which is a typical characteristic of conventional radical polymerizations. Differently, the SEC curve for h-PCMS-1 exhibits a broad multimodal distribution, which can be frequently observed for branched polymers. The component of h-PCMS-1 with a molecular weight lower than 104 g/mol might be attributed to the component with low degree of branching, and the high molecular weight of h-PCMS-1 can be attributed to the highly branched structures. Figure 5 shows the dependence of intrinsic viscosity ([η]) on the Mw.MALLS. The [η] values of h-PCMS-1 are significantly D


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Figure 6. (a) Proposed structure of the resulting polymer. (b) 1H NMR spectra for h-PCMS-2 (top) and l-PCMS-1 (bottom). (c) 13C DEPT NMR spectra of h-PCMS-2 (h-PCMS-2: [CMS]/[NaI]/[AIBN] = 80/10/1.0, [CMS] = 10 M).

Table 1. Polymerization of CMS in the Presence of NaIa sample

[CMS]:[NaI]:[AIBN]

convb (%)

Mn.dRI (103 g/mol)

Mw.MALLSc (103 g/mol)

Đ

αd

l-PCMS-1 h-PCMS-1 h-PCMS-2 h-PCMS-3 h-PCMS-4

80/0/1.0 80/3.0/1.0 80/10/1.0 80/15/1.0 80/3.0/0.5

94.8 91.3 84.5 80.1 60.2

12.2 11.3 3.81 3.07 4.79

24.5 77.4 10.2 8.93 9.40

2.01 3.85 1.75 1.66 1.80

0.66 0.38 0.30 0.31 0.45

a

DGDE was employed as the solvent for all polymerizations, [CMS] = 10 M. bConversion of the double bonds in CMS was detected by 1H NMR spectroscopy. cWeight-average molecular weights were detected by MALLS. dMark−Houwink parameter.

corresponding polymer are 3.81 × 103 g/mol and 1.75, respectively. The molecular weight distribution and Mark− Houwink plots of the product are given in Figures S3 and S4. h-PCMS-2 and l-PCMS-1 were carefully characterized by NMR spectroscopy, and the results are given in Figure 6. The signals at 5.60−5.81 and 5.12−5.33 ppm assigned to the terminal vinyl protons (a) can be clearly observed in the 1H NMR spectrum of h-PCMS-2 (Figure 6b, top) but cannot be found in the 1H NMR spectrum of l-PCMS-l because the polymerization with h-PCMS-2 proceeded via a ITP mechanism, where the polymerization was initiated by the −CH2I group generated in situ from CMS. However, the polymerization of l-PCMS-1, initiated by AIBN, followed a conventional free radical polymerization mechanism. These conclusion can be further confirmed by the 1H NMR signals at 4.21−4.52 ppm (f) in Figure 6b and the 13C DEPT NMR

signals at 6−8 ppm (f) in Figure 6c attributable to the proton and carbon of the methylene adjacent to the iodine, respectively. Moreover, if a branched structure was synthesized, a new signal (g) due to the reaction of −CH2I group should be observed. Unfortunately, this signal overlapped with the methylene and methenyl protons in the main chain, which made it difficult to calculate the degree of branching by using the 1H NMR spectrum. However, the corresponding carbon signal is easily identifiable in the 13C DEPT NMR spectrum at 33.1−33.3 ppm (Figure 6c). In addition, the signals of h, i, and k can be attributed to the terminal vinyl groups arising from the elimination of HI. The NMR results agree with the SEC analysis and prove it is possible to prepare HBPs using CMS by combining SCVP and ITP. After achieving the ITP of CMS to prepare HBPs, we further increased the concentration of NaI from 3.0 to 15. The E


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Figure 7. (a) Conversions (squares) and ln([M]0/[M]) (dots) of double bonds as functions of the reaction time. (b) Variations in Mw.MALLS (squares) and Đ (dots) with ConvCC ([CMS]/[NaI]/[AIBN] = 80/3.0/1.0, [CMS] = 10 M).

before a higher conversion was reached. The Zimm branching factor, g′, is usually used as a qualitative indicator of the degree of branching.47,48 This value can be estimated by the equation g′ = [η]branched/[η]linear, where [η]branched and [η]linear are the intrinsic viscosities of the branched and linear polymers, respectively. For a linear polymer, g′ = 1; for polymers with the same molecular weight, g′ decreases with increasing branching. Figure 8 shows the change in g′ with increasing ConvCC. The

obtained polymer (h-PCMS-3) showed a low molecular weight (Mn.dRI = 3.07 × 103 g/mol) and a narrow distribution (Đ = 1.66). Its Mark−Houwink parameter (α value) was 0.31, suggesting a high degree of branching. In addition, we also reduced the amount of AIBN to half its original amount (hPCMS-4). However, the conversion of the double bonds in CMS dramatically decreased to 60.2%, and its Mark−Houwink parameter increased to 0.45. Kinetics of Branching Behavior and Process. After confirming the branching structure of the resulting polymer, we tracked the kinetics and the evolution of the branching by 1 H NMR spectroscopy. As shown in Figure 7a, the double bonds of CMS were smoothly consumed, and the conversion of CMS finally reached 85.1% after 90 min of polymerization. The value of ln([M]0/[M]) was linearly dependent on time, indicating a constant radical concentration and that the polymerization followed first-order kinetics. Moreover, the first-order kinetics further verified that the polymerization proceeded following an ITP mechanism instead of a conventional radical polymerization mechanism. Additionally, the polymerization process was analyzed using SEC, and the results are given in Figure 7b. For conventional radical polymerizations, polymers with high molecular weights are synthesized at the very beginning of the polymerization. Extending the reaction time does not substantially increase the molecular weights of the resulting polymers. However, in the present system, the Mw.MALLS values gradually increased until the ConvCC was 68.5%, which is typical for “living” radical polymerizations. This result again proves that the alkyl chloride group in CMS could undergo halogen exchange with NaI to produce an initiating species for ITP in situ. Beyond this conversion, rapid increases in both M w.MALLS and its distribution (Đ) were observed because the majority of the branching structures from the coupling reactions between macromonomers were formed at this stage. Similar phenomena were also reported in the SCVP system for branching polymers. Finally, the Mw.MALLS of the resulting polymer reached 6.42 × 104 g/mol, and the corresponding Đ was 3.70. More evidence could be found at the SEC-dRI traces. As shown in Figure S5, the SEC-dRI curves display a monomodal peak with a narrow distribution at low monomer conversions. With increasing reaction time, the curve shifts to higher molecular weights, and a shoulder peak became apparent at 60 min when the ConvCC was 68.5%. Beyond this conversion, the distribution broadened, and the SEC-dRI curve becomes multimodal. The multimodal SEC-dRI curves suggest that large amounts of highly branched structures were present in the reaction mixture, and there was no obvious branching

Figure 8. Changes in the Zimm branching factor (g′) with increasing double-bond conversion (ConvCC) ([CMS]/[NaI]/[AIBN] = 80/ 3.0/1.0, [CMS] = 10 M).

value of g′ is always 99.8%, Shanghai Chemical Co.) were purified by passage through an alumina column and distillation from CaH2, and they were stored under a nitrogen atmosphere at −20 °C until use. AIBN (>99.8%, Shanghai Chemical Co.) was recrystallized twice from acetone. Tetrahydrofuran (THF, from Sinopharm) and diethylene glycol dimethyl ether (DGDE, from Sinopharm) were freshly distilled from sodium benzophenone and stored under an argon atmosphere until use. Benzyl chloride (BzCl, >99.8%, Shanghai Chemical Co.) was purified by distillation. NaI (>99.5%, Kanto) was used as received. Analytical Methods. The molecular weights and polydispersities were measured at 35 °C by SEC in THF using a Waters 1515 F


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instrument equipped with a Waters 2414 differential refractive index (dRI) detector, a Wyatt DAWN HELEOS-II multiangle laser-light scattering (MALLS) detector, and a Wyatt Visco Star viscometer detector (VD). HPLC-grade THF at a flow rate of 1.0 mL/min was used as the eluent. A series of narrowly dispersed polystyrene (PS) standards were used for calibrating the number-average molecular weight (Mn.dRI) and the molecular weight distribution (Đ). Polymer structures and conversions of the monomers were determined using a Bruker ARX-500 type NMR spectrometer at 25 °C with deuterated chloroform (CDCl3) as the solvent and tetramethylsilane (TMS) as the internal standard. Small Molecule Model Reaction. In a typical reaction, NaI (0.180 g, 1.20 mmol) was added to a round-bottom flask equipped with a magnetic stirring bar. DGDE (0.1 mL) was introduced as the solvent. The flask was fitted with a septum. After three freeze−thaw pump cycles, CMS (0.153 g, 1.00 mmol) was added to the flask, and the reaction mixture was allowed to stand at room temperature. A small portion of the reaction mixture was taken at 10 min and at 120 min and diluted with CDCl3 for analysis by NMR spectroscopy. The reaction between BzCl and NaI was performed following a similar procedure but at 80 °C. General Procedure for Synthesis of HBPs. In a typical reaction, CMS (1.000 g, 6.55 mmol), AIBN (0.013 g, 0.08 mmol), and NaI (0.037 g, 0.24 mmol) were added to a round-bottom flask equipped with a magnetic stirring bar. DGDE (0.66 mL) was introduced as the solvent. The flask was fitted with a septum, and after three freeze− thaw pump cycles, the reaction mixture was heated in an oil bath at 80 °C. The polymerization reaction was quenched after a certain reaction time by being cooled to room temperature. The mixture was immediately diluted with THF for analysis by SEC. Finally, the polymer was precipitated from the solution by the addition of a large excess of methanol. The precipitate was isolated by filtration, washed with n-hexane, dried under vacuum at room temperature for 6 h, and analyzed by NMR spectroscopy. The linear polymerization of styrene was conducted following a similar procedure but using benzyl chloride instead of CMS.

Hongjun Yang: 0000-0001-5631-4285 Bibiao Jiang: 0000-0002-6999-0503 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support for this work was provided by the National Natural Science Foundation of China (21474010 and 21304010) and the Natural Science Foundation for Excellent Young Scholar of Jiangsu Province (BK20170056), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) is acknowledged.

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CONCLUSION In summary, the alkyl chloride group of CMS could be quickly and efficiently transferred in situ to the alkyl iodide group in the presence of NaI, which could subsequently participate in the iodine transfer polymerization for the preparation of highly branched polymers. On the one hand, this method overcomes the drawbacks associated with the direct use of unstable vinyl alkyl iodides as chain transfer monomers. On the other hand, cross-linking was dramatically reduced due to the presence of a large amount of untransformed CMS as a comonomer. More importantly, this polymerization is quite simple and represents a significant improvement in operational simplicity. All of these features make this method a useful tool in the field of materials chemistry.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b02338.

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REFERENCES

(1) Frechet, J. M.; Henmi, M.; Gitsov, I.; Aoshima, S.; Leduc, M. R.; Grubbs, R. B. Self-condensing Vinyl Polymerization: an Approach to Dendritic Materials. Science 1995, 269 (5227), 1080−1083. (2) Hawker, C. J.; Fréchet, J. M. J.; Grubbs, R. B.; Dao, J. Preparation of Hyperbranched and Star Polymers by a “Living”, SelfCondensing Free Radical Polymerization. J. Am. Chem. Soc. 1995, 117 (43), 10763−10764. (3) Yang, H.; Bai, T.; Xue, X.; Huang, W.; Chen, J.; Qian, X.; Zhang, G.; Jiang, B. A Versatile Strategy for Synthesis of Hyperbranched Polymers with Commercially Available Methacrylate Inimer. RSC Adv. 2015, 5, 60401−60408. (4) Yang, H.; Bai, T.; Xue, X.; Huang, W.; Chen, J.; Qian, X.; Zhang, G.; Jiang, B. A Simple Route to Vinyl-functionalized Hyperbranched Polymers: Self-condensing Anionic Copolymerization of Allyl Methacrylate and Hydroxyethyl Methacrylate. Polymer 2015, 72, 63−68. (5) Baskaran, D. Hyperbranched Polymers from Divinylbenzene and 1,3-Diisopropenylbenzene through Anionic Self-condensing Vinyl Polymerization. Polymer 2003, 44 (8), 2213−2220. (6) Simon, P. F.; Radke, W.; Müller, A. H. Hyperbranched Methacrylates by Self-condensing Group Transfer Polymerization. Macromol. Rapid Commun. 1997, 18 (9), 865−873. (7) Trollsås, M.; Atthoff, B.; Claesson, H.; Hedrick, J. L. Hyperbranched Poly (ε-caprolactone) s. Macromolecules 1998, 31 (11), 3439−3445. (8) Trollsås, M.; Löwenhielm, P.; Lee, V.; Möller, M.; Miller, R.; Hedrick, J. New Approach to Hyperbranched Polyesters: Selfcondensing Cyclic Ester Polymerization of Bis(hydroxymethyl)substituted ε-Caprolactone. Macromolecules 1999, 32 (26), 9062− 9066. (9) Hawker, C. J.; Bosman, A. W.; Harth, E. New Polymer Synthesis by Nitroxide Mediated Living Radical Polymerizations. Chem. Rev. 2001, 101, 3661−3688. (10) Hawker, C. J.; Frechet, J. M.; Grubbs, R. B.; Dao, J. Preparation of Hyperbranched and Star Polymers by a “Living”, Self-condensing Free Radical Polymerization. J. Am. Chem. Soc. 1995, 117 (43), 10763−10764. (11) Tao, Y.; He, J.; Wang, Z.; Pan, J.; Jiang, H.; Chen, S.; Yang, Y. Synthesis of Branched Polystyrene and Poly(styrene-b-4-methoxystyrene) by Nitroxyl Stable Radical Controlled Polymerization. Macromolecules 2001, 34 (14), 4742−4748. (12) Qiang, R.; Fanghong, G.; Bibiao, J.; Dongliang, Z.; Jianbo, F.; Fudi, G. Preparation of Hyperbranched Copolymers of Maleimide Inimer and Styrene by ATRP. Polymer 2006, 47 (10), 3382−3389. (13) Gaynor, S. G.; Edelman, S.; Matyjaszewski, K. Synthesis of Branched and Hyperbranched Polystyrenes. Macromolecules 1996, 29 (3), 1079−1081. (14) Li, X.; Hong, C. Y.; Pan, C. Y. Preparation and Characterization of Hyperbranched Polymer Grafted Mesoporous Silica Nanoparticles via Self-condensing Atom Transfer Radical Vinyl Polymerization. Polymer 2010, 51 (1), 92−99.

Additional 1H NMR spectra, SEC curve, intrinsic viscosity trace, and the linear polymerization data (PDF)

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Macromolecules (15) Wang, Z.; He, J.; Tao, Y.; Yang, L.; Jiang, H.; Yang, Y. Controlled Chain Branching by RAFT-Based Radical Polymerization. Macromolecules 2003, 36, 7446−7452. (16) Alfurhood, J. A.; Bachler, P. R.; Sumerlin, B. S. Hyperbranched Polymers via RAFT Self-condensing Vinyl Polymerization. Polym. Chem. 2016, 7 (20), 3361−3369. (17) Wang, X.; Shi, Y.; Graff, R. W.; Cao, X.; Gao, H. Synthesis of Hyperbranched Polymers with High Molecular Weight in the Homopolymerization of Polymerizable Trithiocarbonate Transfer Agent without Thermal Initiator. Macromolecules 2016, 49 (17), 6471−6479. (18) Roy, S. G.; De, P. Facile RAFT Synthesis of Side-chain Amino Acids Containing pH-responsive Hyperbranched and Star Architectures. Polym. Chem. 2014, 5 (21), 6365−6378. (19) Zheng, Y.; Tang, A.; Weng, Z.; Cai, S.; Jin, Y.; Gao, Z.; Gao, C. Amphiphilic Hyperbranched Polymers: Synthesis and Host-Guest Supermolecular Coloring Application. Macromol. Chem. Phys. 2016, 217 (3), 380−389. (20) Sudo, Y.; Kawai, R.; Nabae, Y.; Hayakawa, T.; Kakimoto, M. Self-condensing Vinyl Polymerization of a Switchable Chain Transfer Monomer for Facile Synthesis of Star-shaped Block Copolymers. Appl. Surf. Sci. 2018, DOI: 10.1016/j.apsusc.2018.03.166. (21) Yang, H.; Wang, Z.; Cao, L.; Huang, W.; Jiang, Q.; Xue, X.; Song, Y.; Jiang, B. Self-condensing Reversible Complexation-mediated Copolymerization for Highly Branched Polymers with in Situ Formed Inimers. Polym. Chem. 2017, 8 (44), 6844−6852. (22) Liu, X.; Bao, Y.; Tang, X.; Li, Y. Synthesis of Hyperbranched Polymers via a Facile Self-condensing Vinyl Polymerization System− Glycidyl Methacrylate/Cp2TiCl2/Zn. Polymer 2010, 51 (13), 2857− 2863. (23) Han, H.; Tsarevsky, N. V. Carboxylic Acids as Latent Initiators of Radical Polymerization Carried out in the Presence of Hypervalent Iodine Compounds: Synthesis of Branched and Transiently Crosslinked Polymers. Polym. Chem. 2012, 3, 1910−1917. (24) Gaynor, S. G.; Edelman, S.; Matyjaszewski, K. Synthesis of Branched and Hyperbranched Polystyrenes. Macromolecules 1996, 29, 1079−1081. (25) Tatemoto, M. Iodine Transfer Polymerization of Fluoroalkenes. Int. Polym. Sci. 1985, 12, 85−97. (26) Tatemoto, M.; Tomoda, M.; Ueda, Y. US Pat. US81895, 1981. (27) Matyjaszewski, K.; Gaynor, S.; Wang, J. Controlled Radical Polymerizations: the Use of Alkyl Iodides in Degenerative Transfer. Macromolecules 1995, 28, 2093−2095. (28) Gaynor, S. G.; Wang, J. S.; Matyjaszewski, K. Controlled Radical Polymerization by Degenerative Transfer: Effect of the Structure of the Transfer Agent. Macromolecules 1995, 28, 8051− 8056. (29) Vana, P.; Goto, A. Kinetic Simulations of Reversible Chain Transfer Catalyzed Polymerization (RTCP): Guidelines to Optimum Molecular Weight Control. Macromol. Theory Simul. 2009, 19 (1), 24−35. (30) Goto, A.; Sanada, S.; Lei, L.; Hori, K. Theoretical and Experimental Studies on Elementary Reactions in Living Radical Polymerization via Organic Amine Catalysis. Macromolecules 2016, 49 (7), 2511−2517. (31) Goto, A.; Zushi, H.; Hirai, N.; Wakada, T.; Kwak, Y.; Fukuda, T. Germanium- and Tin-catalyzed Living Radical Polymerizations of Styrene and Methacrylates. Macromol. Symp. 2007, 248, 126−131. (32) Goto, A.; Tsujii, Y.; Fukuda, T. Reversible Chain Transfer Catalyzed Polymerization (RTCP): a New Class of Living Radical Polymerization. Polymer 2008, 49 (24), 5177−5185. (33) Goto, A.; Ohno, K.; Fukuda, T. Mechanism and Kinetics of Iodide-Mediated Polymerization of Styrene. Macromolecules 1998, 31, 2809−2814. (34) Goto, A.; Tsujii, Y.; Fukuda, T. Reversible Chain Transfer Catalyzed Polymerization (RTCP): A New Class of Living Radical Polymerization. Polymer 2008, 49, 5177−5185.

(35) Boyer, C.; Lacroix-Desmazes, P.; Robin, J.-J.; Boutevin, B. Reverse Iodine Transfer Polymerization (RITP) of Methyl Methacrylate. Macromolecules 2006, 39, 4044−4053. (36) David, G.; Boyer, C.; Tonnar, J.; Ameduri, B.; LacroixDesmazes, P.; Boutevin, B. Use of Iodocompounds in Radical Polymerization. Chem. Rev. 2006, 106, 3936−3962. (37) Yamago, S. Precision Polymer Synthesis by Degenerative Transfer Controlled/Living Radical Polymerization Using Organotellurium, Organostibine, and Organobismuthine Chain-Transfer Agents. Chem. Rev. 2009, 109, 5051−5068. (38) Boyer, C.; Valade, D.; Sauguet, L.; Ameduri, B.; Boutevin, B. Iodine Transfer Polymerization (ITP) of Vinylidene Fluoride (VDF). Influence of the Defect of VDF Chaining on the Control of ITP. Macromolecules 2005, 38, 10353−10362. (39) Wolpers, A.; Vana, P. UV Light as External Switch and Boost of Molar-Mass Control in Iodine-Mediated Polymerization. Macromolecules 2014, 47 (3), 954−963. (40) Wright, T.; Chirowodza, H.; Pasch, H. NMR Studies on the Mechanism of Reverse Iodine Transfer Polymerization of Styrene. Macromolecules 2012, 45 (7), 2995−3003. (41) Kowalczuk-Bleja, A.; Trzebicka, B.; Komber, H.; Voit, B.; Dworak, A. Controlled Radical Polymerization of p-(iodomethyl)styrenea Route to Branched and Star-like Structures. Polymer 2004, 45 (1), 9−18. (42) Xiao, L.; Sakakibara, K.; Tsujii, Y.; Goto, A. Organocatalyzed Living Radical Polymerization via in Situ Halogen Exchange of Alkyl Bromides to Alkyl Iodides. Macromolecules 2017, 50 (5), 1882−1891. (43) Liu, X.; Xu, Q.; Zhang, L.; Cheng, Z.; Zhu, X. Visible-lightinduced Living Radical Polymerization Using in Situ Bromine-iodine Transformation as an Internal Boost. Polym. Chem. 2017, 8 (16), 2538−2551. (44) Weimer, M. W.; Frechet, J. M. J.; Gitsov, I. Importance of Active-Site Reactivity and Reaction Conditions in the Preparation of Hyperbranched Polymers by Self-Condensing Vinyl Polymerization: Highly Branched vs. Linear Poly[4-(chloromethyl)styrene] by MetalCatalyzed “Living” Radical Polymerization. J. Polym. Sci., Part A: Polym. Chem. 1998, 36, 955−970. (45) Weimer, M. W.; Frechet, J. M. J.; Gitsov, I. Importance of Active-Site Reactivity and Reaction Conditions in the Preparation of Hyperbranched Polymers by Self-Condensing Vinyl Polymerization: Highly Branched vs. Linear Poly[4-(chloromethyl)styrene] by MetalCatalyzed “Living” Radical Polymerization. J. Polym. Sci., Part A: Polym. Chem. 1998, 36, 955−970. (46) Lacroix-Desmazes, P.; Severac, R.; Boutevin, B. Reverse Iodine Transfer Polymerization of Methyl Acrylate and n-Butyl Acrylate. Macromolecules 2005, 38, 6299−6309. (47) Yang, H.; Wang, Z.; Zheng, Y.; Huang, W.; Xue, X.; Jiang, B. Synthesis of Highly Branched Polymers by Reversible Complexationmediated Copolymerization of Vinyl and Divinyl Monomers. Polym. Chem. 2017, 8 (14), 2137−2144. (48) Wang, W.; Bai, L.; Chen, H.; Xu, H.; Niu, Y.; Tao, Q.; Cheng, Z. PMDETA as an Efficient Catalyst for Bulk Reversible Complexation Mediated Polymerization (RCMP) in the Absence of Additional Metal Salts and Deoxygenation. RSC Adv. 2016, 6 (99), 97455− 97462.

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Self-Condensing Iodine Transfer Copolymerization for Highly

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