Reversible addition–fragmentation chain transfer polymerization of glycidyl methacrylate with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate as a chain‐transfer agent

A reversible addition–fragmentation chain transfer (RAFT) agent, 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN), was synthesized and applied to the RAFT polymerization of glycidyl methacrylate (GMA). The polymerization was conducted both in bulk and in a solvent with 2,2′‐azobisisobutyronitrile (AIBN) as the initiator at various temperatures. The results for both types of polymerizations showed that GMA could be polymerized in a controlled way by RAFT polymerization with CPDN as a RAFT agent; the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with the monomer conversion up to 96.7% at 60 °C, up to 98.9% at 80 °C in bulk, and up to 64.3% at 60 °C in a benzene solution. The polymerization rate of GMA in bulk was obviously faster than that in a benzene solution. The molecular weights obtained from gel permeation chromatography were close to the theoretical values, and the polydispersities of the polymer were relatively low up to high conversions in all cases. It was confirmed by a chain‐extension reaction that the AIBN‐initiated polymerizations of GMA with CPDN as a RAFT agent were well controlled and were consistent with the RAFT mechanism. The epoxy group remained intact in the polymers after the RAFT polymerization of GMA, as indicated by the ¹H NMR spectrum. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2558–2565, 2004     

Thermally reversible polymer linkages. II. Linear addition polymers

The stepwise addition polymerization reactions of bisazlactones [bis(2-oxazolin-5-one)s] and a variety of 4,4′-bisphenols have been studied for the purpose of making thermally reversible linear polymers. Thus polymerization occurs at or near room temperature, while depolymerization yielding the two monomer species occurs at elevated temperatures. The synthesis of oligomers in solution without the use of catalyst occurs for the reaction of bisazlactones with bisphenols containing an electron-withdrawing moiety between the two phenol groups of the bisphenol. These oligomers regenerate the bisphenol and bisazlactone monomers upon heating to 165–200°C for several hours under dry box conditions. In many cases, these reactions follow the same patterns of reactivity observed in model studies. This chemistry may be useful for forming degradable or recyclable polymers, where shortchain prepolymers, or macromonomers, endcapped with azlactone and phenol moieties could be used to form high molecular weight polymers that are thermoreversible. Such a reaction system might also be used for preventing reactions of bisphenols and/or bisazlactones at low temperatures, with the desired reaction initiated by formation of the reactive species at elevated temperatures. Envisioned uses in this case might be thermally triggered crosslinking or polymerization reactions, or temperature controlled drug release. © 1993 John Wiley & Sons, Inc.     

Chemo-enzymatic synthesis of comb polymers

The paper describes the synthesis and characterization of comb polymers by a two-step chemo-enzymatic process. In the first step macromonomers bearing unsaturation at the chain end were prepared by lipase catalyzed ring-opening polymerization (ROP) of ε-caprolactone (CL) and 1,5-dioxepane-2-one (DXO). The ROP was carried out in bulk at 60 °C under anhydrous conditions using 2-hydroxyethyl methacrylate (HEMA) as the initiator. The DP of the macromonomers was controlled by regulating the monomer: HEMA molar feed concentration. The macromonomers were then homo- or co-polymerized in the second step with alkyl methacrylate monomers (methyl methacrylate or HEMA) using AIBN initiated free radical polymerization. Characterization of the polymers was done by ¹H NMR, SEC and DSC techniques.     

Polymerization of free secondary amine bearing monomers by RAFT polymerization and other controlled radical techniques

This work describes the polymerization of the free secondary amine bearing monomer 2,2,6,6‐tetramethylpiperidin‐4‐yl methacrylate (TMPMA) by means of different controlled radical polymerization techniques (ATRP, RAFT, NMP). In particular, reversible addition‐fragmentation chain transfer (RAFT) polymerization enabled a good control at high conversions and a polydispersity index below 1.3, thereby enabling the preparation of well‐defined polymers. Remarkably, the polymerization of the secondary amine bearing methacrylate monomer was not hindered by the presence of the free amine that commonly induces degradation of the RAFT reagent. Subsequent oxidation of the polymer yielded the polyradical poly(2,2,6,6‐tetramethylpiperidinyloxy‐4‐yl methacrylate), which represents a valuable material used in catalysis as well as for modern batteries. The obtained polymers having a molar mass (M_n) of 10,000–20,000 g/mol were used to fabricate well‐defined, radical‐bearing polymer films by inkjet‐ printing. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

RAFT Polymerization: Adding to the Picture

SUMMARY: Factors affecting the choice of RAFT agent [RSC(Z) = S] for a given polymerization are discussed. For polymerization of methyl methacrylate (MMA), tertiary cyanoalkyl trithiocarbonates provide very good control over molecular weight and distribution and polymerizations show little retardation. The secondary trithiocarbonate RAFT agents with R = CHPh(CN) also gives good control but an inhibition period attributed to slow reinitiation is manifest. Radical induced reduction with hypophosphite salts provides a clean and convenient process for removal of thiocarbonylthio end groups of RAFT-synthesized polymers. Two methods providing simultaneous control over stereochemistry and molecular weight distribution of chains formed by radical polymerization are reported. Polymerization of MMA in the presence of scandium triflate provides a more isotactic PMMA. A similar RAFT polymerization with trithiocarbonate RAFT agents also provides control and avoids issues of RAFT agent instability seen with dithiobenzoate RAFT agents in the presence of Lewis acids. RAFT polymerization of tetramethylammonium methacrylate at 45 °C provides a more syndiotactic PMMA of controlled molecular weight and distribution (after methylation; mm:mr:rr 2:21:77 compared to 3:35:62 when formed by bulk polymerization of MMA).     

Emulsion and controlled miniemulsion polymerization of the renewable monomer γ‐methyl‐α‐methylene‐γ‐butyrolactone

The kinetics of free‐radical emulsion polymerization of γ‐methyl‐α‐methylene‐γ‐butyrolactone (MeMBL), a renewable monomer related to methyl methacrylate, are presented in detail for the first time, and stable polymer latices are prepared. The effects of different reaction parameters on free‐radical emulsion polymerization of MeMBL are presented. Homogeneous nucleation is asserted to be the dominant path for particle formation. Miniemulsion copolymerization of MeMBL and styrene is also reported. In this case, the homogeneous nucleation process appears limited when using an oil soluble initiator. Both the RAFT miniemulsion polymerizations and RAFT bulk polymerizations are well controlled and narrow polydispersity copolymers are produced. Rate retardation is observed in the RAFT miniemulsion polymerizations compared with the free‐radical polymerization and RAFT bulk polymerizations and the possible causes of the retardation are discussed. The reactivity ratios of MeMBL and styrene in RAFT bulk copolymerization are also determined. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5929–5944, 2008     

Kinetics of styrene polymerization at ultrahigh conversion

The radical-initiated bulk polymerization of styrene at low conversion can be adequately described by a simple kinetic scheme that involves initiation by the decomposition of a radical initiator, propagation, and termination by combination of polystyryl radicals. An integrated equation can be derived that will describe the relationship between monomer concentration and time. We have investigated the validity of applying equations of this kind in the 98–99.999% conversion range. From our experimental work we conclude that the initial rates at 130°C, when starting the polymerization at that temperature at more than 98% conversion, can be described by an integrated equation over at least two decades of monomer concentration. Deviations from the simple kinetics at ultrahigh conversion were observed after a certain time at 130°C. These are discussed and explained in terms of the kinetic assumptions made and an extended model is suggested to allow for depolymerization reactions that cannot be neglected at ultrahigh conversion.     

Synthesis of ultra‐high molecular weight polymers by controlled production of initiating radicals

This study demonstrates that the gradual and slow production of initiating radicals (i.e., hydroxyl radicals here) is the key point for the synthesis of ultra‐high molecular weight (UHMW) polymers via controlled radical polymerization. Hydrogen peroxide (H₂O₂) and ferrous iron (Fe²⁺) react via Fenton redox chemistry to initiate RAFT polymerization. This work presents two enzymatic‐mediated (i.e., Bio‐Fenton‐RAFT and Semi Bio‐Fenton‐RAFT) and one syringe pump‐driven Fenton‐RAFT polymerization processes in which the initiating radicals are carefully and gradually dosed into the reaction solution. The “livingness” of the synthesized UHMW polymers is demonstrated by chain extension and aminolysis experiments. Zimm plots obtained from static light scattering (SLS) technique are used to characterize the UHMW polymers. This Fenton‐RAFT polymerization provides access to polymers of unprecedented UHMW (M_w ~ 20 × 10⁶ g mol^?1) with potential in diverse applications. The UHMW polymers made via the controlled Fenton‐RAFT polymerization by using a syringe pump shows that it is possible to produce such materials through an easy‐to‐set up and scalable process. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1922–1930     

Polymerization of α-methyleneindane: A cyclic analog of α-methylstyrene

α-Methyleniedane (MI), a cyclic analog of α-methylstyrene which does not undergo radical homopolymerization under standard conditions, was synthesized and subjected to radical, cationic, and anionic polymerizations. MI undergoes radical polymerization with α,α′-azobis(isobutyronitrile) in contrast to α-methylstyrene, owing to its reduced steric hindrance, though the polymerization is slow even in bulk. Cationic and anionic polymerization of MI with BF₃OEt₂ and n-butyllithium, respectively, proceed rapidly. The thermal degradation behavior of the polymer depends on the polymerization conditions. The anionic and radical polymers are heteortactic-rich. Reactivity ratios in bulk radical copolymerization on MI (M₂) with methacrylate (MMA, M₁) were determined at 60°C (r₁ = 0.129 and r₂ = 1.07). In order to clarify the copolymerization mechanism, radical copolymerization of MI with MMA was investigated in bulk at temperatures ranging from 50 to 80°C. The Mayo–Lewis equation has been found to be inadequate to describe the result due to depolymerization of MI sequences above 70°C.     

Molecular design of outermost surface functionalized thermoresponsive polymeric micelles with biodegradable cores

We prepared well‐defined diblock copolymers of thermoresponsive poly(N‐isopropylacrylamide‐co‐N,N‐dimethylacrylamide) blocks and biodegradable poly(D ,L ‐lactide) blocks by combination of reversible addition‐fragmentation chain transfer radical (RAFT) polymerization and ring‐opening polymerization. α‐Hydroxyl, ω‐dithiobenzoate thermoresponsive polymers were synthesized by RAFT polymerization using hydroxyl RAFT agents. Biodegradable blocks were prepared by ring‐opening polymerization of D ,L ‐lactide initiated by α‐hydroxyl groups of thermoresponsive polymers, which inhibit the thermal decomposition of ω‐dithioester groups. Terminal dithiobenzoate (DTBz) groups of thermoresponsive blocks were easily reduced to thiol groups and reacted with maleimide (Mal). In aqueous media, diblock copolymer products formed surface‐functionalized thermoresponsive micelles. These polymeric micelles had a low critical micelle concentration of 22 μg/L. In thermoresponsive studies of the micelles, hydrophobic DTBz‐surface micelles demonstrated a significant shift in lower critical solution temperature (LCST) to a lower temperature of 30.7 °C than that for Mal‐surface micelles (40.0 °C). In addition, micellar LCST was controlled by changing bulk mixture ratios of respective heterogeneous end‐functional diblock copolymers. Micellar disruption at acidic condition (pH 5.0) was completed within 5 days due to hydrolytic degradation of PLA cores, regardless of showing a slow disruption rate at physiological condition. Furthermore, we successfully improved water‐solubility of hydrophobic drug, paclitaxel by incorporating into the micellar cores. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7127–7137, 2008     

Reversible Addition‐Fragmentation Chain‐Transfer Polymerization for the Synthesis of Poly(4‐acetoxystyrene) and Poly(4‐acetoxystyrene)‐block‐polystyrene by Bulk,Solution and Emulsion Techniques

The living radical polymerization of 4‐acetoxystyrene via the RAFT process has been achieved employing bulk, solution and emulsion techniques. The rate of polymerization was studied between 60°C and 90°C. Increasing the temperature increases the rate of polymerization without affecting the polydispersity. Poly(4‐acetoxystyrene) with narrow polydispersity (1.08) was obtained. Various novel dithiocarboxylic esters and dithiocarbamates were screened as chain‐transfer agents for the RAFT polymerization of 4‐acetoxystyrene. The block copolymerization of poly(4‐acetoxystyrene) with styrene leading to poly(4‐acetoxystyrene)‐block‐polystyrene confirmed the presence of active chain ends in the first block. The acetoxy polymers were hydrolyzed to the corresponding hydroxy polymers under mild basic conditions.     

Orthogonal Cationic and Radical RAFT Polymerizations to Prepare Bottlebrush Polymers

An orthogonal combination of cationic and radical RAFT polymerizations is used to synthesize bottlebrush polymers using two distinct RAFT agents. Selective consumption of the first RAFT agent is used to control the cationic RAFT polymerization of a vinyl ether monomer bearing a secondary dormant RAFT agent, which subsequently allows side‐chain polymers to be grafted from the pendant RAFT agent by a radical‐mediated RAFT polymerization of a different monomer, thus completing the synthesis of bottlebrush polymers. The high efficiency and selectivity of the cationic and radical RAFT polymerizations allow both polymerizations to be conducted in one‐pot tandem without intermediate purification.     

Are o‐nitrobenzyl (meth)acrylate monomers polymerizable by controlled‐radical polymerization?

We report on the controlled‐radical polymerization of the photocleavable o‐nitrobenzyl methacrylate (NBMA) and o‐nitrobenzyl acrylate (NBA) monomers. Atom transfer radical polymerization (ATRP), reversible addition‐fragmentation chain transfer polymerization (RAFT), and nitroxide‐mediated polymerization (NMP) have been evaluated. For all methods used, the acrylate‐type monomer does not polymerize, or polymerizes very slowly in a noncontrolled manner. The methacrylate‐type monomer can be polymerized by RAFT with some degree of control (PDI ∼ 1.5) but leading to molar masses up to 11,000 g/mol only. ATRP proved to be the best method since a controlled‐polymerization was achieved when conversions are limited to 30%. In this case, polymers with molar masses up to 17,000 g/mol and polydispersity index as low as 1.13 have been obtained. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6504–6513, 2009     

SET‐RAFT of MMA mediated by ascorbic acid‐activated copper oxide

In this work, cupric oxide (CuO) or cuprous oxide (Cu₂O) was used as the catalyst for the single electron transfer‐reversible addition‐fragmentation chain transfer (SET‐RAFT) polymerization of methyl methacrylate in the presence of ascorbic acid at 25 °C. 2‐Cyanoprop‐2‐yl‐1‐dithionaphthalate (CPDN) was used as the RAFT agent. The polymerization occurred smoothly after an induction period arising from the slow activation of CuO (or Cu₂O) and the “initialization” process in RAFT polymerization. The polymerizations conveyed features of “living”/controlled radical polymerizations: linear evolution of number‐average molecular weight with monomer conversion, narrow molecular weight distribution, and high retention of chain end fidelity. From the polymerization profile, it was deduced that the polymerization proceeded via a conjunct mechanism of single electron transfer‐living radical polymerization (SET‐LRP) and RAFT polymerization, wherein CPDN acting as the initiator for SET‐LRP and chain transfer agent for RAFT polymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Living free‐radical polymerization of sterically hindered monomers: Improving the understanding of 1,1‐disubstituted monomer systems

The sterically hindered, 1,1‐disubstituted monomers di‐n‐butyl itaconate (DBI), dicyclohexyl itaconate (DCHI), and dimethyl itaconate (DMI) were polymerized with reversible addition–fragmentation chain transfer (RAFT) free‐radical polymerization and atom transfer radical polymerization (ATRP). Cumyl dithiobenzoate, cumyl phenyl dithioacetate, 2‐cyanoprop‐2‐yl dithiobenzoate, 4‐cyanopentanoic acid dithiobenzoate, and S‐methoxycarbonylphenylmethyl dithiobenzoate were employed as RAFT agents to mediate a series of polymerizations at 60 °C yielding polymers ranging in their number‐average molecular weight from 4500 to 60,000 g mol^?1. The RAFT polymerizations of these hindered monomers displayed hybrid living behavior (between conventional and living free‐radical polymerization) of various degrees depending on the molecular structure of the initial RAFT agent. In addition, DCHI was polymerized via ATRP with a CuCl/methyl benzoate/N,N,N′,N″,N″‐pentamethyldiethylenetriamine/cyclohexanone system at 60 °C. Both the ATRP and RAFT polymerization of the hindered monomers displayed living characteristics; however, broader than expected molecular weight distributions were observed for the RAFT systems (polydispersity index = 1.15–3.35). To assess the cause of this broadness, chain‐transfer‐to‐monomer constants for DMI, DBI, and DCHI were determined (1.4 × 10^?3, 1.3 × 10^?3, and 1.0 × 10^?3, respectively) at 60 °C. Simulations carried out with the PREDICI program package suggested that chain transfer to monomer contributed to the broadening process. In addition, the experimental results indicated that viscosity had a pronounced effect on the broadness of the molecular weight distributions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3692–3710, 2006     

Controlled Bimodal Molecular‐Weight‐Distribution Polymers: Facile Synthesis by RAFT Polymerization

The RAFT agents RAFT‐1 and RAFT‐2 were used for RAFT polymerization to synthesize well‐defined bimodal molecular‐weight‐distribution (MWD) polymers. The system showed excellent controllability and “living” characteristics toward both the higher‐ and lower‐molecular‐weight fractions. It is important that bimodal higher‐molecular‐weight (HMW) polymers and block copolymers with both well‐controlled molecular weight (MW) and MWD could be prepared easily due to the “living” features of RAFT polymerization. The strategy realized a mixture of higher/lower‐molecular‐weight polymers at the molecular level but also preserved the features of living radical polymerization (LRP) of the RAFT polymerization.     

One‐pot synthesis of well‐defined multiblock polymer: Combination of ATRP and RAFT polymerization involving cyclic trithiocarbonate

Multiblock polymers were prepared by combination of ATRP (CuBr/tris[(2‐pyridyl)methyl]amine) and RAFT polymerization involving cyclic trithiocarbonate (CTTC). In the combined polymerization system, the ATRP was introduced as constant radical source, CTTC underwent ring‐opening polymerization, and the incorporated trithiocarbonate moieties derived from CTTCs performed as RAFT agent. Through the integrated process, multiblock polymers containing predictable average block number together with controlled molecular weight of the blocks were prepared by one‐pot polymerization. The average block number of polymer was controlled by concentration ratio of CTTC to alkyl halide in ARTP, and the molecular weight of block were well regulated by concentration of CTTC and monomer conversion. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2425–2429, 2010     

可逆加成-断裂链转移活性自由基聚合的应用研究进展

可逆加成-断裂链转移(Reversible addition-fragmentation chain transfer,RAFT)自由基聚合是活性自由基聚合领域的一次突破.由于该方法具有适用单体范围广、反应条件温和以及聚合实施方法多样等优点,已成为一种有效的分子设计和材料设计手段.它不但可实现聚合物链端及链段侧基的功能化和制备特定空间拓扑结构的大分子,比如嵌段、星型、梳状及链端氨基聚合物等,还可用于修饰固体材料表面及生物大分子来赋予其特殊的功能.本文综述了RAFT技术在实际应用中的实施研究进展.     

Controlled polymerization of carbazole‐based vinyl and methacrylate monomers at ambient temperature: A comparative study through ATRP,SET, and SET‐RAFT polymerizations

The polymerization of N‐vinylcarbazole (NVK) and carbazole methacrylate (CMA) was carried out using controlled radical polymerization methods such as atom transfer radical polymerization (ATRP), single electron transfer (SET)‐LRP, and single electron transfer initiation followed by reversible addition fragmentation chain transfer (SET‐RAFT). Well‐controlled polymerization with narrow molecular weight distribution (M_w/M_n) < 1.25 was achieved in the case of NVK by high‐temperature ATRP while ambient temperature SET‐RAFT polymerization was relatively slow and controlled. In the case of CMA, SET‐RAFT is found to be more suitable for the ambient temperature polymerization. The polymerization rate followed first order kinetics with respect to monomer conversion and the molecular weight of the polymer increased linearly with conversion. The controlled nature of the polymerization is further demonstrated by the synthesis of diblock copolymers from PNVK and PCMA macroinitiators using a new flavanone‐based methacrylate (FMA) as the second monomer. All the polymers exhibited fluorescence. The excimer bands in the homopolymers of PNVK and PCMA were very broad, which may be attributed to the carbazole–carbazole overlap interaction. The scanning electron microscopy analysis of the block copolymer reveals interesting morphological features. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Living free‐radical polymerization (reversible addition–fragmentation chain transfer) of 6‐[4‐(4′‐methoxyphenyl)phenoxy]hexyl methacrylate: A route to architectural control of side‐chain liquid‐crystalline polymers

Side‐chain liquid‐crystalline polymers of 6‐[4‐(4′‐methoxyphenyl)phenoxy]hexyl methacrylate with controlled molecular weights and narrow polydispersities were prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization with 2‐(2‐cyanopropyl) dithiobenzoate as the RAFT agent. Differential scanning calorimetry studies showed that the polymers produced via the RAFT process had a narrower thermal stability range of the liquid‐crystalline mesophase than the polymers formed via conventional free‐radical polymerization. In addition, a chain length dependence of this stability range was found. The generated RAFT polymers displayed optical textures similar to those of polymers produced via conventional free‐radical polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2949–2963, 2003