Synthesis of degradable poly(methyl methacrylate) star polymers via RAFT copolymerization with cyclic ketene acetals

Copolymerization of the cyclic ketene acetal 5,6‐benzo‐2‐methylene‐1,3‐dioxepane (BMDO) with methyl methacrylate (MMA) is studied with respect to its copolymerization parameters and the suitability to control BMDO/MMA copolymerizations via the reversible addition‐fragmentation chain transfer (RAFT) technique to obtain linear and 4‐arm star polymers. BMDO shows disparate copolymerization behavior with MMA and r₁ = 0.33 ± 0.06 and r₂ = 6.0 ± 0.8 have been determined for polymerization at 110 °C in anisole from fitting copolymer composition vs. comonomer feed data to the Lewis–Mayo equation. Copolymerization of the two monomers is successful in RAFT polymerization employing a trithiocarbonate control agent. As desired, polymers contain only little amount of polyester units stemming from BMDO units and preliminary degradation experiment show that the polymer degrades slowly, but steadily in aqueous 1 M NaOH dispersion. Within ten days, the polymers are broken down to low molecular weight segments from an initial molecular weight of M_n = 6000 g mol^?1. Star (co)polymerization with an erythritol‐based tetra‐functional RAFT agent following the Z‐group approach proceeds efficiently and polymers with a number‐average molecular weight of 10,000 g mol^?1 are readily obtained that degrade in similar manner as the linear copolymer counterparts. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1633–1641     

A versatile method for cyclic polymers from conjugated and unconjugated vinyl monomers

A versatile method was introduced to prepare cyclic polymers from both conjugated and unconjugated vinyl monomers. It was developed on the combination of the RAFT polymerization and the self‐accelerating double strain‐promoted azide‐alkyne click (DSPAAC) reaction. In this approach, a switchable chain transfer agent 1 was designed to have hydroxyl terminals and a functional pyridinyl group. The protonation and deprotonation of pyridinyl group endowed the chain transfer agent 1 with a switchable control capability to RAFT polymerization of both conjugated and unconjugated vinyl monomers. Based on this, RAFT polymerization and the following hydroxyl end group modification were used to prepare various azide‐terminated linear polymers including polystyrene, poly(N‐vinylcarbazole), and polystyrene‐block‐poly(N‐vinylcarbazole). Using sym‐dibenzo‐1,5‐cyclooctadiene‐3,7‐diyne (DBA) as small linkers, the corresponding cyclic polymers were then prepared via the DSPAAC reaction between DBA and azide terminals of the linear precursors. Due to the self‐accelerating property of DSPAAC reaction, this bimolecular ring‐closing reaction could efficiently produce the pure cyclic polymers using excess molar amounts of DBA to linear polymer precursors. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1811–1820     

Dendrimers as scaffolds for multifunctional reversible addition–fragmentation chain transfer agents: Syntheses and polymerization

The synthesis and characterization of novel first‐ and second‐generation true dendritic reversible addition–fragmentation chain transfer (RAFT) agents carrying 6 or 12 pendant 3‐benzylsulfanylthiocarbonylsulfanylpropionic acid RAFT end groups with Z‐group architecture based on 1,1,1‐hydroxyphenyl ethane and trimethylolpropane cores are described in detail. The multifunctional dendritic RAFT agents have been used to prepare star polymers of poly(butyl acrylate) (PBA) and polystyrene (PS) of narrow polydispersities (1.4 < polydispersity index < 1.1 for PBA and 1.5 < polydispersity index < 1.3 for PS) via bulk free‐radical polymerization at 60 °C. The novel dendrimer‐based multifunctional RAFT agents effect an efficient living polymerization process, as evidenced by the linear evolution of the number‐average molecular weight (M_n) with the monomer–polymer conversion, yielding star polymers with molecular weights of up to M_n = 160,000 g mol^?1 for PBA (based on a linear PBA calibration) and up to M_n = 70,000 g mol^?1 for PS (based on a linear PS calibration). A structural change in the chemical nature of the dendritic core (i.e., 1,1,1‐hydroxyphenyl ethane vs trimethylolpropane) has no influence on the observed molecular weight distributions. The star‐shaped structure of the generated polymers has been confirmed through the cleavage of the pendant arms off the core of the star‐shaped polymeric materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5877–5890, 2004     

A strategy for synthesis of ion‐bonded amphiphilic miktoarm star copolymers via supramolecular macro‐RAFT agent

Amphiphilic supramolecular miktoarm star copolymers linked by ionic bonds with controlled molecular weight and low polydispersity have been successfully synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization using an ion‐bonded macromolecular RAFT agent (macro‐RAFT agent). Firstly, a new tetrafunctional initiator, dimethyl 4,6‐bis(bromomethyl)‐isophthalate, was synthesized and used as an initiator for atom transfer radical polymerization (ATRP) of styrene to form polystyrene (PSt) containing two ester groups at the middle of polymer chain. Then, the ester groups were converted into tertiary amino groups and the ion‐bonded supramolecular macro‐RAFT agent was obtained through the interaction between the tertiary amino group and 2‐dodecylsulfanylthiocarbonylsulfanyl‐2‐methyl propionic acid (DMP). Finally, ion‐bonded amphiphilic miktoarm star copolymer, (PSt)₂‐poly(N‐isopropyl‐acrylamide)₂, was prepared by RAFT polymerization of N‐isopropylacrylamide (NIPAM) in the presence of the supramolecular macro‐RAFT agent. The polymerization kinetics was investigated and the molecular weight and the architecture of the resulting star polymers were characterized by means of ¹H‐NMR, FTIR, and GPC techniques. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5805–5815, 2008     

Surface‐initiated single‐electron transfer reversible addition–fragmentation chain transfer polymerization of 2‐hydroxyethyl acrylamide on silicon substrate at ambient temperature

2‐Hydroxyethyl acrylamide was successfully polymerized via single‐electron transfer initiation on the silicon surface and propagation through the reversible addition–fragmentation chain transfer (SET‐RAFT) polymerization at ambient temperature for different polymerization times. This work is the first time application of the surface‐initiated SET‐RAFT mechanism to afford the preparation of well‐defined poly(2‐hydroxyethyl acrylamide) [poly(HEAAm)] brushes at ambient temperature. The polymerization was well controlled and produced poly(HEAAm) brushes on the silicon surface with a well‐defined target molecular weight. The controlled nature of the polymerization was further demonstrated in the presence of sulfur atoms at the chain ends in X‐ray photoelectron spectroscopy experiments. The grafting density (σ, chains nm^?2) and the average distance between grafting points (D, nm) were found to be 0.42 chains nm^?2 and 1.74 nm, respectively, indicating moderate grafting density. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1140–1146     

Electrochemically mediated atom transfer radical polymerization with dithiocarbamates as alkyl pseudohalides

Electrochemically mediated atom transfer radical polymerizations (ATRPs) provide well‐defined polymers with designed dispersity as well as under external temporal and spatial control. In this study, 1‐cyano‐1‐methylethyl diethyldithiocarbamate, typically used as chain‐transfer agent (CTA) in reversible addition–fragmentation chain transfer (RAFT) polymerization, was electrochemically activated by the ATRP catalyst Cu^I/2,2′‐bipyridine (bpy) to control the polymerization of methyl methacrylate. Mechanistic study showed that this polymerization was mainly controlled by the ATRP equilibrium. The effect of applied potential, catalyst counterion, catalyst concentration, and targeted degree of polymerization were investigated. The chain‐end functionality was preserved as demonstrated by chain extension of poly(methyl methacrylate) with n‐butyl methacrylate and styrene. This electrochemical ATRP procedure confirms that RAFT CTAs can be activated by an electrochemical stimulus. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 376–381     

Thermally amendable tailor‐made functional polymer by RAFT polymerization and “click reaction”

This investigation reports the preparation and characterization of thermally amendable functional polymer bearing furfuryl functionality via reversible‐addition fragmentation and chain transfer (RAFT) polymerization and Diels‐Alder (DA) reaction. In this case, furfuryl methacrylate (FMA) was polymerized using 4‐cyano‐4‐[(dodecylsulfanylthiocarbonyl)sulfanyl] pentanoic acid as RAFT reagent and 4,4′‐azobis(4‐cyanovaleric acid) as thermal initiator. ¹H NMR, ¹³C NMR, and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry analysis showed that furfuryl group in poly(furfuryl methacrylate) (PFMA) was not affected during RAFT polymerization and the tailor‐made polymer had RAFT end group. The DA reaction was successfully carried out between the reactive furfuryl functionality of PFMA and different bismaleimides. The thermoreversible property of these DA polymers was characterized by FT‐IR and DSC analysis. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3365–3374     

Reversible addition fragmentation chain transfer polymerization of sterically hindered monomers: Toward well‐defined rod/coil architectures

The sterically hindered monomers dibutyl itaconate (DBI) and dicyclohexyl itaconate (DCHI) were polymerized via reversible addition fragmentation chain transfer (RAFT) free‐radical polymerization. S,S′‐Bis(α,α′‐dimethyl‐α″‐acetic acid) trithiocarbonate, cumyl dithiobenzoate, and cumyl phenyldithioacetate have been used as RAFT agents to mediate a series of polymerizations at 65 °C yielding rod polymers ranging in number average molecular weight from 9000 to 92,000 g mol^?1. The progress of the polymerization was followed via online Fourier transform–near infrared spectroscopy. The polydispersity indices of the obtained rod polymers were relatively high at 1.4–1.7. The RAFT polymerizations of the hindered monomers used in the present study displayed both ideal living and hybrid behavior between conventional and living polymerization, depending on the RAFT agent used. DCHI rod polymers generated via the RAFT process were subsequently reinitiated in the presence of styrene to produce a range of BAAB and A‐B rod‐coil block copolymers of molecular weights up to 164,000 g mol^?1. The chain extension yields molecular weight distributions that progressively shift to higher molecular weights and are unimodal. Thermogravimetric analysis of the pDCHI‐block‐pStyrene copolymers indicates thermal degradation in two separate steps for the pDCHI and pStyrene blocks. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2432–2443, 2004     

An efficient avenue to poly(styrene)‐block‐poly(ε‐caprolactone) polymers via switching from RAFT to hydroxyl functionality: Synthesis and characterization

The recently introduced procedure of quantitatively switching thiocarbonyl thio capped (RAFT) polymers into hydroxyl terminated species was employed to generate narrow polydispersity (PDI ≈ 1.2) sulfur‐free poly(styrene)‐block‐poly(ε‐caprolactone) polymers (26,000 ≤ M_n/g·mol^?1 < 45,000). The ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) was conducted under organocatalysis employing 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD). The obtained block copolymers were thoroughly analyzed via size exclusion chromatography (SEC), NMR, as well as liquid adsorption chromatography under critical conditions coupled to SEC (LACCC‐SEC) to evidence the block copolymer structure and the efficiency of the synthetic process. The current contribution demonstrates that the RAFT process can serve as a methodology for the generation of sulfur‐free block copolymers via an efficient end group switch. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Multiblock poly(4‐vinylpyridine) and its copolymer prepared with cyclic trithiocarbonate as a reversible addition–fragmentation transfer agent

The polymerization of 4‐vinylpyridine was conducted in the presence of a cyclic trithiocarbonate (4,7‐diphenyl‐[1,3]dithiepane‐2‐thione) as a reversible addition–fragmentation transfer (RAFT) polymerization agent, and a multiblock polymer with narrow‐polydispersity blocks was prepared. Two kinds of multiblock copolymers of styrene and 4‐vinylpyridine, that is, (ABA)_n multi‐triblock copolymers with polystyrene or poly(4‐vinylpyridine) as the outer blocks, were prepared with multiblock polystyrene or poly(4‐vinylpyridine) as a macro‐RAFT agent, respectively. GPC data for the original polymers and polymers cleaved by amine demonstrated the successful synthesis of amphiphilic multiblock copolymers of styrene and 4‐vinylpyridine via two‐step polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2617–2623, 2007     

Direct through anionic,cationic, and radical active species: Terminal carbon–halogen bond for “controlled”/living polymerizations of styrene

In this work, we examined the synthesis of novel block (co)polymers by mechanistic transformation through anionic, cationic, and radical living polymerizations using terminal carbon–halogen bond as the dormant species. First, the direct halogenation of growing species in the living anionic polymerization of styrene was examined with CCl₄ to form a carbon–halogen terminal, which can be employed as the dormant species for either living cationic or radical polymerization. The mechanistic transformation was then performed from living anionic polymerization into living cationic or radical polymerization using the obtained polymers as the macroinitiator with the SnCl₄/n‐Bu₄NCl or RuCp^*Cl(PPh₃)/Et₃N initiating system, respectively. Finally, the combination of all the polymerizations allowed the synthesis block copolymers including unprecedented gradient block copolymers composed of styrene and p‐methylstyrene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 465–473     

Bifunctional 2‐(alkoxycarbonothioylthio)acetic acids for the synthesis of TiO2‐poly(vinyl acetate) nanocomposites via RAFT polymerization

Reversible addition‐fragmentation chain‐transfer (RAFT) polymerization has been known as a convenient method for the synthesis of polymers of designed molecular structures. Of particular interest are bifunctional or multifunctional chain‐transfer agents (CTAs) which could be employed in the development of advanced materials via RAFT polymerization. In the present study, four bifunctional 2‐(alkoxycarbonothioylthio) RAFT CTAs with ? COOH functionalities containing methoxy, ethoxy, isopropoxy, and octyloxy groups, respectively, were synthesized and characterized by FTIR and NMR spectroscopy. Polymerizations of vinyl acetate using these CTAs exhibited increased molecular weight with consumption of monomer and relatively narrow dispersities, indicative of living polymerization behavior. The effect of the concentration of 2‐(ethoxycarbonothioylthio) acetic acid on the polymerization was examined, revealing that higher concentration of CTA led to lower molecular weight and narrower dispersity. As an example of the application of the synthesized bifunctional CTAs, TiO₂‐poly(vinyl acetate) (PVAc) nanocomposites were synthesized via a one‐pot process and characterized by TGA, DSC, TEM, and affinity test, suggesting attachment of PVAc onto the nano‐TiO₂ particles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 606–618     

Synthesis of poly(ω‐pentadecalactone)‐b‐poly(acrylate) diblock copolymers via a combination of enzymatic ring‐opening and RAFT polymerization techniques

Herein the first reported preparation of diblock copolymers of the polyethylene‐like polyester poly(ω‐pentadecalactone) (PPDL) via a combination of enzymatic ring‐opening polymerization (eROP) and reversible addition‐fragmentation chain‐transfer (RAFT) polymerization techniques is described. PPDL was synthesized via eROP using Novozyme 435 as a catalyst and a bifunctional initiator/chain transfer agent (CTA) appropriate for the eROP of ω‐pentadecalactone (PDL) and RAFT polymerization of acrylic and styrenic monomers. Chain growth of the PPDL macro‐CTA was performed to prepare acrylic and styrenic diblock copolymers of PPDL, and demonstrates a facile, metal‐free, and “greener” alternative to preparing acrylic diblock copolymers of polyethylene (PE). Diblock copolymer architecture was substantiated via analysis of ¹H NMR spectroscopic, UV‐GPC chromatographic, DSC onset crystallization (T_c), and MALDI‐ToF mass spectrometric data. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3326–3335     

Exploring amino acid‐tethered polymethacrylates as CO2‐sensitive macromolecules: A concealed property

Carbon dioxide (CO₂)‐responsive polymers have been gaining considerable interest because of their reactions with CO₂, giving rise to gas‐switchable properties, which can easily be reversed by mild heating or purging with inert gases. Herein, the synthesis of a series of side‐chain amino acids (alanine, leucine, isoleucine, phenylalanine, tryptophan) appending poly(meth)acrylates carrying primary amine (? NH₂) groups via reversible addition‐fragmentation chain transfer (RAFT) polymerization method was reported. It was found that alanine, leucine, isoleucine containing polymers displayed solubility–insolubility transition behavior and their associated property changes (solution transmittance, electrical conductivity, pH, zeta potential, and hydrodynamic diameter) in water upon alternate bubbling of CO₂/N₂ at room temperature. Among the three CO₂‐sensitive polymers only leucine based macromolecule was further chain extended with a thermoresponsive motif, di(ethylene glycol) methyl ether methacrylate (DEGMMA), via RAFT polymerization. CO₂‐tunable lower critical solution temperature and self‐assembling behavior of the diblock copolymer was carefully examined by UV–vis, ¹H NMR spectroscopy, dynamic light scattering (DLS), and field emission‐scanning electron microscopy (FE‐SEM) to establish dual thermo and gas‐tunable flip–flop micellizaion from the as‐synthesized block copolymer. Formation of polyammonium methacrylate bearing bicarbonate as counter anion is responsible for pendant primary amine containing polymer induced CO₂‐responsiveness. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2794–2803     

One‐step synthesis of block‐graft copolymers via simultaneous reversible‐addition fragmentation chain transfer and ring‐opening polymerization using a novel macroinitiator

One‐step synthesis of block‐graft copolymers by reversible addition‐fragmentation chain transfer (RAFT) and ring‐opening polymerization (ROP) by using a novel initiator was reported. Block‐graft copolymers were synthesized in one‐step by simultaneous RAFT polymerization of n‐butylmethacrylate (nBMA) and ROP of ε‐caprolacton (CL) in the presence of a novel macroinitiator (RAFT‐ROP agent). For this purpose, first epichlorohydrin (EPCH) was polymerized by using H₂SO₄ via cationic ring‐opening mechanism. And then a novel RAFT‐ROP agent was synthesized by the reaction of potassium ethyl xanthogenate and polyepichlorohydrin (poly‐EPCH). By using the RAFT‐ROP agent, poly[CL‐b‐EPCH‐b‐CL‐(g‐nBMA)] block‐graft copolymers were synthesized. The principal parameters such as monomer concentration, initiator concentration, and polymerization time that affect the one‐step polymerization reaction were evaluated. The block lengths of the block‐graft copolymers were calculated by using ¹H‐nuclear magnetic resonance (¹H NMR) spectrum. The block length could be adjusted by varying the monomer and initiator concentrations. The characterization of the products was achieved using ¹H NMR, Fourier‐transform infrared spectroscopy, gel‐permeation chromatography, thermogravimetric analysis, differential scanning calorimetry, elemental analysis, and fractional precipitation (γ) techniques. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2651–2659     

Exploitation of Compartmentalization in RAFT Miniemulsion Polymerization to Increase the Degree of Livingness

It is demonstrated that the degree of livingness (chain‐end fidelity) in RAFT polymerization for a given degree of polymerization can be markedly increased in miniemulsion polymerization relative to the corresponding homogeneous bulk system. Polymerization of styrene was conducted using a poly(methyl methacrylate) benzodithioate as macroRAFT agent in both miniemulsion and bulk. The substantially higher polymerization rate in miniemulsion, which is attributed to the segregation effect (compartmentalization) causing a reduction in the rate of bimolecular termination, makes it possible to reach a given degree of polymerization in a significantly shorter time than in the corresponding bulk system. As a consequence, fewer initiating radicals are required throughout the polymerization, leading to higher livingness in the more rapid miniemulsion system. It is demonstrated how this approach facilitates synthesis of high‐molecular‐weight block copolymers comprising slowly propagating monomers such as styrene and methacrylates. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1938–1946     

Synthesis of comb polymers via grafting‐onto macromolecules bearing pendant diene groups via the hetero‐Diels‐Alder‐RAFT click concept

Comb polymers were synthesized by the “grafting‐onto” method via a combination of Reversible Addition‐Fragmentation Chain Transfer (RAFT) polymerization and the hetero‐Diels‐Alder (HDA) cycloaddition. The HDA reactive monomer trans, trans‐hexa‐2,4‐dienylacrylate (ttHA) was copolymerized with styrene via the RAFT process. Crosslinking was minimized by decreasing the monomer concentration—whilst keeping monomer to polymer conversions low—resulting in reactive backbones with on average one reactive pendant diene groups for 10 styrene units. The HDA cycloaddition was performed between the diene functions of the copolymer and a poly(n‐butyl acrylate) (PnBA) prepared via RAFT polymerization with pyridin‐2‐yldithioformate, which can act as a dienophile. The coupling reactions were performed within 24 h at 50 °C and the grafting yield varies from 75% to 100%, depending on the number average molecular weight of the PnBA (3500 g mol^?1 < M_n < 13,000 g mol^?1) grafted chain and the reaction stoichiometry. The molecular weights of the grafted block copolymers range from 19,000 g mol^?1 to 58,000 g mol^?1 with polydispersities close to 1.25. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1773–1781, 2010     

Visible light‐induced RAFT polymerization of methacrylates with benzaldehyde derivatives as organophotoredox catalysts

The benzaldehyde derivatives, such as 2,4‐dimethoxy benzaldehyde (PC1) and p‐anisaldehyde (PC2), were successfully used as photoredox catalysts (PCs) in combination with typical RAFT agent 4‐cyano‐4‐(phenylcarbonothioylthio)pentanoic acid (CTP) for the controlled photoinduced electron transfer RAFT polymerization (PET‐RAFT) of methyl methacrylate (MMA) and benzyl methacrylate (BnMA) at room temperature. The kinetics of the polymerizations showed first order with respect to monomer conversions. Besides, the average number molecular weights (M_n) of the produced polymers increased linearly with the monomer conversions and kept relatively narrow polydispersity (PDI = M_w/M_n). For example, the M_n of PMMA increased from about 3400 to 17,300 g mol⁻¹ with the increasing in monomer conversion from 11% to 85%, and the PDI maintained around 1.36. The living features of polymerizations with the PC1 and PC2 as catalysts have also been further supported by chain extension and synthesis of PMMA‐b‐PBnMA diblock copolymer. As a result, the simplicity and efficiency of benzaldehyde derivatives catalyzed PET‐RAFT polymerization have been demonstrated under mild conditions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 229–236     

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     

Reversible addition–fragmentation chain‐transfer graft polymerization of styrene: Solid phases for organic and peptide synthesis

The γ‐initiated reversible addition–fragmentation chain‐transfer (RAFT)‐agent‐mediated free‐radical graft polymerization of styrene onto a polypropylene solid phase has been performed with cumyl phenyldithioacetate (CPDA). The initial CPDA concentrations range between 1 × 10^?2 and 2 × 10^?3 mol L^?1 with dose rates of 0.18, 0.08, 0.07, 0.05, and 0.03 kGy h^?1. The RAFT graft polymerization is compared with the conventional free‐radical graft polymerization of styrene onto polypropylene. Both processes show two distinct regimes of grafting: (1) the grafting layer regime, in which the surface is not yet totally covered with polymer chains, and (2) a regime in which a second polymer layer is formed. Here, we hypothesize that the surface is totally covered with polymer chains and that new polymer chains are started by polystyrene radicals from already grafted chains. The grafting ratio of the RAFT‐agent‐mediated process is controlled via the initial CPDA concentration. The molecular weight of the polystyrene from the solution (PS_free) shows a linear behavior with conversion and has a low polydispersity index. Furthermore, the loading of the grafted solid phase shows a linear relationship with the molecular weight of PS_free for both regimes. Regime 2 has a higher loading capacity per molecular weight than regime 1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4180–4192, 2002