Cumyl Phenyldithioacetate Research Articles

Enhanced Ionization in Electrospray Ionization Mass Spectrometry of Labile End-Group-Containing Polystyrenes Using Silver(I) Tetrafluoroborate as Doping Salt

The use of silver tetrafluoroborate as a doping salt to achieve efficient and soft desorption/ionization of labile end-group-carrying polystyrene during electrospray ionization is demonstrated. Polystyrene carrying a dithioester end group prepared via reversible addition fragmentation chain transfer (RAFT) chemistry (using the RAFT agent cumyl phenyldithioacetate) as well as a commercial polymer standard prepared by anionic polymerization serve as model compounds. By employing silver tetrafluoroborate as ionization agent, an increase in ion count of more than one order of magnitude was achieved compared to ionization with sodium iodide. Little loss of the end group occurred via elimination of the dithioacid to yield vinyl-terminated polymer. A possible mechanism is given for catalysis of the cleavage reaction in the presence of silver salts. Side-product formation due to thermal or collision induced loss of the dithioester was kept at a minimum under optimized source conditions. Thus, we introduce a novel soft ionization protocol for polystyrenes, which are often difficult to ionize.

Verification of Controlled Grafting of Styrene from Cellulose via Radiation-Induced RAFT Polymerization

Reversible addition - fragmentation chain transfer (RAFT) polymerization was applied to radiation-induced graft polymerization of styrene from cellulose. The grafting of styrene from cellulose substrates using the chain transfer agent cumyl phenyldithioacetate was confirmed by Raman and X-ray photoelectron spectroscopy, differential scanning calorimetery, thermogravimetric analysis, scanning electron microscopy, and contact angle analysis. Grafted polystyrene chains were cleaved from the cellulose surface by acidic hydrolysis of the cellulose. The number-average molecular weight and polydispersity index of the grafted and the free (nongrafted) polystyrenes obtained under identical conditions were determined by size exclusion chromatography. Grafted and nongrafted polystyrenes have almost the same (near theoretical) molecular weight and narrow polydispersity, thus proving for the first time the control of the grafting process mediated via RAFT without any prior functionalization of the surface.

CMC and Phase Separation Studies of RAFT Mediated Amphiphilic Diblock Glycopolymers with Methyl Acrylate and Styrene

AbstractSummary: Interesting new CMC and phase separation data of carbohydrate‐based self‐assembling core‐shell nanoparticles which were synthesized via the Reversible Addition‐Fragmentation Transfer (RAFT) process. The macro‐RAFT agent, poly(3‐O‐ Methacryloyl‐1,2:5,6‐di‐O‐isopropylidene‐D‐glucofuranose) (PMAlpGlc), was prepared by RAFT polymerization of the glycomonomer with cumyl phenyl dithioacetate as the chain transfer agent. Chain extension with styrene and methyl acrylate afforded the diblock copolymers (PMAlpGlc‐b‐styrene and PMAlpGlc‐b‐methyl acrylate) having predetermined molecular weight and narrow molecular weight distributions. Acidolysis of these diblock copolymers were undertaken and confirmed by NMR. Core‐shell nanoparticles were observed by TEM.

Electrospray Ionization Mass Spectrometry Investigation of Reversible Addition Fragmentation Chain Transfer Mediated Acrylate Polymerizations Initiated via 60Co γ-Irradiation: Mapping Reaction Pathways

Reversible addition fragmentation chain transfer (RAFT) mediated methyl acrylate and butyl acrylate polymerizations initiated via 60Co γ-irradiation were investigated using electrospray ionization mass spectrometry (ESI−MS). The polymer end-groupings were mapped using both a hybrid quadrupole-time-of-flight instrument and a quadrupole ion trap mass spectrometer. Three potential initiation processes were identified during the cumyl phenyl dithioacetate (CPDA) mediated acrylate polymerizations. CPDA dissociates into a cumyl radical and a phenyl dithioester radical (Z-group). A set of polymer product ions indicates that a small, yet significant, fraction of the γ-generated phenyl dithioacetate radical contributes to the initiation process. Furthermore, the phenyl dithioacetate group undergoes cleavage to yield thiol end groups that react to form disulfide linkages. Additionally, polymer product ions indicative of a small amount of water radiolysis were observed, and evidence that the butyl acrylate monomer i...

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

AbstractThe 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

Reversible addition–fragmentation chain transfer graft copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate from polypropylene lanterns: Solid phases for scavenging applications

AbstractThe γ‐initiated reversible addition–fragmentation chain transfer mediated free‐radical graft copolymerization of styrene and m‐isopropenyl‐α,α′‐dimethylbenzyl isocyanate (TMI) from a polypropylene (PP) solid phase was performed with cumyl phenyldithioacetate (CPDA) as the chain‐transfer agent. The initial CPDA concentration was 8 × 10−3 mol L−1. Polymerizations were performed with a dose rate of 0.18 kGy h−1 at the ambient temperature. Initial comonomer mixtures with 15, 30, and 50 mol % TMI were used. Depending on the amount of TMI in the initial comonomer mixture, the plot of the grafting ratio versus the time showed two grafting regimes (for 15 and 50 mol % TMI) or one (for 30 mol % TMI). Scavenger lanterns with 15 and 50 mol % TMI featured two isocyanate loading regimes, the second with higher loading capacities. The scavenger lanterns with 30 mol % TMI showed a linear loading capacity over the full grafting ratio. A maximum loading capacity of 110 μmol per scavenger lantern was achieved with 50 mol % TMI at a grafting ratio of approximately 60 wt %. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 857–864, 2006

An in-depth analytical approach to the mechanism of the RAFT process in acrylate free radical polymerizations via coupled size exclusion chromatography–electrospray ionization mass spectrometry (SEC–ESI-MS)

Coupled size exclusion chromatography (SEC)–electrospray ionization mass spectrometry (ESI-MS) was applied to carefully map the product spectrum of a series of acrylate free radical polymerizations mediated via the reversible addition fragmentation chain transfer (RAFT) process. The product stream of a significantly rate retarded RAFT system (i.e. n-butyl acrylate (BA)/cumyl dithiobenzoate (CDB)) was compared with the less rate retarded RAFT polymerizations of BA mediated by cumyl phenyl dithioacetate (CPDA) and methyl acrylate (MA)/CPDA. In each case excellent agreement between the theoretical and experimental masses, as well as the simulated isotopic peak distributions, of polymeric species in the product stream was observed. Although conventional disproportionation and combination bimolecular termination products were clearly identified within the product spectra, the presence of irreversibly terminated RAFT intermediates, i.e. 3-armed star polymers, was not observed. The mass spectroscopic results are compared to modeling estimations (carried out via the PREDICI® program package) of the concentration ratios of 3-armed stars vs. conventional termination products. It is demonstrated that the occurrence of conventional termination products should be accompanied by a significant product stream associated with 3-armed star polymer material if cross termination was operational—at least under the current reaction conditions. The absence of three armed star polymer products in the polymers stream suggests that irreversible cross termination reactions may be of minor importance in the present systems.

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

AbstractThe 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

Facile Access to Chain Length Dependent Termination Rate Coefficients via Reversible Addition−Fragmentation Chain Transfer (RAFT) Polymerization: Influence of the RAFT Agent Structure

A recently developed methodology for determining chain length dependent termination rate coefficients, 〈kti,i〉, via reversible addition−fragmentation chain transfer (RAFT) polymerizations has been extended and validated for 1-phenylethyl phenyldithioacetate (PEPDA) and 3-benzylsulfanylthiocarbonylsulfanylpropionic acid (BSPA) mediated styrene (bulk) free radical polymerizations at 80 °C. While the use of cumyl phenyldithioacetate (CPDA) enables a highly precise mapping of the chain length dependence of the termination rate coefficient, employment of PEPDA and BSPA leads to considerable information loss for short chain lengths (i < 10). Careful simulations demonstrate that such behavior is caused by a substantial decrease in the initial transfer effectiveness of the RAFT agents when going from CPDA to BSPA, leading to hybrid behavior between conventional and living free radical polymerization. The observed hybrid behavior is quantifiable via (overall) transfer rate coefficients for the individual RAFT agen...

RAFT Polymerization of N-Isopropylacrylamide in the Absence and Presence of Y(OTf)3: Simultaneous Control of Molecular Weight and Tacticity

The reversible addition−fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) was carried out successfully in the absence and presence of Lewis acid Y(OTf)3 to synthesize controlled molecular weight atactic and isotactic poly(NIPAM)s using both 1-phenylethyl phenyldithioacetate (PEPD) and cumyl phenyldithioacetate (CPDT) as the RAFT agents. The polymerization rate is about 16 times faster in the presence of the Lewis acid than that in the absence and 1.4 times faster with PEPD than with CPDT as the RAFT agent. The polymer with a higher polydispersity was obtained when prepared in the presence of the Lewis acid than that in the absence. A longer induction period was observed using CPDT than PEPD. The chain-end structure of isotactic poly(NIPAM) was determined by 1H NMR and MALDI−TOF mass spectrometry. The RAFT agent derived isotactic poly(NIPAM) was the main product as expected from the well-accepted mechanism of RAFT polymerization. Moreover, a series of stereoblock [atactic(...

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

AbstractThe 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 (PSfree) 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 PSfree 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

Kinetic Investigations of Reversible Addition Fragmentation Chain Transfer Polymerizations: Cumyl Phenyldithioacetate Mediated Homopolymerizations of Styrene and Methyl Methacrylate

A previously published simulation and data fitting procedure for the reversible addition fragmentation chain transfer (RAFT) process using the PREDICI simulation program has been extended to cumyl phenyldithioacetate mediated styrene and methyl methacrylate (MMA) bulk homopolymerizations. The experimentally obtained molecular weight distributions (MWDs) for the styrene system are narrow and unimodal and shift linearly with monomer conversion to higher molecular weights. The MMA system displays a hybrid of conventional chain transfer and living behavior, leading to bimodal MWDs. The styrene system has been subjected to a combined experimental and modeling study at 60 °C, yielding a rate coefficient for the addition reaction of free macroradicals to polymeric RAFT agent, kβ, of approximately 5.6 × 105 L mol-1 s-1 and a decomposition rate coefficient for macroradical RAFT species, k-β, of about 2.7 × 10-1 s-1. The transfer rate coefficient to cumyl phenyldithioacetate is found to be close to 2.2 × 105 L mol-...

Cumyl phenyldithioacetate and 1-phenylethyl phenyldithioacetate: Versatile ambient-temperature RAFT agents

Agents for the reversible addition fragmentation chain transfer (RAFT) polymerization were invented by CSIRO a few years ago [ 1 , 2 ] and have since been proven to be very well suited for controlling both the molecular-weight outcomes and the polydispersity of free-radical polymerization processes. The RAFT process is governed by the RAFT equilibrium depicted below in Scheme 1. Some reported RAFT agents, however, are not suitable for polymerizations of styrene and methyl acrylate (MA) at low reaction temperatures (e.g. 25°C) due to high retardation of the polymerization process. This retardation is most likely associated with significant stabilization of the intermediate RAFT radical (species (1)). If the stabilization of the macroRAFT radical is reduced by substitution of the Z-group with a less stabilizing moiety, the RAFT agents become suitable for ambient-temperature polymerizations. Cumyl phenyldithioacetate (CPDA) and 1-phenylethyl phenyldithioacetate (1-PEPDA) have recently been added to the existing library of available RAFT agents [ 3 , 4 ] and are, due to the relatively poor radical stabilizing ability of the CH 2 Ph group, well suited for controlling styrene (CPDA and 1-PEPDA) and MA (1-PEPDA) polymerizations at ambient temperature. The synthesis of both compounds proceeds by a Grignard reaction of benzyl chloride with carbon disulfide and subsequent reaction of the resulting phenyldithioacetic acid with styrene (to give 1-PEPDA) [ 3 ] or α-methylstyrene (to give CPDA). [ 4 ] formula phys. Z-group Z-group.