Kinetic model of reversible addition‐fragmentation chain transfer polymerization in microemulsions

A simplified kinetic model for RAFT microemulsion polymerization has been developed to facilitate the investigation of the effects of slow fragmentation of the intermediate macro‐RAFT radical, termination reactions, and diffusion rate of the chain transfer agent to the locus of polymerization on the control of the polymerization and the rate of monomer conversion. This simplified model captures the experimentally observed decrease in the rate of polymerization, and the shift of the rate maximum to conversions less than the 39% conversion predicted by the Morgan model for uncontrolled microemulsion polymerizations. The model shows that the short, but finite, lifetime of the intermediate macro‐RAFT radical (1.3 × 10^?4–1.3 × 10^?2 s) causes the observed rate retardation in RAFT microemulsion polymerizations of butyl acrylate with the chain transfer agent methyl‐2‐(O‐ethylxanthyl)propionate. The calculated magnitude of the fragmentation rate constant (k_f = 4.0 × 10¹–4.0 × 10³ s^?1) is greater than the literature values for bulk RAFT polymerizations that only consider slow fragmentation of the macro‐RAFT radical and not termination (k_f = 10^?2 s^?1). This is consistent with the finding that slow fragmentation promotes biradical termination in RAFT microemulsion polymerizations. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 604–613, 2010     

Kinetics of methyl methacrylate and n‐butyl acrylate copolymerization mediated by 2‐cyanoprop‐2‐yl dithiobenzoate as a RAFT agent

The RAFT (co)polymerization kinetics of methyl methacrylate (MMA) and n‐butyl acrylate (BA) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was studied with various RAFT concentrations and monomer compositions. The homopolymerization of MMA gave the highest rate. Increasing the BA fraction f_BA dramatically decreased the copolymerization rate. The rate reached the lowest point at f_MMA ～ 0.2. This observation is in sharp contrast to the conventional RAFT‐free copolymerization, where BA homopolymerization gave the highest rate and the copolymerization rate decreased monotonously with increasing f_MMA. This peculiar phenomenon can be explained by the RAFT retardation effect. The RAFT copolymerization rate can be described by 〈R_p〉/〈R_p〉₀ = (1 + 2(〈k_c〉/〈k_t〉)〈K〉)[RAFT]₀)^?0.5, where 〈R_p〉₀ is the RAFT‐free copolymerization rate and 〈K〉 is the apparent addition–fragmentation equilibrium coefficient. A theoretical expression of 〈K〉 based on a terminal model of addition and fragmentation reactions was derived and successfully applied to predict the RAFT copolymerization kinetics with the rate parameters obtained from the homopolymerization systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3098–3111, 2007     

Addition–fragmentation chain transfer: Molecular weight distributions and retardation in the system methyl methacrylate/methyl α‐(bromomethyl)acrylate

A detailed investigation of addition–fragmentation chain transfer (AFCT) in the free‐radical polymerization of methyl methacrylate (MMA) in the presence of methyl α‐(bromomethyl)acrylate (MBMA) was carried out to elucidate mechanistic details with efficient macromonomer synthesis as an underlying goal. Advanced modeling techniques were used in connection with the experimental work. Curve fitting of simulated and experimental molecular weight distributions with respect to the rate coefficient for addition of propagating radicals to MBMA (k_add) over 60–120 °C resulted in E_add = 21.7 kJ mol^?1 and A_add = 2.18 × 10⁶ M^?1 s^?1 and a very weak temperature dependence of the chain‐transfer constant (E_add ≈ E_p). The rate coefficient for fragmentation of adduct radicals at 60 °C was estimated as k_f ≈ 39 s^?1 on the basis of experimental data of the MMA conversion and the concentration of 2‐carbomethoxy‐2‐propenyl end groups. The approach developed is generic and can be applied to any AFCT system in which copolymerization does not occur and in which the resulting unsaturated end groups do not undergo further reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2640–2650, 2004     

Modeling the reversible addition–fragmentation chain transfer process in cumyl dithiobenzoate‐mediated styrene homopolymerizations: Assessing rate coefficients for the addition–fragmentation equilibrium

A full kinetic scheme for the free‐radical reversible addition–fragmentation chain transfer (RAFT) process is presented and implemented into the program package PREDICI®. With the cumyl dithiobenzoate‐mediated bulk polymerization of styrene at 60 °C as an example, the rate coefficients associated with the addition–fragmentation equilibrium are deduced by the careful modeling of the time‐dependent evolution of experimental molecular weight distributions. The rate coefficient for the addition reaction of a free macroradical to a polymeric RAFT species (k_β) is approximately 5 · 10⁵ L mol^?1 s^?1, whereas the fragmentation rate coefficient of the formed macroradical RAFT species is close to 3 · 10^?2 s^?1. These values give an equilibrium constant of K = k_β/k_?β = 1.6 · 10⁷ L mol^?1. Conclusive evidence is given that the equilibrium lies well on the side of the macroradical RAFT species. The high value of k_β is comparable in size to the propagation rate coefficients reported for acrylates. The transfer rate coefficient to cumyl dithiobenzoate is close to 3.5 · 10⁵ L mol^?1 s^?1. A careful sensitivity analysis was performed, which indicated that the reported rate coefficients are accurate to a factor of 2. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1353–1365, 2001     

Calculations of Monomer Conversion and Radical Concentration in Reversible Addition‐Fragmentation Chain Transfer Radical Polymerization

Simple expressions are derived for the development of monomer conversion, as well as propagating radical, adduct radical, dormant chain, and dead chain concentrations in reverse addition‐fragmentation transfer polymerization (RAFT). The relations for the profiles of propagating radical concentration and conversion versus time are derived and depend on group parameters of rate constants and chemical recipe. The analytical equations are verified against numerical solutions of the mass‐balance differential equations. This derivation involves the steady‐state hypothesis for radical and RAFT agent concentrations. The errors introduced by these assumptions are negligible when the fragmentation rate constant, k_f, is higher than 10 s⁻¹ or when the cross‐termination rate constant, k_ct, is higher than 10⁵ L · mol⁻¹ s⁻¹.

Calculated concentration profiles (points: numerical, lines: analytical) of propagating radical R, adduct radical A, dormant T, and dead D (= P + P′) chains.     

Substituted propenyl end groups as reactive intermediates in radical polymerization

The addition of propagating radicals of methyl acrylate (MA) and styrene (St) to CH₂?C(CO₂CH₃)CH₂? and CH₂?C(C₆H₅)CH₂? ω‐end groups of poly(methyl methacrylate) (PMMA) and polystyrene (PSt) was investigated. The end groups were as reactive as MA and St toward the poly(methyl acrylate) (PMA) and PSt radicals, respectively. The adduct radical derived from the two types of PMMA end groups and PMA radicals underwent β fragmentation exclusively to yield PMMA radicals and end groups bound to PMA chains. The addition of PSt radicals to PMMA with CH₂?C(CO₂Me)CH₂? end groups resulted in adduct radicals that underwent β fragmentation and addition to St or coupling with PSt radicals. Adduct radicals formed by the addition of PMA radicals to both types of end groups of PSt exclusively formed C? C bond by coupling with PMA radicals to form branched structures or by addition to MA monomer to give a copolymer. The fate of the adduct radicals was highly dependent on the type of polymer chain and the substituent bound to the end group. Steric congestion of the adduct radical arising from the α‐methyl group of the PMMA chain was considered to be crucial for fragmentation to expel the PMMA radical. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 645–654, 2003     

Radical‐induced oxidation of RAFT agents—A kinetic study

Radical‐induced oxidation of reversible addition‐fragmentation chain transfer (RAFT) agents is investigated with respect to the effect of molecular structure on oxidation rate. The radicals are generated by homolysis of either azobisisobutyronitrile or alkoxyamine and transformed in situ immediately into peroxy radicals through transfer to molecular oxygen. It is found that the oxidation rate depends on the structure of Z‐ and R‐group of thiocarbonylthio compounds. For dithioesters with identical Z‐phenyl substituent, the oxidation rate decreases in the order of cyanoisopropyl (? C(Me)₂CN) > cumyl (? C(Me)₂Ph) > phenylethyl (? CH(Me)Ph) > 2‐methoxy‐1‐methyl‐2‐oxoethyl (? CH(Me) ? C(?O)OCH₃) > benzyl (? CH₂Ph). For dithioesters with identical R‐group, the oxidation rate decreases in the order of Z = phenyl? ～ benzyl? > RS? (trithiocarbonates) > RO? (xanthates). The stability of the RAFT agents toward oxidation correlates well with the chain transfer abilities as those previously reported by Rizzardo and coworkers. The priority of the oxidation reaction over the RAFT process, and the subsequent influence on RAFT polymerization are also investigated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Kinetic Analysis of Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerizations: Conditions for Inhibition,Retardation, and Optimum Living Polymerization

Careful simulations of conversion vs. time plots and full molecular weight distributions have been performed using the PREDICI® program package in conjunction with the kinetic scheme suggested by the CSIRO group for the reversible addition fragmentation chain transfer (RAFT) process to probe RAFT agent mediated polymerizations. In particular, conditions leading to inhibition and rate retardation have been examined to act as a guide to optimum living polymerization behavior. It is demonstrated that an inhibition period of considerable length is induced by either slow fragmentation of the intermediate RAFT radicals appearing in the pre‐equilibrium or by slow re‐initiation of the leaving group radical of the initial RAFT agent. The absolute values of the rate coefficients governing the core equilibrium of the RAFT process – at a fixed value of the equilibrium constant – are confirmed to be crucial in controlling the polydispersity of the resulting molecular weight distributions: A higher interchange frequency effects narrower distributions. It is further demonstrated that the size of the rate coefficient controlling the addition reaction of propagating radicals to polyRAFT agent, k_β, is mainly responsible for optimizing the control of the polymerization. The fragmentation rate coefficient, k_–β, of the macroRAFT intermediate radical, on the other hand, may be varied over orders of magnitude without affecting the amount of control exerted over the polymerization. On the basis of the basic RAFT mechanism, its value mainly governs the extent of rate retardation in RAFT polymerizations.     

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     

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     

Incubation period in the 2,2,4,4‐tetramethyl‐1‐piperidinyloxy‐mediated thermal autopolymerization of styrene: Kinetics and simulations

Mechanisms and simulations of the induction period and the initial polymerization stages in the nitroxide‐mediated autopolymerization of styrene are discussed. At 120–125 °C and moderate 2,2,4,4‐tetramethyl‐1‐piperidinyloxy (TEMPO) concentrations (0.02–0.08 M), the main source of radicals is the hydrogen abstraction of the Mayo dimer by TEMPO [with the kinetic constant of hydrogen abstraction (k_h)]. At higher TEMPO concentrations ([N?] > 0.1 M), this reaction is still dominant, but radical generation by the direct attack against styrene by TEMPO, with kinetic constant of addition k_ad, also becomes relevant. From previous experimental data and simulations, initial estimates of k_h ≈ 1 and k_ad ≈ 6 × 10^?7 L mol^?1 s^?1 are obtained at 125 °C. From the induction period to the polymerization regime, there is an abrupt change in the dominant mechanism generating radicals because of the sudden decrease in the nitroxide radicals. Under induction‐period conditions, the simulations confirm the validity of the quasi‐steady‐state assumption (QSSA) for the Mayo dimer in this regime; however, after the induction period, the QSSA for the dimer is not valid, and this brings into question the scientific basis of the well‐known expression k_th[M]³ (where [M] is the monomer concentration and k_th is the kinetic constant of autoinitiation) for the autoinitiation rate in styrene polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6962‐6979, 2006     

Thermal‐initiated reversible addition–fragmentation chain transfer polymerization of methyl methacrylate in the presence of oxygen

A novel reversible addition–fragmentation chain transfer polymerization (RAFT) of methyl methacrylate (MMA) in the presence of oxygen was carried out for the first time without added chemical initiators. The polymerization was mediated by 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) or cumyl dithionaphthalenoate (CDN) as RAFT agent. The polymerization demonstrated the features of a living/controlled radical polymerization. The polymerization rate increased with oxygen concentration. Polymers with molecular weight M_n up to 520,000 g/mol, polydispersity M_w/M_n ～1.46 and RAFT efficiency M_n,th/M_n,GPC ～1.026 in the case of CPDN and M_n ～331,500 g/mol, M_w/M_n ～1.35, and M_n,th/M_n,GPC ～1.137 in the case of CDN were obtained. The possible mechanism of the thermal‐initiated RAFT polymerization of MMA in the presence of oxygen was discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3343–3354, 2006     

“Living”/controlled free radical polymerization of MMA in the presence of cobalt(II) 2‐ethylhexanoate: A switch from RAFT to ATRP mechanism

A metal complex, cobalt(II) 2‐ethylhexanoate (CEH), was added to the system of thermal‐initiated reversible addition‐fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as the RAFT agent at 115 °C. The polymerization rate was remarkably enhanced in the presence of CEH in comparison with that in the absence of CEH, and the increase of the CPDN concentration also accelerated the rate of polymerization. The polymerization in the concurrence of CPDN and CEH demonstrated the characters of “living”/controlled free radical polymerization: the number‐average molecular weights (M_n) increasing linearly with monomer conversion, narrow molecular weight distributions (M_w/M_n) and obtained PMMA end‐capped with the CPDN moieties. Meanwhile, CEH can also accelerate the rate of RAFT polymerization of MMA using the PMMA as macro‐RAFT agent instead of CPDN. Similar polymerization profiles were obtained when copper (I) bromide (CuBr)/N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine was used instead of CEH. Extensive experiments in the presence of butyl methacrylate, bis(cyclopentadienyl) cobalt(II) and cumyl dithionaphthalenoate were also conducted; similar results as those of MMA/CPDN/CEH system were obtained. A transition of the polymerization mechanism, from RAFT process without CEH addition to atom transfer radical polymerization in the presence of CEH, was possibly responsible for polymerization profiles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5722–5730, 2007     

Polymerization of neat 2‐ethylhexyl acrylate induced by a pulsed electron beam

The bulk polymerization of 2‐ethylhexyl acrylate (2‐EHA), induced by a pulsed electron beam, was investigated with pulse radiolysis, gravimetry, and Fourier transform infrared spectroscopy. The roles of the dose rate, pulse frequency, and added acrylic acid (AA) in the polymerization of 2‐EHA were examined at ambient temperature. In the range of 12.6–71.2 Gy/pulse, the polymerization of 2‐EHA was dose‐rate‐dependent: at the same total dose, a lower dose rate yielded a higher conversion. Also, a lower pulse rate gave a higher conversion at the same total dose. The addition of up to 10 wt % AA showed no increase in the conversion of 2‐EHA at a low conversion (8 kGy), but at a higher conversion (16 kGy), a 20 wt % increase in the conversion of 2‐EHA was observed. The estimated values (1.6 ± 0.3) × 10^?3 (dm³ s)^3/2 mol^?1 s^?1/2 for k_p(G/2k_t)^1/2 and 2.6 ± 0.8 dm³ s J^?1 for 2k_tG (where k_p is the rate constant of propagation, k_t is the rate constant of bimolecular termination, and G is the yield of free radicals) were obtained at relatively low conversions. The reaction rate constant of the addition of 2‐EHA^· free radicals to the monomer was measured by pulse radiolysis and found to be 2.8 × 10² mol^?1 dm³ s^?1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 196–203, 2003     

Pulsed‐laser polymerization‐gel permeation chromatographic determination of the propagation‐rate coefficient for the methyl acrylate dimer: A sterically hindered monomer

The methyl acrylate dimer (MAD) is a sterically hindered macromonomer, and the propagating radical can fragment to an unsaturated end group. The propagation‐rate coefficient (k_p) for MAD was obtained by pulsed‐laser polymerization (PLP). The Mark–Houwink–Sakaruda parameters required for the analysis of the molecular weight distributions (MWDs) were obtained by multiple‐detector gel permeation chromatography (GPC) with on‐line viscometry. The small radical created by the fragmentation results in a short‐chain polymer that means the MWD may no longer be given by that expected for “ideal” PLP conditions; simulations suggest that the degree of polymerization required for “ideal” PLP conditions can be obtained from the primary point of inflection provided the GPC traces also show a clear secondary inflection point (radicals terminated by the second, rather than the first, pulse subsequent to initiation). Over the temperature range of 40–75 °C, the data can be best fitted by k_p/dm³ mol^?1 s^?1 = 10^6.1 exp(?29.5 kJ mol^?1), with a moderately large joint confidence interval for the Arrhenius parameters. The data are consistent with an increased activation energy and reduced frequency factor as compared with acrylate or methacrylate; both of these changes can be ascribed to hindrance. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3902–3915, 2001     

Controlled radical polymerization of styrene mediated by the C‐phenyl‐N‐tert‐butylnitrone/AIBN pair: Kinetics and electron spin resonance analysis

Kinetics of the free radical polymerization of styrene at 110 °C has been investigated in the presence of C‐phenyl‐N‐tert‐butylnitrone (PBN) and 2,2′‐azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 °C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 °C), and ultimately on the control of the styrene polymerization at 110 °C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide‐mediated polymerization. Only one type of nitroxide (low‐molecular‐mass nitroxide) is formed whatever the prereaction conditions at 85 °C, and the equilibrium constant (K) between active and dormant species is 8.7 × 10^?10 mol L^?1 at 110 °C. At this temperature, the dissociation rate constant (k_d) is 3.7 × 10^?3 s^?1, the recombination rate constant (k_c) is 4.3 × 10⁶ L mol^?1 s^?1, whereas the activation energy (E_a,diss.), for the dissociation of the alkoxyamine at the chain‐end is ～125 kJ mol^?1. Importantly, the propagation rate at 110 °C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 °C, is higher than that for the thermal polymerization at 110 °C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1219–1235, 2007     

Macromolecular brushes synthesized by “grafting from” approach based on “click chemistry” and RAFT polymerization

Well‐defined macromolecular brushes with poly(N‐isopropyl acrylamide) (PNIPAM) side chains on random copolymer backbones were synthesized by “grafting from” approach based on click chemistry and reversible addition‐fragmentation chain transfer (RAFT) polymerization. To prepare macromolecular brushes, two linear random copolymers of 2‐(trimethylsilyloxy)ethyl methacrylate (HEMA‐TMS) and methyl methacrylate (MMA) (poly(MMA‐co‐HEMA‐TMS)) were synthesized by atom transfer radical polymerization and were subsequently derivated to azide‐containing polymers. Novel alkyne‐terminated RAFT chain transfer agent (CTA) was grafted to polymer backbones by copper‐catalyzed 1,3‐dipolar cycloaddition (azide‐alkyne click chemistry), and macro‐RAFT CTAs were obtained. PNIPAM side chains were prepared by RAFT polymerization. The macromolecular brushes have well‐defined structures, controlled molecular weights, and molecular weight distributions (M_w/M_n ≦ 1.23). The RAFT polymerization of NIPAM exhibited pseudo‐first‐order kinetics and a linear molecular weight dependence on monomer conversion, and no detectable termination was observed in the polymerization. The macromolecular brushes can self‐assemble into micelles in aqueous solution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 443–453, 2010     

Modeling the reversible addition–fragmentation transfer polymerization process

A kinetic model has been developed for reversible addition–fragmentation transfer (RAFT) polymerization with the method of moments. The model predicts the monomer conversion, number‐average molecular weight, and polydispersity of the molecular weight distribution. It also provides detailed information about the development of various types of chain species during polymerization, including propagating radical chains, adduct radical chains, dormant chains, and three types of dead chains. The effects of the RAFT agent concentration and the rate constants of the initiator decomposition, radical addition, fragmentation, disproportionation, and recombination termination of propagating radicals and cross‐termination between propagating and adduct radicals on the kinetics and polymer chain properties are examined with the model. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1553–1566, 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     

Selective complete decomposition of poly(n‐hexylisocyanate) and its use in a new molecular design method

Poly(n‐hexylisocyanate) (PHIC‐NH) as a rod‐like polymer having a ? NH group at one end of the polymer chain was found to instantly (less than a few seconds) be completely decomposed by CH₃O^?Na⁺ in tetrahydrofuran/CH₃OH under a mild experimental condition ([CH₃O^?Na⁺] < 1 mol L^?1 at room temperature).The mechanism of the decomposition for the PHIC‐NH consists of two steps: the first is abstraction of the proton for PHIC‐NH by Na⁺ with a slow reaction rate, and the second is the consequent depolymerization of PHIC‐N^? based on the equilibrium polymerization with a rapid depolymerization rate. The decomposition rate constants (k_d) depend on M_w of PHIC‐NH, namely k_d ～ M_w^?1.0. The decomposition of the PHIC‐NR having an end‐capped ? NR group was completely depressed. Using an “all or nothing” mechanism for the decomposition, the (PHIC)_3.43 comb‐shaped polymer and polystyrene (PSt)‐graft‐(PHIC‐NH)_4.28 graft copolymer were, respectively, decomposed to produce (PHIC‐NH)_3.43–1.03 and PSt‐graft‐(PHIC‐NH)_4.28–0 in a series with different numbers of PHIC‐NH combs and PHIC‐NH grafts by regulating the amount of CH₃O^?Na⁺ and the decomposition time. Molecular structure of (PHIC‐NH)_3.43–1.03 and PSt‐graft‐(PHIC‐NH)_4.28–0 was discussed from a viewpoint of PSt‐reduced chain dimension per molar mass. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011