Measurement of Transfer Coefficients to Monomer for n‐Butyl Methacrylate by Molecular Weight Distributions from Emulsion Polymerization

The average kinetic coefficient for chain transfer to monomer 〈k_tr,M〉 in the free‐radical polymerization of n‐butyl methacrylate (BMA) has been determined by the analysis of molecular weight distributions obtained by seeded emulsion polymerization under conditions such that chain transfer to monomer is the dominant chain‐stopping event. Measurements between 40 and 70 °C gave data fitting an Arrhenius‐type relationship with exponential factor E_A = 30 900 ± 4 500 J · mol^?1 and pre‐exponential factor log A = 3.45 ± 0.15. The value for E_A is comparable with published data for chain transfer to monomer from methyl methacrylate (MMA) and n‐butyl acrylate (BA). The A value, however, is 1–3 orders of magnitude smaller, suggesting that there is more hindrance for chain transfer to monomer for BMA than for either MMA or BA.

     

Iron(III)‐Mediated AGET ATRP of Methyl Methacrylate Using Vitamin C Sodium Salt as a Reducing Agent

Vitamin C sodium salt (VC‐Na) is used as a reducing agent for the iron‐mediated AGET ATRP (atom transfer radical polymerization using activators generated by electron transfer) of methyl methacrylate (MMA) with FeCl₃/tris‐(3,6‐dioxa‐heptyl) amine (TDA‐1) as a catalyst complex and ethyl 2‐bromoisobutyrate (EBiB) as an initiator in the absence/presence of a limited amount of air. As compared with the reported iron‐mediated AGET ATRP of MMA, the current catalyst system shows a faster polymerization rate. For example, a conversion of 82.3% is obtained in 3.1 h with a molar ratio of [MMA]₀/[EBiB]₀/[FeCl₃.6H₂O]₀/[TDA‐1]₀/[VC‐Na]₀ = 500:1:1:3:0.5 at 90 °C. The kinetics of polymerizations of MMA in bulk or anisole demonstrate features of “living” or controlled free‐radical polymerization, such as the number‐average molecular weights increasing linearly with monomer conversion and maintaining narrow molecular weight distributions ( / = 1.20–1.44).

     

A Highly Efficient Iron‐Mediated AGET ATRP of Methyl Methacrylate Using Fe(0) Powder as the Reducing Agent

A new method, AGET ATRP mediated by an iron(III) catalyst using Fe(0) powder as a reducing agent and MMA as a model monomer, is reported. The polymerizations can be carried out in the absence or presence of a limited amount of air and show the features of a “living”/controlled radical polymerization. MMA conversions of 90.3 and 80.0% can be obtained in 3.5 and 4.0 h in the absence/presence of a limited amount of air, respectively, for the iron‐mediated AGET ATRP with a molar ratio of [MMA]₀/[EBiB]₀/[FeCl₃ · 6H₂O]₀/[PPh₃]₀/[Fe(0)]₀ = 600:1:0.5:2:0.1 at 90 °C. PMMA with molecular weights of 55 060 and 47 790 g · mol^?1 and with molar‐mass dispersity of 1.24 and 1.28, respectively, can be obtained correspondingly.

     

Combining ATRP of Methacrylates and ROP of L,L‐Dilactide and ε‐Caprolactone

Coupling atom transfer radical polymerization (ATRP) and coordination‐insertion ring‐opening polymerization (ROP) provided a controlled two‐step access to polymethacrylate‐graft‐polyaliphatic ester graft copolymers. In the first step, copolymerization of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) was carried out at 80 °C at high MMA concentration by using ethyl 2‐bromoisobutyrate and [NiBr₂(PPh₃)₂] as initiator and catalyst, respectively. Kinetic and molar masses measurements, as well as ¹H NMR spectra analysis of the resulting poly(MMA‐co‐HEMA)s highlighted the controlled character of the radical copolymerization, while the determination of the reactivity ratios attested preferential incorporation of HEMA. The second step consisted of the ROP of ε‐caprolactone or L ,L ‐dilactide, in THF at 80 °C, promoted by tin octoate (Sn(Oct)₂) and coinitiated by poly(MMA‐co‐HEMA)s obtained in the first step. Once again, kinetic, molar mass, and ¹H NMR data demonstrated that the copolymerization was under control and started on the hydroxyl functions available on the poly(MMA‐co‐HEMA) multifunctional macroinitiator.

Comparison of the SEC traces for the poly(MMA‐co‐HEMA) macroinitiator P2 (line only), the polymethacrylate‐g‐PLA copolymer C2 (line marked by ○), and the polymethacrylate‐g‐PLA C3 (line marked by ?).     

Reverse Atom Transfer Radical Polymerization of Methyl Methacrylate using a New Catalyst,Copper(II) N,N′‐Butyldithiocarbamate

Summary: The homogeneous bulk reverse ATRP using AIBN/Cu(SC(S)N(C₄H₉)₂)₂/bpy as the initiating system has been successfully carried out for methyl methacrylate. Well‐controlled polymerizations with low polydispersities ( = 1.10–1.30) have been achieved. The revised number‐average molecular weights ( 's) increased linearly with monomer conversion and were close to the values. The polymerization rate followed the first‐order kinetics in monomer, while it is about 2.0 order in initiator concentration and 1.15 order in Cu(II) concentration. The k values for the homogeneous bulk reverse ATRP of MMA initiated by AIBN/Cu(SC(S)N(C₄H₉)₂)₂/bpy (1:2:6) at 80, 90, 100 and 110 °C were 0.402 × 10^?4, 1.021 × 10^?4, 2.952 × 10^?4, and 3.687 × 10^?4 (s^?1), respectively. On the basis of the Arrhenius plot, the apparent activation energy was calculated to be ΔE = 87.1 kJ/mol. The obtained PMMA was functionalized with an ultraviolet light sensitive ω‐SC(S)N(C₄H₉)₂ group characterized by means of ¹H NMR spectroscopy, and which was also proved by its chain extension with fresh MMA under UV‐light irradiation at room temperature. A polymerization mechanism for this novel initiation system is proposed.

Dependence of and on the monomer conversion for the homogeneous bulk reverse ATRP of MMA at different concentration of catalyst.     

Nitroxide‐Mediated Radical Polymerization of N‐tert‐Butylacrylamide

The nitroxide‐mediated polymerization of N‐tert‐butylacrylamide (TBAM) in DMF at 120 °C using SG1/DEPN and AIBN has been investigated. Linear growth in number‐average molecular weight ( ) versus conversion and narrow molecular weight distributions (MWDs) with high livingness were obtained up to ≈8 000 g · mol^?1. For higher molecular weights, the MWDs gradually became broader with low molecular weight tailing, and deviated downwards from theoretical values. Quantitative analyses of MWDs, along with specifically designed conventional radical polymerizations at 120 °C, were consistent with chain transfer to monomer limiting the attainable . This finding can be equally applied to existing literature polymerizations of TBAM.

     

Control of the radical polymerization by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl and its sodium salt

The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.

M _n vs. conversion for 3 , 3Na , and TEMPO.     

Nitroxide‐Mediated Polymerization of Methyl Methacrylate Using an SG1‐Based Alkoxyamine: How the Penultimate Effect Could Lead to Uncontrolled and Unliving Polymerization

Summary: The nitroxide‐mediated polymerization (NMP) of MMA initiated with a new crowded SG1‐based alkoxyamine was performed. Contrary to the results expected after a kinetic analysis (Fischer's diagram), the polymerization of MMA at 45 °C with SG1 showed only partial control and livingness during the first 15% of conversion. Simulations using PREDICI highlighted that the kinetic rate constants currently in use had not been correctly estimated and that a strong penultimate effect drastically increased the equilibrium constant K (7 × 10⁻⁷), preventing a well‐controlled polymerization. Experimental determination of the k_c value (1.4 × 10⁴ L · mol⁻¹ · s⁻¹) confirmed a strong penultimate effect on the recombination reaction, whereas for the dissociation reaction this effect is lower (k_d = 10⁻² · s⁻¹).

Nitroxide‐mediated polymerization of MMA at 45 °C initiated with a new crowded SG1‐based alkoxyamine.     

Controlled Radical Polymerization of Vaporized Vinyl Monomers on Solid Surfaces under UV Irradiation

Summary: In order to prepare well‐defined polymers on solid surfaces in the gas phase, a gas phase‐assisted surface polymerization (GASP) of vinyl monomers was carried out on solid surfaces pre‐coated with a photoiniferter, 2‐cyanoprop‐2‐yl N,N′‐dimethyldithiocarbamate, under UV irradiation. The GASP of methyl methacrylate (MMA) resulted in the formation of polymer on the surfaces and showed a proportional relationship between and polymer yield. Consecutive copolymerization of MMA and styrene led to the formation of a block copolymer, which was confirmed by a selective solvent fractionation method. These results demonstrate that controlled radical polymerization of vaporized monomer occurred on the solid surfaces.

Expected mechanism of GASP under UV irradiation.     

Well‐Defined Miktocycle Eight‐Shaped Copolymers Composed of Polystyrene and Poly(ε‐caprolactone): Synthesis and Characterization

A series of well‐defined miktocycle number‐eight‐shaped copolymers composed of cyclic polystyrene (PS) and cyclic poly(ε‐caprolactone) (PCL) have been successfully synthesized by a combination of atom transfer radical polymerization (ATRP), ring‐opening polymerization (ROP), and “click” reaction. The synthesis involves three steps: 1) preparation of tetrafunctional initiator with two acetylene groups, one hydroxyl group and a bromo group; 2) preparation of two azide‐terminated block copolymers, N₃‐PCL‐(CH?C)₂‐PS‐N₃, with two acetylene groups anchored at the junction; and 3) intramolecular cyclization of the block copolymer through “click” reaction under high dilution. The ¹H NMR, FT‐IR, and gel permeation chromatography (GPC) techniques are applied to characterize the chemical structures of the resulting intermediates and the target polymers. Their thermal behavior is investigated by differential scanning calorimeter (DSC). The decrease in chain mobility of eight‐shaped copolymers restricts the crystallization of PCL.

     

Accessing Chain Length Dependent Termination Rate Coefficients of Methyl Methacrylate (MMA) via the Reversible Addition Fragmentation Chain Transfer (RAFT) Process

Summary: The RAFT‐CLD‐T methodology is demonstrated to be not only applicable to 1‐substituted monomers such as styrene and acrylates, but also to 1,1‐disubstituted monomers such as MMA. The chain length of the terminating macromolecules is controlled by CPDB in MMA bulk free radical polymerization at 80 °C. The evolution of the chain length dependent termination rate coefficient, k, was constructed in a step‐wise fashion, since the MMA/CPDB system displays hybrid behavior (between conventional and living free radical polymerization) resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The obtained CLD of k_t in MMA polymerizations is compatible with the composite model for chain length dependent termination. For the initial chain‐length regime, up to a degree of polymerization of 100, k_t decreases with α (in the expression k = k · i^−α) being close to 0.65 at 80 °C. At chain lengths exceeding 100, the decrease is less pronounced (affording an α of 0.15 at 80 °C). However, the data are best represented by a continuously decreasing non‐linear functionality implying a chain length dependent α.

     

Combination of Mechanochemical Degradation of Polymers with Controlled Free‐Radical Polymerization

The result of ultrasound on polymer solutions is the breakage of macromolecular C C‐bonds due to cavitation. The fact that termination reactions of mechanoradicals as disproportionation and combination are suppressed in the presence of radical scavengers makes the following method possible. Thus the use of nitroxides acting as chain‐terminating agents allows the creation of macroinitiators which can be used in controlled free‐radical polymerization. In this work, we investigate the mechanochemical degradation of poly(methyl methacrylate) (PMMA) in the presence of OH‐TEMPO and the application of the irradiated polymers as macroinitiators in a controlled radical polymerization. The content of OH‐TEMPO terminated chains in the degraded product is determined by a computer‐aided procedure on the basis of molecular weight distributions.

Ultrasonic degradation of PMMA, decrease of molar mass (M _n), and polydispersity (Pd) as a function of irradiation time, power output = 200 W, ϑ = 45–50 °C.     

Synthesis of Well‐Defined Poly(methyl methacrylate) by a Normal Atom‐Transfer Radical Polymerization Procedure with a New Catalyst,Cuprous N,N‐Diethyldithiocarbamate

Cuprous N,N‐Diethyldithiocarbamate, Cu(S₂CNEt₂), was successfully used as a catalyst in p‐toluenesulfonyl chloride initiating atom‐transfer radical polymerization of methyl methacrylate in both bulk and solution in a heterogeneous system with 2,2′‐bipyridine as the ligand. The polymerization was controlled under various concentration ratios of the monomer to initiator, the molecular weight matched the predetermined value, and the molecular weight distribution of resulting polymers was quite low (M _w/M _n < 1.10). Solvents with different polarity had no significant effect on the living nature of this process. Well‐defined poly(methyl methacrylate) with α‐p‐toluenesulfonyl and ω‐diethylthiocarbamoylthiyl group was obtained. That the polymer chain was capped with an ultraviolet light sensitive group was confirmed by chain extension reactions.

Dependence of M _n and M _w/M _n on the monomer conversion of bulk polymerization of MMA at 80 °C with p‐TsCl/Cu(S₂CNEt₂)/bpy initiation system. Conditions the same as in Figure 5 .     

A Novel Approach for Investigation of Chain Transfer Events by Pulsed Laser Polymerization

Pulsed laser polymerization (PLP) with subsequent analysis of molecular mass distribution (MMD) is used to determine the rate coefficient of chain transfer to an agent A, k_trA, by varying pulse repetition rate such that the contributions of PLP‐induced and chain‐transfer‐induced peaks to the MMD change to a significant extent. It is shown by simulation that the relative heights of these peaks may be used to estimate k_trA. The method is applied to evaluation of the rate coefficient of chain transfer to dodecyl mercaptan with butyl methacrylate polymerizations at ?11, 0, 20 and 40 °C. The Arrhenius parameters for this coefficient are determined to be: A(k_trA) = (2.2 ± 0.6) × 10⁶ L · mol^?1 · s^?1 and E_a(k_trA) = (22.1 ± 0.7) kJ · mol^?1.

     

Kinetics of Dithiobenzoate‐Mediated Methyl Methacrylate Polymerization

The equilibrium constant, K_eq, of the reversible addition–fragmentation chain transfer (RAFT) model system methyl methacryl dithiobenzoate (MMADB) and of methyl methacrylate (MMA) polymerization mediated by MMADB is studied via electron paramagnetic resonance (EPR) spectroscopy in the range 70 to 110 °C and at ?40 °C, respectively. The measured difference in activation energy of the addition and fragmentation steps is: E_a(k_ad) – E_a(k_frag) ≈ ?36.6 kJ mol^?1. Significant amounts of “missing step” products from reaction of the cross‐termination product with a methyl methacrylyl radical are found. The fast “missing step” reaction and low K_eq, due to slow k_ad, are responsible for rate retardation being absent in dithiobenzoate‐mediated MMA polymerization.

     

Catalytic Chain Transfer Copolymerization of Methyl Methacrylate and Butyl Acrylate

In this work it is shown that catalytic chain transfer is a very efficient way of controlling molecular weight in the copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA). The experimental data are compared to a previously developed model based on copolymerization kinetics and the mechanisms for catalytic chain transfer and for cobalt‐mediated living radical polymerization that can describe the observed transfer constants. Secondly, it is shown that the presence of a catalytic chain transfer agent does not affect the reactivity ratios within the concentration range studied. Finally, the effect of conversion and therewith composition drift on the catalytic chain transfer polymerization of MMA and BA is investigated and it is shown that under the conditions employed in the experiments a certain degree of macromer copolymerization is present at high partial conversions of MMA.

Evolution of MWD with conversion for the CCT copolymerization of MMA and BA in toluene at 60 °C, [AIBN] = 6 × 10^?3 mol · L^?1.     

Radical Polymerization of MMA Co‐initiated by 2‐Phenyloxazoline

The subject of this work is the study of a new type of radical polymerization that occurs at elevated temperatures (80–100 °C) in mixtures of acrylates or (meth)acrylates and imine baes (IBA polymerization). The radical character of this polymerization is proven by the determination of copolymerization ratios and the reaction kinetics. On the basis of these facts and the hypothesis that the vinyl monomer acts as a co‐initiator, calculations reveal the concentration of the initiating species to be very low (K_eq < 10^?6). Furthermore, the choice of the reaction medium plays a crucial role on reaction kinetics and the average molecular weight of the resulting polymer. In combination with computational methodologies on the initiation, the multistep nature of this reaction is indicated.

     

Gas‐Phase Assisted Surface Polymerization of Vinyl Monomers with Fe‐Based Initiating Systems

Summary: Gas‐phase assisted surface polymerization (GASP) of methyl methacrylate (MMA) and styrene (St) was investigated with Fe‐based radical initiating systems, FeCl₂/2,2′‐bipyridine (Bpy)/methyl α‐bromophenylacetate (MBPA), etc. GASP with these initiating systems proceeded to produce corresponding polymers on substrate surfaces. The resulting PMMA had very high PDI values, suggesting an uncontrolled reaction. In an attempt to control the GASP, polymerization with a simple initiating system, Fe(0)/MBPA, was examined on Fe(0)‐metal surfaces, resulting in significant polymerization activity to produce high‐molecular‐weight PMMA. The results of time‐course tests on GASP of MMA and St suggested that a change had taken place to produce physically controlled propagation sites on the Fe(0) powder surfaces.

GASP schemes with a simple initiating system Fe(0)/MBPA.     

Novel Fluorinated Hybrid Polymer by Radical Polyaddition of Bis(α‐trifluoromethyl‐β,β‐difluorovinyl) Terephthalate onto Dialkoxydialkylsilanes

To develop the radical polyaddition of bisperfluoroisopropenyl esters, the reactions of bis(α‐trifluoromethyl‐β,β‐difluorovinyl) terephthalate [CF₂?C(CF₃)OCOC₆H₄COOC(CF₃)?CF₂] (BFP) with dialkoxydialkylsilane were examined to prepare fluorinated hybrid polymers bearing dialkylsilyl groups in the main chain. Prior to polyaddition, the radical addition reaction of 2‐benzoyloxypentafluoropropene [CF₂?C(CF₃)OCOC₆H₅] (BPFP) has been investigated to afford the results that diethoxydimethylsilane (DEOMS) or dimethoxydimethylsilane with BPFP initiated by oxo radical are the best combination for the preparation of polymers. The mechanism of the addition reaction was proposed. Radical polyaddition of BFP with DEOMS initiated by benzoyl peroxide or di‐tert‐butyl peroxide has yielded polymers of up to molecular weight 1 × 10⁶ with rather broad molecular weight distribution. A mechanism for the polyaddition reaction is proposed based on the radical addition reaction between BPFP and DEOMS. The step‐growth polymerization is initiated by hydrogen abstraction of DEOMS to add a perfluoroisopropenyl group, followed by a 1,7‐shift of the radical in the intermediate. The relationship between addition reaction mechanism and polyaddition mechanism was also discussed.

     

Synthesis of Well‐Defined Hybrid Macromonomers of Poly(ethylene oxide) and Their Reactivity in Photoinitiated Polymerization

Summary: α,ω‐Hybrid (hetero‐telechelic) poly(ethylene oxide) (PEO) macromonomers carrying both cationic and radical or anionic polymerizable vinyl end groups were newly synthesized by the living anionic polymerization of ethylene oxide (EO) initiated with partially K‐alkoxidated vinylic alcohols such as the monovinyl ether of tetramethylene glycol or di(ethylene glycol) and p‐vinylbenzyl alcohol (VBA), followed by reaction with methacryloyl chloride (MAC). They possess a couple of α‐ and ω‐end groups that can polymerize concurrently or selectively by radical and/or cationic or anionic mechanism. The reactivity of the radical and cationic species formed upon photolysis of benzophenone and triphenylsulfonium tetrafluoroborate towards these end groups were studied by means of ¹H NMR analysis following the disappearance of the respective olefinic groups. Studies with macromomonomers and model compounds revealed that photoexcited benzophenone abstracts hydrogen atoms from the PEO backbone to form radicals without added hydrogen donors. In the case of the sulfonium salt, both radical and cationic species are formed, which react with the respective functional groups. It was also shown that vinyl ether moieties react more readily than the methacrylate in both radical and cationic processes.

The general synthetic strategy followed for the preparation of the hybrid PEO macromonomers studied here.