Pulsed Laser Polymerization Size Exclusion Chromatography Research Articles

Free‐radical propagation rate coefficients

AbstractThe pulsed laser polymerization‐size‐exclusion chromatography (PLP‐SEC) technique has become the International Union of Pure and Applied Chemistry (IUPAC)‐recommended method for the accurate determination of propagation rate coefficients, kp, for radical polymerization. The fundamental insight provided by Heuts, Gilbert, and Radom into the relevance of transition state dynamics allows for an adequate understanding of the dependence of kp on radical chain length, solvent environment, and monomer conversion. The associated entropic effects are particularly pronounced in aqueous solution, but are also found in less polar media and with non‐polar monomers. Moreover, these arguments are applicable towards the interpretation of copolymerization reactivity ratios. The addition of sodium hydroxide to aqueous solutions of (meth)acrylic acid yields partially and even fully ionized systems with clearly reduced kp, which indicates the action of repulsive forces between the equally charged monomer and radical species. Increasing the concentration of monomer as well as the addition of salts may reverse this effect and increase kp due to counterion activity.

Pulsed laser polymerization–size exclusion chromatography investigations into backbiting in ethylhexyl acrylate polymerization

Rate coefficients for secondary radical propagation, backbiting and tertiary radical monomer addition for ethylhexyl acrylate have been determined.

RAFT Polymerization of Tert-Butyldimethylsilyl Methacrylate: Kinetic Study and Determination of Rate Coefficients.

Well-defined poly(tert-butyldimethylsilyl methacrylate)s (TBDMSMA) were prepared by the reversible addition-fragmentation chain transfer (RAFT) process using cyanoisopropyl dithiobenzoate (CPDB) as chain-transfer agents (CTA). The experimentally obtained molecular weight distributions are narrow and shift linearly with monomer conversion. Propagation rate coefficients (kp) and termination rate coefficients (kt) for free radical polymerization of TBDMSMA have been determined for a range of temperature between 50 and 80 °C using the pulsed laser polymerization-size-exclusion chromatography (PLP-SEC) method and the kinetic method via steady-state rate measurement, respectively. The CPDB-mediated RAFT polymerization of TBDMSMA has been subjected to a combined experimental and PREDICI modeling study at 70 °C. The rate coefficient for the addition reaction to RAFT agent (kβ1, kβ2) and to polymeric RAFT agent (kβ) is estimated to be approximately 1.8 × 104 L·mol−1·s−1 and for the fragmentation reaction of intermediate RAFT radicals in the pre-equilibrium (k-β1, k-β2) and main equilibrium (k-β) is close to 2.0 × 10−2 s−1. The transfer rate coefficient (ktr) to cyanoisopropyl dithiobenzoate is found to be close to 9.0 × 103 L·mol−1·s−1 and the chain-transfer constant (Ctr) for CPDB-mediated RAFT polymerization of TBDMSMA is about 9.3.

Free Radical Propagation Rate Coefficients of N-Containing Methacrylates: Are We Family?

Nitrogen-containing methacrylates are a highly interesting class of monomers, yet only very limited data exist describing their propagation rate coefficients, k(p). Herein, we investigate the propagation behavior of three N-containing monomers, namely 2-(N,N-diethylamino)-ethyl methacrylate (DEAEMA), 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA), and 3-(N,N-dimethylamino)propyl methacrylate (DMAPMAE), where we systematically vary the ester side chain with respect to spacer and branching length with the aim of establishing if all so far investigated N-containing methacrylates display family type behavior with regard to k(p). Thus, the Mark-Houwink-Kuhn-Sakurada parameters alongside the Arrhenius parameters of k(p) were determined for these monomers via triple detection SEC and pulsed laser polymerization-size exclusion chromatography (PLP-SEC). The obtained data result in Arrhenius parameters for DEAEMA of A = 2.07 (-0.79 to +3.98) X 10(6) L mol(-1) s(-1) and E-A = 20.45 (-2.02 to +2.28) kJ mol(-1), for DMAEMA of A = 2.64 (-0.79 to +1.98) X 10(6) L mol(-1) s(-1) and E-A = 20.71 (-1.31 to +1.32) kJ mol(-1), and for DMAPMAE of A = 1.22 (-0.54 to +8.02) x 10(6) L mol(-1) s(-1) and E-A = 19.59 (-2.74 to +3.83) kJ mol(-1). The data of the herein investigated monomers are critically compared to the previously published data of 2-(N-ethylanilino)ethyl methacrylate (NEAEMA), 2-(1-piperidyl)ethyl methacrylate (PipEMA), and 2-morpholinoethyl methacrylate (MOMA). It is found that DEAEMA and the previously investigated monomers can be described by one family, leading to a joint Arrhenius description for the four monomers NEAEMA, MOMA, PipEMA, and DEAEMA, best described by A = 1.55 (-0.57 to +3.88) X 10(6) L mol(-1) s(-1) and E-A = 19.68 (-1.76 to +2.60) kJ mol(-1).

Kilohertz Pulsed-Laser-Polymerization: Simultaneous Determination of Backbiting, Secondary, and Tertiary Radical Propagation Rate Coefficients for tert-Butyl Acrylate.

For the first time, a 1000 Hz pulse laser has been applied to determine detailed kinetic rate coefficients from pulsed laser polymerization-size exclusion chromatography experiments. For the monomer tert-butyl acrylate, apparent propagation rate coefficients kp (app) have been determined in the temperature range of 0-80 °C. kp (app) in the range of few hundreds to close to 50 000 L·mol(-1) ·s(-1) are determined for low and high pulse frequencies, respectively. The apparent propagation coefficients show a distinct pulse-frequency dependency, which follows an S-shape curve. From these curves, rate coefficients for secondary radial propagation (kp (SPR) ), backbiting (kbb ), midchain radical propagation (kp (tert) ), and the (residual) effective propagation rate (kp (eff) ) can be deduced via a herein proposed simple Predici fitting procedure. For kp (SPR) , the activation energy is determined to be (17.9 ± 0.6) kJ·mol(-1) in excellent agreement with literature data. For kbb , an activation energy of (25.9 ± 2.2) kJ·mol(-1) is deduced.

Investigating the propagation kinetics of a novel class of nitrogen-containing methacrylates via PLP-SEC

The Mark–Houwink–Kuhn–Sakurada parameters as well as Arrhenius parameters of the propagation rate coefficient for a new group of nitrogen-containing methacrylates were determined via triple detector SEC and pulsed laser polymerization–size exclusion chromatography, respectively.

Determining Free‐Radical Propagation Rate Coefficients with High‐Frequency Lasers: Current Status and Future Perspectives

Detailed knowledge of the polymerization mechanisms and kinetics of academically and industrially relevant monomers is mandatory for the precision synthesis of tailor-made polymers. The IUPAC-recommended pulsed-laser polymerization-size exclusion chromatography (PLP-SEC) approach is the method of choice for the determination of propagation rate coefficients and the associated Arrhenius parameters for free radical polymerization processes. With regard to specific monomer classes-such as acrylate-type monomers, which are very important from a materials point of view-high laser frequencies of up to 500 Hz are mandatory to prevent the formation of mid-chain radicals and the occurrence of chain-breaking events by chain transfer, if industrially relevant temperatures are to be reached and wide temperature ranges are to be explored (up to 70 °C). Herein the progress and state-of-the-art of high-frequency PLP-SEC with pulse repetition rates of 500 Hz is reported, with a critical collection of to-date investigated 500 Hz data as well as future perspectives for the field.

No Apparent Correlation of kp with Steric Hindrance for Branched Acrylates

The Arrhenius parameters of the propagation rate coefficient, kp, are determined via the pulsed laser polymerization—size exclusion chromatography (PLP‐SEC) method for five branched acrylates (tert‐butyl (tBA), isobornyl (iBoA), benzyl (BnA), 2‐ethylhexyl (EHA), and 2‐propylheptyl acrylate (PHA)) in 1 m solution in butyl acetate (BuAc) to complete the series, published by Haehnel et al. in 2014, of branched acrylates (isononyl (INA‐A), tridecyl (TDA‐A and TDN‐A), heptadecyl (C17A), and henicosyl acrylate (C21A)) in solution that do not show a trend in kp. Furthermore, the propagation rate coefficients of the branched acrylates in 1 m solution are critically compared with the branched acrylates in bulk as well as branched methacrylates. A summary of the trends and family‐type behavior for the linear and branched (meth)acrylates as well as methacrylates with cyclic ester side chains is provided. For the branched acrylates in 1 m solution, no clear trends of the propagation rate coefficients, kp, or Arrhenius parameters A and EA are detectable and—in contrast to the corresponding methacrylates—there is no family‐type behavior observed in solution as well as in bulk.image

Solvent effects on acrylate kp in organic media?-A systematic PLP-SEC study.

The Arrhenius parameters of the propagation rate coefficient, kp , are determined employing high-frequency pulsed laser polymerization-size exclusion chromatography (PLP-SEC) for the homologous series of five linear alkyl acrylates (i.e., methyl acrylate (MA), butyl acrylate (BA), dodecyl acrylate (DA), stearyl acrylate (SA), and behenyl acrylate (BeA)) in 1 m solution in butyl acetate (BuAc) as well as in toluene. The comparison of the obtained kp values with the literature known values for bulk demonstrates that no significant solvent influence neither in BuAc nor in toluene on the propagation reaction compared to bulk is detectable. Concomitantly, the kp values in toluene and in BuAc solution display a similar increase with increasing number of C-atoms in the ester side chain as was previously reported for the bulk systems. These findings are in clear contrast to earlier studies, which report a decrease of kp with increasing ester side chain length in toluene. The additional investigation of the longest and shortest ester side chain acrylate (i.e., BeA and MA) over the entire experimentally available concentration range at one temperature (i.e., 50 °C) does not reveal any general concentration dependence and all observed differences in the kp are within the experimental error.

Determination of Propagation Rate Coefficient for the Polymerization of N-Vinylpyrrolidone in Aqueous Solution by Pulsed Electron Polymerization and Size Exclusion Chromatography

A new method for determination of a propagation rate coefficient in radical polymerization, pulsed electron polymerization-size exclusion chromatography (PEP-SEC), has been tested on N-vinylpyrrolidone in water and shown to yield results very similar to those obtained by the well-established pulsed laser polymerization-size exclusion chromatography (PLP-SEC). A potential advantage of PEP-SEC is its applicability to studying polymerizations in nontransparent systems and lack of any additives. Series of nanosecond pulses of high-energy electrons from an accelerator generate radicals which initiate polymerization. Further analysis of the samples and data processing are the same as in PLP-SEC. The described technique can be potentially developed into a method complementary and/or comparative to PLP-SEC.

Global Trends for kp? The Influence of Ester Side Chain Topography in Alkyl (Meth)Acrylates − Completing the Data Base

The Arrhenius parameters of the propagation rate coefficient, kp, are determined via the IUPAC recommended pulsed laser polymerization–size exclusion chromatography (PLP-SEC) method for two linear alkyl acrylates (stearyl and behenyl acrylate), four branched alkyl acrylates (isononyl (INA-A), tridecyl (TDN-A and TDA-A), and henicosyl acrylate (C21A)), and two branched alkyl methacrylates (tridecyl methacrylates (TDN-MA and TDA-MA)) in bulk. Furthermore, the above stated acrylates and heptadecyl acrylate (C17A) were studied in 1 M solution in butyl acetate (BuAc). On the basis of such a wide data basis in combination with the already literature known data of relatives of the herein investigated monomers, we are able to identify and extend global trends and family type behavior for the propagation rate coefficients of a wide array of alkyl (meth)acrylates. In order to ensure a valid SEC evaluation, the polymer specific Mark–Houwnik–Kuhn–Sakurada (MHKS) parameters are determined for each of the polymers, via multidetector SEC analysis (multi angle laser light scattering (MALLS) in combination with differential viscosimetry (Visco) and refractive index (RI)) of narrowly distributed polymer samples obtained via fraction with a preparative SEC column. By employing further physicochemical polymer specific data (e.g., glass transition temperatures (Tg)), we provide a hypothesis for the reported trends and family type behaviors: (i) the steady increase of kp with increasing ester side chain length for linear alkyl (meth)acrylates may be explained by a decreasing concentration of the polar ester moieties, resulting in a decreasing stabilization of the attacking radical in the transition state of the propagation reaction, and (ii) the family type behavior of the branched alkyl methacrylates can be understood by considering steric and entropic influences. For the branched alkyl acrylates, no clear trend is detectable, and a family type behavior is clearly not observed in contrast to the corresponding methacrylates.

(Meth)acrylic monomers with heteroatom-containing ester side chains: a systematic PLP-SEC and polymerization study

The Arrhenius parameters of the propagation rate coefficient for two hetero-atom containing (meth)-acrylates (studied as 1 M solution in N,N-dimethylacetamide (DMAc)) are determined via the pulsed laser polymerization – size-exclusion chromatography (PLP-SEC) method. Absolute molar mass determination is achieved via SEC coupled to on-line multi-angle laser light scattering (MALLS). The data obtained for hydroxypropylcarbamate acrylate (HPCA, A = 3.97 (−1.44 to 1.63) × 106 L mol−1 s−1 and Ea = 14.3 (−1.38 to 5.13) kJ mol−1) are critically compared with the literature known data sets of two structural derivatives, i.e., 2-(phenylcarbamoyloxy)isopropyl acrylate (PhCPA) and 2-(hexylcarbamoyloxy)isopropyl acrylate (HCPA), indicating an increase in the propagation rate coefficient with increasing ester side chain length. Ureidoethyl methacrylate (UMA, A = 2.08 (−0.45 to 0.91) × 106 L mol−1 s−1 and Ea = 19.9 (−0.89 to 0.91) kJ mol−1) represents the first hetero-atom containing methacrylate to be studied via PLP-SEC, evidencing a significantly higher propagation rate coefficient compared to earlier investigated methacrylate-type monomers. Furthermore, the free-radical polymerization behavior of HPCA and UMA is studied via in situ1H-NMR experiments at elevated temperatures allowing for an estimation of average termination rate coefficients (at low conversion) in conjunction with the determined kp data. Furthermore, the polymerization of UMA was successfully controlled by reversible addition–fragmentation chain transfer (RAFT) polymerization as evidenced by the linear evolution of the number-average molar mass, Mn, with conversion (3000 g mol−1 ≤ Mn ≤ 23 000 g mol−1, 1.15 ≤ Đ ≤ 1.3) as well as by nitroxide-mediated polymerization (NMP), as demonstrated by the linear evolution of Mn with conversion (4000 g mol−1 ≤ Mn ≤ 40 000 g mol−1, 1.3 ≤ Đ ≤ 1.4). In addition, HPCA polymerization was successfully controlled by the RAFT process, as evidenced by the linear evolution of Mn with conversion (2000 g mol−1 ≤ Mn ≤ 21 000 g mol−1, 1.2 ≤ Đ ≤ 1.4) and successful chain extension experiments. Finally, the NMP of HPCA exhibited uniform shifts of the molar mass distributions in the range of 5000 g mol−1 ≤ Mn ≤ 70 000 g mol−1 and successful chain extension experiments.

Understanding the Controlled Polymerization of Methyl Methacrylate with Low Concentrations of 9-(4-Vinylbenzyl)-9H-carbazole Comonomer by Nitroxide-Mediated Polymerization: The Pivotal Role of Reactivity Ratios

Previously, nitroxide-mediated controlled copolymerization (NMP) of methyl methacrylate (MMA) using BlocBuilder unimolecular initiator was found to require much less controlling comonomer when using 9-(4-vinylbenzyl)-9H-carbazole (VBK) compared to styrene (S) as a comonomer (minimum ∼1 mol % VBK versus 4.4 mol % S). Here, we explored why this was the case. Initially, the use of dimethylformamide (DMF) solvent in the copolymerization of MMA/S was studied as the MMA/VBK copolymerizations were done in DMF. The results confirmed that the increased effectiveness of VBK as a controlling comonomer was not due to the solvent or other experimental conditions. Second, the propagation rate constant kP,VBK and various ⟨kP⟩MMA/VBK for MMA/VBK copolymerizations were determined using pulsed laser polymerization–size exclusion chromatography (PLP-SEC), and the dissociation rate constants kd,VBK for the VBK-BlocBuilder adduct and PVBK chains were determined using electron paramagnetic resonance (EPR) spectroscopy, showing...

Global Trends for kp? Expanding the Frontier of Ester Side Chain Topography in Acrylates and Methacrylates

The Arrhenius parameters of the propagation rate coefficient for two linear methacrylates, two branched methacrylates, and two branched acrylates are determined via the pulsed laser polymerization-size exclusion chromatography (PLP-SEC) method. The Mark-Houwink-Kuhn-Sakurada parameters of these polymers are additionally determined via multidetector SEC of narrowly distributed polymer samples obtained through fractionation, allowing for a correct SEC calibration in the PLP-SEC experiment. The data obtained for stearyl methacrylate (SMA, A = 3.45 (-1.17 to +4.46) × 106 L·mol-1·s-1; Ea = 21.49 (-1.59 to +1.90) kJ·mol-1) and behenyl methacrylate (BeMA, A = 2.51 (-0.80 to +3.06) × 106 L·mol-1·s -1; Ea = 20.52 (-1.43 to +1.85) kJ·mol -1) underpin the trend of increasing kp with increasing ester side chain length. Propylheptyl methacrylate (PHMA, A = 2.83 (-0.82 to 3.15) × 106 L·mol-1·s-1; Ea = 21.72 (-1.20 to +1.64) kJ·mol-1) and heptadecanyl methacrylate (C17MA, A = 2.04 (-0.66 to +1.71) × 10 6 L·mol-1·s-1; Ea = 20.72 (-1.42 to +1.38) kJ·mol-1) can be described as a family of branched methacrylates jointly with isodecyl methacrylate and ethylhexyl methacrylate (both published previously), resulting in joint Arrhenius parameters of A = 2.39 (-0.51 to +0.84) × 106 L·mol -1·s-1 and Ea = 21.16 (-0.78 to +0.76) kJ·mol-1. In addition, the corresponding branched acrylates are studied applying high-frequency PLP at a 500 Hz laser repetition rate, resulting in Arrhenius parameters of A = 1.05 (-0.42 to +2.81) × 10 7 L·mol-1·s-1 and Ea = 16.41 (-1.99 to +2.42) kJ·mol-1 for propylheptyl acrylate (PHA) and A = 8.15 (-2.83 to +10.3) × 106 L·mol -1·s-1 and Ea = 14.66 (-1.49 to +1.66) kJ·mol-1 for heptadecanyl acrylate (C17A). © 2012 American Chemical Society.

The Effect of Hydrogen Bonding on Intramolecular Chain Transfer in Polymerization of Acrylates

Propagation rate coefficients (k(p) ) for 2-hydroxyethyl acrylate (HEA) have been determined by pulsed-laser polymerization (PLP) combined with size-exclusion chromatography (SEC) between 20 and 60 °C using pulse repetition rates of 50 and 100 Hz. The success of PLP-SEC under these conditions suggests that HEA is not subjected to the intramolecular chain transfer to polymer (backbiting) reactions dominant for other acrylates; (13) C NMR analysis shows that the quaternary carbon observed in PLP-generated poly(butyl acrylate) (pBA) samples is not observed in pHEA. These results are related to H-bonding in the system, as it is shown that the introduction of H-bonding by addition of n-butanol to BA suppresses backbiting, and the disruption of H-bonding by addition of dimethylformamide to HEA leads to an increased level of backbiting.

Determination of the propagation rate coefficient of acrylonitrile

For the first time, accurate propagation rate coefficients for acrylonitrile are determined via the pulsed laser polymerization–size exclusion chromatography technique.

Transfer to Polymer and Long‐Chain Branching in PLP–SEC of Acrylates

Pulsed laser polymerization (PLP) combined with size exclusion chromatography (SEC) is the method of choice for determining propagation rate coefficients. The influence of the long-chain branching in PLP-SEC is investigated using multiple-detection SEC and a recently developed method to detect long-chain branching [P. Castignolles, R. Grab, M. Parkinson, M. Wilhelm, M. Gaborieau, Polymer 2009, 50, 2373.] While little or no long-chain branching is detected in poly(n-butyl acrylate), the error in relevant molecular weights of poly(2-ethylhexyl acrylate) is large (30-100%) due to long-chain branching. Possible variations of propagation rate coefficient with alkyl groups in alkyl acrylates or with the solvent have to be reconsidered.

Determination of vinyl acetate propagation rate coefficients via high frequency pulsed laser polymerization

AbstractNew data on the propagation rate coefficient, kp, of vinyl acetate (VAc) are obtained via the IUPAC recommended method of pulsed laser polymerization - size exclusion chromatography (PLP-SEC) operated at 500 Hz laser repetition rate. An apparent dependency of the experiment’s outcome on the laser pulsing rate is identified with kp being about 25 % larger at 500 Hz compared to 100 Hz. The temperature dependence of kp was determined to fit ln kp = 17.12 - 2621 K/T; data is in generally good agreement with literature values when the previous underestimation of kp by 100 Hz laser pulsing experiments is taken into account.

Surface‐Initiated PLP‐SEC of Butyl Acrylate and Styrene from Silica Nanoparticles

The pulsed-laser polymerization size-exclusion chromatography (PLP-SEC) technique has been successfully applied to the measurement of the propagation rate coefficient, k(p) , of the surface-initiated polymerizations of butyl acrylate (BA) and styrene, using the silica-immobilized bipedal initiator 4,4'-azobis(4-cyano-N-(3″-triethoxysilylpropyl)-valeric amide) (ACTA). The molecular weight distribution (MWD) of grafted poly(BA) polymerized at 25 °C was structureless, whereas at 5 °C reaction temperature, the MWD exhibited a typical PLP structure with two inflection points. In case of styrene the SEC trace obtained at 26 °C is well structured and shows four inflection points. The propagation rate coefficients k(p) of the surface-initiated polymerizations were about 22% higher in the case of BA and about 27-28% higher in the case of styrene compared to the IUPAC benchmark data.

Free-radical propagation and termination kinetics of the butyl acrylate dimer studied by pulsed laser polymerization techniques

The propagation and termination rate coefficients for bulk polymerization of the butyl acrylate dimer (BA dimer) are determined by pulsed laser techniques. The rate coefficient for propagation, kp, is deduced for temperatures from 20 to 90°C via the pulsed laser polymerization–size exclusion chromatography (PLP–SEC) method at pulse repetition rates between 1 and 10Hz. The Arrhenius parameters were found to be: EA(kp)=(34.2±1.0)kJmol−1 and A(kp)/Lmol−1s−1=(1.08±0.49)×107Lmol−1s−1. The termination rate coefficient, kt, has been measured via SP-PLP–ESR, single pulse-pulsed laser polymerization in conjunction with time-resolved electron spin resonance detection of radical concentration. The resulting Arrhenius parameters as deduced from the temperature range −15 to +30°C are: EA(〈kt〉)=(22.8±3.7)kJmol−1 and log(A/Lmol−1s−1)=10.6±1. The chain-length dependence of kt was studied at 30°C. For short chains a significant dependence was found which may be represented by an exponent α=0.79 in the power-law expression kt(i)=kt0i−α.