Determination of Propagation Rate Coefficients for Methyl and 2-Ethylhexyl Acrylate via High Frequency PLP−SEC under Consideration of the Impact of Chain Branching

Effect of side-group structure and temperature on chain transfer to polymer and branching in acrylate homopolymerizations

The paper reports studies of the effects of ester side-group size and structure on chain transfer to polymer (CTP) and mol% branches (%br) in the final polymers from monomer-starved semi-batch emulsion homopolymerizations of a series of alkyl acrylates with different numbers of ester OR side-group carbon atoms (NsgC) in the range 1–10. Although the high instantaneous conversions and high gel contents in the final polymers show that intermolecular CTP is significant, the kinetics have been analysed principally in terms of intramolecular CTP (intraCTP) because this is expected to be numerically the dominant CTP process. For linear OR side groups, there is a small, continuous increase in %br (from ~ 3.4 to ~ 5.0 mol%) as NsgC increases from 1 to 8, which arises predominantly from the acrylate molar mass (Macrylate) reducing the molar monomer concentration and from the small increase in rate coefficient for propagation (kp) as NsgC increases; no discernible effects of NsgC on the rate coefficient for intraCTP ($${k}_{\mathrm{trP}}^{\mathrm{intra}}$$ k trP intra ) are evident. For isomeric butyl acrylates, there is no measurable effect of isomer structure on %br (4.3–4.4 mol%), indicating that butyl groups are too small for changes in side-group bulkiness to influence $${k}_{\mathrm{trP}}^{\mathrm{intra}}$$ k trP intra and kp. A similar observation was made for n-hexyl acrylate (nHA) and 2-ethylbutyl acrylate (%br 4.7–4.8 mol%). However, cyclohexyl acrylate (cHA) gives a much higher %br (~ 7.2 mol%), which has been assigned to steric effects increasing $${k}_{\mathrm{trP}}^{\mathrm{intra}}$$ k trP intra because kp values for nHA and cHA are very similar. For OR side-groups with NsgC of 8 and10, there is a strong effect of side-group non-linearity (2-ethylhexyl, iso-octyl and iso-decyl) increasing %br, with polymers from n-alkyl acrylates having much lower %br (~ 4.5–5.0 mol%) than those from the equivalent non-linear acrylates (~ 6.7–7.1 mol%); since the kp values are expected to be similar for these acrylates, it is evident that the much bulkier non-linear OR groups cause a significant increase in $${k}_{\mathrm{trP}}^{\mathrm{intra}}$$ k trP intra compared to the linear equivalents. Tentative hypotheses for these steric effects have been postulated. Studies of the effect of temperature (0–80 °C) on CTP and %br for methyl acrylate solution homopolymerization (in which intraCTP should be completely dominant) show the expected reduction in %br as temperature reduces, such that CTP is negligible at 0 °C; Arrhenius analysis gives an activation energy of 40.7 kJ mol−1 for intraCTP, which is within the range of values reported for n-butyl acrylate.

Chain-Length Dependence of Propagation Rate Coefficient for Methyl Acrylate Polymerization at 25 °C Investigated by PLP-SEC Method

When applying the pulsed laser polymerization–size exclusion chromatography (PLP-SEC) method to determine the propagation rate coefficient (kp) for bulk methyl acrylate at 25 °C, the characteristic ratio L1/L2 of chain...

Pulsed Laser Polymerization – Size Exclusion Chromatography Investigations into Backbiting in Ethylhexyl Acrylate Polymerization

Free radical acrylate polymerization is associated with a considerable number of side reactions occurring during chain growth. Most notably, the secondary chain propagating radicals can undergo intramolecular transfer reactions, forming...

Update and Critical Reanalysis of IUPAC Benchmark Propagation Rate Coefficient Data

We present an updated and expanded dataset of benchmark propagation rate coefficient (kp) data obtained from pulsed laser polymerization (PLP) of 13 vinyl monomers (styrene, methyl methacrylate, ethyl methacrylate, butyl...

A machine-readable online database for rate coefficients in radical polymerization

An online database created and curated by an IUPAC subcommittee is introduced.

On the Recovery of PLP-Molar Mass Distribution at High Laser Frequencies: A Simulation Study

Due to the inherent difficulties in determination of the degree of branching for polymers produced in pulsed laser polymerization (PLP) experiments, the behavior of the degree of branching and backbiting reaction in high laser frequency and relatively high reaction temperatures have not been well-established. Herein, through a simulation study, the validity of different explanations on the recovery of PLP-molar mass distribution at high laser frequencies is discussed. It is shown that the reduction of the backbiting reaction rate at high laser frequency, and consequent decrease in the degree of branching, is not a necessary condition for recovering the PLP-molar mass distribution. The findings of this work provide simulation support to a previous explanation about the possibility of using high laser frequency for reliable determination of the propagation rate coefficient for acrylic monomers.

Modeling of the Free Radical Copolymerization Kinetics of n-Butyl Acrylate, Methyl Methacrylate and 2-Ethylhexyl Acrylate Using PREDICI®

Kinetic modeling of the bulk free radical copolymerizations of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (EHA); methyl methacrylate (MMA) and EHA; as well as BA, MMA and EHA was performed using the software PREDICI®. Predicted results of conversion versus time, composition versus conversion, and molecular weight development are compared against experimental data at different feed compositions. Diffusion-controlled effects and backbiting for BA were incorporated into the model as they proved to be significant in these polymerizations. The set of estimated global parameters allows one to assess the performance of these copolymerization systems over a wide range of monomer compositions.

Propagation rate coefficient for acrylic acid polymerization in bulk and in propionic acid by the PLP–SEC method: experiment and 3D simulation

The k_p values for acrylic acid polymerization in bulk and in propionic acid are found to depend on the number of laser pulses used in PLP experiment and decrease from bulk value upon dilution with propionic acid.

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.

Separation and Characterization of Synthetic Polyelectrolytes and Polysaccharides with Capillary Electrophoresis

The development of macromolecular engineering and the need for renewable and sustainable polymer sources make polymeric materials progressively more sophisticated but also increasingly complex to characterize. Size-exclusion chromatography (SEC or GPC) has a monopoly in the separation and characterization of polymers, but it faces a number of proven, though regularly ignored, limitations for the characterization of a number of complex samples such as polyelectrolytes and polysaccharides. Free solution capillary electrophoresis (CE), or capillary zone electrophoresis, allows usually more robust separations than SEC due to the absence of a stationary phase. It is, for example, not necessary to filter the samples for analysis with CE. CE is mostly limited to polymers that are charged or can be charged, but in the case of polyelectrolytes it has similarities with liquid chromatography in the critical conditions: it does not separate a charged homopolymer by molar mass. It can thus characterize the topology of a branched polymer, such as poly(acrylic acid), or the purity or composition of copolymers, either natural ones such as pectin, chitosan, and gellan gum or synthetic ones.

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.

In the (Very) Long Run We Are All Dead: Activation and Termination in SET-LRP/SARA-ATRP

The rate constants of activation and termination were determined for SET-LRP/SARA-ATRP polymerizations of methyl acrylate. Measurement of the rate of generation of CuBr₂ throughout the reaction (using data from Levere et al., Macromolecules 2012, 45, 8267-8274) allowed evaluation of the chain length dependence of the two rate constants, which were found to be 1.25(9) × 10^-4DP_n^-0.51(3) cm·s^-1 (activation) and 3.1(1) × 10⁹DP_n^-0.49(2) L·mol^-1·s^-1 (termination). Addition of the CuBr₂ deactivator at the beginning of the reaction is found to result in a higher proportion of dead chains due to rapid termination of short chains.

Critically evaluated rate coefficients in radical polymerization – 7. Secondary-radical propagation rate coefficients for methyl acrylate in the bulk

Benchmark propagation rate coefficient (k_p) data for the radical polymerization of methyl acrylate are provided.

Size-exclusion-chromatography separation of randomly branched polymers with tetrafunctional branch points and local dispersity

The SEC separation of a randomly branched polymer, in particular local dispersity due to branching, are theoretically examined. A model of the SEC separation of randomly branched polymer with tetrafunctional branch points enabling the estimation of local dispersity was developed. Measurable quantities (branching indices) were compared with real data. Local dispersity due to branching is demonstrated to depend on elution volume and degree of branching and in the area of the beginning of the elution curve it can reach non-negligible values.