Marek Stach

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

Propagation rate coefficient (kp) data for radical polymerization of methyl acrylate (MA) in the bulk are critically evaluated and a benchmark dataset is put forward by a task-group of the IUPAC Subcommittee on Modeling of Polymerization Kinetics and Processes. This dataset comprises previously published results from three laboratories as well as new data from a fourth laboratory. Not only do all these values of kp fulfill the recommended consistency checks for reliability, they are also all in excellent agreement with each other. Data have been obtained employing the technique of pulsed-laser polymerization (PLP) coupled with molar-mass determination by size-exclusion chromatography (SEC), where PLP has been carried out at pulse-repetition rates of up to 500 Hz, enabling reliable kp to be obtained through to 60 °C. The best-fit – and therefore recommended – Arrhenius parameters are activation energy EA = 17.3 kJ mol−1 and pre-exponential (frequency) factor A = 1.41 × 107 L mol−1 s−1. These hold for secondary-radical propagation of MA, and may be used to calculate effective propagation rate coefficients for MA in situations where there is a significant population of mid-chain radicals resulting from backbiting, as will be the case at technically relevant temperatures. The benchmark dataset reveals that kp values for MA obtained using PLP in conjunction with MALDI-ToF mass spectrometry are accurate. They also confirm, through comparison with previously obtained benchmark kp values for n-butyl acrylate, methyl methacrylate and n-butyl methacrylate, that there seems to be identical family-type behavior in n-alkyl acrylates as in n-alkyl methacrylates. Specifically, kp for the n-butyl member of each family is about 20% higher than for the corresponding methyl member, an effect that appears to be entropic in origin. Furthermore, each family is characterized by an approximately constant EA, where the value is 5 kJ mol−1 lower for acrylates.

Thermal lag and its practical consequence in the dynamic mechanical analysis of polymers

The thermal lag associated with the temperature ramping experiment in a dynamic mechanical analysis is demonstrated on carbon black filled vulcanised rubber samples by using a DMTA MkIII from Rheometric Scientific. The importance of achieving thermal equilibrium on the sample before starting the measurement is emphasised. By running a combination of isothermal and ramping steps, the impact of thermal lag on the obtained dynamic mechanical properties can be estimated. For the measurement in tensile mode at a rate of heating of 2°C/min and vertical orientation of the driveshaft motion, the isothermal step applied at the sample glass transition temperature revealed that the temperature equilibration of the sample takes at least 15 min. Consequently, the storage modulus measured during the heating step is overestimated by around two times and the glass transition temperature is shifted to higher values. For the given chamber geometry, the bending mode of measurement exhibits a lower thermal lag than the tensile one. The experimental data indicate that the major factors responsible for thermal lag are heat transfer from the sample environment to the sample surface (which is given by the chamber design), sample position in the chamber and the mutual position of the sample and thermometer Pt-100. Based on the results presented, a recommendation for selecting the experimental conditions is given in order to recognise and minimise the effect of thermal lag on the data obtained by dynamic mechanical analysis.

Method for preparation of planar alginate hydrogels by external gelling using an aerosol of gelling solution.

Preparation of planar alginate hydrogels by external gelling requires slow rate of exposure of alginate solution to gelling ions to control gelling process and hydrogel properties. We tackled this issue by exposing solution of sodium alginate to solution of CaCl2 applied as aerosol at exposure rate of 7.5 mg cm(-2) s(-1). Gelling conditions varied with respect to concentrations of sodium alginate (1-3 wt.%) and CaCl2 (0.5-4 wt.%), exposure time (2.5-40 min), the 2nd gelling step in the presence of barium ions, and the storage step. Dimensional stability and Youngs modulus values were the principal determined quantities to examine the correlation between hydrogel properties and gelling protocol. The content of calcium ions in hydrogel after gelling by CaCl2 aerosol reveals that the maximum binding capacity of calcium ions by alginate chains was reached. Obtained data suggest that an unusual gelling mechanism related to exposure of sodium alginate to aerosol of gelling solution does not need to be considered since the properties of planar alginate hydrogels follow the trends relevant to general knowledge about alginate hydrogels.

(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.

Adhesion of acrylate-based water dispersion to polypropylene hybrid fabrics

The increase in the content of crosslinking agent and surfactant in acrylate-based water dispersion results in an increase of surface parameters e.g. total SFE and its polar component, interfacial and mechanical work of adhesion of polyacrylate to PP hybrid fabrics. UV irradiation of polyacrylate coating in the course of accelerating ageing has the same effect on surface and adhesive properties as a crosslinking agent or surfactant and leads to a considerable growth of the total SFE, its polar component, interfacial and mechanical work of adhesion. The increase in the interfacial and mechanical work of adhesion with the increase of the crosslinking agent and/or surfactant content in acrylate-based water dispersion is higher for PES/PP fabrics compared to the PA/PP system., The adhesive properties of the film obtained from acrylate-based water dispersion are substantially influenced by the presence of a surfactant and a crosslinking agent.