Jaromir Snuparek

New applications of catalytic chain transfer polymerization to waterborne binders for automotive paint systems

Abstract Catalytic chain transfer polymerization (CCTP) is a conventional free radical polymerization technique that allows the preparation of macromonomers in a one step process. Acid functional macromonomers can be copolymerized with acrylate backbone monomers to form graft copolymers that, after neutralization with a base, are water dispersible. Low molecular weight oligomers from CCTP act as chain transfer agents themselves for methacrylate monomers via addition–fragmentation mechanism and lead to (semi) AB-block copolymers. Group transfer polymerization (GTP) is another polymerization technique to make AB-block copolymers but economically less attractive for functional comonomers since they interfere with the initiation mechanism. Graft and AB-block copolymer dispersions offer advantages in waterborne coatings compared to linear polymers of the same overall composition and molecular weight. Examples discussed in this paper are pigment dispersants and dispersion resins in which the backbone or A-segment of the copolymer has specific groups to anchor to the pigment surface and the side chains or B-segment give both charge and steric stabilization. AB-block copolymers with one block water soluble or dispersible also function as copolymerizable surfactants in an emulsion polymerization process and allow the synthesis of surfactant-free emulsions with low amounts of hydrophilic groups. The catalytic chain transfer agents (CCTAs) used in CCTP do have a high chain transfer activity for methacrylate monomers at very low concentrations so that low molecular weight oligomers (e.g. dimers) can be made. This chain transfer activity is lost in an emulsion polymerization process if the CCTA is (partly) water soluble. The paper will further demonstrate the use of dimers in the control of molecular weight in emulsion copolymerization.

Hydroplasticization effect in structured latex particles film formation

Series of emulsion copolymers with structured particles were synthesized comprising copolymerized acrylic or methacrylic acid in the outer layer. All samples were based on particles, containing identical cores slightly crosslinked by allyl methacrylate and variable shells, weight ratio core/shell being constant 1/1. Each sample contained 10 wt% HEMA in the shell to achieve the film crosslinkability. In both series samples with different hardness and polarity (varible styrene/butyl acrylate ratio) of the shell layer were prepared. It was shown that the extent of particle swelling and hydroplasticization depends not only on the content of dissociated carboxylic groups, but also on the composition and crosslinking of the rest of polymer chain i.e. on its polarity and rigidity and on the origin of carboxylic groups. The effect of dissociated carboxylic groups on lowering the minimum film forming temperature was much more pronounced if the polymer chains were more polar.

Application of A4F-MALS for the Characterization of Polymers Prepared by Emulsion Polymerization: Comparison of the Molecular Structure of Styrene-Acrylate and Methyl Methacrylate-Acrylate Copolymers

ABSTRACT In this paper, organic asymmetric flow field flow fractionation coupled to a multi-angle light scattering detector is presented as a very efficient tool for the characterization of copolymers prepared by emulsion polymerization. The molar mass distribution and the extent of branching of styrene–acrylate copolymers have been compared with corresponding copolymers of methyl methacrylate. It has been found that the presence of acrylate monomer results in the increase of molar mass and formation of branched macromolecules due to intermolecular chain transfer to polymer similarly as in case of methyl methacrylate–acrylate copolymers. However, the effect is far less pronounced. GRAPHICAL ABSTRACT