Thermally expandable core/shell particles with a poly(acrylonitrile-co-methacrylonitrile) shell and a hydrocarbon core (blowing agent) have been prepared by suspension polymerization. The objective of this study was to gain a deeper understanding of the parameters determining the expansion properties of these microspheres. It was found that the amount, the boiling point, and the structure of the blowing agent are important parameters for the expansion properties. For example, a higher maximum expansion was reached when using bulkier blowing agents and thus a lower diffusion rate through the polymer shell. Further, the amount and structure of the crosslinker were also found to be essential for the expansion properties. For this particular system, it was found that a dimethacrylate-functional crosslinker gave significantly better expansion when compared with diacrylate-or divinylether-based crosslinkers. Beside these parameters, it was also observed that the particle-size distribution influence the expansion properties of the microspheres. V C

Free-radical suspension polymerization was used to synthesize thermally expandable microspheres (TEMS); in this process, a poly(acrylonitrile-co-methacrylonitrile) shell encapsulated isooctane. Different amounts of dimethacrylate, diacrylate, or divinyl ether functional crosslinker were added to investigate the effects on the crosslinking density of the polymer and the expansion properties of the TEMS. The optimum amount of crosslinker was found to be approximately 0.05-0.1 mol %. However, a significantly better expansion could be obtained with 1,4-butanediol dimethacrylate as a crosslinker, compared to 1,4-butanediol divinyl ether or 1,4-butanediol diacrylate. From monitoring the conversion of monofunctional analogues by gas chromatography, we suggest that the differences in expansion obtained with different crosslinkers, originated from the difference in the reactivity of the radicals in the system toward the vinyl functionalities of the crosslinkers. This regulated the incorporation of the crosslinker into the polymer and, thereby, the mechanical properties of the microsphere shell.

Herein, we report the free-radical polymerization of the biobased α-methylene-γ-butyrolactone and α-methylene-γ-valerolactone, either into homopolymers or together with fossil-based (meth)­acrylate monomers, methyl acrylate and methyl methacrylate in different ratios. The polymerization was thermally initiated by 2,2′-azobisisobutyronitrile or lauroyl peroxide to investigate their effect on the polymerization behaviors. Polymerizations were monitored by monomer conversion, and the final polymers were characterized with respect to molecular weight, composition, glass transition temperature, and thermal degradation. NMR showed significant differences in conversion rates of each monomer in the copolymerizations which suggest differences in reactivity ratios, sometimes to such an extent that the polymers exhibited a substantial compositional drift as corroborated by assessed thermal properties. Tailored T g’s and increased thermal stability were achieved by copolymerizing the lactones and the (meth)­acrylates.

No abstract

No abstract