The impact of architecture on the behavior of siloxane-grafted polymethacrylate.

In this paper, we studied for the first time the impact of the molecular weight, M n , and the topology on the molecular dynamics of a series of grafted poly(poly(dimethylsiloxane methacrylate)) (polyPDMSMA). The behavior of grafted (molecular brushes) polyPDMSMA and their three-armed counterparts of tailor-made properties prepared by Atom Transfer Radical Polymerization (ATRP) was monitored by means of broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC) and comprehensive rheology analysis. Surprisingly, the dielectric loss spectra of all studied polyPDMSMA exhibit the presence of two dielectric relaxation processes above their glass transition temperature, T g. A comparison of dielectric, calorimetric and mechanical data indicated that the faster and slower relaxation processes identified in loss spectra can be related to the segmental and chain dynamics, respectively. Interestingly, we observed that the "local" segmental dynamics of studied polyPDMSMA, involving the mobility of few repeatable units creating a segment, is almost unaffected by neither the length of polymer chain, number of grafts nor its topology. This is also reflected in a weak molecular weight-dependences of T g of studied polyPDMSMA independently to their topology. On the other hand, the time-scale separation between segmental and the chain modes as well as the amplitude of the latter process increase with growing M n of all examined polyPDMSMA. Additionally, it should be mentioned that the mechanical data collected for samples characterized by high molecular weight (of M n > 280 kg/mol) reveal the emergence of additional process (most likely related to the grafts and/or the star arm relaxation) at the intermediate regime, independently to their topology. Interestingly, this mode was observed to be much slower for the star-shaped macromolecules when compared to the grafted polymers, despite their lower M n. This implies that the observed differences are not a result of different molecular weights, but rather originate from a various molecular mechanism due to the different topology of the studied samples. In this context, one can assume that in the case of high-molecular-weight macromolecules, the backbone architecture has a significant influence on the behavior of polymers, including their molecular dynamics. [Display omitted] • Increase of the glass transition of studied polyPDMSMA with their molecular weight. • Loss spectra of polyPDMSMA exhibit multiple dielectric relaxation processes. • Observed dielectric processes were assigned as the chain and segmental modes. • Presence of grafts/arms relaxation (or entanglement segments) in mechanical data. [ABSTRACT FROM AUTHOR]