Sequence Analysis of Styrenic Copolymers by Tandem Mass Spectrometry

Styrene and smaller molar amounts of either <i>m</i>-dimethylsilylstyrene (<i>m</i>-DMSS) or <i>p</i>-dimethylsilylstyrene (<i>p</i>-DMSS) were copolymerized under living anionic polymerization conditions, and the compositions, architectures, and sequences of the resulting copolymers were characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and tandem mass spectrometry (MS²). MS analysis revealed that linear copolymer chains containing phenyl–Si­(CH₃)₂H pendants were the major product for both DMSS comonomers. In addition, two-armed architectures with phenyl–Si­(CH₃)₂–benzyl branches were detected as minor products. The comonomer sequence in the linear chains was established by MS² experiments on lithiated oligomers, based on the DMSS content of fragments generated by backbone C–C bond scissions and with the help of reference MS² spectra obtained from a polystyrene homopolymer and polystyrene end-capped with a <i>p</i>-DMSS block. The MS² data provided conclusive evidence that copolymerization of styrene/DMSS mixtures leads to chains with a rather random distribution of the silylated comonomer when <i>m</i>-DMSS is used, but to chains with tapered block structures, with the silylated units near the initiator, when <i>p</i>-DMSS is used. Hence, MS² fragmentation patterns permit not only differentiation of the sequences generated in the synthesis, but also the determination of specific comonomer locations along the polymer chain

Polymer Dynamics of Well-Defined, Chain-End-Functionalized Polystyrenes by Dielectric Spectroscopy

A novel strategy is described to study polymer dynamics by using a combination of dielectric spectroscopy and functionalized polymers. The first results are presented using various well-defined, chain-end-functionalized polystyrenes (PS) synthesized using a combination of modern anionic polymerization techniques and hydrosilylation chemistry. The end-functionalized polystyrenes investigated contain the cyano (−CN), hydroxyl (−OH), acetyl (−OCOCH3, −Ac), or ethyl ether (−OCH2CH3, −OEt) groups. By applying broadband dielectric spectroscopy (BDS) over an extensive temperature range (approximately 50−413 K), it was possible to fully characterize the polymer dynamics associated with the segmental α-relaxation as well as the local secondary process related to the specific movement of the functional groups themselves. Combining these data with the results from differential scanning calorimetry (DSC), it is shown that for rather large functional groups the overall polymer matrix properties are altered, giving rise to a decrease in the glass transition temperature. The trend can be rationalized in terms of free volume effects caused by the bulky functional groups and points toward matrix plasticization effects. However, for cyano-functionalized PS the inclusion of this group does not significantly affect the matrix properties. By taking advantage of the strong dipole moment of the CN group, a clear dielectric signal can be obtained that can be used to selectively study the specific dynamics where the group is located. In other words, by appropriately attaching cyano groups at different parts of the chains, these can be exploited as in situ dielectric probes that allow determination of specific contributions to dynamical processes in polymers

Synthesis of In-Chain-Functionalized Polystyrene-<i>block</i>-poly(dimethylsiloxane) Diblock Copolymers by Anionic Polymerization and Hydrosilylation Using Dimethyl-[4-(1-phenylvinyl)phenyl]silane

Synthesis of In-Chain-Functionalized Polystyrene-block-poly(dimethylsiloxane) Diblock Copolymers by Anionic Polymerization and Hydrosilylation Using Dimethyl-[4-(1-phenylvinyl)phenyl]silan