title: Unexpected Temperature Behavior of Polyethylene Glycol Spacers in Copolymer Dendrimers in Chloroform.
abstract: We have studied copolymer dendrimer structure: carbosilane dendrimers with terminal phenylbenzoate mesogenic groups attached by poly(ethylene) glycol (PEG) spacers. In this system PEG spacers are additional tuning to usual copolymer structure: dendrimer with terminal mesogenic groups. The dendrimer macromolecules were investigated in a dilute chloroform solution by (1)H NMR methods (spectra and relaxations). It was found that the PEG layer in G = 5 generations dendrimer is "frozen" at high temperatures (above 260 K), but it unexpectedly becomes "unfrozen" at temperatures below 250 K (i.e., melting when cooling). The transition between these two states occurs within a small temperature range (~10 K). Such a behavior is not observed for smaller dendrimer generations (G = 1 and 3). This effect is likely related to the low critical solution temperature (LCST) of PEG and is caused by dendrimer conformations, in which the PEG group concentration in the layer increases with growing G. We suppose that the unusual behavior of PEG fragments in dendrimers will be interesting for practical applications such as nanocontainers or nanoreactors.
authors.affiliation: St. Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg, 199034, Russia.|St. Petersburg National Research University of Information Technologies, Mechanics and Optics, Kronverkskiy pr. 49, St. Petersburg, 197101, Russia.
authors.forename: Denis A
authors.initials: DA
authors.lastname: Markelov
authors.affiliation: St. Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg, 199034, Russia.
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Matveev
authors.affiliation: Instrument Centre, Department of Chemistry, University of Turku, Vatselankatu 2, FI-20014, Turku, Finland.
authors.forename: Petri
authors.initials: P
authors.lastname: Ingman
authors.affiliation: Institute of Macromolecular Compounds, Russian Academy of Sciences, Bolshoi Prospect 31, V.O., St. Petersburg, 199004, Russia.
authors.forename: Marianna N
authors.initials: MN
authors.lastname: Nikolaeva
authors.affiliation: St. Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg, 199034, Russia.
authors.forename: Anastasia V
authors.initials: AV
authors.lastname: Penkova
authors.affiliation: Laboratory of Physics, Lappeenranta University of Technology, Box 20, 53851, Lappeenranta, Finland.
authors.forename: Erkki
authors.initials: E
authors.lastname: Lahderanta
authors.affiliation: Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119991, Russia.
authors.forename: Natalia I
authors.initials: NI
authors.lastname: Boiko
authors.affiliation: St. Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg, 199034, Russia.
authors.forename: Vladimir I
authors.initials: VI
authors.lastname: Chizhik