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Abstract
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Linear poly(ethylene glycol) (PEG)-block-poly(N-isopropylacrylamide)
(PNIPAM) and star-like three-arm PEG-star-(PNIPAM)2 copolymers having
one PEG and two PNIPAM blocks are synthesized by atom transfer radical
polymerization (ATRP). Single crystals of these block copolymers are grown
from amyl acetate and toluene dilute solutions. To recognize PNIPAM and
PEG thicknesses, small angle X-ray scattering (SAXS) is applied. V-type
brushes behave differently from linear brushes because doubly grafted
PNIPAM blocks from a common point onto PEG substrate exert a higher
osmotic pressure, leading to a thinner crystal. In addition to three ordinary
regimes, a fourth or extremely stretched regime is detected for V-type
PNIPAM brushes. Although in PEG5000-star-(PNIPAM)2 single crystals with
overall PNIPAM molecular weight of 37 000 g/mol, each PNIPAM arm is
shorter than PNIPAM grafts in linear PEG5000-block-PNIPAM26000 single
crystals, their switching point from second to third regime is significantly
lower (22 vs 33 °C). The V-type configuration of PNIPAM brushes cause them
to be entered into the extremely stretched or fourth regime, which has not
been previously detected for coily brushes. The boundary between third and
fourth regimes for PEG5000-star-(PNIPAM)2 single crystals is verified at 31.5
and 23.5 °C in amyl acetate and toluene, respectively.
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