Abstract:
N-isopropylacrylamide (NIPA) homopolymers having carboxylic
acid-end groups were synthesized by using mercaptoacetic acid
(MAA) as the chain transfer agent. Polymerization was achieved in
ethanol using azobisisobutyronitrile (AIBN) as the initiator.Average
molecular weight of the homopolymer estimated by titration was
1958. This carboxylic acid-ended poly(NIPA) was then copolymerized
with polyethylenimine (PEI, MW-2000) using a water soluble
carbodiimide (EDAC).With respect to carboxyl-ended poly(NIPA),
the block copolymers exhibited a pH dependent-temperature sensitivity
and higher LCST values in acidic pH. Scanning tunneling
microscopy (STM) images of both the homopolymer and the copolymer
were obtained at 25 and 45◦C with tip-sample bias voltages of
up to 800 mV and tunneling currents ∼1 nA. These images showed
that STM can be used to visualize both the formation of copolymer
chains and their structure, and also their stimuli-responsive
behavior.
