A series of six polyurethane (PU) networks was synthesized from BoltornR
hydroxy-functional hyperbranched polyester (HBP) of the second pseudo
generation as a crosslinking agent, ?,?- dihydroxy-(ethylene
oxide-poly(dimethylsiloxane)-ethylene oxide) (EO-PDMS-EO) and 4,4?-
methylenediphenyl diisocyanate, by a two-step polymerization in solution.
Each sample of the prepared PUs had different EO-PDMS-EO content. The
chemical structure of the synthesized networks was analyzed by FTIR
spectroscopy. The influence of the EO-PDMS-EO content and type of the solvent
on the swelling behavior of the PUs in 2-propanol and toluene was
investigated. During the swelling measurements certain amount of sol
fractions was extracted from the PUs by solvents. According to the 1H NMR
results, sol fractions are mainly composed of the soluble hyperbranched PU,
formed during the polymerization by partial modification of the end hydroxyl
groups of HBP with NCO-terminated prepolymer synthesized in the first step of
the reaction. Chains of the so reacted prepolymer can then fold back and form
cyclic products by reaction of the free -NCO group from the NCO-terminated
prepolymer with free -OH group of HBP. As the EO-PDMS-EO content increases
the amount of the sol fractions and swelling degree also increased,
indicating that networks with lower EO-PDMS-EO content are more crosslinked
and have higher solvent resistance.
Fate and Potential Environmental Effects of Methylenediphenyl Diisocyanate and Toluene Diisocyanate Released into the Atmosphere
