Novel
amphiphilic conetworks (APCN) consisting of thermoresponsive poly(N-isoproplyacrylamide) (PNiPAAm) cross-linked by hydrophobic
methacrylate-telechelic polyisobutylene (MA-PIB-MA) were successfully
synthesized in a broad composition range. The resulting PNiPAAm-l-PIB conetworks (“l” stands
for “linked by”) were obtained by radical
copolymerization of NiPAAm with MA-PIB-MA in tetrahydrofuran, a cosolvent
for all the components. Low amounts of extractables substantiated
efficient network formation. The composition dependent two glass transition
temperatures (Tg) by DSC analysis indicate
microphase separation of the cross-linked components without mixed
phases. It was found that the PNiPAAm-l-PIB conetworks
are uniformly swellable in both water and n-hexane;
i.e., these new materials behave either as hydrogels or as hydrophobic
gels in aqueous or nonpolar media, respectively. The uniform swelling
in both polar and nonpolar solutes indicates cocontinuous (bicontinuous)
phase morphology. The equilibrium swelling degrees (R) depend on composition,
that is, the higher the PIB content, the lower the R in water and
the higher in n-hexane. The PNiPAAm phase keeps its
thermoresponsive behavior in the conetworks as shown by significant
decrease of the swelling degree in water between 20 and 35 °C.
The lower critical solubility temperature (LCST) values determined
by DSC are found to decrease from 34.1 °C (for the pure PNiPAAm
homopolymer) to the range of 25–28 °C in the conetworks,
and the extent of the LCST decrease is proportional with the PIB content.
Deswelling-swelling, i.e., heating–cooling, cycle indicates
insignificant hysteresis in these new thermoresponsive materials.
This indicates that PNiPAAm-l-PIB conetworks with
predetermined and thermoresponsive swelling behavior can be designed
and utilized in several advanced applications on the basis of results
obtained in the course of this study.