local maxima in monolayer compressibility for the two low pressure transitions increase as the

PCL chain length decreases, suggesting PEO-related phase transitions as previously observed for

comb-like polymers consisting of a poly(vinyl amine) backbone with 2kDa PEO side chains.143

The maximum in monolayer compressibility for the high pressure transition increases as the PCL

chain length increases, suggesting a PCL-related phase transition. Comparison with the

isotherms of PEO2670 and PCL2000 indicates that the transitions around 6.5 and 13.5 mN/m

arise from dissolution of the PEO block in the water subphase and crystallization of the PCL

block above the water surface, respectively. The transition at 10.5 mN/m was not observed for

PEO2670, but has been previously described as a brush formation of the PEO chains stretching

away from the interface when anchored by hydrophobic blocks for other PEO-based amphiphilic

block copolymers.144,145 In the following, we report our investigations on the behavior of the

linear PEO-b-PCL diblock copolymers in the low (r < 12 mN/m) and high (r > 12 mN/m)

surface pressure regions.

 30

 25 -1 \ PEOo-b-PCL,,
 I~ PEOo-b-PCL27
 E 20 -- PEOo-b-PCL19
 7 ~- PEOo-b-PCL,
 E 15-







 0 2000 4000 6000
 Mean Molecular Area (A2)

Figure 4-20. Isotherms of the PEO-b-PCL linear diblock copolymers.