CLOUD-POINT TEMPERATURES OF BNEMBN AND PNEMPN TYPE TRIBLOCK COPOLYMERS IN AQUEOUS-SOLUTION

The cloud-point temperatures (T-cl) of 1 wt % y(oxybutylene)-poly(oxye thylene)-poly(oxybutylene) (BnEmBn) and of 1 wt % poly(oxypropylene)-p oly(oxyethylene)-poly(PnEmPn) were measured by detecting the sharp dec rease in transmittance of the incident laser beam when phase separatio n occurs. The cloud-point temperatures were studied as a function of t he length of both hydrophobic and hydrophilic blocks. A linear increas e in the hydrophobic block length (B or P) leads to an exponential dec rease in the cloud-point temperature. However, the middle hydrophilic block (E) shows only a weak positive effect; i.e., an exponential incr ease in the block length leads to a linear increase in the cloud-point temperature. On the basis of the available data, we can summarize our results in mathematical form and present a three-dimensional plot to predict the T-cl of BnEmBn (or PnEmPn) triblock copolymers. The middle E block has a stronger effect on PnEmPn than BnEmBn. It is also noted that one oxybutylene (B) unit has the effect equivalent to about 4.4 oxypropylene (P) units.