Session D40 - Poster Session I.
POSTER session, Monday afternoon, March 12
Exhibit Hall, Washington State Convention Center
Polymer solutions, made in volatile solvents, phase-separate at a Lower Critical Solution Temperature (LCST),Ti ,due to the difference in solvent and polymer expansion coefficients. As Ti is molecular weight (MW)-dependant ,the MW distribution of a sample can be obtain through a thermogram .This is a set of hi (Ti) where ,hi, is the turbidity for a fraction phase-separating a at Ti, in a step by step T-increase.The range of Ti is 70 K lower for polyethylene (PE) than for polypropylene (PP) .Random copolymers of ethylene (E) and propylene (P) such as synthetic rubbers are expected to phase-separate, as do homopolymers , on a continuous range of Ti such as Ti (PE)< (Ti (copolymers) < Ti(PP) as is indeed found. In the present work, a sonication is used to avoid raising T for the dissolution of rubber samples in pentane.In these conditions,two distributions are observed,separated by 30-40 K.The range of Ti suggests that micelles with E segments and inverse micelles with P segments at the molecular surface are stable in solution and probably reflect the morphology of the solid.The thermograms of samples with the same average E/P content are found catalyst-dependent. They can be tracers of the length of E and P sequences in the sample.