Structure and dynamics of melt poly(epsilon-caprolactone) from inverse rheological calculation

The linear viscoelastic behavior of poly(epsilon-caprolactone) (PCL) in sit u synthesized between the plates of the rheometer was investigated. The pol ymerization of epsilon-caprolactone was initiated and catalyzed by titanium tetrapropoxide. These polymers are very sensitive to hydrolysis of the alk oxy-titanium bonds included in the polymer chains. Two different forms of P CL can be studied: hydrolyzed or non-hydrolyzed PCL. However, only the mole cular weight distribution (MWD) of the hydrolyzed chains can be accessed fr om size exclusion chromatography (SEC) analysis. The MWD of the in-situ syn thesized poly(epsilon-caprolactone) was calculated by solving the inverse p roblem of determination of the MWD from rheological data. A continuous form of the relaxation function was derived and an a priori shape (Wesslau or b i-modal Wesslau) of the MWD was assumed. Then MWDs calculated from complex moduli curves were used to investigate the structure of the poly(epsilon-ca prolactone) at the end of the polymerization process. About 85% of the poly mer chains consist of a single branched linear structure. The remaining 15% are assumed to be mainly two fold branched. The presence of star structure s cannot be precluded. The present work describes an illustrative example o f the suitability of the quasi on-line estimation of the MWD from the inver sion data.