Phase separation of blends of polydisperse polymers: Comparison between experiment and theory for the system poly(dimethylsiloxane)/poly(ethylmethylsiloxane)

Publisher Website
Google Scholar
Abstract
Cloud point curves were measured turbidimetrically for blends (upper critical solution temperatures; UCSTs) of poly(ethylmethylsiloxane) (PEMS) and four different samples of poly(dimethylsiloxane) (PDMS); the weight average molar masses in kg/mol are 31.2 for PEMS and 10.4, 15.5, 18.1 and 24.0 for PDMS; all components have polydispersity indices D (= M̄w/M̄n) within the range from 1.82 to 2.67. Corresponding calculations on the basis of the Flory‐Huggins theory (three adjustable parameters) account for the poly‐dispersity; molecular weight distributions are represented by the generalized Schulz‐Flory equation. Calculated cloud point curves agree very well with those measured, if individual sets of parameters are admitted for each of the different mixtures. Even for an identical set of parameters the maximum deviations remain moderate. Realistic model calculations concerning the influences of D on cloud points and on critical points were performed with this set of parameters. For the present (only slightly endothermal) system, the precipitation threshold increases from 318 to 558.6 K as DPEMS is raised from 1.87 to 4.00, keeping the number average degree of polymerization constant.