| Abstract
| - Size exclusion chromatography and matrix-assisted laser desorption ionization massspectrometry (SEC/MALDI) coupled with selective degradation reactions have been applied for characterization of polyurethane soft and hard blocks. A series of model PUR's were prepared from 4,4‘-diphenylmethane diisocyanate (MDI) and poly(butylene adipate) (pBA)−polyols with molecular weightsof 1000 and 4000 Da. The weight ratio of the pBA polyols was varied: 1:3, 1:1, and 3:1; the amount ofMDI was adjusted accordingly. In these model PUR systems no additional chain extender was added inaddition to that in the polyester soft segments (butanediol), as a consequence their Flory distributionwas used. Therefore, the model systems only have a minimum of so-called hard segments (oligo urethanesconsisting of MDI and butanediol). Molecular weights of soft blocks, liberated by isocyanatolysis usingphenyl isocyanate and measured by SEC/MALDI, showed reasonable agreement with those estimatedfrom tandem light scattering and SEC (MALS/SEC). The increase in molecular weights observed withincreasing amounts of pBA4000 indicated that selective degradation combined with SEC/MALDI issensitive to the polymer soft block composition. Polydispersity indices (PDs), determined for the soft blocksrecovered from phenyl isocyanate degradation, were lower than those expected on the basis of reactiontheory. Partial acid-catalyzed hydrolysis was applied to determine the hard block chain length distributionfor polyester-based PUR samples having different amounts of MDI. MALDI spectra of the degradedproducts provided proof for a degradation mechanism proposed in the literature. The results presentedhere demonstrate that applying partial acid hydrolysis to polyester−polyurethane generates exclusivelya series of hydroxy-terminated oligomers, which can be identified as former hard segments of thepolyester−polyurethane elastomer. The methodology hydrolyzes selectively all ester bonds while leavingthe urethane groups containing hard segments completely intact, thus providing an additional tool forthe complete characterization of polyurethanes.
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