Polydispersity of Hyperbranched Polyesters Based on 2,2-Bis(hydroxymethyl)propanoic Acid: SEC/MALDI−TOF MS and 13C NMR/Kinetic-Recursive Probability Analysis

详细信息    查看全文

• 作者：Linda Chikh ; Martine Tessier ; Alain Fradet
• 刊名：Macromolecules
• 出版年：2008
• 出版时间：December 9, 2008
• 年：2008
• 卷：41
• 期：23
• 页码：9044-9050
• 全文大小：179K
• 年卷期：v.41,no.23(December 9, 2008)
• ISSN：1520-5835

文摘

The absolute average molar masses and polydispersity index of a series of polyesters based on 2,2-bis(hydroxymethyl)propanoic acid (BMPA, AB₂-type monomer), 2,2-bis(hydroxymethyl)-1,3-propanediol (PE, B₄-type monomer), and 1,1,1-tris(hydroxymethyl)propane (TMP, B₃-type monomer) were determined by SEC/MALDI−TOF off-line coupling. The _w/_n values, in the 1.8−3.1 range, were surprisingly very close to those found by SEC using the conventional linear polystyrene calibration method, but dramatically lower than those calculated from conversion and composition of initial monomer mixture assuming equal reactivity of functional groups. The mol ratios of the various monomer units in final polyesters were determined by ¹³C NMR. The kinetic-recursive probability approach assuming first-shell substitution effects was then applied to calculate the branching factors and the average molar masses of these polyesters from their final composition. The AB- and B-branching factors were significantly lower than expected for random polymerizations, reflecting the existence of both negative A−B and B−B substitution effects, i.e. lower reaction rate of a given A or B group after reaction of the other groups present on the same monomer unit. The calculated values of _w and _w/_n were reasonably close to the experimental ones for all hyperbranched polyesters. Intramolecular esterifications and intermolecular etherifications side reactions were taken into account in the calculations with some simplifying assumptions and found to marginally broaden MW distributions.