Macromolecules, Vol.43, No.7, 3268-3276, 2010
Aromatic-Aliphatic Polyesters with Tailored Degree of Branching Based on AB/AB(2) and ABB*/AB(2) Monomers
The synthesis and characterization of aromatic aliphatic polyesters with tailored degree of branching (DB), i.e. hyperbranched (hb), gradually branched, and linear polymers, are described. The dilute solution properties of polymers resulting from two different synthetic approaches are compared. The ABB*/AB, approach leads to homopolymers with different DB based on the same AB(2) monomer, 4,4-bis(4'-hydroxyphenyl)pentanoic acid, employing the protection of one phenolic group (B*) in the AB(2) monomer followed by copolymerization with AB, monomer at different molar ratios. Because of their identical chemical origin, well-tunable DB, comparable molar masses, an absence of aggregation in common solvents, and high refractive index increments, they are suitable as model systems in branching characterization. Their solution properties are compared to those of polymers obtained by the AB/AB(2) approach. In order to study the influence of the end-groups on thermal and solution polymer properties, all terminal OH groups were modified with tert-butyldimethylsilyl chloride (SY-Cl). A different dependence of the thermal properties on branching was found for OH- and SY-terminated samples produced by the ABB*/AB(2) approach. While the difference in the T-g values between linear and hb structures was found to be 16 degrees C for SY-terminated samples, nearly identical values were obtained for OH-terminated linear and hb polyesters due to strong effect of hydrogen bond formation.