Timothy E. Long, Gozde I. Ozturk, Musan Zhang
Dept of Chemistry
Macromolecules & Interfaces Institute
Virginia Tech

Polyesters for Sustainable Adhesive Technologies:  From PSAs to Thermoplastic Elastomers

Melt polycondensation synthesis of polyesters presents a solvent-free and environmentally friendly approach of producing pressure sensitive adhesives (PSAs) due to their inherent biodegradability and low cost manufacturing process.  Low glass transition temperature (-40 °C) all-aliphatic polyester PSAs were synthesized using melt polymerization.  Careful selection of diester, diol, and monomer stoichiometry enabled tailoring of the glass transition temperature and adhesive properties as investigated using adhesive testing methods.  Melt rheological experiments indicated a correlation between polyester molecular weight and adhesive performance. These studies enabled us to design a new family of segmented copolyesters for their potential in adhesive applications due to controlled sequence distribution and morphological consequences of microphase-separated block copolymers.  Incorporating electrostatic interactions into copolymers also affords an avenue for the modification of thermally labile adhesive properties on the molecular level.  We have recently developed a synthetic strategy that allows for melt transesterification of segmented block copolyesters using the sterically hindered and cyclic monomer, 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO).  This monomer has also received significant industrial attention as a replacement for bisphenol-A based polycarbonates.  High-T¬g polyester polyols containing CBDO and 0-5 mol% sulfonation were synthesized using conventional melt transesterification.  Further reaction of the hard segment polyols with diesters and diols that comprise the resulting soft block demonstrates a one-pot synthetic method towards a new class of thermoplastic elastomers.  Herein, we describe the influence of ionic interactions on sulfonated segmented copolyesters.  Specifically, transesterification resistance studies and melt rheological experiments indicated a correlation between hard segment block content and sequence regularity to the adhesive and mechanical properties of the copolyesters. In addition, atomic force microscopy revealed the surface morphology of the copolyesters.  These ion-containing segmented copolyesters permit modification of adhesive properties on both the molecular and morphological level.

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