Sustainable glucose-based block copolymers exhibit elastomeric and adhesive behavior†
Herein, we present the direct modification of glucose, an abundant and inexpensive sugar molecule, to produce new sustainable and functional polymers. Glucose-6-acrylate-1,2,3,4-tetraacetate (GATA) has been synthesized and shown to provide a useful glassy component for developing an innovative family of elastomeric and adhesive materials. A series of diblock and triblock copolymers of GATA and n-butyl acrylate (n-BA) were created via Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization. Initially, poly(GATA)-b-poly(n-BA) copolymers were prepared using 4-cyano-4-[(ethylsulfanylthiocarbonyl)sulfanyl] pentanoic acid (CEP) as a chain transfer agent (CTA). These diblock copolymers demonstrated decomposition temperatures of 275 °C or greater and two glass transition temperatures (Tg) around −45 °C and 100 °C corresponding to the PnBA and PGATA domains, respectively, as measured by differential scanning calorimetry (DSC). Triblock copolymers of GATA and n-BA, with moderate dispersities (Đ = 1.15–1.29), were successfully synthesized when S,S-dibenzyl trithiocarbonate (DTC) was employed as the CTA. Poly(GATA)-b-poly(nBA)-b-poly(GATA) copolymers with 14–58 wt% GATA were prepared and demonstrated excellent thermomechanical properties (Td ≥ 279 °C). Two well-separated glass transitions near the values for homopolymers of n-BA and GATA (∼−45 °C and ∼100 °C, respectively) were measured by DSC. The triblock with 14% GATA exhibited peel adhesion of 2.31 N cm−1 (when mixed with 30 wt% tackifier) that is superior to many commercial pressure sensitive adhesives (PSAs). Use of 3,5-bis(2-dodecylthiocarbonothioylthio-1oxopropoxy)benzoic acid (BTCBA) as the CTA provided a more efficient route to copolymerize GATA and n-BA. Using BTCBA, poly(GATA)-b-poly(nBA)-b-poly(GATA) triblock copolymers containing 12–25 wt% GATA, with very narrow molar mass distributions (Đ ≤ 1.08), were prepared. The latter series of triblock copolymers showed excellent thermal stability with Td ≥ 275 °C. Only the Tg for the PnBA block was observed by DSC (∼−45 °C), however, phase-separation was confirmed by small-angle X-ray scattering (SAXS) for all of these triblock copolymers. The mechanical behavior of the polymers was investigated by tensile experiments and the triblock with 25% GATA content demonstrated moderate elastomeric properties, 573 kPa stress at break and 171% elongation. This study introduces a new family of glucose-based ABA-type copolymers and demonstrates functionality of a glucose-based feedstock for developing green polymeric materials.