Title “Chain and Pendant Architecture Effects in Associating Polyolefins”
Friday, February 28, 2025 – 1:00 pm – Wu and Chen Auditorium
Abstract: The United States recycles less than 9% of plastic waste, representing a tremendous environmental catastrophe and a loss of embodied value. This dissertation presents the structure-property relationships of functional polymers made from an upcycling approach targeting polyolefins for polymer-to-polymer conversions. The overall strategy proceeds by first dehydrogenating polyolefins, then functionalizing the resulting C=C to generate functional polymers. This upcycling route retains the backbone architecture and enables control of the pendant, accessing architectures otherwise unattainable by the free radical polymerization (FRP) that is typically used to produce polyolefin copolymers. Within this larger strategy, this dissertation explores the chain and pendant effects on the structure-property relationships of the resulting associating polymers. Starting with polycyclcooctene (PCOE), a model for partially dehydrogenated polyethylene, the polymer is functionalized with alcohol, carboxylic acid, and acrylate groups. These polymers have a linear backbone, in contrast to commercial functional polymers with branched backbones.
X-ray scattering reveals that long pendants terminating in OH (-S(CH2)2OH, or SC2OH) do not incorporate into polymer crystals when added to PCOE. By contrast, when added directly to the backbone, OH incorporates into crystals. Linear OH-PCOE crystallizes faster and to a greater extent than commercial branched EVOH, as demonstrated by differential scanning calorimetry and in situ X-ray scattering. This difference in structure as a consequence of pendant architecture tunes the surface and adhesive properties. The more crystalline OH-PCOE exhibits a higher contact angle (lower surface polarity) than commercial EVOH or SC2OH-PCOE; this difference in contact angle is explained by the distribution of OH groups between the amorphous and crystalline regimes. The difference in surface polarity leads SC2OH-PCOE to exhibit greater adhesive strength than OH-PCOE at functionalization <15 % of ethylene units. At higher functionalization, the loss of crystallinity in SC2OH-PCOE decreases adhesive strength below that of OH-PCOE due to a loss of bulk strength.
Functionalizing PCOE with COOH-terminated pendants with a variety of methylene spacers (-S(CH2)nCOOH, where n = 1, 2, 7) enables further exploration of pendant effects on mechanical properties. Dynamic mechanical analysis identifies that the storage modulus in the rubbery plateau (E’ rubbery) depends on both the extent of functionalization and pendant length. Similarly, functionalizing PCOE with ethyl acrylate (EA) decreases E’ rubbery and tunes tensile mechanical properties. From 0 to 18 mol% EA functionalization, extensibility increases to over 4000% strain at break. An increase in molar mass between entanglements facilitates the high elongation of EA-PCOE. Ultimately, the polymer-to-polymer upcycling route discussed here enables a greater degree of control over the chain and pendant architecture than is conventionally achievable by FRP. This dissertation elucidates the structure-property relationships tuned by the chain and pendant architecture of associating polyolefins, contributing to a broader strategy for polymer-to-polymer upcycling.