Marc Hillmyer

Block polymers are marvelous self-assembling materials that have found uses from the ordinary (eg, pressure sensitive adhesives) to the fantastic (eg, templates for nanolithography). By incorporating blocks that can undergo subsequent chemical transformations, the set of self-assembled morphologies that block polymers adopt can be modified to take advantage of the nanoscopic dimensions and narrow feature size distributions to generate new functional materials that have technological potential in wide ranging applications. In this presentation I will present our work over the past two decades on the design and development of block polymers that contain an etchable component for the generation of nanoporous materials from block polymer precursors. I will emphasize the preparation of both bulk and thin film nanoporous materials and the production of nanoporous materials from both ordered and disordered …

Poly(L-lactide) (PLLA)’s broad applicability is hindered by its brittleness and slow crystallization kinetics. Among the strategies for developing tough, thermally resilient PLLA-based materials, the utilization of neat PLLA block polymers has received comparatively little attention despite its attractive technological merits. In this work, we comprehensively describe the microstructural, thermal, and mechanical properties of two compositional libraries of PLLA-rich PLLA-b-poly(γ-methyl-ε-caprolactone) (PγMCL)-b-PLLA (“LML”) triblock copolymers. The rubbery PγMCL domains microphase separate from the matrix in the melt and intercalate between PLLA crystal lamellae on cooling. Despite the mobility constraints associated with mid-block tethering, the PLLA end-blocks crystallize as rapidly as a PLLA homopolymer control of similar molar mass. Independent of their degree of crystallinity, LML triblocks exhibit vastly improved tensile toughnesses (63-113 MJ m-3) over that of PLLA homopolymer (1.3-2 MJ m-3), with crystallinities of up to 55% and heat distortion temperatures (HDTs) as high as 148 °C. We investigated the microstructural origins of this appealing performance using X-ray scattering and microscopy. In the case of a largely amorphous PLLA matrix, the PγMCL domains cavitate to enable concurrent PLLA shear yielding and strain-induced crystallization. In highly crystalline PLLA matrices, PγMCL facilitates a lamellar-to-fibrillar transition during tensile deformation, the first such transition reported for PLLA drawn at room temperature. These results highlight the unique attributes of PLLA block polymers and prompt future architectural and …

Sustainable polyesters are promising materials to replace petroleum-based non-degradable polymers. Unfortunately, the high crystallinity degree of some polyesters limits their applications due to poor mechanical properties and low melting temperatures. A suitable strategy to broaden their applications is introducing functional groups into their backbone to enhance intermolecular interactions which can impact the thermal properties of the material. Nevertheless, a comprehensive understanding of these interactions on the crystallization properties is still lacking. In this work, we have studied the impact of incorporating additional ester and amide groups into aliphatic polyesters with varying numbers of methylene groups between the functional groups. We show that functional groups that induce strong intermolecular interactions increase the melting and crystallization temperature. However, these groups slow down …

These files contain primary data along with associated output from instrumentation supporting all results reported in Sample et al. "Crosslinked Polyolefins Through Tandem ROMP/Hydrogenation". Crosslinked polyolefins have important advantages over their thermoplastic analogues, particularly improved impact strength and abrasion resistance, as well as increased chemical and thermal stability; however, most strategies for their production involve post-polymerization crosslinking of polyolefin chains. Here, a tandem ring-opening metathesis polymerization (ROMP)/hydrogenation approach is presented. Cyclooctene (COE)-co-dicyclopentadiene (DCPD) networks are first synthesized using ROMP, after which the dispersed Ru metathesis catalyst is activated for hydrogenation through addition of hydrogen gas. The reaction temperature for hydrogenation must be sufficiently high to allow mobility within the system, as dictated by thermal transitions (i.e., glass and melting transitions) of the polymeric matrix. COE-rich materials exhibit branched-polyethylene-like crystallinity (25% crystallinity) and melting points (Tm = 107 °C), as well as excellent ductility (>750 % extension), while majority DCPD materials are glassy (Tg = 84 °C) and much stiffer (E = 710 MPa); all materials exhibit high tensile toughness. Importantly, hydrogenation of olefins in these crosslinked materials leads to notable improvements in oxidative stability, as saturated networks do not experience the same substantial degradation of mechanical performance as their unsaturated counterparts upon prolonged exposure to air at high temperature.

High-density polyethylene (HDPE) is a widely used commercial plastic due to its excellent mechanical properties, chemical resistance, and water vapor barrier properties. However, less than 10% of HDPE is mechanically recycled, and the chemical recycling of HDPE is challenging due to the inherent strength of the carbon–carbon backbone bonds. Here, we report chemically recyclable linear and branched HDPE with sparse backbone ester groups synthesized from the transesterification of telechelic polyethylene macromonomers. Stoichiometrically self-balanced telechelic polyethylenes underwent transesterification polymerization to produce the PE-ester samples with high number-average molar masses of up to 111 kg/mol. Moreover, the transesterification polymerization of the telechelic polyethylenes and the multifunctional diethyl 5-(hydroxymethyl)isophthalate generated branched PE-esters. Thermal and …

This work aimed to decrease the water permeability (PH2O) while simultaneously maintaining low oxygen permeability (PO2) in ethylene vinyl alcohol (EVOH)-based copolymers by introducing high levels of backbone regioregularity and stereoregularity. Both regioregular atactic and isotactic EVOH samples with 75 mol % ethylene were prepared by a ring-opening metathesis polymerization (ROMP)-hydrogenation-deprotection approach and then compared to commercial EVOH(44) (containing 44 mol % ethylene) as a low PO2 standard with poor water barrier characteristics (i.e., high PH2O). The high levels of regioregularity and stereoregularity in these copolymers increased the melting temperature (Tm), degree of crystallinity (χc), and glass-transition temperature (Tg) compared to less regular structures. EVOH(44) demonstrated the highest Tm but lower χc and Tg values as compared to that of the isotactic …

Poly(l-lactide) (PLLA)’s broad applicability is hindered by its brittleness and slow crystallization kinetics. Among the strategies for developing tough, thermally resilient PLLA-based materials, the utilization of neat PLLA block polymers has received comparatively little attention, despite its attractive technological merits. In this work, we comprehensively describe the microstructural, thermal, and mechanical properties of two compositional libraries of PLLA-rich PLLA-b-poly(γ-methyl-ε-caprolactone) (PγMCL)-b-PLLA (“LML”) triblock copolymers. Rubbery PγMCL domains microphase separate from the matrix in the melt and intercalate between PLLA crystal lamellae on cooling. Despite the mobility constraints associated with midblock tethering, the PLLA end-blocks crystallize as rapidly as a PLLA homopolymer control of similar molar mass. Independent of their degree of crystallinity, LML triblocks exhibit vastly improved …

These files contain primary data along with associated output from instrumentation supporting all results reported in "Chemically Recyclable Linear and Branched Polyethylenes Synthesized from Stoichiometrically Self-balanced Telechelic Polyethylenes" by Jang et al. The abstract of this document is the following, High-density polyethylene (HDPE) is a widely used commercial plastic due to its excellent mechanical properties, chemical resistance, and water vapor barrier properties. However, less than 10% of HDPE is mechanically recycled, and chemical recycling of HDPE is challenging due to inherent strength of the carbon-carbon backbone bonds. Here, we report chemically recyclable linear and branched HDPE with sparse backbone ester groups synthesized from transesterification of the telechelic polyethylene macromonomers. Stoichiometrically self-balanced telechelic polyethylenes underwent transesterification polymerization to produce the PE-ester samples with high number average molar masses up to 111 kg/mol. Moreover, transesterification polymerization of the telechelic polyethylenes and the multifunctional diethyl 5-(hydroxymethyl)isophthalate generated branched PE-esters. Thermal and mechanical properties of the PE-esters were comparable to commercial HDPE and tunable through control of the ester content in the backbone. In addition, branched PE-esters showed higher levels of melt-strain hardening compared to linear versions. The PE-ester was depolymerized into telechelic macromonomers through straightforward methanolysis and the resulting macromonomers could be effectively repolymerized to generate high …