Molecularly architected polymers enabled by frontal polymerization dynamics

Paul, Justine Elizabeth

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https://hdl.handle.net/2142/122201 Copy

Description

Title

Molecularly architected polymers enabled by frontal polymerization dynamics

Author(s)

Paul, Justine Elizabeth

Issue Date

2023-10-02

Director of Research (if dissertation) or Advisor (if thesis)

Sottos, Nancy R

Doctoral Committee Chair(s)

Sottos, Nancy R

Committee Member(s)

• Moore, Jeffrey S
• Geubelle, Philippe H
• Leal, Cecilia
• Evans, Christopher

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Frontal Polymerization
• Molecuarly Architected Polymers
• Functionally Graded Materials
• Nonplanar Front Dynamics
• Convective Flow

Abstract

There has been significant interest in the customized behaviors of architected materials, resulting from the harmonious interplay between material properties and geometry. Despite additive manufacturing offering spatial control over material constituents for the fabrication of architected materials, the challenge remains to achieve hierarchical architectures across multiple length scales. Frontal ring-opening metathesis polymerization (FROMP) has emerged as a promising and energy-efficient manufacturing technique, with the potential for autonomously fabricating architected materials. FROMP is sustained by the exothermic polymerization of a cyclic olefin monomer and a ruthenium-centered initiator, resulting in a self-propagating wave or "front" that locally transforms uncured monomer into polymer until all the monomer is consumed or the front quenches due to extensive heat loss to the surroundings. This thesis describes advancements in FROMP, where we harness the rapid reaction-thermal transport to fabricate spatially varying material patterns and tailor properties during the fabrication of architected polymers. The fabrication of thermoset materials with varying material properties is enabled using different ruthenium initiators for FROMP. In this work, nine commercially available ruthenium initiators were examined for their efficacy in frontally copolymerizing dicyclopentadiene (DCPD) and 5-ethylidene-2-norbornene (ENB). Distinct initiators exhibited variations in their front-related characteristics, including maximum front temperature, front velocity, and heat of reaction. These discrepancies subsequently resulted in differences in the properties of the resulting copolymer materials. The majority of the copolymers exhibited glass transition temperatures (Tg) within the range of 110 to 130 °C. However, three initiator formulations yielded copolymers with two distinct transition temperatures. Additionally, when fabricating copolymers with a DCPD:ENB volume ratio of 60:40, their stress-strain responses displayed elastic modulus values ranging from 1.3 to 1.6 GPa. Notably, one initiator formulation yielded a polymer with distinctive elastomeric properties, characterized by a lower Young's modulus and a higher strain to failure. By carefully selecting the resin formulation and boundary conditions, deliberate control of nonplanar front dynamics in a closed mold allowed for the efficient production of molecularly architected polymers. Minor variations in the inhibitor concentration brought about significant differences in both the macroscopic and microscopic characteristics of the resulting polymers. The material domain spacing was precisely regulated by adjusting the ambient temperature and the size of the specimen geometry. This was further validated and confirmed through numerical modeling. Moreover, the utilization of ruthenium initiators with different alkylidene species led to distinct ambient temperature conditions, directly impacting the material domain spacing, polymer chain/lamellae orientation, and the resulting mechanical properties. Experimental data and numerical modeling were coupled to gain a deeper understanding of the intricate dynamics that take place during the frontal polymerization of cyclic olefins in both open and closed mold configurations. We established the design space for tuning the reaction kinetics and boundary conditions to harness and control the fluid convection during FROMP in both closed and open mold geometries. Unique characteristics of the reaction-diffusion-convection (RDC) dynamics were characterized and exploited to enable topology control and pattern formation during the polymerization process. Furthermore, we expand the use of convective flow for the fabrication of functionally graded materials (FGM). Utilizing the density differences of two cyclic olefin monomers, DCPD and 1,5-cyclooctaidne (COD) we layer the two resins in the rectilinear open mold. The convective flow and differences in monomer reactivities led to materials with compositionally graded material properties. The resulting material properties of the FGM were characterized by differential scanning calorimetry (DSC) and nanoindentation.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Justine Paul

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