Bottlebrush Amphiphilic Polymer Co-Networks

Abstract

We report the synthesis of novel poly(ethylene glycol) and poly(dimethyl siloxane) (PEG and PDMS, respectively) bottlebrush amphiphilic polymer co-networks (B-APCNs) with high gel fractions by a grafting-through ring-opening metathesis polymerization. By varying the volume fraction of PEG (ϕ PEG ), we alter the crystallinity of the networks, achieving complete suppression of PEG crystallinity at ϕ PEG = 0.35. Furthermore, we show that the crystallinity of these networks can be tuned to alter their moduli. Through dynamic mechanical analysis, we show that the storage and loss moduli of networks with completely suppressed crystallinity (ϕ PEG = 0.35) behave similarly to a PDMS homopolymer bottlebrush network. These bottlebrush networks represent an unexplored architecture for the field of amphiphilic polymer co-networks. ■ INTRODUCTIONRecent advances in polymer chemistry are revolutionizing tailor-made soft materials. One area experiencing significant advancement is polymeric networks with precise control over the molecular chains that constitute the network. 1−12 Polymer networks are ubiquitous as the basis of a wide range of products including structural materials, adhesives, membranes, and biomaterials. 7,13,14 The next generation of materials are expected to exhibit a broader range of properties and be multifunctional. 14−17 One subset of polymer networks that appears to be gaining interest in this regard are amphiphilic polymer co-networks (APCNs). 15 Generally, APCNs are multicomponent networks with two disparate macromolecular strands that phase separate. 15−19 APCNs are typically prepared by either crosslinking preformed chains post-polymerization or copolymerizing monomers and crosslinkers, with the different components of the system acting as either the hydrophilic or hydrophobic segments. 10,20−26 These systems display properties of either or both strands that comprise the network. 15,27−32 This feature endows APCNs with a diversity of applications including functional membranes (e.g., soft contact lenses), gas sensing matrices, antifouling coatings, and tissue engineering. 9,33−40 Adding to the interest in APCNs are the wide variety of design parameters available for manipulation, allowing for a myriad of novel materials to be created. Recently, Patrickios and Matyjaszewski provided a taxonomy of APCNs (Figure 1) illustrating the diversity of "knobs" (e.g., the arrangement of

The Impact of Polymerization Chemistry on the Mechanical Properties of Poly(dimethylsiloxane) Bottlebrush Elastomers

“…Bottlebrush networks are receiving increased attention due to the unique architectural possibilities afforded by the side chains densely grafted upon strands of the network. − The high local density of side chains extends the backbone and produces networks where the strands are rigid cylinders that are less likely to form physical entanglements, resulting in supersoft materials with moduli similar to biological tissue without the need for solvent swelling. , Major architectural parameters of bottlebrush networks are n g , n sc , and n x the degree of polymerization between side chains, of side chains, and between crosslinks, respectively (Figure ). This diversity of parameters allows for bottlebrush elastomers (BBEs) to have a wide degree of tunability, enabling the design of solvent-free materials with moduli ranging from 10 2 to 10 6 Pa. ,, …”

Network Constitutional Isomers

“…Fortunately, the easy-to-manipulate architecture of bottlebrush polymers and bottlebrush networks (BBNs) present an elegant solution to this problem. − BBNs are a class of polymer networks where the high grafting density and length of side chains stretch the polymeric backbone and its side-chains due to steric repulsion, leading to a marked lack of physical entanglements. − Polymerization of BBNs via a living polymerization method would provide direct control over R K in a material in which the effects of entanglements can be disregarded. The highly popular ring-opening metathesis polymerization (ROMP) is uniquely positioned to study the role of R K in BBNs due to its high conversion, living nature, lack of chain transfer, and established use in synthesizing BBNs. ,− Using ROMP, R K can be easily controlled by varying the monomer-to-initiator ratio ( M / I ), with large M / I s producing longer R K s.…”

Shear Thinning from Bond Orientation in Model Unentangled Bottlebrush Polymer Melts

“…This is complicated by the challenges in the controlled synthesis and characterization of branched polymers. 29,30 Several studies have been conducted to investigate the rheological properties of melts or solutions of bottlebrushes (synthetic or biological) such as their viscoelasticity, 31,32 shearinduced crystallinity, 33,34 and shear-thinning behavior in aggrecan solutions. 35 A few experimental studies shed light on the complex contribution of the bottlebrush architectural parameters to their melt rheology.…”