Structure–Property Relationships of Shape Memory, Semicrystalline Polymers Fabricated by In Situ Polymerization and Crosslinking of Octadecyl Acrylate/Polybutadiene Blends

Abstract

The current work presents the study of a semicrystalline, shape memory polymer synthesized by simultaneous free radical polymerization and crosslinking in a blend of polybutadiene (PB) and octadecyl acrylate. Blending elastomers and phase change materials provide a modular method for new smart materials, such as shape memory polymers. In this system, grafted, side-chain crystalline poly(octadecyl acrylate) (PODA) fixes a programmed shape in the shape memory cycle, while crosslinked polybutadiene drives shape recovery. This work focuses on improving material parameters important for shape memory (crystallinity, gel fraction, melting temperature) by tuning the processing and formulation parameters (amount of crosslinker and PB weight fraction). The result is a shape memory PB-PODA copolymer that can be fabricated by melt processing and programmed without cooling below ambient temperature. It is found that good shape memory (i.e., high shape fixity and recovery) is obtained at a low PB weight fraction where a percolating PODA crystal network is formed at room temperature. The optimized sample shows excellent shape memory properties (fixity > 99%, recovery = 96%). It is shown that it is possible to mold this material into complex 3D shapes or topography with potential use in anticounterfeiting and antitampering applications.

Thermal Annealing of High cis-1,4-Polybutadiene/Octadecyl Acrylate Blends as a One-Step Process for Fabricating Shape Memory Polymers

“…This is done without any peroxide initiator and therefore avoids the potential hazards of working with peroxide-containing materials as examined in our previous work. 18,19 This present work follows the previous reports of Luchtenberg et al who showed the grafting of ODA to PB by an Alder-ene reaction. 23 They observed no gelation when they heated PB (M n = 1700 g/mol, 75 mol % 1,4-cis, 24 mol % 1,4trans, and 1 mol % vinyl) with ODA in the presence of N,Ndiphenyl-p-phenylenediamine, and acetylacetone in a dark reaction vessel under a nitrogen atmosphere at 180 °C for 25 h. However, in this current study, a higher MW PB (M n = 234,322 g/mol) was used where gelation occurs due to a thermally driven cross-linking reaction along with simultaneous ODA grafting of PB, resulting in a cross-linked graft network mixed with ODA crystals capable of exhibiting shape memory properties.…”

“…Figure 11b,c compares the shape memory properties of annealed PB-xODA (current study) and annealed PB-xPODA-yDCP samples (previous study using peroxide curing and using PB with a different molecular weight and higher 1,2 content 18 ). While a plateau is observed in the fixity at high ODA loading in the peroxide cured samples, a more continuous decrease is observed in annealed PB-xODA.…”

“…e o av sol ex,est PB g ODA 1/3 1,PB PB i k j j j j j y { z z z z z i k j j j j j y { z z z z z = (18) where ϕ PB-g-ODA is the volume fraction of PB grafted with ODA given as S6, Supporting Information. A smooth curve was not obtained for (υ e / V o N av ) sol ex, est as f ODA-R varies with [ODA]/[B].…”

“…Nevertheless, a recent approach to capitalize on the positive attributes of polymer/small molecule blends in fabricating SMPs is to use a monomer as the small molecule additive, which after blending can be polymerized making it more difficult to remove from the SMP. Both Cavicchi and coworkers and Okay and coworkers have investigated the free radical polymerization of octadecyl acrylate (ODA) and simultaneous cross-linking of unsaturated elastomer precursor polymers to produce SMPs by thermal (Cavicchi) , and photo-polymerization (Okay). − Poly­(octadecyl acrylate) (PODA) is a side-chain crystalline polymer that produces thermoplastic domains in cross-linked materials resulting in excellent shape memory properties. In both cases, while PODA serves as the network that promotes shape fixing, the cross-linked elastomer drives the material to revert to its original shape.…”

Reconfigurable and Reprocessable Thermadapt Stress‐Free Two‐Way Shape Memory Polymers Based on a Dual Crosslinking Network with Outstanding Mechanical Properties

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shape changes in response to external stimuli, are a class of most important candidates for biomimetic smart materials. [7][8][9][10] According to whether the shape deformation was reversible, SMPs could be classified into one-way (1W-SMPs) and two-way SMPs (2W-SMPs). Considering that 2W-SMPs could perform reversible shape deformation between two distinct shapes back and forth without new programming, they were more suitable for realizing complex functions.

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