Cross‐linked Poly(Octadecyl Acrylate)/Polybutadiene Shape Memory Polymer Blends Prepared by Simultaneous Free Radical Cross‐linking, Grafting and Polymerization of Octadecyl Acrylate/Polybutadiene Blends

Abstract

A semi‐crystalline, shape memory polymer (SMP) is fabricated by free radical cross‐linking, polymerization, and grafting in a blend of n‐octadecyl acrylate and polybutadiene (PB). Poly(n‐octadecyl acrylate) (PODA) is a side‐chain crystalline polymer, which serves as the structure‐fixing network counterbalancing the elastically deformed, cross‐linked polymer network. At a constant 50/50 ratio of monomer and polymer the amount of free radical initiator, dicumyl peroxide (DCP) is varied from 1% to 5% w/w PB. From swelling measurements and calculation of the cross‐link density it is determined that DCP produces greater than one cross‐link per DCP molecule. It is found that lower cross‐linking efficiency is favorable for higher shape fixity. This lower efficiency is found to produce a higher degree of crystallinity of the PODA in the 2–5% DCP samples, which is determined to be the main driver of higher shape fixity of the polymer. A SMP with >90% fixity and 100% recovery at uniaxial strains from 34–79% is achieved. This material should be useful for mold processing of shape memory articles. This approach provides a method to decouple the elastomeric and thermoplastic portions of a SMP to convert commodity elastomers into SMPs and tailor the shape memory response.

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

“…To address this issue, we recently investigated fabricating SMPs by blending polybutadiene (PB), the elastomer base, with octadecyl acrylate (ODA), a crystalline monomer, and dicumyl peroxide (DCP), a free radical initiator. [ 28 ] On heating, simultaneous crosslinking, polymerization, and grafting take place, producing an SMP whose shape fixing is enabled by the side‐chain crystallinity of the poly(octadecyl acrylate) (PODA) chains. In the PB/ODA/DCP materials, a single formulation with a 50/50 weight ratio of PB and ODA was investigated with varying amounts of DCP.…”

Stiffness Variable Polymers Comprising Phase‐Changing Side‐Chains: Material Syntheses and Application Explorations

“…Similarly, polybutadiene rubber was also used to interconnect stearyl acrylate, achieving high fixity (>90%) and recovery (> 99%). [ 97 ] Block copolymers containing a SA block also show improved shape recovery performance. [ 113 ]…”

“…Thus, the change of storage modulus during the rigid-to-rubbery transition of the SA-UDA copolymers attenuates from 1066-fold to only 15-fold when the SA fraction is reduced from 80% to 40%. Other elastic materials, such as synthetic rubbers [97,98] and hydrogels, [102,103] are also utilized as additives to increase the strain capacity and recovery performance of the s-SVP.…”

“…Similarly, polybutadiene rubber was also used to interconnect stearyl acrylate, achieving high fixity (>90%) and recovery (> 99%). [97] Block copolymers containing a SA block also show improved shape recovery performance. [113] Hydrogels incorporating an s-SVP like hydrophobic moiety have also been investigated for high strain and shape recovery.…”

“…When a pre‐polymerized elastomer, such as polybutadiene [ 97 ] and butyl rubber, [ 98 ] is added in the s‐SVP matrix, the melting and recrystallization temperatures of the alkyl chain domain are independent of the rubber content, as a result of clear phase separation between the elastomer matrix and the newly‐formed s‐SVP domain. By a similar principle, when paraffin, a phase‐changing compound, is added to an allyl‐based epoxy resin, an s‐SVP, the resulting blend exhibited both the transition temperatures of the s‐SVP matrix (35.9 °C) and pristine paraffin (59.0 °C).…”