The focus of this work is to synthesize a monomer from a fatty acid methyl ester capable of forming high molecular weight polymers. The mono-unsaturation in the starting material, methyl oleate, was first epoxidized using a peroxy acid. This intermediate material was further modified using acrylic acid. The acrylated molecule is able to participate in free-radical polymerization reactions to form high molecular weight polymers. The rate of polymerization was low because of the long aliphatic structure of the monomer. It is hypothesized that the polymerization reaction occurred in the interface between the particle and water, thereby slowing down the reaction. After 18 h of reaction, a monomer conversion of approximately 91% was achieved. A maximum weight-average molecular weight of approximately 10 6 g/mol was observed after 14 h of reaction. At early reaction times linear polymers were formed. However, as the reaction time increased, the amount of branching that occurred on the polymer molecule increased, as indicated by gel permeation chromatography and light scattering. This has been attributed to chain transfer to polymer via hydrogen abstraction from a tertiary backbone C-H bond. The resulting polymer may be of considerable interest for pressure-sensitive adhesive applications.

No abstract

Medium to low density thermoplastic nanofoams have previously been produced using nanoparticles as nucleating center. Here we show that by designing the molecular structure of the polymer matrix to achieve high CO 2 solubility while controlling the glass transition temperature, it is possible to produce nanofoams with cell nucleation densities as high as 10 16 /cm 3 without introducing nucleation aids. This was achieved by maximizing foam expansion without uncontrolled cell ripening for a series of acrylic copolymers, which were foamed under a set of standard conditions. To predict the role of foaming conditions on foam characteristics, a theoretical foaming model was built to simulate cell nucleation, growth and foam stabilization. Experimental or predicted properties of the polymer/carbon dioxide mixture were used as inputs. Despite simplifying assumptions, such as the use of classical nucleation equations, the semi-quantitative model provides insight into the foam expansion behavior and validates experimental observations.

Abstract

Abstract:Adhesion at polymer-solid interfaces was explored for a new bio-based pressure sensitive adhesive (PSA) in terms of sticker groups φ X on the polymer phase, receptor groups φ Y on the solid surface and the bond strength of the sticker-receptor X-Y acid-base interaction, χ. The polymer-solid interface restructuring models of Gong and Lee et al were extended with new percolation models of entanglements and interface strength to determine the optimal sticker group concentration φ* X . For the general case where φ Y and χ are constant, it is predicted that when φ X < φ* X , that the critical peel energy behaves as G 1c ~ φ X /φ* X and the locus of failure is adhesive between the polymer and the solid.However, when φ X > φ* X , failure occurs cohesively in a polymer-polymer interface adjacent to the solid and the strength decreases as G 1c ~ φ* X /φ X . The switch from adhesive to cohesive failure can be understood in terms of the changes in the chain conformations of the adhered chains and their decreasing interpenetration X i with the bulk chains, via X i ~ 1/r, where r = χφ X φ Y . The optimal value of φ X which maximizes the adhesion and determines the mode of failure is given by φ* X ≈0.129/C ∝ , and for typical values of the characteristic ratio C ∝ in the range 7-20, φ* X ≈ 1% mole fraction, corresponding to about 2 sticker groups per entanglement molecular weight M e . This result was verified for a biobased pressure sensitive adhesive synthesized from an acrylated high oleic fatty acid, which was copolymerized with maleic anhydride as the sticker group. The observed behavior is counterintuitive to the current wisdom for the effect of acid-based interactions on adhesion, where the strength is expected to increase with the number of X-Y contacts. The surprisingly low value of φ* X ≈ 1% sticker groups which maximizes the adhesion strength can now be readily calculated using the percolation model of entanglements and fracture.