It’s all about diffusion: Measurements and modeling of particle morphologies in dispersed-phase polymerization

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Contrasting acrylate versus methacrylate crosslinking reactions and the impact of temperature

Divinyl monomers containing multiple vinyl groups are commonly used in polymerization reactions to introduce crosslinked networks. The reactivity of the second vinyl group in a crosslinker monomer decreases once it becomes incorporated in a polymer chain. This Reduced Reactivity Parameter (Ψ) depends on the monomer-crosslinker pair. To date, our group has developed this concept exclusively from methacrylate-based copolymerization systems1,2. Acrylate co-monomers introduce another level of complexity from a competing mechanism toward gel content and macromolecular network development; long chain branching from chain transfer to polymer. The later form networks via α-hydrogen abstraction, which is a prominent reaction with acrylates. Moreover, the differences in reactivity ratio between acrylates and methacrylates add another layer of heterogeneity through the polymerization which also impacts the kinetics and ultimate network structure. In this work, we compare the network formation reaction and the Ψ-parameters for 1,4 butanediol dimethacrylate (BDDMA, containing methacrylate groups) with its acrylate-based counterpart (BDDA, containing acrylate groups) in copolymerization reactions with either n-butyl methacrylate (nBMA) or n-butyl acrylate (nBA). The Ψ-parameter for all systems is estimated by comparing the experimental results with Monte Carlo simulations of the polymerization reactions. The goal of the work is to decouple the contributions of pendent-vinyl based crosslinking and long-chain branching (α-hydrogen abstraction) from the resulting kinetic profile that the Ψ parameter is determined from. Moreover, we contrast the balance of contributions from propagation, chain transfer, reactivity ratios, and utility of the pendent vinyl groups for crosslinking between reactions at either 60 or 70 °C. Even this seemingly small shift in temperature has a marked impact on the kinetics and resulting network for the different pairs of (meth)acrylate comonomers. Tripathi, A.K.; Neenan, M.L.; Sundberg, D.C.; Tsavalas, J.G., Influence of n-Alkyl Ester Groups on Efficiency of Crosslinking for Methacrylate Monomers Copolymerized with EGDMA: Experiments and Monte Carlo Simulations of Reaction Kinetics and Sol-Gel Structure , Polymer (2016), 96, 130–145, DOI:10.1016/j.polymer.2016.04.017 Tripathi, A.K.; Tsavalas, J.G.; Sundberg, D.C., “Monte Carlo Simulations of Free Radical Polymerizations with Divinyl Crosslinker: Pre- and Post-Gel Simulations of Reaction Kinetics and Molecular Structure , Macromolecules (2015) 48, 184−197, DOI: 10.1021/ma502085

Mechanistic insights into topological network formation in free radical co-polymerization

The first part of the talk will discuss reaction kinetics and molecular architecture development during free-radical, bulk copolymerizations of a homologous series of methacrylate monomers with a series of dimethacrylate crosslinkers of varying alkyl spacer lengths. The overall objective of this work was to determine the extent to which the ester side chains of the methacrylate monomers hinder chain-end radical propagation reactions through the pendent vinyl groups of the crosslinking monomer. We have determined that this steric hindrance is quite significant and increases to the point where the sweeping radius of the pendent vinyl can be obstructed by the neighboring monomer ester side groups. The effective sweeping radius of the pendent vinyl can be equivalently expressed by various combinations of dimethacrylate and methacrylate. Please download the file below for full content

An experimental investigation of "end-block" reinforcing in prestressed concrete beams

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Civil and Sanitary Engineering, 1959.MIT copy bound with: Built-up plastic forms for concrete / by Granville Hardwick Sewell [1959]Includes bibliographical references (leaf 25).by George John Tsavalas.B.S

A molecular level investigation of hybrid miniemulsion polymerization

Ph.D.F. Joseph Schor

Water-based crosslinkable coatings via miniemulsion polymerization of acrylic monomers in the presence of polyester resin

M.S.F. Joseph Schor

A surprisingly gentle approach to cavity containing spherocylindrical microparticles from ordinary polymer dispersions in flow

Herein, we demonstrate a facile approach to fully transform spherical polymeric microparticles to elongated spherocylinders containing an internal cavity under ambient and mild stirring conditions. Critical to the process is to deform the amorphous and non-crosslinked particles under glassy conditions for an unusually long time; 120 hours for the poly(styrene-co-glycidyl methacrylate) microparticles discussed in greatest detail. Larger particles in the 5 micron and greater range were markedly more susceptible to the shear imposed by stirring the aqueous dispersion. The resulting morphology is robust and kinetically frozen yet reverts to the original spherical shape if annealed above the glass transition temperature with suitable temperature or plasticizer. The volume fraction of the internal void can be modulated by particle composition and process conditions and is irregular in shape we believe as a result of a cavitation event during plastic deformation

Kinetic Monte Carlo simulation of emulsion copolymerization reactions with divinyl crosslinker monomer: Effect of process parameters on final properties

Crosslinking agents like ethylene glycol dimethacrylate are widely used emulsion polymerization. A computationally efficient Monte Carlo method was used to simulate the reaction kinetics and molecular structure development during emulsion copolymerization with crosslinker monomers. A single parameter was used to describe the reduced reactivity of the pendent vinyl groups incorporated within the polymer backbone. In these studies, various process parameters like the rate of monomer feed, the glass transition temperature of the polymer and the amount of crosslinker monomer were varied. The effect of these variations on the reaction kinetics and final polymer properties like gel point, sol-gel fraction, crosslinking density and fraction of utilized pendent vinyl groups were tested