Triallyl Trimesate Research Articles

Hydrolytic degradation of branched PLA produced by reactive extrusion

Reactive extrusion using dicumyl peroxide (DCP) and a tri-functional coagent, triallyl trimesate (TAM) is implemented to introduce long-chain branching (LCB) in poly(lactic acid) (PLA). The effects of this modification on the long-term hydrolysis of PLA are assessed by monitoring the mass, molar mass distributions, and thermal properties of specimens exposed to hydrolytic degradation at a temperature of 60 °C. A slow initial rate of mass loss coupled with an immediate and rapid loss in molar mass are characteristic of a bulk erosion mechanism. Significant loss is observed in all molar mass averages within the first 20 days. In LCB PLA the most drastic decrease was observed in the z-average molar mass, Mz, as a result of the cleavage of the LCB segments from the polymer chain. Degradation induced crystallinity is observed in all formulations, attributed to the combined influence of annealing and the plasticizing effect of water. Although the hydrolysis profile is altered, reactive modification does not affect negatively the degradability of LCB PLA over a 12-week period, suggesting that these modified PLAs can be used in commodity applications that require degradable polymers.

Peroxide-initiated graft modification of thermoplastic BioPolyesters: Introduction of long-chain branching

The chemical modification of polylactic acid (PLA) and related polyesters by peroxide-initiated grafting of multifunctional allylic and acrylic monomers is described. Solvent-free, melt-state reactions of PLA and triallyl trimesate (TAM) are shown to be remarkably efficient compared to analogous reactions of polyolefins such as poly(ethylene-co-octene) (EOC), requiring very low reagent loadings to produce a long chain branched (LCB) architecture. A systematic study of potential transesterification chemistry confirms that ionic reactions do not contribute significantly to PLA reactivity under typical grafting conditions. Further explorations of H-atom abstraction and monomer addition yields demonstrate that PLA is relatively unreactive toward the radical reactions that support LCB production. Careful examination of the solubility of coagent intermediates reveal dramatic differences in oligomer solubility between a hydrocarbon system and an ester-based matrix. Whereas TAM conversion in hydrocarbon leads to a precipitation polymerization that removes coagent from solution, reactions conducted in the polyester do not incur losses of oligomeric intermediates, indicating that the ability of PLA to retain multi-functional intermediates is the underlying cause of its remarkable LCB grafting yields.

Manipulating the structure of medium-chain-length polyhydroxyalkanoate (MCL-PHA) to enhance thermal properties and crystallization kinetics

We investigated the effects of the structure of medium-chain-length polyhydroxyalkanoates (MCL-PHAs) on their thermal properties and crystallization kinetics. The predominantly homopolymeric poly(3-hydroxydecanoate), P(3HD)-98, and the poly(3-hydroxydodecanoate), P(3HDD), exhibited sharp crystallization peaks upon cooling, with the latter exhibiting faster crystallization rates. A chemical modification strategy involving reaction with dicumyl peroxide and triallyl trimesate coagent was implemented to introduce branching and enhance the crystallization kinetics of P(3HD-98). Increases in the exothermic crystallization temperature by 8 °C and in the overall crystallinity of the P(3HD)-98 were observed upon chemical modification. The Avrami crystallization kinetic parameters obtained by fitting the isothermal crystallization data revealed a significant increase in the crystallization rate of the modified P(3HD)-98.

Tuning the Rheological, Thermal, and Solid-State Properties of Branched PLA by Free-Radical-Mediated Reactive Extrusion

The purpose of this work is to establish structure–property relations of poly(lactide) (PLA) formulations that were branched by peroxide-mediated reactive extrusion, in the presence of triallyl trimesate (TAM) coagent. Based on detailed evaluations of the molar mass distributions and rheological properties we deduce that modified PLA consists of a population of linear, and long chain branched (LCB) PLA chains, depending upon the amount of the peroxide and coagent. Even though peroxide alone does not induce significant changes in the architecture, TAM is very effective in producing LCB structures, which result in substantial increases in viscosity, elasticity, as well as strain hardening characteristics. At high DCP and TAM loadings, cross-linked structures are obtained. The reactively modified formulations have higher molar mass, which results in improved Izod impact strength, whereas the rest of the properties, including their capacity to degrade hydrolytically, are maintained. Furthermore, these materia...

Coagent Modified Polypropylene Prepared by Reactive Extrusion: A New Look into the Structure-Property Relations of Injection Molded Parts

AbstractPeroxide-mediated reactive extrusion of linear isotactic polypropylene (L-PP) was conducted in the presence of trimethylolpropane trimethacrylate (TMPTMA) and triallyl trimesate (TAM) coagents, using a twin screw extruder. The resulting coagent-modified polypropylenes (CM-PP) had higher viscosities and elasticities, as well as increased crystallization temperature compared to PP reacted only with peroxide (DCP-PP). Additionally, deviations from terminal flow, and strain hardening were observed in PP modified with TAM, signifying the presence of long chain branching (LCB). The CM-PP formulations retained the modulus and tensile strength of the parent L-PP, in spite of their lower molar mass and viscosities, whereas their elongation at break and the impact strength were better. This was attributed to the finer spherulitic structure of these materials, and to the disappearance of the skin-core layer in the injection molded specimens.

Chain extended poly(3-hydroxybutyrate) with improved rheological properties and thermal stability, through reactive modification in the melt state

Branching and crosslinking of polyhydroxybutyrate (PHB) is accomplished for the first time through reactive modification in the melt state, using dicumyl peroxide (DCP) as the free-radical initiator and a tri-functional coagent, triallyl trimesate (TAM). The dynamic oscillatory rheological properties, as well as extensional viscosities provide strong evidence of branching and crosslinking, depending on the amounts of DCP and TAM. In addition to the significant increases in viscosity due to branching/crosslinking, coagent modified samples exhibit a significant increase in the crystallization temperature, indicative of a nucleating effect, accompanied by a decrease of crystal spherulite sizes. In addition, the solid-state storage modulus in DMTA experiments is 65% higher in formulations that contain high gel contents, whereas the glass transition temperature of the cured formulations is slightly lower. Coagent modified PHB exhibit a substantial improvement in the thermal stability, both in isothermal dynamic oscillatory temperature sweeps, as well as non-isothermal TGA experiments.

Improvements in the melt and solid-state properties of poly(lactic acid), poly-3-hydroxyoctanoate and their blends through reactive modification

Poly(3-hydroxyoctanoate) (PHO), poly(lactic acid) (PLA) and PHO/PLA blends were reactively modified in the melt state, using dicumyl peroxide (DCP) and triallyl trimesate (TAM) trifunctional coagent. The viscosity and elasticity of PHO and PLA increased substantially following reactive modification. The processability of the partially cross-linked PHO was improved, whereas coagent-modified PLA displayed strain hardening and enhanced crystallization. Reactive compounding of PLA and PHO in the presence of DCP and TAM resulted in blends with enhanced strain hardening, indicative of high melt strength, and improved crystallinity compared to the unreacted blend. Furthermore these blends had a finer morphology, which was attributed to a compatibilizing effect possibly arising from copolymer formation at the interface. The elongation at break and impact properties of the blends were improved compared to the neat PLA, while the heat deflection temperature remained unaffected.

Foaming of reactively modified polypropylene: Effects of rheology and coagent type

A series of linear controlled rheology polypropylenes were produced through reaction with dicumyl peroxide in the melt state, to investigate the effect of molecular weight and viscosity on foaming. Foaming experiments by compression molding, using a chemical blowing agent (azodicarbonamide), and by batch foaming using nitrogen-blowing agent, revealed that lower viscosity promoted higher expansion ratios and larger cells, due to reduced resistance to cell growth. Linear polypropylene was further modified using trimethylolpropane trimethacrylate and triallyl trimesate coagents. Coagent modification resulted in pronounced changes in the shear thinning and elasticity of the modified polypropylenes. However, evidence of long-chain branching was only present in polypropylene modified by triallyl trimesate. Foams based on coagent-modified polypropylenes had higher expansion ratios than their degraded counterparts. This was ascribed in part to the lower viscosities, and to a nucleating effect, arising from the presence of a finely dispersed phase of coagent-rich nanoparticles. Strain hardening in polypropylenes modified by triallyl trimesate further resulted in a finer cell structure, due to suppressed coalescence.

Crystallization of Coagent-Modified Polypropylene: Effect of Polymer Architecture and Cross-Linked Nanoparticles

Linear isotactic polypropylene (PP) was chemically modified by solvent-free, peroxide-initiated grafting of trimethylolpropane trimethacrylate and triallyl trimesate. The resulting coagent-modified PP materials possessed bimodal molecular weight and branching distributions, whose populations varied with coagent structure. In addition to changing polymer chain architecture, these chemical modifications generated a small amount of well-dispersed, coagent-derived nanoparticles. When compared with the parent material and PP samples treated with peroxide alone, coagent-modified materials demonstrated significantly higher crystallization temperatures and crystallization rates, as well as a finer spherulitic structure. The importance of a particle-induced, heterogeneous nucleation mechanism is confirmed by comparative analysis of a long-chain branched PP derivative synthesized by homogeneous silane grafting and moisture curing chemistry. Crystallization studies show that whereas branching has a moderate effect on crystallization kinetics, heterogeneous nucleation effects dominate the crystallization of coagent-modified PP materials.

Dramatic Improvements in Strain Hardening and Crystallization Kinetics of PLA by Simple Reactive Modification in the Melt State

Poly(lactic acid) (PLA) is chemically modified by radical mediated solvent-free, peroxide-initiated grafting of triallyl trimesate (TAM) coagent in the melt state. When compared with the parent material and with PLA samples treated with peroxide alone, coagent-modified materials demonstrate higher molar mass and improved melt rheological properties, including substantial improvements in melt elasticity and strain hardening under uniaxial extension. Although similar rheological modifications are obtained by PLA chain extension using a multi-functional epoxide oligomeric chain extender, the coagent-modified material demonstrates significantly enhanced crystallinity and crystallization rates. The appearance of a distinct crystallization exothermic peak and the disappearance of the cold crystallization temperature point to a nucleation effect in the coagent modified PLA, which together with the rheological enhancements can promote the processability of this material in conventional thermoplastics operations.

Thermal analyses of organic powders made from precipitation polymerization of triallyl monomers

Organic solids have been prepared from radical-initiated activation of solutions composed of tetradecane and triallyl trimesate (TAM) monomer or triallyl phosphate (TAP) monomer using a recently developed variation of precipitation polymerization methods. The powders, which comprise fused aggregates, are shown to be rich in monomer (83–88 wt% TAM or 86–92 wt% TAP), and are believed to be formed by a combination of hydrocarbon addition and allyl group oligomerization. TAM-g-tetradecane primary particles are on the order of 500 nm in diameter, while TAP-g-tetradecane particles are on the order of 100–200 nm diameter. These products are thermochemically assessed using a combination of differential scanning calorimetry, thermogravimetry and pyrolysis combustion flow calorimetry. The phosphorus-containing TAP-g-tetradecane shows exothermic activity around 230 °C, likely due to thermal decomposition of the trialkyl phosphate moiety, and may find use in advanced materials applications.

Preparation of crosslinked microspheres and porous solids from hydrocarbon solutions: A new variation of precipitation polymerization chemistry

AbstractA new variation of precipitation polymerization is described wherein CH bond addition to a triallyl monomer contributes to molecular weight growth, thereby incorporating a significant amount of saturated hydrocarbon into the solid phase. The extent of monomer oligomerization relative to hydrocarbon addition is shown to increase with the concentration of allyl benzoate in cyclooctane. An extension to the trifunctional monomer, triallyl trimesate, results in phase separation of hydrocarbon‐monomer adducts to give a dispersed phase whose continued reactivity leads to crosslinked microspheres. The relationships between reaction conditions and solid‐phase composition and morphology are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6561–6570, 2009

Selectivity of allylic coagent‐mediated polypropylene maleation

AbstractThe peroxide‐initiated cografting of maleic anhydride (MAn) and allylic coagents to polypropylene (PP) is described. Both triallyl trimesate (TAM) and triallyl phosphate (TAP) are shown to be compatible with MAn, as the presence of either coagent has no apparent effect on the yield or distribution of anhydride grafts within functionalized PP. Therefore, the influence of chain scission on the melt‐state rheological properties of maleated PP can be mitigated using coagent‐assisted crosslinking. The success of this cografting strategy for controlling melt viscosity is shown to depend on the extent that a bimodal, branched architecture can provide the rheological properties demanded by a given application. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Structure–rheology relationships of long-chain branched polypropylene: Comparative analysis of acrylic and allylic coagent chemistry

The relationship between product structure and melt-state rheological properties is established for series of branched PP derivatives prepared by the radical-mediated grafting of tri-functional coagents. Peroxide-initiated, solvent-free additions of linear PP to triallyl trimesate (TAM), trimethylolpropane triacrylate (TMPTA) and triallyl phosphate (TAP) at high temperature are shown to produce bimodal molecular weight and branching distributions. Low-frequency dynamic shear viscosities as well as extensional viscosities are shown to be highly responsive to a hyper-branched chain population, whose abundance and molecular weight correlate with the kinetic chain length of the grafting process, and the propensity of a coagent to oligomerize.

Coagent-induced transformations of polypropylene microstructure: Evolution of bimodal architectures and cross-linked nano-particles

Polypropylene is transformed by simultaneous, radical-mediated chain scission and cross-linking to generate branched architectures. While macroradical fragmentation reduces the molar mass of the dominant chain population, cross-linking by triallyl trimesate (TAM) activation yields a minority population of hyper-branched chains that is less susceptible to molecular weight loss. This disparity in chain reactivity leads to bimodal molecular weight and branching distributions. Furthermore, a precipitation polymerization of TAM can proceed concurrently with PP branching to produce a low yield of cross-linked, TAM-rich nano-particles. The mechanisms through which unimodal composition and molecular weight distributions evolve toward a bimodal condition are discussed, along with the factors that lead to particle formation.