Constant Copolymer Composition Research Articles

An Efficient Monte Carlo Representation of Semi‐Batch Starved‐Feed Acrylate‐Methacrylate Multicomponent Radical Polymerization

AbstractThe introduction of functional groups through radical copolymerization under starved‐feed conditions is a cost‐effective means to produce acrylate resins for coatings applications. The semi‐batch recipes often include a large fraction of nonfunctional acrylates and methacrylates, with a low percentage of functional comonomer added to become statistically distributed within the chains. A previous kinetic Monte Carlo representation is extended to efficiently consider multicomponent recipes consisting of both functional and nonfunctional acrylate (or methacrylate) components by taking advantage of the family type behavior of polymerization mechanisms and rate coefficients. The extended model is used to simulate the semi‐batch production of a terpolymer consisting of 2‐hydroxyethyl acrylate (HEA), butyl acrylate, and butyl methacrylate, examining the impact of recipe formulation as well as HEA preloading on the distribution of HEA units within the polymer chain sequences. The preload strategy does not provide significant improvement, as the most important factor for minimizing the amount of nonfunctional chains produced is to maintain constant copolymer composition and polymer molecular weight throughout the course of the entire reaction.

Synthesis of poly(acrylic-co-itaconic acid) through precipitation photopolymerization for glass-ionomer cements: Characterization and properties of the cements

ObjectiveThe aim of this study was to synthesize poly(acrylic acid-co-itaconic acid) (PAA-co-PIA) ionomer through a novel precipitation photopolymerization technique. The ionomer was characterized and the effect of its structural parameters, such as molecular weight and copolymer composition were investigated on the mechanical properties of glass-ionomer prepared using the ionomer. MethodsDesign of experiment (DOE) was used to examine the effect of monomer ratio and the amount of chain transfer agent on the molecular weight and final conversion of the ionomers synthesized through the precipitation photopolymerization. The copolymer compositions were identified using FTIR and 1H-NMR spectroscopy. The molecular weights of the copolymers were evaluated by GPC. A series of PAA-co-PIA copolymers were then synthesized via the photopolymerization technique in three monomer ratios and two molecular weight ranges (high and low) to study the properties of the glass ionomers thereof. Experimental dental glass-ionomer cements were prepared by mixing the synthesized polymers with glass powder and their compressive properties were determined according to ISO 9917-1:2007 after storing for 0, 1, 7 and 28 days in distilled water. The scanning electron microscopy (SEM) was used to study the fracture surface morphology of the cements. ResultsThe PAA-co-PIA polymers were synthesized by the photopolymerization method in a short time and high purity. The DOE showed that by decreasing the acrylic acid/itaconic acid ratio and increasing the amount of transfer agent, the molecular weight and final conversion decreased significantly. By increasing the itaconic acid content in the copolymer composition and increasing the molecular weight in a constant copolymer composition, the compressive strength and modulus were increased. Microstructures revealed that cements made of the higher molecular weight poly acids showed lower cracks and voids. SignificanceThe precipitation photopolymerization technique provides a promising and facile method in the synthesis of ionomers which are used in dental cements and other application.

Communication: Molecular-level description of constrained chain topologies in multiblock copolymer gel networks.

Network characteristics in physical gels composed of solvated block copolymers varying in molecular design are examined here by dynamic rheology and computer simulations. In two triblock copolymer series, one with chain length (N) varied at constant copolymer composition (f) and the other with f varied at constant N, we discern the dependence of equilibrium network metrics on both N and f. Increasing the block number in a linear multiblock series at constant N and f escalates conformational complexity, which dominates network connectivity classified according to a midblock conformation index.

Improved Network Development in Bidisperse AB/ABA Block Copolymer Gels

Blending a B-selective solvent and an ordered ABA triblock copolymer can, at sufficiently high solvent concentrations, produce a physical gel composed of a network of B midblocks stabilized by A-rich micelles. We demonstrate here that addition of short AB diblock copolymer molecules to such a gel at constant copolymer composition can enhance the solid-like character of the gel, as indicated by an increase in the magnitude of the dynamic elastic modulus. Similarly, addition of AB molecules to a nongelled ABA/solvent system can induce gelation. In light of recent theoretical predictions and related experimental evidence, these results are consistent with a scenario in which tail-induced volume exclusion (due to the presence of AB molecules) within the micellar coronas improves network development through an increase in the population of bridged B midblocks.

Long-chain and short-chain branches in ethene-methyl acrylate copolymers studied by quantitative13C NMR spectroscopy

The frequency of long-chain branches (LCBs) in ethene (E)-methyl acrylate (MA) copolymers is investigated for material that was synthesized at 150°C and 2000 bar at different levels of conversion but constant copolymer composition. The copolymers exhibit significantly more LCBs than found to LDPE synthesized under similar conditions. Moreover it is found that the LCB frequence increases with conversion. At 0.3 mol-% conversion, 0.3 LCBs and at 4.0 mol-% conversion, 1.1 LCBs per 1000 C atoms are observed. In addition, the frequency of of short-chain branches (SCBs) in the copolymers is investigated. About 9 mol-% of the acrylate units are alkylated, which corresponds to numbers given in literature. As sensors, both LCB and SCB indices provise valuable information for simulations for determine rate coefficients for inter- and intramolecular transfer reactions.

Micellization of triblock copolymers in a solvent selective for the middle block: Influence of the molar mass

The micellization thermodynamics and micelle structural parameters for polystyrene- b -poly(ethylene/butylene) b -polystyrene copolymers (SEBS) in n -octane were studied. This solvent is selective for the middle poly(ethylene/butylene) block of the copolymer. The copolymer samples have similar chemical composition and different molar mass. Standard thermodynamic functions of micellization (Δ G °, Δ H ° and Δ S °) were determined by light scattering. All the functions showed more negative values for the SEBS copolymer with a larger molar mass. The structural parameters of micelles formed by different triblock copolymers were determined from static light scattering and viscosity measurements. Micelle molar mass, association number and viscometric hydrodynamic radius increase with the length of the copolymer chain for a constant copolymer composition; however, the radius of gyration decreases. Finally, the results found for SEBS micelles in n -octane are compared to those found for SEBS micelles in 4-methyl-2-pentanone. The different behaviour found supports the idea that the micelles of a triblock copolymer in a selective so vent of the middle block will show a shell formed by loops of the middle block in order that the two outer blocks go into the micelle core and even some poorly solvated outer blocks could be extended out of the micelle.

Living Carbocationic Copolymerizations. V. Synthesis of Isobutylene/p-Methylstyrene Copolymers with the Constant Copolymer Composition Technique in the Leidenfrost Reactor

Abstract Living copolymerization of the isobutylene (IB)-p-methylstyrene (pMeSt) monomer pair in combination with the constant copolymer composition (CCC) technique produces high molecular weight ( M n ≈ 100,000 g·mol−1) and narrow molecular weight distribution ( M w/ M n ≈ 1.45) compositionally uniform IB/pMeSt copolymer molecules in the industrially important IB/pMeSt = 97–99/3–1 mol% composition range. Syntheses were carried out with TiCl4 coinitiator in n-butyl chloride homogeneous solution at −85°C by the use of the Leidenfrost reactor (i.e., by direct cooling of the charge with liquid nitrogen). In order to carry out the CCC technique it was necessary to obtain reliable copolymerization reactivity ratios. These investigations led to rIB = 0.5 ± 0.1 and r pMeSt = 10 ± 4. The attainment of CCC and living copolymerization conditions has been quantitatively demonstrated by dedicated diagnostic plots. Specifically, the attainment of CCC conditions was proven by the analysis of composite rate plots (comon...

Morphologies in Blends of Diblock Copolymer and Homopolymer: Morphology Diagrams and the Intermaterial Dividing Surface

AbstractBinary blends of diblock copolymer (AB) and homopolymer (hA) self assemble upon solvent evaporation into a great variety of microphase separated morphologies. The ordered lamellar, bicontinuous double diamond, cylindrical and spherical morphologies were observed by TEM and SAXS in our studies, as well as a range of micellar morphologies.The mean curvature (H) and the area per copolymer junction (σj), which characterize the intermaterial dividing surface, increased with increasing homopolymer concentration in the blend and/or with decreasing homopolymer molecular weight. These trends were generally obeyed both between and within ordered morphology types. The increase in H and σjwas related to an increased degree of mixing between the homopolymer and the block of the copolymer.Two types of isothermal morphology diagrams were constructed to consolidate the extensive morphological data and to illustrate the general morphological transitions in AB/hA blends. The constant molecular weight morphology diagrams illustrated the interdependence of the copolymer composition and the homopolymer concentration. The constant copolymer composition diagrams emphasized the importance of the relative homopolymer molecular weight and the overall blend composition.

Amphiphilic block copolymers as phase transfer agents in toluene‐water two‐phase systems

AbstractAmphiphilic block and star‐shaped copolymers based on polystyrene and poly(ethylene oxide) were used as phase transfer catalysts in the reaction of aqueous potassium iodide with 1‐bromooctane in toluene. The effects of composition and molecular architecture on observed reaction rates were examined. At constant copolymer composition, reaction rates increased with decrease of molecular weight of the copolymer. The catalytic activity of the amphiphilic block copolymers was correlated with their ability to extract potassium picrate from water into toluene. The results are discussed on the basis of the concept of one ion, one ligand transport.

Minimum end time policies for batchwise radical chain polymerization. Part VI: The initiator addition policies for copolymerization with constant copolymer composition control

AbstractFor batchwise radical chain solution copolymerization, the minimum end time problem with constant copolymer composition control is studied by considering the initiator concentration (or feed rate) and temperature as two control variables. During copolymerization, the more rapidly depleting monomer is continuously fed to the reactor to maintain the comonomer ratio constant. The volume variation due to contraction during copolymerization, in addition to monomer and solvent feeding, is also considered. It is found that the optimal initiator addition policy is to make the rate of initiation (2fkdIV) constant. The volume factor V is for taking account of volume variation. For the isothermal case, the number of moles of initiator in the reactor should remain constant. Experimental verification for acrylonitrile and styrene isothermal copolymerization with the proposed stepwise feeding of the more rapidly depleting monomer to simulate the optimal continuous monomer feeding policy shows that the present method is applicable.

Effect of structure of copolymers on the extent of selective sorption in dilute solutions in mixed solvents

The selective sorption of 2,2,3,3-tetrafluoropropanol (TFP) on to the macromolecules of polystyrene, poly(methyl methacrylate) and mixtures of these homopolymers, and also on to the macromolecules of the corresponding random and alternating copolymers has been measured. Dilute polymer solutions in a binary mixed solvent (benzene with 20 vol.-% TFP) have been studied by equilibrium dialysis and differential refractometry. The selective sorption of TFP in this system increases (at a constant copolymer composition) with increasing number of bonds between nonidentical monomer units; it takes up its highest value for the alternating copolymer and its lowest value for the mixture of the homopolymers.