Core/shell acrylates

PVC (small diameter) Core-shell acrylic (large diameter) Bimodal vinyl dispersion resins Yang U.S. Pat. 4,461,869, 1984 Goodrich... 

The most common POM blends are homologous mixtures of POMs having different molecular structures (linear, branched, cross-linked) (Matsuzaki 1991), different molecular weights (Ishida and Sato 1970), or with different end groups (Nagasaki et al. 1991 Hanezawa and Ono 1991). On the secmid place are blends of POM with TPU, preferably polyester type. POMs are also blended with core-shell acrylic elastomers, MBS or MBA. Commercial blends of POM with PEST are available. To improve weatherability of POM, the resin was blended with PMMA and a fluoropolymer (viz. PTFE, PVF, PVDF) (Katsumata 1991). 

Acrylic elastomers have previously been used only in the rubber industry and conventional polymers (EEA or core-shell acrylate polymers) are based on the rubber in hard phases. Based on the soft phase only, however, EniChem s Europrene AR uses original technology for modification of PA 6 with conventional acrylic rubber in granule form. It increases the specific rubber efficiency in the impact resistance characteristics, so differing from other traditional elastomers (EPR, SEES) used in modification of nylon. 

Many elastomers have been blended with PBT, but the greatest Interest appears to have developed in the core/shell acrylates [25], [26]. These additives reduce stiffness proportionally with their concentration, but do not much depress heat deflection temperature of the base resin. They do make a major change in notch sensitivity, causing a propagating crack to lose Itself In a welter of crazes and other energy absorbing mechanisms. 

These are all examples of soluble polymers. Combinations of soluble with insoluble polymers have also been reported. Polychloroprene or chlorosulfonated polyethylene was eombined with core-shell polymer particles to give an adhesive with improved cold impact resistance [33]. The fascinating chemistry of chlorosulfonated polyethylene in acrylic adhesives will be further discussed in the section on initiators. In many cases chlorosulfonated polyethylene is chemically attached to the acrylic matrix. 

Figure 14.9 Effect of various impact modifiers (25wt%) on the notched Izod impact strength of recycled PET (as moulded and annealed at 150°C for 16 h) E-GMA, glycidyl-methacrylate-functionalized ethylene copolymer E-EA-GMA, ethylene-ethyl acrylate-glycidyl methacrylate (72/20/8) terpolymer E-EA, ethylene-ethyl acrylate EPR, ethylene propylene rubber MA-GPR, maleic anhydride grafted ethylene propylene rubber MBS, poly(methyl methacrylate)-g-poly(butadiene/styrene) BuA-C/S, poly(butyl acrylate-g-poly(methyl methacrylate) core/shell rubber. Data taken from Akkapeddi etal. [26]...

In another recent example, dtrate-capped Au NPs are modified with 1-dodeca-nethiol in a first step. These premade nanoparticles were encapsulated with block copolymers such as poly(styrene-block-acrylic acid) (PS-b-PAA) and poly(methyl-methacrylate-block-acrylic acid) (PMMA-b-PAA) leading to core-shell hybrid materials. The Au NP diameters are 12 and 31 nm with average shell thickness of about 15 nm [121] (Scheme 3.18). 

In the agglomeration step, the latexes are partially agglomerated using a core/shell agglomerating agent latex, which consists of an elastomeric 1,3-butadiene/slyrene copolymer core and an ethyl acrylate/methacrylic acid copolymer shell. This partial agglomeration operation should not be confused with a coagulation operation where the emulsion is fully destabilized (13). 

Core-shell rubber (CSR) particles are prepared by emulsion polymerization, and typically exhibit two or more alternating rubbery and glassy spherical layers (Lovell 1996 Chapter 8). These core-shell particles are widely used in thermoplastics, especially in acrylic materials (Lovell, 1996), and have also been used to modify thermosets, such as epoxies, cyanates, vinyl ester resins, etc. (Becu et al., 1995). 

Wide angle light scattering is used as the principal probe to examine the core-shell structure proposed for certain acrylic acid acrylate ester copolymer latexes. Additional techniques were sedimentation and photon correlation spectroscopy. 

Transmission and scanning electron microscopy, differential scanning calorimetry and minimum film temperature analysis supports a core/shell morphology for the two-stage latex polymers, consisting predominantly of a polystyrene rich core surrounded by a soft acrylic rich shell. 

Using this approach, hydrophilic (neutral or ionic) comonomers, such as end-captured short polyethylene oxide (PEO) chains (macromonomer), l-vinyl-2-pyrrolidone (VP), acrylic acid (AA) and N,N-dimethylacrylamide (DMA), can be grafted and inserted on the thermally sensitive chain backbone by free radical copolymerization in aqueous solutions at different reaction temperatures higher or lower than its lower critical solution temperature (LCST). When the reaction temperature is higher than the LOST, the chain backbone becomes hydrophobic and collapses into a globular form during the polymerization, which acts as a template so that most of the hydrophilic comonomers are attached on its surface to form a core-shell structure. The dissolution of such a core-shell nanostructure leads to a protein-like heterogeneous distribution of hydrophilic comonomers on the chain backbone. 

For quite some time, there have been indications for a phase-separation in the shell of polyelectrolyte block copolymer micelles. Electrophoretic mobility measurements on PS-PMAc [50] indicated that a part of the shell exhibits a considerable higher ionic strength than the surrounding medium. This had been corroborated by fluorescence studies on PS-PMAc [51-53] and PS-P2VP-heteroarm star polymers [54]. According to the steady-state fluorescence and anisotropy decays of fluorophores attached to the ends of the PMAc-blocks, a certain fraction of the fluorophores (probably those on the blocks that were folded back to the core/shell interface) monitored a lower polarity of the environment. Their mobility was substantially restricted. It thus seemed as if the polyelectrolyte corona was phase separated into a dense interior part and a dilute outer part. Further experimental evidence for the existence of a dense interior corona domain has been found in an NMR/SANS-study on poly(methylmethacrylate-fr-acrylic acid) (PMMA-PAAc) micelles [55]. 

The acylation of alcohol-containing monomers, e.g. hydroxyethyl acrylates or vinyl benzyl alcohol with maleic, succinic or sulfosuccinic anhydride leads to bifunctional polymerizable surfactants. A range of such products has been synthesized and tested in batch polymerization and core-shell polymerization of styrene and butyl acrylate [26]. In both cases good stability, high conversion and little burying of the Surfmers were observed. Water rebound was also limited. These advantageous features were however offset by an unacceptable resistance to electrolytes and to freeze-thaw. 

The maleic Surfmers were tested in core-shell emulsion polymerization of styrene/butyl acrylate in comparison with a standard nonreactive surfactant (nonyl phenol reacted with 30 mol of EO - NP30). While the methacrylic-derived Surfmer was completely incorporated during the polymerization (although about one-third of it was buried inside the particles) the NP30, the maleic Surfmer and the allylic and vinyl Surfmers were not incorporated and could be extracted with acetone (for the last two probably because of the formation of acetone-extractable oligomers due to a chain transfer behavior) [31]. 

The copolymer composition in miniemulsion copolymerization of vinyl acetate and butyl acrylate during the initial 70% conversion was found to be less rich in vinyl acetate monomer units [34]. Miniemulsion polymerization also allowed the synthesis of particles in which butyl acrylate and a PMMA macromonomer [83, 84] or styrene and a PMMA macromonomer [85] were copolymerized. The macromonomer acts as compatibilizing agent for the preparation of core/shell PBA/PMMA particles. The degree of phase separation between the two polymers in the composite particles is affected by the amount of macromonomer used in the seed latex preparation. 

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