Styrenic networks

The term IPN was first used in 1960 to describe the apparently homogeneous product obtained from styrene crosslinked with divinylbenzene. IPNs were prepared from this system by taking a crosslinked poly(styrene) network and allowing it to absorb a controlled amount of styrene and a 50% divinylbenzene-toluene solution containing initiator. Polymerisation of this latter component led to the formation of an IPN, the density of which was... 

J. L. Thiel and R. E. Cohen, Synthesis, Characterization, and Viscoelastic Behavior of Single-Phase Interpenetrating Styrene Networks, Polym. Eng. Sci. 19, 284 (1979). Polystyrene/polystyrene homo-IPNs. Swelling equation for single-phase IPNs. Equilibrium swelling studies as a function of crosslink level. 

Chains of polybutadiene were trapped in the network formed by cooling a butadiene-styrene copolymer until phase separation occurred for the styrene, effectively crosslinking the copolymer. At 25°C the loss modulus shows a maximum which is associated with the free chains. This maximum occurst at the following frequencies for the indicated molecular weights of polybutadiene ... 

Pour-Point Depressants. The pour point of alow viscosity paraffinic oil may be lowered by as much as 30—40°C by adding 1.0% or less of polymethacrylates, polymers formed by Eriedel-Crafts condensation of wax with alkylnaphthalene or phenols, or styrene esters (22). As wax crystallizes out of solution from the Hquid oil as it cools below its normal pour point, the additive molecules appear to adsorb on crystal faces so as to prevent growth of an interlocking wax network which would otherwise immobilize the oil. Pour-point depressants become less effective with nonparaffinic and higher viscosity petroleum oils where high viscosity plays a dominant role in immobilizing the oil in a pour-point test. 

As the quinone stabilizer is consumed, the peroxy radicals initiate the addition chain propagation reactions through the formation of styryl radicals. In dilute solutions, the reaction between styrene and fumarate ester foUows an alternating sequence. However, in concentrated resin solutions, the alternating addition reaction is impeded at the onset of the physical gel. The Hquid resin forms an intractable gel when only 2% of the fumarate unsaturation is cross-linked with styrene. The gel is initiated through small micelles (12) that form the nuclei for the expansion of the cross-linked network. 

Styrene—butadiene—styrene modified bitumen is an elastomeric material mixed into an asphalt between 10 and 15%. By using high energy mixing, the SBS is uniformly dispersed throughout the asphalt to form a network, referred to as phase reversal because the minor component s (SBS) physical properties are displayed by the final mixture. A properly formulated SBS asphalt blend has an elongation of 100% or greater and is flexible down to temperatures below —6°C. 

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

In Chapters 3 and 11 reference was made to thermoplastic elastomers of the triblock type. The most well known consist of a block of butadiene units joined at each end to a block of styrene units. At room temperature the styrene blocks congregate into glassy domains which act effectively to link the butadiene segments into a rubbery network. Above the Tg of the polystyrene these domains disappear and the polymer begins to flow like a thermoplastic. Because of the relatively low Tg of the short polystyrene blocks such rubbers have very limited heat resistance. Whilst in principle it may be possible to use end-blocks with a higher Tg an alternative approach is to use a block copolymer in which one of the blocks is capable of crystallisation and with a well above room temperature. Using what may be considered to be an extension of the chemical technology of poly(ethylene terephthalate) this approach has led to the availability of thermoplastic polyester elastomers (Hytrel—Du Pont Amitel—Akzo). 

The study of acid-base interaction is an important branch of interfacial science. These interactions are widely exploited in several practical applications such as adhesion and adsorption processes. Most of the current studies in this area are based on calorimetric studies or wetting measurements or peel test measurements. While these studies have been instrumental in the understanding of these interfacial interactions, to a certain extent the interpretation of the results of these studies has been largely empirical. The recent advances in the theory and experiments of contact mechanics could be potentially employed to better understand and measure the molecular level acid-base interactions. One of the following two experimental procedures could be utilized (1) Polymers with different levels of acidic and basic chemical constitution can be coated on to elastomeric caps, as described in Section 4.2.1, and the adhesion between these layers can be measured using the JKR technique and Eqs. 11 or 30 as appropriate. For example, poly(p-amino styrene) and poly(p-hydroxy carbonyl styrene) can be coated on to PDMS-ox, and be used as acidic and basic surfaces, respectively, to study the acid-base interactions. (2) Another approach is to graft acidic or basic macromers onto a weakly crosslinked polyisoprene or polybutadiene elastomeric networks, and use these elastomeric networks in the JKR studies as described in Section 4.2.1. 

Sheu and coworkers [111] produced polysty-rene-polydivinylbenzene latex interpenetrating polymer networks by the seeded emulsion polymerization of styrene-divinylbenzene in the crosslinked uniform polystyrene particles. In this study, a series of uniform polystyrene latexes with different sizes between 0.6 and 8.1... 

A wide range of polymer networks are constructed in this manner. Poly(vinyltrichloacetate) was used as the coinitiator with styrene, MMA and chloroprene as cross-linking units. Polycarbonates, polystyrene, N-haloge-nated polyamide, polypeptides, and cellulose acetate, suitably functionalized, have been used as a coinitiator... 

The organic resin material is often a styrene divinylbenzene (DVB) copolymer in a network or matrix, to which are attached functional groups such as a sulfonic acid, carboxylic acid, and quaternary ammonium. The nature of these groups determines whether the resin is classified as a strong/weak acid (cation resin) or strong/weak base (anion resin) ion-exchanger. 

Resin bead polymer composition Either acrylic resins or, more generally, styrene (vinylbenzene, VB) are cross-linked with typically 4 to 20% divinylbenzene (DVB) in a copolymer network or matrix. 

Using magnesium ether carboxylates as emulsifier a porous polyvinylchloride can be made [218] and a propoxylated ether carboxylate is described as emulsifier to make an ethyl acrylate-styrene copolymer [219]. A crosslinked latex with a three-dimensional network is achieved by polymerizing an ethylenically unsaturated monomer with a reactive saturated monomer using ether carboxylate as emulsifier [220]. 

Since this pioneering work a number of IPNs have been prepared. Poly(styrene) has been used as the second network polymer in conjunction with several other polymers, including poly(ethyl acrylate), poly(n-butyl acrylate), styrene-butadiene, and castor oil. Polyurethanes have been used to form IPNs with poly(methyl methacrylate), other acrylic polymers, and with epoxy resins. 

IPNs are found in many applications though this is not always recognised. For example conventional crosslinked polyester resins, where the polyester is unsaturated and crosslinks are formed by copolymerisation with styrene, is a material which falls within the definition of an interpenetrating polymer network. Experimental polymers for use as surface coatings have also been prepared from IPNs, such as epoxy-urethane-acrylic networks, and have been found to have promising properties. 

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