Styrenics cross-linking

TosoHaas columns are styrene cross-linked with divinylbenzene (DVB). Columns of similar composition are available from Polymer Laboratories (PL Gel), Waters (Ultrastyragel), Shodex, Jordi (JordiGel), and many others. Columns based on derivatized silica are also available, but are less widely used. 

G 5. Ghanem, N. A. Studies in the cross-linked polyesters. III. The composition of styrene cross-linked polyester using 14C-labelled maleic anhydride. Makromol. Chem. 36, 109 (1960). 

J. A. Hiltz, Pyrolysis-gas chromatography mass-spectrometry identification of styrene cross-linked polyester and vinyl ester resins, J. Anal. Appl. Pyrolysis, 22, 113-128, (1991). 

The thermoset acrylics (20) of major importance in the coating industry, in recent years, have been developed primarily by Canadian Industry Ltd. and by Pittsburgh Plate Glass Co. in this country (4). Raw materials are acrylamide, acrylic acid, acrylates, and styrene. Cross-linking agents are amino and epoxy resins. The materials are also self-cross-linking. They are usually sold as solutions in paint solvents. 

Wool Acetate, Hydroxyethyl ether. Acrylate, Styrene, Cross-linked, Cationic, High amylose. Polyvinyl alcohol, CMC, Blends and other polymers... 

In the TEM samples, the rubber domains are uniformly distributed and on the order of a few hundred angstroms in size. The micrographs also show the presence of domains that have no rubber in them. The rubber-free domains probably contain polyester and epoxy that have reacted, but it is not possible to confirm this possibility. Styrene-cross-linked polyester has a Tg of 185 °C. When the epoxy is introduced in a 1 2 ratio (epoxy-.polyester), Tg de-... 

Flemion (Asahi Glas Co. Ltd.) Sulfonated styrene/cross-linked with 1.4... 

Porous polymer beads of uniform size arc manufactured from styrene cross-linked with divinylbenzene (Section 28F-2). The pore size of these beads is uniform and is controlled by the amount of cross-linking. Porous polymers have found considerable use in the separation of gaseous polar species such as hydrogen. sulfide, oxides of nitrogen, water, carbon dioxide, methanol, and vinyl chloride. A typical application of an open tubular column lined with a porous polymer (PLO Tcolumn) is shown in Figure 27-2lb,... 

Figure 10-23. Glass transition temperature as a function of the reciprocal number average molar mass for linear,/ = 2, and star-shaped branched poly(styrenes) with/ = 3 or/ = 10-12 arms, as well as for poly(styrenes) cross-linked with divinyl benzene with mean degrees of cross-linking per chain of/= 3, 5-7, or 10-12 (according to data from F. Rietsch, D. Daveloose and D. Froelich).

Copolymerization is by no means restricted to two monomeric components. Copolymerization is also the term used to describe the uniting of linear polymers or polycondensates that still possess a reactive component (trifunctional monomers) with polymerizable (bifunctional) monomers. The result is a cross-linked plastic, for example unsaturated polyester -i- styrene cross-linked polyester resin. 

Typical homogeneous membranes have a polymer matrix of styrene cross-linked with divinylbenzene (DVB) and ion-exchange functional groups of sulfonic acid or quaternary amines. Manufacture of DVB yields an impure product containing nearly 50% of ethylstyrene, which participates in the polymerization but does not accept functional groups readily. In some cases the film of styrene-DVB copolymer is made in one step, and the functional groups are added in subsequent steps. 

Three main types of styrene-based polymers have been used (a) insoluble copolymers of styrene cross-linked with divinylbenzene (b) linear, soluble polystyrenes of different molecular weights and (c) isotactic polystyrenes. 

Earner et al. [174] recently reported the synthesis of core-shell poly(divinylbenzene) (PDVB) microspheres via the RAFT graft polymerization of styrene. Cross-linked PDVB core microspheres containing double bonds on the particle surface were used directly to attach polymers from the surface by RAFT without prior modification of the core microspheres. The RAFT agent 1-phenyl-ethyl dithiobenzoate (PEDB) was used. PEDB controlled the particle weight gain, the particle volume, and the molecular weight of the soluble polymer. 

McGarey [150] has used the theoretical SANS approaches for studying sequential IPNs based on poly(dimethylsiloxane) (PDMS) (host) and styrene cross-linked by DVB (guest). PDMS had a certain amount of end vinyl groups... 

FIGURE 27 14 A section of polystyrene showing one of the benzene rings modified by chloromethylation Indi vidual polystyrene chains in the resin used in solid phase peptide synthesis are con nected to one another at various points (cross linked) by adding a small amount of p divinylbenzene to the styrene monomer The chloromethylation step is carried out under conditions such that only about 10% of the benzene rings bear —CH2CI groups... 

Styrene-Butadiene-Styrene Block Copolymers. Styrene blocks associate into domains that form hard regions. The midblock, which is normally butadiene, ethylene-butene, or isoprene blocks, forms the soft domains. Polystyrene domains serve as cross-links. 

Haward et al.t have reported some research in which a copolymer of styrene and hydroxyethylmethacrylate was cross-linked by hexamethylene diisocyanate. Draw the structural formula for a portion of this cross-linked polymer and indicate what part of the molecule is the result of a condensation reaction and what part results from addition polymerization. These authors indicate that the crosslinking reaction is carried out in sufficiently dilute solutions of copolymer that the crosslinking is primarily intramolecular rather than intermolecular. Explain the distinction between these two terms and why concentration affects the relative amounts of each. 

Thermal Oxidative Stability. ABS undergoes autoxidation and the kinetic features of the oxygen consumption reaction are consistent with an autocatalytic free-radical chain mechanism. Comparisons of the rate of oxidation of ABS with that of polybutadiene and styrene—acrylonitrile copolymer indicate that the polybutadiene component is significantly more sensitive to oxidation than the thermoplastic component (31—33). Oxidation of polybutadiene under these conditions results in embrittlement of the mbber because of cross-linking such embrittlement of the elastomer in ABS results in the loss of impact resistance. Studies have also indicated that oxidation causes detachment of the grafted styrene—acrylonitrile copolymer from the elastomer which contributes to impact deterioration (34). 

Cross-linked macromolecular gels have been prepared by Eriedel-Crafts cross-linking of polystyrene with a dihaloaromatic compound, or Eriedel-Crafts cross-linking of styrene—chloroalkyl styrene copolymers. These polymers in their sulfonated form have found use as thermal stabilizers, especially for use in drilling fluids (193). Cross-linking polymers with good heat resistance were also prepared by Eriedel-Crafts reaction of diacid haUdes with haloaryl ethers (194). 

Sulfonated styrene—divinylbensene cross-linked polymers have been appHed in many of the previously mentioned reactions and also in the acylation of thiophene with acetic anhydride and acetyl chloride (209). Resins of this type (Dowex 50, Amherljte IR-112, and Permutit Q) are particularly effective catalysts in the alkylation of phenols with olefins (such as propylene, isobutylene, diisobutylene), alkyl haUdes, and alcohols (210) (see Ion exchange). Superacids. 

Other Polymers. Besides polycarbonates, poly(methyl methacrylate)s, cycfic polyolefins, and uv-curable cross-linked polymers, a host of other polymers have been examined for their suitabiUty as substrate materials for optical data storage, preferably compact disks, in the last years. These polymers have not gained commercial importance polystyrene (PS), poly(vinyl chloride) (PVC), cellulose acetobutyrate (CAB), bis(diallylpolycarbonate) (BDPC), poly(ethylene terephthalate) (PET), styrene—acrylonitrile copolymers (SAN), poly(vinyl acetate) (PVAC), and for substrates with high resistance to heat softening, polysulfones (PSU) and polyimides (PI). 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

The second largest use at 21% is for unsaturated polyester resins, which are the products of polycondensation reactions between molar equivalents of certain dicarboxyhc acids or thek anhydrides and glycols. One component, usually the diacid or anhydride, must be unsaturated. A vinyl monomer, usually styrene, is a diluent which later serves to fully cross-link the unsaturated portion of the polycondensate when a catalyst, usually a peroxide, is added. The diacids or anhydrides are usually phthahc anhydride, isophthahc acid, and maleic anhydride. Maleic anhydride provides the unsaturated bonds. The exact composition is adjusted to obtain the requked performance. Resins based on phthahc anhydride are used in boat hulls, tubs and spas, constmction, and synthetic marble surfaces. In most cases, the resins contain mineral or glass fibers that provide the requked stmctural strength. The market for the resins tends to be cychcal because products made from them sell far better in good economic times (see Polyesters,unsaturated). 

Uses. About 35% of the isophthahc acid is used to prepare unsaturated polyester resins. These are condensation products of isophthahc acid, an unsaturated dibasic acid, most likely maleic anhydride, and a glycol such as propylene glycol. The polymer is dissolved in an inhibited vinyl monomer, usually styrene with a quinone inhibitor. When this viscous hquid is treated with a catalyst, heat or free-radical initiation causes cross-linking and sohdification. A range of properties is possible depending on the reactants used and their ratios (97). 

Combination techniques such as microscopy—ftir and pyrolysis—ir have helped solve some particularly difficult separations and complex identifications. Microscopy—ftir has been used to determine the composition of copolymer fibers (22) polyacrylonitrile, methyl acrylate, and a dye-receptive organic sulfonate trimer have been identified in acryHc fiber. Both normal and grazing angle modes can be used to identify components (23). Pyrolysis—ir has been used to study polymer decomposition (24) and to determine the degree of cross-linking of sulfonated divinylbenzene—styrene copolymer (25) and ethylene or propylene levels and ratios in ethylene—propylene copolymers (26). 

Isophthahc (y -phthahc) acid [121 -91 -5] (IPA) is selected to enhance thermal endurance as well as to produce stronger, more resiUent cross-linked plastics that demonstrate improved resistance to chemical attack. TerephthaUc (p-phthaUc) acid [100-21-0] (TA) provides somewhat similar properties as isophthahc acid but is only used in selective formulations due to the limited solubiUty of these polyester polymers in styrene [100-42-5] (see Phthalic acid AND OTHERBENZENEPOLYCARBOXYLIC ACIDS). 

The temperature of esterification has a significant influence on isomerization rate, which does not proceed above 50% at reaction temperatures below 150°C. In resins produced rapidly by using propylene oxide and mixed phthaUc and maleic anhydrides at 150°C, the polyester polymers, which can be formed almost exclusively in the maleate conformation, show low cross-linking reaction rates with styrene. 

Isomerization is faciUtated by esterification at temperatures above 200°C or by using catalysts, such as piperidine and morpholine (6), that are effective in raising isomerization of fumarate to 95% completion. Resins made by using fumaric acid are exclusively fumarate polymers, demonstrate higher reactivity rates with styrene, and lead to a complete cross-linking reaction. 

---