Racemization viaenol


Both compounds react by an S l mechanism and their relative rates reflect their acti vation energies for carbocation formation Because the allylic chloride is more reactive we reason that it ionizes more rapidly because it forms a more stable carbocation Struc turally the two carbocations differ m that the allylic carbocation has a vinyl substituent on Its positively charged carbon m place of one of the methyl groups of tert butyl cation  [c.392]

Poly(vinyl acetal) resin  [c.797]

Poly(vinyl butyral) resin  [c.798]

Resin and Polymer Solvent. Dimethylacetamide is an exceUent solvent for synthetic and natural resins. It readily dissolves vinyl polymers, acrylates, ceUulose derivatives, styrene polymers, and linear polyesters. Because of its high polarity, DMAC has been found particularly useful as a solvent for polyacrylonitrile, its copolymers, and interpolymers. Copolymers containing at least 85% acrylonitrile dissolve ia DMAC to form solutions suitable for the production of films and yams (9). DMAC is reportedly an exceUent solvent for the copolymers of acrylonitrile and vinyl formate (10), vinylpyridine (11), or aUyl glycidyl ether (12).  [c.85]

The most widely, and perhaps the eadiest, elastomer used to formulate pressure-sensitive adhesives is natural mbber. In 1845 a patent was granted for a formulation including India mbber, gum of southern pine, balsam of Pern, and ground Htharge (12). This formulation provided a material akin to a pressure-sensitive adhesive. Other elastomers which have been used are the butyl mbbers, poly(vinyl ether)s, acryHcs (especially those having long chain alkyl groups), and siHcones. The modes of tackifying depend upon the elastomers. Natural mbber, butyl mbber, and acryHc materials are typically tackified by the addition of a tackifying agent of the type described above. Block copolymers such as the styrene—butadiene—styrene block or the styrene—isoprene—styrene block must be treated so that the continuous phase is the tackified material. Thus, the choice of tackifying resin depends upon the solubiHty of the tackifying agent in the continuous phase. Vinyl ethers are tackified by adding lower molecular weight poly(vinyl ether). SiHcone pressure-sensitive adhesives are typically tackified by the addition of siHcone gum and siHcone resin to the siHcone elastomer.  [c.234]

Pentaerythritol in rosin ester form is used in hot-melt adhesive formulations, especially ethylene—vinyl acetate (EVA) copolymers, as a tackifier. Polyethers of pentaerythritol or trim ethyl ol eth an e are also used in EVA and polyurethane adhesives, which exhibit excellent bond strength and water resistance. The adhesives maybe available as EVA melts or dispersions (90,91) or as thixotropic, one-package, curable polyurethanes (92). Pentaerythritol spko ortho esters have been used in epoxy resin adhesives (93). The EVA adhesives are especially suitable for cellulose (paper, etc) bonding.  [c.466]

The beater additive process starts with a very dilute aqueous slurry of fibrous nitrocellulose, kraft process woodpulp, and a stabilizer such as diphenylamine in a felting tank. A solution of resin such as poly(vinyl acetate) is added to the slurry of these components. The next step, felting, involves use of a fine metal screen in the shape of the inner dimensions of the final molded part. The screen is lowered into the slurry. A vacuum is appHed which causes the fibrous materials to be deposited on the form. The form is pulled out after a required thickness of felt is deposited, and the wet, low density felt removed from the form. The felt is then molded in a matched metal mold by the appHcation of heat and pressure which serves to remove moisture, set the resin, and press the fibers into near final shape (180—182).  [c.53]

Extrusion. Conventional melt-extmsion equipment is used in processing FEP resins. Commercial pigments are mixed with the resin before extmsion into wke coating, tubing, rods, mol ding, heading channels, etc. Coating thicknesses of 0.076—2.54 mm have been extmded over such materials as sihcone mbber, poly(vinyl chloride), glass braid, metal-shielded cables, twisted conductors, and parallel multiconductor cables.  [c.361]

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations.  [c.386]

There are two principal PVC resins for producing vinyl foams suspension resin and dispersion resin. The suspension resin is prepared by suspension polymerization with a relatively large particle size in the 30—250 p.m range and the dispersion resin is prepared by emulsion polymerization with a fine particle size in the 0.2—2 p.m range (245). The latter is used in the manufacture of vinyl plastisols which can be fused without the appHcation of pressure. In addition, plastisol blending resins, which are fine particle size suspension resins, can be used as a partial replacement for the dispersion resin in a plastisol system to reduce the resin costs.  [c.420]

The chemical expansion method is most widely used for the manufacture of flexible PVC foam. The three general methods used to produce flexible vinyl foam (246) are (/) the pressure mol ding technique, which consists of the decomposition of the blowing agent and fusion of the plastisol in a mold under pressure at elevated temperatures, cooling the mold, removing the molded part, and post expansion at some moderate temperature (2) the one-stage atmospheric foaming method in which the blowing agent is decomposed in the hot viscosity range that Hes between the gelation and complete fusion of the plastisol and (J) the two-stage atmospheric foaming method in which the blowing agent is decomposed below the gelation of the plastisol, followed by heating at high temperature to fuse the foamed resin (247).  [c.420]

The Dynamit-Nobel extmsion process (252) utilizes a volatile plasticizer such as acetone which is injected into the decompression section of a two-stage screw and is uniformly dispersed in the vinyl resin containing a stabilizer. The resulting PVC foam has low density and closed cells.  [c.420]

Vinyl organosol coatings, which incorporate a high molecular weight thermoplastic PVC organosol dispersion resin, are extremely flexible. Soluble thermosetting resins, including epoxy, phenoHc, and polyesters, are added to enhance the film s product resistance and adhesion.  [c.450]

Miscellaneous industrial and PET resin uses consume the remaining 12.5% of the ethylene glycol. These markets typically utilize the freeze point depressing, polarity, and reactivity of ethylene glycol. Specially formulated fluids are used for defrosting and deicing aircraft anti-icing or deicing airport mnways and taxi-ways and heat-transfer solutions for a wide temperature range (—51 to 135°C). Ethylene glycol is used in adhesive, latex paint, and asphalt-emulsion water-based formulations to provide freeze protection. High purity ethylene glycol is a solvent and suspending medium for ammonium perborate, the conductor used in most electrolytic capacitors. Polyester resins based on maleic and phthaHc anhydrides, ethylene glycol and higher glycols, and vinyl-type monomers are important in the low pressure laminating of glass fibers for furniture, suitcases, boat hulls, aircraft parts, and automobile bodies.  [c.361]

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated.  [c.355]

In many cases, the softening points of vinyl aromatic resins are controUed by monomer concentration and polymerization temperature. Two general rules are that the lower the monomer concentration, the higher the softening point, and the lower the polymerization temperature, the higher the softening point. These techniques may also lead to high molecular weights, which may be detrimental to many appHcations. Recent processes have revealed the production of high softening point (>140°C) a-methylstyrene—pi ra-methylstyrene resins which do not rely on low monomer concentration. Resin yields of greater than 96% (based on reactive monomers) have been obtained using 1.2 wt % BF as the catalyst system (80).  [c.356]

Polymer Applications. The reaction of sahcylaldehyde with poly(vinyl alcohol) to form an acetal has been used to provide dye receptor sites on poly(vinyl alcohol) fibers (89) and to improve the light stabihty of blend fibers from vinyl chloride resin and poly(vinyl alcohol) (90) (see Fibers, POLY(VINYL alcohol)).  [c.508]

The lower molecular weight aUphatic ketones and cycloaUphatic ketones are stable, colorless Hquids and generally have a pleasant, slightly aromatic odor. They are relatively volatile with boiling points slightly above those of corresponding alkanes. Unsymmetrical ketones are lower melting and higher boiling than corresponding symmetrical ketones. The members of the series up to are fairly soluble in water and are excellent solvents for nitrocellulose, vinyl resin lacquers, cellulose ethers and esters, and various natural and synthetic gums and resins.  [c.485]

Methyl Isopropenyl Ketone. Methyl isopropenyl ketone [814-78-8] (3-methyl-3-buten-2-one) is a colorless, lachrymatory Hquid, which like methyl vinyl ketone readily polymerizes on exposure to heat and light. Methyl isopropenyl ketone is produced by the condensation of methyl ethyl ketone and formaldehyde over an acid cation-exchange resin at 130°C and 1.5 MPa (218 psi) (274). Other methods are possible (275—280). Methyl isopropenyl ketone can be used as a comonomer which promotes photochemical degradation in polymeric materials. It is commercially available in North America (281).  [c.496]

Alkenylsuccinic anhydrides made from several linear alpha olefins are used in paper sizing, detergents, and other uses. Sulfosuccinic acid esters serve as surface active agents. Alkyd resins (qv) are used as surface coatings. Chlorendric anhydride [115-27-5] is used as a flame resistant component (see Flame retardants). Tetrahydrophthalic acid [88-98-2] and hexahydrophthalic anhydride [85-42-7] have specialty resin appHcations. Gas barrier films made by grafting maleic anhydride to polypropylene [25085-53-4] film are used in food packaging (qv). Poly(maleic anhydride) [24937-72-2] is used as a scale preventer and corrosion inhibitor (see Corrosion and corrosion control). Maleic anhydride forms copolymers with ethylene glycol methyl vinyl ethers which are partially esterified for biomedical and pharmaceutical uses (189) (see Pharmaceuticals).  [c.461]

Polyurethane dispersions are used in specialty appHcations, where high levels of sizing are needed. Wax emulsions and wax—rosin emulsions also are used by themselves as surface-appHed sizing agents to produce very high resistance to Hquid penetration in paper and paperboard. Other products that ate used as surface sizes include CMC and poly(vinyl alcohol), which provide oU- and grease-repeUent coatings, improve paper strength, and decrease paper porosity.  [c.21]

Heat resistance is an important characteristic of the bond. The strength of typical abrasive stmctures is tested at RT and at 300°C. Flexural strengths are between 24.1 and 34.4 MPa (3500—5000 psi). An unmodified phenoHc resin bond loses about one-third of its room temperature strength at 298°C. Novolak phenoHc resins are used almost exclusively because these offer heat resistance and because the moisture given off during the cure of resole resins results in undesirable porosity. Some novolaks modified with epoxy or poly(vinyl butyral) resin are used for softer grinding action.  [c.305]

Glass-Reinforced Composites. These composites are prepared from SMC and by LIM. PhenoHc resins are usually not amenable to LIM because of the volatiles generated. However, a resin suitable to LIM has been prepared (87). The properties of the 60% glass-mat-reinforced product obtained from this resin were compared to conventional isophthaHc polyester and vinyl ester sheet-molding compounds at equivalent glass loading the mechanical properties are shown in Table 14 (88). The phenoHc resin systems have slightly lower strength values but measurably higher impact resistance.  [c.307]

A wide variety of color concentrates ate available for coloring rigid and flexible (plasticized) poly(vinyl) chlorides (PVC). Color concentrates for rigid PVC are made by dispersing a pigment in the resin. The flexible vinyls, on the other hand, use either concentrates made in plasticized resins or in a plasticizer, such as dioctyl phthalate (DOP) which is a Hquid. The dispersions in the plasticizer are produced as a paste on a three-roll mill. The pigment concentration in the paste is typically 20—35%. The soHd color concentrates for PVC are produced from free-flowing granules to a very fine powder (see Vinyl polya rs, vinyl cm oRiDE and pvc).  [c.515]

Suspension PVC. These polymers are produced by suspending vinyl chloride in water and polymerizing this monomer using a monomer-soluble initiator. PVC polymers produced via a suspension polymerization route have a relatively large particle size (typically 100—150 Tm). Additionally, suspension polymers produced for the flexible sector have particles that are highly porous and are therefore able to absorb large amounts of hquid plasticizer during a formulation mixing cycle. A typical flexible PVC formulation (Table 2) using a suspension polymer is typically processed by a dry-blend cycle, during which all formulation ingredients are heated (typically 70—110°C) and intimately mixed to form a dry powder (the PVC dry blend or powder blend), ie, a powder that contains all formulation ingredients. This dry blend can be either stored or processed immediately. Processing of suspension resin formulations is performed by a variety of techniques such as extmsion, injection molding, and calendering to totally fuse the formulation ingredients and therefore produce the desired product.  [c.125]

The presence of stable free radicals in the final polycondensate is supported by the observation that traces of (11) have a strong inhibiting effect on the thermal polymerization of a number of vinyl monomers. Radical polymerization was inhibited to a larger extent by a furfural resin than by typical polymerization inhibitors (34). Thermal degradative methods have been used to study the stmcture of furfural resinifted to an insoluble and infusible state, leading to proposed stmctural features (35).  [c.77]

PVA is isomeric with POE however, it can enter iato hydrogen bonds with both water and with the other hydroxyl units of the repeating polymer chain, forming both iater- and iatrahydrogen bonds. The extensive hydrogen bonding can lead to crystallinity, an occurrence that compHcates its water solubihty. Commercial PVA is essentially atactic. With most chain-growth polymers, crystallinity is associated with stereoregularity, but the small size of the hydroxyl substituent group promotes crystallinity even ia the atactic polymer. For this reason poly(vinyl acetate) is seldom hydrolyzed completely it is manufactured retaining three acetate levels 25, 12, and 2 mole percents (these numbers represent averages). With higher acetate percentages the polymer is more surface  [c.317]

The eadiest known elastomeric modification of a stmctural adhesive occurred during Wodd War II, when it was demonstrated that phenohc resin adhesives could be modified with poly(vinyl acetal) resins (10). Aluminum sheet was coated using a phenohc resin and then particles of poly(vinyl acetal) [26591-54-8] were sprinkled onto the uncured phenohc resin. The bond was closed, cured at high temperature and high pressure, and a fracture-resistant bond having improved performance was obtained. Phenohc resins have also been modified by acrylonitrile—butadiene elastomers, which provide higher peel strength of the cured adhesive than poly(vinyl acetal) modification. In both cases, flexibilization is presumably effected because the elastomer is soluble within the phenohc resin. This is fairly clearly demonstrated in the case of the acrylonitrile—butadiene elastomer modification because the glass-transition temperature of these phenohc materials is typically below room temperature.  [c.233]

Felted Nitrocellulose Compositions. A combustible case containing the propellant charge offers tactical, logistic, and performance advantages in certain types of munitions such as those used for tank weapons, mortars, and howitzers. This case is rigid and completely combustible, replacing metallic cases or flexible cases having low mechanical strength. Because nitrocellulose itself caimot be molded into a stmcture having the desired mechanical characteristics, inert fibers and a resin are added. A typical composition (wt %) consists of nitrocellulose (12.6% N), 55 kraft fiber, 9 acryflc fiber, 25 poly(vinyl acetate) resin, 10 and diphenylamine, 1.  [c.52]

Calendering is used principally for poly(vinyl chloride) film and sheet, both flexible and rigid. The use of the process had been in decline since the 1970s, but since 1986 sales have improved so that in 1993 12% of all PVC resin is used in calendering operations. The main products of calendering are flexible sheet for combination with textile backing for use in seating and wall coverings, flooring, and packaging. Rigid vinyl sheet is used for credit cards and packaging.  [c.381]

A series of compounded flame retardants, based on finely divided insoluble ammonium polyphosphate together with char-forming nitrogenous resins, has been developed for thermoplastics (52—58). These compounds are particularly useful as iatumescent flame-retardant additives for polyolefins, ethylene—vinyl acetate, and urethane elastomers (qv). The char-forming resin can be, for example, an ethyleneurea—formaldehyde condensation polymer, a hydroxyethylisocyanurate, or a piperazine—triazine resin.  [c.476]

A calenderprocessingis also used to produce substantial quantities of vinyl-fabric laminates. Raw materials are first blended in a Banbury mixer operated at either elevated or room temperatures to dissolve the plasticizer into the PVC resin. The blended materials are fluxed into a homogeneous mass of vinyl compound. The material is then discharged to a Banbury mill to cool the batch down. The material can now be fed to an extmder and passed through the various nips between the calender roUs to obtain a sheet of weU-controUed gauge. Vinyl foam-fabric laminates may be produced by combining a vinyl film to be used as the skin layer and a vinyl sheet containing blowing agent with fabric and activating the blowing agent by passing through a forced air convection oven.  [c.420]

In the manufacture of unsaturated polyester resins the polyester is synthesi2ed and then diluted with a vinyl reactive monomer such as styrene (see Polyesters, unsaturated). A portion of the dibasic acid of the polyester is maleic or some other vinyl reactive diacid that can be polymeri2ed with the styrene to yield a highly cross-linked, high performance polymer system. Other esters made with propylene glycol, dipropylene glycol, and tripropylene glycol are used as emulsifiers in foods, as plastici2ers in polymer systems, and as part of acrylate resin systems.  [c.366]

The two main types of process for the production of low density polyethylene (LDPE), the stirred autoclave and the tubular reactor, have been modified in many ways to enlarge the range of products that can be made and to increase conversion. The introduction of low pressure processes for the manufacture of high density polyethylene (HDPE) in the late 1950s and those for the manufacture of linear low density polyethylene (LLDPE) in the years following 1968 have reduced the dependence of the plastics industry on high pressure processes for some types of resin, but as long as there is a need for LDPE and copolymers such as ethylene-vinyl acetate (EVA), high pressure processes will continue to be of importance. It is estimated that the current annual production of LDPE throughout the world exceeds 15 x 10 t (see Olefin polymers).  [c.76]

Processes for the hydrogenation of catalytic resins are usually carried out using the same catalysts and reaction conditions as those used for thermally polymerized precursors. Rainey nickel has been shown to be an effective catalyst for the hydrogenation of catalytic aromatic resins (65). By varying reaction times at a temperature of 280°C and a pressure of 19.6 MPa (200 kg/cni2) in an autoclave, the degree of hydrogenation of the aromatic rings may be optimized to between 30 and 80%. Optimizing the reduction of the aromatic nuclei within a resin, as measured by the absorbance at 700 cm , is conducted to optimize resin compatibiHty with ethylene—vinyl acetate copolymers.  [c.355]

Adhesives. The largest use for hydrocarbon resins is in adhesives (qv). There are numerous classes of adhesives, but the largest classes utilising hydrocarbon resins are hot melt adhesives (HMA) and pressure sensitive adhesives (PSA). Hot melt adhesives are typically composed of a higher molecular weight polymer, a tackifier, a wax, and an antioxidant. HMAs do not utilize a solvent. Typical polymers that are used in HMA appHcations are ethylene—vinyl acetate (EVA), ethylene—methyl acrylate (EMA), and low molecular weight polyethylene. Depending on the comonomer content (eg, vinyl acetate) of the polymers (polarity), useful tackifiers may range from C-5 aUphatic to C-9 aromatic resins and rosin esters.  [c.358]

Diacyl peroxides are used in a broad spectmm of apphcations, including curing of unsaturated polyester resin compositions, cross-linking of elastomers, production of poly(vinyl chloride), polystyrene, and polyacrjlates, and in many nonpolymeric addition reactions.  [c.223]

GeEtlon. Drying by gelation is accompHshed by dispersing fine particles of a high molecular weight polymer, eg, poly(vinyl chloride) resin, in a latent plasticizer for the polymer. At room temperature the dispersed polymer behaves like a pigment but at elevated temperatures it solvates, causing an immediate gel formation which is dry to the touch.  [c.247]

Uses. The principal uses of MIBK are categorized in Table 8. Like methyl ethyl ketone, the principal use of MIBK is as a coating solvent. As a solvent for ceUulose-based (eg, nitrocellulose and cellulose acetate butyrate) and resin-based (eg, acryUc, alkyd, and vinyl) coating systems, MIBK is unsurpassed. Attempts to replace MIBK with straight-chain solvents which are exempt from Rule 66 of the Los Angeles, California Air Pollution Control District, and other regulations restricting emission of photoreactive organic materials, have not been implemented as rapidly as expected. MlBK s solvent use has been sustained by the increasing use of high soHds coatings, which use less solvent and require the superior solvent quaUties offered by MIBK. Another increasingly important non-VOC use of MIBK is as a raw material in the production of mbber antioxidants such as /V-(1,3-dimethy1huty1)-/V-phenyl- -phenylenediamine.  [c.492]

Chemical Bonding. Sometimes called resin bonding, chemical bonding is a general term describing the technologies employed to intedock fibers by the appHcation and curing of a chemical binder. The chemical binder most ftequendy used to bond nonwovens is waterborne latex (see Latex technology). Most latex binders are made from vinyl materials, such as vinyl acetate, vinyl chloride, styrene, butadiene, acryHc, or combinations thereof The monomer is polymerized in water, and the polymeric material takes the form of suspended (emulsified) particles. Thus the emulsion polymerization of vinyl acetate yields a vinyl acetate polymer binder and the copolymerization of styrene and butadiene yields a styrene-butadiene copolymer or styrene—butadiene—mbber (SBR) binder.  [c.153]

Thermal Degradation. HDPE is relatively stable under heat. Chemical reactions at high temperature in the absence of oxygen become noticeable only above 290—300°C. Thermocracking of HDPE is a free-radical C—C bond scission reaction. The reaction reduces the resin molecular weight, introduces vinyl double bonds in polymer chains, and produces low molecular weight hydrocarbons. Pyrolysis in an inert atmosphere becomes significant at 500°C it produces mostly waxes, low molecular weight alkanes, alkenes, and dienes.  [c.379]

Organic peroxides also ate used as flame-retardant synergists for polystyrene (306), for preparing block and graft copolymers, for reactive processing, for reducing the molecular weight of polypropylene (ie, controlled theology or vis-breaking), for curing adhesives, for drying alkyd resin films, and for initiating cationic polymerization with cycHc ethers and maleic anhydride (44). Di- and triperoxides, which contain at least two peroxide moieties having different 10-h HLTs, decompose sequentially in the presence of vinyl monomers, yielding petoxypolymets and block copolymers (307,308). Organic peroxide initiators containing attached uv light absorbers, hindered amine light stabiLizers (HALS), and antioxidants yield polymers to which uv-light stabiLizer, HALS, and antioxidant groups are bound (309—311). Organic peroxides containing aEyl groups have been used as molecular weight regulators in vinyl monomer polymerizations (312) and for attachment of epoxide groups to polymers and copolymers (313—315).  [c.135]

The in situ process is simpler because it requires less material handling (35) however, this process has been used only for resole resins. When phenol is used, the reaction system is initially one-phase alkylated phenols and bisphenol A present special problems. As the reaction with formaldehyde progresses at 80—100°C, the resin becomes water-insoluble and phase separation takes place. Catalysts such as hexa produce an early phase separation, whereas NaOH-based resins retain water solubiUty to a higher molecular weight. If the reaction medium contains a protective coUoid at phase separation, a resin-in-water dispersion forms. Alternatively, the protective coUoid can be added later in the reaction sequence, in which case the reaction mass may temporarily be a water-in-resin dispersion. The protective coUoid serves to assist particle formation and stabUizes the final particles against coalescence. Some examples of protective coUoids are poly(vinyl alcohol), gum arabic, and hydroxyethjlceUulose.  [c.298]

The other significant by-product is acetaldehyde which is produced by thermal degradation of the PET unit. Random oxygen—alkyl scission of ester units leaves a vinyl ester end and a carboxyl-ended chain. The vinyl ester reacts with a polymer end group to form a new polymer link and expel acetaldehyde, the tautomer of vinyl alcohol (92). The vinyl ester end can also thermally polymerize to give chain-branched and cross-linked products and gel particles, and further thermal degradation of these polyvinyl units gives rise to colored polyenes (93,94). Although acetaldehyde is highly volatile, its presence is particularly objectionable in PET resin used for soda botties. Its presence cannot exceed 3 ppm in the final container if used for potable substances as it imparts an off-taste to popular cola drinks (95). Every time PET is melted during its processing, more acetaldehyde is generated one reason for bottie resin undergoing a final soHd-phase polymerization before stretch blow mol ding is to remove the last traces of residual acetaldehyde. Only the tiny amount of fresh acetaldehyde produced during the actual bottie mol ding is present in the final article and this is within specification.  [c.295]

Weathering. Polyester resins in the form of laminates, coatings (gel coats), and castings perform well in outdoor exposures marine craft, tanks, pipes, and architectural facia produced in the 1960s are stiU in service. Polyesters undergo some change in their surface features in direct sunlight, discoloration or yellowing being most obvious. Hulling and microcrazing occur only in products not appropriately formulated for the exposure. Long-term surface erosion of laminates exposes the glass fibers, which, unless corrected, can lead to rapid loss of stmctural integrity. Absorption of water influences the interfacial bond between the resin matrix and either the fibrous or aggregate reinforcement, leading to some loss of mechanical properties over 30 years. However, observations indicate that most appHcations reach this equiHbrium after three—five years and do not show much significant change thereafter. Most ERP products are designed with protective and decorative gel coats (19) formulated from neopentyl glycol, which, in combination with some methyl methacrylate monomer and benzophenone uv stabilizers, provides improved weather resistance. Platelet fillers such as talcs and clays as weU as high pigment levels are incorporated into gel coats to obscure the underlying laminate from the effects of direct sunlight. Surface oxidation and discoloration can also be controUed by using uv-resistant lacquers based on polymethacrylate resins or by cladding with poly(vinyl fluoride) (PVE) or acryHc and poly(ethylene terephthalate) (PET) films.  [c.322]


See pages that mention the term Racemization viaenol : [c.169]    [c.420]    [c.225]    [c.70]    [c.70]    [c.321]   
Carey organic chemistry (0) -- [ c.768 ]