Low-Molecular-Weight Resins

Ionomer resins consisting of ethylene—methacrylic acid copolymers partially neutralized with sodium or zinc were commercially introduced in 1964 by Du Pont under the Sudyn trademark (1). More recently, a similar line of products, sold as Hi-Mdan resins, has been commercialized by Mitsui—Du Pont in Japan. lolon ionomeric resins, based on ethylene—acrylic acid, are produced by Exxon in Belgium. Ionomers containing about 1 mol % of carboxylate groups are offered by BP in Europe as Novex resins. Low molecular weight, waxy Aclyn ionomers are produced and sold by AHiedSignal. 

Bulky AlkyllAryl Substituted Phenol-Formaldehyde Novolak Resins. Low molecular weight cresol-formaldehyde Novolak resins tend to have high solubility rates in alkaline developers. To increase developer resistance, Novolak resins containing a hydrophobic chain incorporated on a portion of the phenol group were synthesized, as shown below (17). As the number of alkyl... 

Precursor Matrix resin - low molecular weight, lots of end groups... 

Low building tack An inherent characteristic of SBR elastomers, which normally requires the addition of taekifying resins, low molecular weight polymers, or plasticizers, or master batch processing. 

Production procedure, coatings Production procedure Coatings—production procedure High quality resins Low molecular weight polyanhydrides... 

Epoxy novolac resins are produced by glycidation of the low-molecular-weight reaction products of phenol (or cresol) with formaldehyde. Highly cross-linked systems are formed that have superior performance at elevated temperatures. 

Furfural reacts with ketones to form strong, crosslinked resins of technical interest in the former Soviet Union the U.S. Air Force has also shown some interest (42,43). The so-called furfurylidene acetone monomer, a mixture of 2-furfurylidene methyl ketone [623-15-4] (1 )> bis-(2-furfurylidene) ketone [886-77-1] (14), mesityl oxide, and other oligomers, is obtained by condensation of furfural and acetone under basic conditions (44,45). Treatment of the "monomer" with an acidic catalyst leads initially to polymer of low molecular weight and ultimately to cross-linked, black, insoluble, heat-resistant resin (46). 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

Aldehydes fiad the most widespread use as chemical iatermediates. The production of acetaldehyde, propionaldehyde, and butyraldehyde as precursors of the corresponding alcohols and acids are examples. The aldehydes of low molecular weight are also condensed in an aldol reaction to form derivatives which are important intermediates for the plasticizer industry (see Plasticizers). As mentioned earlier, 2-ethylhexanol, produced from butyraldehyde, is used in the manufacture of di(2-ethylhexyl) phthalate [117-87-7]. Aldehydes are also used as intermediates for the manufacture of solvents (alcohols and ethers), resins, and dyes. Isobutyraldehyde is used as an intermediate for production of primary solvents and mbber antioxidants (see Antioxidaisits). Fatty aldehydes Cg—used in nearly all perfume types and aromas (see Perfumes). Polymers and copolymers of aldehydes exist and are of commercial significance. 

Engineering problems involved in the production of TEE seem simple compared with those associated with polymeriza tion and processing of PTEE resins. The monomer must be polymerized to an extremely high molecular weight in order to achieve the desired properties. The low molecular weight polymer does not have the strength needed in end use appHcations. 

Hydrocarbon resin is a broad term that is usually used to describe a low molecular weight thermoplastic polymer synthesized via the thermal or catalytic polymerization of coal-tar fractions, cracked petroleum distillates, terpenes, or pure olefinic monomers. These resins are used extensively as modifiers in the hot melt and pressure sensitive adhesive industries. They are also used in numerous other appHcations such as sealants, printing inks, paints, plastics, road marking, carpet backing, flooring, and oil field appHcations. They are rarely used alone. 

With the improvement of refining and purification techniques, many pure olefinic monomers are available for polymerization. Under Lewis acid polymerization, such as with boron trifluoride, very light colored resins are routinely produced. These resins are based on monomers such as styrene, a-methylstryene, and vinyltoluene (mixed meta- and i ra-methylstyrene). More recently, purified i ra-methylstyrene has become commercially available and is used in resin synthesis. Low molecular weight thermoplastic resins produced from pure styrene have been available since the mid-1940s resins obtained from substituted styrenes are more recent. 

Petroleum resins are low molecular weight thermoplastic hydrocarbon resins synthesized from steam cracked petroleum distillates. These resins are differentiated from higher molecular weight polymers such as polyethylene and polypropylene, which are produced from essentially pure monomers. Petroleum resin feedstocks are composed of various reactive and nonreactive aliphatic and aromatic components. The resins are usually classified as C-5... 

A wide variety of chromium oxide and Ziegler catalysts was developed for this process (61,62). Chromium-based catalysts produce HDPE with a relatively broad MWD other catalysts provide HDPE resins with low molecular weights (high melt indexes) and resins with a narrower MWD (63,64). 

Highly branched fractions of nonuniformly branched resins have low molecular weights and are easily soluble, even at room temperature, in saturated hydrocarbons. These highly branched fractions are called extractables, an excessive amount of which in an LLDPE resin can be detrimental to certain end use properties, especially in food packaging appHcations. 

Oxidation of LLDPE starts at temperatures above 150°C. This reaction produces hydroxyl and carboxyl groups in polymer molecules as well as low molecular weight compounds such as water, aldehydes, ketones, and alcohols. Oxidation reactions can occur during LLDPE pelletization and processing to protect molten resins from oxygen attack during these operations, antioxidants (radical inhibitors) must be used. These antioxidants (qv) are added to LLDPE resins in concentrations of 0.1—0.5 wt %, and maybe naphthyl amines or phenylenediamines, substituted phenols, quinones, and alkyl phosphites (4), although inhibitors based on hindered phenols are preferred. 

Phenolic resin substantially increases open time and peel strength of the formulation (80). For example, higher methylol and methylene ether contents of the resin improves peel strength and elevated temperature resistance. Adhesive properties are also influenced by the molecular weight distribution of the phenoHc low molecular weight reduces adhesion (82). 

The resins should dry quickly and cure weU at low temperatures. They usually are made at a high pH with high ratios of formaldehyde to phenol and held to fairly low molecular weight. Typical viscosities are 15, 000 mPa-s(=cP) at 75% soHds content for a first coat and 1000 mPa-s(=cP) at 50% soHds for the top resin. For dense backing materials, such as fiber disks, a typical resin has a viscosity of 50, 000 mPa-s(=cP) at 80% soHds and is cured at 148°C. 

Laminates. Laminate manufacture involves the impregnation of a web with a Hquid phenoHc resin in a dip-coating operation. Solvent type, resin concentration, and viscosity determine the degree of fiber penetration. The treated web is dried in an oven and the resin cures, sometimes to the B-stage (semicured). Final resin content is between 30 and 70%. The dry sheet is cut and stacked, ready for lamination. In the curing step, multilayers of laminate are stacked or laid up in a press and cured at 150—175°C for several hours. The resins are generally low molecular weight resoles, which have been neutralized with the salt removed. Common carrier solvents for the varnish include acetone, alcohol, and toluene. Alkylated phenols such as cresols improve flexibiUty and moisture resistance in the fused products. 

The resins used in air and oil filters are moderate-to-low molecular weight, catalyzed by caustic in one step 10—20% alcohol is added soHds content is in the range of 50—60%. These resins are designed to penetrate the sheet thoroughly, yet not to affect the porosity of the paper. In the B-stage, the resin must have sufficient flexibiHty to permit pleating the C-stage should have stiffness and resistance to hot oil. 

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