Resins self-curing

Phenolic Resins. Phenohc resins (qv) are formed by the reaction of phenol [108-95-2] C H O, and formaldehyde [50-00-0] CH2O. If basic conditions and an excess of formaldehyde are used, the result is a resole phenohc resin, which will cure by itself Hberating water. If an acid catalyst and an excess of phenol are used, the result is a novolac phenohc resin, which is not self-curing. Novolac phenohc resins are typically formulated to contain a curing agent which is most often a material known as hexamethylenetetraamine [100-97-0] C H22N4. Phenohc resin adhesives are found in film or solution... 

Early phenoHc resins consisted of self-curing, resole-type products made with excess formaldehyde, and novolaks, which are thermoplastic in nature and require a hardener. The early products produced by General BakeHte were used in molded parts, insulating varnishes, laminated sheets, and industrial coatings. These areas stiH remain important appHcations, but have been joined by numerous others such as wood bonding, fiber bonding, and plywood adhesives. The number of producers in the 1990s is approximately 20 in the United States and over 60 worldwide. 

The developmenf of self-curing resins, i.e., systems curing without photoinitiators or, in some cases, with just small amounts of photoinitiators, has been reported recently. Such resins are synthesized by Michael reaction of acrylic functional materials with Michael donor compounds such as acetoacetates. The resulting product has an increased molecular weight compared to the parent acrylate(s). This provides resins with reduced volatility and propensity for skin absorpfion. This new technology is versatile and flexible and opens a possibility of synfhesis of a large number of different acrylate resins. The novel resins reportedly exhibit unique depth of cure capability. In the absence of a photoinitiator (PI), film of approximately 10 mils (0.25 mm) thick can be cured at a line speed of 100 fpm (30.5 m/min). When only 1% of PI is added, the thickness of film that can be cured increases to over 100 mils (2.5 mm). 

Hydroxyl-terminated polydiene resins gelled by the reaction with orthosilicate esters have increased thermal stability. These polymeric gels, like silicone rubbers, exhibit outstanding electrical properties. The polymeric gels crosslinked at ambient temperature are castable as self-curing liquids. For example, they are used as binders for rocket solid fuels, in coatings for pipes, tanks, etc. They can be mixed with rubbers. 

Polybutenes have heen used for almost a century and while they are still used, most of this type sealant contains butyl rubber, which is a copolymer of butene and isoprene. Most building specifications, including Federal Specification, TT-S-001637, require solutions of butyl rubber instead of oil-based caulking compositions. Self curing butyl rubber sealants may contain phenolic resins,IS. resorcinol and hexamethylenetetramine. ... 

R. L. Bowen and H. Argentar, A method for determining the optimum peroxide-to-amine ratio for self-curing resins, J. Appl. Polymer Sci. 17 (1973). 

Self-cure versions are available, where polymerization is initiated by a two-part initiator system that comes together when the material is mixed. This type of resin-modified glass-ionomer can be placed in full ( bulk fiU ) within a cavity. 

More recently, the question of the performance of light-cured resin-based calcinm hydroxide materials has been considered [41], In this study, the brand Biocal was compared with two self-cure calcium hydroxide chelate cements, Dycal and Hidro C. Two criteria were evaluated, namely water sorption and solubility, with pure water being the medinm in both cases. Results are shown in Tables 9.4 and 9.5. 

Polyvinyl alcohol is copolymerized with cross-linkable comonomers N-methylol acrylamide is self-curing. Carboxylic acid comonomers are cured by epoxy, urea, or phenolic resins. 

Resole PF resins are produced by the reaction of phenol with excess formaldehyde (P F molar ratio 1 1.8 to 1 2.2) in the presence of an alkali catalyst (Fig. 3). Because resole resins contain reactive methylol groups, they are self-curing resins that can condense with active sites on the phenol rings to form a cross-linked network in the presence of heat even without additional hardener. Resole resins have a very branched structure (Fig. 3) and are by far the more important of the two types of PF resins for wood composites. 

Conversely, novolac PF resins are produced by the reaction of excess phenol with formaldehyde (P F molar ratio 1 0.8 to 1 1) in the presence of an acid catalyst. Unlike resole resins, novolac PF resins have a more linear structure (Fig. 4) and do not self-cure because they lack the residual reactive methylol groups of resoles. Therefore, an external curing agent such as hexamethylenetetraamine must be added to novolac resins to yield a cross-linked structure. Novalac PF resins cured under acidic conditions are not recommended for wood composites for long-term structural applications. 

The fixation of the impiant parts in the bone may be achieved by self-curing polymer resins (bone cements) such as PMMA (see above) or via direct integration of micro- or macroporous implant surfaces into the host bone. The UHMWPE used for knee and hip joints is usually highly cross-linked [17]. 

Stripping [59]. A practical application embodying these concepts has led to the preparation of self-curing phenol-formaldehyde resins [60]. 

Masuhara, E., Studies of dental self curing resins. 4. Bonding of dental self curing resins to dentine surface for the use of alkylboron as initiator. Reports Res. Inst. Dent. Mater. Tokyo Med. Dent. Univ., 2, 511, 1964. 

This new product is cured by any conventional curing technique including UV radiation, thermal baking, metal-catalyzed air drying, and the like. Because of the ease with which it cures thermally the resin could also be apphed as a water-borne self-curing coating. Where one wants to employ UV curing system, one must add a photosensitizer. 

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