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Synthesis of 3D-PEPS According to 2 Related Pathways

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Laboratory of Macromolecular And Physical Organic Chemistry Department of Chemistry Katholieke Universiteit Leuven Celestijnenlaan, 200F B-3001 Leuven Belgium Surface Protection Coatings Against Corrosive Materials. Synthesis of 3D-PEPS (Three Dimensional Polyester-Polystyrene) According to 2 related pathways. Introduction In the confusing jungle of commercial nomenclature of polymer chemicals and reactions, a scientific proof is given that 3D-PEPS (three dimentional polyester-polystyrene) copolymer matrix materials are synthesed according to 2 pathways which start from the same classes of raw materials and use the same reaction mechanisms. The intermediate prepolymers of both pathways belong to the same family of reactive prepolymers. More specific: Raws materials classes: Carboxyl acids and diols Reaction mechanisms: Condensation; for the creation of prepolymers Free radical vinyl copolymerisation; crosslinking of prepolymers with vinyl monomers (eg styrene) to form 3D-PEPS matrix. Intermediate prepolymers: DVDE (divinyl-diester) and MVME (multivinyl-multiester) are subfamilies of the PVPE (polyvinyl-polyester) family. Definitions 3D-PEPS = three dimentional polyester-polystyrene: copolymer matrix with multiple ester groups and multiple styrene groups. Commercial names: (crosslinked) polyester PVPE = polyvinyl-polyester : prepolymer with 2 or more vinyl groups and 2 or more ester groups. Commercial names: “unsaturated polyester and vinyl ester”. DVDE = divinyl-diester: prepolymer with 2 vinyl groups and 2 ester groups. The vinyl groups are at the ends of the prepolymer, the ester groups next to them. Commercial names: vinyl ester, unsaturated epoxy, epoxy vinyl ester, phenacrylate, unsaturated monocarboxyl-epoxypolymer condensate, unsaturated monocarboxyl-diol condensate. MVME = multivinyl-multiester: prepolymer with multi (>2) vinyl and multi (>2) ester groups. The vinyl groups and ester groups are located inside the prepolymer. The ends of the prepolymer are at on side a carboxyl group and at the other side a hydroxyl group. Commercial names: unsaturated polyester, dicarboxyl-diol condensates. PVPE resin = polyvinyl-polyester resin: blend of polyvinyl-polyester prepolymer and vinyl monomer (eg. styrene). Commercial names: “unsaturated polyester resin and vinyl ester resin”. DVDE-resin = divinyl-diester resin: blend of divinyl-diester prepolymer and vinyl monomer (eg. styrene). Commercial names: vinyl ester resin, unsaturated epoxy resin, epoxy vinyl ester resin, phenacrylate resin, unsaturated monocarboxyl- epoxy resin, unsaturated monocarboxyl-diol resin. MVME resin = multivinyl-multiester resin: blend of multivinyl-multiester prepolymer and vinyl monomer (eg. styrene). Commercial names: unsaturated polyester resin, dicarboxyl-diol resin. Polyester: molecule with more than one ester group. Polyvinyl: molecule with more than one vinyl group. Ester: condensate of a carboxylic acid and an alcohol, with the elimination of a water molecule. Carboxylic acid can be replaced by an acid chloride or an anhydride. Vinyl: molecule with a double bond between 2 C atoms. Can be created in numeruous ways. Ester group: -COO- connection group of a condensate of a carboxylic acid and an alcohol. Vinyl group: -C=C- double bond between 2 C atoms. Commercial names: unsaturated, ethylene group, reactive bond, double bond Free radical vinyl copolymerisation: multilinking of 2 different monomers and/or prepolymers via free radical vinyl step polymerisation, using an initiator and, at lower temperature, an accelerator. Example in the context of this paper: crosslinking of PVPE prepolymers with vinyl monomers (eg styrene), to form 3D-PEPS. Commercial names: curing, hardening, matrix formation Initiator: chemical that initiates the reaction between other chemicals by reacting with one of them, to allow it to react with the others. Example in the contect of this paper: organic peroxide which is, at room tempeature, under influence of a specific accelerator, decomposed into 2 radicals. These radicals initiate the free radical vinyl copolymerisation. Commercial names: catalyst, curing agent, hardener Accelerator: chemical that accelerates a reaction of other chemicals, acting usually as a catalyst. Example in the contect of this paper: catalyst that, at room tempeature, decomposes an organic peroxide into 2 radicals. Diol: molecule with 2 hydroxyl groups. Commercial names: glycol Epoxide: molecule with epoxide group. Epoxide group: CH2-(O)-CH- small triangular ring end group, composed of 1 oxygen, 2 carbon and 3 hydrogen atoms. Epoxy: condensation of an alcohol with and epoxide, normally epichlorohydrin, with the elimination of HCl. Diepoxy: polycondensate of n diol and n+1 epichlorohydrin molecules, with the elimination of n+1 HCl molecules, resulting in a short chain polyether, with n diol monomers and 2 epoxide end groups (structure on page 3). Laboratory of Macromolecular And Physical Organic Chemistry Page 1 of 8 Department of Chemistry, KUL Katholieke Universiteit Leuven Belgium 1. Synthesis of the PVPE prepolymers Ester formation results from the reaction of a carboxylic acid and an alcohol by a condensation reaction (elimination of a molecule of water), following the general reaction scheme: RCOOH + R’OH RCOOR’ + H2O In some cases instead of an acid, an acid chloride and alcohol in the presence of base is used. Anhydrides in the presence of alcohol can also lead to the formation of ester. Polyesters result from the reaction of dicarboxylic acid and diol (glycol) by a polycondensation (elimination of several molecules of water), following ther general reaction scheme: n HOOCRCOOH + n HOR’OH HOR’O-[OCRCOOR’O]n-1-OCRCOOH + nH2O If one or both of the constituents is unsaturated (= contains one or more reactive bonds = vinyl groups), the resulting polyester is unsaturated, more precisely it is a PVPE (polyvinyl-polyester), or exactly a MVME (multivinyl-multiester). 1.1. MVME prepolymers Since there are a large number of dicarboxyl acids and glycols available and, furthermore, different dicarboxyl acids (saturated and/or unsaturated) and/or different glycols can be mixed, there are potentially a very large number of MVME’s (multivinyl-multiester). They are created along the classic pathway as discribed above. The backbone of the prepolymer is a chain of unsaturated carboxylic monomers and diol monomers, connected by ester groups. If mixtures of unsaturated and saturated dicarboxyl acid is used, the double bonds (=vinyl groups) can be found, in theory, every 4th monomer in the chain. In practice, they are randomly arranged along the prepolymer chain. Most MVME prepolymers are made from ethylene glycol (1,2 ethane diol, HO-CH2-CH2-OH) and a mixture of saturated and unsaturated dicarboxyl acids. The saturated dicarboxyl acid is mainly phthalic acid (HOOC-C6H4-COOH) in one or more of its isomers (ortho-, iso-, tere-). The unsaturated dicarboxyl acid is mainly an ethylene dicarboxyl acid (HOOC-CH=CH-COOH) (mainly maleic acid). Other useful saturated dicarboxyl acids and anhydrides are: adipic acid, tetrahydrophthalic acid, sebacic acid, phthalic acid anhydride, … Other useful unsaturated dicarboxyl acids and anhydrides are: fumaric acid, maleic acid anhydride, … Other useful diols are: diethylene glycol, propylene glycol, 1,3-propane diol, dipropylene glycol, glycerol, neopentyl glycol, 1,6-hexane diol, bisphenol-A, … In the commercial literature numeruous names are given to the different combinations of dicarboxyl acids and diols. Most commonly the MVME prepolymers are classified as: orthophthalic-, isophthalic- , neopentyl glycol (NPG)-, bisphenol-A-“unsaturated polyesters”. In some extreme cases, the properties of the MVME based parts and coatings show some disadvantages: they shrink a good deal when they're cured, they can absorb water very easily and their impact strength is low. They are also not very chemically resistant. This is because the matrix of these 3D-PEPS still contains reactive bonds and the end groups of the crosslinked prepolymers contain a carboxyl group or an hydroxyl group. 1.2. DVDE prepolymers In the search for a even more stable (protective) 3D-PEPS, an alternative pathway was developed almost 40 years ago. The idea was to make first a stable polymer backbone (without vinyl groups) and to link this backbone, via a condensation reaction, to an unsaturated carboxyl acid. The resulting DVDE (divinyl-diester) prepolymer would then crosslink with its ends with vinyl monomers (styrene), to make an even more stable matrix without double bonds nor reactive end groups. Laboratory of Macromolecular And Physical Organic Chemistry Page 2 of 8 Department of Chemistry, KUL Katholieke Universiteit Leuven Belgium Epoxy (diepoxy prepolymer) was used to create DVDE prepolymers to incorporate in a network (three dimensional, crosslinked) structure; more stable 3D-PEPS. The first step is the formation of the diepoxy prepolymer: 2 Diepoxy prepolymer is a polyether, obtained by a condensation reaction of bisphenol-A with epichlorohydrin, in the presence of NaOH, to eliminate HCl produced in the reaction medium. The diepoxy prepolymers, are rather small chains with maximum 25 monomers. Mostly the chain contains less than 10 monomers. The length of the chain depends of the mol concentration of the constituents, with n mol of diols and (n+1) mol of epichlorohydrin, eliminating (n+1) mol of HCl molecules. In a second step, the diepoxy prepolymer is reacted, via a condensation reaction of the epoxide groups of the diepoxy prepolymer
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