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 with the carboxyl group of the unsaturated monocarboxyl acid, normally acrylic acid, or methacrylic acid, to form DVDE (divinyl-diester) prepolymer.

The following scheme gives an illustration of how the reaction takes place:

DVDE prepolymers have the following structure:

The synthesised prepolymers are DVDE’s (divinyl-diester): they have 2 vinyl groups, one at each end, next to them they have an ester group. In the polyester chain neither more vinyl groups nor ester groups

Laboratory of Macromolecular And Physical Organic Chemistry Page 3 of 8 Department of Chemistry, KUL Katholieke Universiteit Leuven Belgium can be observed. That’s why they are commercially named “vinyl ester”. Alternatively they are also called “phenacrylate” because of the constituents.

DVDE cure the same way as the MVME (“unsaturated polyester”), by free radical vinyl polymerization with a vinyl monomer (see point 3). The resulting 3D-PEPS based on DVDE has some advantages over the classic MVME based types: it doesn't absorb as much water, it doesn't shrink nearly as much when cured and it has very good chemical resistance. Also because of the hydroxyl groups, it bonds well to glass, other fillers and substrates.

A large number of alternative DVDE’s can be made: . The most simple are condensates of a diol (e.g. ethylene glycol, bisphenol-A) with a monocarboxyl acid (eg acrylic acid). . The most common are the “bisphenol-A vinyl esters” (see above): diepoxide based on bisphenol-A and epichlorhydrin, condensed with monocarboxylic acid (eg acrylic acid, methacrylic acid).

2. Synthesis of the PVPE resins The PVPE resins are blends from PVPE prepolymer and a vinyl monomer, usually styrene. The styrene is between 30 and 50% weight of the blend, usually ± 35%. The vinyl monomer is a reactive diluent (solvent or thinner) that is a building block, and plays an active role, in the free radical vinyl copolymerisation (see point 3). It also regulates the viscosity of the resin, lowers the cost and improves the wetting behavior.

In most commercial grades, an inhibitor is added in very small quantities, less than 100 ppm, to improve the shelf live.

The above resin blending is identical for DVDE and MVME resins.

3. Synthesis of 3D-PEPS: free radical vinyl copolymerisation 3D-PEPS is the result of crosslinking of PVPE prepolymers with vinyl monomers (normally styrene), via free radical vinyl copolymerisation. Two basic options exist: . Conventionally, by initiation with organic peroxide or hydroperoxide (dibenzoyl peroxide, cyclohexanone peroxide, MEKP (methyl ethyl ketone peroxide), etc…) . Photochemically under UV light using a photoinitiator (derivates of benzoin, acetophenone and benzophenone).

In this paper we concentrate on the conventional curing, using a organic peroxide as initiator, which is possible at high temperature (force-drying), room temperature or below. Coatings based on PVPE resins are normally cured at room temperature. This requires the addition of an accelerator to the resin as curing would otherwise not take place or would take days or even weeks. Two initiator/accelerator combinations are used predominantly to crosslink PVPE resins: . Dibenzoyl peroxide + tertiair aromatic amine. . Cyclohexanone peroxide + cobalt octoate.

Initiation The accelerator catalyses the decomposition of the peroxides into a pair of radicals, by reducing the dissociation energy:

R-O-O-R accelerator 2 R-O°

These unpaired electrons (on the radicals) will be quite discontent with being alone and still want to be paired. If they can find ANY electrons to pair up with, they will do so. The carbon-carbon double bond in a vinyl monomer or in a PVPE, has a pair of electrons which is very easily attacked by the free radical. The unpaired electron, when it comes near the pair of electrons, can't help but swipe one of them to pair with itself. This new pair of electrons forms a new chemical bond between the initiator fragment and one of the double bond carbons of the vinyl monomer or PVPE. The other electron of the double bond

Laboratory of Macromolecular And Physical Organic Chemistry Page 4 of 8 Department of Chemistry, KUL Katholieke Universiteit Leuven Belgium (vinyl group), attaches to the other carbon atom of a double bond (the C that is not bonded to the initiator fragment). Now we have a new free radical.

This two steps process, namely first the decomposition of the initiator into a pair of free radicals and secondly the reaction of the free radical with present vinyl groups (double bonds) from styrene or PVPE, is called “initiation” in free radical (co)polymerisations.

Chain propagation The new radical, created in the initiation step, reacts with another vinyl monomer or PVPE in the exact same way as the initiator fragment did. Because we keep remaking a radical, which recombines (reacts) with double bonds (vinyl groups) either from PVPE or styrene, we can keep adding more and more vinyl monomers or PVPE’s, and build a long chain of them. Self-perpetuating reactions like this one are called chain reactions.

Termination The polymer chain propagation will tend to terminate. Radicals are unstable, and eventually they are going to find a way to become paired without generating a new radical. Then the chain reaction will come to a halt. This happens in several ways.

The simplest way is that the radical sites of two growing chains find each other. The two unpaired electrons then join to form a pair, and a new chemical bond joining their respective chains. This is called coupling or recombination.

Another way in which our unpaired electrons can shut down the polymerization is called disproportionation. This is a rather complicated way in which two growing polymer chains solve the problem of their unpaired electrons. The mechanism takes place through transfer of a hydrogen atom from one polymer chain radical to an other.

Laboratory of Macromolecular And Physical Organic Chemistry Page 5 of 8 Department of Chemistry, KUL Katholieke Universiteit Leuven Belgium 3.1. 3D-PEPS formed by crosslinking MVME resin. In case of MVME, the prepolymer has multiple vinyl groups and multiple ester groups in the polymer chain, a hydroxyl group at one end and a carboxyl group at the other. The prepolymer is relatively long (max. ± 50 monomers).

During the free radical vinyl copolymerisation, the interior vinyl groups of the MVME are crosslinked with styrene. This means that polystyrene “bridges” are inter-connecting (crosslinking) the long MVME prepolymers, to form a giant molecule, namely a 3D-PEPS (three dimensional polyester-polystyrene). The resulting 3D-PEPS has carboxyl and hydroxyl end groups and eventually rest double bonds inside the network=crosslinked structure, making it still a bit susceptible for chemical attack.

3.2. 3D-PEPS formed by crosslinking DVDE resin. In case of DVDE, the prepolymer has only 2 double bonds, one at each end of the prepolymer. Next to the double bond (vinyl group) we find an ester group. Inside the prepolymer are no vinyl groups nor ester groups. The prepolymer is relatively short (max. ± 25 monomers).

During the free radical vinyl copolymerisation, the exterior vinyl groups of the DVDE are crosslinked with styrene. This means that polystyrene “bridges” are extra-connecting (crosslinking) the relatively short DVDE prepolymers, to form a giant molecule, namely a 3D-PEPS (three dimensional polyester- polystyrene). The resulting 3D-PEPS has no carboxyl nor hydroxyl end groups and no double bonds, making it less susceptible for chemical attack.

4. PVPE resin based formulations In point 2 we saw that the resin is a mixture of the PVPE prepolymer and styrene, eventually with some inhibitor, to prevent auto-polymerisation in the packaging. Next to a wide range of prepolymers, an exponentially large number of PVPE resin based formulations can be made by adding additives and fine fillers. This can be done by the resin producer in the plant, by a formulator in his plant and/or by the final customer.

Additives are added to the resin, in function of the targetted application: thixotropy agents, thixotropy improvers, coupling agents, air release agents, UV stabilisers, wetting agents, anti-tacky agents (reduces the interaction of atmospheric oxygen on the copolymerisation at the surface, eg. waxes), LSE-agents (low styrene emission), hydrophobers, inhibitors, fire retarders, etc…

Also fine solid material (fillers) can be added to the resin: pigments, MIO(Micaceous Iron Oxide), mika, glass flakes, …

Sometimes the accelerator is already added into the resin, resulting in a reduced shelf-live (thickens after 1 to 2 months).

Sometimes different PVPE prepolymers are blended to combine their properties and/or to create new properties.

Sometimes other resins are added. Most well-known is the addition of anti-shrink resins. These are normally blends of a thermoplast or thermoplastic elastomers dissolved in styrene. They are commercially classified as LS (low shrink; reduces shrink) and LP (low profile; zero shrink). Useful thermoplasts are PS (polystyrene), high impact modified polystyrene, PMMA (polymethyl- methacrylate), PVA (polyvinylacetate), ethylene vinyl acetate copolymer and related copolymers, some saturated polyesters and polyurethanes. Useful thermoplastic elastomers are: rubber-like blockpolymers from a diolefin (butadiene, isoprene, chloroprene) and an aromatic vinyl monomer (styrene, p-methyl styrene). Most commen is HIPS (high impact polystyrene), which is a block copolymer of polystyrene block - polybutadiene block – polystrene block, also called SBS rubber.

Formulation rules are the same for MVME and DVDE resins.

Laboratory of Macromolecular And Physical Organic Chemistry Page 6 of 8 Department of Chemistry, KUL Katholieke Universiteit Leuven Belgium 5. Composites with 3D-PEPS matrix The PVPE prepolymers are extremely versitile, easy to handle, can be used alone or in combination with other prepolymers, have good wetting properties and can be polymerised, by free radical vinyl copolymerisation with a vinyl monomer (styrene), with many different additives, to form 3D-PEPS matrices. These matrices, in combination with a large range of fillers, make composite materials in the form of parts and protective coatings. They have high anti-corrosion resistance, protecting the parts or the coated substrate against chemical, mechanical and temperature agression.

Dependent of the application, hundreds of combinations are known of 3D-PEPS polymer composites. These final products can be divided in two major groups:

Corrosion resistant Parts: (Mostly moulded and cured at higher temperature or at room temperature.) Resins with additives and fillers. The fillers are mostly fibers (glass, carbon, kevlar, etc…), that is why they are called FRP (fiber reinforced plastics). They are used to make resistant parts like: automotive parts, chemical equipment, storage and transport tanks, vessels, pipes, furniture, swimming pools, … Sometime other fillers are used (eg. quartz) for mortars, to make ducts and sewage channels.

Protection of Surfaces: (Mostly hand lay-up (spray, roll, trowel, etc..) at room temperature.) . Coatings: resins with additives and fine fillers (eg glass flakes, MIO (Micaceous Iron Oxide), mica,…), with, next to chemical corrosion protection, some extra properties like: flexible, flame- retardant, topcoat, gelcoat, … They are used for the protection of steel, concrete, and other constructions: floors, walls, retention basins, sockles, pipe lines, sewage pipes,… . Linings: resins with additives, which impregnated fibers (eg glass or synthetic mats) at the jobsite. They are used for the protection of steel, concrete and other constructions: swimming pool, waste water basins, storage tanks, pipe relinings, … . Polymer concrete or mortars: resins with additives, which are mixed at the jobsite with granular inorganic fillers (eg sand (quartz), quartz flower, chalk, talc, dolomite, gravel, silica, cement, …). The mixture can be self-leveling and/or has to be troweled. They are used for the protection of concrete constructions: floors, walls, drains, sockles, …

6. Conclusion 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, namely MVME (“unsaturated polyesters”) and DVDE (“vinyl esters”) belong to the same family of reactive prepolymers; PVPE (polyvinyl-polyesters). The general properties (curing, interaction with additives, etc…) are the same for both sub-families.

In both pathways: . The raw materials, belong to the same classes, namely unsaturated carboxylic acids and diols. . The prepolymers are condensation products of the raw materials. . The reactive diluent (also co-polymerising unit) is an aromatic vinyl monomer, usually styrene. . The resin contains 30-50 % of styrene, normally ± 35 %. . The prepolymers are crosslinked with styrene. . The crosslinking is done by free radical vinyl copolymerisation. . The crosslinked matrix material is a 3D-PEPS (three dimensional polyester-polystyrene); a giant solid polymer, containing polyester chains, connected with polystyrene “bridges”. . The same initiators and accelerators are used to start this copolymerisation at ambient temperature. . The resin can easely be mixed with a wide range of additives, other prepolymers, resins and fillers. . The resulting composite materials are in the first place protecting the moulded part or the underlying surface against corrosive materials.

Guido Dockx MBE & MBA Professor C. Samyn Managing Director Director STAC Industrial Coatings Laboratory of Macromolecular And Physical Organic Chemistry Department of Chemistry of the Katholieke Universiteit Leuven May 2003

Laboratory of Macromolecular And Physical Organic Chemistry Page 7 of 8 Department of Chemistry, KUL Katholieke Universiteit Leuven Belgium Bibiography . Encyclopedia of Polymer Science an Technology, volume 11, John Wiley & Sons Inc, (1969) . Priciples of Polymer Chemistry, 6th print, Paul J. Flory, Cornell University Pres N.Y. (1967) . Reinforced Plastics, R.H. Leitheiser, R.J. Hellmer and E.T. Clocker (1968) . Sheet Moulding Compounds Sience and Technology, chapter 4: Low-Profile Additives: shrinkage control mechanisms and applications, Hamid G. Kia, Kennith E. Atkins, Carl Hanser Verlag, Munich Vienna New York Barcelona (april 1993) . Macrogalleria, Intelligent Systems Laboratory, Michigan State University . Nottingham University Composites Institute . DIN 18820: Laminate aus textilglasverstärkten ungesättigten Polyester- und Phenacrylatharzen für tragende Bauteile (GF-UP, GF-PHA) . Unsaturated polyester resins, United States Patent 4.036.819, July 19, 1977 . Unsaturated polyester resins, United States Patent 5.373.058, December 13, 1994 . Hochfüllbare LS-UP Harzformmasse mit guter Pigmentierbarkeit, BASF, European Patent 294.771, December 1988 . Verfahren zur Herstellung von pigmentierten, härtbaren Polyesterformmassen, BASF, European Patent 419.977, April 1991 . The preparation and application of Vestopal reactive resin mortar and concrete, HULS, November 1984

Laboratory of Macromolecular And Physical Organic Chemistry Page 8 of 8 Department of Chemistry, KUL Katholieke Universiteit Leuven Belgium