CA1038529A

CA1038529A - Flame-retardant polyester molding compositions

Info

Publication number: CA1038529A
Application number: CA195,029A
Authority: CA
Inventors: David R. Williams
Original assignee: Koppers Co Inc
Current assignee: Beazer East Inc
Priority date: 1973-03-15
Filing date: 1974-03-14
Publication date: 1978-09-12
Also published as: FR2221486B1; JPS5025687A; IT1004335B; GB1449735A; DE2410787A1; FR2221486A1

Abstract

ABSTRACT OF THE DISCLOSURE

Polyester articles having improved flame-retardant pro-perties are prepared by curing a polymerizable molding composi-tion comprised of an unsaturated polyester, a vinyl monomer that is copolymerizable with the polyester, a finely divided inorganic filler material, and a halogenated vinyl copolymer.
The unsaturated polyester is halogenated although it may be mixed with non-halogenated polyester, the filler is preferably hydrated alumina, and the halogenated vinyl copolymer is selected from those that are soluble in the monomer, that are at least partially immiscible and incompatible with the poly-ester, and that have functional groups, preferably acid or epoxy functionality. Reinforcing materials, such as glass fibers, as well as other materials generally included in poly-merizable polyester compounds, can also be used.

Description

FIELD OF THE INVEN~ION ~ :

This invention relates to polyester resi.n systems and, :~
more particularly, to those from which molded articles can be prepared that undergo little or no gross shrinkage during curing, that conform closely to the surface profile of the molding die, that are substantially free from surface imperfections, that requ~ire minimal sanding or smoothing, and that have improved - flame-retardant properties.
The fabrication of thermosçt polyester resin articles ~rom polymerizable compositions comprised of an unsaturated polyester disqolved in a monomeric material . :~

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which is capable of polymerizing or cross-linking with the resin is well known. Articles made from such resin ~
~ ' systems have excellent chemical and electrical properties and, by combining fibrous reinforcernents, such as glass S fibers, with the polymerizable unsaturated polyester resin formulation, articles haviny relatively high strength-to-weight ratios can be produced.
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, :. , In recent years the flame-retardant properties of various materials have received increasing attention and are assuming greater importance. Governmental regu}a-tions concerning the flammability of materials used in the manufacture of furniture and in the construction oE
buildings, vehicles, aircraft and the like, axe being promulyated regularly and with increasingly higher re-quirements. ~or example, in providing seating in schoolauditoriums, it is considered of great importance that ..
the materials used in the construction of the seats have good flame-retardant properties and, preferably, sel~- ~
extinguishing fire ratings. Articles molded from currently ~ `
20 available polyester resins frequently do not meet estab- ;~
lished specifications, however, and it is a solution to this problem to which this invention relates.
In fabricating reinforced polyester articles, it ~;
has been recognized that there is difficulty in molding the 25 articles in a manner in which good conformity with the sur- ;--```-face profile of the molding die is obtained and in which the surfaces of the articles are smooth, ripple-free and do not show a pattern of fibrous xeinforcements. This may ~ ~

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~(~38529 be a serious disadvantage when the article is one that has a surface that is expected to be aesthetical].y flawless ~
for example, the exterior surfaces of automobile body parts, furniture, and the like. One rather satisfactory solution to this problem, which is now accepted commercial practice, is to include a thermoplastic polymer within the polymeri-zable unsaturated poly.ester resin formulation. This polymer is selected to be soluble in the monomeric cross-linking agent of the formulation and should be at leas~. partially i 10 immiscible and incompatible wlth the cured polyester resin .
The thermoplastic polymer counteracts shrinkage of the polymerizable formulation as it cures and, in some cases,. ~ ~ ;
it may even cause the formulation to expand slightly. It has now been discovered that if this polymeric material : 15 is a properly selected halogenated vinyl copolymer, it will not only prevent undue cure shrinkage, but it also .
will improve the flame-retardant properties of the molded article. . -Accordingly, it is the principal object of this 20 invention to improve the flame-retardant properties of ~ :
articles molded from polyester resins.
Another object of this invention-is to prepare polyester articles that combine the desirable properties o conformity with the suxface profile of the molding die, ~5 low shrinkage, good surfaces, good mechanical strength, :
and improved flame-retardancy.
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SUMMARY OF THE INVENTION
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These and other objects of this invention are .
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achieved by molding articles from a polymerizable polyester `~
molding composition, which composition includes an unsatu~
rated polyester, a vinyl monomer that is copolymerizable with the polyester, a finely divided inorganic filler material, and a halogenated vinyl copolymer. The polyester is halogenated although it may be mixed with non-halogenated polyester, the filler material is preferably hydrated alumina, and the halogenated vinyl copolymer is selected from those that are soluble in the monomer, that are at least partly immiscible and incompatible with the polyester, and that have functional groups, preferably acid or epoxy functionality.
In addition to the above components, other materials, such as glass fiber reinforcement, catalysts, qtabilizers, chemical thickeners, flame-retardant syner-15 gists and the like, are generally included within the ~ ~;
polymerizable compounds. These are variously discussed under the separate headings below.
The Unsaturated Polyester , , Unsaturated polyesters that can be utilized in the composition of this invention are those formed by con-densing an ethylenically unsaturated dicarboxylic acid or its anhydride with a dihydric alcohol. Saturated dicar-boxylic ac1ds or their anhydrides may also be included in the esterification polymerization. The unsaturated polyesters produced by such reactions are well known, a~ are the processes for preparing them.
Examples of ethylenically unsaturated dicarboxy-lic acids and anhydrides that can be used to prepare the ~ 30 ". ~.. -.

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unsaturated polyesters are maleic anhydride, ~umaric acid, chloromalelc acid, ~taconic acid, citraconic acid, and mesaconcic acid. ;
Examples of dihydric alcohols that can be used to prepare the unsaturated polyesters are ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and isopropylidene bis-(p-phenyleneo~ypropanol-2), cyclohexanedimethanol, neopentyl glycol and cyclobutanediol. ;
Examples of saturated dicarboxylic acids and ~ ;
anhydrides that can be used in preparing the unsatura~d polyesters are phthalic anhydride, isophthalic acid, ~ , tetrahydrophthalic anhydride, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid.
In addition, other unsaturated polyesters useful in this invention may contain alcohols having more than ~ -~
two hydroxyl groups or acids, either saturated or unsatu~
rated, containing more than two carboxyl groups. Examples of such ingredients are glycerol, pentaaerythritol, tri~
mellitic acid and pyromellitic acid.
The acid number and the molecular weight of the unsaturated polyester can vary over a wide range, for example from about 10 to about 100 and from about 750 to about 5,000 respectively. Preferably, the acid number , shouId be less than about 35 and the molecular weight within the range of about 1/000 to about 3,000.
The reactivity of the unsaturated polyester ' ~-- 5 - ~
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should be within the range of about 20 to about 100 mol per cent of tlle total acid component of the resin and preferably within the range of about 50 to about 100. .
The particular unsaturated polyester used in the formulation should be selected on the basis of the desired properties of the articles that are being made.
In producing articles where the surace properties are extremely important and where good over-all strength is ~ . .
desired, it is preferred to. use polyesters that are pre~
pared by condensing propylene glycol, dipropylene glycol, maleic anhydride and isophthalic acid. ~-The amount of un~aturated polyester comprising the formulakion may vary over a wide range - for example, ~.
from about 10 to about 75 weight per cent, and preferably from about 25 to about 65 weight per cent of the total resin system.
Significant increases in the flame-retardant properties of molded polyester articles have been noted ~, .
when halogenated unsaturated polyesters are used in the `
20 practice of this invention. By way of example, there ~ :~
may be mentioned unsaturated polyesters prepared from ethylene glycol/tetrabromo phthalic anhydride/maleic anhydride; 4,4'-bis-2-hydroxy ethylamino octachlorobi-phen~l!maleic anhydride; ethylene glycol/chlorendic anhyd.ride/maleic anhydride; ethylene glycol/tetrabromo~
ph~halic anhydride/maleic anhydride; 4,4'-bis--2-hydroxy-propyl tetrabromo bisphenol A/maleic anhydride; and ~:
dibromo neopentyl glycol/maleic anhydride, . . ~

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The Vinyl Monomer A vinyl monomeric material which iS capable of cross-linking (that is, has ethylenic unsaturation) with the unsaturated polyester is included within the resin S system. Examples of suitable cross-linking agents which contain ethylenic unsaturation are styrene, vinyl toluene, diallyl phthalate, alphamethyl styrene and methylmethacry~
late. Mixtures of cross-linking agents can be used, but, most commonly, skyrene is the preferred cross-linkiny agent.
The amounk of cross-linking agent comprising the polymeri~able formulation can vary over a wide range for example, from about 2~0 to about 70 weight per cent -; and preferably the cross-linking agent comprises from about lS 30 to about 60 weight per cent of the total resin system.
The Thermoplastic Polymer t In order that the thermoplastic polymer may be ;
most effective, it is necessary that it be soluble in the ~ ~
monomeric cross-linking agent, which most commonly is ~ ;
styrene. The degree of solubility must be sufficiently high to permit dissolution of the desired quantity of thermoplastic copolymers necessary to reduce shrinkage, e.g., in a broad range of from 3 to 50 weight per cent of the resin system, and more preferably in a range of from 5 to 20 weight per cent. Also, the solution vis~
cosity of the polymer should be low enough to avoid an excessi~e rise in viscosity of the solution. ~The term "resin" or "resin system" as used herein refers collec-- " ~

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tively to the combination of unsaturated polyester, mono~
mer and thérmoplastic polymer.3 Preferably, the viscosity ~ ;
of the solution of the copolymer in the monomer should not exceed 10,000 cent.i.poise at a 40% solids :Level. As 5 somewhat of a generalization, it may be said that the .
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molding grade or higher molecular weight chlorinated vinyl homopolymers are less suitable for use in this invention as they do not have the desi.red solubility in the cross-linking monomer. .~
Another criterion by which the haiogenated . ~ :-vinyl copolymers useful in this invention are selected :
is by their ability to participate in chemical thickening.
By way of background, ik should be noted that it is :~
common practice to add chemical thickening agents to resin formulations to cause the molding system to increase in viscosity.following the inclusion of fibrous reinforce~
ments resulting in the formation of prethickened res.in ~
mats (sometimes referred to as "prepreys") which can be ~.
molded and cured to form various art.icles. The use of ~-.
such aurable prethickened resin mats to mold polyester articles has many processing advantages si.nce the mats . . .
can be handled very conveniently, material waste is rela-tively small in amount, improved surface properties can be obtained, and intricately shaped articles can be made 25 relatively quickly and conveniently. -It has been obierved that some polymeric halo- :
genated vinyls do not interfere with chemical thickening, but actually may participate in it if the polymer has an & ..
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acid or epoxy functionality. For this reason, homopolymPrs are not desi~ed since they do not contain the desired func~
tional groups to make this possible. Copolymers having an acid number (based on titration with potassium hydrox- ~ ~
5 ide) in excess of 2, and preferably in excess of 5, are ~ ~-particularly desirable in the practice of his invention.
In selecting a thermoplastic polymer to control polymerization shrinkage, it is important that it be at least partially immiscible or incompatible with the cured polyester. This is true since, to perform its function, the thermoplastic polymer must retain its entity so that it will exist, a~ter curing, essentially as discrete particles in a discontinuo~s phase held in a continuous phase of the cured polyester.
15Preferred types of haIogenated copolymers that i-~
meet the above requirements may include, for example, -comonomers polymerized with vinyl chloride such as various combinations of vinyl acetate, mono- and dialkyl fumarate, methyl methacrylate and its homologs, glycidyl acrylate, maleic acid, maleic anhydride, acrylic acid, chloromaleic acid, itaconic acid, citraconic acid, mesaconic acid, fumaric acid, lower alkyl acrylate esters, and the like.
The Chemical Thickener As mentioned above, chemical thickeners are ~ `
usually included in the resin system since they permit the use of chemically thickened mats'or prepregs from which articles having excellent properties, including surface properties, can be molded in a simple,trouble~

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free manner. Any of the available chemical thickening agents ~hich are effective in thickening unsaturated polyester resin formulations can be used and the thickenecl mats can be form~d by any of the available techniques.
Examples of re~orted chemical thickening agents include oxides and hydroxides of the metals of Group I and II of the Peri~

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odic Table. (For example see U.S. Patent Nos. 2 628 209;
3 390 205; and 3 631 217.) Specific examples of reported -~ -~
chemical thickening agents include: magnesium oxide;
zinc oxide; a mixture of magnesium oxide and aliphatic ;~
monocarboxyl acid (or anhydride thereof); potassium hydroxide; calcium oxide; and calcium hydroxide. U.S.
Patent No. 3 431 320 descrlb~s the u~e o a preferred thick-en~ng agent consisting of a mixtur~ of calc~um oxide and either magnesium ox.id~ or calcium hydroxide. It should be understood that the thickening of the polymerizable poly-ester resin formulation is not effected by the commence- ~
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ment of vinyl copolymerization between the unsaturated poly-ester and the cross-linking agents nor is it effected by ~ ;
the addition of fillers to the formulation which have a tendency to increase its viscosity. The amount of ch~mical thickening agent added to the polym~rizahle formulation should he of cour~e sufficient to effect the desired degree of thickening and this will depend to an extent ~ ?
on the other components comprising the composition. By way of example the thickening ayent may comprise from about 0.25 to about 10 weight per cent and preerably !, from about 0.5 to about 5 weight per cent of the composi-tion based on the total weight of the composition. After adding the chemical thickening a~ent to the compo~ition -10 ' thickened mats or prepregs can be formed according to any of the available techniques. It is noted that the chemical -~
thickening agent will cause the viscosity of the composition - to increase over a period of time. The mat or prepreg should be allowed to increase in ViSCOSlty to the extent that when the mat is molded and cured, there will be sub-stantially uniform flow of the resin and fibrous reinforce~
ment portions of the composition.
After thickening has progressed to some extent, there is a greatly reduced tendency for separate layers of unsaturated polyester and thermopla.stic polymer to form.
It appears that the increased viscosity reduces the tend~ncy toward such gross phase separation. ~s discussed in mora detail above, the halogenated vinyl copolymexs of this invention are desirable not only for their fire-retardant and shrink-counteracting properties, but also for their ability to participate beneficially in this chemical thick~
ening process. Such participation in the thickening process greatly aids in maintainin~ the thermoplastic phase finely 0 and homogeneously dispersed throughout the molding system.
E'illers and Other Materials .
Other materials are generally incorporated into polymerizable unsaturated polyester resin formulations and may~be used in the compositions included within the scope 2S of this invention. Thus, fillers, initiators or catalysts, cross-linking and stabilizing inhibitor~, accelerators or promoters, pigments, mold release additives, fire-retardant ~385~i9 . ~ ~

; synergists, etc., can also be incorporated in the composi~
~ tion. In addition, fibrous re-inforcements, preferably glass fibers, can be added to the formulations or impreg~
nated therewith according to available techniques to ~ ;~
5 increase or upgrade the physical properties, particularly ~ `
the strength, of the articles produced.
While the preferred filler for use in this inven- -tion is hydrated alumina due to its marked effect upon the flame~retardant properties of molded polyester articles, lO examples of other fillers that can be used are calcium carbonate, clays and caJcium silicate. The presence of fillers appears to aid in maintaining the thermoplastic ~, copolymer homogeneously dispersed in thickened formulations - and to inhibit its separation until the product has in - 15 creased sufficiently in viscosity via chemical thickening.
For this reason, it is preferred that the thickened for-mulations contain fillers in amounts rangin~ up to about 70 weight per: cent and preferably in an amount in the range o~ about 20 to about 60 weight per cent based on ;
20 the total ~eight of the composition.
7 Examples of initiators or catalysts that can be :.i .
used are t-butyl perbenzoate, t-butyl hydroperoxide, suc~
cinic acid peroxide and cumene hydroperoxide.
Examples of cross-linking and stabilizing inhi-, ` , `~ 25 bitors that can be used are hydroquinone and t-butyl catechol.
Examples of accelerators or promoters ~hich can be used are cobalt naphthenate, diethyl aniline and dimethyl ., ,; ~ . ~ , ..
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aniline. ~ ;
Examples of: pigments that ca~ be utilized are iron oxides, titanium dioxide and phthalocyanins.
~n exampIe of a flame-retardant synergist is antimonous oxide and may be used in an amount from about : ~ .
0.5 to about 5 parts by weight p0r hundred parts resin.
~ - Glass fiber reinforcements in any of their avail~
i able forms can be used including, for example, mats of chopped or continuous strands of glass, glass fabrics, -chopped glass rovings and chopped glass strands It should be understood that other fibrous reinforcements aan be used also, such as, for example, asbestos and synthetic fibers such as acrylonitrile fibers and linear -l polyester fibers.
The amount of fibrous reinforcements used in the composition can vary over a wide range, for example, from about 5 to about 70 weight per cent based on the total weight of the composition. Preferably, the amoùnt of fibrous reinforcements should be within the range of about 10 to about 40 weight per cent based on the total weight of the composition.
` The polymerizable unsaturated polyester resin formulations included within the scope of this invention .1 can be polymerized and cured into articles according to any of the available techniques. For example, vacuum and pressure bag techniques can be used, or-the articles can he made in a matched~metal mold utilizing premix or wet ; lay-up techniques. In addition, articles can be made hy .,.' .
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the pultrusion technique.
As mentioned above, excellent surface properties ;~
can be obtained by curing and ~olding chemically thickened mats in a matched-metal mold. The pressure and temperature ~ ~ ~
5 of the mold, as well as molding time, will depend on the` ~ ;
particular components comprising the composition and on other factors - for example, the catalyst used and the size and thickness of the charge. For best results, , these variahles should be selected on the basis of exper- `
ience. In general, however, pressures within the ranye ~, of about 50 p~ to about 3,000 psi, temperaturès in the range of about 180 to about 330F, and a molding time ~;~
of about 30 seconds to about 30 minutes can be used.
EXAMPLES
In the following Examples, test specimens were prepared by molding unsaturated polyester resins having the following general composition (percentages are by , weiyht):

~s Resin Composition: 40% unsaturated polyester; 45 20styrene; 15~i thermoplastic polymer ~ :
Molding Composition: 40% resin; 40% inorganic filler; `~`
20~ glass fibers In addition to the foregoing, the following . principal additives were included in the reactive resin 25 system (parts by weight added to 100 parts resin): ~ ~ `
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Catalyst: tertiary butyl perbenzoate, 1 part ~ `~

Synergist: antimonous oxide, 5 ~arts ; Chemical Thickenex: calcium oxide, 0.5 parts; calcium ! hydroxide 0.75 part . ~ i ... :
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~0;38S;~9 Mold Release: zinc stearate, 2 parts Stabilizer (used optionally with some halogenated - copolymers): basic*lead silico sulphate, 5 parts (Epistatic 110 by Eagle-Pich~r Industries) ~` In order to provide data to show the effective-ness of this invention in improving the flame~retardarlt ,~ properties of molded polyester articles, two sets of materials i were selected for use in the resin system: one set being ;. 10 selected from standard materials now in common use and the ~ other set from materials selected in accordance with the - teachings of this invention.
An unsaturated polyester prepared from propylene .
glycol and maleic anhydride was selected as -the standard and '`I , .
a halogenated resin was prepared from ethylene glycol, tetrachlorophtha:Lic anhydride, maleic anhydride, and 1 to 3%
~'~ tetrahydrophthalic anhydride.
; For use as the thermplastic polymeric material, ,j .
`! a polymer of styrene and maleic anhydride was selected as ql 20 the standard and the halogenated polymer used was a ter-; polymer of vinyl chloride, dibutyl fumarate and monobutyl ~ fumarate (FPC 470 by Firestone). The terpolymer on analysis `~, showed 40.3% by weight chlorine, 85 mol % vinyl chloride, :: .
l 12.3 mol % dibutyl fumarate, and 2.8 mol % monobutyl fumar--. ate. The terpolymer has an acid number of 18.1 and, at l 40% solids, forms a clear solution with styrene with a solu-.j! ~
~ tion viscosity of about 4,000 centipoise.
'~J Calcium carbona-te was used as the standard inor-'' ganic filler material and hydrated alumina was used as a ~'', ~ .
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flame-retarding filler. 1~3~5Z9 'I'he results of the testing are tabularized below.
'I`he "LOI" is the limiting oxygen index which i5 a measure ;
of the minimwn oxygen that must be present in the ambient gaseous environment to support combustion once a sample has been ignited. Thus, assuming a normal atmoshphere containing about 20% oxygen, an LOI of less than 0.20 indi- ~
cates a non-self-extinguishing material, and with increas~ ~;
- ing LOI values, the level of flammability diminishes.
~ 10 The "HLT-15" rating is another index of flamma-r', bglity in common use, and it is Hooker Laboratories Test 15. Briefly, a standard specimen is exposed to a standard ~ flame for a predetermined time and, if the specimen ignites, ;,: the time until the fire ex-tinguishes after the flame is `j 15 removed is measured. The test is contlnued over a number ~ of reignitions and time periods and the per~`ormance is .'~ rated against an arbitrary scale of values ranging from O to 100. A zero is the lowest rating and 100 is the ;~`~
~'1 highest rating that can be achieved on this test.
;~s Example Resin Polymer Filler LOI HLT-15 ... ~ .
'~ I Unhalogenated Unhalogenated Calcium carbona-te 0.19 0 II Unhalogenated Halogenated Calcium carbonate 0.27 45 III Unhalogenated Halogenated Hydrated alumina 0.37 80 IV Halogenated Halogenated Hydrated alumina 0.4196 The samples prepared in Examples I-IV all exhibited .-:
,~ low shrinkage, good surface characteristics, and good mechanical ;~
j strength.

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, mine the effect of blending nonhalogenated polyesters with ~:
halogenated polyesters and it was found that blends contain~
ing as mu~h as 50% by weight of a nonhaLogenated polyester can be used ~ithout significant loss of flame-retardant : properties while at the s~ne time obtaining improved sur~ace :- characteristics of the molded article. ~ ;
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PRIVILEGE OR PROPERTY IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A polymerizable molding composition comprised of unsaturated polyester comprising halogenated unsaturated polyester; a vinyl monomer that is copolymerizable with the polyester; a finely divided inorganic filler; and about 5 to about 20 weight percent of a thermoplastic halogenated vinyl co-polymer that is:
soluble in the monomer, at least partially immiscible and incompatible with the polyester, and contains acid or epoxy functional groups.

2. A molding composition according to claim 1 in which the filler is hydrated alumina.

3. A molding composition according to claim 2 in which the hydrated alumina is present in an amount of from about 20% to about 70% by weight of the composition.

4. A molding composition according to claim 1 in which unsaturated non-halogenated polyester is mixed with the halogenated polyester.

5. A molding composition according to claim 4 in which the halo-genated polyester is present in at least 50 weight per cent of the total amount of unsaturated polyester.

6. A molding composition according to claim 1, 2 or 4 further comprising fibrous reinforcing material.

7. A molding composition according to claim 1 or 4 in which the total resin system includes about 25 to about 65 weight per cent of un-saturated polyester, and about 30 to about 60 weight per cent of the vinyl monomer.

8. A molding composition according to claim 1 in which the solubility of the polymer in the monomer is sufficient so that at 40%
solids, the viscosity of the solution is less than 10,000 centipoise.

9. A molding composition according to claim 8 in which the viscosity of the solution is less than 5,000 centipoise.

10. A molding composition according to claim 1 in which the functional groups are acid and the acid number is greater than 2.

11. A molding composition according to claim 10 in which the acid number is greater than 5.

12. A molding composition according to claim 1 in which the copolymer is polymerized from vinyl chloride and other monomers selected from the group consisting of vinyl acetate, mono- and dibutyl fumarate, methyl methacrylate and its homologs, glycidyl acrylate, maleic acid, maleic anhydride, acrylic acid, chloromaleic acid, itaconic acid, citraconic acid, mesaconic acid, fumaric acid, and lower alkyl acrylate esters.

13. A molding composition according to claim 12 in which the polymer is a terpolymer of vinyl chloride, dibutyl fumarate and monobutyl fumarate.

14. A method for preparing flame-retardant polyester articles having smooth surfaces and good mechanical strength by polymerizing a mixture of unsaturated polyester comprising unsaturated halogenated polyester with a copolymerizable vinyl monomer, in the presence of a finely divided inorganic filler comprised of hydrated alumina, fibrous reinforcing material, and about 5 to about 20 weight percent of a thermoplastic polymer to control polymerization shrinkage, wherein the thermoplastic polymer is a halogenated vinyl copolymer that is soluble in the monomer, is at least partially immiscible and incompatible with the polyester, and contains acid or epoxy functional groups.

15. A method according to claim 14 in which the functional groups are acid and the acid number is in excess of 2.

16. A method according to claim 14 in which up to 50% by weight, of unsaturated polyester is non-halogenated polyester.

17. As an article of manufacture, a molded article having a smooth surface and a high strength-to-weight ratio prepared by curing a mixture of unsaturated polyester comprised of unsaturated halogenated poly-ester with a copolymerizable vinyl monomer, in which is included a finely divided inorganic filler comprised of hydrated alumina, a fibrous reinforcement material, and about 5 to about 20 weight percent of a thermo-plastic halogenated vinyl copolymer soluble in the monomer, at least partially immiscible and incompatible with the polyester and containing acid or epoxy functional groups, said article having a limiting oxygen index in excess of 0.25 and a Hooker Laboratory Test 15 rating in excess of 40.

18. An article according to claim 17 in which the limiting oxygen index is in excess of 0.4 and the Hooker Laboratory Test 15 rating is in excess of 90.

19. An article according to claim 17 wherein the unsaturated polyester contains up to 50 weight per cent of non-halogenated polyester.

20. A molding composition according to claim 1 in which there is included a chemical thickening agent.

21. A molding composition according to claim 20 in which the chemical thickening agent is included in an amount between about 0.25 to about 10 wt. % based on the total weight of the molding composition.

22. A molding composition according to claim 21 in which the chemical thickening agent is included in an amount between about 0.5 to about 5 wt. % based on the total weight of the molding composition.

23. A molding composition according to claim 20 in which the chemical thickening agent is a mixture of calcium oxide and magnesium oxide or calcium hydroxide.

24. A method according to claim 14 or 16 in which the mixture contains a chemical thickening agent in an amount from about 0.25 to 10 wt. % of the total weight of the mixture.

25. An article according to claim 17 in which the mixture includes a chemical thickening agent.