Polyol(allyl carbonate) compositions and polymerizates thereof that have an enhanced resistance to yellowing on exposure to external heating are described. In particular, a polyol(allyl carbonate) composition comprising (a) from about 55 to about 90 weight percent of a polyol(allyl carbonate), e.g., diethylene glycol bis(allyl carbonate), from about 10 to about 40 weight percent of aliphatic polyurethan having terminal ethylenic unsaturation, e.g., an aliphatic polyesterurethan diacrylate, and from about 0 to about 5 weight percent of a difunctional monomer selected from the group consisting of allyl methacrylate and allyl acrylate and (b) from about 0.01 to about 0.5 weight percent of a dialkyl pyrocarbonate, e.g., diethyl pyrocarbonate, based on the weight of the polymerizable reactants is described. Polymerizates of such polyol(allyl carbonate) compositions have an enhanced resistance to yellowing when heated at elevated temperatures, e.g., 130.degree. C.

BACKGROUND OF THE INVENTION 
The present invention relates to certain polymerizable polyol(allyl 
carbonate) compositions and to polymerizates prepared from such 
compositions. Such polymerizates, e.g., articles such as optical lenses, 
are characterized by an improved resistance to yellowing when heated at 
elevated temperatures, e.g., at temperatures in the range of from about 
80.degree. C. to about 180.degree. C. 
Polymerizates prepared from aliphatic polyol(allyl carbonate) monomers, 
e.g., diethylene glycol bis(allyl carbonate) are characterized by 
hardness, impact resistance and optical clarity. For these reasons, 
optical articles, e.g., lenses, have been prepared from such 
polymerizates. Moreover, such lenses offer a weight advantage, vis a vis, 
glass lenses. It has also been proposed to prepare photochromic articles 
from such polymerizates. Frequently, photochromic articles are prepared by 
imbibing a photochromic substance within the preformed polymerizate, e.g., 
by immersion of the polymerizate in a hot solution containing the 
photochromic substance or by other thermal transfer mechanisms described 
in the art. It is also common to tint or dye such polymerizates (with or 
without the added photochromic substance) by immersion of the polymerizate 
in a heated aqueous dispersion of the selected dye. 
When subjected to heat aging or heat treatments, such as those involved in 
tinting of the polymerizate or imbibition of a photochromic substance by 
thermal transfer, polymerizates prepared from polyol (allyl carbonate) 
compositions containing an aliphatic polyurethane, tend to take on a 
slight yellow cast. Such yellowing may adversely affect the commercial 
utility of such polymerizates, particularly in optical applications, and 
may, if significant, adversely affect the optical transparency and clarity 
of articles prepared from such polymerizates. There is, therefore, a 
continuing need for materials that are compatible with the polymerizable 
polyol(allyl carbonate) monomer composition and polymerizates prepared 
therefrom, which will prevent or mitigate yellowing of the polymerizate 
caused by heating at elevated temperatures, e.g. temperatures that may be 
used during post treatment of a pre-formed polymerizate. Such post 
treatment temperatures may range from about 80.degree. C. to about 
180.degree. C., customarily from about 100.degree. C. to about 150.degree. 
C., e.g., 130.degree. C. 
It has now been discovered that the addition of small amounts of a diakyl 
pyrocarbonate to a polymerizable polyol(allyl carbonate) monomer 
composition containing an aliphatic polyurethan component provides a 
polymerizate that exhibits enhanced resistance to yellowing caused by post 
formation heating. 
DETAILED DESCRIPTION OF THE INVENTION 
Dialkyl pyrocarbonates that may be used to enhance resistance to yellowing 
of polymerizates prepared from polyol(allyl carbonate) monomer 
compositions containing an aliphatic polyurethan component may be 
represented by the graphic formula: 
EQU R--O--C(O)--O--C(O)--O--R, 
wherein R is selected from the group consisting of C.sub.1 -C.sub.12 alkyl 
and C.sub.6 -C.sub.10 cycloalkyl. More particularly, R is selected from 
the group consisting of C.sub.2 -C.sub.4 alkyl, such as ethyl, propyl and 
tertiary butyl. As used in the description and claims, the term "alkyl" 
when referring to dialkyl pyrocarbonates is intended to mean and include 
both linear and branched chain alkyls as well as cycloalkyl groups, e.g., 
cyclohexyl and tertiary butyl cyclohexyl. 
Suitable examples of dialkyl pyrocarbonates that may be used with 
polyol(allyl carbonate) compositions include: dimethyl pyrocarbonate, 
diethyl pyrocarbonate, diisopropyl pyrocarbonate, di-n-propyl 
pyrocarbonate, di-n-butyl pyrocarbonate, di-isobutyl pyrocarbonate, 
di-secondary butyl pyrocarbonate, di-tertiary butyl pyrocarbonate, 
di-pentyl pyrocarbonate, di-hexyl pyrocarbonate, di-heptyl pyrocarbonate, 
di-2-ethylhexyl pyrocarbonate, di-nonyl pyrocarbonate, di-decyl 
pyrocarbonate, di-dodecyl pyrocarbonate, di-cyclohexyl pyrocarbonate and 
di-4-tertiary butyl cyclohexyl pyrocarbonate. Economically preferred are 
diethyl pyrocarbonate, diisopropyl pyrocarbonate and di-tertiary butyl 
pyrocarbonate. 
The dialkyl pyrocarbonates may be prepared by reacting alkali metal alkyl 
carbonate, e.g., sodium ethyl carbonate, with alkyl halocarbonate, e.g., 
ethyl chlorocarbonate (ethyl chloroformate). The alkyl groups of the alkyl 
carbonate and halocarbonate are chosen to correspond to the alkyl group 
desired for the pyrocarbonate. For example, sodium ethoxide, which can be 
prepared by dissolving sodium metal in toluene solution of ethyl alcohol, 
is carbonated with carbon dioxide to prepare sodium ethyl carbonate. 
Thereafter, the sodium ethyl carbonate is reacted with ethyl chloroformate 
to form diethyl pyrocarbonate and sodium chloride. The chloride salt is 
filtered and the pyrocarbonate recovered by distillation. 
Dialkyl pyrocarbonates may also be prepared by reacting alkyl 
halocarbonate, e.g., ethyl chloroformate, with sodium hydroxide in the 
presence of a catalyst of a tertiary amine or quaternization product 
thereof having at least one omega-hydroxyalkyl, omega-hydroxyalkyl ether, 
or omega-hydroxyalkyl polyether group connected to the nitrogen atom. See, 
for example, Example 6 of U.S. Pat. No. 3,326,958. 
In a preferred embodiment, the dialkyl pyrocarbonate incorporated into the 
polymerizable polyol(allyl carbonate) composition is a colorless material 
that is soluble in the polyol(allyl carbonate) monomer composition. More 
preferably, the dialkyl pyrocarbonate is a liquid that can be readily 
poured and admixed with the polymerizable components of the polyol(allyl 
carbonate) composition. 
The amount of dialkyl pyrocarbonate incorporated into the polymerizable 
polyol(allyl carbonate) composition may vary. Only that amount which is 
sufficient to enhance the resistance to yellowing from externally applied 
heat of polymerizates prepared from such compositions is required. Such 
amount may be referred to as a heat-stabilizing amount and typically will 
range from about 0.01 to about 0.5 weight percent, based on the weight of 
the polymerizable components of the polymerizable polyol(allyl carbonate) 
composition. More particularly, the amount of dialkyl pyrocarbonate used 
may range from about 0.05 to about 0.15, e.g., 0.10, weight percent. The 
aforesaid amount of dialkyl pyrocarbonate is incorporated into the 
polymerizable liquid polyol(allyl carbonate) composition by admixing the 
selected amount with mild agitation until the pyrocarbonate is dissolved 
in the polymerizable composition. 
Polymerizable polyol(allyl carbonate) compositions to which are added the 
aforedescribed dialkyl pyrocarbonate include liquid blends of 
copolymerizable monomeric materials; e.g., polyol(allyl carbonate) 
monomer, aliphatic polyurethan having ethylenic unsaturation at its 
terminal ends, and optionally a difunctional monomer selected from the 
group consisting of allyl methacrylate and allyl acrylate. More 
particularly, the polymerizable polyol(allyl carbonate) monomer represents 
from about 55 to about 90 weight percent, preferably from about 60 to 
about 80, e.g., about 70, weight percent of the copolymerizable 
composition. 
Polyol(allyl carbonate) monomers that may be used in the aforedescribed 
polymerizable composition are allyl carbonates of linear or branched 
aliphatic or aromatic liquid polyols, e.g., aliphatic glycol bis(allyl 
carbonate) compounds, or alkylidene bisphenol bis(allyl carbonate) 
compounds. These momomers may be described as unsaturated polycarbonates 
of polyols, e.g., glycols. The monomers may be prepared by procedures well 
known in the art, e.g., as described in U.S. Pat. Nos. 2,370,567 and 
2,403,113. 
Polyol(allyl carbonate) monomers may be represented by the graphic formula: 
EQU R'--[--O--C(O)--O--R.sub.a ].sub.m I 
wherein R.sub.a is the radical derived from an unsaturated alcohol and is 
commonly an allyl or substituted allyl group, R' is the radical derived 
from the polyol and m is a whole number from 2-5, preferably 2, that 
depends on the number of hydroxy groups in the polyol. The allyl group may 
be substituted at the 2-position with a halogen, most notably chlorine or 
bromine, or an alkyl group containing from 1 to 4 carbon atoms. Generally 
the alkyl substituent is a methyl or ethyl group. The allyl group may be 
represented by the graphic formula: 
EQU H.sub.2 C.dbd.C(R.sub.o)--CH.sub.2 -- II 
wherein R.sub.o is hydrogen, halogen or a C.sub.1 -C.sub.4 alkyl group. 
Most commonly, R.sub.a is the allyl group, H.sub.2 C.dbd.CH--CH.sub.2 --. 
R' is a polyvalent radical derived from the polyol which can be an 
aliphatic or aromatic polyol that contains 2, 3, 4 or 5 hydroxy groups. 
Typically, the polyol contains 2 hydroxy group, i.e., a glycol or 
bisphenol. The aliphatic polyol may be linear or branched and contain from 
2 to 10 carbon atoms. Commonly, the aliphatic polyol is an alkylene glycol 
having from 2 to 4 carbons atoms or poly(C.sub.2 -C.sub.4) alkylene 
glycol, e.g., ethylene glycol, propylene glycol, trimethylene glycol, 
tetramethylene glycol, or diethylene glycol, triethylene glycol, etc. 
Specific examples of polyol(allyl carbonate) monomers include ethylene 
glycol bis(2-chloroallyl carbonate), ethylene glycol bis(allyl carbonate), 
diethylene glycol bis(2-methallyl carbonate), diethylene glycol bis(allyl 
carbonate), triethylene glycol bis(allyl carbonate), propylene glycol 
bis(2-ethylallyl carbonate), 1,3-propanediol bis(allyl carbonate), 
1,3-butanediol bis(allyl carbonate), 1,4-butanediol bis(2-bromoallyl 
carbonate), dipropylene glycol bis(allyl carbonate), trimethylene glycol 
bis(2-ethylallyl carbonate), pentamethylene glycol bis(allyl carbonate), 
and isopropylidene bisphenol bis(allyl carbonate). Diethylene glycol 
bis(allyl carbonate) is the preferred polyol(allyl carbonate) monomer. 
A detailed description of polyol(allyl carbonate) monomers that may be used 
to form the polyol(allyl carbonate) composition of the present invention 
are described in U.S. Pat. No. 4,637,698 at column 3, line 33 through 
column 5, line 61. That disclosure is hereby incorporated by reference and 
is summarized above. As used in the present description and claims, the 
term polyol(allyl carbonate) monomer or like names, e.g., diethylene 
glycol bis(allyl carbonate), are intended to means and include the named 
monomer or prepolymers thereof and any related monomers species contained 
therein. 
The polyol(allyl carbonate) composition of the present invention may 
contain from about 10 to about 40 weight percent of an aliphatic 
polyurethan having terminal ethylenic unsaturation, e.g., an aliphatic 
polyurethan diacrylate or triacrylate. In a preferred embodiment of the 
present invention, the composition contains from about 20 to about 30 
weight percent of the aliphatic polyurethan, which may be represented by 
the expression: 
EQU D--R"--B--A--B--R"--D III 
wherein D represents the terminal functional group containing ethylenic 
unsaturation, R" represents a bivalent alkylene group containing from 1 to 
about 10 carbon atoms, B represents an aliphatic biscarbamate moiety 
originating from the corresponding aliphatic diisocyanate, and A 
represents the residue of a saturated aliphatic polyol, e.g., a diol such 
as a C.sub.2 -C.sub.6 alkane diol, a polyether diol, a polycarbonate, diol 
or a polyester diol. Preferably, A is a polyester diol. The polyurethan 
should form a homogeneous mixture in and be copolymerizable with the 
polyol(allyl carbonate), e.g., diethylene glycol bis(allyl carbonate), 
with which it is blended. 
The terminal functional group containing ethylenic unsaturation (D) is 
typically selected from members of the group acrylate, methacrylate, allyl 
carbamate and allyl carbonate. The acrylate and methacrylate functional 
groups may be represented by the formula, CH.sub.2 
.dbd.C(R.sub.1)--C(O)O--, wherein R.sub.1 is hydrogen or methyl. The allyl 
carbamates and carbonates may be represented by the formulae, CH.sub.2 
.dbd.CH--CH.sub.2 --NH--C(O)O--, and CH.sub.2 .dbd.CH--CH.sub.2 
--O--C(O)O--, respectively. 
The group R" in formula III represents a bivalent C.sub.1 -C.sub.10 
alkylene, including branched and straight chain alkylenes. Most commonly, 
R" is a bivalent C.sub.2 -C.sub.4 alkylene, e.g., ethylene (--CH.sub.2 
CH.sub.2 --). 
Diisocyanates that may be used to prepare the aliphatic polyurethan 
component of the polyol(allyl carbonate) composition are aliphatic 
diisocyanates and cycloaliphatic diisocyanates. For convenience and 
brevity, such isocyanates will be referred to collectively as aliphatic 
diisocyanates. Such materials are substantially free of aromatic moieties. 
By substantially free of aromatic moieties is meant that the aliphatic 
diisocyanate (and thus the aliphatic polyurethan component) contains 1 
percent or less of aromatic diisocyanate groups. Examples of suitable 
diisocyanates include 1,6-hexamethylene diisocyanate, 1,4-tetramethylene 
diisocyanate and 1,10-decamethylene diisocyanate, 
4,4'-methylene-bis(cyclohexyl isocyanate), 4,4'-methylene-bis(3-methyl 
cyclohexyl isocyanate), hydrogenated toluene diisocyanate (including 
hydrogenated products of: (a) the 2,4-isomer, (b) the 2,6-isomer, (c) the 
80/20-2,4/2,6-isomer mixture and (d) the 65/35-2,4/2,6-isomer mixture), 
4,4'-isopropylidene-bis(cyclohexyl isocyanate), 1,4-cyclohexane 
diisocyanate, 4,4'-dicyclohexyl diisocyanate, 2,4'-dicyclohexyl 
diisocyanate and isophorone diisocyanate. The group B in formula III may 
originate from such aliphatic diisocyanates. 
In formula III, A represents the residue of a saturated aliphatic diol, 
such as alkane diols containing from 2 to 6, e.g., 2 to 4, carbon atoms, 
polyether diols, polycarbonate diols and polyester diols. 
Polyester diols may be prepared by techniques well-known in the art, e.g., 
using saturated dicarboxylic acids or anhydrides thereof (or combination 
of acids and anhydrides) and polyhydric alcohols, or by ring opening of 
caprolactones, e.g., epsilon caprolactone. Such polyester diols and their 
manner of preparation are well known and are fully described in the 
published literature. Many are commercially available in various molecular 
weights. Aliphatic dicarboxylic acids suitable for preparing polyesters 
are those containing from about 4 to about 14, preferably from about 6 to 
about 10, carbon atoms inclusive. Examples of such dicarboxylic acids 
include: succinic acid, glutaric acid, adipic acid, pimelic acid, suberic 
acid, azelaic acid and sebacic acid. Corresponding anhydrides can also be 
used. Typically, adipic and azelaic acids are used. 
The polyhydric alcohols used in the preparation of polyester diols are 
typically aliphatic alcohols containing at least 2 hydroxy groups, e.g., 
straight chain glycols containing from 2 to 15, preferably from 4 to 8, 
carbon atoms inclusive. More preferably, the aliphatic alcohols contain 
only 2 hydroxy groups. The glycols contain hydroxyl groups preferably in 
the terminal positions. Examples of such polyhydric alcohols include 
ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene 
glycol, 1,3-propane diol, 1,3-butane diol, 1,4-butane diol, 1,5-pentane 
diol, 2,2-dimethylpropane diol, 1,5-hexane diol, 1,7-heptane diol, 
1,8-octane diol, 1,10-decane diol and mixtures of such polyhydric 
alcohols. 
In preparing the polyester diol, the dicarboxylic acid (or anhydride 
thereof) is reacted with the polyhydric alcohol usually in the presence of 
a small amount of esterification catalyst, such as a conventional organo 
tin catalyst. The amount of acid and alcohol used will vary and depend on 
the molecular weight polyester desired. Hydroxy terminated polyesters are 
obtained by utilizing an excess of the alcohol, thereby to obtain linear 
chains containing a preponderance of terminal hydroxyl groups. Examples of 
polyesters include: poly(1,4-butylene adipate), poly(1,4-butylene 
succinate), poly(1,4-butylene glutarate), poly(1,4-butylene pimelate), 
poly(1,4-butylene suberate), poly(1,4-butylene azelate), poly(1,4-butylene 
sebacate) and poly(epsilon caprolactone). Polyester diols contemplated for 
use may have a weight average molecular weight from about 500 to about 
3000, e.g., from about 500 to 2500, more particularly from about 900 to 
about 1300. 
Polycarbonate diols that may be used to prepare the aliphatic polyurethan 
component of the polyol (allyl carbonate) composition may have weight 
average molecular weights ranging from about 500 to about 5000, e.g., 550 
to 3300, more particularly from 750 to 1500, as determined by hydroxyl end 
group analysis. Aliphatic polycarbonate diols are described in U.S. Pat. 
Nos. 3,248,414, 3,248,415, 3,248,416, 3,186,961, 3,215,668, 3,764,457 and 
4,160,853. Such hydroxy-terminated polycarbonates may be prepared from (1) 
carbon dioxide and 1,2-epoxides, (2) cyclic carbonates, such as ethylene 
carbonate, or (3) from cyclic carbonates and 1,2-epoxides by methods known 
in the art. Polycarbonate diols may also be prepared by reacting aliphatic 
diols with bischloroformates of aliphatic diols in the presence of inert 
solvents and acid acceptors, e.g., tertiary amines. In addition, 
polycarbonate diols may be prepared from glycols, such as ethylene glycol, 
propylene glycol and diethylene glycol, and dialkyl carbonates, such as 
diethyl carbonate and dimethyl carbonate, by a transesterification 
reaction. 
In particular, U.S. Pat. No. 4,160,853 describes the synthesis of aliphatic 
polycarbonate diols by the reaction of an aliphatic diol and a dialkyl 
carbonate in the presence of a titanium catalyst. The reaction sequence 
may be depicted by the following equation: 
##STR1## 
wherein n is a number from 4 to 46, R.sub.2 is an aliphatic group (linear 
or cycloaliphatic) containing from 4 to about 10 carbon atoms, and R.sub.3 
is a lower alkyl group containing 1 to 4 carbon atoms. Preferred aliphatic 
diols include: 1,4-butane diol, and 1,6-hexane diol. Diethylcarbonate is a 
preferred dialkyl carbonate. The preferred catalysts are tetra-alkyl 
esters of titanium, particularly, tetrabutyl titanate. The disclosures of 
the aforedescribed patents relating to the preparation of aliphatic 
polycarbonate diols are hereby incorporated by reference. 
Polyether diols, e.g., poly(oxyethylene)glycols, 
poly(oxy-1,2-propylene)glycols, and poly(oxy-1,4-butylene)glycol, that may 
be used to prepare the aliphatic polyurethan component of the polyol(allyl 
carbonate) composition may also vary in molecular weight. 
Poly(oxyethylene)glycols may range in molecular weight from about 
200-4000, more particularly, 750-3300, e.g., 1000-2800. Liquid 
poly(oxyethylene)glycols having molecular weights of below about 750, as 
determined by hydroxyl end group analysis, are particularly contemplated. 
Poly(oxyethylene)glycols may be prepared by reaction of ethylene oxide 
with water or ethylene glycol in the presence of a catalytic amount of a 
Lewis acid at 50.degree.-70.degree. C. or Lewis base at 
120.degree.-200.degree. C. 
Poly(oxypropylene)glycols may be prepared in a manner similar to 
poly(oxyethylene)glycols. Molecular weights of the 
poly(oxypropylene)-glycols that may be used to prepare the polyol(allyl 
carbonate) composition may vary from about 400 to about 4000, e.g., 400 to 
about 2000, or 400 to about 1200, as determined by hydroxyl end group 
analysis. Liquid poly(oxypropylene)glycols are particularly contemplated. 
In addition, block and random hydroxyl terminated copolymers of ethylene 
oxide and propylene oxide may be used. Further, polyether diols prepared 
from 1,2-butylene oxide, i.e., poly(oxy-1,2-butylene)glycol, and 
tetrahydrofuran are also contemplated. Alkane diols contemplated for use 
in preparing the polymerizable polyol (allyl carbonate) composition are 
alkane diols containing from 2 to 6 carbon atoms, e.g., ethylene glycol, 
propylene glycol, 1,4-butane diol, 1,5-pentane diol and 1,6-hexane diol. 
Preferably, the alkane diols contain terminal hydroxy groups. 
The aliphatic polyurethan may be prepared by methods well documented in the 
literature and known to those skilled in the art, e.g., by reacting an 
excess of the aliphatic diisocyanate with the saturated aliphatic diol, 
e.g., polyester diol, thereby to form the corresponding urethane having 
terminal isocyanate functionality. Thereafter, the resulting urethane 
diisocyanate may be reacted with a material having acrylic (or allylic) 
and hydroxyl functionality, e.g., a monoacrylate of a diol, e.g., 
2-hydroxyethyl acrylate, to prepare the aliphatic urethan having terminal 
functional groups containing ethylenic unsaturation. As used herein, the 
phrase "containing terminal ethylenic unsaturation" with respect to the 
aliphatic polyurethan means that each terminal end of the urethane 
contains a functional group containing ethylenic unsaturation, e.g., an 
acrylate functional group. Diacrylate-terminated polyester-based 
polyurethans are commercially available in various molecular weights. Of 
particular utility is the commercial polyesterurethan, Uvithane.RTM. 893 
urethane diacrylate. 
Polyesterurethans containing terminal acrylate functionality may be further 
depicted by the following graphic formula: 
##STR2## 
wherein R.sub.1 and R" have the same meaning as described hereinabove, A 
is the residue of the polyester diol, and R'" is the hydrocarbon portion 
of the aliphatic diisocyanate. Polyesterurethans having terminal allyl 
carbamate or allyl carbonate groups may be depicted similarly by 
substituting the allyl carbamate or allyl carbonate group for the acrylate 
functional group in graphic formula V, i.e., for the CH.sub.2 
.dbd.C(R.sub.1)--C(O)O-- group. 
In a further embodiment, a difunctional monomer that is capable of 
enhancing cross-linking of the polyol(allyl carbonate) and aliphatic 
polyurethan components of the polymerizable composition is incorporated in 
such composition. The addition of the difunctional monomer enhances 
development of a three-dimensional cross-linked structure in the 
polymerizate which increases the polymerizate's hardness. Typically, the 
difunctional monomer represents from about 0 to about 5 weight percent, 
more typically from about 1 to about 4, e.g., about 1.5 to 2, weight 
percent, based on the total weight of the polymerizable polyol(allyl 
carbonate) composition. Customarily, the difunctional monomer is allyl 
methacrylate or allyl acrylate. 
Polymerization of the polyol(allyl carbonate) composition may be 
accomplished by adding to the composition an initiating amount of material 
capable of generating free radicals, such as organic peroxy compounds and 
diazo compounds. Methods for polymerizing polyol(allyl carbonate) 
compositions are well known to the skilled artisan and any of those well 
known techniques may be used to polymerize the aforedescribed 
polymerizable composition. Suitable examples of organic peroxy compounds 
include: peroxymonocarbonate esters, such as tertiarybutylperoxy isopropyl 
carbonate; peroxydicarbonate esters, such as di(2-ethylhexyl) 
peroxydicarbonate, di(secondary butyl) peroxy dicarbonate and diisopropyl 
peroxydicarbonate; diacylperoxides, such as 2,4-dichlorobenzoyl peroxide, 
isobutyryl peroxide, decanoyl peroxide, lauroyl peroxide, propionyl 
peroxide, acetyl peroxide, benzoyl peroxide, p-chlorobenzoyl peroxide; 
peroxyesters such as t-butylperoxy pivalate, t-butylperoxy octylate, and 
t-butylperoxyisobutyrate; methylethylketone peroxide, acetylcyclohexane 
sulfonyl peroxide, and azobisisobutyronitrile. Preferred initiators are 
those that do not discolor the resulting resin polymerizate, such as 
diisopropyl peroxydicarbonate. 
The amount of initiator used to initiate and polymerize the polyol(allyl 
carbonate) composition may vary and will depend on the particular 
initiation used. Only that amount that is required to initiate and sustain 
the polymerization reaction is required, i.e., an initiating amount. With 
respect to the preferred peroxy compound, diisopropyl peroxydicarbonate, 
typically between about 2 and about 3 parts of that initiator per 100 
parts of the polymerizable composition (phm) may be used. More usually, 
between about 2.25 and about 2.60 parts of that initiator per 100 parts of 
polymerizable composition is used to prepare the polymerizate of the 
present invention. The amount of initiator and the consequent cure cycle 
should be adequate to produce a polymerizate having a 15 second Barcol 
hardness of at least 10, preferably, at least 12, e.g., 10 to 35. 
Typically, the cure cycle involves heating the polymerizable composition 
in the presence of the initiator from room temperature to about 
105.degree. C. over a period of about 17 hours. The surface of the cured 
matrix should not be so hard that imbibition of photochromic substances 
into the matrix by immersion or thermal transfer is inhibited or prevented 
if that method of incorporating the photochromic substance is used. In one 
embodiment, the matrix is slightly undercured to enhance permeation of the 
photochromic substance into the matrix. 
Polymerizates obtained by polymerization of polyol(allyl carbonate) 
compositions will most preferably be transparent or optically clear so 
that articles prepared therefrom may be used for optical lenses such as 
plano and ophthalmic lenses, goggles, face shields, windows, automotive 
transparencies, e.g., windshields, T-roofs, sidelights and backlights and 
for aircraft transparencies, etc.

The present invention is more particularly described in the following 
examples, which are intended as illustrative only, since numerous 
modifications and variations therein will be apparent to those skilled in 
the art. 
EXAMPLE 1 
A polyol(allyl carbonate) polymerizable composition of 3000.0 grams 
composed of 68.5 weight percent diethylene glycol bis(allyl carbonate), 30 
weight percent of Uvithane.RTM. 893 urethane diacrylate and 1.5 weight 
percent allyl methacrylate was mixed with 2.45 phm (parts per hundred 
parts of monomer) of diisopropyl peroxy-dicarbonate. To this mixture was 
also added 250 ppm of 4-hydroxy anisole--a polymerization inhibitor and 
200 ppm Zelec UN--a mold release agent. The polymerizable mixture was 
stirred at room temperature for 2 hours. A portion of this mixture was 
used to prepare ten 6-base plano lenses by filling glass molds separated 
by an 11.8 millimeter thick copoly(ethylene-vinyl acetate) gasket. The 
polymerizable composition was cured anaerobically by heating the filled 
mold slowly from about 44.degree. C. to 105.degree. C. over 17 hours. Two 
resulting representative plano lenses were subsequently treated in a air 
circulating oven for 3 hours at 130.degree. C. and the luminous 
transmission and color coordinates measured on a color spectrometer 
(Spectrogard II). The values obtained for these two lenses are tabulated 
in Table I as samples Control-A and Control-B. The magnitude of the 
positive b* is proportional to yellowness. The higher the measured b* 
value, the more "yellow" is the material tested. 
EXAMPLE 2 
The procedure of Example 1 was used to prepare a polymerizable mixture of 
1144.25 grams of the same polymerizable components in the same weight 
ratio as that described in Example 1. In addition, 0.5 weight percent of 
diethyl pyrocarbonate was added to the polymerizable mixture. A portion of 
this mixture was used to prepared ten 6-base plano lenses in the manner 
described in Example 1. Two representative resulting lenses were 
subsequently treated in a air circulating oven for 3 hours at 130.degree. 
C. and the luminous transmission and color coordinates measured as 
described in Example 1. The values obtained for these two lenses are 
tabulated in Table I as Samples 1-A and 1-B. 
EXAMPLE 3 
A portion of the polymerizable mixture (500 grams) prepared in Example 2 
and containing 0.5 weight percent diethyl pyrocarbonate was diluted with 
500 grams of additional polymerizable mixture prepared as in Example 1. 
The resulting mixture contained 0.25 weight percent diethyl pyrocarbonate 
and was used to prepare ten 6-base plano lenses in the manner described in 
Example 1. Two of the resulting representative lenses were heat treated 
and tested in the manner described in Example 1. Values for these two 
lenses are tabulated in Table I as Samples 2-A and 2-B. 
EXAMPLE 4 
A portion of the solution (350 grams) prepared in Example 3 and containing 
0.25 weight percent diethyl pyrocarbonate was further diluted with 350 
grams of additional polymerizable mixture prepared as in Example 1, 
thereby to prepare a polymerizable composition containing 0.125 weight 
percent diethyl pyrocarbonate. This polymerizable mixture was used to 
prepare ten 6-base plano lenses in the manner described in Example 1. Two 
resulting representative lenses were heat treated and tested in the manner 
described in Example 1. Values obtained for these 2 lenses as tabulated in 
Table I as Samples 3-A and 3-B. 
TABLE I 
______________________________________ 
Diethyl Luminous Transmission (Y, %) and 
Pyrocarbon- Color Coordinates (a*, b*) 
ate (Conc. Initial Final.sup.1 
Sample wt. %) Y (%) a* b* Y (%) a* b* 
______________________________________ 
Control-A 
-- 91.5 -0.7 2.6 89.7 -1.1 6.0 
B -- 91.3 -0.7 2.6 89.8 -1.1 5.9 
1-A (0.50) 91.6 -0.8 2.8 90.9 -1.0 4.2 
B (0.50) 91.3 -0.8 2.7 90.7 -1.0 4.3 
2-A (0.25) 91.3 -0.8 2.8 90.6 -1.0 4.3 
B (0.25) 91.1 -0.7 2.7 90.8 -0.9 4.2 
3-A (0.125) 91.2 -0.7 2.7 90.7 -0.9 4.2 
B (0.125) 91.4 -0.7 2.7 90.6 -1.0 4.3 
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.sup.1 After heating for three hours at 130.degree. C. 
The data of Table I shows that the addition of a small amount, e.g., 0.125 
weight percent, of diethyl pyrocarbonate resulted in a lens that is 
significantly less yellow after heat treatment than the control lens. 
Although the present invention has been described with reference to the 
specific details of particular embodiments thereof, it is not intended 
that such details be regarded as limitations upon the scope of the 
invention except insofar as and to the extent that they are included in 
the accompanying claims.