NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

311.05-11-3110561 June 30, 1970

NBS REPORT

10 in

Progress Report

on TERTIARY AROMATIC AMINE ACCELERATORS

WITH MOLECULAR WEIGHTS ABOVE 400

by R. L. Bowen* and H. Argentar"^

* Associate Director, American Dental Association Research Program

in the Dental Research Section, National Bureau of Standards,

Washington, D. C. 20234 + Research Associate, American Dental Association Research Program

in the Dental Research Section, National Bureau of Standards,

Washington, D. C. 20234

This investigation was supported in part by Research Grant DE02494-03

to the American Dental Association from the National Institute of

Dental Research and is part of the dental research program conducted

by the National Bureau of Standards, in cooperation with the Council

on Dental Research of the American Dental Association; the Dental Research Division of the U. S. Army Medical Research and Development

Command; the Dental Sciences Division of the School of Aerospace

Medicine, USAF; the National Institute of Dental Research; and the

Veterans Administration.

IMPORTANT NOTICE NATIONAL BUREAU OF ST

for use within the Government, and review. For this reason, th whole or in part, is not autho Bureau of Standards, Washingti

the Report has been specitically

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

!ss accounting documents intended

subjected to additional evaluation

I listing of this Report, either in e Office of the Director, National

by the Government agency for which

;opies for its own use.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

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TERTIARY AROMATIC AMINE ACCELERATORS

WITH MOLECULAR WEIGHTS ABOVE 400

Synopsis

With the proper ring substituents, tertiary aromatic amines

with large substituents on the nitrogen atom can be effective

accelerators in free radical polymerization. Resistance to

discoloration appears to be primarily a function of the substituents on the aromatic ring of the amine, while the rate

of polymerization is dependent on both the alkyl substituents

on the ring and the groups attached to the nitrogen atom.

( i
TERTIARY AROMATIC AMINE ACCELERATORS

WITH MOLECULAR WEIGHTS ABOVE 400

Most of the presently -available composite restorative

materials oontaiB an amine-peroxide initiator system to

polymerize their methacrylate monomers. These amineperoxide systems have certain disadvantages including

a tendency to discolor the resin or composite filling

material,^ and in some cases^ the working and hardening

times^ of the materials may not be optimum for the dentists'

requirements

The liquids used in these composite materials contain

very large proportions of cross linking dimtcthacry late

monomers^’ ^ and are relatively viscous. These high molecular

weight viscous dimethacrylates polymerize much more rapidly

than do less-viscous non-crosslinking monomers such as

methyl methacrylate. This is due to the Trommsdorf f

^ ^ autoacceleration, or gel effect,® attributed to lessened translational mobility (and concurrent termination reactions)

of growing polymer radicals, with increasing viscosity.

Therefore, there is less need for rapid-acting initiators.
3

In other words, a slower release of free radicals may well

give a longer working time and still give the hardening time

that is desired.

In order to get adequate working time with these quickhardening resin systems, one alternative has been to decrease

the concentration of fast-acting amine accelerators. This

low initial concentration of amine may run the risk of what

has been called "dead end" polymerization, ^ that is, the

depletion of amine accelerator (and initiator free radicals)

before the conversion has reached its maximum extent; if so,

the ultimate chemical and physical properties would suffer.

Another alternative has been to increase the amount of

inhibitor above the minimal amount required for storage

stability. This would increase the working time at the cost

of increased discoloration, in the case of some inhibitors,®

and possibly at the cost of increased polymerization inhibition

at surfaces that are exposed to air (including bubbles of air

that have been entrapped within , the material itself during

mixing and placement), if it is assumed that the peroxy
radical R-0-0* (formed by addition of O2 to the growing

polymer radical) is capable of initiating polymerization

of the methacrylate monomer,® and that the peroxy radical

is inactivated by interaction with "excess" inhibitor.

The foregoing suggests that steric hindrance of an

amine accelerator may be useful in slowing down the release

of free radicals, and thus the rate of polymerization, at

equal or higher concentrations of amine (peroxide and

stabilizers being maintained at optimum concentrations),

when compared to the amine accelerators currently being used.

If higher molar concentrations . of such slow-acting,

but efficient amine accelerators were used, it would give

a more prolonged release of free radicals, but would put

more demand on the inherent color stability of the amine

and other ingredients in the formulation.®

There has been convincing evidence of various degrees

of pulpal inflammatory response to the use of resin and

composite restorative mater ials . ^ ° ^ ^ It has not yet been
5

shown which ingredients in these formulations are primarily

responsible for the inflammation. Since the lower-molecularweight aromatic amines are capable of skin penetrat ion^ ^

and are systemically poisonous , ^ ^ ^ ^ it is conceivable that

the amine accelerators presently used in direct filling resins

and composites might be contributing to pulpal irritation.

Accordingly^ for the last few years, amine accelerators

have been investigated in the Dental Research Section at the

National Bureau of Standards with objectives of: increased

understanding of the factors that reduce discoloration,

improved polymer ization- initiating characteristics, and

reduced toxicity. ’ The extant and innovated hypotheses

bearing on these structure-property relationships required

the synthesis of a number of aromatic amine compounds, since

such compounds were not available. Most of this report

involves only the synthesis of certain amine accelerators

and a few preliminary results obtained v;ith them. Factors

bearing on the tendency to discolor have already been reported.®
6

Although no evaluations of toxicity have yet been made

on these compounds, the underlying provisional hypothesis

is that the toxicity of amine accelerators (as well as the

other ingredients in the formulations) will be inversely

related to the molecular weight, other things being equal.

Furthermore, increasing the bulkiness of a molecule (as determined by its shape in distinction to its molecular weight)

may reduce its permeability.^®

There is evidence that tissue penetration by organic

compounds goes through maxima (depending on the nature of

the body tissues) as the oil/water partition coefficient is

varied between its limits . ^ ^ ^ Since the physical properties

of highly hydrophilic organic materials might be adversely

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affected by the aqueous oral environment, the water- insoluble

end of this oil/water partition coefficient spectrum would

appear to be required. Substituents allowing for biotr ansformat io

1 3 and excretion by the human body should be considered.

I

The feasibility of utilizing the foregoing considerations

depends on the extent to which bulky substituents on the aromatic |

I

II
7

amines sterically hinder and electronically alter their interaction with peroxide initiators. In a previous study it

became apparent that steric hindrance of the nitrogen atom

of tertiary aromatic amines having suitable ring substituents

is not as much a problem as had previously been expected.

For example, in one composite formulation in which the dimethacrylate monomer liquid contained one percent of N,Ndidodecy l-_p-toluidine (DPT), the hardening time at room

temperature was about four minutes.

With this encouragement, the present study was undertaken to investigate tertiary aromatic amine accelerators

containing effective ring substituents such as methyl groups

in the 3 and 5 positions, and also large, bulky nitrogen

substituents of such a nature that they would not only raise

the molecular weight appreciably but also would yield crystallizable compounds having miclting points above room temperature.

This latter feature would allow for purification of these

compounds by crystallization; consequently, production,

product quality control, and storage stability might be facilitated .
Materials and Methods*

Most of the materials that were used are listed in Table 1.

They were used as received.

SYNTHESIS OF BPX*-The first such compound synthesized was

presumed to be N,N-bis (4-phthalimidobuty l)-3^ 5-xylidine (BPX)

(BPX)

This compound was prepared by combining 4.3 ml (4.0 gm,

0.033 mol) of 3 , 5-xy lidine, 23.3 gm (0.082 mol) of N-

(4-bromobuty 1 )phthalimide, 6.5 gm (0.077 mol) sodium

bicarbonate, and 140 ml of distilled water in a 250 ml

round bottom flask, and refluxing for about 18 hours. A

* Certain commercial materials and equipment are identified

in this paper to specify adequately the experimental procedure. In no instance does such identification imply recommedation or endorsement by the National Bureau of Standards

or that the material or equipment identified is necessarily

the best available for the purpose.
9

yellow precipitate formed, which was recrystallized from

ethanol and ethanol-water. The bright yellow crystals had

a melting point of 119-120°C. The yield was 86% of theoretical (based on the 3 , 5-xy lidine)

.

SYNTHESIS OF BCX* -The next amine accelerator that was

synthesized was N, N-bis ( 3-^-chlorophenoxy-2-hydroxypropy 1

)

-3 , 5-xy lidine, F.W. 490, (BCX):

Cl

H

I O

H

t O

f c-H

Cl

This compound was prepared in a 500 mi 3-necked roundbottom flask equipped with a dropping funnel, reflux

condenser and heating source. To 15.4 ml (15 gm, 0.124 mol)

of 3,5-xylidine was added 44 ml of methanol in the flask.

Water was added to the stirred solution to the cloud point

(when 40 ml of water had been added, the solution became

slightly turbid). After the xylidine solution had been
10

heated to refluxing, a solution of 50 gm (0.274 mol) of

p-chloropheny 1 - 2 , 3-epoxypropy 1 ether dissolved in 200 ml

of methanol (forming what appeared to be a nearly saturated

solution) was added dropwise from a dropping funnel over a

period of about five hours. The combined solutions were

refluxed for an additional six hours with stirring. The

solvents were then evaporated under partial vacuum, leaving

an off-white solid. Recrystallization from acetone yielded

several fractions of white crystals, the total amounting to

62% of the theoretical yield (based on xylidine). Since the

reaction product would be expected to consist of three stereoisomers ( meso and d, 1 ) ,^ ° the higher melting fraction was

recrystallized from acetone yielding 15.9 gm of white,

crystalline material having a melting point of 180-181°C.

The elemental analysis for the high-melting fraction, C26 H29 NCI 2

was calculated: C, 63.7; H, 6.0; N, 2.9; and Cl, 14.5%; found:

C, 63.6; H, 6.0; N, 2.9; and Cl, 14.5%.

The lower-melting fraction was recrystallized several

times from 9:1 methanol-water, yielding 6.2 gm of colorless
11

crystals with a melting point of 126-129°C; its elemental

analysis was: C, 64.2; H, 6.2; N, 2.9; and Cl, 14.5%.

SYNTHESIS OF BTX*-As will be seen, the high-melting fraction

of the foregoing compound had limited solubility in the dimethacrylate monomer formulation; consequently, this

suggested the synthesis of a similar but lower-melting

compound, namely N, N-bis ( 3-pi-toly loxy-2-hy droxypropy 1 ) - 3 , 5-

xylidine, F.W. 450, (BTX)

H

CH.

In a 500 ml, 3-necked round-bottom flask equipped with a

dropping funnel, reflux condenser and heating equipment,

were mixed 15.4 ml (15 gm, 0.124 mol) of 3 , 5-xy lidine, 45 ml

methanol and enough water (40 ml) to just bring about a

perceptible turbidity. A mixture of 41.3 ml (44.9 gm, 0.274

mol) of 1, 2-epoxy-3- (_p-methy Iphenoxy ) propane and 200 ml of

methanol were placed in the dropping funnel. After the

xylidine solution had been heated to reflux temperature,

the epoxy solution was added dropwise over a period of

2.5 hours, and reflux was continued for an additional hour.
12

A colorless precipitate formed on cooling. The solvents

were removed under partial vacuum and mild heating. Two

fractions were obtained after several recrystallizations

from acetone-water: 12.5 gm melting at 102. 5- 106° C and

21.8 gm melting at 146-148°C; together^ these constituted

61% yield (based on the xylidine) . The results of an

elemental analysis of the higher-melting fraction were:

calculated: C, 74.8; H, 7.9; 3.1; found: 75.2;

H, 7.9; and N, 3.0%. The elemental analysis on the lower

melting fraction was: C, 75.1; H, 7.9; and N, 3.2%.

SYNTHESIS OF BMX* -Another somewhat similar compound that

had previously been synthesized was N, N-bis (2-hydroxy-3-

methacryloxypropyl)-3, 5-xylidine, F.W. 405 (BMX)

H H

0 0 0 0

H2C=C-C-0-CH3 -C-CH2-N-CH2-C-CH2-0-C-C=CH2

CH^ H H cHo

H.C OCH3

(BMX)

It was prepared in a 2,000 ml, 3-necked round-bottom flask

equipped with a stirrer, condenser, thermometer, and hot water
13

bath. The following were added to the flask: 112 ml

(109 gm, 0.90 mol) of 3 , 5-xy lidine, 248 ml (266 gm, 1.87

mol) glycidyl methacrylate^ 9.8 ml water^ 0.571 gm of an

acid-catalyzed condensation product of _p-hydroxybenzoic

acid and 2-hydroxy ethy 1 methacrylate (MHB)^-'-® 0.272 gm of

di-Jt-butyl sulfide^ and 0.206 gm of butylated hydroxytoluene

(BHT). The latter three compounds were added to prevent

(premature) polymerization of the methacrylate groups. The

mixture was stirred at 70 ± 10°C for about 8 hours until

the reaction appeared to be complete as evidenced by a plot

of the refractive index against reaction time. When the index

of refraction had reached a plateau, a small aliquot was

mixed with reinforcing filler containing 0.52% bertzoyl

peroxide plus 0.85% lauroyl peroxide; the thin mix hardened

in 2.0 minutes at room temperature. The rapid hardening

gave supportive evidence that there was little if any residual primary or secondary aromatic amine remaining which

would act as a free-radical polymerization inhibitor.^

The water was removed with vacuum, stirring and slight
- 14

warming^ Leaving a clear, viscous (but pourable) yellow

liquid having a refractive index n^^ of 1.528. More of

the stabilizers (polymerization inhibitors) were added

(0.608 gm of MHB; 0.2 73 gm of di-jt-butyl sulfide, and

0.365 gm of butylated hydroxy toluene), and the hardening

time of this liquid mixed with the same powder was thus

increased to about 9.5 minutes at room temperature. An

attempt to obtain a crystalline product by cooling a

saturated ethanol-water solution of the product was unsuccessful. An elemental analysis of the product calculated

for BMX was: C, 65.2; H, 7.7; N, 3.5%. Found: C, 64.7;

H, 7.8; and N, 3.3%.

SYNTHESIS OF PBX*-The polymeric adduct (addition reaction

product) of the diglycidyl ether of bisphenol A and 3,5-

xylidine was prepared:

O

/ \

C-CH

H

(PBX) n = 1 to “, with an average of 2; where n = 2, F.W. =

1262. In a 1,000 ml round-bottom flask equipped with a reflux
15

condenser and heating equipment, 104.4 gm (0.31 mol) of the

diepoxide DoE.R.® 332, 24.8 ml (24.2 gm, 0.20 mol) of 3,5-

xylidine, and 500 ml of methanol were mixed, and two poly-

( tetraf luoroethylene ) pellets were added to prevent bumping.

The mixture was refluxed for 12 hours, during which time

the clear solution became turbid. After cooling and settling,

the supernatant was decanted off and methanol was removed

from the residue under partial vacuum, yielding a clear yellow

amorphous product. This product (PBX) was soluble in acetone

and in the dimethacrylate liquid (Table 2).

SPECIMEN PREPARATION --The various aromatic amines were formulated with a liquid dimethacrylate monomer as given in Table 2.

These liquids were then mixed with a powder containing 0.85%

benzoyl peroxide dispersed in an inorganic siliceous filler

treated with 3-methacryloxypropy 1-tr imethoxysilane, as described

previously . ^ ^ The filler made up about 70% of the mixed

material. The methods of mixing, measurement of hardening

times, comparisons of relative color formation and discoloration

under the sun lamp for 24 hours were also the same as described

in a prior report.^^
1IIII
15aRe^ ^ i on

HARDENING TIMES* -The hardening times were determined at room

temperature (22.5 ± 1.0°C) three times for each amine-containing formulation; the results are given in Tables 3 and 4.

Useful hardening times of about 3 to 4 minutes can be

obtained by the use of each of these aromatic amine accelerators providing that the proper concentration of amine, inhibitor

(BHT or other stabilizer) and peroxide are utilized. However,

the limited solubility of the high-melting fraction of BCX

in this particular monomer formulation restricted the concentration to low values giving hardening times that were too long

for practical purposes. High-melting compounds tend to be

less soluble in a given solvent, and higher-molecular-weight

solvents tend to dissolve less of a given solute than do

low-molecular-weight solvents, other factors being similar.

The monomers which are the solvents in these cases, have

formula weights of 390.
16

In agreement with evidence previously reported,

the hardening times appeared to be somewhat longer for

formulations containing amines having bulky nitrogen substituents in contrast to those having small methyl groups

attached to the nitrogen atom. However^ it is important

to note that hardening times are only moderately increased

(at equimolar concentrations). If the bulky groups (e.g.,

rings) had been connected to the nitrogen atom by linear

chains of less than four atoms, the effects of steric

hindrance might have been greater.

It may well be that the efficiency (number of free

radicals produced per mole) of the amine accelerator is

not reduced, but that only the rate of interaction with

benzoyl peroxide is reduced (due to moderate steric hindrance).

Such slower-acting but efficient amines, used at higher

concentrations, might result in a lower ratio of hardening

time to working time and in a more rapid increase in desirable

physical properties following hardening because of a
17

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higher concentration of amine accelerator in the later stages

of polymerization. In other words, such amines might provide

for "snap-hardening" characteristics desired by dentists.

In a plot of rotational (T ) versus linear (T ) hardening

R L

times, there was a nearly linear relation such that, as a

first approximation: Tj^ = 1.1 + 0.1. Plots of versus

T might be useful in evaluating the so-called "snap-hardening"

characteristics of direct filling resins and composites.

There was some evidence that certain liquid formulations

that had aged resulted in mixes with slightly longer hardening

times than the same solutions used immediately after they had

been prepared. The reason for this is not presently understood,

but should be determined.

The effect of BHT on hardening times is shown in

Figure 1.

DISCOLORATION* -In the previous study, an ultraviolet absorber

was included in the liquid formulation. This resulted in no

1
18

color change for DMSX (referred to as; N, N-dimethy 1- sym-mxylidine; N, N-dimethy 1-3 , 5-xylidine; N-dimethy 1-3 , 5-

dimethylaniline^ or N^ N, 3, 5-tetramethy laniline by various

sources) on exposure to the sun lamp. In the present study,

the ultraviolet absorbers were not included so as to enable

a more critical comparison of the amine accelerators with

respect to discoloration by exposure to the sun lamp.

In a careful comparison of the colors of the hardened

specimens and their color change when exposed to the sun

lamp for 24 hours, there was no perceptible difference between formulations containing 0.275% DMSX and those containing

equimolar concentrations of the high-melting fraction of BTX,

the low-melting fraction of BCX or BMX, each containing 0.159%

of BHT.

There was little if any variation in color or susceptibility to discoloration under the sun lamp with varying

amounts of BHT, DMSX, BCX, and BTX, within the small range

of concentrations used in this study.

The specimens prepared with the amorphous, polymeric

PBX had very slightly more coloration (a barely perceptible

pinkish tint) and discoloration when exposed to the sun lamp

than did specimens with equimolar concentrations of the
19

other amines. Since it was used without re-precipitation

or other purification, impurities may have contributed

to specimen discoloration.

Although the bright yellow crystalline BPX was sufficiently soluble in the monomer liquid and was an effective

polymerization accelerator, it imparted a yellow coloration

to the solutions and specimens in which it was used. The

yellow color of the composites produced with BPX was darker

than the typical yellow of natural teeth, although no darker

than some teeth. The color change induced by exposure to

the sun lamp appeared to be no greater than the color change

of specimens utilizing any of the other amines (described

here) in equimolar proportions.

The bright yellow color of BPX was assumed to be the

result of charge transfer complex formation between the

electron-rich aromatic amine moiety and the electron-deficient

phthalimide groups. This hypothesis was supported by the
20

observation that when clear, colorless 95% ethanol solutions

of DMSX

or of N, N-dimethy l-^-_t-buty 1-

aniline (DMBA) were mixed with a colorless solution of

N- (4-bromobutyl)phthalimide, a yellow solution formed; when

a solution of DMBA was mixed with one of ^-chloropheny

glycidyl ether, the mixture remained colorless.

Cpr^]aasipn^

Relatively high-molecular-weight polymerization accelerators can be prepared by the addition reaction of certain

ring-substituted anilines and glycidyl ethers or esters.

Some of these have melting points above room temperature

and can be purified readily by crystallization. Although

it has not been demonstrated, there are theoretical reasons

for expecting such high-molecular-weight accelerators to

be less able to penetrate body tissues and thus be less

toxic than the tertiary aromatic amine accelerators that

are being used in commercial dental composites and direct

filling resins. There may also be advantages in polymerization

kinetics
21

Although certain limitations were noted, [for example,

the aniline derivative having phthalimide substituents

(BPX) appeared to give a colored charge-transfer complex,

and the highest-melting amine (the BCX melting at 180-181°C)

was not sufficiently soluble in the monomer formulation

being investigated to be effective] practical, useful

hardening times of about 3 to 4 minutes can be obtained

by the use of most of these aromatic amine accelerators

providing that the proper concentration of amine, inhibitor

(BHT or other stabilizer) and peroxide are used.
MATERIALS

USED

u

u

G • G M • 0 IH 0 u o % <-a W u • « • 0 • B •rH O Cl 0 u H 0 , 0) 4-1 u G rH G G G u 0

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m rG 03 0 +Jw

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c;

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G 0 • 03 •rH 0 •H 0 G XC B C_3 -p E-i rG G •rH G G -P G

44 0) 03 Di iH 0 4->

G ca If) >

fd • •rH 1-^

U rH

B

X >1

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2i G) IH < Cl c <C

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4-> <o o -P iH

G 0 OP

(d 1—

rH * 1 03 as rH

G 00

0) c 03 ro o G •H

B

as Cn U o +J r- Cn 4J o G G

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O cu

u • 1—1 03 v£) 0 CP

B 0 CTi

G • Td 03 U 1 4-> 0 1 03 as B 03 1 0 w c u • 0 G f—t G 0 0 G m 0 • cu c CTi G1 a o G CX U D o> H Q 1 % 1 CM w] G 03 1 03 G 1—

• «« rG as >1

a) -P Cl

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X 0 1—1 G a CG O G 0

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H 0 G

t-H 03

G o >,

G 0

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G

G pH

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B 0 U 0 Cl 1—1 4J •rH X rG G G 0) 03 0) rH o Cl G *H rH 6 03 Cl, rH 0 G X G u •rH rG 03 -P 0 0

(D OCS -P 1 rG

G 2 G

G 4-) 1 rG m +J rH 1 0 G 0

rd lD

a 0 >1 og

G S CN B G 0 •rH

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n r-H 1 — 1 U - G

G 0 • ^ >1 G >1 G 1—1 G G +J G 1—1 o G 0 G (U D G 1 •P rH D'J W G 0 c rQ 03 ro 0 G G G

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G 03G 0 Gm

u

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w 0 •rH

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Pg 1 -H rG .G 1 -P u 03 G| rH ^ rH — G U C4 0 >1 S9 >1 1 tn - 1 03 1 U rH S G •iH •H ro X S P4 1—

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CD >1 rd -P a P r-H rd 0 -P >1 S <U (U p 0 iG •V T3 a -P P

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pq ro

Q

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24

TABLE 2

LIQUID DIMETHACRYLATE RESIN FORMULATIONS USED FOR

ASSESSING POLYMERIZATION ACCELERATORS

% Compound Source

47 Bis (2-methacryloxy ethyl) isophthalate The Epoxy 1 ite Corp .

38 Bis ( 2-methacry loxy ethy 1 )phthalate The Epoxy lite Corp .

15 Bis ( 2-methacry loxyethyl ) terephthalate The Epoxy lit

Corp - *

As

in

g iven

Tables

DMSX or

equimolar weight of one of the

other aromatic amines for comparison

Given in Table1 1

3 and 4

As

in

3

given

Tables

and 4

Butylated hydroxytoluene

(Tenox® BHT; food grade) Eastman Kodak Co

* Custom syntheses'^
25

TABLE 3

HARDENING TIMES, AS AN INDICATION OF

POLYMERIZATION-ACCELERATING EFFECTIVENESS

%

] BHT

Equimolar Concentrations

of Amines

Linear

Hardening

Times*

Rotat ional

Hardening

Times*

minutes minutes

-0.004 1.81% BCX (low-melting fraction) A • O -+ 1.25t

0.004 2.23% PBX 0.92 (0.14)

1.42(0.14)+

0.004

j

1.66% BTX (high-melting fraction;

almost all dissolved)

2.00(0.00) 2.25(0.00

)

J 0.142 1.81% BCX (low-melting fraction) 2.17(0.14) 2.58(0.14)

jo. 220 0.55% DMSX 2.58(0.14) 3.00(0.00)

-0.159 1.81% BCX (low-melting fraction) 2.83(0.14) 3.08(0.14)

0.220 1.93% BPX 3.42(0.14) 3.83(0.14)

0.220 1.81% BCX (low-melting fraction) 3.67(0.29) 4.25(0.43)

0 . 129 2 . 2 3% PBX 3.83(0.14) 4.42 (0.14)

0.129

1

2 . 2 3% PBX (aged solution) 4.58(0.14) 5.00(0.24)

of 3 measurements, each to the nearest 0.25 minutes, determined at room

temperature; the times in parentheses are the standard deviations as

estimated by

s =

n^x" - (Zx)^

n ( n- 1

)

where x is the measured value and n equals 3, the number of measurements.

Hardening time of a single measurement made with an extra-thin mix.

1 Thin mix.
TABLE 4

HARDENING TIMES, AS AN INDICATION OF

POLYMERI ZAT ION-ACCELERAT I NG EFFECT I VENE S

%

BHT

Equimolar Concentrations

of Amines

Linear

Hardening

Times*

Rotational

Hardening

Times*

minutes minutes

0.159 0.275% DMSX (fresh solution) 2.67(0.14) 3.00(0.00)

0.159 0.275% DMSX (solution aged 11 weeks) 3.42 (0.29) 3.92 (0.14)

0.159 0.905% BCX (low-melting fraction) 3.92 (0. 52) 4.33(0.63)

0.159 0.83% BTX (low-melting fraction) 4.92 (0.29) 5.42(0.29)

0.004 0.905% BCX (high-melting fraction

partly dissolved)

5.08(0.14) 5.92(0.14)

0.159 0.83% BTX (high-melting fraction) 5.83(0.38) 6.42 (0 .29)

0.159 0.747% BMX 6.00(0.43) 6.58(0.29)

0.220 0.275% DMSX 6.83(0.29) 7.58(0.29)

0.159 0.83% BTX (high-melting fraction;

7. 50(0.25) 8.33(0.38) aged solution)
27

nj^e s

1. Caulf H. J., and Schoonover, I. C.: Color Stability

of Direct Filling Resins, JADA ^:448-452, 1953.

2. Lai, J., and Green, R.: Effect of Amine Accelerators

on the Polymerization of Methyl Methacrylate with

Benzoyl Peroxide, J Polymer Sci ]^:403- , 1955.

3. Bowen, R. L. Dental Filling Material Comprising Vinyl

Silane Treated Fused Silica and a Binder Consisting of

the Reaction Product of Bisphenol and Glycidy 1 [Meth-]

Acrylate, U. S. Patent No. 3,066,112, Nov. 27, 1962.

4. Bowen, R. L.: Crystalline Dimethacrylate Monomers

[accepted for publication in the J Dent Res (Jul-Aug, 1970)]

5. Pryor, W. A.: Free Radicals . New York, McGraw-Hill Book

Co., Inc., 1966, p. 317.

6. Walling, C.: Free Radicals in Solution . New York, John

Wiley & Sons, Inc., 1957, p. 189.

7. Ibid . , p. 592.

8. Bowen, R. L., and Argentar, H. : Diminishing Discoloration

in Methacrylate Accelerator Systems, JADA 75:918-923, 1967.
28

References - 2 - 9.

Caldwell^ R. G.^ and Ihrig^ J. L. : The Reactivity of

Phenols Toward Peroxy Radicals. I. Inhibition of the

Oxidation and Polymerization of Methyl Methacrylate by

Phenols in the Presence of Air^ JAGS 84:2878-2886, 1962.

10. Suarez, C. L.; Stanley, H. R.; and Gilmore, H. W.;

Histopathologic Response of the Human Dental Pulp

to Restorative Resins, JADA ^:792-800, 1970.

11. Gilmore, H. W. : Recent Consensus on the Pulpal Reaction

To Restorative Materials, J Pros Den ^:434-440, 1970.

12. Albert, A.; Selective Toxicity . London, Methuen and Co.,

Ltd., 1968 ip 258, 106, 107, 114, 71, 437.

13. LeFraux, R.: Practical Toxicology cf Plastics , Cleveland,

The Chem. Rubber Co. Press, 1968 pp 161, 105, 547.

14. Patty, F. A. (ed.): Industrial Hygiene and Toxicology

(2nd ed.), Vol II. New York, Interscience Publishers,

1962, pp 2105-2169.

15. Bowen, R. L., and Argentar, H. : Amine Accelerators for

Methacrylate Resin Systems (submitted to J Dent Res )
References 3

16. Salame, M. : The Prediction of Liquid Permeation in

Polyethylene and Related Polymers, SPE Transactions

pp 153-163, Oct., 1961.

17. Hansch, C.; A Quantitative Approach to Biochemical

Structure-Activity Relationships. Accounts of Chem

Res , 2:232-239, 1969.

18. Long, R. F.: Biochemical Pharmacology Part 2: Absorption,

Distribution and Metabolism of Drugs, The Pharmaceutical J

pp 543-550, 1969.

19. Bowen, R. L.: Adhesion-Promoting Materials, patent

application serial no. 12423, filed Feb. 18, 1970.

20. Kier, L. B., and Penland, R. B. : Reaction of Aniline

with 3-Phenoxy-l, 2-Epoxypropane, J Org Chem 2_5il865-

1 67, 1960.
Figure 1: Semi- logarithmic graph of the relationship between

linea*' O , and rotational • hardening times

in minutes (test method described in ref. 15) of

composites (each containing 1.81% of the low-melting

fraction of BCX) and varying amounts of the stabilizer

butylated hydroxy toluene (BHT) as the sole compositional variable. The starred point is a single

determination; the other points represent averages;

of three measurements each.

USCOMM-NBS-DC
BHT,

%

p

CO