Ind. Eng. Chem. Prod. Res. Dev. 1984, 23,586-590
586
Literature Cited Brosreit. E. Thin SolM Films 1982, 95, 133. Feidstein, N. Meter. Eng. W81. 38, 38. Hubner. H.: Ostermann, A. Gslvanotechnik 1976. 67(6). 452. Ishimori, Sh.; Shimlzu, M.; Honda. Sh.; Otsuka, Sh.; Toyoda. M. J . Met. Finish. Soc. Jpn. 1977, 28, 508. Kedward, E. C.; Wright, K. W. Plat. Surf. Finish. 1978, 6 5 , 38.
Lukschandel, J. Metell 1980, 34(5), 425. Metzger, W.; Ott, R. Metalloberff4che 1877. 3 1 , 404. Thoma, M.; Bunger, P. Gslvanotechnik 1984, 75(4), 425. Weissenberger. M. MetaN 1978, 30(12), 1134.
Received for review March 19, 1984 Accepted July 13, 1984
Preparation, Polymerization, and Evaluation of Blocked I socyanatoethyl Methacrylate Harold 0. Fravel, Jr.,* Thomas W. Regulskl, and Mary R. Thomas Dow Chemical U.S.A., Midland, Michigan 48640
The blocking of isocyanatoethylmethacrylate (IEM) with 20 compounds from eight organic classes is described. These adducts were polymerized with methyl methacrylate and ethyl acrylate. The resultant polymers were characterized and used to determine deblocking temperatures for the various derivatives. Blocked isocyanates have applications as latent cross-linking agents in systems containing active hydrogen such as water. The preparation, polymerization, and evaluation of blocked IEM will be presented along with several application areas in which it has been studied.
Introduction Ismyanatoethyl methacrylate is a difunctional monomer with a reactive isocyanate group and a polymerizable double bond. Either functionality can react independently without affecting the latent utility of the other group. Relative reactivity of the isocyanate and the methacrylate has been investigated by numerous investigators and reported by Thomas (1983). With the increase of interest in isocyanate-based systems for urethane coatings and adhesives, the availability of a polymerizable vinyl isocyanate in blocked form is very attractive. These blocked isocyanates offer more versatility and cleaner chemistry than the diisocyanate adducts commonly used for aqueous based systems, as well as one-component cross-linking systems in water or solvent, or a latent thermally activated cross-linking system. Blocking the isocyanate can also dramatically increase the shelf-life of an isocyanate-based reaction system and is accomplished by reacting the isocyanate group with an active hydrogen compound. The great benefit of the blocked isocyanate is the thermal reversibility of the reaction so that a reactive isocyanate group can be thermally generated and enter into a new equilibrium with the other active hydrogen species. The blocking group in large part determines the temperature at which the isocyanate can be regenerated.
i
CHz =C(CH,)COCHzCHzNCO
t
RH
-
i
i)i
CHZ=C(CH~)COCH~CH~NHCR
(1)
The desirable cross-link species are hydroxyls or carboxyls in the polymer backbone or in a second component. A blocking group should be chosen so that the desired interchange of blocking group for cross-linking group may take place. Wick's recent review (1981) discusses the literature (since 1975) in blocked isocyanates. Polymers containing
these derivatives are useful for powder coatings, wire coatings, tire cord-rubber adhesives, pressure-sensitive and hot melt adhesives, crease resistant finishes for fabric, anti-felting treatments of wool, leather treatments, and many more. Many of the references entail diisocyanate adducts to hydroxy-containing polymer backbones. With the blocked IEM monomer, a versatile and controllable method becomes available to approach these same applications. The monomers may be easily copolymerized with most acrylic and styrenic monomers at reasonable rates to give very stable resins without the complications of contaminating diisocyanates which might be released in use. Suling and Kuntz (1969) have prepared acrylonitrile graft copolymers using blocked IEM as a comonomer for use as a latent cross-linker in textile fibers. At Dow Chemical, Saunders (1981) has prepared latex polymers that contained blocked IEM by using conventional emulsion polymerization procedures. Two recent European patents by Gimpel et al. (1982a,b) describe the use of polymerizable isocyanates in blocked form in electrodeposition resins. Following their procedures, resins have been prepared by use of blocked IEM and were electrocoated onto steel panels. This paper will describe the preparation and characterization of the blocked IEM derivatives, along with their subsequent polymerization.
Experimental Section Preparation of Blocked IEM Derivatives. The preparation of the blocked IEM derivatives was done by two procedures. If the blocking agent was a liquid, the preparation was done neat. The blocking agent was charged into a reaction flask with dibutyltin diacetate (if used) and IEM was added dropwise over a 15 to 60-min period. The catalyst was used at 0.05 to 0.25 mol % (based on monomer). If an exotherm occurred, the temperature was controlled below 60 "C to prevent vinyl polymeriza-
0 1 9 ~ - 4 3 2 1 ~ a 4 ~ 1 2 2 3 - 0 5 a ~ ~ 0 10 . 5 01984 ~ 0 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 4, 1984 587
tion. The products of the liquid blocking agents were usually liquids and were used without further purification for subsequent polymerizations. When the blocking group was a solid, it was dissolved along with the tin catalyst (if used) in a solvent, usually toluene. The IEM was added over 15-60 min and the exotherms were much smaller. The solvent was removed and the adduct, generally a solid, was used for polymerization. Preparation of Copolymers of Blocked IEM. Solvent was placed in a reaction flask equipped with a thermometer, stirrer, nitrogen bubbler, reflux condenser, and addition funnel. The solvent was heated to 100 "C and a solution of methyl methacrylate (MMA), ethyl acrylate (EA), blocked IEM, and initiator was added dropwise over several hours. In most cases the monomers including the blocked IEM were totally miscible, but when the blocked adduct would not go into solution, enough solvent was added to give a homogeneous mixture. After monomer addition, a post-addition of initiator was used to reduce residual monomer in a 2-h finishing step. The polymer solutions were analyzed for percent solids, molecular weight, and molecular weight distribution. Formulations. Formulation of the Coatings. Twenty grams of a commercial acrylic polyol, a stoichiometric amount of a 50 wt % solution of the MMA-EAblocked IEM polymer in ethoxyethyl acetate and 0.1 g of dibutyltin diacetate were charged to a wide-mouth bottle and shaken for 10 min. Bonderite 37, 24-gauge steel panels, were rinsed with acetone and air-dried. The formulation was drawn down on the panel using a no. 60 wire wound stainless steel rod, 16 in. in length, and had a wet film thickness of 5.40 mils. The panels were air-dried for 5-10 min and cured at the appropriate temperature for 30 min. MEK Solvent Resistance Test. Cheesecloth folded eight thicknesses was wrapped around the peen of a ball-peen hammer and saturated with methyl ethyl ketone. The hammer was dragged back and forth over the width of the panel 50 times. The panel was allowed to dry and then was compared to sample panels and graded depending on the degree of film deterioration. Deblocking1 cross-linking cure temperatures were determined from the solvent resistance test results.
-
Results and Discussion Blocked Isocyanate Derivatives. In considering the blocking agents, for IEM, several criteria were set up to judge the potential utility. (1) A 30-min schedule was chosen to determine deblocking and cross-linking. (2) The toxicity of the blocking agent as well as that of the block derivative was considered. (3) For convenience, the blocked monomer should be a liquid and/or have a high solubility in the other commonly used monomers so that manufacture of the copolymers can be done by normal metering procedures. (4) The blocking agent should be readily available on a commercial scale. All were considered in planning this research on the deblocking agents for IEM. Over twenty derivatives were made from eight different chemical classes. These classes include some of the classic isocyanate blocking agents and some are relatively unknown. All rely on the chemistry of the isocyanate in equilibrium with the active hydrogen-containing product. A range of deblocking temperatures from 110 to 250 "C was found for these derivatives. Details of the deblocking studies of polymer films are discussed below. Representative blocking groups from the classes of alcohols, phenols, lactams, oximes, N-hydroxyimides, and
two miscellaneous nitrogen ring compounds were used as blocking groups. Table I shows these compounds, physical form, and yield. The isocyanate blocking is a clean reaction without byproducts so that 1:l equivalences could be used. However, it was found that some blocking groups such as Ecaprolactam interfered with copolymerization of the derivatized monomer, so in making the derivatives a slight excess of IEM monomer was added to the pot and 2propanol was used to block the excess monomer. In the phenol class, the electron donating phenols (phenol, 2,4-dimethylphenol, and 2,4-di-tert-butylphenol) gave normal addition products with good to excellent yields with the tin catalyst. The electron-withdrawing phenols (methyl p-hydroxybenzoate and methyl salicylate) each took special efforts. For the methyl p-hydroxybenzoate blocked IEM preparation, dibutyltin dilaurate was used as a catalyst with heating 1.5 h at 80-85 OC. The stability of the methyl salicylate seemed to indicate that at temperatures greater than 60 "C the equilibrium of the reaction is in favor of the unblocked monomer. In the best preparation scheme found, this derivative was synthesized at room temperature over a 2-3 day period using dibutyltin dilaurate as a catalyst. It was done in toluene so that the product would crystallize out. In the attempts to shorten the reaction time, higher temperature and/or nitrogen containing catalysts such as piperazine or triethylbenzylammonium chloride gave unwanted byproducts. Ethyl acetoacetate and 2,5-pentanedione were tried as blocking groups. Limited success was seen with ethyl acetoacetate when using sodium methoxide as the active catalyst. c-Caprolactam and pyrrolidinone were representatives of the lactam group of compounds. For pyrrolidinone, stannous octoate gave the best yield in the shortest time with little or no by product formed. Caprolactam is one of the most commonly used blocking groups for isocyanates. It has a relatively high deblocking temperature and is a useful candidate for powder coatings. Here, in contrast to methyl salicylate, the reaction lies favorable to the blocked form to above 100 "C and could be accomplished without the tin catalyst. A preparation on a larger scale was done without solvent using 1000 ppm of 2,6dibutyl-4-methylphenol as an inhibitor to vinyl polymerization. IEM was added dropwise into a stirred solution of molten caprolactam at 100 "C over 25 min. After an additional 30 min at 110 "C, the temperature was lowered to 90 "C and 0.4% n-propyl alcohol was added to scavenge any remaining isocyanate. The caprolactam-blocked IEM is a slightly yellow viscous liquid at room temperature. One of the newest groups to be used as blocking agents are the N-hydroxyimidks. These derivatives were easily made from IEM and blocking agent by heating to 60 OC using dibutyltin dilaurate in tetrahydrofuran. Two oximes were used to derivatized IEM, acetone oxime and methyl ethyl ketoxime. The derivatives could be made without catalyst in toluene giving an exotherm >40 "C during addition of IEM to acetone oxime. In the case of the methyl ethyl ketoxime derivative it was found that residual ketoxime led to lower polymer conversions in emulsion polymerization, and therefore an inverse addition method was used for synthesis. The methyl ethyl ketoxime was added dropwise to a neat solution of IEM maintained by exotherm at 60 OC. A preferred method to prepare added dropwise to is to add IEM to methyl ethyl ketoxime that contains 0.7 wt % dibutyltin diacetate. Use of the catalyst allows the temperature to be maintained at 15-20 "C. (see reactive chemical testing.)
588
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23,No. 4, 1984
Table I. Yields and Physical State of IEM Derivatives structure (-R)
group
mP
yield
2-ethylhexanol
Alcoh 01s -OCH,CHCH,CH,CH,CH,
liquid
- 99%
methoxypropanol
-OCHCH,OCH,
liquid
-99%
liquid
- 99%
I CH,CH,
I
CH, 0
ethyl lactate
/I
-OCHCOCH,CH, I
CH,
Oximes acetone oxime
CH,CCH,
methyl ethyl ketoxime
CH,CCH,CH,
67-69°C
/I
NOliquid
ll
91%
- 99%
NOMiscellaneous Blocking Agents imidazole
N A N -
u
CHnCH3
ethyl imidazoline
AuN -
pentols
-OCH,CH,CH,CH,CH, -OCH,CHCH,CH, I
CH, -OCH,CH,CHCH, I CH,
(36 wt %) (44 wt %)
82-85 "C
96%
63-65°C
85%
liquid
- 99%
(20 wt %)
Phenols phenol
106 "C
94%
waxy solid
88%
126 "C
87%
methyl p-hydroxybenzoate
98-100 "C
88%
methyl salicylate
7 1 "C
93%
31%
n.d.
liquid
- 99%
-
c
a
2,4 -dimethylphenol -
O
b
C
H
3
2,4-di-tert-butylphenol -
ethyl acetoacetate
o
b
Active Methylene Compound 0 0 I/
I1
CH,CCH,COCH,CH,
Lactams €-caprolactam
pyrrolidinone
0
p.-
54-46 "C
77%
90-91 "C
72%
116 "C
88%
N-H ydroxyimides N-hydroxy succinimide
N-hydroxy phthalimide
&;0
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 4, 1984 588
Table 11. Molecular Weight Properties of Several Polymers methyl methacrylate/ethyl acrylate/IEM-methyl salicylate composition: 30.2:30.2:39.6 % initiator 3.0% 2,2’-azobis(2,4-dimethylvaleronitrile) Mw = 29890 gn=-11900 M,/M,, = 2.5 methyl methacrylate/ethyl acrylate/IEM-methyl p -hydroxybenzoate composition: 30.2:30.2:39.6 % initiator 1.5% 2,2’-azobis(2,4-dimethylvaleronitrile) M w = 54300 M“ = 10100 Mw/Mn= 5.4 Table 111. Molecular Weight of Several Polymerso compn of MMA/ % EAJIEM-CAPc initiatorb Mm Mw/fim 33.7-32.7-34.6 1% Vazo 64 16900 35 000 2.1 10 800 20 400 33.3-33.2-33.5 2% Vazo 64 1.9 8 100 14900 33.3-33.2-33.5 3% Vazo 64 1.8 6 900 12 400 33.3-33.2-33.5 4% Vazo 64 1.8 33.3-33.2-33.5 1.5% Vazo 52 14 600 28 900 2.0 14 600 28 700 2.0 1% Vazo 64 70.0-0.0-30.0 13 200 25 OOO 1.9 50.0-0.0-50.0 1% Vazo 64 13 000 26 700 0.0-0.0-100.0 1% Vazo 64 2.1 All molecular weights relative to polystyrene standards. Vazo 52: 2,2’-azobis(2,4-dimethylvaleronitrile); Vazo 6 4 2,2’-azobis(isobutyronitrile). Methyl methacrylate/ethyl acrylate/IEM-caprolactam.
The imidazole blocked IEM and ethyl imidazole blocked IEM were made in toluene without catalyst giving high yield. The reaction exothermed to 60-70 “C. These blocked derivatives were demonstrated and the review articles by Wickes (1975,1981) suggest others that could be made. Preparation of Copolymers of Blocked IEM. To demonstrate copolymerization, fourteen of the blocked IEM monomers were polymerized with methyl methacrylate (MMA) and ethyl acrylate (EA). The standardized copolymer contained equal weights MMA and EA and either 22.5 or 25% by weight IEM after deblocking. In this way the polymers could be directly compared in physical properties and in deblocking/cross-linking experiments. Polymerization problems were observed when the deblocking temperatures of the derivatives were low. In these cases, small amounts of liberated blocking agent could act as a chain-transfer agent and broader M J M , values were observed. Table I1 shows this for a methyl salicylateblocked IEM polymerization. Significant amounts of NCO could be seen in the IR band at 2270 cm-l in the polymer before the finishing step.
The p-hydroxybenzoate derivative shows the same kind of dissociation and chain transfer problems. Both polymers had low molecular weight oligomers (300-600mol wt) that were visible in the distribution curve. Table 111shows the results of copolymerizations of methyl methacrylate, ethyl acrylate, and caprolactam-blocked IEM. Deblocking/Cross-linking of the Derivative-Containing Polymers. Representatives of the two lowest temperature deblocking groups, methyl salicylate and methyl p-hydroxybenzoate, in copolymers gave poor stability in formulation with a poly01 in the presence of tin catalyst. Each took about 7 days to gel at room temperature, showing that the equilibrium was reversible enough to regenerate small amounts of isocyanate at room temperature. Because of this experience it is assumed for the purpose of the study that cross-linking takes place (in the presence of the tin catalyst) immediately upon the deblocking of the isocyanate. The isocyanate band at 2270 cm-’ was, in fact, observed in the deblocking of polymer MMA/EA/ IEM-caprolactam. The deblocking/cross-linking temperatures were determined for each of the IEM derivatives according to the criteria: (1)the derivative was part of a copolymer that had the composition after deblocking, MMA (38.8) EA (38.7) IEM (22.5); (2) the acrylic copolymers had similar molecular weight distribution; (3) the amount of second component poly01 used and hydroxy groups equimolar to the isocyanate; (4) dibutyltin diacetate was used 0.5 w t ?& based on polyol; (5) deblocking/cross-linking was determined by heating 30 min at each temperature in an air flow oven; (6) temperature of deblock/cross-link was indicated by resistance of the coating to methyl ethyl ketone solvent rubs. Once the deblocking/cross-linking temperature was found, the films were characterized with respect to several physical properties: solvent resistance, percent gloss at 20 and 60 “C, adhesion, pencil hardness, and impact resistance. Some typical examples are shown in Table IV. Volatility of the Blocking Group. The blocking group will have an effect on the final physical properties of the coating depending on whether it remains in the coating or volatilizes. The methyl ethyl ketoxime derivative is often used in urethane coatings because it is a liquid with a boiling point (152 “C) near the deblocking temperature and therefore acts as a solvent on leveling of the coating through the cross-linking reaction. Other derivatives with higher deblocking temperature such as caprolactam are expected to remain in the film after cure, and plasticization of the coating must be allowed for in the formulation. Reactive Chemicals Caution. IEM-Methyl Ethyl Ketoxime. Heating neat IEM-blocked with oximes at or about 100 “Cmay produce an exotherm which may initiate
Table IV. Physical ProDerties of Several Polymers” glossC formulationbg
20° MMA(32.7)-EA(32.7)-IEM-PM(34.5) 89% MMA(3l.O)-EA(31.0)-IEM-EHOL(38.0) 83% MMA(34.3)-EA(34.3)-IEM-Pentols(31.4) 83% MMA(32.4)-EA(32.4)-IEM-EL(35.2) 79% MMA(30.2)-EA(30.2)-IEM-MS(39.6) 78% MMA(32.7)-EA(32.7)-IEM-C1(34.7) 80%
60’ 89% 91% 100%+ 94% 94% 91%
pencild hardness 2-3H H-2H 2-3H 2-3H 2H-3H 2H-3H
R.I./D.Le (mils) 2“-#/>30“-#(1.0-1.4) 2”-#/>30”-#(0.9-1.2) 2”-#/>30”-#(1.0-2.2) 30”-#(0.4-0.6) 5”-#/>30”-#(0.8-1.0) 30”-#(0.6-2.0)
MEKf resistance 100 D.R. (exc.) 50 D.R. (fair) 50 D.R. (exc.) 50 D.R. (good) 100 D.R. (exc.) 50 D.R. (exc.)
“All formulations were made by using 20 g of an acrylic poly01 and a polymer solution containing an equivalent mole amount of the isocyanate. All formulations contained DBTDA as a catalyst at the 0.5 wt % level based on the poly01 only. *All formulations were coated on Bonderite phosphatized steel panels and cured at 200 OC for 30 min. Measured on a Gardner Multi-gloss meter. dEagle Turquoise pencils were used. eR.I./D.I. 3: reverse impactldirect impact; mils = thickness of the coating. fD.R. = double rubs with a cheesecloth (8 layers) covered ballpeen hammer. exc = excellent resistance. gPM = methoxypropanok EHOL = ethylhexanok EL = ethyl lactate; MS = methyl salicylate; C1 = caprolactam.
Ind. Eng. Chem. Prod. Res. Dev. 1904, 23, 590-593
590
another exotherm at a higher temperature (175 "C). The second exotherm is due to the degradation of the oxime yielding heat and gaseous products. "The Handbook of Reactive Chemicals Hazards", L. Bretherick, Ed. (Butterworth: London) lists this potential hazard as characteristic of oximes. T o x i c i t y . Acute toxicity testing was carried out on IEM/methyl salicylate, IEM/methyl ethyl ketoxime, and IEM/t-caprolactam. In each case the acute oral toxicity was low to moderate in rats. In each, skin contact with rabbit showed slight irritation. Instillation in the eyes of rabbits resulted in slight discomfort, transient slight conjunctival redness, and very slight conjunctival redness and very slight corneal injury. However, for the methyl salicylate derivatives, greater danger was shown for eyes with reddening and corneal damage. Conclusions
Over 20 derivatives of IEM were synthesized with blocking groups from the classes of alcohols, phenols, lactams, oximes, N-hydroxyimides, and miscellaneous nitrogen ring compounds. Most gave good yields. These new monomeric blocked isocyanates make possible applications of isocyanates in copolymers for water-borne systems, latent cross-linking in water and solvent systems, and adhesives in a number of different applications. The 14 blocked E M derivatives were used to synthesize over 30 polymers. These copolymerizations were easily carried out with free radical initiator and the polymers that resulted had the predicted molecular weight with a narrow Xtw/Xtn distribution. These polymers were formulated with a commercial polyester poly01 and urethane acrylic catalyst to define the deblocking temperature and to give
films for evaluation of g l w , adhesion, pencil hardness,and solvent resistance. The lowest curing temperatures demonstrated for IEM derivatives were in the phenols and imidazole (110-130 "C). These were followed by the oximes (130-150 "C) and ethyl acetoacetate (>175 "C). The oximes, lactams, and alcohols gave the most stable formulation. Registry No. IEM-CAP, 78279-08-0; IEM-PM, 89777-74-2; IEM-EHOL, 86166-85-0; IEM-EL, 89761-51-3; IEM-MS, 8977084-3; IEM-acetone oxime, 24499-73-8; EM-methyl ethyl ketoxime, 78279-10-4; IEM-imidazole, 89743-58-8; IEM-ethyl imidazoline, 89819-94-3; EM-pentol isomer 1,89761-49-9; IEM-pentol isomer 2, 89743-64-6; IEM-pentol isomer 3, 89743-66-8; IEM-phenol, 89819-91-0; IEM-2,4-dimethylphenol, 89819-92-1; IEM-2,4-ditert-butylphenol, 89819-93-2; IEM-methyl p-hydroxybenzoate, 89743-56-6; IEM-ethyl acetoacetate, 89761-55-7; IEMpyrrolidinone, 89761-53-5; IEM-N-hydroxysuccinimide, 6079941-9; IEM-N-hydroxyphthalimide,89743-61-3;IEM, 30674-80-7; (MMA)-(EA).(IEM-MS) (polymer), 89770-85-4; (MMA).(EA). (IEM-methyl p-hydroxybenzoate) (polyher), 89743-57-7; (MMA).(EA).(IEM-CAP) (polymer), 78279-09-1; (MMA).(EA). (IEM-PM) (polymer), 89777-75-3; (MMA),-(EA).(IEM-EHOL) (polymer), 89823-31-4; (MMA).(EA).(IEM-pentol) (polymer), 90900-10-0; (MMA).(EA).(IEM-EL) (polymer), 89761-52-4. Literature Cited Gimpel, J.; Schenck, H.; Hartmann, H. U S . Patent 4310398, 1982a. Gimpel, J.; Feuerherd, K.; Schenck, H. U.S. Patent 4336346, 1982b. Saunders, F. Dow Chemical Co, Midland, MI. unpublished work, 1981. Suilng. C.; Kuntz, E. U.S. Patent 3 453 223, 1969. Thomas, M. R. J . Coat. Technol. 1983, 55, 55. Wicks, Z., Jr. ffog. Org. Chem. 1975, 3, 75. Wicks, Z..Jr. f r o g . Org. Chem. 1981, 9 . 3.
Received for review November 30, 1983 Revised manuscript received March 12, 1984 Accepted March 23, 1984
Quantitation of Silanol in Silicones by FTIR Spectroscopy Greg W. GrHflth The Bendix Corporation, Kansas City, Missouri 64 1 1 1
Many silicone polymer systems involve the reaction of a silane-hydrogen (SIH) component with a silanol (SiOH) component. Regardless of whether component preparation, formulation, characterization, or quality control Is of concern, a means of quantitating these functional groups Is needed. There are rhany good procedures for determining SiH, but most of the methods for SIOH are difficult to use and have many interferences. An FTIR method for SiOH has been developed which is fast, has no major interferences, and appears to be accurate. The method involves measuring the nonbonded SIOH band at 3685 cm-' of very dilute solutions of the SiOH in carbon tetrachloride. Interferences resulting from water and siloxane are subtracted digitally.
Introduction
Silicone polymers are playing an increasing role in industry because of their chemical inertness, excellent physical and electrical properties, and wide availability. For two-component resin systems, there are two general cure mechanisms used to produce a polymer. Vinyl-addition systems rely on the addition of a silane-hydrogen (SiH) group across a vinyl group. The remaining systems involve the reaction of an SiH group with a silanol (SiOH) group, resulting in the liberation of hydrogen gas. The liberated gas is used normally to blow the polymer into a cellular product. This second class of polymer resin systems is addressed in this paper.
To formulate a silicone system for a particular application, manufacturers must cbnsider many parameters including the amount of SiH and SiOH present along with the number of these groups per molecule. These parameters affect molecular weight, cross-link density, and cellular foam density. Users of the product are interested in both the consistency (quality control) of the resins and in its long-term stability. Either way, methods must be available for determining SiH and SiOH in a variety of resin systems. SiH is relatively easy to quantitate by infrared, manometric, or iodine-monochloride-reaction procedures. SiOH analysis is not as straightforward. The literature has many
0196-4321/84/1223-0590$01.50/00 1984 American Chemical Society
