9 Solvent Systems for Hydrocarbon Resins
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P A U L O.
POWERS
1
Pennsylvania Industrial Chemical Corp., Clairton, Pa. 15025
In many applications of low molecular weight hydrocarbon resins, including flooring, adhesives, rubber compounds, inks, and coatings, the best performance is often associated with plasticizers that are marginal solvents rather than perfect ones. The difference between the resin parameter and the plasticizer parameter indicates the place of the system in the Flory-Huggins phase diagram. The separation of phases is responsible for the improved physical properties. While the difference of the parameters readily explains the behavior, the parameters for many industrial materials are not sufficiently well defined, and specific solubility tests must be used to control both resin and plasticizer.
This study was made to reconcile the behavior of low molecular weight hydrocarbon resins and the behavior of their plasticizers with the solubility parameter and with the Flory-Huggins treatment of phase separation from polymer solutions. These resins are widely used industrially for coatings, floorings, adhesives, rubber compounds, and many other applications. Since they are usually hard and brittle, they are used with rubber, drying oils, plastics, or with plasticizers. These resins are made b y the polymerization of linear and cyclic olefins and diolefins and aromatic olefins to form hard resins averaging from 700 to 1400 i n average molecular weight with some over 3,000 molecular weight. The distribution of these polymers has been described (J, 2 ) , and while the distribution is narrow, two or even three peaks are found i n the distribution curve. This may be attributable to both the diversity of the feed and to the conditions of polymerization; thus fractions may vary i n composition as well as molecular weight. 1
Present address: 742 Ayres Ave., North Plainfield, N. J. 07063.
131 In Solvents Theory and Practice; Tess, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
132
SOLVENTS THEORY A N D PRACTICE
While the parameter of the solvents is useful in formulating these resins, the solubility parameter is useful in choosing a plasticizer. There must be an appreciable difference between the solubility parameter of the resin and the parameter of the plasticizer to obtain the optimum properties in the compounds in which they are used. T h e Flory-Huggins analysis of phase separation in the low molecular weight range is in good agreement with the observed behavior of these resins with plasticizers and solvents. T h e results indicate that neither a very good solvent nor a very bad one gives satisfactory results with these Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0124.ch009
hydrocarbon resins. T h e area of optimum behavior may be defined by the difference between the parameter of the resin and the parameter of the solvent or plasticizer.
Solubility
Parameter
Hildebrands solubility parameter (3) is the most useful index of the solubility of resins in solvents and plasticizers. W i t h volatile materials it is derived from the change of vapor pressure with changes in temperature and can be measured very accurately. T h e parameter of the polymer is the same as that of its monomer. F o r many hydrocarbon resins, monomers may enter into the polymer, and the complete composition of the resin is not known. In such cases the solubility parameter is estimated from the range of the parameters of the solvents for the polymer. Parameters of Solvents. T h e parameters of typical compounds in hydrocarbon solvents are shown in Table I.
These values have been
derived from the vapor pressure of the pure materials
(4).
Styrene and d-limonene are included in the table since they are monomers for some resins. Tetralin is used as a model for indene for which no parameter values are available. Neopentane represents
a high
concentration of methyl
groups.
Toluene and trimethylpentane (isooctane) show the effect of the methyl group in reducing the parameter as compared with benzene and n-octane. A typical parameter of the methylene group is seen in octadecane and cyclohexane. T h e simplest aromatic compound is benzene, and the parameter of nine is i n the range of aromatics. L i q u i d olefin polymers and mineral oils are often used as plasticizers for the low molecular weight hydrocarbon resins. A rough estimate of the parameters of these materials can be made from their structure, but only approximate values have been offered. Parameters of Resins. Some of the manufacturers of the low molecular weight hydrocarbon resins have offered estimates (5, 6) of solubility parameters of some of their resins. These values have been established by determining the solvents (in one case at 50% solids) for the
In Solvents Theory and Practice; Tess, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
9.
POWERS
Table I.
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133
Solvent Systems for Hydrocarbon Resins
Solubility Parameter of Hydrocarbons at 2 5 ° C Hydrocarbon
Parameter
Neopentane Isoprene Diisobutylene Octane Isooctane Octadecane Cyclohexane Methylcyclohexane d-Limonene Tetralin Benzene Toluene Styrene
6.29 7.4 7.7 7.52 6.86 8.04 8.20 8.13 8.2 9.5 9.16 8.8 9.3
Table II.
Solubility Parameter of Polymers at 2 5 ° C
Low Polymers of:
δ
Indene Styrene a-Methylstyrene Olefines Terpenes Cyclopentadiene
9.5 9.2 9.0 8.3 8.2 9.1
resin at room temperature. measured at low solids.
High Polymers of:
δ
Ethylene Butadiene Isobutyleme Styrene Natural rubber
8.1 8.3 7.7 9.1 8.2
T h e solvents may not all be the same if
However the parameters of several polymers
determined by precipitation from dilute solution (7)
agree with the
values determined by other methods. The solubility parameter will vary with the polarity of the solvent used.
Manufacturers report the values for nonbonded, moderately, and
highly hydrogen-bonded solvents. In this study parameter values in polar solvents have not been considered since the interpretation of the values with polar compounds is not the same as with hydrocarbons
(8).
The values in Table II for low polymers are from the trade litera ture; values for the high polymers are from the literature
(8)
or are
calculated (9). While the solubility varies greatly with molecular weight, the solu bility parameters remain the same. T h e parameter for polystyrene re mains the same whether the molecular weight is 1,000 or 200,000; in fact the monomer has substantially the same parameter. Smalls method (9) which was used to determine the parameters of some of the high polymers in Table II relies on the structure of the poly mer and affords an estimate although it s probably no better than using the parameter of the monomer.
In Solvents Theory and Practice; Tess, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0124.ch009
134
SOLVENTS THEORY
80 Figure 1.
60 40 % RESIN
A N D PRACTICE.
20
Flory-Huggins phase diagram—low poly mers
The low molecular weight hydrocarbon resins have solubility pa rameter values in the range of 8.2 to 9.5. This might seem narrow, but the solubility behavior of the various resins is quite different and parame ter values to the second decimal point are required in choosing a formu lation. Usually a solubility test in specific solvents and a cloud point determination are needed for precise control. Phase Separation Flory s approach (JO) has often been used to study phase separation, but this method does not always predict the exact conditions of separa tion. The equation of Huggins was used to draw the phase diagram of Figure 1 since values could be calculated over the whole range of con centrations. Also the ft values agreed more closely with the parameter values. This equation is (II): Ιηαχ = In Vx +
(1 ~ X i / X 2 ) V 2 +
M
V22
In Solvents Theory and Practice; Tess, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.
9.
POWERS
135
Solvent Systems for Hydrocarbon Resins
where
