Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-03-28
2002-06-11
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S298000, C525S327300, C526S273000, C526S333000
Reexamination Certificate
active
06403714
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to liquid epoxy-functional resins. More particularly, the invention relates to epoxy-functional resins from epoxy-functional allylic monomers.
BACKGROUND OF THE INVENTION
Lowering resin molecular weight is a common approach to high-solids and low-VOC (Volatile Organic Compound) thermosetting acrylic coatings. This approach, however, is limited. When the resin molecular weight is reduced, so is its functionality (i.e., the number of functional groups per polymer chain). Thus, a hydroxyl-acrylic resin of reduced molecular weight often needs to be compensated by increasing the hydroxyl number to maintain high functionality. An increase in hydroxyl number, in turn, increases the solution viscosity due to inter-chain hydrogen bonding. Therefore, lowering the resin molecular weight, while increasing its hydroxyl number, cannot always achieve a higher-solids, or lower-VOC, coating.
Substituting allylic alcohol or alkoxylated allylic alcohol for hydroxyalkyl acrylate or methacrylate is another approach to high-solids and low-VOC hydroxyl acrylic resins. See, e.g., U.S. Pat. No. 5,525,693. These resins are characterized by an even distribution of hydroxyl groups. See S. Guo,
Solvent
-
Free Polymerization and Process,
ACS series book, 713, Chapter 7, pp.113-126 (1998). The even hydroxyl group distribution gives the resins a reduced amount of non-functional or mono-functional polymeric impurities. The non-functional or mono-functional polymers do not undergo crosslinking and, in effect, plasticize the coating. Hydroxyl acrylic resins produced with allylic alcohols or alkoxylated allylic alcohols have adequate functionality even at lower molecular weights. Thus, the coatings derived from these resins show both reduced VOC contents and high performance. See, e.g., U.S. Pat. No. 5,646,213. However, hydroxyl acrylic resins still have relatively high solution viscosities because of the hydrogen bonding.
Epoxy-functional acrylic resins are also known. For example, U.S. Pat. No. 4,181,784 teaches copolymers of an epoxy-functional monomer such as glycidyl acrylate or allyl glycidyl ether, ordinary acrylates such as methyl methacylate and butyl methacrylate, and vinyl aromatics such as styrene. The resins are prepared by solution polymerization at the refluxing temperature of the solvent. The resins are solid at ambient temperature.
U.S. Pat. No. 2,687,405 teaches copolymers of allyl glycidyl ether and acrylates. In one example, the patent teaches a copolymer of allyl glycidyl ether and n-octyl methacrylate. The polymerization is conducted at 60° C. for 16 hours. The monomer conversion is only 24%. The resin has very high molecular weight and broad molecular weight distribution. It is a semi-solid at ambient temperature.
New epoxy-functional resins are needed. The ideal epoxy-functional resins would be liquid at ambient temperature and could be used for formulating solvent-free or ultra-high solids coatings. More importantly, the resin could be efficiently prepared.
SUMMARY OF THE INVENTION
The invention is a liquid, epoxy-functional acrylic resin. The resin comprises 10-90 wt % of recurring units of an epoxy-functional allylic monomer and 10-90 wt % of recurring units of a C
2
-C
10
alkyl acrylate or methacrylate that has homopolymer Tg (glass transition temperature) less than 0° C. The epoxy-functional allylic monomer has the general structure:
R is hydrogen, a C
1
-C
10
alkyl, or a C
6
-C
12
aryl group; A is an oxyalkylene group; and n is an average number of oxyalkylene groups, which is within the range of 0 to about 15. The epoxy-functional resins have a number average molecular weight (Mn) less than about 5,000, a weight average molecular weight (Mw) less than about 10,000, molecular weight distribution (Mw/Mn) less than about 3.5, and viscosity less than about 20,000 cps at 25° C.
The invention also includes a process for making a liquid epoxy-functional resin. The process comprises initially charging a reactor with an epoxy-functional allylic monomer, 0-50% of the total amount to be used of a C
2
-C
10
alkyl acrylate or methacrylate that has homopolymer Tg less than 0° C., and 0-100% of the total amount to be used of a free-radical initiator. The remaining acrylic monomer and initiator are gradually added into the reactor during the course of polymerization. The polymerization is conducted at a temperature within the range of about 100° C. to about 185° C.
DETAILED DESCRIPTION OF THE INVENTION
The invention is a liquid epoxy-functional acrylic resin. By “liquid,” we mean that the resin flows at 25° C. without solvent. The resin comprises 10-90 wt % of recurring units of an epoxy-functional allylic monomer. Preferably, the resin comprises 10-50 wt % of recurring units of an epoxy-functional allylic monomer.
The epoxy-functional allylic monomer has the general structure:
R is hydrogen, a C
1
-C
10
alkyl, or a C
6
-C
12
aryl group. Preferably, R is hydrogen or methyl group. A is an oxyalkylene group. Preferably, A is selected from the group consisting of oxyethylene, oxypropylene, oxybutene, and mixtures thereof. The n is an average number of oxyalkylene groups in the molecule, which is within the range of 0 to about 15. Preferably, n is within the range of 0 to about 5. More preferably, n is within the range of 0 to about 2. Epoxy-functional allylic monomers can be prepared, for example, by reacting epichlorohydrin with an allylic alcohol or alkoxylated allylic alcohol in the presence of a Lewis acid catalyst such as BF
3
.
The liquid epoxy-functional acrylic resin also comprises 10-90 wt % of recurring units of a C
2
-C
10
, alkyl acrylate or methacrylate. Preferably, the resin comprises 50-90 wt % of recurring units of the acrylic monomer. Suitable acrylic monomers have homopolymer Tg (glass transition temperature) less than 0° C., preferably less than −10° C., and more preferably less than −20° C. Examples of suitable acrylic monomers are ethyl acrylate, 2-ethylbutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, 2-octyl acrylate, propyl acrylate, n-butyl acrylate, sec-butyl acrylate, lauryl acrylate, decyl methacrylate, 2-ethylhexyl methacrylate, hexyl methacrylate, n-octyl methacrylate, lauryl methacrylate, and the like, and mixtures thereof. It is essential to select an acrylic monomer that has homopolymer Tg below 0° C. because otherwise the resin produced is not a liquid at ambient temperature. 2-Ethylhexyl acrylate and n-butyl acrylate are preferred because they are commercially available and relatively inexpensive.
The resin has a number average molecular weight (Mn) less than about 5,000, weight average molecular weight (Mw) less than about 10,000, and molecular weight distribution less than about 3.5. Preferably, Mn is less than about 3,000 and Mw less than about 6,000. Preferably, Mw/Mn is less than about 2.5. The resin has a viscosity less than about 20,000 cps at 25° C. Preferably, the viscosity is less than 10,000 cps, and more preferably less than 5,000 cps at 25° C. The resin viscosity depends on the molecular weight and molecular weight distribution.
We have surprisingly found that a liquid epoxy-functional acrylic resin is obtained when the resin is designed according to the invention. See Examples 1-3. In contrast, the resins made according to the teachings of prior arts, e.g., U.S. Pat. No. 2,687,405, are solids or semi-solids. See Comparative Examples 4-5.
The invention includes a process for making liquid epoxy-functional acrylic resins. The process comprises initially charging a reactor with an epoxy-functional allylic monomer, 0-50% of the total amount to be used of an acrylic monomer and 0-100% of the total amount to be used of a free-radical initiator. Suitable epoxy-functional monomers and acrylic monomers are discussed above.
Suitable free-radical initiators include peroxides, hydroperoxides, azo compounds, and many others known to the polymer industry. Examples of suitable free-radical initiators are hydrogen peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, 2,2&p
Guo Shao-Hua
Pourreau Daniel B.
Wang Wei
Arco Chemical Technology L.P.
Aylward D.
Dawson Robert
Guo Shao
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