Partially branched polymers

Details Partially branched polymers Partially branched polymers

2003-01-21

2004-08-10

Pezzuto, Helen L. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S230000, C526S320000, C526S323000, C526S323100, C526S328500

Reexamination Certificate

active

06774198

ABSTRACT:

The present invention relates to partially branched polymers having a number-average molecular weight M
n
in the range from 500 to 20 000 daltons.
Low molecular weight polymers, i.e., polymers having number-average molecular weights of 20 000 daltons maximum, are of interest for a large number of applications, examples including the preparation of coating compositions in the paints field, the preparation of paper coating compositions, printing inks, adhesives, and floor polishes. In the aforementioned applications they are frequently used as cobinders or auxiliaries. Furthermore, low molecular weight polymers are employed as industrial waxes and also as additives for motor fuels and oils, whether as detergents or as thickeners. An important advantage of low molecular weight polymers over their higher molecular weight homologs is the lower viscosity of these polymers and their solutions, which generally means that less solvent is expended in their processing.
An important class of low molecular weight polymers are those known as functionalized polymers, containing two or more reactive functional groups. Reactive functional groups are those functional groups which are capable of forming bonds with other functional groups at room temperature or on heating. They are therefore used as building blocks in the preparation of polymers of higher molecular weight. For example, low molecular weight polymers functionalized with hydroxyl groups are used as building blocks in the preparation of polyurethanes and polyesters. Furthermore, functionalized polymers are used as a reactive component in thermosettable coating compositions and also in the reaction injection molding (RAM) process.
U.S. Pat. No. 5,534,598 discloses low molecular weight acrylic polymers which are derived from allyl alcohols or propoxylated allyl alcohols and which therefore include OH functional groups. U.S. Pat. No. 4,117,235 and DE 42 03 277 disclose processes for preparing low molecular weight polymers which may contain reactive functional groups.
The prior art low molecular weight polymers based on ethylenically unsaturated monomers generally have a linear structure, having been prepared using exclusively monoethylenically unsaturated monomers. Polyethylenically unsaturated monomers have not been used to date to prepare such low molecular weight polymers on account of the fact that they lead to a rapid buildup in molecular weight and, in extreme cases, to the development of a high molecular weight, three-dimensional network.
For example, DE 36 30 187 describes copolymers based on from 70 to 99.5% by weight of diethylene glycol monomethacrylate and from 0.5 to 30% by weight of esters and/or amides of acrylic acid or of methacrylic acid, containing from 0.1 to 2% by weight of a crosslinking bifunctional monomer in copolymerized form. The polymers obtained by polymerization at low temperatures, e.g. 60° C., are high molecular weight networks, which combined with the hydrophilic monomer bases results in the polymers having a high level of swellability by water.
It is an object of the present invention to provide new polymers.
We have found that this object is achieved by purposively copolymerizing ethylenically unsaturated monomers including up to 20% by weight of monomers containing at least two nonconjugated ethylenically unsaturated double bonds to prepare low molecular weight polymers at least some of whose chains contain one or more branching sites (partially branched polymers).
The present invention accordingly provides partially branched polymers having a number-average molecular weight M
n
in the range from 500 to 20 000 daltons and synthesized from ethylenically unsaturated monomers including
i) from 80 to 99.9% by weight and preferably from 90 to 99% by weight of monoethylenically unsaturated monomers A, and
ii) from 0.1 to 20% by weight and preferably from 1 to 10% by weight of monomers B containing at least two nonconjugated ethylenically unsaturated double bonds,
the weight fraction of the monomers A and B being based on the total amount of the ethylenically unsaturated monomers that constitute the polymer.
The present invention additionally provides a process for preparing such polymers, which comprises copolymerizing the aforementioned monomers A and B in the specified amounts at temperatures above 150° C., preferably 160° C., and in particular above 170° C.
The molecular weights M
n
indicated here and below are number-average molecular weights as may be determined, for example, by exploiting the colligative properties of the polymers, e.g., by vapor pressure or membrane osmosis, by ebullioscopy, by cryoscopy or by gel permeation chromatography. The M
n
figures stated here were determined by means of gel permeation chromatography (GPC) using polystyrene standards. The process used is described, for example, in DIN 55672-1.
The polymers of the invention preferably have a number-average molecular weight M
n
in the range from 700 to 10 000 daltons and in particular in the range from 1 000 to 6 000 daltons.
The monoethylenically unsaturated monomers A used to prepare the polymers of the invention include compounds containing an ethylenically unsaturated polymerizable double bond. Preferably at least 60% by weight and in particular at least 80% by weight of the monomers A have a polymerizable double bond in the form of an acrylic or methacrylic group.
In one preferred embodiment the polymers of the invention contain a reactive group. Reactive groups are functional groups suitable for crosslinking reactions, whether at room temperature or at elevated temperature. They include carboxyl, ketone, aldehyde, isocyanate, amino and, in particular, hydroxyl and epoxy groups. Monomers containing reactive functional groups are therefore referred to below as monomers A1 and those without reactive functional groups are referred to as monomers A2. In this preferred embodiment of the present invention, the proportion of the monomers A1 among the overall amount of the monomers is generally from 10 to 80% by weight and preferably from 20 to 70% by weight.
Preferred monomers A1 are esters of acrylic acid and of meth-acrylic acid that contain OH groups or oxirane groups. Examples of OH-bearing esters of acrylic acid and/or of methacrylic acid are the C
1
-C
8
hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate, 2- or 3-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 4-hydroxybutyl acrylate, 6-hydroxyhexyl acrylate, and the corresponding methacrylates. Examples of esters of acrylic acid and of methacrylic acid that carry oxirane groups are glycidyl acrylate, glycidyl methacrylate, and 2,3-epoxycyclohexyl or 3,4-epoxycyclohexyl acrylate or methacrylate. Examples of carboxyl monomers are acrylic acid and methacrylic acid and also, furthermore, fumaric acid, maleic acid, and the monoesters of these acids with C
1
-C
8
alkanols. Examples of amino monomers A1 are 2-aminoethyl acrylamide, 2-aminoethyl methacrylamide, 2-amino-ethyl acrylate and methacrylate, and the corresponding mono- and di-C
1
-C
4
alkylamino compounds.
Examples of the preferred monomers A2 are C
1
-C
20
alkyl acrylates and methacrylates and C
5
-C
10
cycloalkyl acrylates and methacrylates, it being possible for the aforementioned compounds to be halogenated in the alkyl and/or cycloalkyl moiety or to contain one or two nonadjacent oxygen atoms and/or imino groups instead of a CH
2
group.
Examples of such monomers include the following: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylbutyl acrylate, 2-ethylhexyl acrylate, 2-propylheptyl acrylate, lauryl acrylate, stearyl acrylate, cyclopentyl acrylate, cyclohexyl acrylate, 3-methoxybutyl acrylate, 2-methoxybutyl acrylate, 2-ethoxyethyl acrylate, tetrahydrofuryl acrylate, and the corresponding esters of methacrylic acid. Further suitable monomers A2 containing acrylic or methacrylic groups are phenyl acrylate, benzyl acrylate, phenethyl acrylate, 2-phenoxye

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