Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-12-08
2003-11-11
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S195000, C526S222000, C526S224000, C526S321000, C526S329700, C524S504000, C524S832000, C524S833000
Reexamination Certificate
active
06646068
ABSTRACT:
The present invention relates to a polymer composition, in particular to a branched polymer and a method of preparation therefor.
Branched polymers are polymer molecules of a finite size which are branched, often having many branches. Branched polymers differ from crosslinked polymer networks which tend towards an infinite size having interconnected molecules and which are generally not soluble. Branched polymers are usually soluble in solvents which dissolve analogous linear polymers but have the advantage that solutions of branched polymers are usually less viscous than solutions of the same concentration of the corresponding linear polymer having a similar molecular weight. Therefore solutions of branched polymers are easier to handle especially at high solids content and may be made using less solvent than solutions of linear polymers. For this reason, branched polymers are useful additives to solvent-based coatings and inks, for example and they also have many other applications. Additionally, branched polymers also have a lower melt viscosity than analogous linear polymers and are useful for improving melt processability in injection moulding, compression moulding, extrusion moulding or powder coatings.
Branched polymers may be made by a two-step process in which a linear polymer containing branching sites is subjected to a further polymerisation or modification step to form branches from the branching sites. The inherent complications of a two-step process may be unattractive and make the resulting branched polymer expensive to use. Alternatively a one-step process can be used in which a polyfunctional monomer is present to provide functionality in the polymer chain from which polymer branches may grow. However, a limitation on the use of conventional one-step processes is that the amount of polyfunctional monomer must be carefully controlled, usually to substantially less than about 0.5% w/w in order to avoid extensive cross-linking of the polymer and the formation of insoluble gels. It is very unusual to avoid crosslinking using this system, especially in the absence of a solvent as diluent and/or at high conversion of monomer to polymer.
GB-A-2294467 describes a branched polymethylmethacrylate polymer which has a molecular weight of 80,000-400,000 in which the molecular weight between the branching points is between 30,000 and 1,000,000 which includes 0.05-0.2% of a polyfunctional monomer and <0.5 mole % of a chain transfer agent. U.S. Pat. No. 5,767,211, published Jun. 16 1998, describes the synthesis of multi-functional hyperbranched polymers by free-radical polymerisation of di- or tri-vinyl monomers in the presence of a chain transfer catalyst and a non-peroxide free radical initiator. The resulting polymers are oily, low Tg materials.
EP-A-103199 describes copolymers of t-butyl acrylate with 0.1-3% polyfunctional acrylate and 1-30% of functional comonomer made by solution polymerisation in the presence of a chain transfer agent. The functional comonomer provides an active cross-linking site used to form a coating composition crosslinked by condensation chemistry.
U.S. Pat. No. 4,880,889 describes a pre-crosslinked soluble polymer containing 10-60% of OH-functionalised monomer, 5-25% of a monomer with at least 2 olefinically unsaturated double bonds and 15-82% of further monofunctional monomers. The polymer composition is made by a solution polymerisation process in organic solvent at a low polymerised solids content of about 50% in order to produce an ungelled copolymer, using >0.5% of a polymerisation regulator. The polymers are used in crosslinked coatings where the OH group is reacted with melamine-formaldehyde crosslinkers. U.S. Pat. No. 4,988,760 and U.S. Pat. No. 5,115,064 define similar compositions which include functionalised monomers having different cross-linkable groups which include carboxyl and isocyanate.
In a first aspect of the invention a method of preparing a branched polymer comprises the steps of mixing together a monofunctional monomer having one polymerisable double bond per molecule with from 0.3-100% w/w (of the weight of the monofunctional monomer) of a polyfunctional monomer having at least two polymerisable double bonds per molecule and from 0.0001-50% w/w (of the weight of the monofunctional monomer) of a chain transfer agent and optionally a free-radical polymerisation initiator and thereafter reacting said mixture to form a polymer. In this way a soluble branched polymer may be prepared by a simple one-step process.
In a second aspect of the invention, we provide a polymer comprising residues of a monofunctional monomer having one polymerisable double bond per molecule, from 0.3-100% w/w (of the weight of the monofunctional monomer) of a polyfunctional monomer having at least two polymerisable double bonds per molecule, from 0.0001-50% w/w (of the weight of the monofunctional monomer) of a chain transfer agent and a polymerisation initiator.
For simplicity, a monomer having one polymerisable double bond per molecule will be referred to hereinafter as a monofunctional monomer (MFM) and a monomer having at least two polymerisable double bonds per molecule will be referred to as a polyfunctional monomer (PFM).
It is surprising that a soluble branched polymer may be prepared from a mixture containing a relatively large proportion of a polyfunctional monomer because such mixtures would normally be expected to produce an insoluble cross-linked polymer network. Significantly, the polymerisation can be performed in one-step in the absence of solvent and taken to high conversion of monomer to polymer (>90%) to yield a soluble branched polymer.
The polymerisation of the monomer mixture may be performed using any free-radical polymerisation method, e.g. solution, suspension, emulsion and bulk polymerisation methods may all be used. For many applications of the branched polymers of the invention, the material is required in solid form. For these applications, polymers made by solution polymerisation require the solvent to be removed before use. This increases the cost and it is difficult to remove all of the solvent providing deficiencies in utilisation of the polymer. Alternatively when the polymer is required for use in solution form, it is necessary to conduct the polymerisation in the solvent which is to be present in the end-use application if the step of isolating the polymer is to be avoided. Therefore it may be advantageous to produce the branched polymer by a non-solution method, e.g. suspension or bulk polymerisation. It is surprising that branched polymers may be successfully formed from polyfunctional monomers in a non-solution method because the formation of gels would be expected. U.S. Pat. No. 4,880,889 teaches that special reaction conditions, including carrying out the polymerisation in solution at a relatively low solids content of about 50%, are required to obtain ungelled polymer.
Therefore in a further aspect of the invention, we provide a method of preparing a branched polymer by suspension polymerisation comprising
(i) mixing together a monofunctional monomer having one polymerisable double bond per molecule with from 0.3-100% w/w (of the weight of the monofunctional monomer) of a polyfunctional monomer having at least two polymerisable double bonds per molecule and from 0.0001-50% w/w (of the weight of the monofunctional monomer) of a chain transfer agent;
(ii) dispersing the resulting mixture as a discontinuous phase in a continuous phase in which the monomers are relatively insoluble in the presence of a dispersing agent which is capable of maintaining the mixture of monomers as a discontinuous phase in the continuous phase;
(iii) initiating polymerisation of the monomer mixture;
iii) maintaining the dispersion of monomer in continuous phase at a reaction temperature for sufficient time to enable the monomers to react to form a polymer; and
iv) subsequently separating the dispersed phase containing the polymer from the continuous phase.
The continuous phase is normally water. Suitable dispersing agents are w
Chisholm Michael Stephen
O'Brien Nial
Sherrington David
Slark Andrew Trevithick
Lucite International UK Limited
Pillsbury & Winthrop LLP
Yoon Tae H.
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