IN A NUTSHELL: During the last few years MMI scientists have developed an impressive portfolio of patents related to hyperbranched polymers prepared by bimolecular nonlinear polymerization reactions. These patents include polymers such as polyamides, polyureas, polyamidoamines, polyesters, polycarbosilanes, polycarbosiloxanes, polycarbosilazanes, their perfluorinated variants, etc. These polymers are ideally suited for a variety of specialty coating applications including antimicrobial, antifouling and decontamination coatings, superhydrophobic and superhydrophilic coatings, chemical and biological sensors, semipermeable membranes, electronic and photonic parts and materials, etc. Many of these applications are described in more detail on separate pages of this website.

WHAT ARE HYPERBRANCHED POLYMERS? Hyperbranched polymers are imperfect architectural relatives of dendrimers which have pronounced similarities but also differences compared to the latter. For example, similar to dendrimers, hyperbranched polymers have highly branched molecular architecture and a multitude of reactive or non-reactive end-groups, but in contrst to dendrimers they do not contain molecular core, have less defined intramolecular cargo space and often quite broad distribution of molecular shapes and sizes. As a consequence, while dendrimers dominate the fields of highly precise nanotechnology (including electronics, photonics, lithography, patterning, templating,  etc.), catalysis and biomedicine, hyperbranched polymers are considered as much more suitable candidates for large scale materials engineering applications, such as topical drug delivery, biotechnical reactor-based processes, special functional and protective coatings, sensors, decontamination and antifouling surfaces, biomimetic materials, and others where distributions of molecular sizes may represent an advantage rather than a deficiency. 

THE STATE OF TECHNOLOGY: Because of their architectural similarities, hyperbranched polymers have attracted considerable research attention as possible cheaper alternatives to the more precise dendrimers. This expectation was primarily based on the fact that in contrast to long multi-step reiterative syntheses that both divergent and convergent approaches require for higher generation dendrimers, resulting in high costs of labor and energy associated with repeated reaction and separation procedures, hyperbranched polymers can be prepared by relatively simple, one-pot-one-shot, relatively rapid polymerization reactions. This technology uses “branched” monomers of the general type ABx where A and B represent functional groups that can react with each other (i.e., A + B → -A-B-) but not with themselves (i.e., A + A → no reaction and B + B → no reaction), while x is an integer equal or larger than 2. For the simplest case of AB₂ monomers, this polymerization can be represented as shown in the following scheme:

This is a typical step-growth polymerization process in which the resulting polymer molecules are composed of –(A-B)< repeat units which contain 1→2 (or, in a general case 1→x) branch junctures. Since this process is governed by the statistical occurrence of individual reaction steps, and because of steric hindrance associated with increasing polymer molecular sizes, it results in different lengths of branches within the polymer molecules, leading to generally broad distributions of molecular weights, sizes and shapes. In addition, there is also frequent occurrence of intramolecular cyclization reactions which lead to complete disappearance of the focal A groups, thus limiting the polymer molecular growth. In order to eliminate this problem, various methods for carrying out these polymerization reactions have been developed resulting in a variety of different types of hyperbranched polymers reported in the scientific and patent literature.

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OUR NOVELTIES: Over the last few years MMI scientists have developed an impressive patent portfolio on an alternative technology for the preparation of hyperbranched polymers by what is now known as the bimolecular non-linear polymerization, BMNLP. Just like the traditional monomolecular polymerizations of AB_X monomers, BMNLP also utilizes a step-growth reaction mechanism, but in contrast to the former, it involves, two reactive monomers A_X and B_Y, where A and B also denote two types of mutually reactive functional groups, while x and y are integers which must both be equal to or larger than 2, while one of them (either x or y) must be equal to or larger than 3. Thus, the most common BMNLP systems include A₂ + B₃, A₂ + B₄, and A₃ + B₄ monomer combinations. In general, the simplest of these, the A₂ + B₃ system, in which the minor component has completely reacted, can be represented as shown in the following scheme: 

The essential and common feature of all BMNLP systems is the need for careful control of the polymerization process, by appropriate selection of the relative concentrations of the reacting A and B groups and the extent of the reaction, in order to prevent their natural tendency to crosslink to a gel. Although very stringent requirements must be satisfied in order to meet these conditions, reaction parameters can be selected so as to shift the polymerization equilibria to the formation of desired soluble hyperbranched polymer products in consistent and reproducible manners. When such selections and adjustments are appropriately made, BMNLP reactions offer some important advantages over traditional AB_X polymerization systems. Of these, of particular interest are: (i) the extreme versatility of the process to yield a practically unlimited variety of polymer compositions from a vast number of commercially available monomers, (ii) the unique ability to produce compositionally identical polymers, -[AB]_n<, with different (A or B) end-groups, and (iii) the complete elimination of the monomer shelf-life problems that are often encountered with many AB_X compounds which can polymerize either without the need for reaction catalyst or under less stringent storage conditions. A comparison of some fundamental properties of AB_X and A_X + B_Y hyperbranching polymerization systems is shown in the table below.

Utilizing the BMNLP approach, we have developed and patented a wide variety of different hyperbranched polymers, including polyamides, polyamidoamines, polyureas, polyurethanes, polyesters, polycarbosilanes, polycarbosiloxanes, polycarbosilazanes, perfluorinated derivatives of many of the preceding polymers, etc. They are ideally suited for a variety of specialty coating applications including antimicrobial, antifouling and decontamination coatings, superhydrophobic and superhydrophilic coatings, chemical and biological sensors, semipermeable membranes, electronic and photonic parts and materials, etc.

Some general characteristics of non-linear polymerization systems ABx and Ax + By 

* MW = molecular weight; DB = degree of branching.