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Polyethylenimine, often called PEI, entered chemical conversations back in the 1950s. Since then, labs and factories have kept coming up with ways to shape its properties and broaden its uses. Early work focused mainly on understanding its polymer structure and practical synthesis. Researchers figured out that you could fiddle with the amount of branching—either keeping the chains linear or going for heavy branching. This branching has a lot to do with how the polymer interacts with other molecules, which led to a surge in interest from chemical engineers and pharmaceutical companies looking for new solutions. Over the last few decades, the demand for branched PEI picked up because of its unique set of amine groups—making it suitable for everything from water treatment to gene delivery. The story of PEI mirrors a lot of mid-20th-century chemical exploration, where academic curiosity often crossed over into innovations for commercial and clinical applications. At every stage, new applications built on this foundation, but not without generating controversy about safety and the effects it has on health and the environment.
Branched PEI stands out because its structure carries a tangled network of primary, secondary, and tertiary amino groups. You don’t see many synthetic polymers that offer such density of functionality. This structure gives the polymer a near tree-like shape, letting it wrap itself around ions, nanoparticles, and biomolecules. Such branching isn’t just academic—it affects how the product dissolves, clings to surfaces, and forms complexes. Branched PEI usually shows up as a clear to yellowish viscous liquid at room temperature, but it can also arrive in solid form. One of the most talked-about features among techs and chemists is its ability to act as a cationic polyelectrolyte, grabbing on to negatively charged compounds and cells. The key difference between branched and linear PEIs boils down to this jumble of amine groups, which changes everything from solubility to toxicity.
In the lab, branched PEI comes in with a molecular weight range that covers everything from a couple hundred to hundreds of thousands of daltons. The overall viscosity climbs as the molecular weight rises, and so does the polymer’s stickiness. With a high density of aliphatic amines, its pH shifts from basic to strongly basic, which often complicates handling and requires pretty good ventilation. Its strong buffering capacity, a feature that makes it appealing in gene therapy and cell culture, lets it dampen-out acids and bases across a wide pH range. At the same time, the high charge density means it tends to bind biological membranes, sometimes with unintended effects. PEI attracts water and most polar solvents but doesn’t want to go near organic solvents like hexane. This property makes cleanup, containment, and waste handling extra important, both in the plant and in research settings.
Technical data from suppliers typically include average molecular weight, viscosity, concentration, and amine content. The degree of branching is usually flagged since it drives much of the performance story. Like most specialty chemicals, labeling gets detailed about hazard symbols, recommended storage, and personal protective equipment. Several industries have their own standards for acceptable levels of impurity and residual solvents in bulk shipments, reflecting a growing awareness of quality and safety issues. Laboratory stocks often require extra labeling about restricted uses, especially in regulated environments like pharmaceutical development and water treatment.
Making branched PEI starts from aziridine (ethylenimine) monomers, which join up in a complex cationic polymerization. The process works under strong acid or base conditions, sometimes with added catalysts. The branching comes from how the aziridine rings open and connect during polymerization. Most industrial plants use batch reactors where they can closely monitor chain length, branching, and end-group modification by tweaking temperature, time, and reactant concentration. Careful washing, neutralization, and filtration follow, since even trace amounts of unreacted aziridine bring serious health risks. The whole setup demands real discipline in safety—aziridine itself is highly toxic and flammable. Long-time operators know this isn’t a “set-and-forget” kind of process.
Branched PEI works like a Swiss Army knife in chemical reactions. Chemists can attach all kinds of groups onto the primary or secondary amines. They convert native PEI into PEGylated forms, which then enter biomedical experiments for gene and drug delivery, often trying to lower toxicity and boost selectivity. By crosslinking PEI with aldehydes or epoxides, material scientists make hydrogels and films for separation membranes or adhesives. Grafting side-chains changes how the polymer dissolves or adheres, which matters everywhere from wastewater remediation to biotechnology labs. These modifications get scrutinized because every addition can trigger new biological responses, sometimes good and sometimes risky.
In catalogs, branched PEI hides behind a lot of synonyms—PEI, polyaziridine, or “Epomin” in some cases. Chemical suppliers rename the grades to signal different molecular weights, branching ratios, and purification levels. This wall of names sometimes leads to confusion in research publications or procurement, so experienced researchers double-check with the manufacturers, making sure they get the right grade for their project—not just something with a matching name on a datasheet.
No one in the chemical trade takes PEI lightly. Direct skin or eye contact causes burns and irritation, and fumes bring respiratory problems. Unmodified branched PEI isn’t just rough on the skin—it acts as a cytotoxic agent in cell systems, which limits casual handling and puts sharp boundaries around concentrations used in live-cell experiments. Companies and university labs outline clear SOPs, with full-face shields, gloves, and chemical-resistant aprons as standard. Storage requires sealed, clearly labeled containers away from incompatible substances like strong oxidizers. In developed countries, handling and use tie back to workplace safety rules that stress fume hoods, spill controls, and documented waste disposal procedures. The high reactivity of PEI means that any shortcut or mistake could cause a serious incident or environmental release. Regular risk assessments—not just annual tick-the-box exercises—keep people alert to new information about the substance. In my own work with amine-rich polymers, even small spills travel farther and cause more trouble than you expect, so investing in prevention and quick-response supplies pays off every time.
Researchers and industry leaders put branched PEI to work across a long roster of fields. As a flocculant and coagulant, it treats industrial and municipal water, binding to suspended particles and dragging them down. In molecular biology labs, PEI takes on the role of a gene delivery agent, momentarily opening up cells to genetic payloads. Paint and adhesive manufacturers use it to improve bonding and surface interactions. It appears in paper making, textile modification, and as a catalyst support in organic synthesis. Environmental engineers value its ability to neutralize charged waste streams, clean up dyes, and capture heavy metals. Each application draws on either its strong amine content or cationic structure, so it’s no surprise to see PEI keep getting new roles as technology evolves. These uses bring clear benefits, but the downside is that any escape or improper disposal means significant risk to downstream users and the environment.
PEI sets off intense debates in the research community, since the same mechanisms that make it a potent tool also spell trouble for living systems. Scientists look for clever ways to lower toxicity by capping free amines or grafting biodegradable side-chains. In gene therapy, breakthroughs came from tweaking PEI with polyethylene glycol or sugars, which help reduce immune responses and boost cell compatibility. Material scientists go after tailored modifications that make PEI membranes filter selective ions, or control sustained drug release. Some teams focus on green chemistry approaches that swap out harsh solvents or catalysts in PEI synthesis. Researchers keep publishing data on structure-property relationships, hoping to one day hit just the right balance of function and safety. I’ve seen collaboration across fields speed up—biologists, chemists, engineers sharing samples and protocols—because problems in the lab often show up as challenges out in the field.
Toxicologists stay busy with branched PEI. Its high charge density disrupts cell membranes, leading to cytotoxicity in a wide range of organisms. Even low-dose exposure shows adverse effects in sensitive cells. In animal models, toxicity varies depending on the molecular weight and the method of administration. Regulatory reviews stress this point—only highly purified, well-characterized forms earn any kind of approval for clinical use, and even then with strict dosing controls. Wastewater containing PEI needs advanced treatment before discharge, since aquatic life reacts to amine overloads. Chronic exposure remains a big question mark, especially with increased production for research and manufacturing. Worldwide, scientists press for more long-term environmental and health studies, pushing for open data and transparent reporting. From my own perspective, advances in PEI-based delivery systems always run up against the need to map unintended side effects, making it easy to understand why regulation lags behind laboratory innovation.
Branched PEI stands at a crossroads. Its ability to bind, transport, and react makes it a building block for next-generation materials and therapies. At the same time, questions about toxicity and safe handling won’t fade away. The future may belong to modified derivatives—engineered to keep all the useful chemistry and shed some of the risks. Researchers look for biodegradable backbones and safer synthetic pathways. In water treatment and resource recovery, PEI keeps drawing attention, with teams racing to recycle and extract valuable materials without leaving behind persistent pollutants. Demand for safer, smarter chemical products drives both startups and established players to invest in green chemistry and digital tracking for the entire material lifecycle. To really unlock PEI’s promise, I see the need for partnerships across industry, academia, and government—balancing new technology with tough, honest risk assessments and public transparency. The story of branched polyethylenimine hasn’t ended; the next chapter will depend as much on responsible stewardship as on brilliant molecular design.
Branched polyethylenimine, or PEI, looks a bit plain at first—just a tangled mess of repeating units. Under that tangled surface, it packs a charge. Its many amine groups give it a strong positive charge. This charge lets PEI stick to things and pull in molecules in a way few other polymers can. Chemistry textbooks might call it a “polycation,” but people who have worked with it see PEI as a clever tool that can bind, wrap, and shuttle.
In research labs and biotech companies, PEI shows up almost every day in gene delivery experiments. Anyone who’s tried to get DNA into cells knows the challenge—cells resist foreign material. PEI, with its positive charge, grabs DNA, wrapping it up into bundles small enough to sneak through cell membranes. Scientists appreciate how PEI gets DNA into a wide range of cell types. Some medical researchers still search for safer methods since PEI can stress or even harm cells at higher doses, but nothing matches its straightforward efficiency for many tough cell lines. That’s a big reason why university labs and industrial settings often keep a bottle of branched PEI close at hand for transfection work.
Lakes and rivers can suffer from contamination—heavy metals like copper, lead, and mercury don’t just vanish on their own. Ordinary filters often miss these small, charged atoms, but PEI sees them and grabs hold. The strong pull of amines locks down these positive ions, letting PEI sweep unwanted metals out of solution. Environmental engineers have developed both bulk and bead-based forms of branched PEI to filter water, keeping drinking supplies safer or cleaning up industrial spills. PEI doesn’t solve every water problem, but it fills a valuable gap where regular treatments fall short.
Working in a printing shop, you see the headaches that come with getting ink to stick to specialty papers. Papermakers use branched PEI to give paper a little extra grip. Coating paper with PEI turns its surface more attractive to dye, toner, and ink. This change isn’t about the white color or texture—it’s the chemistry on the surface. PEI-treated paper soaks up ink without smudging, and it helps labels or banknotes resist tampering. People rarely think about the science inside a glossy magazine or a crisp business card, but a little branched PEI can make a real difference behind the scenes.
In adhesives, PEI doesn’t work alone but teams up with epoxies and other resins. The tangle of its branches gives adhesives extra holding force—handy for tough industrial jobs and book-binding. Wastewater treatment plants use branched PEI to clump particles together, making it easier to settle out impurities. The food industry, too, relies on PEI for clarifying juices and beer, trapping particles that cloud the final product.
Branched PEI isn’t perfect. High toxicity at strong doses pushes researchers to search for safer options, especially for medicines. Some labs experiment with tweaking the structure or mixing PEI with other materials. Others focus on dose control to get good results with the lowest risk. Transparency with safety data and long-term studies build trust—in research, in medicine, and in manufacturing. The story of PEI keeps moving, but its impact across so many fields speaks for itself.
Polyetherimide, often shortened to PEI, draws attention in plastics for good reasons. The molecular weight and viscosity of any batch determine how it works in the real world. These numbers aren’t just stats in a brochure—each one shapes how the finished product will hold up, form, and last.
Molecular weight points to the length of the polymer chains in the resin. In basic terms, longer chains give a tougher product. Think of it like a pile of cooked spaghetti: if the strands are long and tangled, the mass is hard to pull apart; that’s a high molecular weight PEI. Shorter spaghetti, easier to break, doesn’t hold together as well. This difference decides if the plastic will stretch, snap, or bend deep in a medical device or under a car hood.
Viscosity speaks about flow. High viscosity resins feel thick and resist pouring, just like honey versus water. This matters for anybody shaping PEI. Melt viscosity at processing temperature shows how this polymer runs in a mold, how it coats, and even how it accepts effects like fiber reinforcement. If the resin flows too easily, the end part could end up weak or incomplete. Too thick, and it might not fill every corner, leaving gaps and stress points. I’ve seen more than one crowd around an injection molding machine, all eyes on a thick resin struggling into a cavity, because that one number didn’t match what the job demanded.
In manufacturing, these values are front and center. PEI’s molecular weight often shows up as a “number-average” or “weight-average,” with typical grades ranging in the tens of thousands of grams per mole. Many producers mention “standard flow PEI” at about 30,000 g/mol to 40,000 g/mol. High-flow types, trimmed down, come in lower. The right type can make or break productivity.
Viscosity usually shows as “melt flow index” (MFI), a number in grams per 10 minutes under a set load at around 340°C. Lower MFI means thicker, tougher resin. For example, Ultem 1000 (one of the classic PEI types) might clock in with an MFI around 6-7 grams/10 min. For some delicate electronics or medical devices, customers want a resin that melts and races through even narrow molds, so they’ll pick a grade with a much higher MFI, sometimes 20 or 30.
It’s never enough to guess. I’ve watched engineers dig through technical datasheets, desperate for the exact molecular weight and MFI before starting a production run. A mismatch between the real value and the expectation can cause thousands in scrap and lost production time. Distributors and suppliers, if they don’t supply hard data, only add to the confusion.
Anyone in plastics quickly learns the need for verification. Running a melt viscometer or bringing in GPC testing (gel permeation chromatography) gives clear answers about the product in hand. If a customer doesn’t get the spec sheet, there’s nothing stopping them from running their own test before a batch hits the extrusion line.
Shops benefit from setting clear material requirements upstream—with raw data, not just trade names. Taking a close look at the resin’s certificate of analysis, not just the number on the catalog, helps avoid hidden shifts between supplier lots. In busier factories, communicating with resin makers keeps surprises low. If a problem does sneak in, catching it quick avoids a mountain of defective parts and lost hours.
Standards do exist. ASTM and ISO lay out test methods so producers and users talk the same language. Checking the ASTM D1238 melt flow for PEI keeps everyone on track, from the supplier to the person making the final part.
Branched polyethylenimine carries a lot of weight in research labs and chemical plants. Folks run into it during synthesis, gene delivery, and even wastewater treatment. My first swing at managing it happened years ago, and I’ve seen what happens if you cut corners. People think of it as a tool, but it’s worth remembering this polymer can burn skin and create toxic vapors if you ignore basic rules. Safety helps people go home healthy and keeps costly accidents off the company’s books.
Polyethylenimine usually shows up as a sticky liquid or white solid. Once a container gets cracked open, moisture in the room crawls right in, and the substance can react. That’s why factory and lab workers keep it in airtight, sealed bottles. I stick to plastic or glass containers with leak-proof screw caps. I never let unlabeled jars sit around—a clear label should call out the name, strength, and date, with a hazard warning where everyone can see.
Forget about tucking this chemical into a shared shelf. Polyethylenimine belongs in a cool, dry spot, far from heat sources or direct sunlight. High temps bump up the risk of fumes and even decomposition, which no serious chemist wants. I’ve learned to steer clear of oxidizers and strong acids too. Mixing these in tight quarters triggers unwanted reactions, which leads to fire or toxic gas. Setting up a dedicated chemical cabinet with good ventilation pays off—nobody wants to open a door and get hit with fumes.
I’ve seen gloves melt when people try handling this compound bare-handed or with the wrong material. For real protection, nitrile gloves, splash goggles, and lab coats do the trick. Respirators sometimes seem excessive, but once, during a spill, I saw a coworker cough uncontrollably even after a quick cleanup. A simple mask would’ve cut that risk. Simple protections stack up and mean fewer emergency room visits.
Pouring or transferring branched polyethylenimine always creates risks. Pumps and syringes help limit direct contact, and I avoid pipetting by mouth at all costs—a rule drilled in from day one. Spills aren’t rare, but they don’t have to become disasters. Absorbent pads and soda neutralize most small messes, then used materials get sealed before heading to hazardous waste pickup. Open flames or sparks nearby can turn a mistake lethal. I never rush through cleanup.
Rules and labels only go so far. Before training sessions, some people roll their eyes, thinking the rules are common sense. After a few years and a handful of close calls, they change tone quickly. Regular drills—like mock spills and PPE checks—teach folks how to react fast. Sharing stories about near misses keeps new team members sharp. An open-door rule to report problems helps catch small warnings before they balloon into health issues.
Labs and companies stay safer by writing clear safety guidelines and making sure every employee knows them by heart. I’ve seen success when workplaces combine real-life examples with hands-on, in-person training. Adding fume hoods, emergency eyewash stations, and regular audits turns theory into reality. Technology can help too—temperature and humidity monitors inside storage cabinets shout warnings way before the human nose detects trouble. A small financial investment on the front end beats paying hospital bills or replacing burned-out labs.
Many folks working in science or manufacturing will bump into polyethyleneimine, or PEI. Out in the field, the branched kind stands out for its job in everything from gene delivery to water treatment. Thinking about whether PEI will dissolve or clump up sits at the center of making these applications work. I remember back in grad school we struggled with stubborn clumps in samples, only to realize we had skipped some basic chemistry rules. Years later, that lesson sticks: ignore solubility and you waste good time and materials.
Branched PEI is packed with amines — these are nitrogen atoms holding onto hydrogens. Toss it in water, and those amines snag hydrogen bonds with water molecules, nudging the whole polymer to break up and disappear into the solution. Try to dissolve PEI in something oily or nonpolar, like hexane, and you just end up with a goopy mess. This isn’t a quirk. Amines love water because water’s polar, and polar likes polar. Greasy solvents have no pull on the amines, so PEI stubbornly stays a solid.
In most labs, you’ll see folks grab distilled water or weaker acids like acetic acid to get branched PEI into solution. Sometimes, you’ll spot folks switching to methanol or ethanol when playing with certain chemical reactions or coatings. It’s easy to see why this matters — use the wrong solvent and your experiment stalls. In drug delivery research, for example, where PEI helps escort genes into cells, the polymer needs to dissolve fully, or it just won’t work the way you want.
Something that surprises newcomers: even if you have water, pH changes everything. PEI turns friendlier to water as the pH drops into the acidic range, since more of those amines grab hydrogen ions and sport a positive charge. That charge helps unlock more hydrogen bonds with water, boosting solubility. Up at higher pH, charges slide away and the polymer grows shy, sometimes even crashing out of the solution. It’s like tuning a radio — miss the right frequency and the song vanishes into static.
It’s easy to think this only matters in the lab. But out in industry, solubility shapes everything from how a company makes PEI-based coatings to whether a water treatment plant can rely on the polymer to pull out metals. Sometimes, folks run into clogged pipes or see filters coat up faster than they can clean them. The root cause? A PEI solution that was too concentrated, not well mixed, or exposed to the wrong pH for too long.
Several manufacturers work around these issues by diluting PEI far below its maximum solubility, keeping the solution moving, or tailoring process pH with careful acid or base additions. Others turn to different molecular weights, since smaller PEI chains slip into solution more smoothly. It pays to remember that more isn’t always better — chase a thicker mix and you just might make sludge instead of a product.
In the end, branched PEI isn’t just a jumble of numbers and names. Its solubility isn’t a background fact, but a basic need that shapes research and industry. From lesson learned in the lab to big machinery on the shop floor, respecting how and why branched PEI dissolves saves money, produces better results, and pares down waste. Diving into the details early on, and keeping an eye on the small tweaks like pH and dilution, sets up everyone for success.
Branched polyethylenimine (PEI) gets a lot of attention in gene delivery. Its unique structure offers scientists an accessible way to pack DNA and move it into cells, something every lab in molecular medicine attempts at some point. Anyone who’s set foot in a gene therapy lab recognizes the bright blue bottles and the slightly sticky sensation—a reminder of how potent this material is. Branched PEI carries a high density of amines, letting it bind DNA tightly and protect it as it passes through volatile and enzyme-rich environments. That tight bond matters most in cell culture, where unguarded DNA degrades fast.
Researchers appreciate how branched PEI delivers. Its efficiency rivals or even surpasses viral carriers in some cases, pushing genes into mammalian cells and driving expression. For just a fraction of the cost of commercial reagents, labs can tweak ratios and optimize protocols. High molecular weight forms (25 kDa is well known) find use in everything from basic academic experiments to early stage therapy design. Scientists have reported over 95% transfection for some cell lines in ideal conditions, a feat that can make or break a grant deadline.
Still, nobody gets a free lunch. The trouble with branched PEI comes from its power—too much of a good thing. PEI kills cells, in some cases stripping membranes or stressing crucial metabolic pathways. Dosage has to be tailored carefully. The same property that helps PEI punch holes in endosomes for gene release ends up being harsh on fragile tissues. In animal work or human therapy, unpredictable toxicity closes doors that open easily in a dish.
Labs have looked for workarounds. Lowering the concentration can ease stress, but the gene delivery rate falls just as hard. Chemists have explored coating or modifying PEI with sugars, polyethyleneglycol (PEG), or targeting moieties. These changes soften the edges, making the polymer more forgiving. You can spot these innovations in academic journals where terms like "PEGylated PEI" and "targeted nanoparticles" come up. Results show less cell damage, but each solution brings fresh hurdles. Modified PEI can cost a lot, and the regulatory landscape gets more tangled the further you push from the basics.
Branched PEI often succeeds in early-stage experiments where reproducibility, speed, and customization take top billing over safety—think in vitro work, rapid screenings, or fundamental gene function studies. Many startups and university labs tap PEI for proof-of-concept. Still, for clinical transfection or in vivo gene therapy, researchers often turn to alternatives that balance delivery with long-term biocompatibility, even if that means sacrificing some transfection rate. Lipid nanoparticles or naturally-derived carriers answer these needs, riding on better safety profiles and established regulatory track records.
Branched PEI remains a reliable tool. If you treat every experiment as a learning moment—balancing delivery success with live cell counts—you can tap its full value without running into avoidable setbacks. By supporting development of less toxic variants and combining insights from chemistry, biology, and real-world practice, the field keeps moving toward genetic tools that serve not just science, but living patients. That drive for safe delivery continues pushing innovation, one transfection at a time.
| Names | |
| Preferred IUPAC name | poly(aziridine) |
| Other names |
Polyaziridine PEI Poly(ethylene imine) Ethylenimine polymer Branched PEI Poly(iminoethylene) |
| Pronunciation | /ˌpɒliˌɛθ.ɪˈliːn.ɪˌmɪn/ |
| Identifiers | |
| CAS Number | 9002-98-6 |
| Beilstein Reference | 104601 |
| ChEBI | CHEBI:53231 |
| ChEMBL | CHEMBL1200292 |
| ChemSpider | 23809 |
| DrugBank | DB04409 |
| ECHA InfoCard | 03-2119471994-40-0000 |
| EC Number | **25987-06-8** |
| Gmelin Reference | 52955 |
| KEGG | C06046 |
| MeSH | D010908 |
| PubChem CID | 25945 |
| RTECS number | RR0470000 |
| UNII | 6F1V9E0A4Y |
| UN number | UN2076 |
| CompTox Dashboard (EPA) | DTXSID8020345 |
| Properties | |
| Chemical formula | (C2H5N)n |
| Molar mass | 800 g/mol |
| Appearance | Colorless to pale yellow viscous liquid |
| Odor | Ammonia-like |
| Density | 1.03 g/mL at 25 °C |
| Solubility in water | Soluble |
| log P | -2.17 |
| Vapor pressure | <1 mm Hg (20 °C) |
| Acidity (pKa) | 8.0-9.0 |
| Basicity (pKb) | 4.5 |
| Refractive index (nD) | 1.485 |
| Viscosity | 2500 mPa·s (25% in H₂O, 25 °C) |
| Dipole moment | 1.53 D |
| Thermochemistry | |
| Std molar entropy (S⦵298) | 324.3 J·mol⁻¹·K⁻¹ |
| Std enthalpy of formation (ΔfH⦵298) | -21.0 kJ/mol |
| Std enthalpy of combustion (ΔcH⦵298) | -8488 kJ/mol |
| Pharmacology | |
| ATC code | D08AX59 |
| Hazards | |
| Main hazards | Causes severe skin burns and eye damage. Toxic if swallowed. Toxic in contact with skin. Toxic if inhaled. Causes severe respiratory irritation. |
| GHS labelling | GHS02, GHS05, GHS06, GHS08 |
| Pictograms | GHS06, GHS08 |
| Signal word | Warning |
| Hazard statements | Harmful if swallowed. Causes severe skin burns and eye damage. Toxic to aquatic life with long lasting effects. |
| Precautionary statements | H260-H301-H311-H314-H332-H335 |
| NFPA 704 (fire diamond) | 3-1-0 |
| Flash point | > 110 °C |
| Autoignition temperature | > 385 °C |
| Lethal dose or concentration | LD50 Oral Rat 1200 mg/kg |
| LD50 (median dose) | LD50, Oral (Rat): 1200 mg/kg |
| NIOSH | SDC6694710 |
| PEL (Permissible) | Not established |
| REL (Recommended) | 10-50 mg/L |
| IDLH (Immediate danger) | 900 mg/m3 |
| Related compounds | |
| Related compounds |
Polyethyleneimine (linear) Polypropyleneimine Poly(vinylamine) Polyacrylamide Poly(allylamine) |
