Weak Polyampholyte · pH-Responsive Copolymer
Poly(4VP-co-AA)
Also known as P(4VP-co-AA), 4VP-AA copolymer | Custom composition — no single CAS
A random copolymer of 4-vinylpyridine (4VP), a weak base, and acrylic acid (AA), a weak acid, on one backbone. Because the two units carry opposite, independently pH-switchable charges, the copolymer behaves as a weak polyampholyte: net cationic at low pH, net anionic at high pH, and near-neutral around its isoelectric point — where chain collapse and complex coacervation are most pronounced.
- Custom 4VP:AA ratio, multiple Mw grades
Custom composition
(C₇H₇N)ₘ-co-(C₃H₄O₂)ₙ
Poly(4VP-co-AA)
Appearance: White to off-white powder
Character: Weak polyampholyte
Architecture: Random copolymer
Storage: -2–8 °C, sealed, dry
ISO 9001:2015
Manufactured under certified quality management
Custom 4VP:AA Ratio
Synthesized to order, sets where the isoelectric point falls
Batch-Level COA
Mn, Đ, and composition confirmation per lot
Sample to Bulk
Gram-scale R&D up to bulk supply
CAS No.
Composition-dependent
Molecular Formula
(C₇H₇N)ₘ-co-(C₃H₄O₂)ₙ
Character
Weak polyampholyte
Mn Range
8K – 120K
Form
Powder
Two opposite pH switches on one chain
4VP and AA don't just each respond to pH — they respond in opposite directions, which is what gives this copolymer a true isoelectric point rather than a single-charge response.
4VP: cationic below its pKa
The pyridine N (apparent pKa ~4–5) protonates at low pH, making 4VP units positively charged; above that pH they're neutral.
AA: anionic above its pKa
The carboxylic acid (pKa ~4.5) deprotonates at high pH, making AA units negatively charged; below that pH they're neutral.
Ratio sets the isoelectric point
A pyridine-rich feed shifts the IEP higher; an AA-rich feed shifts it lower — letting you place the near-neutral point where your process needs it.
Minimum solubility at the IEP
Near-balanced charge reduces intrachain repulsion, so chains collapse and the copolymer is least soluble — and most prone to complex coacervation — right around its IEP.
The exact isoelectric pH depends on the 4VP:AA ratio, ionic strength, and local environment — it is not a fixed constant, and should be measured (e.g. by potentiometric titration or turbidimetry) for a specific batch.
Values below are representative for this monomer pair. Batch-specific COAs with GPC and composition data are available on request.
Chemical Name | Poly(4-vinylpyridine-co-acrylic acid) |
|---|---|
| Synonyms | P(4VP-co-AA) · 4VP-AA copolymer · Poly(4VP-r-AA) · pH-responsive polyampholyte |
| Monomer Units | 4-vinylpyridine (4VP) · acrylic acid (AA) |
| Architecture | Random (statistical) copolymer — not block or graft |
| 4VP : AA Ratio | Custom / composition-dependent — commonly 80:20 to 20:80 mol% |
| Approximate Isoelectric Point | ~pH 5–7, shifts with 4VP:AA ratio and ionic strength (batch-dependent) |
| CAS Number | Not applicable — composition-specific random copolymers are not assigned a single CAS RN |
| Molecular Weight (Mn) | Custom synthesis, typically 8,000–120,000 g/mol |
| Dispersity (Đ) | 1.1–1.3 (RAFT/ATRP) · broader for free-radical routes |
| Appearance | White to off-white powder |
| Solubility | Water-soluble away from the IEP (acidic or basic aqueous media); reduced solubility / precipitation near the IEP |
| Key Functional Groups | Pyridine (basic, quaternizable) · carboxylic acid (weak acid, metal-chelating) |
| Storage | Sealed, dry, 2–8 °C, protected from light |
Need a specific 4VP:AA ratio or a targeted isoelectric point? Talk to technical sales →
Choose the ratio that fits your target pH
4VP:AA feed ratio sets where the isoelectric point falls and how strongly the copolymer responds on each side of it.
4VP : AA ≈ 80:20
Pyridine-rich
Higher isoelectric point; stronger, wider cationic response and more available pyridine N for quaternization.
4VP : AA ≈ 50:50
Balanced
Isoelectric point centered near neutral pH; the most symmetric polyampholyte behavior across the pH range.
4VP : AA ≈ 20:80
AA-rich
Lower isoelectric point; stronger anionic response and more available carboxylic acid for chelation or crosslinking.
Applications
Layer-by-layer (LbL) assembly
The same chain can act as either the polycation or polyanion layer depending on the assembly pH, or bridge both roles.
Metal ion chelation
Pyridine N and carboxylate O⁻ together offer mixed-donor coordination sites for transition-metal binding and sequestration.
Water treatment flocculants
Charge neutralization near the IEP promotes particle aggregation and settling in coagulation/flocculation processes.
pH-triggered drug delivery
Charge switching across physiological pH windows drives swelling, disassembly, or release from micelles and nanoparticles.
Complex coacervation encapsulation
Near its IEP, or when paired with an oppositely charged partner polymer, the chain phase-separates into a dense coacervate for encapsulating actives.
Smart hydrogel networks
Swelling is minimal near the IEP and increases on either side as charge repulsion builds — a tunable, dual-direction swelling response.
pH-responsive biosensor interfaces
Reversible protonation/deprotonation of both units gives a measurable, pH-dependent surface charge for sensing applications.
Chelating protective coatings
Mixed N/COOH donor sites bind surface metal ions, supporting corrosion-inhibiting or anti-scaling coating chemistries.
Data & safety documents
Batch-specific COAs with GPC, composition (¹H-NMR), and titration data available for order confirmations. Contact us for a specific lot number.
Safety Data Sheet
GHS-format · EN / ZH
Certificate of Analysis
Ratio + Mw confirmation
Potentiometric Titration Curve
Isoelectric point determination
FAQ
Most frequent questions and answers
It’s primarily used wherever a pH-switchable, dual-charge material is needed — layer-by-layer films, metal ion chelation, flocculants, pH-triggered drug delivery, and complex coacervation encapsulation — because the same chain can present a positive, negative, or near-neutral surface depending on pH.
4VP is a weak base: its pyridine N protonates (becomes cationic) at low pH and is neutral at high pH. AA is a weak acid: its carboxylic acid deprotonates (becomes anionic) at high pH and is neutral at low pH. Because they switch in opposite directions, the copolymer as a whole has both a cationic regime and an anionic regime.
Yes — around the pH where the protonated pyridine’s positive charge and the deprotonated carboxylate’s negative charge roughly balance, typically pH 5–7 depending on the 4VP:AA ratio and ionic strength. Solubility is generally lowest and coacervation tendency highest near this point.
No. A true zwitterion like MPC carries permanently balanced positive and negative charge at every pH. Poly(4VP-co-AA) is a polyampholyte — its net charge changes with pH and is only near-neutral around its isoelectric point, not across the whole pH range.
Response spans roughly pH 2–10: strongly cationic below ~pH 4, transitioning through a near-neutral region around the isoelectric point, to strongly anionic above ~pH 8. Exact transition pH values depend on composition and should be confirmed by titration for a specific batch.
Yes — by choosing the assembly pH, the same copolymer can be deposited as a cationic layer (low pH) or an anionic layer (high pH) against an oppositely charged partner, which is useful when you want fewer distinct polymers in an LbL stack.
No — composition-specific random copolymers like this one are not assigned a single CAS Registry Number, since the 4VP:AA ratio, Mn, and dispersity are set per synthesis batch. Each lot’s COA documents the actual composition.
Store sealed, dry, at 2–8 °C, protected from light. For dissolution, move away from the isoelectric point — dilute acid (for a cationic solution) or dilute base (for an anionic solution) typically dissolves it faster than near-neutral water.