Polyvinyl alcohol (PVA) is a synthetic polymer with various grades or types, each having slightly different properties depending on its molecular weight and degree of hydrolysis. The numbers you mentioned, 1788 and 1799, typically refer to specific grades of polyvinyl alcohol. The key difference between them lies in their molecular weight and degree of hydrolysis:

1. PVA 1788:
- Molecular Weight: PVA 1788 typically has a lower molecular weight compared to PVA 1799.
- Degree of Hydrolysis: The degree of hydrolysis in PVA 1788 is usually lower, meaning it has more acetate groups remaining in the polymer chain.

2. PVA 1799:
- Molecular Weight: PVA 1799 generally has a higher molecular weight compared to PVA 1788.
- Degree of Hydrolysis: The degree of hydrolysis in PVA 1799 is typically higher, indicating that more acetate groups have been hydrolyzed to hydroxyl groups in the polymer chain.

These differences in molecular weight and degree of hydrolysis can result in variations in the physical and chemical properties of the PVA grades. For example, PVA 1799, with its higher molecular weight and greater degree of hydrolysis, tends to have better film-forming and adhesive properties, making it suitable for applications like packaging materials, adhesives, and coatings. PVA 1788, with its lower molecular weight and lower degree of hydrolysis, might have different characteristics, making it suitable for different applications.