The grades of three chemicals stocks are on the rise this week on Portfolio Grader. Each of these stocks is rated an “A” (“strong buy”) or “B” overall (“buy”).

PolyOne Corporation (POL) is progressing from last week’s rating of B (“buy”) as the company improves to an A (“strong buy”) this week. PolyOne is an international polymer services company with operations in North America, Europe, Asia, Australia, and South America. In Portfolio Grader’s specific subcategories of Margin Growth and Sales Growth, POL also gets A’s. For more information, get Portfolio Grader’s complete analysis of POL stock.

Sensient Technologies Corporation (SXT) ups its rating to a B (“buy”) this week after earning a C (“hold”) in the week before. Sensient Technologies is a global manufacturer and marketer of colors, flavors and fragrances for products in the food and beverage, cosmetic and pharmaceutical, inkjet and other speciality markets. For more information, get Portfolio Grader’s complete analysis of SXT stock.

The rating of Taminco Corp. (TAM) moves up this week, rising from a C to a B. TAM is a holding company that provides domestic and international scheduled air travel through the subsidiaries TAM Linhas Aereas and TAM Mercosur. For more information, get Portfolio Grader’s complete analysis of TAM stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.