This week, the overall grades of four chemicals stocks are lower, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, PolyOne Corporation (POL) falls to a D (“sell”), worse than last week’s grade of C (“hold”). 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 Earnings Growth, Earnings Momentum and Sales Growth, POL also gets an F. For more information, get Portfolio Grader’s complete analysis of POL stock.

Marrone Bio Innovations, Inc. (MBII) earns an F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). In Earnings Momentum, Equity, Cash Flow and Sales Growth the stock gets F’s. Shares of the stock are changing hands at twice the rate they were a week ago. To get an in-depth look at MBII, get Portfolio Grader’s complete analysis of MBII stock.

This is a rough week for Kraton Performance Polymers, Inc. (KRA). The company’s rating falls to F from the previous week’s D. Kraton Performance Polymers produces engineered polymers and styrenic block copolymers. The stock gets F’s in Earnings Momentum and Earnings Surprise. For more information, get Portfolio Grader’s complete analysis of KRA stock.

Huntsman Corporation (HUN) earns a D this week, falling from last week’s grade of C. Huntsman manufactures differentiated and commodity chemical products. The stock gets F’s in Earnings Momentum, Earnings Revisions and Earnings Surprise. To get an in-depth look at HUN, get Portfolio Grader’s complete analysis of HUN 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.