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”).

PolyOne Corporation’s (POL) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. 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. The stock’s trailing PE Ratio is 47.30. To get an in-depth look at POL, get Portfolio Grader’s complete analysis of POL stock.

Marrone Bio Innovations, Inc.’s (MBII) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). The stock receives F’s in Earnings Momentum, Equity, Cash Flow and Sales Growth. For more information, get Portfolio Grader’s complete analysis of MBII stock.

Kraton Performance Polymers, Inc. (KRA) is having a tough week. The company’s rating falls from a D to an F. Kraton Performance Polymers produces engineered polymers and styrenic block copolymers. The stock gets F’s in Earnings Momentum and Earnings Surprise. The stock has a trailing PE Ratio of 287.00. To get an in-depth look at KRA, get Portfolio Grader’s complete analysis of KRA stock.

The rating of Huntsman Corporation (HUN) slips from a C to a D. Huntsman manufactures differentiated and commodity chemical products. The stock gets F’s in Earnings Momentum, Earnings Revisions and Earnings Surprise. For more information, 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.